Silver-Decorated CFA/DA/NBP Nanocomposite for Adsorptive Removal of Methylene Blue Dye from Water

Silver-Decorated CFA/DA/NBP Nanocomposite for Adsorptive Removal of Methylene Blue Dye from Water | 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 Silver-Decorated CFA/DA/NBP Nanocomposite for Adsorptive Removal of Methylene Blue Dye from Water Pragya Singh, Shashank Sharma, Nakshatra Bahadur Singh This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7419899/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract A multifunctional nanocomposite, CFA/DA/NBP@Ag, was synthesized via a simple route involving coal fly ash (CFA) functionalized with dopamine (DA), incorporation of neem bark powder (NBP), and in situ reduction of silver nanoparticles (AgNPs) using silver nitrate. The composite effectively adsorbed methylene blue (MB) dye from water, achieving 80% removal within 210 minutes. UV–Vis spectrophotometry (664 nm) was used to monitor dye removal, and adsorption efficiency was found to increase with pH (68%, 80%, and 89% at pH 4, 7, and 9, respectively). PXRD confirmed the presence of Ag, NBP, DA, and CFA phases, while SEM revealed mostly spherical particles (20–50 nm). Kinetic analysis followed pseudo-first-order behavior with a rate constant of 0.0089 min⁻¹. These results underscore the potential of CFA/DA/NBP@Ag as a sustainable and low-cost adsorbent for wastewater treatment. Nanocomposite Methylene Blue Silver nanoparticle PXRD SEM Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1.0 Introduction Water is an essential natural resource for humans on Earth; however, the high amount of pollutants produced by industrial processes generates eutrophication, consumes oxygen from water, and causes the death of living species, which has a negative impact on the ecosystem[ 1 ], [ 2 ]. Therefore, further research is necessary to minimize these environmental pollutants or find alternative ways to eliminate them [ 3 ]. Organic dyes are particularly problematic among the many types of waste produced by industries worldwide [ 4 ]. Organic dyes resist biodegradation and block sunlight from reaching water, thereby hindering photosynthesis[ 5 ]. Furthermore, organic dyes are typically poisonous, chemically resistant, stable, potentially carcinogenic, and mutagenic[ 5 ], [ 6 ]. These organic dyes are used in the pharmaceutical, food, cosmetic, plastic, textile, and other industries. The textile industry is one of the main causes of organic dye pollution[ 7 ], [ 8 ]. According to the report, 700,000 tons of colorants are produced annually from an average of 10,000 colorants[ 9 ], [ 10 ]. To address this issue, researchers have developed technologies such as adsorption, microbiological processes, Fenton reactions, ion exchange, and ozonation[ 11 ], [ 12 ], [ 13 ]. However, these methods are costly, employ hazardous chemicals, produce harmful byproducts, and fail to eradicate the cause of toxicity[ 14 ]. Recent advancements in nanotechnology have provided many alternative solutions for wastewater treatment, particularly through the development of multifunctional nanocomposites[ 15 ], [ 16 ]. Coal fly ash is a waste byproduct of coal combustion that is abundant and inexpensive; however, it exhibits limited adsorption capabilities owing to its crystalline structure and relatively low surface area[ 17 ]. Research has focused on surface modification and functionalization to enhance adsorption efficiency for environmental remediation[ 18 ]. In addition, dopamine (DA) is a biomolecule with the potential to self-polymerize to form polydopamine (PDA)[ 19 ]. It has catechol and amine groups that can bind to the NPs surface and help various nanoparticles improve their activity. In addition, neem bark powder (NBP), which is rich in polyphenols and bioactive compounds, acts as a natural reducing and capping agent, offering further enhancement in adsorptive and catalytic activity[ 20 ]. In this regard, Moradi et al. used an agar/GO/ZnO nanocomposite to degrade MB dye by 91%.[ 21 ]. In addition, the BC/PDA/TiO2 nanocomposite degraded 80% of the MB dye[ 22 ]. In this context, silver nanoparticles are highly active for various applications because of their high surface reactivity and catalytic efficiency in dye degradation. When combined with a reducing agent such as sodium borohydride (NaBH4), AgNPs can mediate rapid electron transfer processes that facilitate the breakdown of dye molecules into less toxic byproducts. Herein, we report the synthesis of an Ag-based nanocomposite coated with coal fly ash (CFA) using dopamine (DA), followed by the incorporation of neem bark powder (NBP), known as CFA/DA/NBP@Ag, for the adsorption of methylene blue dye from aqueous solutions. CFA/DA/NBP@Ag NPs were synthesized by functionalizing coal fly ash (CFA) with dopamine (DA), followed by the incorporation of neem bark powder (NBP) and in situ reduction of silver nanoparticles (AgNPs) using silver nitrate. The adsorption efficiency of the CFA/DA/NBP @Ag nanocomposite for methylene blue dye was assessed, and the kinetics of adsorption were studied. We also studied the pH-dependent adsorption of this composite at pH 4, 7, and 9. The CFA/DA/NBP@Ag nanocomposite demonstrated strong potential as a sustainable, low-cost material for dye removal and wastewater treatment. 2.0 Materials and method: Dopamine (DA) was purchased from SRL India Pvt. Ltd. Silver nitrate was purchased from Fisher Scientific. Coal fly ash (CFA) was collected from a cement industry in Jhajjar. The adsorbent neem (A. indica) bark was taken from the neem tree available on the Sharda University campus. Deionized water was used at pH 7.0. Methylene blue dye was purchased from Sigma-Aldrich. The nanocomposite was characterized using scanning electron microscopy (SEM) and PXRD. The size and morphology of the NPs were analyzed using SEM. SEM was conducted using Zeiss EVO 50 and EVO scanning electron microscopes. A 20 mg/mL sample was uniformly dispersed in acetone for 20 min and then deposited onto carbon tape (for FE-SEM) using the drop-casting method. The samples were dried overnight at room temperature. Once the sample was dried, it was used for analysis. X'Pert PRO was used to acquire nanoparticle P-XRD data. For X-ray diffraction (XRD), 25 mg of the sample was applied to glass slides. The glass slide was scanned in the range of 20–50 degrees for two hours. 