Catalytic Reduction of 4‑Nitrophenol to 4‑Aminophenol Using Ag@α-Ti(HPO₄)₂·H₂O: Experimental and Computational Studies

A simple hydrothermal method was developed for the synthesis of Ag supported on α-titanium bismonohydrogen orthophosphate monohydrate, Ag@α-Ti(HPO₄)₂·H₂O (Ag@α-TiP), using ilmenite (FeTiO₃) mineral sand. The prepared nanoparticles (NPs) were characterized using powder X-ray diffraction, high-resolution transmission electron microscopy, energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, and diffuse-reflectance spectroscopy. The catalytic efficiency of Ag@α-TiP NPs in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol with sodium borohydride (NaBH₄) in the presence/absence of ultraviolet–visible (UV–vis) radiation was examined. The reduction rate increased when Ag@α-TiP was present in the reaction mixture. The catalytic efficiency was further enhanced when the reaction mixture was exposed to UV–vis light. An ab initio molecular dynamic approach, coupled with slab model density functional theory (DFT) calculations, was used to find the optimal geometry for the model catalyst Ag₄@α-TiP. The formation enthalpies and binding geometries for 4-NP and 4-nitrophenolate ion (4-NP^–) on Ag₄@α-TiP were calculated using DFT.