Synthesis of a carbon dots modified g-C3N4/SnO2 Z-scheme photocatalyst with superior photocatalytic activity for PPCPs degradation under visible light irradiation.

As an emerging carbon nanomaterial, carbon dots (CDs) have superior prospects for applications in the area of photocatalysis due to their unique optical and electronic properties. In this study, a novel CDs modified g-C3N4/SnO2 photocatalyst (CDs/g-C3N4/ SnO2) was successfully synthesized by the thermal polymerization. Under visible light irradiation, the resulting CDs/g-C3N4/SnO2 photocatalyst exhibited excellent photocatalytic activity for the degradation of indomethacin (IDM). It was demonstrated that a 0.5 % loading content of CDs led to the highest IDM degradation rate, which was 5.62 times higher than that of pristine g-C3N4. This improved photocatalytic activity might have been attributed to the unique up-conversion photoluminescence (PL) properties and efficient charge separation capacities of the CDs. Moreover, the combination of g-C3N4 with SnO2 improved the separation of photoinduced carriers and augmented the specific surface area. Reactive species (RSs) scavenging experiments and electron spin resonance (ESR) revealed that superoxide radical anions (O2·-) and photogenerated holes (h+) played critical roles during the photocatalytic process. The results of the detection of H2O2 and ESR confirmed that CDs/g-C3N4/ SnO2 was a Z-scheme heterojunction photocatalyst. Further, HRAM LC-MS/MS was employed to identify the byproducts of IDM, and the major IDM degradation pathways of the CDs/g-C3N4/SnO2 photocatalyst were proposed. This study provides new ideas for the design of novel CDs modified photocatalysts for environmental remediation.

Activation of peroxymonosulfate by Fe doped g-C3N4 /graphene under visible light irradiation for Trimethoprim degradation.

Fe-doped g-C3N4 / graphene (rGO) composites were investigated as catalysts for the activation of peroxymonosulfate (PMS) to degrade Trimethoprim (TMP) under visible light irradiation. The rapid recombination of photogenerated electron-hole pairs in g-C3N4 may be suppressed by doping with Fe and incorporating rGO. The TMP degradation efficiency using 0.2% Fe-g-C3N4/2 wt% rGO/PMS was 3.8 times than that of g-C3N4/PMS. The degradation efficiency of TMP increased with higher catalyst dosages and PMS concentrations. Acidic condition (pH = 3) was observed to significantly enhance the TMP degradation efficiency from 61.4% at pH = 6 to nearly 100%. By quenching experiments and electron spin resonance (ESR), O2- was found to play an important role for the activation of PMS to accelerate the generation of reactive radicals for the TMP degradation. A total of 8 intermediates derived from hydroxylation, demethoxylation and carbonylation were identified through theoretical calculations and the HRAM/LC-MS-MS technique, and transformation pathways of TMP oxidation were proposed. TOC removal rate of TMP increased as reaction time was prolonged. Acute toxicity estimation by quantitative structure-active relationship analysis indicated that most of the less toxic intermediates were generated. The aim of this study was to elucidate and validate the functionality of a promising polymeric catalyst for the environmental remediation of organic contaminants.

Study on heterogeneous photocatalytic ozonation degradation of ciprofloxacin by TiO2/carbon dots: Kinetic, mechanism and pathway investigation.

In this study, the objective was mainly focusing on the mechanism investigation of ciprofloxacin (CIP) degradation by photocatalytic ozonation process which carried out by ozone and TiO2 with a low content of carbon-dots (CDs) under simulated sunlight irradiation. The physicochemical properties of the prepared photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM) X-ray photoelectron spectroscopy (XPS) and zeta potential. Comprehensive investigation has proven the process to be efficient in the removal of CIP with high yield of reactive species (OH, O2-, h+, etc.). Kinetic model on pH investigation found out a repulsive force between the photocatalysts and CIP intensified with the increasing pH, so did the production rate of hydroxyl radicals (OH), while eventually reached a balance and achieved a maximum degradation rate. The results indicated that the enhancement mechanism was triggered by the photoexcited electron accumulated on CDs and transferred by ozone, resulting in the continuous generation of h+, O3- and O2-. Possible photocatalytic ozonation degradation pathways of CIP were proposed according to the identifications of intermediates using high-resolution accurate-mass spectrometry (HRAM) LC-MS/MS.

Thermo-activated peroxydisulfate oxidation of indomethacin: Kinetics study and influences of co-existing substances.

The widespread occurrence of non-steroidal anti-inflammatory drugs (NSAIDs) (e.g., Indomethacin) in the ambient environment has attracted growing concerns due to their potential threats to ecosystems and human health. Herein, we investigated the degradation of indomethacin (IM) by thermo-activated peroxydisulfate (PDS). The pseudo first-order rate constant (kobs) of degradation of IM was increased significantly with higher temperatures and PDS doses. Moreover, when the initial pH value was raised from 5 to 9 the IM degradation was initially decreased and then increased. Basic conditions were favorable for the removal of IM in the thermo-activated peroxydisulfate system. A response surface methodology based on the Box-Behnken design (BBD) was successfully employed for the optimization of the thermo-activated peroxydisulfate (PDS) system. The presence of chlorine ions manifested a dual effect on the degradation of IM, while bicarbonate and SRFA (as a NOM model) reduced it. Radical scavenging tests and electron spin resonance (ESR) revealed that the dominant oxidizing species were SO4- and OH at pH 9. Furthermore, the TOC removal efficiency attained 28.8% and the release of Cl-was 38.5% at 60 °C within 24min, while the mineralization rate of IM were 85.5% with the PDS concentration up to 20  mM at 2 h oxidation. To summarize, thermo-activated PDS oxidation is a promising technique for the remediation of IM-contaminated water.