Cobalt mediated perovskite as efficient Fenton-like catalysts for the tetracycline removal over a neutral condition: The importance of superoxide radical

Synergy of F-Fe dual sites in KFeF3 promoting Fenton-like cycle and refractory organics degradation through direct electron transfer

The electron cycling of single active site on catalyst was commonly restrict in Fenton-like reactions, thus limits the degradation of refractory organics in water treatment. In this work, a novel strategy for inducing efficient Fenton-like reaction through F-Fe dual sites on the surface of perovskite fluoride KFeF3 was practiced. The KFeF3 and a series of perovskite fluoride material were synthesized by simple hydrothermal method. The KFeF3 exhibited very high performance for remove of multiple refractory organics and chemical oxygen demand in lignin wastewater. Rhodamine B and phenol could be completely removed within 2 s and 16 s respectively and the mineralization rate of phenol reached ∼90 % within 5 min. Detection of ROS and in situ analysis combining density functional theory calculation of the interface proved that the rapid degradation of phenol was attribute to the synergistic effect of F-Fe dual sites and degradation pathway through direct electron transfer. F site serves as the activation site of H2O2 and reduce H2O2 to form OH, whereas, OH attacking was not the dominating pathway for degradation. The redox reaction between F site and H2O2 triggered the direct electron transfer from the Fe-phenol (or hydroxylation intermediates of phenol) complex to F site thus avoided the passivation of Fe site and accelerated Fenton-like cycle. This work revealed a fire-new mechanism of Fenton-like reaction and was expected to impulse treatment of refractory wastewater.

Engineering oxide speciation in CoMnOx catalysts for achieving an ideal selective oxidation of benzyl alcohol at room temperature with atmospheric pressure air

In this work, based on unique dual-component cobalt-manganese oxide catalysts (CoMnOx) fabricated by a solid phase mixed foaming method, we demonstrate an embodiment of the ideal selective oxidation process simultaneously featured by low-cost catalysts, highly efficient utilization of air as oxidant at room temperature, impeccable balancing of high activity and perfect selectivity, high durability, super-facile unit operation at room temperature and atmospheric pressure. Based on their significantly higher catalytic activity than other reported non-noble metal catalysts, in the selective oxidation of benzyl alcohol (BzOH) with atmospheric pressure air as oxidant, CoMnOx catalysts exhibit remarkable activity at room temperature. A 23 % BzOH conversion with 100 % benzaldehyde (BzO) selectivity has been achieved at room temperature and atmospheric pressure while a 100 % BzOH conversion with 100 % BzO selectivity can be achieved at 55 °C. According to the structural characterizations, it was found that the MnCo2O4-Co3O4 oxide pairs characterized by rich Co3+/Co2+ and Mn3+/Mn2+ redox pairs can be formed in CoMnOx catalysts, and then highly effectively utilize the molecular oxygen in air to produce O2- radical, which initializes a highly efficient three-step radical-driven selective oxidation process of BzOH to produce BzO. An impeccable balancing of high activity and perfect selectivity has been achieved in this CoMnOx-air catalytic system. This room temperature and atmospheric pressure CoMnOx-air system provides a potential approaching to lucrative industrial oxidation processes, and also raises the expectation of new full spectrum oxidation catalysts based on transition metal oxides.

High-efficiency electro-Fenton synergistic electrocoagulation for enhanced removal of refractory organic pollutants

The persistence and stability of refractory organic compounds such as dyes in water bodies cause serious toxicity to humans. The present study provides an in-depth investigation into the evolution law of electro-Fenton (EF) oxidation to in situ electrocoagulation (EC) process and its mechanism for highly efficient removal of refractory organic pollutants. A comprehensive evaluation of the energy efficiency by EC, EF (constant pH = 3) and electrocatalytic oxidation (EO) processes under the same research levels was conducted. The results showed that in the EF-EC mode, the removal efficiency of Rhodamine B (RhB) was enhanced by 33.41% compared to the EC system. Additionally, electrode consumption is 52.9% of the EF system, and current efficiency was improved by 272.98% compared to the EO system. Hydroxyl radical (·OH) and polynuclear species (Fe(b)) are the main species to remove refractory organics and intermediates. Unlike the synergistic effect of ·OH homogeneous oxidation and electrocoagulation in the EF-EC process, the ·OH produced in the EO process mainly undergoes heterogeneous oxidation at the electrode interface. The formed iron oxides were mainly Fe2O3 and ɑ-FeOOH. Density functional theory calculations and liquid chromatograph-mass spectrometer analysis indicated that the degradation of RhB mainly included deethylation, deamination, degradation, ring-opening and mineralization reactions. This study provides a valuable reference for related research in the field of environmental electrochemical remediation.

