Photodegradation of tetracycline hydrochloride by biochar/Cu ₂ O coupled with persulfate: Insights into the factors and intermediates toxicity

In this research, p-type semiconductor Cu
2
O was loaded onto biochar (BC) to prepare the BC/Cu
2
O photocatalyst. The BC exhibited excellent electron transfer ability, significantly enhancing the utilization efficiency of photogenerated electrons. Furthermore, coupling this photocatalysis system with persulfate (PS) activation synergistically enhanced the degradation efficiency of tetracycline hydrochloride (TC-HCl). The reaction rate constant (K
obs
=0.0355min
-1
) of the proposed system was 4.12 times that of the single photocatalysis, which was mainly due to the effective separation of photogenerated electron-hole and formation of sulfate radicals (SO
4
•−
). Over 95% of 50 mg/L TC-HCl was removed within 90 min under optimal conditions. Electron Paramagnetic Resonance (EPR) analysis and quenching experiments identified h
+
, SO
4
•−
,
•
OH, and
•
O
2
as the dominant reactive species for the degradation. The influence of BC/Cu
2
O dosage, TC-HCl, and PS concentration, and solution pH was investigated by batch experiments. Response Surface Model (RSM) study further revealed that solution pH and PS concentration had a significant influence on TC-HCl degradation. Based on the high-performance liquid chromatography-mass spectrometry (HPLC-MS) and the Fukui function of TC-HCl, the degradation intermediates were inferred, and their toxicity was assessed using ECOSAR software, revealing a toxicity alleviation process during degradation. This work presents an efficient BC/Cu₂O-PS system with significant potential for antibiotic remediation.