Up-cycling of waste A4 paper into a CaCO₃/biochar nanocomposite for wastewater purification: efficiency, mechanism and biotoxicity evaluation

Waste A4 paper, which is mainly composed of cellulose, is a renewable, low-cost and easily accessible material. Converting waste paper into a carbon-based catalyst is a green and sustainable way to recycle waste paper. Herein, we report a strategy of treating waste with waste to synthesize a calcium carbonate/biochar nanocomposite (CCBN), based on a hydrothermal method and the calcination of waste A4 paper, as a high-efficiency nanocatalyst in activating PMS for the treatment of antibiotic wastewater. Full physical characterizations confirmed that the waste A4 paper was successfully converted into a calcium carbonate/biochar nanocomposite (CCBN) with the structure of porous biochar after calcination at 400 °C. CCBN-400 was composed of biochar and CaCO₃, and was favorable for PMS activation. The quenching tests, electrochemical analysis and EPR analysis suggest that ¹O₂ and e⁻ are the primary active species in the CCBN-400/PMS system. Moreover, a germination experiment suggested that the bio-toxicity of tetracycline to wheat seeds was significantly decreased by treatment with the CCBN-400/PMS system. Here, we successfully up-cycled waste A4 paper into a carbon-based catalyst for water decontamination.