Removal of Fluoride from Aqueous Solution by CaFe2O4–GO Composite

Removal of Fluoride from Aqueous Solution by CaFe2O4–GO Composite | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Removal of Fluoride from Aqueous Solution by CaFe 2 O 4 –GO Composite Abdul Matin Ali, Nibedita Kapil, Susmita Sen Gupta, Dhruba Chakraborty This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4458894/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Interactions of graphene calcium ferrite nano (GCF) composite have been investigated for the utilization as adsorbent for fluoride in aqueous medium. Batch adsorption studies were carried out with various fluoride concentrations, amount of adsorbent, pH, agitation time and temperature. The adsorption process was strongly influenced by the pH of the solution. The extent of adsorption decreased from 79.5 to 70.1% by changing the initial fluoride concentration from 1.0 to 9.0 mg L − 1 (for adsorbent load 2.0 g L − 1 ). The kinetic study of the interaction was tested with pseudo first order Lagergren equation, second order kinetics, Elovich equation, liquid film diffusion model and intra particle diffusion model; however the interaction was much more close to the second order kinetics (k 2 = 0.0518 g mg − 1 min − 1 at 303 K). The adsorption data gave good fits with Langmuir monolayer capacity of ̴11.90 mg g −1 at 303 K. The uptake of fluoride was also preferred by higher solution temperature. The results established good potentiality for graphene calcium ferrite nano (GCF) composite to take up and separate fluoride from aqueous medium through adsorption-mediated immobilization. Graphene calcium ferrite nano composite Fluoride Kinetic Isotherm Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 Figure 20 Figure 21 1. Introduction Fluorine (F) is one of the most essential trace elements found in human beings and other animals. Human beings are exposed to fluoride through food, water and other products. Lower concentration of fluoride in water is considered as an essential micronutrient to prevent dental caries and facilitate the mineralization hard tissues while at higher level fluoride can harm to human health [ 1 ]. According to WHO, the maximum acceptable fluoride concentration in drinking water is 1.00 mg/L [ 2 , 3 ]. Bureau of Indian standard (BIS) has recommended a desirable limit of fluoride concentration 1.00 mg/L in drinking water, which can be extended to 1.5 mgL − 1 as permissible limit[ 4 ]. Above this concentration limit fluoride in drinking water can result in multidimensional health problem such as dental and skeletal fluorosis, mottling of teeth, bone diseases and lesions of liver, thyroid and other organs [ 5 , 6 ]. Excessive fluoride concentration also causes low haemoglobin level, muscle fibre degeneration, deformities in red blood cells (RBC’s) excessive thirst, headache, skin rashes, neurological manifestation [ 7 ]. Therefore, more attention should be taken for the research on defluoridation of water to protect human health. Among all the separation techniques, adsorption is a common practice used for fluoride removal from water mainly because of its cost effectiveness. Moreover, the technique is robust, environmentally friendly, versatile and simple [ 8 ]. However, the choice of adsorbent is very important in an adsorbent-adsorbate system to get maximum removal efficiency. Graphene, a single layer of carbon atoms arranged in six member rings in which carbon atoms are in sp 2 hybridized and formation of a two dimensional honeycomb lattice which possesses strong mechanical, electrical and thermal properties with specific surface area at 2630 m 2 /g [ 9 , 10 ]. This property suggests the possibility of synthesis of graphene based composite material with metal oxide [ 11 , 12 , 13 ]. Graphene oxide (GO) is derived from the graphene which is functionalized graphene with various oxygen containing functional groups. The high adsorption capacity of GO and separation convenience of magnetic material can be increased by addition of magnetic properties in to GO. This gives the available surface area and enhancement of adsorption capacity [ 14 ]. The calcium ferrite, a magnetic Ca – Fe oxide, contains Ca 2+ and Fe 3+ in the spinel structure, so the combination of magnetic spinel ferrite can result in interesting characteristics which are useful in various purposes [ 15 ]. For example, NiFe 2 O 4 /graphene was used in lithium-ion batteries as a high performance anode material [ 16 ]. ZnFe 2 O 4 /ZnO-graphene [ 17 ] and CoFe 2 O 4 /graphene [ 18 ] were used as high performance and recyclable visible light photo catalysts, arsenate removal by using fabricated Cu 2 Fe 2 O 4 [ 19 ], sulfonated graphene oxide composite used as removing Cu(ll) from aqueous solution [ 20 ], etc. The literature review indicates the use of magnetic spinel calcium ferrite – graphene composites as adsorbent for the removal of F − has not been reported so far. In this work, graphene calcium ferrite nano (GCF) composite was synthesized and used as magnetic adsorbent to remove fluoride (F − ) from drinking water. 2. Experimental 2.1. Material and method Graphene powder was procured from SIGMA- ALDRICH CHEMIE, Gmbh a product of Swizerland. All other chemical and reagents including, Ca(NO 3 ) 2 4H 2 O, Fe(NO 3 ) 2 9H 2 O, H 2 SO 4 (98%), KMnO 4 , H 2 O 2 (30%) were received from E-Merk, Mumbai, India. H 3 PO 4 (85%) was purchased from S.d fine chemical Ltd. Mumbai, India. All of these are analytical grade and used it without further purification. NaF solution (1000 ppm) was prepared by dissolving 1.105 g NaF in 500 ml distilled water and was used as stock solution. From this stock solution the required concentration of F- was prepared and was used for various experiments at room temperature. 2.2. Preparation of Graphene oxide GO was synthesized by modified Hummers process in which graphite flakes (1.5 g) and KMnO 4 (9.0 g) were successively added in to a 9:1 mixture of con. H 2 SO 4 and H 3 PO 4 under continuous stirring. The reaction was heated at 323 K and stirred for 12 hours. The reaction was cooled and poured in to ice with 30% H 2 O 2 . Then mixture was repeatedly washed with 30% HCl and ethanol and then dried it at 353 K. 2.3. Preparation of graphene-calcium ferrite composite 1.0 g GO was sonicated for 1 hr. To it, 0.118 g Ca(NO 3 ) 2 .4H 2 O and 0.404 g Fe(NO 3 ) 2 9H 2 O was added with constant stirring for 1 hr. The mixture was kept in an autoclave for 4 hrs at 393 K. The mixture was cooled to room temperature, washed with water and oven dried. Characterization The powdered X- ray diffraction (XRD) measurement was recorded by Bruker AXS(Germany) X- ray powder diffractometer Model D8 using Cu Kα monochromatized radiation with a step size 0.02º(2θ). The high resolution transmission electron microgram (HRTEM) image was obtained using JEM-2100, Jeol, Akishima, japan for the study of morphological surface. The Field Emission Scanning Electron Microgram (FESEM) image and energy dispersive X-ray (EDX) were obtained using by Zeiss FESEM model Sigma for morphological structure and elemental composition of the composite. FTIR spectra were obtained by Perkin Elmer (USA), FTIR spectrometer in the range of 400–4000 cm − 1 . The Raman spectra were recorded by using Renishaw (UK) Raman Spectrometer model Renishaw Basis Series with 514 Lasers. The surface area of the composite were determined by Brunauer-Emmett-Teller (BET) N 2 gas method using with the help of Quantachrome Autosorb 1C surface area analyser. The Zeta potential was measured (Zeta, Malvern) for the surface charge of the composite. 2.4. Batch adsorption Adsorption experiment was carried out in the plastic flasks by adding a fixed amount of adsorbent with 50 ml NaF solution. The mixture was agitated in a water bath incubator shaker (NAVYUG, India) for a predetermined time interval as per the experiment required. The mixture was centrifuged and unadsorbed F − present in the supernatant was determined spectrophotometrically (λmax = 568 nm). The pH of the adsorbate solution was maintained using 0.01 N NaOH solution and 0.01 N HNO 3 solution. The adsorption amount and rate (percentage of removal) of fluoride were calculated from the difference between the concentration of aqueous solution before and after adsorption according to the following equation q e =(C 0 -C e )V/m (1) Extent of adsorption(%) =(C 0 -C e /C 0 ) x100 (2) where q e is the amount of fluoride adsorbed (mg g –1 ) per gram of the adsorbent at equilibrium. C 0 (mg L –1 ) and C e (mg L –1 ) is the initial and equilibrium concentration of fluoride. V (L) is the volume of the solution taken and m (g) is mass of the adsorbent. The adsorption was studied various experimental conditions of initial fluoride concentrations, adsorbent load, interaction time, pH and solution temperature. 3. Result and discussion 3.1. XRD study The broad diffraction peaks in the X-ray diffractogram (Fig. 1 A and 1 B) indicates that the mean crystallite size is in the range of nanometre. Presence of all the fundamental Bragg reflection belonging to Fe 3 O 4 type fcc structure and absence of impurity peaks in these diffraction patterns, confirming that the annealed samples were also formed in single phase and retains the fcc spinel structure. Calcium ferrite exhibited typical peaks that appeared at 2θ range of 13–70º. No typical diffraction peaks of GO (0 0 1) was observed in the XRD patterns of the CaFe 2 O 4 -GO composite. The absence of GO (0 0 1) peak may be ascribed to the fact that GO was reduced to graphene during the hydrothermal reaction in the presence of alcohols. The crystal growth of CaFe 2 O 4 between the interlayer of graphene destroyed the regular layer stacking, leading to the exfoliation of graphene. The graphene layers could be randomly restacked by the reduction process which results in amorphous behaviour in XRD patterns. 3.2 TEM Analysis The formation of GO and CaFe 2 O 4 is can be confirmed by the TEM measurement. It is employed to study the morphology and shape of the adsorbent materials. It can be seen from the TEM image exfoliated GO (Fig. 2 A), large sheets (a few 100 square nanometers) were observed to be situated on the top of the grid. They were transparent and entangled with each other. Figure 2 B shows that the CaFe 2 O 4 particles uniformly disperse on the surface of the graphene oxide sheets. From the figure(Fig. 2 C) it can be seen that the selected area electron diffraction (SAED) pattern indicates that nanoparticles are polycrystals. 3.3 SEM Analysis The morphology and structure can be investigated from the FESEM study. The SEM image of GO is a smooth surface [ 21 ]. It is clearly seen from the FESEM micrograph (Fig. 3 A, Fig. 3 B, Fig. 3 C) that CaFe 2 O 4 stacked on the graphene sheet. The graphene sheet separated the nano particles. In some cases, agglomeration occurred, might be due to the magnetic properties of the prepared materials. The morphology of the prepared materials have changed due to the adsorption of fluoride on to it which was seen in the FESEM micrograph (Fig. 3 D). 3.4 EDX analysis Energy Dispersive X- Ray analysis (EDX) confirms the presence of various elements, namely calcium, iron, carbon and oxygen in the prepared CaFe 2 O 4 -GO composite (Fig. 4 A). The adsorption of F- in the composite is confirmed by the presence of fluoride on to materials EDX analysis (Fig. 4 B). 3.5 FTIR Analysis Figure 5 (A), 5(B) and 5(C)represent the FTIR spectra of GO, CaFe 2 O 4 - GO and CaFe 2 O 4 –GO with fluoride loaded respectively. In the FTIR Spectra of GO a characteristics peak is observed in around 3387 cm − 1, 1745 cm − 1 , 1402 cm − 1 and 1128 cm − 1 corresponds to the OH stretching, carbonyl stretching and C-OH stretching and C-O-C an epoxide stretching vibration respectively [ 22 ]. The stretching vibration of OH slightly shift near 3390 for CaFe 2 O 4 –GO Composite. The Ca- Fe metal vibrations of CaFe 2 O 4 -GO composites vibration peak is occurred at 1044 cm − 1 [ 23 ]. The peaks occurred at 526 cm − 1 and 566 cm − 1 also be observed due to the Ca-O and Fe-O stretching vibration [ 24 ]. The new peak for CaFe 2 O 4 –GO after adsorption at 423 cm − 1 confirm the fluoride adsorption [ 25 ]. The appearance of peak at 1110 cm − 1 due to the fluoride adsorption which is corresponds to C-O-Ca stretching vibration. 3.6 Raman study The characteristic Raman peak of CaFe 2 O 4 observed nearly at 440, 566, 649[ 26 ] (Fig. 6 ). The Raman plot of CaFe2O4-GO shows the extra additional peak nearly at 1359 cm-1 and 1571 cm-1 which was called D and G peak. 3.7 BET Surface area Analysis. The surface area of CaFe 2 O 4 -GO Composite was determined by BET method. This method was characterised using N 2 adsorption – desorption isotherm(Fig. 7 ). The BET surface area of the adsorbent CaFe 2 O 4 - GO composite is 220.80 m 2 g − 1 which was the much higher surface area of GO is 31.4 m 2 g − 1 .The total pore volume is found to be 0.265 cm 3 g − 1 and the average pore diameter is 4.3 cm 3 g − 1 . The mesoporous nature of the adsorbent confirmed by the N 2 adsorption – desorption isotherm which is type IV isotherm with H3 type loop, this porous nature is more favourable for the fluoride adsorption. 3.8Zeta Potential study Figure 8 The measurement of zeta potential of CaFe 2 O 4 - GO composite indicates that the within the pH range nearly 5 to 9 did not passes the zero point charge, indicating that the composite is negatively charged. 