A green and efficient method was employed for the synthesis of CuO nanoparticles (CuO NPs) using natural Aloe vera powder as a reducing and stabilizing agent. The as-synthesized CuO NPs were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). The XRD results confirmed the formation of a single-phase monoclinic CuO with good crystallinity. The FESEM and TEM images of the CuO NPs displayed nearly spherical morphology with an average particle size of 20-25 nm. BET analysis showed a mesoporous structure with a specific surface area of 22.407 m²/g. The catalytic efficiency of the CuO nanoparticles was evaluated for the NaBH4-mediated reduction of 4-nitrophenol to 4-aminophenol. The reduction process was observed using UV–Vis spectroscopy, which indicated a gradual decline in the 400 nm absorption peak of 4-NP and the appearance of a new absorption peak around 300 nm, corresponding to 4-aminophenol, as time progressed. The optimization studies concluded that the reduction process was complete in 9 minutes with the addition of 0.04 g of CuO and 0.02 M NaBH4. The catalyst used was recyclable and can be utilized for four consecutive cycles with minimal reduction in catalytic efficiency.
