Multifunctional AgNPs@Chitosan-g-C3N4-OH Nanocomposite: Efficient Catalytic Reduction of Nitro Pollutants, Antibacterial and Antioxidant Applications

Abstract A ternary nanocomposite comprising silver nanoparticles anchored on glutaraldehyde-cross-linked chitosan supported on hydroxyl-functionalized graphitic carbon nitride (AgNPs@CS-g-C3N4-OH) was synthesized via in situ reduction of silver in a stepwise method. Structural and physicochemical characterization confirmed successful formation of the material. HR-TEM analysis showed uniformly distributed, quasi-spherical AgNPs with a lattice fringe spacing of ∼0.22 nm, corresponding to the (111) plane of crystalline silver. XPS revealed Ag(0) as the dominant species, while ICP-MS determined the silver loading to be 0.84 wt %. BET analysis indicated a mesoporous structure with surface areas of 10.75 and 7.04 m2 g–1 for CS-g-C3N4-OH and the Ag-loaded composite, respectively. The nanocomposite exhibited excellent catalytic activity in NaBH4-mediated reduction reactions. Conversion efficiencies of 99.79%, 97.91%, and 95.93% were achieved for 4-nitrophenol, metronidazole, and nitrofurantoin within 8, 6, and 2.5 min, respectively. The reactions followed pseudo-first-order kinetics with rate constants of 0.9871, 0.9819, and 0.9774 min–1, and half-lives of ∼0.70 min. Antibacterial studies showed strong activity against Aeromonas hydrophila and Enterococcus faecalis, with inhibition zones up to 16.45 ± 0.35 mm and 17.10 ± 0.70 mm at 500 μg mL–1. The MIC50 values were 28.45 and 13.40 μg mL–1, respectively. The material also exhibited moderate antioxidant activity with an IC50 of 104.6 μg mL–1 and 71.09% scavenging efficiency.