Preparation of Cu-doped g-C3N4 photocatalysts using desulfurization wastewater by-salt and the mechanism analysis of their efficient degradation of formaldehyde

Formaldehyde, as a common pollutant in industrial exhaust gases, poses a serious threat to human health due to its highly toxic nature. Therefore, the development of efficient catalysts for formaldehyde removal is of great environmental significance. The accumulation of by-salts in the desulfurization waste stream of coking industry has become a major challenge in environmental protection. This paper used the by-salt ammonium thiocyanate as a precursor to prepare Cu-based g-C 3 N 4 (CN) by impregnation pyrolysis method, and applied it to the efficient catalytic oxidation of formaldehyde. The results showed that CN/Cu-10 %-a exhibited the best catalytic performance, with its specific surface area increasing 2.07 times compared to pure CN. The formaldehyde removal rate reached 98 %, which is 7.38 times higher than before modification, and it decreased by only 7.91 % after six cycles, demonstrating excellent cyclic stability. The improved photocatalytic performance is due to Cu doping, which increases the number of active sites, boosts visible light absorption, and facilitates the separation and transfer of photogenerated carriers. The secondary calcination further optimized the close contact between the metal Cu ions and the semiconductor interface, enhanced the specific surface area and the electron transfer efficiency to the metal Cu ions, and suppressed the charge carrier recombination. This study provides a new strategy and theoretical basis for the resourceful utilization of desulfurization waste liquid and the efficient degradation of formaldehyde.