Enhanced persulfate activation by ethylene glycol-mediated bimetallic sulfide for imidacloprid degradation.

CuFeS2 is regarded as a promising catalyst for heterogeneous activation to remove organic contaminants in wastewater. However, effects of solvents in regulating material synthesis and catalytic activity are still not clear. Herein, we reported the role of water, ethanol, ethylene glycol (EG), glycerol, and polyethylene glycol 200 on the synthesis of CuFeS2 micro-flowers and their performance in activating persulfate (PS) to remove imidacloprid (IMI) pesticide. The results showed that the solvent had an effect on the morphology, crystallinity, yields, specific surface areas and unpaired electrons of CuFeS2 micro-flowers. The degradation experiments revealed the efficient catalytic activity of EG-mediated CuFeS2 for heterogeneous PS activation. SO4•- and •OH were identified in EG-CuFeS2/PS system and •OH (90.4%) was the dominant reactive species. Meanwhile, stable 20% of η[PMSO2] (the molar ratio of PMSO2 generation to PMSO consumption) was achieved and demonstrated that Fe(IV) was also involved in the degradation process. Moreover, S2- promoted the cycling of Fe3+/Fe2+ and Cu2+/Cu+, enhancing the synergistic activation and reusability of the catalyst. Density functional theory (DFT) calculations verified that PS was adsorbed by Fe atom and electron transfer occurred on the catalyst surface. Three possible degradation pathways of IMI were proposed by analysis of the degradation intermediates and their toxicities were evaluated by ECOSAR. This study not only provides a theoretical foundation for catalyst design, but also promotes the industrial application of bimetallic sulfide Fenton-like catalysts for water management.

Jiang M ，Xu Z ，Zhang X ，Han Z ，Zhang T ，Chen X ... -  《-》

Synergistic activation of persulfate by FeS@SBA-15 for imidacloprid degradation: Efficiencies, activation mechanism and degradation pathways.

In this work, FeS supported SBA-15 mesoporous silica catalyst (FeS@SBA-15) was synthesized successfully, characterized and first applied to persulfate (PS) activation for the degradation of imidacloprid in wastewater. The as-prepared 3.5-FeS@SBA-15 presented an impressive imidacloprid removal efficiency of 93.1% and reaction stoichiometric efficiency (RSE) of 1.82% after 5 min, ascribed to the synergetic effects of improved FeS dispersion and abundant surface sites by SBA-15. Electron paramagnetic resonance spectra and quenching experiments proved that both SO4·- and ·OH were produced in FeS@SBA-15/PS system, and SO4·- played a dominant role in the degradation process. The S2- can accelerate the cycling of Fe(III)/Fe(II) during activation and increase the steady-state concentration of Fe(II). More importantly, the constructed heterogeneous system exhibited an efficient and stable catalytic activity over a wide range of pH (3.0-9.0), temperature (283K-313K), inorganic ion (NO3-) and humic acid (1-20 mg/L). Moreover, the density functional theory calculations were conducted to predict the potential reaction sites of imidacloprid. Based on eighteen identified intermediates, four main degradation pathways were proposed: hydroxylation, dechlorination, hydrolysis, and the ring cleavage of the imidazolidine. ECOSAR analysis indicated hydroxylation and dechlorination played a key role in the detoxification of the formed compounds. These findings would provide new insights into the application of FeS@SBA-15 catalyst in wastewater treatment and the removal mechanism of imidacloprid from wastewater.

Jiang M ，Xu Z ，Zhang T ，Zhang X ，Liu Y ，Liu P ，Chen X ... -  《-》

Photo-assisted reductive cleavage and catalytic hydrolysis-mediated persulfate activation by mixed redox-couple-involved CuFeS(2) for efficient trichloroethylene oxidation in groundwater.

