Construction of spherical montmorillonite supported Cu-based catalyst doping with a covalent organic framework for 4-nitrophenol removal

Abstract Developing cost-effective catalysts for the reduction of carcinogenic and highly toxic 4-nitrophenol to chemical and pharmaceutical intermediate 4-aminophenol has received considerable attention in recent years. Here, spherical montmorillonite (SMt) supported Cu-based catalyst doping with a covalent organic framework (COF) was constructed. Microsized SMt could be easily picked up from the mixture due to its self-sedimentary ability, which could easily solve the recycling issues of catalysts. Furthermore, granular SMt with uniform morphology and structure facilitated supporting and preparing catalysts with homogeneous properties. Moreover, SMt with a large specific surface area was suitable as the substrate for loading catalysts with high content. COF acted as a cocatalyst to accelerate the reaction processing. Cu+/Cu2+ ions presented considerable catalytic ability for 4-nitrophenol removal due to their electron transferability and low cost. The valence of Cu ions on the prepared catalyst was analyzed and an apparent reduction rate constant (Kapp) of 5.3 min−1 and turnover frequency (TOF) of 955.5 h−1 were obtained at pH = 5 and 40 °C. The mechanism of the pH influence on the catalytic activity of our prepared heterostructure was further investigated. Moreover, the prepared heterostructure could be easily recovered and reused without any devices, and Kapp could be maintained after being recycled 5 times. Our strategy to fabricate cost-effective heterogeneous catalysts may provide a promising way to apply for these kinds of catalysts.