Efficient activation of peroxymonosulfate by porous Co-doped LaFeO3 for organic pollutants degradation in water

Insight into cobalt substitution in LaFeO3-based catalyst for enhanced activation of peracetic acid: Reactive species and catalytic mechanism

In this study, a hollow sphere-like Co-modified LaFeO3 perovskite catalyst (LFC73O) was developed for peracetic acid (PAA) activation to degrade sulfamethoxazole (SMX). Results indicated that the constructed heterogeneous system achieved a 99.7% abatement of SMX within 30 min, exhibiting preferable degradation performance. Chemical quenching experiments, probe experiments, and EPR techniques were adopted to elucidate the involved mechanism. It was revealed that the superior synergistic effect of electron transfer and oxygen defects in the LFC73O/PAA system enhanced the oxidation ability of PAA. The Co atoms doped into LaFeO3 as the main active site with the original Fe atoms as an auxiliary site exhibited high activity to mediate PAA activation via the Co(III)/Co(II) cycle, generating carbon-centered radicals (RO·) including CH3C(O)O· and CH3C(O)OO·. The oxygen vacancies induced by cobalt substitution also served as reaction sites, facilitating the dissociation of PAA and production of ROS. Furthermore, the degradation pathways were postulated by DFT calculation and intermediates identification, demonstrating that the electron-rich sites of SMX molecules such as amino group, aromatic ring, and S-N bond, were more susceptible to oxidation by reactive species. This study offers a novel perspective on developing catalysts with the coexistence of multiple active units for PAA activation in environmental remediation.

Preparation of Novel C/N-Doped LaFeO3 Type Perovskite for Efficient Photocatalytic Degradation of Sodium Humate

LaFeO3 chalcocite precursor was prepared by solid-phase milling method, and LaFeO3-type chalcocite composite catalyst, referred to as LFCN catalyst, was synthesized by in situ doping of carbon and nitrogen (urea, melamine, dicyandiamide, and carbon powder), The catalytic performance of the catalysts was investigated by the different mass ratios of LaFeO3 chalcocite precursor and carbon and nitrogen (1:1, 1:2, and 2:1) and the degradation mechanism. Various characterization analyses, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET), showed that the doped composite LFCN catalysts exhibited a hemispherical network structure with a larger specific surface area than that of the pure phase LaFeO3 material. In addition, the LaFeO3 material adjusted the electronic structure of the original LaFeO3 chalcogenide material to a certain extent after in situ doping with organic C and N elements, which enhanced its lattice oxygen oxidation ability. In the study of the catalytic degradation of sodium humate solution under natural light conditions, the catalytic performance was significantly improved compared to that of the pure phase LaFeO3, and 10 mg of the catalyst degraded 30 mg/L of sodium humate solution in 50 min, with a degradation rate increasing from 40 to 98%. The degradation rate increased from 40 to 98% after 4 applications, indicating that the LFCN catalyst has good stability and significant catalytic degradation performance.

Applications of vacancy defect engineering in persulfate activation: Performance and internal mechanism

The vacancy defects in heterogeneous catalysts have received extensive attention for persulfate (PS) activation. Vacancy defects can tune the electronic structure of metal oxides and generate unsaturated coordination sites. Meanwhile, the adsorption energy of reactants on catalyst surface is optimized. Thereby, the reaction energy barrier between catalysts and PS decreases, which could promote catalytic activation and accelerate pollutants degradation. Nowadays, oxygen vacancy (OV), nitrogen vacancy (NV), sulfur vacancy (SV), selenium vacancy (SeV) and titanium vacancy (TiV) have been widely studied with great potential for water remediation. So far, no review was reported regarding the vacancy activated persulfate systems. This paper summarized the types, preparation, mechanism and applications of vacancy in PS systems systematically. In addition, we put forward possible development of vacancy engineering in PS activation systems. It is expected that this review will contribute to the controllable synthesis and applications of vacancies in catalysts for PS activation and contaminants removal.

Zinc-doped and biochar support strategies to enhance the catalytic activity of CuFe2O4 to persulfate for crystal violet degradation

Sulfate radicals-based Fenton-like technology has placed more emphasis on effectively dealing with the threat of dye wastewater. In this work, the Zn-doped CuFe₂O₄@biochar composite (Cu_0.9Zn_0.1Fe₂O₄@BC) was prepared through the convenient sol-gel pyrolysis process and applied as heterogeneous persulfate (PS) activator for crystal violet (CV) degradation. The crystal morphology and physicochemical properties of Cu_0.9Zn_0.1Fe₂O₄@BC were investigated by scanning electron microscope (SEM), X-ray diffractometer (XRD), vibrating sample magnetometer (VSM), Brunauer-Emmett-Teller method (BET), and X-ray photoelectron spectroscopy (XPS). The morphology of the catalyst changed before and after Zn doping. The crystallite size, lattice constant, saturation magnetization, and oxygen vacancy content increased after doping Zn. Compared with CuFe₂O₄@BC, the CV degradation efficiency of Cu_0.9Zn_0.1Fe₂O₄@BC activating PS increased from 87.7 to 96.9%, and the corresponding reaction rate constant increased by about 3.69 times. The effect of experimental conditions was systematically studied on the degradation progress. The degradation efficiency of CV was 91% after five times cycle experiments. Multiple experiments indicated that SO₄^•-, •OH and O₂^•- predominated for CV degradation. The degradation mechanism of CV in the Cu_0.9Zn_0.1Fe₂O₄@BC/PS system involved both free radical (SO₄^•-, •OH and O₂^•-) and non-free radical pathways (electron transfer). The possible degradation pathways were investigated according to the ultra-performance liquid chromatography mass spectrometry (UPLC-MS) analysis of degradation intermediates. The result showed that Cu_0.9Zn_0.1Fe₂O₄@BC have an excellent catalyst performance, which provides a new strategy for improving catalytic activity.