2.1. Preparation of Neem Bark Powder (NBP) Neem (A. indica) bark was collected from a neem tree on the Sharda University campus. The major compounds present in neem bark (Azadirachta indica) include a variety of bioactive phytochemicals, predominantly limonoids, flavonoids, and tannins. The neem bark was washed with distilled water until it was free of dust particles. The bark was then shade-dried to remove all moisture. They were then ground to a fine powder using an electric grinder, and the obtained powder was sieved to obtain a uniform particle size. The powder was washed five times with distilled water. The bark powder (30 g) was boiled in a beaker with 5N HCl (10 mL) to remove the dark color of the bark; after that, it was boiled four times with distilled water, filtered, and dried for 48 h at 80°C. Thus, activated neem bark powder (NBP) was obtained. 2.2. Preparation of Coal Fly Ash/Dopamine (CFA/DA) A mixture of 1 g CFA and 1 g DA was added to 250 mL Tris buffer (10 mM) and stirred continuously for 24 h, followed by filtration. The residue was dried in an oven at room temperature and used for further processing. 2.3. Preparation of CFA/DA/NBP @Ag Nanoparticles CFA/DA (0.5 g) was dispersed in 250 mL of double-distilled water in a 500 mL round-bottomed flask. Then, 0.01 M of silver nitrate was added to the above mixture, and the reaction was heated at 70 °C for 5 min. Then, 30 mL of Neem bark powder (NBP) is added to the above solution. The reaction mixture was stirred for 18 h. After 18 h, the resultant powder mixture was centrifuged for 20 min and washed multiple times with water, followed by acetone. The CFA/DA/NBP @Ag nanoparticles were obtained by drying overnight in an oven. 2.4. Adsorption experiment of Methylene blue dye The CFA/DA/NBP@Ag NPs were assessed for the absorption of methylene blue dye. The MB dye solution was prepared at a concentration of 15 mg/L in 50 mL of deionized water. Specimens with 8 ppm were added to the methylene blue solution. 100 µL of 0.1 M of NaBH4 was added in each experiment. The solution was stirred in the dark for 5 min to reach the adsorption-desorption equilibrium. The solution was then kept under sunlight for 3 h. The methylene blue dye degradation study was performed using a Shimadzu UV-Vis 1800 spectrophotometer in the 200–800 nm range. The absorbance of the dye was determined over time at a wavelength of 664 nm using a UV-Vis spectrophotometer. The experiment was performed at a pH of 7.0. In addition, the effect of pH on adsorption was studied by varying the pH. 3.0 Results and Discussion 3.1. Synthesis and Characterization The CFA/DA/NBP@Ag nanocomposite was synthesized using a wet chemical synthesis method using silver nitrate at 70°C, and the resultant powder mixture was centrifuged for 20 min and washed multiple times with water, followed by acetone. Figure 1 shows the synthetic procedure of CFA/DA/NBP@Ag nanocomposite from their respective component. The NBP was characterized using FT-IR spectra. NBP contains a rich blend of bioactive compounds that contribute to its medicinal properties[ 23 ]. It is recognized for its abundance of triterpenoids, flavonoids, saponins, alkaloids, polysaccharides, and glycosides, all of which contribute to its diverse therapeutic applications in traditional and modern medicine[ 24 ]. These compounds function as both capping and reducing agents in the synthesis of silver nanoparticles, inhibiting nanoparticle agglomeration owing to the presence of long-chain natural products in plant extracts. These chemicals can reduce Ag + to Ag 0 , and upon heating, metallic silver can be converted into Ag nanoparticles[ 25 ]. The first FT-IR spectra of NBP were recorded, as shown in Fig. 2 a. FT-IR spectra were recorded in the 440–4000 cm − 1 range. FTIR confirmed the successful modification and conjugation of neem bark biomolecules with dopamine-functionalized carbonaceous fly ash and silver nanoparticles (AgNPs ). The spectral shifts, new peaks, and intensity changes validate the surface interactions and incorporation of AgNPs, potentially enhancing their adsorption, catalytic properties, and antimicrobial properties. The FTIR spectrum of Neem Bark Powder (NBP) (Fig. 2 a) exhibits absorption bands characteristic of various phytoconstituents present in the NBP. The broad band at approximately 3372 cm⁻¹ corresponds to the O–H stretching vibrations of hydroxyl groups typically present in phenolic compounds and polysaccharides[ 26 ]. The peaks at 2926 and 2854 cm⁻¹ are attributed to the asymmetric and symmetric C–H stretching of aliphatic –CH₂ and –CH₃ groups, respectively. The sharp peak at 1721 cm⁻¹ indicates the presence of C = O stretching of carboxylic acids or esters, whereas the band at 1622 cm⁻¹ may correspond to aromatic C = C or conjugated carbonyl functional group vibrations. Additional peaks at 1452, 1236, 1163, and 1016 cm⁻¹ represent C–H bending and C–O stretching vibrations, suggesting the presence of cellulose, hemicellulose, and lignin in the NBP matrix[ 27 ], respectively. In contrast, the FTIR spectrum of the CFA/DA/NBP@Ag nanoparticles (Fig. 2 b) displays spectral shifts and new absorption features, indicating successful functionalization and nanoparticle incorporation. Bands observed in the region 2666–2090 cm⁻¹ may be ascribed to the formation of new functional groups such as C ≡ C or C ≡ N stretching vibrations or altered carbonyl environments due to dopamine (DA) and carbonaceous fly ash (CFA) modification. The characteristic carbonyl and aromatic stretching bands between 1875 and 1386 cm⁻¹ were broadened and shifted, suggesting coordination interactions between the NBP active sites and Ag nanoparticles. Moreover, the absorption bands at approximately 1037 and 756 cm⁻¹ correspond to C–O–C and aromatic C–H bending vibrations, which may arise from the modified lignin or DA-Ag complex structures. Compared to raw NBP, the reduction in intensity and shift of the O–H and C = O bands confirm the involvement of these functional groups in nanoparticle binding and stabilization, supporting successful nanocomposite synthesis[ 28 ], [ 29 ], [ 30 ]. We also performed FE-SEM for NBP. Figure 3 displays the FE- SEM images of NBP. The surface appears to be irregular, porous, and a mix of smooth and coarse regions. The particles exhibited a flaky and fibrous texture, which is a major characteristic of plant-based powders. The structure showed a heterogeneous matrix, which is a characteristic of organic lignocellulosic materials, such as bark. The particles were asymmetric and non-spherical with angular edges. The images