A new powerful magnetic dark catalyst based on rGO/Fe3O4/CdSe nanocomposite for ultrafast degradation of methylene blue dye

A new powerful magnetic dark catalyst based on rGO/Fe3O4/CdSe nanocomposite for ultrafast degradation of methylene blue dye | 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 A new powerful magnetic dark catalyst based on rGO/Fe3O4/CdSe nanocomposite for ultrafast degradation of methylene blue dye Afrasiab Salehi Moghanlou, Mehdi Molaei, Fang Tao This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4851672/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 03 Oct, 2024 Read the published version in Journal of Fluorescence → Version 1 posted 12 You are reading this latest preprint version Abstract In the present study, rGO/Fe3O4/CdSe as a dark catalyst material was synthesized by a refluxing method. The synthesized magnetic nanocomposites were studied by various analyzes such as Fourier transform infrared (FTIR), energy-dispersive X-ray spectroscopy (EDS), field emission scanning electron microscopy (FESEM), X-ray diffractometer (XRD), Raman, Zeta and vibrating sample magnetometer (VSM). XRD, EDS, FESEM and FTIR spectra showed that the nanocomposites were successfully synthesized. Absorption spectrum was used to determine the dark catalyst activity of rGO/Fe3O4/CdSe nanocomposite. Analysis of the absorption spectrum showed that the prepared nanocomposites degrade the MB organic dye completely after 2 min of stirring in the dark, also doing experiment at different pH showed that the best performance for the degradation of MB occurs in neutral and alkaline media. The Raman spectrum analyzes showed that the Fe3O4/CdSe QDs were correctly incorporated on the reduced graphene oxide (rGO) nanosheets. Zeta potential analysis showed that rGO/Fe3O4/CdSe has a large amount of negative charge on its surface, also the radical scavenger experiment showed that electrons play an essential role in the process of degradation. VSM analysis showed that the prepared nanocomposites have excellent superparamagnetic behavior, this advantage enables the easy collection of nanocatalysts by magnets from wastewater after dye degradation. rGO/Fe3O4/CdSe Dark catalyst Dye degradation Wastewater treatment Magnetic nanocomposite Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1. Introduction Environmental issues such as the water shortage crisis and increasing the discharge of dye effluents from various industries to the water resources, have become an important challenge. So, in order to reduce the risks caused by water pollutants for humans and the ecology, due to their toxicity and non-biodegradability, the treatment of water pollutant matrices is an issue that should be systematically investigated [ 1 – 2 ]. Todays, preparation and fabrication of nanostructures that can improve catalytic performance and have strong dye degradation in a short time has attracted a lot of attention. Recently, many efforts have been made to increase the photocatalytic efficiency of various nanostructures in relation to various pollutants under UV light or sunlight [ 3 ]. Kumar et al, synthesized rGO/Fe 3 O 4 nanocomposites for degradation of MB by solvothermal method [ 4 ]. Zhang et al, synthesized CdSe QDs@ Fe-based composites with heterojunction at atmospheric pressure by stirring in oil bath to enhance the photocatalytic degradation efficiency of rhodamine B (RhB) in the visible light conditions [ 5 ]. Conventional methods of removing organic dyes from wastewater treatment include filtration processes, chemical precipitation processes, biological decomposition, reverse osmosis and absorption [ 5 – 7 ]. These methods are not very efficient and economical to remove organic dye from wastewater. Advanced oxidation processes (AOP) like as ozonation, fenton and semiconductor-based photocatalyst, have recently attracted much attention for the removal of organic dyes from industrial effluents. In AOP methods, there is a need to create free radical species such as superoxide and hydroxyl radicals [ 8 ]. Due to narrow and favorable conduction band gap (Eg ≈ 1.74 eV) and as effective type in the II-VI group of semiconductor family, also tunable and size-dependent electronic properties, CdSe has been widely studied as photocatalysts [ 5 ]. Particularly, the absorption band of CdSe includes the entire visible light region. Also CdSe nanoparticles are introduced as an excellent photocatalyst due to the rapid generation of electron-hole pairs upon light excitation [ 2 – 9 ]. However, photoelectron-hole pairs of CdSe recombine easily and quickly. Therefore, increasing the lifetime of photo-generated pairs, due to the transfer of holes and electrons between the two coupled semiconductors, plays an important role in optical activity [ 5 – 10 ]. In order to prevent recombination of electrons and holes, graphene are a good option that can be used. One of the unique properties of graphene quantum dots (GQDs) is that they can absorb long-wavelengths and emit UV photons with shorter wavelengths, Due to the up conversion effect. Also, the GQDs band confirm the separation of charge and allows to electrons transfers easily from of the excited surface of catalyst and enhance the amount of available charge carriers for reactions in aqueous media. Therefore, it can be find out that the interaction between GQDs and catalyst increases the catalytic performance of the catalyst [ 2 – 11 ]. One of the important challenges in the practical application of graphene-based composites is its easy separation and recycling for reuse. For this purpose, Fe 3 O 4 nanoparticles can be added to the compound due to their significant magnetic properties. In addition, due to its unique properties, Fe 3 O 4 nanoparticles can interact with graphene oxide and lead to improved properties and overall performance. Also, having high surface area and good catalytic activity, iron oxide nanoparticles can promote efficient charge transfer kinetics and increase the catalytic performance of composite materials [ 8 – 12 ]. Therefore, considering all of above, in this research we have prepared rGO/Fe 3 O 4 /CdSe magnetic nanocomposite by a refluxing method. Prepared nanocomposite was investigated by different analysis and indicated excellent dark catalyst performance for the degradation of MB organic dye. 2. Experimental 2.1. Materials Cadmium sulfate(CdSO 4 ), Thioglycolic acid (TGA), Sodium hydroxide (NaOH), Potassium permanganate (KMnO 4 ), Iron (III) chloride hexahydrate (FeCl 3 ×6H 2 O), Phosphoric acid (H 3 PO 4 ), Sulfuric acid (H 2 SO 4 ), Hydrogen peroxide (H 2 O 2 ) (37%), graphite flakes (99%), Hydrochloric acid (HCl) (37%) and ammonium solution (25%), were purchased from the Merck chemical company. Sodium selenite (Na 2 SeO 3 ) was purchased from Sigma-Aldrich Company. 2.2. Preparation of CdSe Fast and easy microwave method was used for the synthesis of CdSe QDs [ 13 ]. In the first step, 0.064 g of cadmium sulfate was solved in 30 ml of deionized (DI) water for 25 min on a magnetic stirrer, then 50 µl of thioglycolic acid (TGA) was added to the cadmium sulfate solution as a capping agent. Due to the use of thiols as capping agent, to convert the media from acidic to alkaline by adding NaOH, pH reached to 9.5. Separately, 0.43 g of sodium selenite (Na 2 SeO 3 ) was poured into a beaker containing 20 ml of DI water and stirred for 15 min on a magnetic stirrer. In the second step, with the preparation of solutions containing ions, the solution containing Se 2− was added to the solution containing Cd 2+ which was being stirred on the magnetic stirrer. In the third step, the final solution, which was 50 ml, was exposed in the microwave radiation center for 90 s with a power of 720w. Finally, for the next use, the samples must be in powder form, the obtained solution was centrifuged for 5 min at 6000 rpm, then the samples were collected and dried at room temperature. 2.3. Preparation of Fe 3 O 4 For the synthesis of Fe 3 O 4 , in the first step, 0.47 g of sodium sulfite (Na 2 SO 3 ) was added to 12.5 ml of DI water and placed on a magnetic stirrer for 3 min to dissolve. Separately, 250 µl of HCl 0.2 mM and 2.07g of FeCl 3 ×6H 2 O were added to a beaker that contained 20 ml of DI water and sonicated by ultrasonic probe for about 3 min, until the color of solution turns to yellow. In the second step, 10 ml of Na 2 SO 3 (0.3 M) solution was slowly added to the beaker containing iron chloride and hydrochloric acid and sonicated for 8 min until the solution turned to yellow again. The solution prepared in the previous step was added to 30 mL of ammonia dissolved in 170 mL of DI water and sonicated for about 30 min. Finally, for the next use the Fe 3 O 4 were separated by a magnet and dried at 45°C for 24 h after washing 5 times. 2.4. Synthesis of CdSe/Fe 3 O 4 nanocomposites For the synthesis of CdSe/Fe 3 O 4 nanocomposites, 0.1g of pre-prepared Fe 3 O 4 were dispersed in 50 ml DI water for 3 min by ultrasonic probe. Simultaneously, in another beaker, 0.1 g of CdSe powder was dispersed in 50 ml of DI water for 3 min. Then, the Fe 3 O 4 solution was slowly injected into the beaker containing the CdSe solution and dispersed by an ultrasonic probe for 30 min. The obtained solution was refluxed for 24 h at 80°C. Then, to obtain the final product, the obtained nanocomposite was washed several times after being separated by a magnet, then dried in an oven at 44°C for 24 h [ 14 ]. 