One-pot synthesis of CuO/TiO2 nanocomposites for improved photocatalytic hydrogenation of 4-nitrophenol to 4-aminophenol under direct sunlight

The excellent photocatalytic hydrogenation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with NaBH 4 in the aqueous medium is still a big challenge. Herein, we report a facile one-pot evaporation-induced self-assembly (EISA) method to synthesize a series of CuO/TiO 2 nanocomposites. The as-synthesized CuO/TiO 2 photocatalysts exhibit remarkable catalytic activity under direct sunlight in selective hydrogenation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) due to the synergistic interaction of guest copper nanoparticles with host titanium dioxide (TiO 2 ) species. Especially, 5 wt% CuO/TiO 2 nanocomposite revealed superior reaction rate constant (k) value (0.306 min −1 ) when compared to 3 wt% CuO/TiO 2 (0.192 min −1 ) and 7 wt% CuO/TiO 2 (0.240 min −1 ). Moreover, several characterization techniques (XRD, TEM, N 2 adsorption–desorption isotherm, DRS, and XPS) were executed to deeply investigate the effect of copper content on the bulk and interfacial properties of the catalysts. The characterization results proved that the superior photocatalytic hydrogenation over 5 wt% CuO/TiO 2 catalyst can be ascribed to moderate CuO loading as well as even dispersion of CuO species on the surface of active TiO 2 host, which can largely improve the light absorption ability within visible light region. Besides, the 5 wt% CuO/TiO 2 catalyst exhibits remarkable recyclability and durability, retaining its superior activity (above 95%) up to several repeating cycles, proving its practical applicability for hydrogenation reactions at domestic and industrial levels.