reveal that the shapes range from flat sheet-like fragments to granular lumps. The particle size appears to be between 10 and 100 µm. Next, coal fly ash and dopamine (CFA/DA) were added to synthesize the composite, and a mixture was obtained for further use. Finally, nanocomposites were prepared using CFA/DA and NBP. CFA/DA/NBP@Ag nanocomposites were synthesized using wet chemical synthesis using silver nitrate at 70°C, and the resultant powder mixture was centrifuged for 20 min and washed multiple times with water, followed by acetone. The CFA/DA/NBP@Ag nanoparticles were obtained overnight by drying them in an oven. After synthesizing the CFA/DA/NBP@Ag nanocomposite, FE-SEM images were obtained, as shown in Fig. 4 . Figure 4 a and Fig. 4 b are at two resolutions, Fig. 4 a is at low resolution, and Fig. 4 b is at high resolution. Figure 4 b shows that the nanoparticles are generally spherical with slightly irregular shapes. The size predominantly ranges from 20–50 nm in the low-resolution image. The SEM images show that the surface morphology was relatively smooth with a moderate level of agglomeration, which could be due to the biological and chemical interactions among the phytochemical functional groups present in the neem bark powder, dopamine, and coal fly ash. In the low-resolution image, the 1 µm scale bar, the distribution of CFA/DA/NBP @Ag NPs over a border surface can be easily observed. The NPs were found to be in clusters/aggregates, possibly due to the interaction of the nanoparticles with the supporting matrix derived from various precursors such as neem bark powder, dopamine, and coal fly ash. The morphology at this scale suggests a porous and heterogeneous surface, which is a characteristic of composite materials synthesized from natural and waste-derived components. Overall, the images indicate the successful synthesis of Ag silver nanoparticles with a moderately uniform morphology and nanoscale size distribution. Next, powder X-ray diffraction (PXRD) was performed on the CFA/DA/NBP@Ag nanoparticles, as shown in Fig. 5 . The PXRD pattern analysis revealed the crystallographic phase of the synthesized nanocomposite comprising Ag, NBP, DA, and CFA. The most predominant peaks identified for face-centered cubic (FCC) silver were at 2θ ≈ 38.1° (111), 44.3° (200), 64.5° (220), and 77.4° (311), confirming the presence of metallic silver nanoparticles[ 31 ], [ 32 ]. In addition, the peak corresponding to CFA includes the broad reflection typically associated with SiO2 and 3Al₂O₃·2SiO₂, appearing near 21°, 26°, and 36°[ 33 ], [ 34 ]. The NBR and dopamine components were found to be amorphous and contributed to either broad or small peaks. The peak in the 10°–25°region indicates the presence of organic functional groups or biomolecules involved in the reduction and stabilization processes. All the data confirm the formation of CFA/DA/NBP@Ag nanoparticles with crystalline silver as the dominant phase and supporting evidence of biogenic and inorganic phases from DA, NBS, and CFA. 3.2. Adsorption Experiment of CFA/DA/NBP@Ag NPs The adsorption potential of CFA/DA/NBP@Ag NPs was studied using methylene blue (MB) dye. The details of the procedure are mentioned in the experimental section. The adsorption of methylene blue was monitored using UV-Vis spectroscopy at an absorbance wavelength of 664 nm[ 35 ]. Figure 6 a shows the UV-Vis spectra of the decrease in absorbance over time of the MB dye for the CFA/DA/NBP@Ag nanocomposite. The percentage of dye degradation was calculated using the following formula: % degradation = (C 0 -C t ) /C 0 where C0 = Initial Concentration of dye, Ct = time-dependent dye concentration at time t[ 36 ]. Figure 6 b shows the degradation percentage over time. During the process, it was observed that after 210 min, 82% of the dye was adsorbed by the CFA/DA/NBP@Ag NPs. Because the absorbance of the dye is directly proportional to the initial concentration of the dye, the concentration of the dye was determined at a particular time by checking the absorbance at a wavelength of 664 nm. The dye concentration decreased over time, and the absorbance decreased by more than 80 percent after 210 min. The pseudo-first-order kinetics equation further assessed the result, 𝑘𝑡 = − ln (𝐶 𝑡 /𝐶 0 ), where k and t represent the rate constant and degradation time, respectively, C0 represents the initial concentration of methylene blue, Ct represents the concentration of methylene blue at time t. We also calculated the rate constant from the pseudo-first-order kinetics equation (Fig. 6 c and 6 d). The rate constant was found to be 0.0089 min − 1 for CFA/DA/NBFig.g. We also performed concentration-dependent experiments by varying the concentration from 2 ppm to 10 ppm while keeping the other parameters constant. The dye concentration was fixed at 15 mg/L at pH 7.0. As shown in Fig. 7 a, the adsorption of the removal dye increased with an increase in the concentration of the CFA/DA/NBP@Ag nanocomposite. After 60 min, we recorded 13%, 19%, 34%, 50%, and 65% dye adsorption efficacy at 2, 4, 6, 8, and 10 ppm, respectively. In addition, we performed pH-dependent studies by keeping other parameters constant. The dye concentration was fixed at 15 mg/L, and the CFA/DA/NBP@Ag NPs concentration was maintained at 8 ppm. We chose three pH values: 4, 7, and 9, that is, acidic, basic, and neutral. The pH was maintained by adding 0.1 M NaOH or HCl. As shown in Fig. 7 b, the percentage of dye removal increased with increasing pH values. After 180 min, the percentage of dye removal was 68%, 80%, and 89% at pH 4, 7, and 9, respectively. The MB adsorption mechanism using Ag NPs supported by DA/CFA, NBP, and NaBH₄ could involve both physical adsorption and catalytic degradation[ 36 ]. CFA provides a porous matrix with a high surface area, whereas dopamine forms a DA layer rich in catechol and amine groups that enhance dye binding through hydrogen bonding, π–π stacking, and electrostatic interactions[ 37 ]. NBP further contributes to the natural polyphenolic and carboxylic groups, enhancing the adsorption capacity of the composite. Ag NPs, anchored onto the PDA matrix, serve as electron transfer mediators[ 37 ]. When NaBH₄ is introduced, it donates hydride ions that are transferred via AgNPs to the adsorbed dye molecules, promoting their reductive degradation, which is particularly effective for azo and nitro dyes[ 38 ]. This synergistic system efficiently adsorbs dyes and facilitates their breakdown into less toxic and colorless compounds. 