4. Adsorption study 4.1 Effect of pH The adsorption capacity reaches the maximum at pH 5.0 (Fig. 9 ) (Experimental condition: Adsorbent 2 g L − 1 , F − concentration 1.0–9.0 mgL − 1 , temperature 303 K, time 240 min, pH 3.0–10.0). Above pH 5.0, there is a steady decrease in fluoride adsorption capacity. In low pH range, the lower adsorption capacity may be due to the formation of weak hydrofluoric acid or synergism of both chemical and electrostatic interaction between the oxide surface and fluoride ion. At pH > 5.0, the decreased adsorption capacity is probably due to the competition for adsorption sites between fluoride and hydroxyl ions. 4.2 Influence of initial F- concentration The adsorption of F − onto CaFe 2 O 4 -GO composites was studied by varying the initial F − concentration using an optimum adsorbent dose (Experimental condition: Adsorbent 1.0–5.0 gL − 1 , pH 6.5, time 240 min, temperature 303 K, F − 1 concentration 1.0–9.0 mgL − 1 ) .The extent of adsorption (%) decreases on increasing the F − loading, but amount adsorbed per unit mass (q e ) shows an increasing trend. At low F − concentration, the ratio of the number of F − to the number of available adsorption sites is small and consequently the adsorption is independent of the initial concentration. But as the concentration of F- increases, the situation changes and the competition for adsorption sites becomes fierce. At this case, unit mass of the adsorbent is exposed to larger number of F- and progressively higher number of F- is taken up with the gradual filling up of the appropriate binding sites. This gives rise to an increase in q e although the net adsorption comes down. By increasing the F- concentration in the solution, where the volume of solution used for each adsorption experiment was the same, the average distance between adsorbate and adsorbent would be reduced. Consequently, the dispersive force between adsorbate ion and surface of adsorbent was stronger so that more adsorption would take place. At the same time, the increased diffusivity of adsorbate at its higher concentration was also thought to partly contribute to the enhanced adsorption (Fig. 10 ). 4.3 Influence of adsorbent dose The effect of the adsorbent dose on the removal of fluoride was studied at 303K (Experimental condition: F- concentration 1.0–9.0 mgL − 1 , pH 6.8, temperature 303 K, time 240 min, adsorbent 1.0–5.0 gL − 1 ). The extent of adsorption (%) increases rapidly as more and more of the adsorbent is added. This is to be expected because, for a fixed initial solute concentration, increasing adsorbent amount provides greater surface area or adsorption sites. However, the amount adsorbed per unit mass (q e ) decreases for all the clay adsorbents. When the adsorbent amount is small, the F- can easily access the adsorption sites and q e is high. With the rise in adsorbent load, the corresponding increase in adsorption per unit mass is less because of lower adsorptive capacity utilization of the adsorbent. This may be due to overcrowding of particles which may be termed as a kind of solid concentration effect (Fig. 11 ) 4.4 Influence of interaction time The variation of interaction time (Fig. 12 )( Experimental condition : Adsorbent 2.0 gL − 1 , F − concentration 1.0–9.0 mgL − 1 , pH 6.8, temperature 303 K time 5.0-240 min) showed that the adsorption rapidly increased in first 15 min after which it slowly approached towards equilibrium. With a bare surface initially, the available surface area is very large compared to the density of F − ions and thus, the rate of adsorption was high. However, with increasing coverage, the fraction of the bare surface rapidly diminished and F- ions had to compete among themselves for the adsorption sites. 5. Adsorption isotherm Adsorption isotherm indicates the distribution of adsorption molecule between the liquid phase and solid phase.The adsorption isotherm for the adsorption of fluoride on CaFe 2 O 4 - GO composite at various (303–333 K) temperature investigated for Langmuir [ 27 ]. The linear form of Langmuir [ 28 ] equation expressed by the following equation, Ce/q e =1/(bq m ) +(1/q m )Ce ( 3) Where, Ce = concentration of fluoride at equilibrium (mg L-1), b = Langmuir constant, q e = adsorption capacity at equilibrium (mg g-1) and q m = Langmuir monolayer adsorption capacity (mg g − 1 ). The plot of Ce/q e vs C e for on F − -CaFe 2 O 4 -GO composites interaction is shown in the Fig. 13 .The linearity of the plot suggest that adsorption follows Langmuir isotherms. The Freundlich plots, based on the well known Freundlich isotherm[ 29 ].The linear form of Freundlich [ 30 ] equation expressed by Eq. (4) Log(q e ) = log k f + (1/n)log C e (4) Where, Ce is concentration of fluoride at equilibrium (mgL − 1 ), k f (mg 1–1/n L 1/n g –1 ) is the binding energy constant reflecting the affinity of adsorbent to fluoride and n is the Freundlich constant. The plot of log q e vs log C e is shown in the Fig. 14 at various temperature (303- 333K)which is straight line. The linearity of the plot also suggests the applicability of Freundlich isotherm for removal of fluoride ion. The value of Langmuir and Freundlich isotherm parameters are calculated from the Fig. 13 and Fig. 15 which shown in the Table 1. The value of regression coefficient (R 2 ) is quite close to the unity and the process of removal of fluoride followed Langmuir as well as the Freuindlich isotherm[ 31 ]but the experimental data more fitted with the Langmuir isotherm model. 6. Kinetic study The Lagergren pseudo first order and second order integrated model can be applied for the kinetics and adsorption mechanism [ 32 , 33 ] which shown in the Eqs. (5) and (6). log(q e -q t ) = log q e - K 1 t/2.303( 5) t/q t =1/K 2 q e 2 + t/q e (6) Where q e and q t are amounts of adsorbed per unit mass at equilibrium (mg g − 1 ) and any time t(min) in the adsorption process. K 1 (min − 1 ) and K 2 (g mg − 1 min − 1 ) were the rate constant for pseudo first order and second order kinetics model, respectively. The plot log(q e -q t ) vs t for pseudo first order should give a straight line. This curve is linear (Fig. 15 ) and the rate constant, K 1 is 4.38x10 − 2 min − 1 (Table 2). The q e values obtained from the Lagergren plots differed from the experimental q e values nearly 22.10%. Therefore, the first order kinetics is less likely to explain the rate processes. Again the plots of t/q t vs. t (Fig. 16 ) is linear (R 2 ~ +0.99) with the rate constant, K 2 is found 5.18 x 10 − 2 gmg − 1 min − 1 . A comparison of q e values (experimental and those obtained from the second order plots) indicates that the adsorption is preferably takes place in second order kinetics. Elovich equation The Elovich equation [ 34 ] valid for chemisorptions of heterogeneous solid surface which is expressed as q t = βln(αβ) + lnt (7) where α and β is the Elovich coefficient.The value of Elovich coefficient can be calculated from the plot q t vs ln t (Fig. 17 ). The value of adsorptive coefficient, α and desorption coefficient, β is varies from 87.09 x 10 − 2 to 321.29x 10 − 2 g mg − 1 min 2 and 2.32 to 20.833 mg g − 1 min − 1 respectively with R 2 value ~ 0.918 to 0.935, shown in Table 4 ,which is relatively low value. Intra particle diffusion To provide definite information of the porous adsorbent taken as the consideration of appropriate kinetic adsorption model [ 35 ] q t = k i t 0.5 + C(8) where k i = internal diffusion constant (mg g − 1 min − 0.5 ) q t is the amount offluoride adsorbed at any time t (min).The value of k i and C can be calculated from the intercept of the plot of q t vs t 0.5 curve. The k i value is 0.104 mg g − 1 min − 0.5 to 0.011 mg g − 1 min − 0.5 and Cis 1.676 to 0.233 shown in Table 4 .The linear portions of the curves do not pass through the origin (Fig. 18 ) indicating that the mechanism of fluoride removal on CaFe 2 O 4 -GO composite is not followed solely by inter-particle diffusion although the possibility is not fully ruled out. Liquid film model The equation of liquid film diffusion model (36) is ln(1-q t /q e ) = -k fd t (9) Where k d (min − 1 ) is a rate parameter.The curve is linear with R 2 value + 0.923 to + 990 and the intercept is -0.404 to + 0.378 (Fig. 19 ). The curve do not pass through the origin but the intercept is very close to zero so, diffusion occurs from liquid phase might have great important than intra particle diffusion model. The k d value is in the range of 3.1 x 10 − 2 to 4.9 x10 − 2 min − 1 shown in Table.4. Influence of Temperature and adsorption thermodynamics The interaction between the adsorbent, CaFe 2 O 4 -GO composite and fluoride in the range of 303 K to 333 K indicate the process is endothermic in nature, as the temperature increases the extent of adsorption also increases (Fig. 20 ). The thermodynamic adsorption parameter ∆H,∆S,∆G were computed by the following equation, lnK d =∆S/R - ∆H/RT (10) ∆G =∆H -T∆S (11) Where K d (q e /C e ) is the distribution coefficient,T is the temperature(K),Ideal gas constant R(8.314 JK − 1 mol − 1 ).∆H is change in enthalpy,∆S is change in entropyand ∆G is change in Gibbs free energy.The value of change in enthalpy,∆H and change in entropy,∆S calculated from the plot ln K d vs 1/T. In the present work,the positive ∆H indicates the endothermic behaviour of adsorbate-adsorbent system(Table 5 ). The positive value of change in entropy,∆S indicates the increase of entropy with increase in temperature which suggested the adsorption process is favourable for fluoride adsorption. The negative value of change in Gibbs free energy,∆G with rise in temperature suggested that the adsorption process is favourable. The temperature dependence of a reaction is given by a equation called Arrhenius equation expressed as, K = A exp − Ea/RT (12) lnk = ln A –E a /RT (13) Where k (g mg − 1 min − 1 ) is the pseudo second order rate constant, A (g mg − 1 min − 1 ) is the frequency factor, E a (k j mol − 1 ) is the activation energy for adsorption, R (8.314 j mol − 1 k − 1 ) is the gas constant and T is the temperature in Kelvin scale. The linear fitting curve were obtained by plotting logk vs 1/T (Fig. 21 ) and the activation parameter are found from slope and intercept. The activation energy, E a for the process is found 5.527 k j mol − 1 which signifies the process might be physically controlled [ 33 ]. Conclusion In this work we successfully synthesized the CaFe 2 O 4 -GO composite. Removal of fluoride from aqueous solution by CaFe 2 O 4 -GO composite followed the Langmuir as well as Freundlich isotherm.The Langmuir monolayer capacity is 11.90 mg g − 1 .The change in enthalpy was a positive quantity which suggest the adsorption process was endothermic in nature. The extent of adsorption increases with increase in temperature. The adsorption process was preferably followed the second order kinetics. Removal of fluoride from water by this adsorbent was dependent on pH of the medium. The process was governed by the decrease in Gibbs free energy. Declarations 1. There is no funding for this manuscript submission. 2. The Authors declare no conflict of interest. 3. This is an original research work and new data is incorporated based on the experimental work. 4. Ethical statement for this manuscript is not applicable. Acknowledgement The authors gratefully thank Assam Don Bosco University, Assam and B.N. College, Dhubri, Assam for assisting this research work. 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Temperature (K) Langmuir Isotherm Freundlich Isotherm 303 q m 11.90 mgg -1 b 0.1582 R 2 0.999 n 1.256 mg 1–1/n L 1/n g –1 k f 1.493 R 2 0.996 313 q m 10.00 mgg -1 b 0.235 R 2 0.995 n 1.323 mg 1–1/n L 1/n g –1 k f 1.718 R 2 0.990 323 q m 9.61 mgg -1 b 0.3041 R 2 0.992 n 1.355 mg 1–1/n L 1/n g –1 k f 1.991 R 2 0.989 333 q m 8.547 mgg -1 b 0.4699 R 2 0.991 n 1.479 mg 1–1/n L 1/n g –1 K f 2.350 R 2 0.986 Table : 2 First order and Second order rate coefficient, Experimental and Computed q e values from Lagergren and second order plots for adsorption of fluoride on CaFe 2 O 4 -GO composites at 303 K. Lagergren first order rate coefficient Second order rate coefficient K 1 0.0438 min -1 K 2 0.0518 g mg -1 min -1 R 2 0.93 R 2 0.999 q e (calculated) 2.317 q e (calculated) 1.976 q e (Exp.) 1.898 q e (Exp.) 1.898 Deviation 22.10% Deviation 4.10 % Table: 3 Pseudo Second order kinetic parameters for the fluoride adsorption at different temperature (CaFe 2 O 4 -GO composites- 2gL -1 , F - 5 mgL -1 , pH 6.8) Temperature (K) K 2 (gmg -1 min -1 ) q e,cal (mgg -1 ) q e,Exp (mg g - 1) Deviation R 2 303 5.18 x 10 -2 1.976 1.898 4.10 0.999 313 5.80 x 10 -2 1.972 1.905 3.52 0.999 323 5.92 x 10 -2 2.012 1.950 3.75 0.999 333 6.37 x 10 -2 2.12 2.052 3.31 0.999 Table 4. Different kinetic adsorption parameters for adsorption of fluoride on to CaFe 2 O 4 -GO composite of different initial fluoride concentration at 303K, pH- 6.8 Value Parameters 1 mg/L 3 mg/L 5 mg/L 7 mg/L 9 mg/L Pseudo first order kinetics K 1 (min -1 ) q e (mg g -1 ) R 2 2.53 x 10 -2 0.2023 0.981 2.99 x 10 -2 0.7178 0.996 4.38 x 10 -2 2.317 0.934 3.6848 x10 -2 2.21309 0.972 5.2909 x10 -2 5.333 0.928 Pseudo second order kinetics K 2 (g mg -1 min -1 ) q e (mg g -1 ) R 2 2.87 x10 -1 0.4108 0.999 9.25 x10 -2 1.216 0.999 5.177 x10 -2 1.976 0.999 3.648 x10 -2 2.6525 0.998 2.83 x1010 -2 3.300 0.998 Elovich kinetics equation α β R 2 87.09 x10 -2 20.833 0.928 189.98 x10 -2 6.67 0.929 223.3 x10 -2 3.92 0.935 192.75 x10 -2 2.725 0.918 321.29 x10 -2 2.32 0.932 Intra particle diffusion kinetics equation K i (mg g -1 min -0.5 ) C R 2 0.104 1.676 0.828 0.087 1.314 0.782 0.061 1.038 0.807 0.036 0.669 0.796 0.011 0.233 0.796 Liquid flim kinetics equation K d (min -1 ) Intercept R 2 0.049 -0.404 0.953 0.038 0.150 0.960 0.031 0.129 0.923 0.034 0.217 0.986 0.031 0.378 0.990 Table 5: Thermodynamic data for adsorption of fluoride on CaFe 2 O 4 -GO (CaFe 2 O 4 -GO Composite – 2gL -1 ,F- concentration 5mgL -1 , pH6.8 time 240 minute; ∆H,∆S, ∆G and E a are k J mol -1 , J k -1 mol -1 , k J mol -1 , k J mol -1 respectively) ∆H ∆S E a ∆G 303 K 313 K 323 K 333 K 9.9934 36.274 5.527 -1.0055 -1.368 -1.7315 -2.094 Table 6: Comparisons of Langmuir capacities of some adsorbents for fluoride (F - ) adsorption. Adsorbent q m (mgg -1 ) Experimental Temperature (K) References Fe(III)-Sn(IV) 10.47 303 [38] Graphite 3.31 303 [39] Mg Incorporated Bentonite 2.26 298 [37] Hydrous Bismuth oxide 1.93 298 [4] Lanthanum Impregnated Pumice 7.187 298 [40] bacterial–surfactin hydroxyapatite nanoparticle 7.004 298 [41] Cellulose@Hap 4.20 298 [42] CaFe 2 O 4 -GO composite 11.90 303 This work Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4458894","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":309387441,"identity":"daacaa2e-abdb-49a5-8c7f-49205af40c66","order_by":0,"name":"Abdul Matin Ali","email":"","orcid":"","institution":"Assam Don Bosco University","correspondingAuthor":false,"prefix":"","firstName":"Abdul","middleName":"Matin","lastName":"Ali","suffix":""},{"id":309387442,"identity":"e52a0b66-c333-4289-8de6-2f5114ad8515","order_by":1,"name":"Nibedita Kapil","email":"data:image/png;base64,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","orcid":"","institution":"Assam Don Bosco University","correspondingAuthor":true,"prefix":"","firstName":"Nibedita","middleName":"","lastName":"Kapil","suffix":""},{"id":309387443,"identity":"e1d88341-5378-4c13-9b88-d5321ac3d9cf","order_by":2,"name":"Susmita Sen Gupta","email":"","orcid":"","institution":"B.N. 