MIL88-A as a mediator for the degradation of sulfamethoxazole in PS systems: implication of solar irradiation for process improvement

The aim of this study was to demonstrate a feasible system that utilizes solar irradiation for the activation of persulfate PS using a mediator, MIL88-A, an iron-based MOF since PS is poorly activated under sunlight. UVA was also used to simulate solar irradiation, which contains both UVA and UVB. A solution containing sulfamethoxazole (SMX) antibiotic (5 mg L-1) placed in continuously stirred reactors, irradiated with either UVA or natural solar light and spiked with PS (2 mM) and MIL88-A slurry was investigated. The study showed the combined effects of UVA or solar/MIL88-A/PS on the degradation of SMX. The total degradation of SMX occurred in 2 h using the UVA/MIL88-A/PS system compared to just 5-20 min in the solar/MIL88-A/PS system; the system was also examined for its recyclability and matrix effect such as MOF load, pH and UV irradiation as well as chloride, phosphate and bicarbonate contents. The results showed that (i) MIL88-A is recyclable up to five successive cycles, whereby 100% SMX degradation is achieved after 2 h; (ii) chlorides slightly enhanced SMX degradation, while phosphates and bicarbonates greatly inhibited it. This study also investigated the SMX degradation mechanism using XPS, EPR and TOF-SIMS techniques. They revealed that the degradation mechanism is mainly based on sulfate radical (SR) and hydroxyl radical (HR) oxidation. Three SMX degradation products were identified using an HPLC coupled with a QToF high-resolution mass spectrometer. A MIL88-A/PS/solar system is a highly efficient and cost effective AOP for a full and rapid degradation of SMX antibiotic in a water matrix.