4.0 Conclusion CFA/DA/NBP@Ag nanocomposite was synthesized using coal fly ash, dopamine, neem bark powder, and silver nitrate. Structural and morphological analyses confirmed the formation of silver nanoparticles embedded in a heterogeneous, porous matrix with particle sizes ranging from 20–50 nm. The nanocomposite demonstrated high adsorption efficiency for methylene blue, achieving up to 82% removal within 210 minutes. Kinetic analysis followed a pseudo-first-order model (k = 0.0089 min⁻¹), and adsorption performance improved significantly under alkaline conditions. The combined effects of the porous CFA matrix, functional groups from dopamine and neem bark, and the catalytic activity of AgNPs (aided by NaBH₄) enabled both adsorption and degradation of the dye. These results highlight CFA/DA/NBP@Ag as a promising, sustainable, and low-cost material for efficient dye removal from wastewater, with strong potential for practical, scalable environmental remediation. Funding Declaration The authors declare that no grants or other financial support were received during the preparation of this manuscript. 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Sharma","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABB0lEQVRIiWNgGAWjYDACCQYGZiBlAOYkMDDIgegDD0jRYgzWkkC0FiBIbIDqxQnkZzc//lxQc8eYgb33mMTDPTbp88MOPwTaYien24Bdi8GdY2bSM449M2PgOZcmkfAsLXfj7TQDoJZkY7MDOLRIJJgx87AdtmGQyDE2SDhwOHfj7ASQlgOJ23BokZ+R/vkzzz+gFvk3YC3phrPTP+DVwnAjx0Cat+2wGYMEj+EDoJYEeekc/LYY3Mgpk+btO2zMxpMD0pJmuEE6p+BAggFuvwAdtvkzz7fDhv3sZwwO/jhgIy8/O33zhw8VdnK4tMABG9xesEoDnAqx2dtAiupRMApGwSgYCQAAk7pgj3ZOOA0AAAAASUVORK5CYII=","orcid":"","institution":"Sharda University","correspondingAuthor":true,"prefix":"","firstName":"Shashank","middleName":"","lastName":"Sharma","suffix":""},{"id":514563570,"identity":"1bde38e2-9a02-4325-9e4d-780b0b09c2cf","order_by":2,"name":"Nakshatra Bahadur Singh","email":"","orcid":"","institution":"Sharda University","correspondingAuthor":false,"prefix":"","firstName":"Nakshatra","middleName":"Bahadur","lastName":"Singh","suffix":""}],"badges":[],"createdAt":"2025-08-20 18:08:07","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7419899/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7419899/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":91350099,"identity":"7a254230-e528-47b9-8ed4-895184bbabd8","added_by":"auto","created_at":"2025-09-15 14:25:12","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":19381,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eSynthetic Scheme for the preparation of CFA/DA/NBP@Ag nanoparticles from their respective plant extract, coal fly ash, and dopamine\u003c/em\u003e\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7419899/v1/86b73e4da4caabea8278de48.jpg"},{"id":91351813,"identity":"555cd87b-7e74-47d1-abb3-6dc7cadf2da2","added_by":"auto","created_at":"2025-09-15 14:41:12","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":79207,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e(a) FT-IR spectra of Neam Bark Powder (b) FT-IR of CFA/DA/NBP@Ag nanocomposites\u003c/em\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7419899/v1/11939236bc0d3c5d4adc552c.png"},{"id":91350100,"identity":"2c747c69-53b0-4c05-b143-6cb5ebf9d113","added_by":"auto","created_at":"2025-09-15 14:25:12","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":107835,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eFE-SEM of NBP\u003c/em\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7419899/v1/e03b0bc4749e23957b3a9fc7.png"},{"id":91351815,"identity":"0a672fbc-5356-4a5d-89d2-0c1e456b8bb8","added_by":"auto","created_at":"2025-09-15 14:41:13","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":162336,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eSEM images of CFA/DA/NBP@Ag at different resolutions: (a) low resolution, (b) High resolution\u003c/em\u003e\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7419899/v1/5f847103328e0c4e21e09259.png"},{"id":91350431,"identity":"80b7be19-914b-4f65-b834-2bc6024fc467","added_by":"auto","created_at":"2025-09-15 14:33:12","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":12801,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003ePXRD analysis of CFA/DA/NBP@Ag nanoparticles.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7419899/v1/a95439bf77acf7190f50ed90.jpg"},{"id":91350108,"identity":"15f3ef3c-ae54-4eb9-b84a-0de4272eb9ff","added_by":"auto","created_at":"2025-09-15 14:25:12","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":98633,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e(a) UV-Visible spectra of the degradation of MB dye in the presence of CFA/DA/NBP@Ag NPs. (b) Graph showing the percentage removal of MB dye over time in the presence of 8 ppm CFA/DA/NBP@Ag NPs (c) Kinetic data of methylene blue removal (d) Pseudo-first-order kinetics of MB dye removal.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7419899/v1/0fbeacce3567b3eb6ee054fb.png"},{"id":91351814,"identity":"e4fc4ef6-3a59-42a2-9010-13c683a143da","added_by":"auto","created_at":"2025-09-15 14:41:12","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":59062,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eStudy of Removal of Methylene Blue in Percentage (a) Concentration-dependent (b) pH-dependent\u003c/em\u003e\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-7419899/v1/22cd989fa46bd1f2fcfd8f31.png"},{"id":94467670,"identity":"54988930-69b8-4a89-ac4d-1caa6bb99392","added_by":"auto","created_at":"2025-10-27 15:23:26","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1140631,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7419899/v1/fdd4a402-c2d0-469a-b4ae-9b316a3b899f.pdf"},{"id":91350434,"identity":"0dd06ec5-b807-4f99-bc7f-ce22ad6aaf1b","added_by":"auto","created_at":"2025-09-15 14:33:12","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":170797,"visible":true,"origin":"","legend":"","description":"","filename":"TOC.docx","url":"https://assets-eu.researchsquare.com/files/rs-7419899/v1/dba0153d1edcbec05bb4450a.