Persulfate (PS, S2O82-) activation through transition metal sulfides (TMS) has gained increasing attention since it can decompose a wide variety of refractory halogenated organic compounds in groundwater and wastewater. However, the processes of PS activation by TMS and particularly the formation of •OH radical under anoxic and acidic conditions (pH ∼2.8) remain elusive. Herein, by employing mixed redox-couple-involved chalcopyrite (CuFeS2) (150 mg/L) nanoparticles for PS (3.0 mM) activation, 96% of trichloroethylene was degraded within 120 min at pH 6.8 under visible light irradiation. The combination of experimental studies and theoretical calculations suggested that the Cu(I)/Fe(III) mixed redox-couple in CuFeS2 plays a crucial role to activate PS. Cu(I) acted as an electron donor to transfer electron to Fe(III), then Fe(III) served as an electron transfer bridge as well as a catalytic center to further donate this received electron to the O-O bond of PS, thus yielding SO4•- for trichloroethylene oxidation. Moreover, for the first time, •OH radicals were found to form from the catalytic hydrolysis of PS onto CuFeS2 surface, where S2O82- anion was hydrolyzed to yield H2O2 and these ensuing H2O2 were further transformed into •OH radicals via photoelectron-assisted O-O bond cleavage step. Our findings offer valuable insights for understanding the mechanisms of PS activation by redox-couple- involved TMS, which could promote the design of effective activators toward PS decomposition for environmental remediation.

Huang J ，Zhou Y ，Deng S ，Shangguan Y ，Wang R ，Ge Q ，Feng X ，Yang Z ，Ji Y ，Fan T ，Chen B ，Li B ，Zheng C ，Hu X ，Chen H ... -  《-》

Comparison of radical and non-radical activated persulfate systems for the degradation of imidacloprid in water.

The study focuses on degradation efficiency of non-radical activation and radical activation systems of persulfate (PS) to degrade imidacloprid (IMI) by using sodium persulfate (SPS) as PS source. Copper oxide (CuO)-SPS and CuO/biochar (BC)-SPS were selected as PS non-radical activation systems, and pyrite (PyR)-SPS was selected as PS radical activation system. The degradation by CuO-SPS, CuO/BC-SPS and PyR-SPS systems was investigated from acidic to basic conditions (pH 3.0-11.0). Highest degradation by CuO-SPS and CuO/BC-SPS systems was achieved over pH 11.0. In contrast, highest degradation by PyR-SPS system was achieved over pH 3.0, however, PyR-SPS system was also found effective up to pH 9.0. It was found that degradation was more efficient in PS radical activation system, indicating that IMI could be oxidized by radicals rather than by activated PS. Electron paramagnetic resonance (EPR) analysis was carried out to investigate the generation of sulfate (SO4-) and hydroxyl (OH) radicals, which indicated the presence of SO4- and OH in CuO-SPS, CuO/BC and PyR-SPS systems. However, free radical quenching analysis indicated that radicals were main reactive oxygen species for degradation. The lower degradation in PS non-radical activation systems was probably resulted from radicals existed as minor reactive oxygen species. The findings indicated that non-radical oxidation systems showed low reality for degradation and good degradation could be achieved by radical oxidation system. The degradation was also carried out in real waters to investigate the potential applicability of applied systems, which supported PyR-SPS system for effective degradation.

Hayat W ，Zhang Y ，Hussain I ，Huang S ，Du X ... -  《-》

Synergistic activation of persulfate by natural chalcocite and ferrous ions by promoting the cycling of Fe(3+)/Fe(2+) couple for degradation of organic pollutants.

Natural chalcocite (NCC) was chosen as a co-catalyst for activation of persulfate (PS) to degrade organic contaminants in this study. A synergistic effect between NCC and ferrous ions (Fe2+) was found in catalyzing PS for degradation of orange G (OG). The main role of NCC in the NCC/Fe2+/PS system was to facilitate Fe3+ reduction back to Fe2+ and thus improve the stoichiometric efficiency of PS. The results of scavenging experiments and electron paramagnetic resonance tests proved that both sulfate and hydroxyl radicals were the primary reactive oxidants in the NCC/Fe2+/PS system. Twelve potential intermediate products of OG were identified, and the degradation pathway was proposed. Experiment parameters, such as NCC dose, Fe2+ concentration, initial pH, and the presence of anions (H2PO4‒ and Cl‒), all had important impacts on OG degradation. NCC had good reusability in synergistic activation of PS with Fe2+ for OG degradation for five cycles. This study demonstrated a natural sulfide mineral as an efficient co-catalyst towards PS activation for destruction of organic contaminants in water.

Yuan GE ，Qin Y ，Feng M ，Zhang W ，Ru X ，Zhang X ... -  《-》