Fabrication and characterization of the magnetic separation photocatalyst C-TiO2@Fe3O4/AC with enhanced photocatalytic performance under visible light irradiation

Congo red (CR) is a kind of refractory contaminant. Conventional biological treatment processes are ineffective for the CR degradation. However, photocatalysis technology could be an alternative for the decomposition of CR because of its high efficiency. In this study, we prepared three kinds of photocatalysts, all of which have advanced visible light excitation characteristics. The magnetic catalyst C-TiO2@Fe3O4/AC was produced by loading C-TiO2 and nano-Fe3O4 onto granular activated carbon (AC). C-TiO2@Fe3O4/AC has a band gap of 2.535 eV, stable magnetic characteristics, and stability toward CR removal. C-TiO2@Fe3O4/AC showed the best performance for CR removal under both simulated sunlight (200–800 nm) and visible light (400–800 nm) irradiation compared to the other catalysts. The CR removal rate reached 92.9% after 30 min of simulated sunlight irradiation, and the reaction rate constant was 0.1776 min−1. Under visible light, the CR removal rate reached 65%. The hydroxyl radical (OH) was detected, and its concentration was determined. Furthermore, the spectral analysis results indicated that the azo bonds and aromatic rings in CR were destroyed. The C-TiO2@Fe3O4/AC has a self-cleaning ability to prevent organic contamination. This study provides a new way of thinking and a simple preparation technique for magnetic visible light catalyst synthesis.