Preparation of g-C3N4 from mixed ammonium salts containing NH4SCN and characterization of its cobalt-modified photocatalytic degradation of formaldehyde

This paper aims to achieve high-quality utilization of desulfurization waste liquid mixed salt. CN-MIX was prepared through pyrolysis of a mixture containing ammonium thiocyanate, ammonium thiosulfate, and ammonium sulfate. Additionally, CN-MIX/Co-a was produced via an impregnation-pyrolysis method with cobalt modification. The performance of the photocatalysts was evaluated using the formaldehyde degradation rate as an index, and their stability was tested. The results indicate that the specific surface area and pore volume of CN-MIX/Co-a increase by 1.53-fold and 1.44-fold, respectively, compared to CN prepared from single salt. The cobalt loading inhibits the thermal polymerization of CN-MIX, leading to a reduction in the intensity of the (0 0 2) crystal diffraction peaks. Additionally, CN-MIX/Co-a exhibits an increase in the CN peak at 2000–2200 cm⁻¹, generating more photocatalytic active sites. The absorption sideband in the visible range red-shifts from 429 nm to 458 nm, broadening the photoresponse range. The emission peak in the photoluminescence (PL) diagram decreases, reducing the photogenerated electron-hole recombination rate. The photocatalyst demonstrates enhanced photocatalytic degradation of formaldehyde gas, with the degradation rate of CN-MIX/Co-a increasing from 13.28 % to 99.2 %. Furthermore, after eight cycles of use, the degradation efficiency of CN-MIX/Co-a for formaldehyde remains above 90 %, indicating high stability.