First Evidence and Mechanistic Insights into the Freeze-Thaw-Induced Degradation of LaZnO3-B Photocatalyst for Sulfamethoxazole Sodium Removal

Haze induced eye infections have promoted the widespread use of sulfamethoxazole sodium (SA-Na), and its medical wastewater in cold regions north of 55 °N in the northern hemisphere (150–300 days in cold weather) has failed traditional treatment due to freeze-thaw alternation, urgently requiring efficient low-temperature resistant materials. This study focuses on the degradation kinetics of SA-Na on LaZnO photocatalyst modified with spirulina residue based biochar (LaZnO₃-B) during freeze-thaw cycles (frequency, temperature difference, duration), and systematically investigates its structural performance response at -5 ℃/-15 ℃ and 10 cycles through SEM, FTIR, and XPS characterization analysis. The results showed that freeze-thaw cycles led to a decrease in degradation efficiency by disrupting the microstructure of the catalyst (SEM showed surface cracks and pore collapse), altering the molecular structure (FTIR characteristic peak broadening weakened), and surface chemical state (XPS showed an increase in O element, C-C/C-H converted to C-O-C/C = O); The lower the freezing temperature, the more significant the damage and the greater the decrease in efficiency. This study elucidates the essence of the low-temperature stability of LaZnO₃-B, improves the structure-activity theory of biochar based catalysts, and provides technical support for the treatment of ophthalmic medical wastewater in cold regions.