2.5. Preparation of GO The synthesis of graphene oxide (GO) was carried out by the previously reported hummer method [ 15 ]. Briefly, 67.5 ml of sulfuric acid, 10 ml of phosphoric acid and 22.4 ml of nitric acid were poured into a beaker placed on a magnetic stirrer and mixed for 10 min. Then 1 g of ground graphite powder was slowly added to the acid solution. After adding graphite powder, the solution was stirred for 30 min on a magnetic stirrer. Then, the beaker was placed in an ice bath and 6 g of potassium permanganate was slowly (1 g per 15 min) added to the solution in the ice bath during 90 min. The beaker containing the solution was placed on a heater with a temperature of 40 to 45°C for 2 h until the solution turned a muddy green color. Then the beaker containing the solution was removed from the heater and 100 ml of DI water was added to it at a uniform rate. After that, the beaker containing the solution for 1h was placed in an oil bath whose temperature was set at 85°C. Then the beaker containing the solution was taken out of the oil bath and while stirring on the magnetic stirrer, 15 ml of hydrogen peroxide and 120 ml of DI water simultanesly were added to the solution. The remaining solution was passed through filter until the acid was separated from the solution. Then washed with DI water and hydrochloric acid (HCl) at a ratio of 10:1. The remaining sediments were sonicated for 30 min to disperse, then washed several times until the pH of the compound reached to 5–7. Finally, the solution was placed in a centrifuge at 6000 rpm for 10 min, and then the collected sediments were dried in an oven at 40°C. 2.6. Preparation of rGO /Fe 3 O 4 For the synthesis of rGO/F 3 O 4 , in the first step, 2.07 g of FeCl 3 ×6H 2 O was dissolved in a beaker containing 20 ml of DI water. Then the obtained solution was dispersed by adding 250 µl of 0.2 mM HCl for 3 min by using an ultrasonic probe until it turned to yellow. In the second step, 10 ml of prepared Na 2 SO 3 (0.3 M) solution was added to the solution prepared in the previous step, and then it was dispersed by an ultrasonic probe for 8 min until it turned to yellow again. Separately, 0.02 g of prepared GO powder was dispersed in 30 ml of DI water for 30 min by ultrasonic probe until the solution turned to brown. The solution contain GO was added to the solution prepared in the second step and subjected to sonication for 10 min, then added to a beaker containing 30 ml of ammonia 33% mixed in 170 ml of DI water and dispersed by ultrasonic probe for 30 min. Finally, the rGO/F 3 O 4 compound was collected by a magnet and separated from aqueous media, then after washing 5 times, dried an oven in 45°C for 24 h. 2.7. Synthesis of rGO /Fe 3 O 4 /CdSe magnetic nanocomposites For the synthesis of rGO/Fe 3 O 4 /CdSe nanocomposites, first, 0.1 g of pre-prepared rGO/F 3 O 4 was dispersed in 50 ml of DI water. Separately, 0.1 g of pre-prepared CdSe QDs were dispersed in 50 ml of DI water. Then, the solution containing CdSe was added to the rGO/F 3 O 4 solution. The obtained compound was refluxed for 24 h at 80°C. Finally, the rGO/Fe 3 O 4 /CdSe sediments were collected by a magnet and separated from aqueous media and dried for 24 h at 44°C to obtain rGO/Fe 3 O 4 /CdSe nanocomposites. 2.8. Dark catalyst study To study about the degradation rate of MB organic dye, absorption spectrum was used to determine the dark catalyst activity of rGO/Fe 3 O 4 /CdSe nanocomposite. For this purpose, 30 mg of catalyst was dispersed in 22.5 ml of DI water in an ultrasonic bath for about 3 min. Subsequently, the prepared solution was reacted with 10 ppm of MB organic dye, then it was stirred in a dark chamber with different time intervals. 3. Results and discussions 3.1. Studying the structural characteristics and morphology 3.1.1. XRD pattern An X-ray diffractometer (Cu Kα) was used to study the crystalline phase of the produced nanocomposites. Figure 1A shows the XRD pattern of the samples. Pattern (a) in Fig. 1A, corresponds to the pure Fe 3 O 4 , which has distinct peaks at 2Ѳ = 30.17 ∘ , 35.53 ∘ , 43.2 ∘ , 53.55 ∘ , 57.12 ∘ and 62.69 ∘ , which is refers to the lattice planes points of (220), (311), (400), (422), (511) and (440). The existing peaks indicate that Fe 3 O 4 corresponds to the cubic structure [ 16 – 17 ]. Also, Pattern (b) in Fig. 1A shows the XRD corresponding to pure CdSe, which has peaks at 2Ѳ = 26.12 ∘ , 30.11 ∘ and 43.3 ∘ , that respectively refer to (111), (220), and (311) lattice planes. CdSe exists in both zinc-blend (FCC) and wurtzite (hexagonal) structures. Comparing the peaks in pattern (b) with previous studies shows that the structure of CdSe is cubic [ 5 – 18 ]. Pattern (c) in Fig. 1A shows the XRD of CdSe/Fe 3 O 4 nanocomposite, the diffraction peaks indicate the overlapping of CdSe with Fe 3 O 4 and the formation of CdSe/Fe 3 O 4 structure [ 19 ]. Pattern (d) in Fig. 1A is the XRD of rGO/Fe 3 O 4 /CdSe nanocomposite. It can be seen that, due to the deposition of iron oxide and cadmium selenide particles on the rGO surface, the peaks of rGO not appear clearly [ 16 ]. 3.1.2. VSM analysis VSM was used to determine the magnetic properties of Fe 3 O 4 /CdSe and rGO/Fe 3 O 4 /CdSe at room temperature. From the obtained results that are shown in Fig. 1B, it can be seen that both prepared composites have superparamagnetic behavior [ 20 ]. The obtained magnetic saturation (Ms) values were about 64.48 and 62.50 emu/g for Fe 3 O 4 /CdSe and rGO/Fe 3 O 4 /CdSe, respectively. Compared with Fe 3 O 4 /CdSe, it can be inferred that the saturation magnetization of rGO/Fe 3 O 4 /CdSe decreased, that may be related to the low percentage of Fe 3 O 4 in the rGO/Fe 3 O 4 /CdSe composite [ 21 ]. Saturation magnetization of rGO/Fe 3 O 4 /CdSe nanocomposites indicates that it has excellent superparamagnetic behavior. Therefore, the challenge of separating nanocatalyst from the wastewater can be solved simply by a magnet after the degradation process [ 22 ]. 3.1.3. FTIR spectrums In order to analyze the functional group and determine the structural integrity of the catalysts, FTIR spectroscopy of the composites was performed. FTIR involves observing the vibration of molecules excited by infrared radiation. Figure 2A indicates the FTIR spectrum of GO, Fe 3 O 4 /CdSe binary and rGO/Fe 3 O 4 /CdSe ternary nanocomposite. As can be seen in the relevant spectrum, there are peaks in the wave numbers of 547, 1228, 1379, 1655, 3449 and 3725cm − 1 . The bands near 547 cm − 1 and 1228 cm − 1 originate from the stretching vibrations of Fe-O and the vibrational absorption of C-O bonds, which indicates that Fe 3 O 4 QDs are coordinated with rGO [ 5 – 23 ]. The peaks in wave number 1379 and 1655 cm − 1 are respectively referred to C-OH and C = C bonds [ 2 – 7 ]. The distinctive broad band that exists from the wave number of 3250 to 3750 cm − 1 are related to the OH groups involved in H bonds [ 5 ]. 3.1.4. Raman spectrums Raman spectroscopy can determine the presence of CdSe, Fe 3 O 4 and rGO in the nanocomposites [ 24 ]. Figure 2B indicates the Raman spectrum of Fe 3 O 4 /CdSe, GO and rGO/Fe 3 O 4 /CdSe. Pattern (a) in Fig. 2B shows the Raman spectrum of Fe 3 O 4 /CdSe nanocomposites, which has peaks at 235, 415, 439 and 800 cm − 1 . The two peaks around 235 cm − 1 and 415 cm − 1 are related to LO 1 and LO 2 phonon modes in CdSe [ 25 ]. Weak peaks around 439 and 800 cm − 1 are attributed to Fe 3 O 4 [ 26 ]. GO is usually analyzed by two peaks. Pattern (b) in Fig. 2B indicates the Raman spectrum of pure GO, and pattern (c) shows the Raman spectrum of rGO/Fe 3 O 4 /CdSe nanocomposites. There are two peaks at 1320 cm − 1 and 1605 cm − 1 , which respectively represent the D and G bands of rGO. G pattern is related to the first order scattering of E 2 g photons produced by sp2 carbon atom and D pattern is produced by sp3 carbon atom, which shows the graphitization degree of graphene [ 24 ]. A high value of intensity ratio indicates that the graphite structure has more crystal defects in its lattice and has a more distortion. The D/G ratio for rGO/Fe 3 O 4 /CdSe was 1.15. As shown in pattern (c) in Fig. 2B, there is a small shift to the left in the characteristic peak in the D band for rGO/Fe 3 O 4 /CdSe, indicating that the Fe 3 O 4 /CdSe QDs are correctly grown on the rGO nanosheets [ 27 ]. 3.1.5. FESEM and EDS analyses 3.2. Dye degradation study 3.2.1. MB degradation Absorption spectrum was used to study the ability of magnetic nanocomposites to degrade MB dye. The reduction of the characteristic absorption peak is a way that can be used to measure the degradation of MB dye molecules after the catalytic reaction. To investigate the effectiveness of Fe 3 O 4 /CdSe and rGO/Fe 3 O 4 /CdSe magnetic nanocomposite in degradation of MB, 30 mg of catalyst was reacted with 10 ppm of MB. The degradation rate of the samples are shown in Fig. 5. As shown in Fig. 5a, degradation efficiency of Fe 3 O 4 /CdSe was 55%, but, Fig. 5b indicate that by adding graphene to the compound, the degradation efficiency reached to 100% only after 2 min stirring in the darkness. Table 1 shows the reaction time and degradation efficiency of different dark catalysts and photocatalysts with MB dye in comparison with prepared rGO/Fe 3 O 4 /CdSe magnetic dark nanocatalyst. Table 1 Comparisons of MB dye degradation between the prepared rGO/ Fe 3 O 4 /CdSe nanocomposite and some previous reported dark and photocatalysts. S. NO. Nanocatalyst Photo/Dark catalyst Degradation efficiency Time (min) Ref. 1 MnTiO 3 Photocatalyst 75% 240 [31] 2 3 CdSe- rGO CdTe/ZnSe Photocatalyst Photocatalyst 70% 76% 210 120 [32] [3] 4 ZnO–SnO 2 Photocatalyst 96.53% 60 [33] 5 GO/TiO 2 Photocatalyst 99% 60 [34] 6 rGO/TiO 2 Photocatalyst 90% 15 [35] 7 Ag–In–Ni– S Dark catalyst 98% 12 [36] 8 rGO/Fe 3 O 4 /CdSe Dark catalyst 100% 2 Present work 3.2.2. Study effect of rGO/Fe 3 O 4 /CdSe catalyst mass Another important factor that was studied in the dye degradation efficiency was the mass of the catalyst. To investigate the effect of rGO/Fe 3 O 4 /CdSe mass on the degradation rate of methylene blue, 10, 20, 30 and 40 mg of catalyst were reacted with 10 ppm of MB dye, then stirred in darkness. As shown in Fig. 6a, it can be find out that the best catalyst weight can be use is 30 mg, because it obtained the highest dark degradation efficiency of 100% and the MB solution was degradated completely after 2 min. Degradation efficiency increased from 10 to 30 mg due to the increase in the number of active sites in the degradation process, increasing the mass more than 30 mg did not change the degradation time [ 27 ]. Therefore, 30 mg was selected as the optimal condition of magnetic nanocomposite in the degradation process for more detailed study. 3.2.3. Study reusability of rGO/Fe 3 O 4 /CdSe Figure 6b, shows the effect of prepared rGO/Fe 3 O 4 /CdSe nanocomposite during reuse analysis. The stability and recyclability of nanocatalysts are also very important for practical applications. Surface electrons play an important role in the dark degradation process. Since the number of surface electrons decreases during the reaction with dye molecules in the degradation process, it is expected that the degradation efficiency will decrease in the subsequent cycles [ 7 ]. In order to check the reuse of the prepared catalyst after the degradation in the first step, the reacted nanocomposite with MB was separated from the media by a magnet. Then, in the second step, the degradation process was repeated by adding 10 ppm of MB with the same samples of the first step. After 4 reuse of the prepared dark nanocatalysts for degradation of MB, it still has 83% degradation efficiency. This level of degradation indicate that, the prepared dark catalyst still has the necessary surface electrons for the degradation of organic dyes. 3.2.4. Study of pH effect on degradation The pH was studed as another factor that can be effective in the practical use of prepared nanocomposites and degradation efficiency. Sodium hydroxide (NaOH) and Hydrochloric acid (HCl) were used for this purpose. According to the pH study, which are shown in the Fig. 7a, as the pH increases from 1 to 3, the degradation efficiency increases considerably, then, the highest degradation occurs in neutral and alkaline media. Therefore, it can be understood that prepared nanocomposites perform much better in neutral and alkaline media than in acidic media. 