Iron hydroxyphosphate electro-Fenton catalyst for efficient removal of sulfamethoxazole and resource recycling into slow-release fertiliser ammonium ferrous phosphate

Although the electro-Fenton (EF) process is effective for wastewater treatment , recycling spent catalysts remain a major challenge. Therefore, we introduce a reuse strategy for spent catalysts where an iron hydroxyphosphate [Fe 5 (PO 4 ) 4 (OH) 3 ·2H 2 O] catalyst is utilized. Fe 5 (PO 4 ) 4 (OH) 3 ·2H 2 O obtained •OH and •O 2 − by activating in-situ produced H 2 O 2 , and the degradation rate of sulfamethoxazole reached 94.5% after 120 min and showed excellent stability (maintained above 90%) for 10 cycles. Finally, the used catalyst was converted into slow-release ammonium ferrous phosphate (NH 4 FePO 4 ·H 2 O) fertiliser at a conversion rate of 85.6%. NH 4 FePO 4 ·H 2 O significantly promoted plant and seed growth within 6 days, highlighting the contribution of the resource recycling of the spent catalyst. This study serves as a valuable reference for the efficient utilization of spent catalysts. This study successfully applied EF catalysts and explored the recycling of spent catalysts.