Modification of Crystal-Optimized TiO2 with Biomass-Derived Carbon Quantum Dots for Highly Efficient Degradation of Favipiravir in Water

TiO2 has been extensively used in the photocatalytic degradation of diverse organic pollutants; however, the wide band gap and high recombination of photogenerated electrons and holes severely limit its practical application. Herein, we propose a novel and cost-effective approach for synthesizing a highly efficient TiO2-based photocatalyst by modifying crystalline phase-optimized TiO2 (with a rutile ratio of 78.5%) with blue algae-derived carbon quantum dots (B-CQDs). The as-synthesized photocatalyst (BCQD@TiO2-700) can activate peroxymonosulfate to degrade 98.6% of the COVID-19 drug favipiravir within 60 min (k = 0.0438 min(-1)), which was approximately 10 times that of B-CQD-modified TiO2 and 16 times that of conventional organic-derived CQD-modified TiO2-700. The abundant functional groups (-OH, (CO)-O-<bouble low line>, C-O-C, P-O, etc.) and narrow average particle size (only 1.42 nm) of the B-CQDs, as well as the optimized rutile ratio, are the main reasons for the improved reactivity of BCQD@TiO2-700. The nonradical degradation process with O-1(2) as the main active species dominates favipiravir degradation, which includes the removal of substituents (-F/-NH2) and the opening of a nitrogen heterocyclic ring; these findings are also supported by density functional theory quantum chemical calculations. This work presents a cost-effective TiO2-based photocatalyst for the high-efficiency degradation of emerging organic pollutants.