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CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-GO Composite and SEM image (D) of CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-GO composite with fluoride loaded.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4458894/v1/732f91334409e0170997a469.png"},{"id":57605860,"identity":"8bb15b41-348d-4383-80aa-3a6ea7b82acc","added_by":"auto","created_at":"2024-06-03 09:12:08","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":224088,"visible":true,"origin":"","legend":"\u003cp\u003eEDX analysis of (A) CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-GO and Fluoride loaded 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9","display":"","copyAsset":false,"role":"figure","size":61170,"visible":true,"origin":"","legend":"\u003cp\u003eInfluence of pH on adsorption at 303K\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-4458894/v1/014bc9b0e29d5889cca37368.png"},{"id":57605875,"identity":"0133b836-2494-4928-919d-e7f072148c5f","added_by":"auto","created_at":"2024-06-03 09:12:09","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":60763,"visible":true,"origin":"","legend":"\u003cp\u003eInfluence of initial F- concentration on adsorption at 303K\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-4458894/v1/9c93eb1c81dc58e648a7f3bf.png"},{"id":57605880,"identity":"c27e03e4-e16a-4995-8142-3930b27e090a","added_by":"auto","created_at":"2024-06-03 09:12:09","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":61241,"visible":true,"origin":"","legend":"\u003cp\u003eInfluence of adsorbent dose on adsorption at303 K\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-4458894/v1/7b18afc1d170017b0e595e90.png"},{"id":57605872,"identity":"353bb3b0-6381-4b34-80d5-28414712a1b9","added_by":"auto","created_at":"2024-06-03 09:12:08","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":56183,"visible":true,"origin":"","legend":"\u003cp\u003eAmount of fluoride adsorbed per unit mass (q\u003csub\u003ee\u003c/sub\u003e) on CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-GO composites at different interaction time at 303 K\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-4458894/v1/b0cb607381025c623860afab.png"},{"id":57605862,"identity":"093ce8ea-17ae-43f0-9266-cbe30e013f1f","added_by":"auto","created_at":"2024-06-03 09:12:08","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":42208,"visible":true,"origin":"","legend":"\u003cp\u003eLangmuir plot for fluoride adsorption at (303- 333) K (Adsorbent 2 gL\u003csup\u003e-1\u003c/sup\u003e, pH 6.8)\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-4458894/v1/036042d70c2bfc860589596d.png"},{"id":57605871,"identity":"f7cb9e74-7cb5-4b28-950e-83b9e6226dae","added_by":"auto","created_at":"2024-06-03 09:12:08","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":43821,"visible":true,"origin":"","legend":"\u003cp\u003eFreundlich plot for fluoride adsorption at (303 – 333)K (Adsorbent2 gL\u003csup\u003e-1\u003c/sup\u003e, pH 6.8)\u003c/p\u003e","description":"","filename":"14.png","url":"https://assets-eu.researchsquare.com/files/rs-4458894/v1/f923133355b964e58cff3e58.png"},{"id":57605879,"identity":"647f7b2c-f8b4-4aec-90ec-74af3199dce1","added_by":"auto","created_at":"2024-06-03 09:12:09","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":29743,"visible":true,"origin":"","legend":"\u003cp\u003eLagergren first order plot for F\u003csup\u003e- \u003c/sup\u003eadsorption at 303 K (Adsorbent 2gL\u003csup\u003e-1\u003c/sup\u003e, F\u003csup\u003e- ,\u003c/sup\u003e5 mgL\u003csup\u003e-1\u003c/sup\u003e, pH 6.8)\u003c/p\u003e","description":"","filename":"15.png","url":"https://assets-eu.researchsquare.com/files/rs-4458894/v1/80fafb166179cbab1c42e5dc.png"},{"id":57607203,"identity":"c6363298-9c63-48e2-8eea-16affbeede0b","added_by":"auto","created_at":"2024-06-03 09:28:08","extension":"png","order_by":16,"title":"Figure 16","display":"","copyAsset":false,"role":"figure","size":26916,"visible":true,"origin":"","legend":"\u003cp\u003eSecond order plot for F\u003csup\u003e- \u003c/sup\u003eadsorption at 303 K (Adsorbent 2 gL\u003csup\u003e-1\u003c/sup\u003e, F\u003csup\u003e-\u003c/sup\u003e 5 mgL\u003csup\u003e-1\u003c/sup\u003e, pH 6.8)\u003c/p\u003e","description":"","filename":"16.png","url":"https://assets-eu.researchsquare.com/files/rs-4458894/v1/200a96733ef2a4e6f345c68d.png"},{"id":57605878,"identity":"d1288ed1-6ebe-4289-a161-4d157b441f5f","added_by":"auto","created_at":"2024-06-03 09:12:09","extension":"png","order_by":17,"title":"Figure 17","display":"","copyAsset":false,"role":"figure","size":20778,"visible":true,"origin":"","legend":"\u003cp\u003eElovich plot for F\u003csup\u003e- \u003c/sup\u003eadsorption at 303 K (Adsorbent- 2gL\u003csup\u003e-1\u003c/sup\u003e, F\u003csup\u003e-\u003c/sup\u003e5 mgL\u003csup\u003e-1\u003c/sup\u003e, pH 6.8)\u003c/p\u003e","description":"","filename":"17.png","url":"https://assets-eu.researchsquare.com/files/rs-4458894/v1/3f796918433f54faba454a25.png"},{"id":57606562,"identity":"e647d488-4372-4e1e-8ede-b2ce400e9e07","added_by":"auto","created_at":"2024-06-03 09:20:08","extension":"png","order_by":18,"title":"Figure 18","display":"","copyAsset":false,"role":"figure","size":23632,"visible":true,"origin":"","legend":"\u003cp\u003eIntra particle diffusion plot for F\u003csup\u003e- \u003c/sup\u003eadsorption at 303 K (Adsorbent 2 gL\u003csup\u003e-1\u003c/sup\u003e, F\u003csup\u003e-\u003c/sup\u003e 5 mgL\u003csup\u003e-1\u003c/sup\u003e, pH 6.8)\u003c/p\u003e","description":"","filename":"18.png","url":"https://assets-eu.researchsquare.com/files/rs-4458894/v1/a6c11f7d86ecdd7080d35fed.png"},{"id":57605874,"identity":"102b9142-7a57-4a50-a86b-90a0fe10e32a","added_by":"auto","created_at":"2024-06-03 09:12:08","extension":"png","order_by":19,"title":"Figure 19","display":"","copyAsset":false,"role":"figure","size":25473,"visible":true,"origin":"","legend":"\u003cp\u003eLiquid Flim diffusion plot for F\u003csup\u003e- \u003c/sup\u003eadsorption at 303 K (Adsorption 2gL\u003csup\u003e-1\u003c/sup\u003e, F\u003csup\u003e-\u003c/sup\u003e 5 mgL\u003csup\u003e-1\u003c/sup\u003e, pH 6.8)\u003c/p\u003e","description":"","filename":"19.png","url":"https://assets-eu.researchsquare.com/files/rs-4458894/v1/84c5cf8bac9a6a7a8d88040b.png"},{"id":57605877,"identity":"efa6f55b-d7de-409c-afcd-8ffff44b989a","added_by":"auto","created_at":"2024-06-03 09:12:09","extension":"png","order_by":20,"title":"Figure 20","display":"","copyAsset":false,"role":"figure","size":35117,"visible":true,"origin":"","legend":"\u003cp\u003eExtent of adsorption of fluoride concentration (mgL\u003csup\u003e-1\u003c/sup\u003e) at different temperature(K)\u003c/p\u003e","description":"","filename":"20.png","url":"https://assets-eu.researchsquare.com/files/rs-4458894/v1/166e9f24de3da155309e5996.png"},{"id":57605876,"identity":"c1836c09-ad60-41c4-91b0-fffa36f08658","added_by":"auto","created_at":"2024-06-03 09:12:09","extension":"png","order_by":21,"title":"Figure 21","display":"","copyAsset":false,"role":"figure","size":27329,"visible":true,"origin":"","legend":"\u003cp\u003eArrhenius plots forF\u003csup\u003e-\u003c/sup\u003e adsorption on to CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-GO composite\u003c/p\u003e","description":"","filename":"21.png","url":"https://assets-eu.researchsquare.com/files/rs-4458894/v1/557a2794d36e7ca20da8466d.png"},{"id":57649266,"identity":"37da3f49-6bcf-413c-92de-614931d07914","added_by":"auto","created_at":"2024-06-03 21:31:46","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4237652,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4458894/v1/d68c5047-6c10-482d-8aa7-076b03b3426c.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eRemoval of Fluoride from Aqueous Solution by CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e–GO Composite\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eFluorine (F) is one of the most essential trace elements found in human beings and other animals. Human beings are exposed to fluoride through food, water and other products. Lower concentration of fluoride in water is considered as an essential micronutrient to prevent dental caries and facilitate the mineralization hard tissues while at higher level fluoride can harm to human health [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. According to WHO, the maximum acceptable fluoride concentration in drinking water is 1.00 mg/L [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Bureau of Indian standard (BIS) has recommended a desirable limit of fluoride concentration 1.00 mg/L in drinking water, which can be extended to 1.5 mgL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e as permissible limit[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Above this concentration limit fluoride in drinking water can result in multidimensional health problem such as dental and skeletal fluorosis, mottling of teeth, bone diseases and lesions of liver, thyroid and other organs [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Excessive fluoride concentration also causes low haemoglobin level, muscle fibre degeneration, deformities in red blood cells (RBC\u0026rsquo;s) excessive thirst, headache, skin rashes, neurological manifestation [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Therefore, more attention should be taken for the research on defluoridation of water to protect human health. Among all the separation techniques, adsorption is a common practice used for fluoride removal from water mainly because of its cost effectiveness. Moreover, the technique is robust, environmentally friendly, versatile and simple [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. However, the choice of adsorbent is very important in an adsorbent-adsorbate system to get maximum removal efficiency.\u003c/p\u003e \u003cp\u003eGraphene, a single layer of carbon atoms arranged in six member rings in which carbon atoms are in sp\u003csup\u003e2\u003c/sup\u003e hybridized and formation of a two dimensional honeycomb lattice which possesses strong mechanical, electrical and thermal properties with specific surface area at 2630 m\u003csup\u003e2\u003c/sup\u003e/g [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. This property suggests the possibility of synthesis of graphene based composite material with metal oxide [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Graphene oxide (GO) is derived from the graphene which is functionalized graphene with various oxygen containing functional groups. The high adsorption capacity of GO and separation convenience of magnetic material can be increased by addition of magnetic properties in to GO. This gives the available surface area and enhancement of adsorption capacity [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. The calcium ferrite, a magnetic Ca \u0026ndash; Fe oxide, contains Ca\u003csup\u003e2+\u003c/sup\u003e and Fe\u003csup\u003e3+\u003c/sup\u003e in the spinel structure, so the combination of magnetic spinel ferrite can result in interesting characteristics which are useful in various purposes [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. For example, NiFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/graphene was used in lithium-ion batteries as a high performance anode material [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/ZnO-graphene [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] and CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/graphene [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] were used as high performance and recyclable visible light photo catalysts, arsenate removal by using fabricated Cu\u003csub\u003e2\u003c/sub\u003eFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], sulfonated graphene oxide composite used as removing Cu(ll) from aqueous solution [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], etc. The literature review indicates the use of magnetic spinel calcium ferrite \u0026ndash; graphene composites as adsorbent for the removal of F\u003csup\u003e\u0026minus;\u003c/sup\u003e has not been reported so far. In this work, graphene calcium ferrite nano (GCF) composite was synthesized and used as magnetic adsorbent to remove fluoride (F\u003csup\u003e\u0026minus;\u003c/sup\u003e) from drinking water.