3.2.5. Zeta potential analysis Figure 7b shows the Zeta potential of the samples. Zeta potential was used to measure the amount of charge on the surface of CdSe/Fe 3 O 4 and rGO/CdSe/Fe 3 O 4 nanocomposites. Depending on its sign and amount, surface charges strongly affects the degradation of organic dyes [ 28 ].The results of zeta potential showed that the amount of negative charge on the Fe 3 O 4 /CdSe surface is about − 12 mV, which increases to -28 mV by adding graphene to the structure. Graphene is known as a two-dimensional semimetal with a tiny overlap between the valence and conduction bands and exhibits a strong dipole electric field effect [ 29 ]. The increasing trend of about 16 mV in the value of zeta potential for rGO/Fe 3 O 4 /CdSe nanocomposite may be due to the functionalization of rGOs during partial reduction, and hence it has a higher surface negative charge density than Fe 3 O 4 /CdSe [ 30 ]. Therefore, by increasing the surface charge, it can be expected that the ability of rGO/Fe 3 O 4 /CdSe as a dark catalyst in the dye degradation will increase [ 27 ]. 3.2.6. Scavenger results In order to find out which factor plays the main role in the degradation of MB by rGO/ Fe 3 O 4 /CdSe nanocomposites, radical scavenger experiment was performed. For this purpose, the determining active radical in dye degradation was investigated. Hydroxyl (OH − ), Electrons (e − ), and holes (h + ) radicals, are among the radicals that play the main role in degradation processes [ 7 ]. Hydrogen peroxide (H 2 O 2 ) and silver nitrate (AgNO 3 ) were used as electron trap. Ethylenediaminetetraacetic acid (EDTA) was used as a hole trap and sodium iodide (NaI) was used as a hydroxyl species trap [ 3 – 27 ]. The experiment was done in such a way that H 2 O 2 was added as an electron trap to the solution containing nanocomposite and MB, and the test was performed according to the previous procedure, the result showed a serious impairment in the degradation process. Then, to ensure the role of electrons in the degradation process, AgNO 3 was tested as another electron trap, which confirmed the role of electrons in the degradation process. Then, EDTA was added to the compound as a hole trap and the experiment was repeated, the result showed that the holes didn't play a role in the degradation of the dye and the degradation process was carried out without any disturbance. Also, to determine the role of hydroxyls, the degradation process was carried out with NaI, which showed that it has no effect on the degradation process [ 8 ]. Therefore, according to the results of the scavenger tests, which are shown in Fig. 8, it can be concluded that the main role in MB degradation is the surface electrons produced by rGO/Fe 3 O 4 /CdSe magnetic nanocomposite. [ 5 – 27 ]. Also, to ensure that the process of degradation has taken place and not absorption. After the degradation process, the nanocomposite was separated from the aqueous media by a magnet. Then after drying at room temperature, it was added to a beaker containing 25 ml of DI water and dispersed by an ultrasonic probe for 30 min, but no dye was observed in the aqueous media. Therefore, considering this case, and the fact that the addition of electron traps caused a disruption in the degradation process, it can be sure that the degradation took place and not absorption. 3.2.7. Degradation process mechanism The path of dark catalytic degradation of MB by rGO/Fe 3 O 4 /CdSe nanocomposite was studied. According to the results in Fig. 5b, it can be seen that MB has a characteristic absorption peak at 662 nm. After reaction with rGO/Fe 3 O 4 /CdSe nanocomposite, this peak is significantly reduced and after 2 min of stirring in the darkness, it disappears completely. In combination with the results of the trap experiments, it was found that the main role in MB degradation is the active species of electron (e − ). Also, it can be seen from the zeta potential that rGO/Fe 3 O 4 /CdSe magnetic nanocomposite has the ability to create a large amount of negative charge on its surface, which makes it an ideal option for degradation. Finally, based on all that was studied and discussed above, a catalytic degradation mechanism for MB by rGO/Fe 3 O 4 /CdSe in the dark was proposed. As shown in Fig. 9. The electrons on the surface of the nanocomposite react with the oxygen in the water and produce superoxide •O 2 radicals. On the other hand, reactive hydroxyl species ( ) can also be created from the reaction of superoxide species by H + ions. Therefore, as a result, the reaction between the radicals created by the electrons on the surface of the nanocomposite with MB removes the dye molecules from the wastewater [ 27 ]. 4. Conclusion Briefly, in this research, Fe 3 O 4 /CdSe and rGO/Fe 3 O 4 /CdSe magnetic nanocomposites were synthesized fast and simple by refluxing method. Characteristic spectra of XRD, Raman, FTIR, and SEM showed that Fe 3 O 4 /CdSe and rGO/Fe 3 O 4 /CdSe magnetic nanocomposites were successfully synthesized. VSM spectrum showed that the samples have superparamagnetic behavior. Zeta potential spectrum showed that the samples have negative surface charge necessary for degradation and also the surface charge of rGO/Fe 3 O 4 /CdSe was increased compared to Fe 3 O 4 /CdSe. The dark degradation ability of prepared magnetic nanocomposites was tested on MB dye. The experiment showed that Fe 3 O 4 /CdSe magnetic nanocomposite has 55% degradation ability, but by adding graphene to the compound, rGO/Fe 3 O 4 /CdSe magnetic nanocomposites were able to completely and 100% degrade MB dye within 2 min. Also, the investigation of the effect of pH showed that rGO/Fe 3 O 4 /CdSe magnetic nanocomposites have excellent performance in neutral and alkaline media. The results of radical scavenger test also showed that electrons play the main role in the degradation of MB organic dye. So, due to excellent performance in the degradation, reducing the duration of degradation time and amount of catalyst weight used, the prepared nanocomposites are economical compared to similar samples. Declarations Funding Declaration: There was no Funding CRediT authorship contribution statement Mehdi Molaei: Supervision, Writing – review & editing. Tao Fang: Adviser, review & editing, Afrasiab Salehi Moghanlou: Investigation, Methodology, Writing-original draft, Conceptualization, Data curation and Formal analysis. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Data availability All data will be made available on request. 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Journal of the Chinese Chemical Society 69.11 (2022): 1845-1854. Karimipour, Masoud, Marzieh Dargahzadeh, and Mehdi Molaei. "Near room temperature synthesis of rGO-Fe 3 O 4 nanosheets: Structural, magnetic ordering, charge transport, dye degradation properties and hydrogen evolution reaction." Physica E: Low-dimensional Systems and Nanostructures 118 (2020): 113909. Vo, Ngoc Thuy, et al. "Stability Investigation of Ligand‐Exchanged CdSe/ZnS‐Y (Y= 3‐Mercaptopropionic Acid or Mercaptosuccinic Acid) through Zeta Potential Measurements." Journal of Nanomaterials 2016.1 (2016): 8564648. Mkhalid, I. A., and Ahmed Shawky. "Visible light-active CdSe/rGO heterojunction photocatalyst for improved oxidative desulfurization of thiophene." Ceramics International 46.13 (2020): 20769-20776. ur Rahman, Obaid, Subash Chandra Mohapatra, and Sharif Ahmad. "Fe3O4 inverse spinal super paramagnetic nanoparticles." Materials Chemistry and Physics 132.1 (2012): 196-202. Yang, Ying, et al. "Multifunctional reduced graphene oxide (RGO)/Fe3O4/CdSe nanocomposite for electrochemiluminescence immunosensor." Electrochimica Acta 190 (2016): 948-955. Zhou, Shuai, et al. "Bifunctional luminescent superparamagnetic nanocomposites of CdSe/CdS-Fe 3 O 4 synthesized via a facile method." Journal of Materials Chemistry 22.17 (2012): 8263-8270. Albers, Rebecca F., et al. "A general one-pot synthetic strategy to reduced graphene oxide (rGO) and rGO-nanoparticle hybrid materials." Carbon 143 (2019): 73-84. Li, Pengchao, et al. "A facile method to synthesize CdSe-reduced graphene oxide composite with good dispersion and high nonlinear optical properties." Nanomaterials 9.7 (2019): 957. Xie, Pei, et al. "Morphology-controlled synthesis of CdSe microspheres on graphene oxide sheets and their photocatalytic properties." Ceramics International 42.16 (2016): 18264-18270. Roychowdhury, Anirban, et al. "Tunable properties of magneto-optical Fe3O4/CdS nanocomposites on size variation of the magnetic component." Materials Chemistry and Physics 151 (2015): 105-111. Farahmandzadeh, Farzad, et al. "Simultaneous and fast degradation of methylene blue, methylene orange, and Rhodamine B dyes by high-performance rGO/Fe 3 O 4 /ZnSe magnetic nanocomposites." Colloids and Surfaces A: Physicochemical and Engineering Aspects 685 (2024): 133229. Radchanka, Aliaksandra, et al. "Zeta potential-based control of CdSe/ZnS quantum dot photoluminescence." The Journal of Physical Chemistry Letters 13.22 (2022): 4912-4917. Jastrzębska, Agnieszka Maria, et al. "Synthesis of RGO/TiO2 nanocomposite flakes and characterization of their unique electrostatic properties using zeta potential measurements." Journal of Alloys and Compounds 679 (2016): 470-484. Sadhukhan, Sourav, et al. "Studies on synthesis of reduced graphene oxide (RGO) via green route and its electrical property." Materials Research Bulletin 79 (2016): 41-51. Alkaykh, Suhila, Aïcha Mbarek, and Elbashir E. Ali-Shattle. "Photocatalytic degradation of methylene blue dye in aqueous solution by MnTiO3 nanoparticles under sunlight irradiation." Heliyon 6.4 (2020). Patidar, Dinesh, et al. "Nanohybrids cadmium selenide-reduced graphene oxide for improving photo-degradation of methylene blue." Physica E: Low-dimensional Systems and Nanostructures 114 (2019): 113560. Lin, Jiaojiao, et al. "Photocatalytic degradation of methylene blue in aqueous solution by using ZnO-SnO2 nanocomposites." Materials Science in Semiconductor Processing 87 (2018): 24-31. Kurniawan, Tonni Agustiono, et al. "Functionalizing TiO2 with graphene oxide for enhancing photocatalytic degradation of methylene blue (MB) in contaminated wastewater." Journal of environmental management 270 (2020): 110871. Mohammadi, Mojtaba, et al. "Enhancement of visible and UV light photocatalytic activity of rGO-TiO2 nanocomposites: The effect of TiO2/Graphene oxide weight ratio." Ceramics International 45.10 (2019): 12625-12634. Molla, Aniruddha, Meenakshi Sahu, and Sahid Hussain. "Under dark and visible light: fast degradation of methylene blue in the presence of Ag–In–Ni–S nanocomposites." Journal of Materials Chemistry A 3.30 (2015): 15616-15625. