Catalytic Reduction of 4-Nitrophenol by Ag@HPS-1 Catalyst

Typically, the mixture of Ag@HPS-1 catalyst aqueous suspension (20 mL, 0.8 g/L), 4-nitrophenol (5 mL, 3 mM), and NaBH₄ aqueous solution (5 mL, 0.3 M) was stirred at room temperature. After a period of reaction, the upper solution was transferred to a quartz cuvette for ultraviolet visible spectroscopy (UV-Vis) measurement. Once a spectrum was acquired, the solution was immediately transferred back to the reaction vessel, and stirring was continued for the sequential reduction reaction until the bright yellow gradually turned colorless. To study the catalyst’s recyclability, the catalyst was separated by centrifugation after each reaction was completed. Thereafter, the catalyst was washed three times with deionized water and ethanol and used for the subsequent recycle under the same reaction conditions.