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Material and method\u003c/h2\u003e \u003cp\u003eGraphene powder was procured from SIGMA- ALDRICH CHEMIE, Gmbh a product of Swizerland. All other chemical and reagents including, Ca(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e4H\u003csub\u003e2\u003c/sub\u003eO, Fe(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e9H\u003csub\u003e2\u003c/sub\u003eO, H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e (98%), KMnO\u003csub\u003e4\u003c/sub\u003e, H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (30%) were received from E-Merk, Mumbai, India. H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e(85%) was purchased from S.d fine chemical Ltd. Mumbai, India. All of these are analytical grade and used it without further purification.\u003c/p\u003e \u003cp\u003eNaF solution (1000 ppm) was prepared by dissolving 1.105 g NaF in 500 ml distilled water and was used as stock solution. From this stock solution the required concentration of F- was prepared and was used for various experiments at room temperature.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Preparation of Graphene oxide\u003c/h2\u003e \u003cp\u003eGO was synthesized by modified Hummers process in which graphite flakes (1.5 g) and KMnO\u003csub\u003e4\u003c/sub\u003e (9.0 g) were successively added in to a 9:1 mixture of con. H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003eand H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e under continuous stirring. The reaction was heated at 323 K and stirred for 12 hours. The reaction was cooled and poured in to ice with 30% H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e. Then mixture was repeatedly washed with 30% HCl and ethanol and then dried it at 353 K.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Preparation of graphene-calcium ferrite composite\u003c/h2\u003e \u003cp\u003e1.0 g GO was sonicated for 1 hr. To it, 0.118 g Ca(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e.4H\u003csub\u003e2\u003c/sub\u003eO and 0.404 g Fe(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e9H\u003csub\u003e2\u003c/sub\u003eO was added with constant stirring for 1 hr. The mixture was kept in an autoclave for 4 hrs at 393 K. The mixture was cooled to room temperature, washed with water and oven dried.\u003c/p\u003e \u003cp\u003e \u003cb\u003eCharacterization\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe powdered X- ray diffraction (XRD) measurement was recorded by Bruker AXS(Germany) X- ray powder diffractometer Model D8 using Cu Kα monochromatized radiation with a step size 0.02\u0026ordm;(2θ). The high resolution transmission electron microgram (HRTEM) image was obtained using JEM-2100, Jeol, Akishima, japan for the study of morphological surface. The Field Emission Scanning Electron Microgram (FESEM) image and energy dispersive X-ray (EDX) were obtained using by Zeiss FESEM model Sigma for morphological structure and elemental composition of the composite. FTIR spectra were obtained by Perkin Elmer (USA), FTIR spectrometer in the range of 400\u0026ndash;4000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The Raman spectra were recorded by using Renishaw (UK) Raman Spectrometer model Renishaw Basis Series with 514 Lasers. The surface area of the composite were determined by Brunauer-Emmett-Teller (BET) N\u003csub\u003e2\u003c/sub\u003e gas method using with the help of Quantachrome Autosorb 1C surface area analyser. The Zeta potential was measured (Zeta, Malvern) for the surface charge of the composite.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Batch adsorption\u003c/h2\u003e \u003cp\u003eAdsorption experiment was carried out in the plastic flasks by adding a fixed amount of adsorbent with 50 ml NaF solution. The mixture was agitated in a water bath incubator shaker (NAVYUG, India) for a predetermined time interval as per the experiment required. The mixture was centrifuged and unadsorbed F\u003csup\u003e\u0026minus;\u003c/sup\u003e present in the supernatant was determined spectrophotometrically (λmax\u0026thinsp;=\u0026thinsp;568 nm). The pH of the adsorbate solution was maintained using 0.01 N NaOH solution and 0.01 N HNO\u003csub\u003e3\u003c/sub\u003e solution. The adsorption amount and rate (percentage of removal) of fluoride were calculated from the difference between the concentration of aqueous solution before and after adsorption according to the following equation\u003c/p\u003e \u003cp\u003eq\u003csub\u003ee\u003c/sub\u003e=(C\u003csub\u003e0\u003c/sub\u003e-C\u003csub\u003ee\u003c/sub\u003e)V/m (1)\u003c/p\u003e \u003cp\u003eExtent of adsorption(%) =(C\u003csub\u003e0\u003c/sub\u003e-C\u003csub\u003ee\u003c/sub\u003e/C\u003csub\u003e0\u003c/sub\u003e) x100 (2)\u003c/p\u003e \u003cp\u003ewhere q\u003csub\u003ee\u003c/sub\u003eis the amount of fluoride adsorbed (mg g\u003csup\u003e\u0026ndash;1\u003c/sup\u003e) per gram of the adsorbent at equilibrium. C\u003csub\u003e0\u003c/sub\u003e (mg L\u003csup\u003e\u0026ndash;1\u003c/sup\u003e) and C\u003csub\u003ee\u003c/sub\u003e (mg L\u003csup\u003e\u0026ndash;1\u003c/sup\u003e) is the initial and equilibrium concentration of fluoride. V (L) is the volume of the solution taken and m (g) is mass of the adsorbent. The adsorption was studied various experimental conditions of initial fluoride concentrations, adsorbent load, interaction time, pH and solution temperature.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Result and discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.1. XRD study\u003c/h2\u003e \u003cp\u003eThe broad diffraction peaks in the X-ray diffractogram (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e1\u003c/span\u003eA and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e1\u003c/span\u003eB) indicates that the mean crystallite size is in the range of nanometre. Presence of all the fundamental Bragg reflection belonging to Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e type fcc structure and absence of impurity peaks in these diffraction patterns, confirming that the annealed samples were also formed in single phase and retains the fcc spinel structure. Calcium ferrite exhibited typical peaks that appeared at 2θ range of 13\u0026ndash;70\u0026ordm;. No typical diffraction peaks of GO (0 0 1) was observed in the XRD patterns of the CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-GO composite. The absence of GO (0 0 1) peak may be ascribed to the fact that GO was reduced to graphene during the hydrothermal reaction in the presence of alcohols. The crystal growth of CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e between the interlayer of graphene destroyed the regular layer stacking, leading to the exfoliation of graphene. The graphene layers could be randomly restacked by the reduction process which results in amorphous behaviour in XRD patterns.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.2 TEM Analysis\u003c/h2\u003e \u003cp\u003eThe formation of GO and CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e is can be confirmed by the TEM measurement. It is employed to study the morphology and shape of the adsorbent materials. It can be seen from the TEM image exfoliated GO (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003eA), large sheets (a few 100 square nanometers) were observed to be situated on the top of the grid. They were transparent and entangled with each other. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003eB shows that the CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles uniformly disperse on the surface of the graphene oxide sheets. From the figure(Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003eC) it can be seen that the selected area electron diffraction (SAED) pattern indicates that nanoparticles are polycrystals.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.3 SEM Analysis\u003c/h2\u003e \u003cp\u003eThe morphology and structure can be investigated from the FESEM study. The SEM image of GO is a smooth surface [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. It is clearly seen from the FESEM micrograph (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eA, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eB, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eC) that CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e stacked on the graphene sheet. The graphene sheet separated the nano particles. In some cases, agglomeration occurred, might be due to the magnetic properties of the prepared materials. The morphology of the prepared materials have changed due to the adsorption of fluoride on to it which was seen in the FESEM micrograph (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eD).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.4 EDX analysis\u003c/h2\u003e \u003cp\u003eEnergy Dispersive X- Ray analysis (EDX) confirms the presence of various elements, namely calcium, iron, carbon and oxygen in the prepared CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-GO composite (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). The adsorption of F- in the composite is confirmed by the presence of fluoride on to materials EDX analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003eB).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.5 FTIR Analysis\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e5\u003c/span\u003e(A), 5(B) and 5(C)represent the FTIR spectra of GO, CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e- GO and CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u0026ndash;GO with fluoride loaded respectively. In the FTIR Spectra of GO a characteristics peak is observed in around 3387 cm\u003csup\u003e\u0026minus;\u0026thinsp;1,\u003c/sup\u003e 1745 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 1402 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003eand 1128 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003ecorresponds to the OH stretching, carbonyl stretching and C-OH stretching and C-O-C an epoxide stretching vibration respectively [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. The stretching vibration of OH slightly shift near 3390 for CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e \u0026ndash;GO Composite. The Ca- Fe metal vibrations of CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-GO composites vibration peak is occurred at 1044 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The peaks occurred at 526 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003eand 566 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003ealso be observed due to the Ca-O and Fe-O stretching vibration [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. The new peak for CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u0026ndash;GO after adsorption at 423 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e confirm the fluoride adsorption [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. The appearance of peak at 1110 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e due to the fluoride adsorption which is corresponds to C-O-Ca stretching vibration.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.6 Raman study\u003c/h2\u003e \u003cp\u003eThe characteristic Raman peak of CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003eobserved nearly at 440, 566, 649[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e6\u003c/span\u003e). The Raman plot of CaFe2O4-GO shows the extra additional peak nearly at 1359 cm-1 and 1571 cm-1 which was called D and G peak.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.7 BET Surface area Analysis.\u003c/h2\u003e \u003cp\u003eThe surface area of CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-GO Composite was determined by BET method. This method was characterised using N\u003csub\u003e2\u003c/sub\u003e adsorption \u0026ndash; desorption isotherm(Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e7\u003c/span\u003e). The BET surface area of the adsorbent CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e- GO composite is 220.80 m\u003csup\u003e2\u003c/sup\u003eg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e which was the much higher surface area of GO is 31.4 m\u003csup\u003e2\u003c/sup\u003eg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.The total pore volume is found to be 0.265 cm\u003csup\u003e3\u003c/sup\u003eg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and the average pore diameter is 4.3 cm\u003csup\u003e3\u003c/sup\u003eg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The mesoporous nature of the adsorbent confirmed by the N\u003csub\u003e2\u003c/sub\u003e adsorption \u0026ndash; desorption isotherm which is type IV isotherm with H3 type loop, this porous nature is more favourable for the fluoride adsorption.