Synthesis and catalytic activity of silver- reduced graphene oxide and silver- magnetite- reduced graphene oxide nanocomposites in the reduction of 4-nitrophenol

The catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) is vital for environmental remediation. This study synthesizes and assesses silver-reduced graphene oxide (Ag/rGO) and silver-magnetite-reduced graphene oxide (Ag/Fe₂O₄/rGO) nanocomposites for 4-NP reduction. Various reducing agents-ascorbic acid (AA), hydrazine hydrate (HH), sodium borohydride (SBH), and cellulose nanofibers (NFC)-were employed under reflux (R), hydrothermal (H), and ultrasonic (U) conditions. Drying methods (oven-drying (O) and freeze-drying (F)) and CTAB as a stabilizer were explored to optimize Ag NP distribution. The nanocomposites were characterized using FT-IR, XRD, FE-SEM, EDS, TEM, BET, TGA, ICP-OES, and VSM. XRD confirmed Ag NP formation with crystallite sizes of 12-23 nm. FE-SEM and TEM showed uniform distribution of cubic Fe₂O₄ and spherical Ag NPs (approximately 50 nm) on GO. The Ag/Fe₂O₄/rGO(O)-AA-U-F nanocomposite demonstrated the highest catalytic activity, with a pseudo-first-order rate constant (k) of 1.81 min^-1 and a specific activity parameter (k') of 180.77 min^-1.g^-1. This nanocomposite exhibited a mesoporous structure with a high specific surface area (226.9 m²/g) and uniform Ag and Fe₂O₄ nanoparticle distribution on rGO. The combination of ascorbic acid (AA) and freeze-drying (F) yielded nanocomposites with superior catalytic performance due to their porous structure and uniform nanoparticle dispersion.