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 03 Oct, 2024 Read the published version in Journal of Fluorescence → Version 1 posted Editorial decision: Revision requested 28 Aug, 2024 Reviews received at journal 27 Aug, 2024 Reviews received at journal 26 Aug, 2024 Reviewers agreed at journal 23 Aug, 2024 Reviews received at journal 23 Aug, 2024 Reviewers agreed at journal 23 Aug, 2024 Reviewers agreed at journal 21 Aug, 2024 Reviewers agreed at journal 21 Aug, 2024 Reviewers invited by journal 21 Aug, 2024 Editor assigned by journal 20 Aug, 2024 Submission checks completed at journal 20 Aug, 2024 First submitted to journal 03 Aug, 2024 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. 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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-4851672","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":346296494,"identity":"d6ec1248-47ab-4cea-be61-aad1355ece1f","order_by":0,"name":"Afrasiab Salehi Moghanlou","email":"","orcid":"","institution":"Vali-e-Asr University of Rafsanjan","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Afrasiab","middleName":"Salehi","lastName":"Moghanlou","suffix":""},{"id":346296495,"identity":"556752d2-b7b4-4b75-b417-a38f74e4e9f7","order_by":1,"name":"Mehdi Molaei","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAyUlEQVRIiWNgGAWjYHACxgMMDBJy/CBmQgGRekBajCUbQFoMiNfCkLgBRDIQo0V32uEDB35UWBgbn1+d+OGBAYM8v9gB/FrMbqclHOw5IyFnduPtZgmgwwxnzk4gpCXH4ABvm4Sx2Y2zG0BaEgxuE6Hl4N9/EombZ5zd/INoLYd5GyQSN/D3biPWlrSEwzLHJIwlbvBus0gwkCDGL8kHH76pqZPj7z+7+eaPCht5fmkCWhBAAqxSgljlIMB/gBTVo2AUjIJRMJIAAOewSRhkmlmrAAAAAElFTkSuQmCC","orcid":"","institution":"Vali-e-Asr University of Rafsanjan","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Mehdi","middleName":"","lastName":"Molaei","suffix":""},{"id":346296496,"identity":"cdc28fed-60b7-4920-892d-85b7ba5664cb","order_by":2,"name":"Fang Tao","email":"","orcid":"","institution":"Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Fang","middleName":"","lastName":"Tao","suffix":""}],"badges":[],"createdAt":"2024-08-03 06:21:37","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4851672/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4851672/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10895-024-03982-5","type":"published","date":"2024-10-03T15:57:45+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":64654611,"identity":"ee292052-0932-4b64-89b7-f44ae0c070c4","added_by":"auto","created_at":"2024-09-17 06:28:48","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":113209,"visible":true,"origin":"","legend":"\u003cp\u003eXRD pattern of Fe3O4, CdSe, Fe3O4/CdSeand rGO/Fe3O4/CdSenanocomposites.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4851672/v1/0af687aa9fb95a858011e9d2.png"},{"id":64654621,"identity":"c4af3ebf-f9cd-4387-9426-a5076cc2dfb1","added_by":"auto","created_at":"2024-09-17 06:28:49","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":59040,"visible":true,"origin":"","legend":"\u003cp\u003eVSM analysis of Fe3O4/CdSeand rGO/Fe3O4/CdSe.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4851672/v1/70ba77587254e04eb428fdef.png"},{"id":64654612,"identity":"3be01ecd-4dbe-4377-9129-627eb099565d","added_by":"auto","created_at":"2024-09-17 06:28:48","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":80555,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR analysis of GO, Fe3O4/CdSeand rGO/Fe3O4/CdSe.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4851672/v1/456afff37786607b224d5216.png"},{"id":64654613,"identity":"89e5c398-fc9c-47b2-b888-50f1f3c22bc2","added_by":"auto","created_at":"2024-09-17 06:28:48","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":75856,"visible":true,"origin":"","legend":"\u003cp\u003eRaman spectra’sof GO, Fe3O4/CdSeand rGO/Fe3O4/CdSe.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4851672/v1/9cf15be342377cf4be617c5c.png"},{"id":64655662,"identity":"14ca42fb-ac14-4031-9ba7-439df727ffc8","added_by":"auto","created_at":"2024-09-17 06:44:49","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":481897,"visible":true,"origin":"","legend":"\u003cp\u003eEDS (a), elemental mapping analysis (b \u0026amp; d) and FESEM images of Fe3O4/CdSenanocomposites (c).\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4851672/v1/2a179c7fc5a754473ab8d665.png"},{"id":64654616,"identity":"e92bf3af-a67a-4469-b0f4-5c27d7a3960f","added_by":"auto","created_at":"2024-09-17 06:28:48","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":469989,"visible":true,"origin":"","legend":"\u003cp\u003eEDS (a), elemental mapping analysis (b \u0026amp; d) and FESEM images of rGO /Fe3O4/CdSe nanocomposites (c).\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4851672/v1/98b36c1f2de3367af24d48fb.png"},{"id":64654966,"identity":"b77da406-f9ae-4f64-b38c-f9479d8a5d04","added_by":"auto","created_at":"2024-09-17 06:36:48","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":116571,"visible":true,"origin":"","legend":"\u003cp\u003eMB degradation by Fe3O4/CdSe (a) and rGO/Fe3O4/CdSe (b) magnetic nanocomposite.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-4851672/v1/9dc5bf356efe488dc0c31dc9.png"},{"id":64654620,"identity":"3d13740f-35d2-40df-9d2e-cded4c1e4d5b","added_by":"auto","created_at":"2024-09-17 06:28:49","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":90785,"visible":true,"origin":"","legend":"\u003cp\u003eDegradation of MB by different catalyst mass (a), and reusability of rGO/CdSe/Fe3O4 in 4 cycles (b).\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-4851672/v1/b2de298317605544edacd0ee.png"},{"id":64654614,"identity":"3ad70510-092d-491d-880f-b426d09fa9ff","added_by":"auto","created_at":"2024-09-17 06:28:48","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":92578,"visible":true,"origin":"","legend":"\u003cp\u003eMB degradation on various pH (a), and Zeta potential analysis of Fe3O4/CdSeand rGO/Fe3O4/CdSe(b).\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-4851672/v1/c6a29ba108b99f4639fc5c78.png"},{"id":64654619,"identity":"a9378832-6bed-442c-9c3f-7f86af50a409","added_by":"auto","created_at":"2024-09-17 06:28:49","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":112787,"visible":true,"origin":"","legend":"\u003cp\u003eradical scavenger results\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-4851672/v1/7e246edd3f35c4eb8e8e5ede.png"},{"id":64656343,"identity":"36f22829-c38c-4fd9-9562-47665c944cb7","added_by":"auto","created_at":"2024-09-17 06:52:48","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":104716,"visible":true,"origin":"","legend":"\u003cp\u003eProposed mechanism of dark catalytic degradation of dye by rGO/Fe3O4/CdSe nanocomposite.\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-4851672/v1/c2ed790ae72145c95a01b72a.png"},{"id":66096891,"identity":"dd58c8d6-9177-46e5-9972-9ba7c204a04a","added_by":"auto","created_at":"2024-10-07 16:11:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2617003,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4851672/v1/d02fa0c8-9625-48e7-8507-b418043b3435.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"A new powerful magnetic dark catalyst based on rGO/Fe3O4/CdSe nanocomposite for ultrafast degradation of methylene blue dye","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eEnvironmental issues such as the water shortage crisis and increasing the discharge of dye effluents from various industries to the water resources, have become an important challenge. So, in order to reduce the risks caused by water pollutants for humans and the ecology, due to their toxicity and non-biodegradability, the treatment of water pollutant matrices is an issue that should be systematically investigated [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Todays, preparation and fabrication of nanostructures that can improve catalytic performance and have strong dye degradation in a short time has attracted a lot of attention.\u003c/p\u003e \u003cp\u003eRecently, many efforts have been made to increase the photocatalytic efficiency of various nanostructures in relation to various pollutants under UV light or sunlight [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Kumar et al, synthesized rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanocomposites for degradation of MB by solvothermal method [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Zhang et al, synthesized CdSe QDs@ Fe-based composites with heterojunction at atmospheric pressure by stirring in oil bath to enhance the photocatalytic degradation efficiency of rhodamine B (RhB) in the visible light conditions [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eConventional methods of removing organic dyes from wastewater treatment include filtration processes, chemical precipitation processes, biological decomposition, reverse osmosis and absorption [\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. These methods are not very efficient and economical to remove organic dye from wastewater. Advanced oxidation processes (AOP) like as ozonation, fenton and semiconductor-based photocatalyst, have recently attracted much attention for the removal of organic dyes from industrial effluents. In AOP methods, there is a need to create free radical species such as superoxide and hydroxyl radicals [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDue to narrow and favorable conduction band gap (Eg\u0026thinsp;\u0026asymp;\u0026thinsp;1.74 eV) and as effective type in the II-VI group of semiconductor family, also tunable and size-dependent electronic properties, CdSe has been widely studied as photocatalysts [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Particularly, the absorption band of CdSe includes the entire visible light region. Also CdSe nanoparticles are