With ever-increasing attention toward the removal of pharmaceuticals and personal care products (PPCPs), it is highly essential to study promising approaches for this purpose. We introduced a novel Z-scheme SNO-ACO photocatalyst developed via hydrothermal precipitation for degrading tetracycline (TC-HCl) under visible light. SNO-ACO-9% achieved 93% TC-HCl removal in 30 min, with a high pseudo-first-order kinetic rate (0.064 min^-1), 3.5 times faster than SNO, demonstrating exceptional efficiency and potential in environmental remediation, especially for antibiotic pollution. The photocatalyst’s mechanisms involve enhanced light absorption and charge separation, which was facilitated through the addition of a strong oxidative photocatalyst, Ag₂CO₃, in a comparatively low amount in ratio to the parent reductive photocatalyst, SnNb₂O₆, without using a third agent as a charge mediator. Electron spin resonance (ESR) and scavenging experiments verified the formation of different reactive oxygen species and the Z-scheme heterojunction mechanism. This study will provide insight into using a more efficient system with heightened overall photodegradation activity in emerging contaminant removal.

The UV/Cl2 process (also known as chlorine photolysis, which is the combination of chlorine and simultaneous irradiation of UV light) is conventionally applied at acidic mediums for drinking water treatment and further treatment of wastewater effluents for secondary reuse. This is because the quantum yield of HO• from HOCl (ϕHO•, 254 = 1.4) is greater than the one from OCl- (ϕHO•, 254 = 0.278) by approximately 5 times. Moreover, chlorine photolysis in acidic mediums also tends to have lower radical quenching rates than that of their alkaline counterparts by up to 1000 times. The aim of this research is to investigate the applicability of the UV/Cl2 process by assessing its efficacy on the removal of trimethoprim (TMP) at not only acidic to neutral conditions (pH 6-7), but also alkaline mediums (pH 8-9). At alkaline pH, free chlorine exists as OCl- and since OCl- has a higher molar absorption coefficient as compared to HOCl at higher wavelengths, there would be higher reactive chlorine species (RCS) formation and contribution. TMP removal followed pseudo-first order kinetics and depicted that a maximum fluence based constant (kf′ = 0.275 cm2/mJ) was obtained using 42.25 μM (3 mg/L) of chlorine at pH 9, with an irradiation of 275 nm. At alkaline conditions, chlorine photolysis performance followed the trend of UV (275)/Cl2 > UV (265)/Cl2 > UV (310)/Cl2 > UV (254)/Cl2. RCS like Cl•, Cl2−• and ClO• contributed to the degradation of TMP. When the pH was increased from 6 to 8, contribution from hydroxyl radicals (HO• ) was decreased whilst that of RCS was increased. Application of UV (310)/Cl2 had the highest HO• generation, contributing to TMP removals up to 13% to 48% as compared to 5% to 27% in UV (254, 265, 275)/Cl2 systems at pH 6-9. Artificial neural networks modelling was found to be able to verify and predict the contribution of HO• and RCS conventionally calculated via the general kinetic equations in the UV/Cl2 system at 254, 265, 275 and 310 nm.