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.8Zeta Potential study\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e8\u003c/span\u003e The measurement of zeta potential of CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e - GO composite indicates that the within the pH range nearly 5 to 9 did not passes the zero point charge, indicating that the composite is negatively charged.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Adsorption study","content":"\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Effect of pH\u003c/h2\u003e \u003cp\u003eThe adsorption capacity reaches the maximum at pH 5.0 (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e9\u003c/span\u003e) (Experimental condition: Adsorbent 2 g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, F\u003csup\u003e\u0026minus;\u003c/sup\u003e concentration 1.0\u0026ndash;9.0 mgL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, temperature 303 K, time 240 min, pH 3.0\u0026ndash;10.0). Above pH 5.0, there is a steady decrease in fluoride adsorption capacity. In low pH range, the lower adsorption capacity may be due to the formation of weak hydrofluoric acid or synergism of both chemical and electrostatic interaction between the oxide surface and fluoride ion. At pH\u0026thinsp;\u0026gt;\u0026thinsp;5.0, the decreased adsorption capacity is probably due to the competition for adsorption sites between fluoride and hydroxyl ions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Influence of initial F- concentration\u003c/h2\u003e \u003cp\u003eThe adsorption of F\u003csup\u003e\u0026minus;\u003c/sup\u003e onto CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-GO composites was studied by varying the initial F\u003csup\u003e\u0026minus;\u003c/sup\u003e concentration using an optimum adsorbent dose (Experimental condition: Adsorbent 1.0\u0026ndash;5.0 gL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, pH 6.5, time 240 min, temperature 303 K, F\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e concentration 1.0\u0026ndash;9.0 mgL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) .The extent of adsorption (%) decreases on increasing the F\u003csup\u003e\u0026minus;\u003c/sup\u003e loading, but amount adsorbed per unit mass (q\u003csub\u003ee\u003c/sub\u003e) shows an increasing trend. At low F\u003csup\u003e\u0026minus;\u003c/sup\u003e concentration, the ratio of the number of F\u003csup\u003e\u0026minus;\u003c/sup\u003e to the number of available adsorption sites is small and consequently the adsorption is independent of the initial concentration. But as the concentration of F- increases, the situation changes and the competition for adsorption sites becomes fierce. At this case, unit mass of the adsorbent is exposed to larger number of F- and progressively higher number of F- is taken up with the gradual filling up of the appropriate binding sites. This gives rise to an increase in q\u003csub\u003ee\u003c/sub\u003e although the net adsorption comes down. By increasing the F- concentration in the solution, where the volume of solution used for each adsorption experiment was the same, the average distance between adsorbate and adsorbent would be reduced. Consequently, the dispersive force between adsorbate ion and surface of adsorbent was stronger so that more adsorption would take place. At the same time, the increased diffusivity of adsorbate at its higher concentration was also thought to partly contribute to the enhanced adsorption (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e10\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e4.3 Influence of adsorbent dose\u003c/h2\u003e \u003cp\u003eThe effect of the adsorbent dose on the removal of fluoride was studied at 303K (Experimental condition: F- concentration 1.0\u0026ndash;9.0 mgL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, pH 6.8, temperature 303 K, time 240 min, adsorbent 1.0\u0026ndash;5.0 gL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). The extent of adsorption (%) increases rapidly as more and more of the adsorbent is added. This is to be expected because, for a fixed initial solute concentration, increasing adsorbent amount provides greater surface area or adsorption sites. However, the amount adsorbed per unit mass (q\u003csub\u003ee\u003c/sub\u003e) decreases for all the clay adsorbents. When the adsorbent amount is small, the F- can easily access the adsorption sites and q\u003csub\u003ee\u003c/sub\u003e is high. With the rise in adsorbent load, the corresponding increase in adsorption per unit mass is less because of lower adsorptive capacity utilization of the adsorbent. This may be due to overcrowding of particles which may be termed as a kind of solid concentration effect (Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e11\u003c/span\u003e)\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e4.4 Influence of interaction time\u003c/h2\u003e \u003cp\u003eThe variation of interaction time (Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e12\u003c/span\u003e)( Experimental condition : Adsorbent 2.0 gL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, F\u003csup\u003e\u0026minus;\u003c/sup\u003e concentration 1.0\u0026ndash;9.0 mgL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, pH 6.8, temperature 303 K time 5.0-240 min) showed that the adsorption rapidly increased in first 15 min after which it slowly approached towards equilibrium. With a bare surface initially, the available surface area is very large compared to the density of F\u003csup\u003e\u0026minus;\u003c/sup\u003e ions and thus, the rate of adsorption was high. However, with increasing coverage, the fraction of the bare surface rapidly diminished and F- ions had to compete among themselves for the adsorption sites.\u003c/p\u003e \u003c/div\u003e"},{"header":"5. Adsorption isotherm","content":"\u003cp\u003eAdsorption isotherm indicates the distribution of adsorption molecule between the liquid phase and solid phase.The adsorption isotherm for the adsorption of fluoride on CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e- GO composite at various (303\u0026ndash;333 K) temperature investigated for Langmuir [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. The linear form of Langmuir [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] equation expressed by the following equation,\u003c/p\u003e \u003cp\u003eCe/q\u003csub\u003ee\u003c/sub\u003e=1/(bq\u003csub\u003em\u003c/sub\u003e) +(1/q\u003csub\u003em\u003c/sub\u003e)Ce ( 3)\u003c/p\u003e \u003cp\u003eWhere, Ce\u0026thinsp;=\u0026thinsp;concentration of fluoride at equilibrium (mg L-1), b\u0026thinsp;=\u0026thinsp;Langmuir constant, q\u003csub\u003ee\u003c/sub\u003e = adsorption capacity at equilibrium (mg g-1) and q\u003csub\u003em\u003c/sub\u003e = Langmuir monolayer adsorption capacity (mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). The plot of Ce/q\u003csub\u003ee\u003c/sub\u003e vs C\u003csub\u003ee\u003c/sub\u003efor on F\u003csup\u003e\u0026minus;\u003c/sup\u003e-CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-GO composites interaction is shown in the Fig.\u0026nbsp;\u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e13\u003c/span\u003e.The linearity of the plot suggest that adsorption follows Langmuir isotherms.\u003c/p\u003e \u003cp\u003eThe Freundlich plots, based on the well known Freundlich isotherm[\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].The linear form of Freundlich [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] equation expressed by Eq.\u0026nbsp;(4)\u003c/p\u003e \u003cp\u003eLog(q\u003csub\u003ee\u003c/sub\u003e)\u0026thinsp;=\u0026thinsp;log k\u003csub\u003ef\u003c/sub\u003e + (1/n)log C\u003csub\u003ee\u003c/sub\u003e (4)\u003c/p\u003e \u003cp\u003eWhere, Ce is concentration of fluoride at equilibrium (mgL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), k\u003csub\u003ef\u003c/sub\u003e (mg\u003csup\u003e1\u0026ndash;1/n\u003c/sup\u003e L\u003csup\u003e1/n\u003c/sup\u003e g\u003csup\u003e\u0026ndash;1\u003c/sup\u003e) is the binding energy constant reflecting the affinity of adsorbent to fluoride and n is the Freundlich constant. The plot of log q\u003csub\u003ee\u003c/sub\u003e vs log C\u003csub\u003ee\u003c/sub\u003e is shown in the Fig.\u0026nbsp;\u003cspan refid=\"Fig16\" class=\"InternalRef\"\u003e14\u003c/span\u003e at various temperature (303- 333K)which is straight line. The linearity of the plot also suggests the applicability of Freundlich isotherm for removal of fluoride ion.\u003c/p\u003e \u003cp\u003eThe value of Langmuir and Freundlich isotherm parameters are calculated from the Fig.\u0026nbsp;\u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e13\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig17\" class=\"InternalRef\"\u003e15\u003c/span\u003e which shown in the Table\u0026nbsp;1. The value of regression coefficient (R\u003csup\u003e2\u003c/sup\u003e) is quite close to the unity and the process of removal of fluoride followed Langmuir as well as the Freuindlich isotherm[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]but the experimental data more fitted with the Langmuir isotherm model.\u003c/p\u003e"},{"header":"6. Kinetic study","content":"\u003cp\u003eThe Lagergren pseudo first order and second order integrated model can be applied for the kinetics and adsorption mechanism [\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e] which shown in the Eqs.\u0026nbsp;(5) and (6).\u003c/p\u003e\n\u003cp\u003elog(q\u003csub\u003ee\u003c/sub\u003e-q\u003csub\u003et\u003c/sub\u003e)\u0026thinsp;=\u0026thinsp;log q\u003csub\u003ee\u003c/sub\u003e- K\u003csub\u003e1\u003c/sub\u003et/2.303( 5)\u003c/p\u003e\n\u003cp\u003et/q\u003csub\u003et\u003c/sub\u003e =1/K\u003csub\u003e2\u003c/sub\u003eq\u003csub\u003ee\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;+\u0026thinsp;t/q\u003csub\u003ee\u003c/sub\u003e(6)\u003c/p\u003e\n\u003cp\u003eWhere q\u003csub\u003ee\u003c/sub\u003e and q\u003csub\u003et\u003c/sub\u003e are amounts of adsorbed per unit mass at equilibrium (mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and any time t(min) in the adsorption process. K\u003csub\u003e1\u003c/sub\u003e(min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and K\u003csub\u003e2\u003c/sub\u003e (g mg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003emin\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) were the rate constant for pseudo first order and second order kinetics model, respectively.\u003c/p\u003e\n\u003cp\u003eThe plot log(q\u003csub\u003ee\u003c/sub\u003e-q\u003csub\u003et\u003c/sub\u003e) vs t for pseudo first order should give a straight line. This curve is linear (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e15\u003c/span\u003e) and the rate constant, K\u003csub\u003e1\u003c/sub\u003e is 4.38x10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Table\u0026nbsp;2). The q\u003csub\u003ee\u003c/sub\u003e values obtained from the Lagergren plots differed from the experimental q\u003csub\u003ee\u003c/sub\u003e values nearly 22.10%. Therefore, the first order kinetics is less likely to explain the rate processes. Again the plots of t/q\u003csub\u003et\u003c/sub\u003e vs. t (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e16\u003c/span\u003e) is linear (R\u003csup\u003e2\u003c/sup\u003e\u003csub\u003e~\u003c/sub\u003e +0.99) with the rate constant, K\u003csub\u003e2\u003c/sub\u003e is found 5.18 x 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e gmg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003emin\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eA comparison of q\u003csub\u003ee\u003c/sub\u003e values (experimental and those obtained from the second order plots) indicates that the adsorption is preferably takes place in second order kinetics.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eElovich equation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe Elovich equation [\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e] valid for chemisorptions of heterogeneous solid surface which is expressed as\u003c/p\u003e\n\u003cp\u003eq\u003csub\u003et\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;\u0026beta;ln(\u0026alpha;\u0026beta;)\u0026thinsp;+\u0026thinsp;lnt (7)\u003c/p\u003e\n\u003cp\u003ewhere \u0026alpha; and \u0026beta; is the Elovich coefficient.The value of Elovich coefficient can be calculated from the plot q\u003csub\u003et\u003c/sub\u003e vs ln t (Fig. \u003cspan class=\"InternalRef\"\u003e17\u003c/span\u003e). The value of adsorptive coefficient, \u0026alpha; and desorption coefficient, \u0026beta; is varies from 87.09 x 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e to 321.29x 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e g mg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003emin\u003csup\u003e2\u003c/sup\u003e and 2.32 to 20.833 mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e respectively with R\u003csup\u003e2\u003c/sup\u003e value\u0026thinsp;~\u0026thinsp;0.918 to 0.935, shown in Table \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e,which is relatively low value.