introduced as an excellent photocatalyst due to the rapid generation of electron-hole pairs upon light excitation [\u003cspan additionalcitationids=\"CR3 CR4 CR5 CR6 CR7 CR8\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. However, photoelectron-hole pairs of CdSe recombine easily and quickly. Therefore, increasing the lifetime of photo-generated pairs, due to the transfer of holes and electrons between the two coupled semiconductors, plays an important role in optical activity [\u003cspan additionalcitationids=\"CR6 CR7 CR8 CR9\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. In order to prevent recombination of electrons and holes, graphene are a good option that can be used. One of the unique properties of graphene quantum dots (GQDs) is that they can absorb long-wavelengths and emit UV photons with shorter wavelengths, Due to the up conversion effect. Also, the GQDs band confirm the separation of charge and allows to electrons transfers easily from of the excited surface of catalyst and enhance the amount of available charge carriers for reactions in aqueous media. Therefore, it can be find out that the interaction between GQDs and catalyst increases the catalytic performance of the catalyst [\u003cspan additionalcitationids=\"CR3 CR4 CR5 CR6 CR7 CR8 CR9 CR10\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. One of the important challenges in the practical application of graphene-based composites is its easy separation and recycling for reuse. For this purpose, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanoparticles can be added to the compound due to their significant magnetic properties. In addition, due to its unique properties, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanoparticles can interact with graphene oxide and lead to improved properties and overall performance. Also, having high surface area and good catalytic activity, iron oxide nanoparticles can promote efficient charge transfer kinetics and increase the catalytic performance of composite materials [\u003cspan additionalcitationids=\"CR9 CR10 CR11\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Therefore, considering all of above, in this research we have prepared rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe magnetic nanocomposite by a refluxing method. Prepared nanocomposite was investigated by different analysis and indicated excellent dark catalyst performance for the degradation of MB organic dye.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Materials\u003c/h2\u003e \u003cp\u003eCadmium sulfate(CdSO\u003csub\u003e4\u003c/sub\u003e), Thioglycolic acid (TGA), Sodium hydroxide (NaOH), Potassium permanganate (KMnO\u003csub\u003e4\u003c/sub\u003e), Iron (III) chloride hexahydrate (FeCl\u003csub\u003e3\u003c/sub\u003e\u0026times;6H\u003csub\u003e2\u003c/sub\u003eO), Phosphoric acid (H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e), Sulfuric acid (H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e), Hydrogen peroxide (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e) (37%), graphite flakes (99%), Hydrochloric acid (HCl) (37%) and ammonium solution (25%), were purchased from the Merck chemical company. Sodium selenite (Na\u003csub\u003e2\u003c/sub\u003eSeO\u003csub\u003e3\u003c/sub\u003e) was purchased from Sigma-Aldrich Company.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Preparation of CdSe\u003c/h2\u003e \u003cp\u003eFast and easy microwave method was used for the synthesis of CdSe QDs [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. In the first step, 0.064 g of cadmium sulfate was solved in 30 ml of deionized (DI) water for 25 min on a magnetic stirrer, then 50 \u0026micro;l of thioglycolic acid (TGA) was added to the cadmium sulfate solution as a capping agent. Due to the use of thiols as capping agent, to convert the media from acidic to alkaline by adding NaOH, pH reached to 9.5. Separately, 0.43 g of sodium selenite (Na\u003csub\u003e2\u003c/sub\u003eSeO\u003csub\u003e3\u003c/sub\u003e) was poured into a beaker containing 20 ml of DI water and stirred for 15 min on a magnetic stirrer. In the second step, with the preparation of solutions containing ions, the solution containing Se\u003csup\u003e2\u0026minus;\u003c/sup\u003e was added to the solution containing Cd\u003csup\u003e2+\u003c/sup\u003e which was being stirred on the magnetic stirrer. In the third step, the final solution, which was 50 ml, was exposed in the microwave radiation center for 90 s with a power of 720w. Finally, for the next use, the samples must be in powder form, the obtained solution was centrifuged for 5 min at 6000 rpm, then the samples were collected and dried at room temperature.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Preparation of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/h2\u003e \u003cp\u003eFor the synthesis of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, in the first step, 0.47 g of sodium sulfite (Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e3\u003c/sub\u003e) was added to 12.5 ml of DI water and placed on a magnetic stirrer for 3 min to dissolve. Separately, 250 \u0026micro;l of HCl 0.2 mM and 2.07g of FeCl\u003csub\u003e3\u003c/sub\u003e\u0026times;6H\u003csub\u003e2\u003c/sub\u003eO were added to a beaker that contained 20 ml of DI water and sonicated by ultrasonic probe for about 3 min, until the color of solution turns to yellow. In the second step, 10 ml of Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e3\u003c/sub\u003e (0.3 M) solution was slowly added to the beaker containing iron chloride and hydrochloric acid and sonicated for 8 min until the solution turned to yellow again. The solution prepared in the previous step was added to 30 mL of ammonia dissolved in 170 mL of DI water and sonicated for about 30 min. Finally, for the next use the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e were separated by a magnet and dried at 45\u0026deg;C for 24 h after washing 5 times.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Synthesis of CdSe/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanocomposites\u003c/h2\u003e \u003cp\u003eFor the synthesis of CdSe/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanocomposites, 0.1g of pre-prepared Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e were dispersed in 50 ml DI water for 3 min by ultrasonic probe. Simultaneously, in another beaker, 0.1 g of CdSe powder was dispersed in 50 ml of DI water for 3 min. Then, the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e solution was slowly injected into the beaker containing the CdSe solution and dispersed by an ultrasonic probe for 30 min. The obtained solution was refluxed for 24 h at 80\u0026deg;C. Then, to obtain the final product, the obtained nanocomposite was washed several times after being separated by a magnet, then dried in an oven at 44\u0026deg;C for 24 h [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5. Preparation of GO\u003c/h2\u003e \u003cp\u003eThe synthesis of graphene oxide (GO) was carried out by the previously reported hummer method [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Briefly, 67.5 ml of sulfuric acid, 10 ml of phosphoric acid and 22.4 ml of nitric acid were poured into a beaker placed on a magnetic stirrer and mixed for 10 min. Then 1 g of ground graphite powder was slowly added to the acid solution. After adding graphite powder, the solution was stirred for 30 min on a magnetic stirrer. Then, the beaker was placed in an ice bath and 6 g of potassium permanganate was slowly (1 g per 15 min) added to the solution in the ice bath during 90 min. The beaker containing the solution was placed on a heater with a temperature of 40 to 45\u0026deg;C for 2 h until the solution turned a muddy green color. Then the beaker containing the solution was removed from the heater and 100 ml of DI water was added to it at a uniform rate. After that, the beaker containing the solution for 1h was placed in an oil bath whose temperature was set at 85\u0026deg;C. Then the beaker containing the solution was taken out of the oil bath and while stirring on the magnetic stirrer, 15 ml of hydrogen peroxide and 120 ml of DI water simultanesly were added to the solution. The remaining solution was passed through filter until the acid was separated from the solution. Then washed with DI water and hydrochloric acid (HCl) at a ratio of 10:1. The remaining sediments were sonicated for 30 min to disperse, then washed several times until the pH of the compound reached to 5\u0026ndash;7. Finally, the solution was placed in a centrifuge at 6000 rpm for 10 min, and then the collected sediments were dried in an oven at 40\u0026deg;C.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.6. Preparation of rGO /Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/h2\u003e \u003cp\u003eFor the synthesis of rGO/F\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, in the first step, 2.07 g of FeCl\u003csub\u003e3\u003c/sub\u003e\u0026times;6H\u003csub\u003e2\u003c/sub\u003eO was dissolved in a beaker containing 20 ml of DI water. Then the obtained solution was dispersed by adding 250 \u0026micro;l of 0.2 mM HCl for 3 min by using an ultrasonic probe until it turned to yellow. In the second step, 10 ml of prepared Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e3\u003c/sub\u003e (0.3 M) solution was added to the solution prepared in the previous step, and then it was dispersed by an ultrasonic probe for 8 min until it turned to yellow again. Separately, 0.02 g of prepared GO powder was dispersed in 30 ml of DI water for 30 min by ultrasonic probe until the solution turned to brown. The solution contain GO was added to the solution prepared in the second step and subjected to sonication for 10 min, then added to a beaker containing 30 ml of ammonia 33% mixed in 170 ml of DI water and dispersed by ultrasonic probe for 30 min. Finally, the rGO/F\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e compound was collected by a magnet and separated from aqueous media, then after washing 5 times, dried an oven in 45\u0026deg;C for 24 h.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e2.7. Synthesis of rGO /Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe magnetic nanocomposites\u003c/h2\u003e \u003cp\u003eFor the synthesis of rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe nanocomposites, first, 0.1 g of pre-prepared rGO/F\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e was dispersed in 50 ml of DI water. Separately, 0.1 g of pre-prepared CdSe QDs were dispersed in 50 ml of DI water. Then, the solution containing CdSe was added to the rGO/F\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e solution. The obtained compound was refluxed for 24 h at 80\u0026deg;C. Finally, the rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe sediments were collected by a magnet and separated from aqueous media and dried for 24 h at 44\u0026deg;C to obtain rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe nanocomposites.