Recycling of spent superabsorbent polymer into nitrogen-doped carbon catalyst for enhanced antibiotic degradation in groundwater

Polyacrylate (PA), used as a superabsorbent material, is found in household waste, including diapers, napkins, and ice packs; these items are disposed in landfills, raising concerns regarding their environmental impact and management. The beneficial use of PA-derived waste as a carbon catalyst was examined. Nitrogen-doped superabsorbent polymer-derived carbon (N-SAPC) catalysts were designed to activate peroxymonosulfate (PMS) for the removal of the persistent trimethoprim (TMP) pollutant. N-SAPC carbonized at 800 °C (N-SAPC₈₀₀) exhibited improved adsorption and catalytic performance due to its high specific surface area (216.68 m² g⁻¹), pore volume (0.070 cm³ g⁻¹), and graphitic degree (89.56 %). A 97.78 % removal of TMP (10 mg L⁻¹) was achieved in 180 min using N-SAPC₈₀₀ (0.1 g L⁻¹) and PMS (1.0 mM) at pH 6.8. N-SAPC₈₀₀ was effective over a pH range of 5–11. The breakdown of TMP using N-SAPC₈₀₀/PMS was primarily due to improved electron transfer and the production of non-radical species (¹O₂) on the reactive sites of N-SAPC₈₀₀. These sites include defects and functional groups like C[dbnd]O and C–N within the graphitic structures, which were created by N-doping. TMP degradation pathways were proposed according to the by-products formed, and the toxicity of these intermediates was assessed. TMP degradation was slightly inhibited in natural groundwater (NGW), which was overcome by increasing the PMS and/or N-SAPC₈₀₀ concentrations. The catalyst also demonstrated successful removal of other antibiotics such as ciprofloxacin, tetracycline, and sulfamethoxazole with removal percentages of 88.92%, 100%, and 94.82 %, respectively. This study emphasizes the potential of N-SAPC₈₀₀/PMS in addressing antibiotic contamination in groundwater.