In this study, we investigated the doping of Fe–N–C with ZnO (Fe–N–C@ZnO) to enhance its performance in the reduction of biological toxicity and degradation of enrofloxacin (ENR) in seawater. The steady-state/transient fluorescence analysis and free radical quenching test indicated an extremely low electron–hole recombination rate and the generation of reactive oxygen species in Fe–N–C@ZnO, leading to an improvement in the energy efficiency. We compared the ENR degradation efficiencies of Fe–N–C@ZnO and ZnO using both freshwater and seawater. In freshwater, Fe–N–C@ZnO exhibited a slightly higher degradation efficiency (95.00%) than ZnO (90.30%). However, the performance of Fe–N–C@ZnO was significantly improved in seawater compared to that of ZnO. The ENR degradation efficiency of Fe–N–C@ZnO (58.87%) in seawater was 68.39% higher than that of ZnO (34.96%). Furthermore, the reaction rate constant for ENR degradation by Fe–N–C@ZnO in seawater (7.31 × 10 −3 min −1 ) was more than twice that of ZnO (3.58 × 10 −3 min −1 ). Response surface analysis showed that the optimal reaction conditions were a pH of 7.42, a photocatalyst amount of 1.26 g L −1 , and an initial ENR concentration of 6.56 mg L −1 . Fe–N–C@ZnO prepared at a hydrothermal temperature of 128 °C and heating temperature of 300 °C exhibited the optimal performance for the photocatalytic degradation of ENR. Based on liquid chromatography–mass spectrometry analysis, the degradation processes of ENR were proposed as three pathways: two piperazine routes and one quinolone route.
Supported metal catalysts play a significant role in heterogeneous catalysis in liquid phase reaction systems, but they usually suffer from a stability problem. Encapsulation of active metal species without the compromise of catalytic performance has been considered as an effective strategy. Here, we report an ultrastable Ru-based catalyst with particle size of around 1.1 nm for selective hydrogenation reaction. The highly dispersed Ru species are covered by the in situ formed porous N–C–ZnO overlayer, which is induced through the transforming of ZIF-8 shell that derives from a ZnO substrate. The resulting Ru/ZnO@N–C–ZnO catalyst can exhibit good stability in the hydrogenation of p-chloronitrobenzene after 20 cyclic runs with 100% selectivity toward p-chloroaniline. Comparatively, the naked Ru/ZnO catalyst with larger Ru particles shows serious metal leaching issue with inferior stability and poor selectivity. It is revealed that the excellent performance of Ru/ZnO@N–C–ZnO is attributed to the porous overlayer, which strengthens the bonding of Ru nanoparticles on ZnO.
Water pollution has been worsened by increasing human activities, involving both water-soluble and non-water-soluble contaminants. In this study, a Fe-N-C@ZnO activated PS-AOP (persulfate advanced oxidation process) system was developed through the combination of photocatalysis and PS (persulfate) activation for pollutant degradation in freshwater and seawater. First, the optimal performance was determined by adjusting the Fe-N-C@ZnO to PS ratio, with the best results achieved at 5:3. The degradation efficiency and mechanisms were then examined across different pollutant types. Higher degradation rates were observed in the Fe-N-C@ZnO activated PS-AOP system compared to PS alone, in freshwater, improvements of 70.87%, 61.63%, and 46.26% were recorded for enrofloxacin (ENR), naphthalene, and crude oil, respectively. And in seawater, the increases were 57.53%, 46.87%, and 31.49%. Through radical quenching experiments, h⁺, e⁻, and SO 4 ·⁻ were identified as the dominant reactive species. Additionally, DI-MS analysis was used to propose four degradation pathways for ENR (three Piperazine-Routes and one Quinolone-Route) and two pathways for naphthalene (Benzene ring hydroxylation and Tautomerization). Download: Download high-res image (198KB) Download: Download full-size image
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