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e2.8. Dark catalyst study\u003c/h2\u003e \u003cp\u003eTo study about the degradation rate of MB organic dye, absorption spectrum was used to determine the dark catalyst activity of rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe nanocomposite. For this purpose, 30 mg of catalyst was dispersed in 22.5 ml of DI water in an ultrasonic bath for about 3 min. Subsequently, the prepared solution was reacted with 10 ppm of MB organic dye, then it was stirred in a dark chamber with different time intervals.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussions","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Studying the structural characteristics and morphology\u003c/h2\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e3.1.1. XRD pattern\u003c/h2\u003e \u003cp\u003eAn X-ray diffractometer (Cu Kα) was used to study the crystalline phase of the produced nanocomposites. Figure\u0026nbsp;1A shows the XRD pattern of the samples. Pattern (a) in Fig.\u0026nbsp;1A, corresponds to the pure Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, which has distinct peaks at 2Ѳ = 30.17\u003csup\u003e∘\u003c/sup\u003e, 35.53\u003csup\u003e∘\u003c/sup\u003e, 43.2\u003csup\u003e∘\u003c/sup\u003e, 53.55\u003csup\u003e∘\u003c/sup\u003e, 57.12\u003csup\u003e∘\u003c/sup\u003e and 62.69\u003csup\u003e∘\u003c/sup\u003e, which is refers to the lattice planes points of (220), (311), (400), (422), (511) and (440). The existing peaks indicate that Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e corresponds to the cubic structure [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Also, Pattern (b) in Fig.\u0026nbsp;1A shows the XRD corresponding to pure CdSe, which has peaks at 2Ѳ = 26.12\u003csup\u003e∘\u003c/sup\u003e, 30.11\u003csup\u003e∘\u003c/sup\u003e and 43.3\u003csup\u003e∘\u003c/sup\u003e, that respectively refer to (111), (220), and (311) lattice planes. CdSe exists in both zinc-blend (FCC) and wurtzite (hexagonal) structures. Comparing the peaks in pattern (b) with previous studies shows that the structure of CdSe is cubic [\u003cspan additionalcitationids=\"CR6 CR7 CR8 CR9 CR10 CR11 CR12 CR13 CR14 CR15 CR16 CR17\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Pattern (c) in Fig.\u0026nbsp;1A shows the XRD of CdSe/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanocomposite, the diffraction peaks indicate the overlapping of CdSe with Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and the formation of CdSe/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e structure [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Pattern (d) in Fig.\u0026nbsp;1A is the XRD of rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe nanocomposite. It can be seen that, due to the deposition of iron oxide and cadmium selenide particles on the rGO surface, the peaks of rGO not appear clearly [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e3.1.2. VSM analysis\u003c/h2\u003e \u003cp\u003eVSM was used to determine the magnetic properties of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe and rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe at room temperature. From the obtained results that are shown in Fig.\u0026nbsp;1B, it can be seen that both prepared composites have superparamagnetic behavior [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. The obtained magnetic saturation (Ms) values were about 64.48 and 62.50 emu/g for Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe and rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe, respectively. Compared with Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe, it can be inferred that the saturation magnetization of rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe decreased, that may be related to the low percentage of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e in the rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe composite [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Saturation magnetization of rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe nanocomposites indicates that it has excellent superparamagnetic behavior. Therefore, the challenge of separating nanocatalyst from the wastewater can be solved simply by a magnet after the degradation process [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003e3.1.3. FTIR spectrums\u003c/h2\u003e \u003cp\u003eIn order to analyze the functional group and determine the structural integrity of the catalysts, FTIR spectroscopy of the composites was performed. FTIR involves observing the vibration of molecules excited by infrared radiation. Figure\u0026nbsp;2A indicates the FTIR spectrum of GO, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe binary and rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe ternary nanocomposite. As can be seen in the relevant spectrum, there are peaks in the wave numbers of 547, 1228, 1379, 1655, 3449 and 3725cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The bands near 547 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1228 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e originate from the stretching vibrations of Fe-O and the vibrational absorption of C-O bonds, which indicates that Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e QDs are coordinated with rGO [\u003cspan additionalcitationids=\"CR6 CR7 CR8 CR9 CR10 CR11 CR12 CR13 CR14 CR15 CR16 CR17 CR18 CR19 CR20 CR21 CR22\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The peaks in wave number 1379 and 1655 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are respectively referred to C-OH and C\u0026thinsp;=\u0026thinsp;C bonds [\u003cspan additionalcitationids=\"CR3 CR4 CR5 CR6\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. The distinctive broad band that exists from the wave number of 3250 to 3750 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are related to the OH groups involved in H bonds [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003e3.1.4. Raman spectrums\u003c/h2\u003e \u003cp\u003eRaman spectroscopy can determine the presence of CdSe, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and rGO in the nanocomposites [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Figure\u0026nbsp;2B indicates the Raman spectrum of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe, GO and rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe. Pattern (a) in Fig.\u0026nbsp;2B shows the Raman spectrum of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe nanocomposites, which has peaks at 235, 415, 439 and 800 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The two peaks around 235 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003eand 415 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are related to LO\u003csub\u003e1\u003c/sub\u003e and LO\u003csub\u003e2\u003c/sub\u003e phonon modes in CdSe [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Weak peaks around 439 and 800 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are attributed to Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. GO is usually analyzed by two peaks. Pattern (b) in Fig.\u0026nbsp;2B indicates the Raman spectrum of pure GO, and pattern (c) shows the Raman spectrum of rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe nanocomposites. There are two peaks at 1320 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003eand 1605 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which respectively represent the D and G bands of rGO. G pattern is related to the first order scattering of E\u003csub\u003e2\u003c/sub\u003eg photons produced by sp2 carbon atom and D pattern is produced by sp3 carbon atom, which shows the graphitization degree of graphene [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. A high value of intensity ratio indicates that the graphite structure has more crystal defects in its lattice and has a more distortion. The D/G ratio for rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe was 1.15. As shown in pattern (c) in Fig.\u0026nbsp;2B, there is a small shift to the left in the characteristic peak in the D band for rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe, indicating that the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe QDs are correctly grown on the rGO nanosheets [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section3\"\u003e \u003ch2\u003e3.1.5. FESEM and EDS analyses\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Dye degradation study\u003c/h2\u003e \u003cdiv id=\"Sec19\" class=\"Section3\"\u003e \u003ch2\u003e3.2.1. MB degradation\u003c/h2\u003e \u003cp\u003eAbsorption spectrum was used to study the ability of magnetic nanocomposites to degrade MB dye. The reduction of the characteristic absorption peak is a way that can be used to measure the degradation of MB dye molecules after the catalytic reaction. To investigate the effectiveness of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe and rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe magnetic nanocomposite in degradation of MB, 30 mg of catalyst was reacted with 10 ppm of MB. The degradation rate of the samples are shown in Fig.\u0026nbsp;5. As shown in Fig.\u0026nbsp;5a, degradation efficiency of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe was 55%, but, Fig.\u0026nbsp;5b indicate that by adding graphene to the compound, the degradation efficiency reached to 100% only after 2 min stirring in the darkness. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the reaction time and degradation efficiency of different dark catalysts and photocatalysts with MB dye in comparison with prepared rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe magnetic dark nanocatalyst.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparisons of MB dye degradation between the prepared rGO/ Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe nanocomposite and some previous reported dark and photocatalysts.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS.\u003c/p\u003e \u003cp\u003eNO.