Peroxide-driven activation on NH2 and graphitic-N doped rice-residue carbon for e−/h+ mediated degradation of acetaminophen and diclofenac

This study presents a novel, sustainable, and metal-free photocatalyst based on nitrogen-doped carbon derived from pre-carbonized rice residue (CRHN) for the visible-light degradation of acetaminophen (ACT) and diclofenac (DC). Synthesized via urea-assisted pyrolysis, the material incorporated NH₂ and graphitic-N groups, enhancing surface basicity and reduced the band gap from 2.5 to 2.16 eV. Under optimal conditions (85 W, 0.1 g L⁻¹, pH 7), CRHN achieved mineralization efficiencies of 97% for DC and 70% for ACT within 30 min, outperforming the undoped material. Kinetic modeling followed a pseudo-second-order model, with rate constants of 0.022 and 0.002 L mg⁻¹ min⁻¹ for DC and ACT, respectively. Scavenger experiments confirmed the dominant role of $e^{-}/h+$ pairs, supported by •OH radicals in a peroxide-driven mechanism. Moreover, adsorption was negligible due to the low dosage of CRHN needed in the experiments. These findings highlight CRHN as a high-performance and eco-friendly photocatalyst for pharmaceutical degradation, promoting sustainable water treatment and agro-industrial waste valorization.