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIntra particle diffusion\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo provide definite information of the porous adsorbent taken as the consideration of appropriate kinetic adsorption model [\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/p\u003e\n\u003cp\u003eq\u003csub\u003et\u003c/sub\u003e = k\u003csub\u003ei\u003c/sub\u003et\u003csup\u003e0.5\u003c/sup\u003e+ C(8)\u003c/p\u003e\n\u003cp\u003ewhere k\u003csub\u003ei\u003c/sub\u003e= internal diffusion constant (mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e min\u003csup\u003e\u0026minus;\u0026thinsp;0.5\u003c/sup\u003e) q\u003csub\u003et\u003c/sub\u003e is the amount offluoride adsorbed at any time t (min).The value of k\u003csub\u003ei\u003c/sub\u003eand C can be calculated from the intercept of the plot of q\u003csub\u003et\u003c/sub\u003e vs t\u003csup\u003e0.5\u003c/sup\u003e curve. The k\u003csub\u003ei\u003c/sub\u003evalue is 0.104 mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e min\u003csup\u003e\u0026minus;\u0026thinsp;0.5\u003c/sup\u003e to 0.011 mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003emin\u003csup\u003e\u0026minus;\u0026thinsp;0.5\u003c/sup\u003eand Cis 1.676 to 0.233 shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e.The linear portions of the curves do not pass through the origin (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e18\u003c/span\u003e) indicating that the mechanism of fluoride removal on CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-GO composite is not followed solely by inter-particle diffusion although the possibility is not fully ruled out.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eLiquid film model\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe equation of liquid film diffusion model (36) is\u003c/p\u003e\n\u003cp\u003eln(1-q\u003csub\u003et\u003c/sub\u003e/q\u003csub\u003ee\u003c/sub\u003e) = -k\u003csub\u003efd\u003c/sub\u003e t (9)\u003c/p\u003e\n\u003cp\u003eWhere k\u003csub\u003ed\u003c/sub\u003e (min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) is a rate parameter.The curve is linear with R\u003csup\u003e2\u003c/sup\u003e value\u0026thinsp;+\u0026thinsp;0.923 to +\u0026thinsp;990 and the intercept is -0.404 to +\u0026thinsp;0.378 (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e19\u003c/span\u003e). The curve do not pass through the origin but the intercept is very close to zero so, diffusion occurs from liquid phase might have great important than intra particle diffusion model. The k\u003csub\u003ed\u003c/sub\u003evalue is in the range of 3.1 x 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e to 4.9 x10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003eshown in Table.4.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInfluence of Temperature and adsorption thermodynamics\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe interaction between the adsorbent, CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-GO composite and fluoride in the range of 303 K to 333 K indicate the process is endothermic in nature, as the temperature increases the extent of adsorption also increases (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e20\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eThe thermodynamic adsorption parameter ∆H,∆S,∆G were computed by the following equation,\u003c/p\u003e\n\u003cp\u003elnK\u003csub\u003ed\u003c/sub\u003e =∆S/R - ∆H/RT (10)\u003c/p\u003e\n\u003cp\u003e∆G =∆H -T∆S (11)\u003c/p\u003e\n\u003cp\u003eWhere K\u003csub\u003ed\u003c/sub\u003e (q\u003csub\u003ee\u003c/sub\u003e/C\u003csub\u003ee\u003c/sub\u003e) is the distribution coefficient,T is the temperature(K),Ideal gas constant R(8.314 JK\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003emol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e).∆H is change in enthalpy,∆S is change in entropyand ∆G is change in Gibbs free energy.The value of change in enthalpy,∆H and change in entropy,∆S calculated from the plot ln K\u003csub\u003ed\u003c/sub\u003e vs 1/T.\u003c/p\u003e\n\u003cp\u003eIn the present work,the positive ∆H indicates the endothermic behaviour of adsorbate-adsorbent system(Table \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e). The positive value of change in entropy,∆S indicates the increase of entropy with increase in temperature which suggested the adsorption process is favourable for fluoride adsorption. The negative value of change in Gibbs free energy,∆G with rise in temperature suggested that the adsorption process is favourable.\u003c/p\u003e\n\u003cp\u003eThe temperature dependence of a reaction is given by a equation called Arrhenius equation expressed as,\u003c/p\u003e\n\u003cp\u003eK\u0026thinsp;=\u0026thinsp;A exp\u003csup\u003e\u0026minus;\u0026thinsp;Ea/RT\u003c/sup\u003e (12)\u003c/p\u003e\n\u003cp\u003elnk\u0026thinsp;=\u0026thinsp;ln A \u0026ndash;E\u003csub\u003ea\u003c/sub\u003e/RT (13)\u003c/p\u003e\n\u003cp\u003eWhere k (g mg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) is the pseudo second order rate constant, A (g mg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) is the frequency factor, E\u003csub\u003ea\u003c/sub\u003e (k j mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) is the activation energy for adsorption, R (8.314 j mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e k\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) is the gas constant and T is the temperature in Kelvin scale.\u003c/p\u003e\n\u003cp\u003eThe linear fitting curve were obtained by plotting logk vs 1/T (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e21\u003c/span\u003e) and the activation parameter are found from slope and intercept. The activation energy, E\u003csub\u003ea\u003c/sub\u003e for the process is found 5.527 k j mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e which signifies the process might be physically controlled [\u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this work we successfully synthesized the CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-GO composite. Removal of fluoride from aqueous solution by CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-GO composite followed the Langmuir as well as Freundlich isotherm.The Langmuir monolayer capacity is 11.90 mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.The change in enthalpy was a positive quantity which suggest the adsorption process was endothermic in nature. The extent of adsorption increases with increase in temperature. The adsorption process was preferably followed the second order kinetics. Removal of fluoride from water by this adsorbent was dependent on pH of the medium. The process was governed by the decrease in Gibbs free energy.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e1. There is no funding for this manuscript submission.\u003c/p\u003e\n\u003cp\u003e2. The Authors declare no conflict of interest.\u003c/p\u003e\n\u003cp\u003e3. This is an original research work and new data is incorporated based on the experimental work.\u003c/p\u003e\n\u003cp\u003e4. Ethical statement for this manuscript is not applicable.\u003c/p\u003e\n\u003ch2\u003eAcknowledgement\u003c/h2\u003e\n\u003cp\u003eThe authors gratefully thank Assam Don Bosco University, Assam and B.N. College, Dhubri, Assam for assisting this research work. The authors duly acknowledge Gauhati University, IIT Guwahati, Tezpur University and IASST Guwahati, for their valuable support for characterization of materials.\u003c/p\u003e\n\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eMr. Abdul Matin Ali carried out the experimental research work and prepared manuscript under the mentorship of Dr. Nibedita Kapil, Dr. Susmita Sen Gupta and Dr. Dhruba Chakraborty. He carried out his research work in the Department of Chemistry , B. N. College, Dhubri, Assam, India and Assam Don Bosco University, Assam, India. All authors reviewed the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eZhang,T., Li,Q., Mei,Z., Xiao,H., Lu,H., Zhou,Y.: Adsorption of fluoride ions onto non-thermal plasmamodified CeO2/Al2O3 composites. Desalin. 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Soc. \u003cstrong\u003e69\u003c/strong\u003e, 2836-2848 (1947).\u003c/li\u003e\n\u003cli\u003eThakrea,D., Rayalua,S., Kawadea,R., Meshramb,S., Subrtc,J., Labhsetwar, N.: Magnesium incorporated bentonite clay for defluoridation of drinking water. J. Hazard. Mater. \u003cstrong\u003e180\u003c/strong\u003e, 122\u0026ndash;130 (2010) \u003c/li\u003e\n\u003cli\u003eBiswas,K., Gupta,K., Ghosh,U.C.: Adsorption of fluoride by hydrous iron(III)\u0026ndash;tin(IV) bimetal mixed oxide from the aqueous solutions. Chem. Eng. J. \u003cstrong\u003e149\u003c/strong\u003e ,196\u0026ndash;206 (2009)\u003c/li\u003e\n\u003cli\u003eKarthikeyan,M., Elango,K.P.: Removal of fluoride from aqueous solution using graphite: A Kinetic and thermodynamic study. Indian J. Chem.. Technol. \u003cstrong\u003e15\u003c/strong\u003e, 525-532 (2008)\u003c/li\u003e\n\u003cli\u003eVardhan, C.V., Srimurali, M.: Preparation of Lanthanum Impregnated Pumice for defluoridation of water: Batch and column experiments. J. Environ. Chem. Eng. \u003cstrong\u003e6\u003c/strong\u003e, 858\u0026ndash; 865 (2018)\u003c/li\u003e\n\u003cli\u003eMaity, J.P., Hsu, C.M., Lin, T. J., Lee, W.C., Bhattacharya, P., Bundschuh, J., Chen, C.Y.: Removal of fluoride from water through bacterial\u0026ndash;surfactin mediated novel hydroxyapatite nanoparticle and its efficiency assessment: adsorption isotherm, adsorption kinetic and adsorption thermodynamics. Environ. Nanotechnol. Monit. Manag.\u003cstrong\u003e 9\u003c/strong\u003e, 18\u0026ndash;28 (2018)\u003c/li\u003e\n\u003cli\u003eYu, X., Tong, S., Ge, M., Zuo, J.: Removal of fluoride from drinking water by cellulose@hydroxyapatite nanocomposites. Carbohydr. Polym. \u003cstrong\u003e92\u003c/strong\u003e, 269\u0026ndash;275 (2013)\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTable : 1 The value of Langmuir and Freuindlich isotherm parameters for different temperature(K).\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"650\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.692307692307693%\" valign=\"top\"\u003e\n \u003cp\u003eTemperature (K)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"35.53846153846154%\" valign=\"top\"\u003e\n \u003cp\u003eLangmuir Isotherm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"40.76923076923077%\" valign=\"top\"\u003e\n \u003cp\u003eFreundlich Isotherm\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.692307692307693%\" valign=\"top\"\u003e\n \u003cp\u003e303\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"35.53846153846154%\" valign=\"top\"\u003e\n \u003cp\u003eq\u003csub\u003em \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/sub\u003e11.90 mgg\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eb \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; 0.1582\u003c/p\u003e\n \u003cp\u003eR\u003csup\u003e2 \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/sup\u003e0.999 \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"40.76923076923077%\" valign=\"top\"\u003e\n \u003cp\u003en \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; 1.256 mg\u003csup\u003e1\u0026ndash;1/n\u0026nbsp;\u003c/sup\u003eL\u003csup\u003e1/n\u0026nbsp;\u003c/sup\u003eg\u003csup\u003e\u0026ndash;1\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003ek\u003csub\u003ef\u003c/sub\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; 1.493\u003c/p\u003e\n \u003cp\u003eR\u003csup\u003e2 \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/sup\u003e0.996\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.692307692307693%\" valign=\"top\"\u003e\n \u003cp\u003e313\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"35.53846153846154%\" valign=\"top\"\u003e\n \u003cp\u003eq\u003csub\u003em \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/sub\u003e10.00 mgg\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eb \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; 0.235\u003c/p\u003e\n \u003cp\u003eR\u003csup\u003e2 \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/sup\u003e0.995\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"40.76923076923077%\" valign=\"top\"\u003e\n \u003cp\u003en \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;1.323 \u0026nbsp; mg\u003csup\u003e1\u0026ndash;1/n\u0026nbsp;\u003c/sup\u003eL\u003csup\u003e1/n\u003c/sup\u003e g\u003csup\u003e\u0026ndash;1\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003ek\u003csub\u003ef \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/sub\u003e1.718\u003c/p\u003e\n \u003cp\u003eR\u003csup\u003e2\u0026nbsp;\u003c/sup\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;0.990\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.692307692307693%\" valign=\"top\"\u003e\n \u003cp\u003e323\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"35.53846153846154%\" valign=\"top\"\u003e\n \u003cp\u003eq\u003csub\u003em \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/sub\u003e9.61 \u0026nbsp;mgg\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eb \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; 0.3041\u003c/p\u003e\n \u003cp\u003eR\u003csup\u003e2 \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/sup\u003e0.992\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"40.76923076923077%\" valign=\"top\"\u003e\n \u003cp\u003en \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; 1.355 \u0026nbsp; \u0026nbsp;mg\u003csup\u003e1\u0026ndash;1/n\u0026nbsp;\u003c/sup\u003eL\u003csup\u003e1/n\u003c/sup\u003e g\u003csup\u003e\u0026ndash;1\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003ek\u003csub\u003ef\u003c/sub\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; 1.991\u003c/p\u003e\n \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; 0.989\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.692307692307693%\" valign=\"top\"\u003e\n \u003cp\u003e333\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"35.53846153846154%\" valign=\"top\"\u003e\n \u003cp\u003eq\u003csub\u003em \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/sub\u003e8.547 \u0026nbsp;mgg\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eb \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; 0.4699\u003c/p\u003e\n \u003cp\u003eR\u003csup\u003e2 \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/sup\u003e 0.991\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"40.76923076923077%\" valign=\"top\"\u003e\n \u003cp\u003en \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;1.479 \u0026nbsp; \u0026nbsp;mg\u003csup\u003e1\u0026ndash;1/n\u0026nbsp;\u003c/sup\u003eL\u003csup\u003e1/n\u003c/sup\u003e g\u003csup\u003e\u0026ndash;1\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eK\u003csub\u003ef\u003c/sub\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; 2.350\u003c/p\u003e\n \u003cp\u003eR\u003csup\u003e2\u0026nbsp;\u003c/sup\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; 0.986\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003eTable : 2 First order and Second order rate coefficient, Experimental and Computed q\u003csub\u003ee\u003c/sub\u003e values from Lagergren and second order plots for adsorption of fluoride on CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-GO composites at 303 K.