Composite material derived from ZIF-67 and biochar promotes ozonation of 4-nitrophenol.

Cobalt 2-methylimidazole (ZIF-67) have abundant nitrogen and cobalt elements, which can be used as an excellent precursor for catalyst synthesis. In this study, a new Co, N co-doped carbon-based catalyst (Co-N-BC) was synthesized from ZIF-67 and biochar, which can significantly improve the degradation of 4-nitrophenol (4-NP) in catalytic ozonation. The mineralization rate of 4-NP achieves 65.8% within 60 min. The catalyst showed high recycling stability in the four cycles of reuse experiment. Different operating parameters, such as solution pH, the concentration of O3 and 4-NP, have been studied in the Co-N-BC catalytic ozonation. O3, O2-· and ·OH are determined as the main reactive species for 4-NP degradation, and ·OH is especially responsibly for 4-NP mineralization. The existence of inorganic ions, such as Cl-, NO2-, CO32- and PO43-, all significantly inhibited the degradation of 4-NP to different extend, respectively. The effect of substituent on a series of organics with similar structure of 4-NP was also investigated in Co-N-BC catalytic ozonation. This study provides a new composite material for heterogeneous catalytic ozonation, which is very promising in 4-NP contained complex wastewater treatment.

Comprehensive effect of water matrix on catalytic ozonation of chloride contained saline wastewater.

Chloride ion (Cl-) is one of the most common anions in wastewater and saline wastewater, but its elusive effects on organics degradation are not clear yet in many cases. In this paper, the effect of Cl- on organic compounds degradation is intensively studied in catalytic ozonation of different water matrix. It was found that the effect of Cl- is almost completely reflected by transforming ·OH to reactive chlorine species (RCS), which is simultaneously competitive with organics degradation. The competition between organics and Cl- for ·OH directly determines the ratio of their consumption rate of ·OH, which depends on their concentration and reactivity with ·OH. Especially, the concentration of organics and solution pH may change greatly during organics degradation process, which will correspondingly influence the transformation rate of ·OH to RCS. Therefore, the effect of Cl- on organics degradation is not immutable, and may dynamically change. As the reaction product between Cl- and ·OH, RCS was also expected to affect the degradation of organics. But we found that Cl· had no significant contribution to the degradation of organics in catalytic ozonation, which may due to its reaction with ozone. Catalytic ozonation of a series of benzoic acid (BA) with different substituents in chloride contained wastewater was also investigated, and the results showed that the electron-donating substituents can weaken the inhibition of Cl- on BAs degradation, because they increase the reactivity of organics with ·OH, O3 and RCS.

The structure-activity relationship of aromatic compounds in advanced oxidation processes：a review.

Advanced oxidation processes (AOPs) are widely used as efficient technologies to treat highly toxic and harmful substances in wastewater. Taking the most representative aromatic compounds (monosubstituted benzenes, substituted phenols and heterocyclic compounds) as examples, this paper firstly introduces their structures and the structural descriptors studied in AOPs before, and the influence of structural differences in AOPs with different reactive oxygen species (ROS) on the degradation rate was discussed in detail. The structure-activity relationship of pollutants has been previously analyzed through quantitative structure-activity relationship (QSAR) model, in which ROS is a very important influencing factor. When electrophilic oxidative species attacks pollutants, aromatic compounds with electron donating groups are more favorable for degradation than aromatic compounds with electron donating groups. While nucleophilic oxidative species comes to the opposite conclusion. The choice of advanced oxidation processes, the synergistic effect of various active oxygen species and the used catalysts will also change the degradation mechanism. This makes the structure-dependent activity relationship uncertain, and different conclusions are obtained under the influence of various experimental factors.