Insights on the efficiency and contribution of single active species in photocatalytic degradation of tetracycline: Priority attack active sites, intermediate products and their toxicity evaluation

Photocatalysis has been proven to be an excellent technology for treating antibiotic wastewater, but the impact of each active species involved in the process on antibiotic degradation is still unclear. Therefore, the S-scheme heterojunction photocatalyst Ti3C2/g-C3N4/TiO2 was successfully synthesized using melamine and Ti3C2 as precursors by a one-step calcination method using mechanical stirring and ultrasound assistance. Its formation mechanism was studied in detail through multiple characterizations and work function calculations. The heterojunction photocatalyst not only enabled it to retain active species with strong oxidation and reduction abilities, but also significantly promoted the separation and transfer of photo-generated carriers, exhibiting an excellent degradation efficiency of 94.19 % for tetracycline (TC) within 120 min. Importantly, the priority attack sites, degradation pathways, degradation intermediates and their ecological toxicity of TC under the action of each single active species (·O2-, h+, ·OH) were first positively explored and evaluated through design experiments, Fukui function theory calculations, HPLC-MS, Escherichia coli toxicity experiments, and ECOSAR program. The results indicated that the preferred attack sites of ·O2- on TC were O20, C7, C11, O21, and N25 atoms with high f+ value. The toxicity of intermediates produced by ·O2- was also lower than those produced by h+ and ·OH.

Radical-driven selective oxidation of benzyl alcohol on MnCoOx catalysts with no oxidant other than air in reactor

Mn reinforced Co3O4 catalysts (MnCoOx) were prepared by a facile solid phase mixed foaming method with an in-situ heating enhancement for the formation of spinel phase mixed oxide species, and studied in the selective oxidation of benzyl alcohol just the air in reactor as oxygen donor. It was found that the MnCoOx catalysts are composed of relatively minimal spinel MnCo2O4 mixed oxide and massive Co3O4 to form MnCo2O4-Co3O4 oxide pair. The micro-domains of MnCo2O4-Co3O4 oxide pair present two redox couples of Mn3+/Mn2+ and Co3+/Co2+ instead of the single one of Co3+/Co2+ in Co3O4, and then dramatically enhance the formation of superoxide radicals (•O2-) species from the O2 in air, which can efficiently initiate the conversion of benzyl alcohol to benzaldehyde in a Fenton-like processes. With no oxidant other than air in reactor, the interaction between MnCo2O4 and Co3O4 in MnCoOx catalysts leads to a benzyl alcohol conversion up to 98 % with a 100 % benzaldehyde selectivity at atmospheric pressure while single component Co3O4 can only present a benzyl alcohol conversion at 37 %. This embodiment of highly efficient heterogeneous selective oxidation just with air as oxidant provides a probability for developing a low-cost and super-facile radical-induced selective oxidation process for alcohols.

Contamination distribution and non-biological removal pathways of typical tetracycline antibiotics in the environment: A review

While the occurrence and removal technologies of tetracyclines in the environment have been reported, a comprehensive systematic summary and analysis remain limited, especially for new generations compounds such as doxycycline. In this review, the latest information regarding the distribution of various tetracyclines in different countries over the past seven years (2017-2023) reveals a notable absence of research reports in North America and Oceania. With China as the representative country, the investigation indicates that the maximum concentrations of TCs exceed 5 µg/L. The maximum concentration of tetracyclines in feces (26.22 µg/L) can reach one order of magnitude higher than that in other media. Furthermore, advanced oxidation technologies, such as Fenton processes, electrochemical oxidation, photolysis, ozonation, etc., were also examined, and the median degradation rate achieved 91.9-97.67%. Reactions such as methylation, demethylation, hydroxylation, dehydration, ring cleavage, and oxidation were observed during degradation. The most common intermediate product was identified as m/z = 461 (C22H25N2O9). This review indicates that future efforts should emphasize understanding the occurrence and fate of new-generation tetracyclines in the environment.