Co-doped Fe3O4/α-FeOOH for highly efficient peroxymonosulfate activation to degrade trimethoprim: Occurrence of hybrid non-radical and radical pathways

Trimethoprim (TMP), as a widely used chemotherapeutic antibiotic agent, has caused potential risks to the aquatic environment. In this study, magnetic Co-doped Fe₃O₄/α-FeOOH was fabricated by a facile one-step ageing method and used for activation of peroxymonosulfate (PMS) in TMP degradation. It was found that low catalyst (0.5 g/L) and PMS addition (0.2 mM) led to the high degradation efficiency of TMP (97.2%, k_obs = 0.11211 min^-1) over a wide range of pH. The oxidation of active radical (SO₄·^-) and non-radical singlet oxygen (¹O₂) co-acted on TMP degradation. Besides, PMS was activated through the cycles between Co(II)/Co(III) and Fe(II)/Fe(III). Fifteen degradation intermediates of TMP were identified by LC-MS, and three possible degradation pathways including hydroxylation, demethylation, and cleavage were proposed. The recovered catalysts exhibited high stability and reusability, maintaining 80% TMP removal efficiency with inappreciable metal leaching (0.012 mg/L of Co, 0.113 mg/L of Fe) after six cycles. Besides, the Co-Fe₃O₄/α-FeOOH/PMS system was highly tolerant to inorganic anions and actual water bodies (river water, lake water, tap water, and sewage plant effluent). Overall, this work provided a promising way to the potential application of Fe-based binary metal oxide for PMS activation.

Application of perovskite oxides and their composites for degrading organic pollutants from wastewater using advanced oxidation processes: Review of the recent progress

In the recent years, perovskite oxides are gaining an increasing amount of attention owing to their unique traits such as tunable electronic structures, flexible composition, and eco-friendly properties. In contrast, their catalytic performance is not satisfactory, which hinders real wastewater remediation. To overcome this shortcoming, various strategies are developed to design new perovskite oxide-based materials to enhance their catalytic activities in advanced oxidation process (AOPs). This review article is to provide overview of basic principle and different methods of AOPs, while the strategies to design novel perovskite oxide-based composites for enhancing the catalytic activities in AOPs have been highlighted. Moreover, the recent progress of their synthesis and applications in wastewater remediation (pertaining to the period 2016-2022) was described, and the related mechanisms were thoroughly discussed. This review article helps scientists to have a clear outlook on the selection and design of new effective perovskite oxide-based materials for the application of AOPs. At the end of the review, perspective on the challenges and future research directions are discussed.

Mesoporous LaFeO3: Synergistic Effect of Adsorption and Visible Light Photo-Fenton Processes for Phenol Removal from Refinery Wastewater

Mesoporous LaFeO3 as a visible light-driven photocatalyst was prepared by a nanocasting method using mesoporous silica (SBA-15) as a hard template. The as-prepared LaFeO3 photocatalyst was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption, X-ray photoelectron spectroscopy (XPS), and optical absorption spectra. The characterization studies and experimental results showed that LaFeO3 with porous structure caused by the removal of SBA-15 hard template could enhance the specific surface area of the resulting photocatalyst, which improves the phenol adsorption ability of the photocatalyst and in turn enhances its photo-Fenton catalytic activity. The photo-Fenton catalytic activity of the photocatalyst was investigated by photo-Fenton degradation of aqueous phenol under visible light irradiation. The effects of catalyst dosage, H2O2 concentration, and solution pH on the photo-Fenton catalytic degradation of phenol using mesoporous LaFeO3 were studied and optimized. Under the optimal conditions of 20 mg L−1 phenol, 1.0 g L−1 catalyst, and 10 mM H2O2 at pH = 5, the photo-Fenton degradation of phenol (93.47%) was achieved in 180 min under visible light irradiation. Furthermore, our results proved the stability and reusability of mesoporous LaFeO3 and revealed its catalytic mechanism for the photo-Fenton degradation of phenol.

Enhanced visible-light photoactivities of porous LaFeO3 by synchronously doping Ni2+ and coupling TS-1 for CO2 reduction and 2,4,6-trinitrophenol degradation

TOC showing the enhanced visible-light photoactivities of porous LaFeO3 by synchronously doping with Ni2+ and coupling with TS-1 for CO2 reduction and 2,4,6-trinitrophenol degradation.