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Silver-Decorated CFA/DA/NBP Nanocomposite for Adsorptive Removal of Methylene Blue Dye from Water","fulltext":[{"header":"1.0 Introduction","content":"\u003cp\u003eWater is an essential natural resource for humans on Earth; however, the high amount of pollutants produced by industrial processes generates eutrophication, consumes oxygen from water, and causes the death of living species, which has a negative impact on the ecosystem[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e], [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Therefore, further research is necessary to minimize these environmental pollutants or find alternative ways to eliminate them [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Organic dyes are particularly problematic among the many types of waste produced by industries worldwide [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Organic dyes resist biodegradation and block sunlight from reaching water, thereby hindering photosynthesis[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Furthermore, organic dyes are typically poisonous, chemically resistant, stable, potentially carcinogenic, and mutagenic[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. These organic dyes are used in the pharmaceutical, food, cosmetic, plastic, textile, and other industries. The textile industry is one of the main causes of organic dye pollution[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. According to the report, 700,000 tons of colorants are produced annually from an average of 10,000 colorants[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. To address this issue, researchers have developed technologies such as adsorption, microbiological processes, Fenton reactions, ion exchange, and ozonation[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. However, these methods are costly, employ hazardous chemicals, produce harmful byproducts, and fail to eradicate the cause of toxicity[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eRecent advancements in nanotechnology have provided many alternative solutions for wastewater treatment, particularly through the development of multifunctional nanocomposites[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Coal fly ash is a waste byproduct of coal combustion that is abundant and inexpensive; however, it exhibits limited adsorption capabilities owing to its crystalline structure and relatively low surface area[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Research has focused on surface modification and functionalization to enhance adsorption efficiency for environmental remediation[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. In addition, dopamine (DA) is a biomolecule with the potential to self-polymerize to form polydopamine (PDA)[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. It has catechol and amine groups that can bind to the NPs surface and help various nanoparticles improve their activity. In addition, neem bark powder (NBP), which is rich in polyphenols and bioactive compounds, acts as a natural reducing and capping agent, offering further enhancement in adsorptive and catalytic activity[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. In this regard, Moradi et al. used an agar/GO/ZnO nanocomposite to degrade MB dye by 91%.[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. In addition, the BC/PDA/TiO2 nanocomposite degraded 80% of the MB dye[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. In this context, silver nanoparticles are highly active for various applications because of their high surface reactivity and catalytic efficiency in dye degradation. When combined with a reducing agent such as sodium borohydride (NaBH4), AgNPs can mediate rapid electron transfer processes that facilitate the breakdown of dye molecules into less toxic byproducts.\u003c/p\u003e\u003cp\u003eHerein, we report the synthesis of an Ag-based nanocomposite coated with coal fly ash (CFA) using dopamine (DA), followed by the incorporation of neem bark powder (NBP), known as CFA/DA/NBP@Ag, for the adsorption of methylene blue dye from aqueous solutions. CFA/DA/NBP@Ag NPs were synthesized by functionalizing coal fly ash (CFA) with dopamine (DA), followed by the incorporation of neem bark powder (NBP) and in situ reduction of silver nanoparticles (AgNPs) using silver nitrate. The adsorption efficiency of the CFA/DA/NBP @Ag nanocomposite for methylene blue dye was assessed, and the kinetics of adsorption were studied. We also studied the pH-dependent adsorption of this composite at pH 4, 7, and 9. The CFA/DA/NBP@Ag nanocomposite demonstrated strong potential as a sustainable, low-cost material for dye removal and wastewater treatment.\u003c/p\u003e"},{"header":"2.0 Materials and method:","content":"\u003cp\u003eDopamine (DA) was purchased from SRL India Pvt. Ltd. Silver nitrate was purchased from Fisher Scientific. Coal fly ash (CFA) was collected from a cement industry in Jhajjar. The adsorbent neem \u003cem\u003e(A. indica)\u003c/em\u003e bark was taken from the neem tree available on the Sharda University campus. Deionized water was used at pH 7.0. Methylene blue dye was purchased from Sigma-Aldrich. The nanocomposite was characterized using scanning electron microscopy (SEM) and PXRD. The size and morphology of the NPs were analyzed using SEM. SEM was conducted using Zeiss EVO 50 and EVO scanning electron microscopes. A 20 mg/mL sample was uniformly dispersed in acetone for 20 min and then deposited onto carbon tape (for FE-SEM) using the drop-casting method. The samples were dried overnight at room temperature. Once the sample was dried, it was used for analysis. X'Pert PRO was used to acquire nanoparticle P-XRD data. For X-ray diffraction (XRD), 25 mg of the sample was applied to glass slides. The glass slide was scanned in the range of 20\u0026ndash;50 degrees for two hours.\u003c/p\u003e\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1. Preparation of Neem Bark Powder (NBP)\u003c/h2\u003e\u003cp\u003eNeem \u003cem\u003e(A. indica)\u003c/em\u003e bark was collected from a neem tree on the Sharda University campus. The major compounds present in neem bark \u003cem\u003e(Azadirachta indica)\u003c/em\u003e include a variety of bioactive phytochemicals, predominantly limonoids, flavonoids, and tannins. The neem bark was washed with distilled water until it was free of dust particles. The bark was then shade-dried to remove all moisture. They were then ground to a fine powder using an electric grinder, and the obtained powder was sieved to obtain a uniform particle size. The powder was washed five times with distilled water. The bark powder (30 g) was boiled in a beaker with 5N HCl (10 mL) to remove the dark color of the bark; after that, it was boiled four times with distilled water, filtered, and dried for 48 h at 80\u0026deg;C. Thus, activated neem bark powder (NBP) was obtained.