green synthesis of copper-loaded chitin/hydroxyapatite hydrogels for efficient catalytic reduction of 4-nitrophenol

4-Nitrophenol (4-NP) is an important industrial intermediate that poses serious ecological risks and affects human health if exposed directly to the environment without treatment. 4-NP is less toxic when reduced to 4-aminophenol (4-AP) and can be used in a wide range of applications. In this study, copper-loaded chitin/hydroxyapatite composite hydrogels (Ch/HA-Cu) were prepared by in situ reduction of Cu 2+ . The catalytic reduction performance of Ch/HA-Cu catalysts for 4-NP was investigated. 10 mg of Ch/HA-Cu catalysts reduced 4-NP (0.1 mM) in 4 min. The increase in the starting concentration of 4-NP significantly improved the reduction of 4-NP, but also prolonged the reaction time. The activation energy required for the reduction of 4-NP by Ch/HA-Cu was about 40.68 kJ mol −1 and the reaction rate constant k was 0.61 min −1 . The interfering substances affected the replacement efficiency of the reactants on the surface of Ch/HA-Cu and slowed down the reaction. The catalytic efficiency of Ch/HA-Cu for the reduction of 4-NP still reached more than 97% after five cycles of experiments, showing excellent catalytic activity and reaction stability for 4-NP, indicating that the prepared Ch/HA-Cu can be used as an economical and reusable multiphase reactor for the abatement of organic pollutants. In this study, the in situ reduction of Ch/HA hydrogel with adsorbed Cu 2+ was used for the efficient catalytic reduction of 4-nitrophenol, which provides a new idea for the reuse of water treatment agents and the reduction of secondary pollution.