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNanocatalyst\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePhoto/Dark catalyst\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDegradation efficiency\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTime (min)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eRef.\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMnTiO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePhotocatalyst\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e75%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e240\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[31]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCdSe- rGO\u003c/p\u003e \u003cp\u003eCdTe/ZnSe\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePhotocatalyst\u003c/p\u003e \u003cp\u003ePhotocatalyst\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e70%\u003c/p\u003e \u003cp\u003e76%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e210\u003c/p\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[32]\u003c/p\u003e \u003cp\u003e[3]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eZnO\u0026ndash;SnO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePhotocatalyst\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e96.53%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[33]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGO/TiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePhotocatalyst\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e99%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[34]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003erGO/TiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePhotocatalyst\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e90%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[35]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAg\u0026ndash;In\u0026ndash;Ni\u0026ndash; S\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDark catalyst\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e98%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[36]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003erGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDark catalyst\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e100%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ePresent work\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section3\"\u003e \u003ch2\u003e3.2.2. Study effect of rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe catalyst mass\u003c/h2\u003e \u003cp\u003eAnother important factor that was studied in the dye degradation efficiency was the mass of the catalyst. To investigate the effect of rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe mass on the degradation rate of methylene blue, 10, 20, 30 and 40 mg of catalyst were reacted with 10 ppm of MB dye, then stirred in darkness. As shown in Fig.\u0026nbsp;6a, it can be find out that the best catalyst weight can be use is 30 mg, because it obtained the highest dark degradation efficiency of 100% and the MB solution was degradated completely after 2 min. Degradation efficiency increased from 10 to 30 mg due to the increase in the number of active sites in the degradation process, increasing the mass more than 30 mg did not change the degradation time [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Therefore, 30 mg was selected as the optimal condition of magnetic nanocomposite in the degradation process for more detailed study.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section3\"\u003e \u003ch2\u003e3.2.3. Study reusability of rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;6b, shows the effect of prepared rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe nanocomposite during reuse analysis. The stability and recyclability of nanocatalysts are also very important for practical applications. Surface electrons play an important role in the dark degradation process. Since the number of surface electrons decreases during the reaction with dye molecules in the degradation process, it is expected that the degradation efficiency will decrease in the subsequent cycles [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. In order to check the reuse of the prepared catalyst after the degradation in the first step, the reacted nanocomposite with MB was separated from the media by a magnet. Then, in the second step, the degradation process was repeated by adding 10 ppm of MB with the same samples of the first step. After 4 reuse of the prepared dark nanocatalysts for degradation of MB, it still has 83% degradation efficiency. This level of degradation indicate that, the prepared dark catalyst still has the necessary surface electrons for the degradation of organic dyes.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section3\"\u003e \u003ch2\u003e3.2.4. Study of pH effect on degradation\u003c/h2\u003e \u003cp\u003eThe pH was studed as another factor that can be effective in the practical use of prepared nanocomposites and degradation efficiency. Sodium hydroxide (NaOH) and Hydrochloric acid (HCl) were used for this purpose. According to the pH study, which are shown in the Fig.\u0026nbsp;7a, as the pH increases from 1 to 3, the degradation efficiency increases considerably, then, the highest degradation occurs in neutral and alkaline media. Therefore, it can be understood that prepared nanocomposites perform much better in neutral and alkaline media than in acidic media.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec23\" class=\"Section3\"\u003e \u003ch2\u003e3.2.5. Zeta potential analysis\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;7b shows the Zeta potential of the samples. Zeta potential was used to measure the amount of charge on the surface of CdSe/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and rGO/CdSe/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanocomposites. Depending on its sign and amount, surface charges strongly affects the degradation of organic dyes [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].The results of zeta potential showed that the amount of negative charge on the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe surface is about \u0026minus;\u0026thinsp;12 mV, which increases to -28 mV by adding graphene to the structure. Graphene is known as a two-dimensional semimetal with a tiny overlap between the valence and conduction bands and exhibits a strong dipole electric field effect [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. The increasing trend of about 16 mV in the value of zeta potential for rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe nanocomposite may be due to the functionalization of rGOs during partial reduction, and hence it has a higher surface negative charge density than Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Therefore, by increasing the surface charge, it can be expected that the ability of rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe as a dark catalyst in the dye degradation will increase [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section3\"\u003e \u003ch2\u003e3.2.6. Scavenger results\u003c/h2\u003e \u003cp\u003eIn order to find out which factor plays the main role in the degradation of MB by rGO/ Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe nanocomposites, radical scavenger experiment was performed. For this purpose, the determining active radical in dye degradation was investigated. Hydroxyl (OH\u003csup\u003e\u0026minus;\u003c/sup\u003e), Electrons (e\u003csup\u003e\u0026minus;\u003c/sup\u003e), and holes (h\u003csup\u003e+\u003c/sup\u003e) radicals, are among the radicals that play the main role in degradation processes [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Hydrogen peroxide (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e) and silver nitrate (AgNO\u003csub\u003e3\u003c/sub\u003e) were used as electron trap. Ethylenediaminetetraacetic acid (EDTA) was used as a hole trap and sodium iodide (NaI) was used as a hydroxyl species trap [\u003cspan additionalcitationids=\"CR4 CR5 CR6 CR7 CR8 CR9 CR10 CR11 CR12 CR13 CR14 CR15 CR16 CR17 CR18 CR19 CR20 CR21 CR22 CR23 CR24 CR25 CR26\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe experiment was done in such a way that H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e was added as an electron trap to the solution containing nanocomposite and MB, and the test was performed according to the previous procedure, the result showed a serious impairment in the degradation process. Then, to ensure the role of electrons in the degradation process, AgNO\u003csub\u003e3\u003c/sub\u003e was tested as another electron trap, which confirmed the role of electrons in the degradation process. Then, EDTA was added to the compound as a hole trap and the experiment was repeated, the result showed that the holes didn't play a role in the degradation of the dye and the degradation process was carried out without any disturbance. Also, to determine the role of hydroxyls, the degradation process was carried out with NaI, which showed that it has no effect on the degradation process [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Therefore, according to the results of the scavenger tests, which are shown in Fig.\u0026nbsp;8, it can be concluded that the main role in MB degradation is the surface electrons produced by rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe magnetic nanocomposite. [\u003cspan additionalcitationids=\"CR6 CR7 CR8 CR9 CR10 CR11 CR12 CR13 CR14 CR15 CR16 CR17 CR18 CR19 CR20 CR21 CR22 CR23 CR24 CR25 CR26\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Also, to ensure that the process of degradation has taken place and not absorption. After the degradation process, the nanocomposite was separated from the aqueous media by a magnet. Then after drying at room temperature, it was added to a beaker containing 25 ml of DI water and dispersed by an ultrasonic probe for 30 min, but no dye was observed in the aqueous media. Therefore, considering this case, and the fact that the addition of electron traps caused a disruption in the degradation process, it can be sure that the degradation took place and not absorption.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec25\" class=\"Section3\"\u003e \u003ch2\u003e3.2.7. Degradation process mechanism\u003c/h2\u003e \u003cp\u003eThe path of dark catalytic degradation of MB by rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe nanocomposite was studied. According to the results in Fig.