Efficient activation of peroxodisulfate by Cu-loaded carbon catalysts for the degradation of highly concentrated Congo red

Cu cluster-loaded carbon (CuC) catalysts were synthesized through a one-step pyrolysis process utilizing chlorophyllin sodium copper salt. The degradation efficiency of CuC₇₀₀-activated peroxodisulfate (PDS) against high concentration Congo red (100 mg/L) was 90.69 % after 10 min. The degradation rates of Congo red after 600 min of dynamic degradation were 90.26 %. Increasing the heat treatment temperature enhances the crystallinity of Cu clusters. After heat treatment, the pyrrole nitrogen content in the blocky, low-porosity CuC catalyst increases, and Cu⁺ species are generated. A neutral environment is most favorable for the degradation of Congo red; however, the presence of humic acid inhibits the degradation rate. During the Congo red degradation, it is primarily mediated by species such as ¹O₂ and •O₂⁻, with first-principles calculations indicating that Cu clusters loaded on carbon layers markedly enhance the adsorption energy of PDS, leading to an increase in the length of the O-O bond from 1.469 to 1.512 Å. Nitrogen doping and Cu cluster loading on carbon improve the adsorption and electron transport from CuC₇₀₀ to PDS. The N-N bond within the Congo red molecule as primary cleavage site, and quantitative structure-activity relationship analyses indicate a reduction in the collective toxicity of the resulting degradation intermediates. Finally, potential degradation pathways and mechanisms for Congo red are proposed.