In situ growth of CuO on porous zeolite–geopolymer composite spheres for enhanced photocatalytic degradation of dyes

Porous geopolymer spheres were prepared using slag, metakaolin, and zeolite as raw materials via a direct molding method, followed by in situ growth of nano-CuO on their surface. The effects of metakaolin/slag ratio, foaming agent concentration, surfactant type, and different calcination temperatures on the microstructure, porosity, mechanical properties, and photocatalytic performance of the composite spheres were investigated. It was found that at a slag content of 75%, hydrogen peroxide concentration of 3%, and calcination temperature of 400°C, the spheres exhibited good integrity and a more uniform pore size distribution. The CuO/geopolymer composite spheres exhibited a 71.1% photocatalytic degradation efficiency for methyl violet under 120 min of UV irradiation. The material also showed excellent reusability, maintaining 50.3% efficiency after nine cycles. Remarkably, the degradation efficiency was significantly enhanced to 98.1% through synergistic catalysis with H2O2. The synergistic catalytic degradation mechanism was thoroughly investigated. The preparation of composite catalysts by loading nano-CuO semiconductors onto a solid waste–based geopolymer matrix represents a relatively simple and environmentally friendly approach, showing promising development potential in wastewater treatment applications.