Preparation of multilayer strontium-doped TiO2/CDs with enhanced photocatalytic efficiency for enrofloxacin removal

Multilayer strontium-doped TiO₂/carbon dots (CDs) materials (TC) were produced via sol-gel-layered carbonization method. A thorough analysis of the fabricated composites via XRD, SEM, and XPS revealed that strontium ions, TiO₂ and CDs, were combined with each other to form layered structures. According to the UV-Vis diffuse reflectance spectrograms and (αhv)^1/2 vs. hv plots, the electron-donor property of strontium ions caused a more positive TC conduction band position than that in the pure TiO₂, thereby increasing the visible-light absorption range of TC. Based on the photocatalytic degradation data, the degradation rate of enrofloxacin was 84.7% at the dosage of 0.05 g·L^-1 and the concentration of 10 mg·L^-1. The capture experiments and ESR results showed that ·O₂^- and e^- played a major role in the degradation process of TC. The possible degradation mechanism of enrofloxacin was explained in terms of decarboxylation and defluorination, as was detected via ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) analysis.

Heterogeneous activation of peroxydisulfate by sulfur-doped g-C3N4 under visible-light irradiation: Implications for the degradation of spiramycin and an assessment of N-nitrosodimethylamine formation potential

In this study, peroxydisulfate (PDS) was activated by synthesized sulfur-doped g-C₃N₄ (SCN) under visible-light irradiation and was adopted to enhance the removal of spiramycin, which is an important precursor of N-nitrosodimethylamine (NDMA). Specifically, 95.4% of spiramycin (≤10 mg/L) was removed in 60 min under the conditions of an initial value of pH of 7.0, an SCN dose of 1.0 g/L, and a PDS dose of 200 mg/L, and its degradation fitted well with the pseudo first-order kinetics. Electron paramagnetic resonance analysis and trapping experiments confirmed that ·O₂^- and h⁺ were the main oxidizers for the degradation of spiramycin, and ·SO₄^- and ·OH also participated in the removal of spiramycin. The removal of spiramycin in the PDS/SCN visible-light catalytic system occurred through three different pathways: aldehyde oxidation, cleavage of C-O bond and demethylation. Notably, 61.4% of NDMA formation potential (FP) was reduced after the reaction. The SCN catalyst was stable and its catalytic performance was excellent in the PDS/SCN system, as the spiramycin removal efficiency decreased only slightly from 95.4% to 87.3% after being reused three times. Therefore, our study not only provides an alternative method for removing spiramycin but can also can significantly reduce NDMA FP.