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2. Preparation of Coal Fly Ash/Dopamine (CFA/DA)\u003c/h2\u003e\u003cp\u003eA mixture of 1 g CFA and 1 g DA was added to 250 mL Tris buffer (10 mM) and stirred continuously for 24 h, followed by filtration. The residue was dried in an oven at room temperature and used for further processing.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3. Preparation of CFA/DA/NBP @Ag Nanoparticles\u003c/h2\u003e\u003cp\u003eCFA/DA (0.5 g) was dispersed in 250 mL of double-distilled water in a 500 mL round-bottomed flask. Then, 0.01 M of silver nitrate was added to the above mixture, and the reaction was heated at 70 \u0026deg;C for 5 min. Then, 30 mL of Neem bark powder (NBP) is added to the above solution. The reaction mixture was stirred for 18 h. After 18 h, the resultant powder mixture was centrifuged for 20 min and washed multiple times with water, followed by acetone. The CFA/DA/NBP @Ag nanoparticles were obtained by drying overnight in an oven.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4. Adsorption experiment of Methylene blue dye\u003c/h2\u003e\u003cp\u003eThe CFA/DA/NBP@Ag NPs were assessed for the absorption of methylene blue dye. The MB dye solution was prepared at a concentration of 15 mg/L in 50 mL of deionized water. Specimens with 8 ppm were added to the methylene blue solution. 100 \u0026micro;L of 0.1 M of NaBH4 was added in each experiment. The solution was stirred in the dark for 5 min to reach the adsorption-desorption equilibrium. The solution was then kept under sunlight for 3 h. The methylene blue dye degradation study was performed using a Shimadzu UV-Vis 1800 spectrophotometer in the 200\u0026ndash;800 nm range. The absorbance of the dye was determined over time at a wavelength of 664 nm using a UV-Vis spectrophotometer. The experiment was performed at a pH of 7.0. In addition, the effect of pH on adsorption was studied by varying the pH.\u003c/p\u003e\u003c/div\u003e"},{"header":"3.0 Results and Discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e3.1. Synthesis and Characterization\u003c/h2\u003e\u003cp\u003eThe CFA/DA/NBP@Ag nanocomposite was synthesized using a wet chemical synthesis method using silver nitrate at 70\u0026deg;C, and the resultant powder mixture was centrifuged for 20 min and washed multiple times with water, followed by acetone. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the synthetic procedure of CFA/DA/NBP@Ag nanocomposite from their respective component.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe NBP was characterized using FT-IR spectra. NBP contains a rich blend of bioactive compounds that contribute to its medicinal properties[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. It is recognized for its abundance of triterpenoids, flavonoids, saponins, alkaloids, polysaccharides, and glycosides, all of which contribute to its diverse therapeutic applications in traditional and modern medicine[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. These compounds function as both capping and reducing agents in the synthesis of silver nanoparticles, inhibiting nanoparticle agglomeration owing to the presence of long-chain natural products in plant extracts. These chemicals can reduce Ag\u003csup\u003e+\u003c/sup\u003e to Ag\u003csup\u003e0\u003c/sup\u003e, and upon heating, metallic silver can be converted into Ag nanoparticles[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. The first FT-IR spectra of NBP were recorded, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea. FT-IR spectra were recorded in the 440\u0026ndash;4000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e range.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFTIR confirmed the successful modification and conjugation of neem bark biomolecules with dopamine-functionalized carbonaceous fly ash and silver nanoparticles (AgNPs\u003cb\u003e).\u003c/b\u003e The spectral shifts, new peaks, and intensity changes validate the surface interactions and incorporation of AgNPs, potentially enhancing their adsorption, catalytic properties, and antimicrobial properties. The FTIR spectrum of Neem Bark Powder (NBP) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea) exhibits absorption bands characteristic of various phytoconstituents present in the NBP. The broad band at approximately 3372 cm⁻\u0026sup1; corresponds to the O\u0026ndash;H stretching vibrations of hydroxyl groups typically present in phenolic compounds and polysaccharides[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. The peaks at 2926 and 2854 cm⁻\u0026sup1; are attributed to the asymmetric and symmetric C\u0026ndash;H stretching of aliphatic \u0026ndash;CH₂ and \u0026ndash;CH₃ groups, respectively. The sharp peak at 1721 cm⁻\u0026sup1; indicates the presence of C\u0026thinsp;=\u0026thinsp;O stretching of carboxylic acids or esters, whereas the band at 1622 cm⁻\u0026sup1; may correspond to aromatic C\u0026thinsp;=\u0026thinsp;C or conjugated carbonyl functional group vibrations. Additional peaks at 1452, 1236, 1163, and 1016 cm⁻\u0026sup1; represent C\u0026ndash;H bending and C\u0026ndash;O stretching vibrations, suggesting the presence of cellulose, hemicellulose, and lignin in the NBP matrix[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], respectively.\u003c/p\u003e\u003cp\u003eIn contrast, the FTIR spectrum of the CFA/DA/NBP@Ag nanoparticles (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb) displays spectral shifts and new absorption features, indicating successful functionalization and nanoparticle incorporation. Bands observed in the region 2666\u0026ndash;2090 cm⁻\u0026sup1; may be ascribed to the formation of new functional groups such as C\u0026thinsp;\u0026equiv;\u0026thinsp;C or C\u0026thinsp;\u0026equiv;\u0026thinsp;N stretching vibrations or altered carbonyl environments due to dopamine (DA) and carbonaceous fly ash (CFA) modification. The characteristic carbonyl and aromatic stretching bands between 1875 and 1386 cm⁻\u0026sup1; were broadened and shifted, suggesting coordination interactions between the NBP active sites and Ag nanoparticles. Moreover, the absorption bands at approximately 1037 and 756 cm⁻\u0026sup1; correspond to C\u0026ndash;O\u0026ndash;C and aromatic C\u0026ndash;H bending vibrations, which may arise from the modified lignin or DA-Ag complex structures. Compared to raw NBP, the reduction in intensity and shift of the O\u0026ndash;H and C\u0026thinsp;=\u0026thinsp;O bands confirm the involvement of these functional groups in nanoparticle binding and stabilization, supporting successful nanocomposite synthesis[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e], [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eWe also performed FE-SEM for NBP. