High-nitrogen carbon quantum dots-enhanced auricularia auricula biochar: A promising catalyst for peroxydisulfate activation in wastewater treatment

Naproxen (NPX), a persistent pharmaceutical pollutant, requires efficient degradation for environmental safety. The activation of peroxydisulfate (PDS) has proven to be an effective advanced oxidation process method for the degradation of refractory organic pollutants. This study investigates the enhancement of Auricularia auricula -derived biochar's catalytic performance in PDS activation through modification with nitrogen-doped carbon quantum dots (CQD).The CQD were synthesized via one-step hydrothermal treatment of urea and ammonium citrate. The modified biochar, denoted as CQD-a-BC-800, was obtained by carbonizing the CQD with KOH-activated Auricularia auricula biochar (a-BC) at 800 °C. Compared with a-BC-800, which was obtained by carbonizing a-BC at 800 °C, CQD-a-BC-800 exhibited a significantly enhanced specific surface area, reaching 1.58 times that of a-BC-800 (2622 m 2 /g vs. 1660 m 2 /g)，and the nitrogen content increased from 0.93 % to 2.11 %. The catalytic activity of CQD-a-BC-800 for PDS activation was higher than that of a-BC-800, U-AC-a-BC-800 (directly obtained by carbonizing the mixture of urea, ammonium citrate and a-BC-800), and the mixture of a-BC-800/CQD-800. The NPX degradation ratereached 96.6 % within 30 mins using CQD-a-BC-800 with higher PDS utilization efficiency. This represents a 14.2 % and 6 % increase in NPX degradation rate compared to a-BC-800/PDS and a-BC-800/CQD-800/PDS,respectively..The growth of single-cell Chlorella and Test toxicity prediction indicated that the biotoxicity of intermediate products generated during NPS degradation was lower. Moreover, CQD-a-BC-800/PDS exhibited a wide pH tolerance range (pH 3–9).The mineralization degree of NPX was 80.9 %. Mechanistic studies revealed free radical pathways (SO₄• − , •OH) and non-free radical pathways ( 1 O₂, electron transfer). This work presents an innovative approach combining alkali activation, high-temperature carbonization, and CQD integration to optimize biochar performance for PDS activation, offering a sustainable solution for environmental remediation.