Photochemical Synthesis of g-C ₃ N ₄ Quantum-Dot-Anchored Ag, Pd, and AgPd Alloy Nanoparticles for Catalytic Reduction of 4-Nitrophenol and Antibacterial Activity

The rational design of multifunctional nanomaterials with synergistic properties is central to advancing applied nanotechnology. Herein, we report a stabilizer-free photochemical strategy for the synthesis of monometallic (Ag and Pd) and bimetallic alloy (AgPd) nanoparticles anchored on g-C₃N₄ quantum dots (g-C₃N₄ QDs), where the photoactive carbon nitride platform functions as both a light-driven reducing agent and a stabilization matrix. Comprehensive characterization by PXRD, HRTEM, EDS, UV-vis spectroscopy, and X-ray photoelectron spectroscopy confirms uniform nanoparticle dispersion, alloy formation, and preservation of the g-C₃N₄ framework. The catalytic performance of the synthesized nanomaterials was evaluated using the NaBH₄-assisted reduction of 4-nitrophenol as a model aqueous phase reaction. Among the catalysts, the g-C₃N₄-AgPd alloy exhibits markedly enhanced activity, delivering a rate constant of 17.92 × 10⁻² min⁻¹, which is approximately 11.5 times higher than that of pristine g-C₃N₄ QDs and ∼1.9 times higher than that of the monometallic counterparts. This enhancement is attributed to electronegativity-driven charge redistribution within the AgPd alloy, leading to electron-enriched Pd sites that promote reactant adsorption and activation, coupled with efficient electron transfer mediated by Ag. In addition to catalytic performance, the g-C₃N₄-AgPd system demonstrates enhanced antibacterial activity against Escherichia coli, producing inhibition zones of up to 18 mm at 100 μL. Overall, this work highlights a versatile photochemical platform for engineering alloy nanocatalysts with synergistic catalytic and antimicrobial properties, relevant to applied nanomaterial research.