Construction of SnO2/Bi2O2CO3 Z-type heterojunction for photocatalytic degradation of humic acid under sunlight.

The presence of humic acid (HA) significantly affects water purification and subsequent reuse processes. Its toxicity and potential to form carcinogenic trihalomethanes make the effective removal of HA particularly critical. In this study, SnO2/Bi2O2CO3 photocatalysts were synthesized via a one-step method without external carbonate addition and applied for the photocatalytic degradation of HA. Photocatalyst synthesis was verified by performing comprehensive characterization. In situ XPS and charge density differences indicate the transfer of e- from SnO2 to Bi2O2CO3, confirming the formation of Z-type heterojunction. This structure effectively promotes the separation of photogenerated e--h+ pairs, enhances the generation of ·O2- and ·OH, and thus improves photocatalytic performance. The removal rates of UV254, color number (CN) and TOC of SnO2/Bi2O2CO3 under sunlight were 87.53%, 92.16% and 78.50%, respectively. The seed germination experiment demonstrated that the seed germination index increased by 7.31% to reach 86.33% after photocatalytic degradation, indicating a decrease in toxicity of the HA. Photocatalysis mainly decomposed most CHO and CHON compounds through carboxylic acid reactions, oxygen addition reactions, and dealkylation reactions, and significantly reduced the number of molecules (from 7240 to 4018). Some fulvic acid and hyaluronic acid substances are degraded to form tyrosine substances and soluble microbial byproducts. This study uses CO2 in the air and does not require additional carbonates to synthesize Bi2O2CO3, providing a simple, green and feasible method for synthesizing SnO2/Bi2O2CO3 with excellent recyclability and reusability.