Green Synthesized Silver Nanoparticles from Biowaste for Rapid Dye Degradation: Experimental Investigation and Computational Mechanistic Insights

Silver nanoparticles (Ag NPs) green-synthesized using <i>Nypa fruticans</i> fruit husk (NF) extract were applied as catalysts for the degradation of organic dyes in water for the first time. The synthesized Ag NPs, which were well-dispersed, highly stable, and small in size with an average diameter of ~4 nm, efficiently catalyzed the degradation of methyl orange (MO) in the presence of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi>NaBH</mi></mrow><mrow><mn>4</mn></mrow></msub></mrow></semantics></math></inline-formula>, achieving complete degradation (>99%) within one minute under optimized conditions. The application to a commercial synthetic dye resulted in over 89% degradation within five minutes. To elucidate the degradation mechanism at the atomistic level, molecular dynamics (MD) simulations and density functional theory (DFT) calculations were employed. MD simulations revealed the adsorption behavior of MO on the Ag(111) surface. DFT calculations clarified the reaction pathway of MO degradation, identifying direct hydride transfer from <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msubsup><mrow><mi>BH</mi></mrow><mrow><mn>4</mn></mrow><mrow><mo>−</mo></mrow></msubsup></mrow></semantics></math></inline-formula> to the azo group of MO as the rate-determining step, with the subsequent step influenced by the pH conditions. These findings illustrate the potential of NF extract in the green synthesis of catalytically active Ag NPs and contribute to understanding their role in dye degradation processes relevant to environmental remediation.