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e displays the FE- SEM images of NBP. The surface appears to be irregular, porous, and a mix of smooth and coarse regions. The particles exhibited a flaky and fibrous texture, which is a major characteristic of plant-based powders. The structure showed a heterogeneous matrix, which is a characteristic of organic lignocellulosic materials, such as bark. The particles were asymmetric and non-spherical with angular edges. The images reveal that the shapes range from flat sheet-like fragments to granular lumps. The particle size appears to be between 10 and 100 \u0026micro;m.\u003c/p\u003e\u003cp\u003eNext, coal fly ash and dopamine (CFA/DA) were added to synthesize the composite, and a mixture was obtained for further use. Finally, nanocomposites were prepared using CFA/DA and NBP. CFA/DA/NBP@Ag nanocomposites were synthesized using wet chemical synthesis using silver nitrate at 70\u0026deg;C, and the resultant powder mixture was centrifuged for 20 min and washed multiple times with water, followed by acetone. The CFA/DA/NBP@Ag nanoparticles were obtained overnight by drying them in an oven.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAfter synthesizing the CFA/DA/NBP@Ag nanocomposite, FE-SEM images were obtained, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb are at two resolutions, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea is at low resolution, and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb is at high resolution. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb shows that the nanoparticles are generally spherical with slightly irregular shapes. The size predominantly ranges from 20\u0026ndash;50 nm in the low-resolution image. The SEM images show that the surface morphology was relatively smooth with a moderate level of agglomeration, which could be due to the biological and chemical interactions among the phytochemical functional groups present in the neem bark powder, dopamine, and coal fly ash. In the low-resolution image, the 1 \u0026micro;m scale bar, the distribution of CFA/DA/NBP @Ag NPs over a border surface can be easily observed. The NPs were found to be in clusters/aggregates, possibly due to the interaction of the nanoparticles with the supporting matrix derived from various precursors such as neem bark powder, dopamine, and coal fly ash. The morphology at this scale suggests a porous and heterogeneous surface, which is a characteristic of composite materials synthesized from natural and waste-derived components. Overall, the images indicate the successful synthesis of Ag silver nanoparticles with a moderately uniform morphology and nanoscale size distribution.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eNext, powder X-ray diffraction (PXRD) was performed on the CFA/DA/NBP@Ag nanoparticles, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The PXRD pattern analysis revealed the crystallographic phase of the synthesized nanocomposite comprising Ag, NBP, DA, and CFA. The most predominant peaks identified for face-centered cubic (FCC) silver were at 2θ\u0026thinsp;\u0026asymp;\u0026thinsp;38.1\u0026deg; (111), 44.3\u0026deg; (200), 64.5\u0026deg; (220), and 77.4\u0026deg; (311), confirming the presence of metallic silver nanoparticles[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e], [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. In addition, the peak corresponding to CFA includes the broad reflection typically associated with SiO2 and 3Al₂O₃\u0026middot;2SiO₂, appearing near 21\u0026deg;, 26\u0026deg;, and 36\u0026deg;[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e], [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. The NBR and dopamine components were found to be amorphous and contributed to either broad or small peaks. The peak in the 10\u0026deg;\u0026ndash;25\u0026deg;region indicates the presence of organic functional groups or biomolecules involved in the reduction and stabilization processes. All the data confirm the formation of CFA/DA/NBP@Ag nanoparticles with crystalline silver as the dominant phase and supporting evidence of biogenic and inorganic phases from DA, NBS, and CFA.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.2. Adsorption Experiment of CFA/DA/NBP@Ag NPs\u003c/h2\u003e\u003cp\u003eThe adsorption potential of CFA/DA/NBP@Ag NPs was studied using methylene blue (MB) dye. The details of the procedure are mentioned in the experimental section. The adsorption of methylene blue was monitored using UV-Vis spectroscopy at an absorbance wavelength of 664 nm[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea shows the UV-Vis spectra of the decrease in absorbance over time of the MB dye for the CFA/DA/NBP@Ag nanocomposite.\u003c/p\u003e\u003cp\u003eThe percentage of dye degradation was calculated using the following formula: % degradation = (C\u003csub\u003e0\u003c/sub\u003e-C\u003csub\u003et\u003c/sub\u003e) /C\u003csub\u003e0\u003c/sub\u003e where C0\u0026thinsp;=\u0026thinsp;Initial Concentration of dye, Ct\u0026thinsp;=\u0026thinsp;time-dependent dye concentration at time t[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb shows the degradation percentage over time. During the process, it was observed that after 210 min, 82% of the dye was adsorbed by the CFA/DA/NBP@Ag NPs. Because the absorbance of the dye is directly proportional to the initial concentration of the dye, the concentration of the dye was determined at a particular time by checking the absorbance at a wavelength of 664 nm. The dye concentration decreased over time, and the absorbance decreased by more than 80 percent after 210 min. The pseudo-first-order kinetics equation further assessed the result, \u0026#119896;\u0026#119905; = \u0026minus; ln (\u0026#119862;\u003csub\u003e\u0026#119905;\u003c/sub\u003e /\u0026#119862;\u003csub\u003e0\u003c/sub\u003e), where k and t represent the rate constant and degradation time, respectively, C0 represents the initial concentration of methylene blue, Ct represents the concentration of methylene blue at time t. We also calculated the rate constant from the pseudo-first-order kinetics equation (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec and \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed). The rate constant was found to be 0.0089 min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for CFA/DA/NBFig.g.