Efficient electro-Fenton degradation of organic pollutants via the synergistic effect of 1O2 and •OH generated on single FeN4 sites.

The electro-Fenton with in situ generated 1O2 and •OH is a promising method for the degradation of micropollutants. However, its application is hindered by the lack of catalysts that can efficiently generate 1O2 and •OH from electrochemical oxygen reduction. Herein, N-doped stacked carbon nanosheets supported Fe single atoms (Fe-NSC) with FeN4 sites were designed for simultaneous generation of 1O2 and •OH to enhance electro-Fenton degradation. Due to the synergistic effect of 1O2 and •OH, a variety of contaminants (phenol, 2,4-dichlorophenol, sulfamethoxazole, atrazine and bisphenol A) were efficiently degraded with high kinetic constants of 0.037-0.071 min-1 by the electro-Fenton with Fe-NSC as cathode (-0.6 V vs Ag/AgCl, pH 6). Moreover, the superior performance for electro-Fenton degradation was well maintained in a wide pH range from 3 to 10 even with interference of various inorganic salt ions. It was found that FeN4 sites with pyridinic N coordination were responsible for its good performance for electro-Fenton degradation. Its 1O2 yield was higher than •OH yield, and the contribution of 1O2 was more significant than •OH for pollutant degradation.

Trivalent iron-tartaric acid metal-organic framework for catalytic ozonation of succinonitrile.

As porous crystal materials, metal-organic frameworks (MOFs) have attracted wide attention in the field of environmental remediation. In this study, a trivalent iron-tartaric acid metal-organic framework (T2-MOF) was successfully synthesized using the inexpensive raw materials ferric chloride (FeCl3.6H2O) and tartaric acid (C4H6O6). The physical and chemical properties of T2-MOF were studied by using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and Brunauer-Emmett-Teller. After that, T2-MOF was used as a catalyst for catalytic ozonation of succinonitrile. The results show that T2-MOF has obvious crystal characteristics and uniform structure. In addition, T2-MOF exhibits strong catalytic performance in ozonation of succinonitrile. The results indicate that the chemical oxygen demand (COD) removal rate is affected by various operating parameters including catalyst characteristics dosages and initial pH values. In the ozonation with 30 mg L-1 T2-MOF, the COD removal rate of 100 mg L-1 succinonitrile reached 73.1% (±4.6%) within 180 min, which was 67.3% (±4.4%) higher than that obtained in the process without catalyst. T2-MOF maintained strong catalytic performance with the pH range of 3.0-7.0. By monitoring the Fe2+ concentration at different reaction time, it was found that the homogeneous catalysis occurred simultaneously with the heterogeneous catalysis.

Mineralization of petrochemical wastewater after biological treatment by ozonation catalyzed with divalent iron tartaric acid chelate.

The petrochemical wastewater includes many toxic organic compounds, which are refractory substances. It is difficult for the wastewater to meet discharge standards after biological treatment, therefore, the further effective treatment of post-biochemical petrochemical wastewater has become an urgent problem to be solved. This study used iron tartaric acid chelate (ITC) catalytic ozonation to treat the petrochemical wastewater. Various key factors were investigated, such as hydraulic retention time (HRT), catalyst dosage, ozone concentration, initial pH values and oxidation efficiency. The kinetics of catalytic ozonation were established. The results indicate that the chemical oxygen demand (COD) removal rate reached a maximum of 58.5%, when the Fe2+ dosage is 0.25 mmol L-1, the initial pH value is neutral, the liquid phase ozone concentration is about 1.95 mg L-1, and HRT is equal to 180 min. In addition, when HRT is equal to 90 min, the B/C ratio of wastewater increases to 0.31, the catalytic ozone reaches maximum oxidation efficiency, and the most economical HRT was 90 min. Finally, the kinetics of ITC catalytic ozonation catalyzed with ITC is consistent with the pseudo-first-order kinetic reaction, and its rate constant is 0.00484 min-1.