\u0026nbsp;5b, it can be seen that MB has a characteristic absorption peak at 662 nm. After reaction with rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe nanocomposite, this peak is significantly reduced and after 2 min of stirring in the darkness, it disappears completely. In combination with the results of the trap experiments, it was found that the main role in MB degradation is the active species of electron (e\u003csup\u003e\u0026minus;\u003c/sup\u003e). Also, it can be seen from the zeta potential that rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe magnetic nanocomposite has the ability to create a large amount of negative charge on its surface, which makes it an ideal option for degradation. Finally, based on all that was studied and discussed above, a catalytic degradation mechanism for MB by rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe in the dark was proposed. As shown in Fig.\u0026nbsp;9. The electrons on the surface of the nanocomposite react with the oxygen in the water and produce superoxide \u0026bull;O\u003csub\u003e2\u003c/sub\u003e radicals. On the other hand, reactive hydroxyl species (\u003cspan class=\"InlineEquation\"\u003e\u003c/span\u003e) can also be created from the reaction of superoxide species by H\u003csup\u003e+\u003c/sup\u003e ions. Therefore, as a result, the reaction between the radicals created by the electrons on the surface of the nanocomposite with MB removes the dye molecules from the wastewater [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eBriefly, in this research, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe and rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe magnetic nanocomposites were synthesized fast and simple by refluxing method. Characteristic spectra of XRD, Raman, FTIR, and SEM showed that Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe and rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe magnetic nanocomposites were successfully synthesized. VSM spectrum showed that the samples have superparamagnetic behavior. Zeta potential spectrum showed that the samples have negative surface charge necessary for degradation and also the surface charge of rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe was increased compared to Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe. The dark degradation ability of prepared magnetic nanocomposites was tested on MB dye. The experiment showed that Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe magnetic nanocomposite has 55% degradation ability, but by adding graphene to the compound, rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe magnetic nanocomposites were able to completely and 100% degrade MB dye within 2 min. Also, the investigation of the effect of pH showed that rGO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CdSe magnetic nanocomposites have excellent performance in neutral and alkaline media. The results of radical scavenger test also showed that electrons play the main role in the degradation of MB organic dye. So, due to excellent performance in the degradation, reducing the duration of degradation time and amount of catalyst weight used, the prepared nanocomposites are economical compared to similar samples.\u003c/p\u003e\n"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding Declaration:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThere was no Funding\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCRediT authorship contribution statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMehdi Molaei:\u0026nbsp;\u003c/strong\u003eSupervision, Writing \u0026ndash; review \u0026amp; editing.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTao Fang:\u003c/strong\u003e Adviser, review \u0026amp; editing, \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAfrasiab Salehi Moghanlou:\u0026nbsp;\u003c/strong\u003eInvestigation, Methodology, Writing-original draft, Conceptualization, Data curation and Formal analysis.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of Competing Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data will be made available on request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics Approval Declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThere was no Ethics Approval\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors wish to thank the University of Vali-e-Asr Rafsanjan (Iran) for the support provided.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAhmed, M. 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Ali-Shattle. \u0026quot;Photocatalytic degradation of methylene blue dye in aqueous solution by MnTiO3 nanoparticles under sunlight irradiation.\u0026quot; Heliyon 6.4 (2020).\u003c/li\u003e\n\u003cli\u003ePatidar, Dinesh, et al. \u0026quot;Nanohybrids cadmium selenide-reduced graphene oxide for improving photo-degradation of methylene blue.\u0026quot; Physica E: Low-dimensional Systems and Nanostructures 114 (2019): 113560.\u003c/li\u003e\n\u003cli\u003eLin, Jiaojiao, et al. \u0026quot;Photocatalytic degradation of methylene blue in aqueous solution by using ZnO-SnO2 nanocomposites.\u0026quot; Materials Science in Semiconductor Processing 87 (2018): 24-31.\u003c/li\u003e\n\u003cli\u003eKurniawan, Tonni Agustiono, et al. \u0026quot;Functionalizing TiO2 with graphene oxide for enhancing photocatalytic degradation of methylene blue (MB) in contaminated wastewater.\u0026quot; Journal of environmental management 270 (2020): 110871.\u003c/li\u003e\n\u003cli\u003eMohammadi, Mojtaba, et al. \u0026quot;Enhancement of visible and UV light photocatalytic activity of rGO-TiO2 nanocomposites: The effect of TiO2/Graphene oxide weight ratio.\u0026quot; Ceramics International 45.10 (2019): 12625-12634.\u003c/li\u003e\n\u003cli\u003eMolla, Aniruddha, Meenakshi Sahu, and Sahid Hussain. \u0026quot;Under dark and visible light: fast degradation of methylene blue in the presence of Ag\u0026ndash;In\u0026ndash;Ni\u0026ndash;S nanocomposites.\u0026quot; Journal of Materials Chemistry A 3.30 (2015): 15616-15625.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-fluorescence","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jofl","sideBox":"Learn more about [Journal of Fluorescence](https://www.springer.com/journal/10895)","snPcode":"10895","submissionUrl":"https://submission.nature.com/new-submission/10895/3","title":"Journal of Fluorescence","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"rGO/Fe3O4/CdSe, Dark catalyst, Dye degradation, Wastewater treatment, Magnetic nanocomposite","lastPublishedDoi":"10.21203/rs.3.rs-4851672/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4851672/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"In the present study, rGO/Fe3O4/CdSe as a dark catalyst material was synthesized by a refluxing method. The synthesized magnetic nanocomposites were studied by various analyzes such as Fourier transform infrared (FTIR), energy-dispersive X-ray spectroscopy (EDS), field emission scanning electron microscopy (FESEM), X-ray diffractometer (XRD), Raman, Zeta and vibrating sample magnetometer (VSM). XRD, EDS, FESEM and FTIR spectra showed that the nanocomposites were successfully synthesized. Absorption spectrum was used to determine the dark catalyst activity of rGO/Fe3O4/CdSe nanocomposite. Analysis of the absorption spectrum showed that the prepared nanocomposites degrade the MB organic dye completely after 2 min of stirring in the dark, also doing experiment at different pH showed that the best performance for the degradation of MB occurs in neutral and alkaline media. The Raman spectrum analyzes showed that the Fe3O4/CdSe QDs were correctly incorporated on the reduced graphene oxide (rGO) nanosheets. Zeta potential analysis showed that rGO/Fe3O4/CdSe has a large amount of negative charge on its surface, also the radical scavenger experiment showed that electrons play an essential role in the process of degradation. VSM analysis showed that the prepared nanocomposites have excellent superparamagnetic behavior, this advantage enables the easy collection of nanocatalysts by magnets from wastewater after dye degradation.","manuscriptTitle":"A new powerful magnetic dark catalyst based on rGO/Fe3O4/CdSe nanocomposite for ultrafast degradation of methylene blue dye","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-09-17 06:28:44","doi":"10.21203/rs.3.rs-4851672/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-08-28T12:13:41+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-08-27T19:23:13+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-08-26T21:49:17+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"49900705157229767298400113979516985821","date":"2024-08-23T18:14:19+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-08-23T09:49:35+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"230915848472268608194459336494858909443","date":"2024-08-23T08:36:19+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"228811696674068922936398253449734335705","date":"2024-08-21T20:10:47+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"153733954238539802572651178940420274689","date":"2024-08-21T19:34:25+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-08-21T17:19:39+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-08-20T05:18:57+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-08-20T05:16:43+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Fluorescence","date":"2024-08-03T06:19:12+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-fluorescence","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jofl","sideBox":"Learn more about [Journal of Fluorescence](https://www.springer.com/journal/10895)","snPcode":"10895","submissionUrl":"https://submission.nature.com/new-submission/10895/3","title":"Journal of Fluorescence","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"f52be08d-0a32-48ac-8bff-f112381feaf2","owner":[],"postedDate":"September 17th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-10-07T16:03:17+00:00","versionOfRecord":{"articleIdentity":"rs-4851672","link":"https://doi.org/10.1007/s10895-024-03982-5","journal":{"identity":"journal-of-fluorescence","isVorOnly":false,"title":"Journal of Fluorescence"},"publishedOn":"2024-10-03 15:57:45","publishedOnDateReadable":"October 3rd, 2024"},"versionCreatedAt":"2024-09-17 06:28:44","video":"","vorDoi":"10.1007/s10895-024-03982-5","vorDoiUrl":"https://doi.org/10.1007/s10895-024-03982-5","workflowStages":[]},"version":"v1","identity":"rs-4851672","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4851672","identity":"rs-4851672","version":["v1"]},"buildId":"cBFmMYwuxLRRLfASyISRj","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}