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eWe also performed concentration-dependent experiments by varying the concentration from 2 ppm to 10 ppm while keeping the other parameters constant. The dye concentration was fixed at 15 mg/L at pH 7.0. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea, the adsorption of the removal dye increased with an increase in the concentration of the CFA/DA/NBP@Ag nanocomposite. After 60 min, we recorded 13%, 19%, 34%, 50%, and 65% dye adsorption efficacy at 2, 4, 6, 8, and 10 ppm, respectively. In addition, we performed pH-dependent studies by keeping other parameters constant. The dye concentration was fixed at 15 mg/L, and the CFA/DA/NBP@Ag NPs concentration was maintained at 8 ppm. We chose three pH values: 4, 7, and 9, that is, acidic, basic, and neutral. The pH was maintained by adding 0.1 M NaOH or HCl. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb, the percentage of dye removal increased with increasing pH values. After 180 min, the percentage of dye removal was 68%, 80%, and 89% at pH 4, 7, and 9, respectively.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe MB adsorption mechanism using Ag NPs supported by DA/CFA, NBP, and NaBH₄ could involve both physical adsorption and catalytic degradation[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. CFA provides a porous matrix with a high surface area, whereas dopamine forms a DA layer rich in catechol and amine groups that enhance dye binding through hydrogen bonding, π\u0026ndash;π stacking, and electrostatic interactions[\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. NBP further contributes to the natural polyphenolic and carboxylic groups, enhancing the adsorption capacity of the composite. Ag NPs, anchored onto the PDA matrix, serve as electron transfer mediators[\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. When NaBH₄ is introduced, it donates hydride ions that are transferred via AgNPs to the adsorbed dye molecules, promoting their reductive degradation, which is particularly effective for azo and nitro dyes[\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. This synergistic system efficiently adsorbs dyes and facilitates their breakdown into less toxic and colorless compounds.\u003c/p\u003e\u003c/div\u003e"},{"header":"4.0 Conclusion","content":"\u003cp\u003eCFA/DA/NBP@Ag nanocomposite was synthesized using coal fly ash, dopamine, neem bark powder, and silver nitrate. Structural and morphological analyses confirmed the formation of silver nanoparticles embedded in a heterogeneous, porous matrix with particle sizes ranging from 20\u0026ndash;50 nm. The nanocomposite demonstrated high adsorption efficiency for methylene blue, achieving up to 82% removal within 210 minutes. Kinetic analysis followed a pseudo-first-order model (k\u0026thinsp;=\u0026thinsp;0.0089 min⁻\u0026sup1;), and adsorption performance improved significantly under alkaline conditions. The combined effects of the porous CFA matrix, functional groups from dopamine and neem bark, and the catalytic activity of AgNPs (aided by NaBH₄) enabled both adsorption and degradation of the dye. These results highlight CFA/DA/NBP@Ag as a promising, sustainable, and low-cost material for efficient dye removal from wastewater, with strong potential for practical, scalable environmental remediation.\u003c/p\u003e\u003cp\u003e\u003cb\u003eFunding Declaration\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe authors declare that no grants or other financial support were received during the preparation of this manuscript.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eEthics declaration\u003c/strong\u003e\u003cp\u003eNot applicable\u003c/p\u003e\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003ePS - Prepared main textSS - Overall concept, writing and editingNBS - Supervision\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003ena\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAyele A, Haile S, Alemu D, Kamaraj M (2021) Comparative Utilization of Dead and Live Fungal Biomass for the Removal of Heavy Metal: A Concise Review, \u003cem\u003eSci. 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Comments Inorg Chem 45(1):1\u0026ndash;29. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1080/02603594.2024.2312394\u003c/span\u003e\u003cspan address=\"10.1080/02603594.2024.2312394\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Nanocomposite, Methylene Blue, Silver nanoparticle, PXRD, SEM","lastPublishedDoi":"10.21203/rs.3.rs-7419899/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7419899/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eA multifunctional nanocomposite, CFA/DA/NBP@Ag, was synthesized via a simple route involving coal fly ash (CFA) functionalized with dopamine (DA), incorporation of neem bark powder (NBP), and in situ reduction of silver nanoparticles (AgNPs) using silver nitrate. The composite effectively adsorbed methylene blue (MB) dye from water, achieving 80% removal within 210 minutes. UV\u0026ndash;Vis spectrophotometry (664 nm) was used to monitor dye removal, and adsorption efficiency was found to increase with pH (68%, 80%, and 89% at pH 4, 7, and 9, respectively). PXRD confirmed the presence of Ag, NBP, DA, and CFA phases, while SEM revealed mostly spherical particles (20\u0026ndash;50 nm). Kinetic analysis followed pseudo-first-order behavior with a rate constant of 0.0089 min⁻\u0026sup1;. These results underscore the potential of CFA/DA/NBP@Ag as a sustainable and low-cost adsorbent for wastewater treatment.\u003c/p\u003e","manuscriptTitle":"Silver-Decorated CFA/DA/NBP Nanocomposite for Adsorptive Removal of Methylene Blue Dye from Water","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-15 14:25:08","doi":"10.21203/rs.3.rs-7419899/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"f095a53c-06c6-459c-acb2-7ca293553d45","owner":[],"postedDate":"September 15th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-10-27T13:35:50+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-15 14:25:08","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7419899","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7419899","identity":"rs-7419899","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}