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"50%\" colspan=\"2\" valign=\"top\"\u003e\n \u003cp\u003eLagergren first order rate coefficient\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"50%\" colspan=\"2\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp;Second order rate coefficient\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.376623376623378%\" valign=\"top\"\u003e\n \u003cp\u003eK\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"26.623376623376622%\" valign=\"top\"\u003e\n \u003cp\u003e0.0438 min\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.837662337662337%\" valign=\"top\"\u003e\n \u003cp\u003eK\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25.162337662337663%\" valign=\"top\"\u003e\n \u003cp\u003e0.0518 g mg\u003csup\u003e-1\u003c/sup\u003e min\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.376623376623378%\" valign=\"top\"\u003e\n \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"26.623376623376622%\" valign=\"top\"\u003e\n \u003cp\u003e0.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.837662337662337%\" valign=\"top\"\u003e\n \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25.162337662337663%\" valign=\"top\"\u003e\n \u003cp\u003e0.999\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.376623376623378%\" valign=\"top\"\u003e\n \u003cp\u003eq\u003csub\u003ee\u003c/sub\u003e (calculated)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"26.623376623376622%\" valign=\"top\"\u003e\n \u003cp\u003e2.317\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.837662337662337%\" valign=\"top\"\u003e\n \u003cp\u003eq\u003csub\u003ee\u003c/sub\u003e(calculated)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25.162337662337663%\" valign=\"top\"\u003e\n \u003cp\u003e1.976\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.376623376623378%\" valign=\"top\"\u003e\n \u003cp\u003eq\u003csub\u003ee\u003c/sub\u003e(Exp.)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"26.623376623376622%\" valign=\"top\"\u003e\n \u003cp\u003e1.898\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.837662337662337%\" valign=\"top\"\u003e\n \u003cp\u003eq\u003csub\u003ee\u003c/sub\u003e(Exp.)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25.162337662337663%\" valign=\"top\"\u003e\n \u003cp\u003e1.898\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.376623376623378%\" valign=\"top\"\u003e\n \u003cp\u003eDeviation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"26.623376623376622%\" valign=\"top\"\u003e\n \u003cp\u003e22.10%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.837662337662337%\" valign=\"top\"\u003e\n \u003cp\u003eDeviation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25.162337662337663%\" valign=\"top\"\u003e\n \u003cp\u003e4.10 \u0026nbsp;%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003eTable: 3 Pseudo Second order kinetic parameters for the fluoride adsorption at different temperature (CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-GO composites- 2gL\u003csup\u003e-1\u003c/sup\u003e, F\u003csup\u003e-\u003c/sup\u003e 5 mgL\u003csup\u003e-1\u003c/sup\u003e, pH 6.8)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"631\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.164817749603802%\" valign=\"top\"\u003e\n \u003cp\u003eTemperature\u003c/p\u003e\n \u003cp\u003e(K)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.225039619651348%\" valign=\"top\"\u003e\n \u003cp\u003eK\u003csub\u003e2\u003c/sub\u003e(gmg\u003csup\u003e-1\u003c/sup\u003emin\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.164817749603802%\" valign=\"top\"\u003e\n \u003cp\u003eq\u003csub\u003ee,cal\u003c/sub\u003e(mgg\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.9080824088748%\" valign=\"top\"\u003e\n \u003cp\u003eq\u003csub\u003ee,Exp\u003c/sub\u003e(mg g\u003csup\u003e-\u003c/sup\u003e1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.492868462757528%\" valign=\"top\"\u003e\n \u003cp\u003eDeviation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.044374009508717%\" valign=\"top\"\u003e\n \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.164817749603802%\" valign=\"top\"\u003e\n \u003cp\u003e303\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.225039619651348%\" valign=\"top\"\u003e\n \u003cp\u003e5.18 x 10\u003csup\u003e-2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.164817749603802%\" valign=\"top\"\u003e\n \u003cp\u003e1.976\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.9080824088748%\" valign=\"top\"\u003e\n \u003cp\u003e1.898\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.492868462757528%\" valign=\"top\"\u003e\n \u003cp\u003e4.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.044374009508717%\" valign=\"top\"\u003e\n \u003cp\u003e0.999\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.164817749603802%\" valign=\"top\"\u003e\n \u003cp\u003e313\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.225039619651348%\" valign=\"top\"\u003e\n \u003cp\u003e5.80 x 10\u003csup\u003e-2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.164817749603802%\" valign=\"top\"\u003e\n \u003cp\u003e1.972\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.9080824088748%\" valign=\"top\"\u003e\n \u003cp\u003e1.905\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.492868462757528%\" valign=\"top\"\u003e\n \u003cp\u003e3.52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.044374009508717%\" valign=\"top\"\u003e\n \u003cp\u003e0.999\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.164817749603802%\" valign=\"top\"\u003e\n \u003cp\u003e323\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.225039619651348%\" valign=\"top\"\u003e\n \u003cp\u003e5.92 x 10\u003csup\u003e-2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.164817749603802%\" valign=\"top\"\u003e\n \u003cp\u003e2.012\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.9080824088748%\" valign=\"top\"\u003e\n \u003cp\u003e1.950\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.492868462757528%\" valign=\"top\"\u003e\n \u003cp\u003e3.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.044374009508717%\" valign=\"top\"\u003e\n \u003cp\u003e0.999\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.164817749603802%\" valign=\"top\"\u003e\n \u003cp\u003e333\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.225039619651348%\" valign=\"top\"\u003e\n \u003cp\u003e6.37 x 10\u003csup\u003e-2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.164817749603802%\" valign=\"top\"\u003e\n \u003cp\u003e2.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.9080824088748%\" valign=\"top\"\u003e\n \u003cp\u003e2.052\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.492868462757528%\" valign=\"top\"\u003e\n \u003cp\u003e3.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.044374009508717%\" valign=\"top\"\u003e\n \u003cp\u003e0.999\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003eTable 4. Different kinetic adsorption parameters for adsorption of fluoride on to CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-GO composite of different initial fluoride concentration at 303K, pH- 6.8\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"100%\" colspan=\"6\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Value\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.70860927152318%\" valign=\"top\"\u003e\n \u003cp\u003eParameters\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.735099337748345%\" valign=\"top\"\u003e\n \u003cp\u003e1 mg/L\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.556291390728475%\" valign=\"top\"\u003e\n \u003cp\u003e3 mg/L\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.556291390728475%\" valign=\"top\"\u003e\n \u003cp\u003e5 mg/L\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.721854304635762%\" valign=\"top\"\u003e\n \u003cp\u003e7 mg/L\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.721854304635762%\" valign=\"top\"\u003e\n \u003cp\u003e9 mg/L\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.70860927152318%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"64.56953642384106%\" colspan=\"4\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; Pseudo first order kinetics\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.721854304635762%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.70860927152318%\" valign=\"top\"\u003e\n \u003cp\u003eK\u003csub\u003e1\u003c/sub\u003e(min\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e\n \u003cp\u003eq\u003csub\u003ee\u003c/sub\u003e(mg g\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e\n \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.735099337748345%\" valign=\"top\"\u003e\n \u003cp\u003e2.53 x 10\u003csup\u003e-2\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e0.2023\u003c/p\u003e\n \u003cp\u003e0.981\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.556291390728475%\" valign=\"top\"\u003e\n \u003cp\u003e2.99 x 10\u003csup\u003e-2\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e0.7178\u003c/p\u003e\n \u003cp\u003e0.996\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.556291390728475%\" valign=\"top\"\u003e\n \u003cp\u003e4.38 x 10\u003csup\u003e-2\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e2.317\u003c/p\u003e\n \u003cp\u003e0.934\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.721854304635762%\" valign=\"top\"\u003e\n \u003cp\u003e3.6848 x10\u003csup\u003e-2\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e2.21309\u003c/p\u003e\n \u003cp\u003e0.972\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.721854304635762%\" valign=\"top\"\u003e\n \u003cp\u003e5.2909 x10\u003csup\u003e-2\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e5.333\u003c/p\u003e\n \u003cp\u003e0.928\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.70860927152318%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"64.56953642384106%\" colspan=\"4\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; Pseudo second order kinetics\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.721854304635762%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.70860927152318%\" valign=\"top\"\u003e\n \u003cp\u003eK\u003csub\u003e2\u003c/sub\u003e(g mg\u003csup\u003e-1\u003c/sup\u003emin\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e\n \u003cp\u003eq\u003csub\u003ee\u003c/sub\u003e(mg g\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e\n \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.735099337748345%\" valign=\"top\"\u003e\n \u003cp\u003e2.87 x10\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e0.4108\u003c/p\u003e\n \u003cp\u003e0.999\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.556291390728475%\" valign=\"top\"\u003e\n \u003cp\u003e9.25 x10\u003csup\u003e-2\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e1.216\u003c/p\u003e\n \u003cp\u003e0.999\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.556291390728475%\" valign=\"top\"\u003e\n \u003cp\u003e5.177 x10\u003csup\u003e-2\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e1.976\u003c/p\u003e\n \u003cp\u003e0.999\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.721854304635762%\" valign=\"top\"\u003e\n \u003cp\u003e3.648 x10\u003csup\u003e-2\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e2.6525\u003c/p\u003e\n \u003cp\u003e0.998\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.721854304635762%\" valign=\"top\"\u003e\n \u003cp\u003e2.83 x1010\u003csup\u003e-2\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e3.300\u003c/p\u003e\n \u003cp\u003e0.998\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.70860927152318%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"64.56953642384106%\" colspan=\"4\" valign=\"top\"\u003e\n \u003cp\u003eElovich kinetics equation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.721854304635762%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.70860927152318%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026alpha;\u003c/p\u003e\n \u003cp\u003e\u0026beta;\u003c/p\u003e\n \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.735099337748345%\" valign=\"top\"\u003e\n \u003cp\u003e87.09 