Silver Nanoparticles Immobilized on Inexpensive Candle Soot Particles for the Efficient Reduction of Aqueous Nitroarenes and Azo Dyes

ABSTRACT A facile in–situ method for preparing stable silver nanoparticles (Ag NPs) decorated on heat–treated candle soot (o–CS) is reported in this article. The synthesized Ag@o–CS nanocomposite with ∼7.2% wt./wt. Ag loading was thereafter investigated for its efficacy toward catalytic reduction of aqueous nitroarenes like 4–Nitrophenol (4–NP), 4–Nitroaniline (4–NA), and 2,4–Dinitrophenol (2,4–DNP), and azo dyes like Methylene Blue (MB), using sodium borohydride (NaBH 4 ) as the reducing agent under ambient conditions. Key experimental parameters like NaBH 4 dosage, catalyst dosage, pH and temperature were systematically examined for their influence on the efficiency of catalytic reduction. The Ag@o–CS catalyzed chemical reduction with NaBH 4 followed pseudo–first–order kinetics, achieving near–complete reduction of aqueous 4–NP (99.51% in 6 min), 4–NA (99.46% in 7 min), 2,4–DNP (99.02% in 15 min), and MB (99.79% in 60 min), at pH 10, 298 K, and 1:10 molar excess of NaBH 4 . The superior reduction capability of Ag@o–CS was attributed to the high surface area (S BET = 152.3 m 2 /g) and hydrophilicity of o–CS (average contact angle = 22.4°). This facilitates the rapid adsorption of BH 4 − ions and pollutant molecules on the catalyst surface, followed by Ag NPs–mediated electron transfer to generate active hydrogen species that drive the reduction process. Common co–existing anions like SO 4 2– , CO 3 2– , NO 3 − , and PO 4 3– offered marginal resistance to the reduction process. Moreover, the synthesized nano–catalyst demonstrated good recyclability, retaining its structural integrity and catalytic activity with minimal leaching of silver for at least 6 consecutive cycles of reduction.