x10\u003csup\u003e-2\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e20.833\u003c/p\u003e\n \u003cp\u003e0.928\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.556291390728475%\" valign=\"top\"\u003e\n \u003cp\u003e189.98 x10\u003csup\u003e-2\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e6.67\u003c/p\u003e\n \u003cp\u003e0.929\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.556291390728475%\" valign=\"top\"\u003e\n \u003cp\u003e223.3 x10\u003csup\u003e-2\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e3.92\u003c/p\u003e\n \u003cp\u003e0.935\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.721854304635762%\" valign=\"top\"\u003e\n \u003cp\u003e192.75 x10\u003csup\u003e-2\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e2.725\u003c/p\u003e\n \u003cp\u003e0.918\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.721854304635762%\" valign=\"top\"\u003e\n \u003cp\u003e321.29 x10\u003csup\u003e-2\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e2.32\u003c/p\u003e\n \u003cp\u003e0.932\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.70860927152318%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"64.56953642384106%\" colspan=\"4\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp;Intra particle diffusion kinetics equation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.721854304635762%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.70860927152318%\" valign=\"top\"\u003e\n \u003cp\u003eK\u003csub\u003ei\u003c/sub\u003e(mg g\u003csup\u003e-1\u003c/sup\u003emin\u003csup\u003e-0.5\u003c/sup\u003e)\u003c/p\u003e\n \u003cp\u003eC\u003c/p\u003e\n \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.735099337748345%\" valign=\"top\"\u003e\n \u003cp\u003e0.104\u003c/p\u003e\n \u003cp\u003e1.676\u003c/p\u003e\n \u003cp\u003e0.828\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.556291390728475%\" valign=\"top\"\u003e\n \u003cp\u003e0.087\u003c/p\u003e\n \u003cp\u003e1.314\u003c/p\u003e\n \u003cp\u003e0.782\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.556291390728475%\" valign=\"top\"\u003e\n \u003cp\u003e0.061\u003c/p\u003e\n \u003cp\u003e1.038\u003c/p\u003e\n \u003cp\u003e0.807\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.721854304635762%\" valign=\"top\"\u003e\n \u003cp\u003e0.036\u003c/p\u003e\n \u003cp\u003e0.669\u003c/p\u003e\n \u003cp\u003e0.796\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.721854304635762%\" valign=\"top\"\u003e\n \u003cp\u003e0.011\u003c/p\u003e\n \u003cp\u003e0.233\u003c/p\u003e\n \u003cp\u003e0.796\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.70860927152318%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"64.56953642384106%\" colspan=\"4\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp;Liquid flim kinetics equation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.721854304635762%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.70860927152318%\" valign=\"top\"\u003e\n \u003cp\u003eK\u003csub\u003ed\u003c/sub\u003e(min\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e\n \u003cp\u003eIntercept\u003c/p\u003e\n \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.735099337748345%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;0.049\u003c/p\u003e\n \u003cp\u003e-0.404\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;0.953\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.556291390728475%\" valign=\"top\"\u003e\n \u003cp\u003e0.038\u003c/p\u003e\n \u003cp\u003e0.150\u003c/p\u003e\n \u003cp\u003e0.960\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.556291390728475%\" valign=\"top\"\u003e\n \u003cp\u003e0.031\u003c/p\u003e\n \u003cp\u003e0.129\u003c/p\u003e\n \u003cp\u003e0.923\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.721854304635762%\" valign=\"top\"\u003e\n \u003cp\u003e0.034\u003c/p\u003e\n \u003cp\u003e0.217\u003c/p\u003e\n \u003cp\u003e0.986\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.721854304635762%\" valign=\"top\"\u003e\n \u003cp\u003e0.031\u003c/p\u003e\n \u003cp\u003e0.378\u003c/p\u003e\n \u003cp\u003e0.990\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003eTable 5: Thermodynamic data for adsorption of fluoride on CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-GO (CaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-GO Composite \u0026ndash; 2gL\u003csup\u003e-1\u003c/sup\u003e,F- concentration 5mgL\u003csup\u003e-1\u003c/sup\u003e, pH6.8 time 240 minute; ∆H,∆S, ∆G and E\u003csub\u003ea\u003c/sub\u003eare k J mol\u003csup\u003e-1\u003c/sup\u003e, J k\u003csup\u003e-1\u003c/sup\u003emol\u003csup\u003e-1\u003c/sup\u003e, k J mol\u003csup\u003e-1\u003c/sup\u003e, k J mol\u003csup\u003e-1\u003c/sup\u003e respectively)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"14.285714285714286%\" valign=\"top\"\u003e\n \u003cp\u003e∆H\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.285714285714286%\" valign=\"top\"\u003e\n \u003cp\u003e∆S\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.285714285714286%\" valign=\"top\"\u003e\n \u003cp\u003eE\u003csub\u003ea\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"57.142857142857146%\" colspan=\"4\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;∆G\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"42.857142857142854%\" colspan=\"3\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.285714285714286%\" valign=\"top\"\u003e\n \u003cp\u003e303 K\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.285714285714286%\" valign=\"top\"\u003e\n \u003cp\u003e313 K\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.285714285714286%\" valign=\"top\"\u003e\n \u003cp\u003e323 K\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.285714285714286%\" valign=\"top\"\u003e\n \u003cp\u003e333 K\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"14.285714285714286%\" valign=\"top\"\u003e\n \u003cp\u003e9.9934\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.285714285714286%\" valign=\"top\"\u003e\n \u003cp\u003e36.274\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.285714285714286%\" valign=\"top\"\u003e\n \u003cp\u003e5.527\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.285714285714286%\" valign=\"top\"\u003e\n \u003cp\u003e-1.0055\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.285714285714286%\" valign=\"top\"\u003e\n \u003cp\u003e-1.368\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.285714285714286%\" valign=\"top\"\u003e\n \u003cp\u003e-1.7315\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.285714285714286%\" valign=\"top\"\u003e\n \u003cp\u003e-2.094\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003eTable 6: Comparisons of Langmuir capacities of some adsorbents for fluoride (F\u003csup\u003e-\u003c/sup\u003e) adsorption.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"37.25165562913907%\" valign=\"top\"\u003e\n \u003cp\u003eAdsorbent\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.185430463576157%\" valign=\"top\"\u003e\n \u003cp\u003eq\u003csub\u003em\u003c/sub\u003e(mgg\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"26.32450331125828%\" valign=\"top\"\u003e\n \u003cp\u003eExperimental Temperature (K)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.23841059602649%\" valign=\"top\"\u003e\n \u003cp\u003eReferences\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"37.25165562913907%\" valign=\"top\"\u003e\n \u003cp\u003eFe(III)-Sn(IV)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.185430463576157%\" valign=\"top\"\u003e\n \u003cp\u003e10.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"26.32450331125828%\" valign=\"top\"\u003e\n \u003cp\u003e303\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.23841059602649%\" valign=\"top\"\u003e\n \u003cp\u003e[38]\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"37.25165562913907%\" valign=\"top\"\u003e\n \u003cp\u003eGraphite\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.185430463576157%\" valign=\"top\"\u003e\n \u003cp\u003e3.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"26.32450331125828%\" valign=\"top\"\u003e\n \u003cp\u003e303\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.23841059602649%\" valign=\"top\"\u003e\n \u003cp\u003e[39]\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"37.25165562913907%\" valign=\"top\"\u003e\n \u003cp\u003eMg Incorporated Bentonite\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.185430463576157%\" valign=\"top\"\u003e\n \u003cp\u003e2.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"26.32450331125828%\" valign=\"top\"\u003e\n \u003cp\u003e298\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.23841059602649%\" valign=\"top\"\u003e\n \u003cp\u003e[37]\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"37.25165562913907%\" valign=\"top\"\u003e\n \u003cp\u003eHydrous Bismuth oxide\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.185430463576157%\" valign=\"top\"\u003e\n \u003cp\u003e1.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"26.32450331125828%\" valign=\"top\"\u003e\n \u003cp\u003e298\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.23841059602649%\" valign=\"top\"\u003e\n \u003cp\u003e[4]\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"37.25165562913907%\" valign=\"top\"\u003e\n \u003cp\u003eLanthanum Impregnated Pumice\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.185430463576157%\" valign=\"top\"\u003e\n \u003cp\u003e7.187\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"26.32450331125828%\" valign=\"top\"\u003e\n \u003cp\u003e298\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.23841059602649%\" valign=\"top\"\u003e\n \u003cp\u003e[40]\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"37.25165562913907%\" valign=\"top\"\u003e\n \u003cp\u003ebacterial\u0026ndash;surfactin\u003c/p\u003e\n \u003cp\u003ehydroxyapatite nanoparticle\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.185430463576157%\" valign=\"top\"\u003e\n \u003cp\u003e7.004\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"26.32450331125828%\" valign=\"top\"\u003e\n \u003cp\u003e298\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.23841059602649%\" valign=\"top\"\u003e\n \u003cp\u003e[41]\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"37.25165562913907%\" valign=\"top\"\u003e\n \u003cp\u003eCellulose@Hap\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.185430463576157%\" valign=\"top\"\u003e\n \u003cp\u003e4.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"26.32450331125828%\" valign=\"top\"\u003e\n \u003cp\u003e298\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.23841059602649%\" valign=\"top\"\u003e\n \u003cp\u003e[42]\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"37.25165562913907%\" valign=\"top\"\u003e\n \u003cp\u003eCaFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-GO composite\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.185430463576157%\" valign=\"top\"\u003e\n \u003cp\u003e11.90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"26.32450331125828%\" valign=\"top\"\u003e\n \u003cp\u003e303\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.23841059602649%\" valign=\"top\"\u003e\n \u003cp\u003eThis work\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Graphene calcium ferrite nano composite, Fluoride, Kinetic, Isotherm","lastPublishedDoi":"10.21203/rs.3.rs-4458894/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4458894/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eInteractions of graphene calcium ferrite nano (GCF) composite have been investigated for the utilization as adsorbent for fluoride in aqueous medium. Batch adsorption studies were carried out with various fluoride concentrations, amount of adsorbent, pH, agitation time and temperature. The adsorption process was strongly influenced by the pH of the solution. The extent of adsorption decreased from 79.5 to 70.1% by changing the initial fluoride concentration from 1.0 to 9.0 mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (for adsorbent load 2.0 g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). The kinetic study of the interaction was tested with pseudo first order Lagergren equation, second order kinetics, Elovich equation, liquid film diffusion model and intra particle diffusion model; however the interaction was much more close to the second order kinetics (k\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.0518 g mg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003emin\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003eat 303 K). The adsorption data gave good fits with Langmuir monolayer capacity of ̴11.90 mg g\u003csup\u003e\u0026minus;1\u003c/sup\u003e at 303 K. The uptake of fluoride was also preferred by higher solution temperature. The results established good potentiality for graphene calcium ferrite nano (GCF) composite to take up and separate fluoride from aqueous medium through adsorption-mediated immobilization.\u003c/p\u003e","manuscriptTitle":"Removal of Fluoride from Aqueous Solution by CaFe2O4–GO Composite","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-03 09:12:03","doi":"10.21203/rs.3.rs-4458894/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"0ada002f-284e-4c1a-a58a-f02f115ead4f","owner":[],"postedDate":"June 3rd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-06-03T21:23:36+00:00","versionOfRecord":[],"versionCreatedAt":"2024-06-03 09:12:03","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4458894","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4458894","identity":"rs-4458894","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}