A controllable reduction-oxidation coupling process for chloronitrobenzenes remediation: From lab to field trial

Efficient reduction-oxidation coupling degradation of nitroaromatic compounds in continuous flow processes

Nitroaromatic compounds (NACs) with electron-withdrawing nitro (-NO2) groups are typical refractory pollutants. Despite advanced oxidation processes (AOPs) being appealing degradation technologies, inefficient ring-opening oxidation of NACs and practical large-scale applications remain challenges. Here we tackle these challenges by designing a reduction-oxidation coupling (ROC) degradation process in LaFe0.95Cu0.05O3@carbon fiber cloth (LFCO@CFC)/PMS/Vis continuous flow system. Cu doping enhances the photoelectron transfer, thus triggering the -NO2 photoreduction and breaking the barriers in the ring opening. Also, it modulates surface electronic configuration to generate radicals and non-radicals for subsequent oxidation of reduction products. Based on this, the ROC process can effectively remove and mineralize NACs under the environmental background. More importantly, the LFCO catalyst outperformed most of the recently reported catalysts with lower cost (13.72 CNY/ton) and higher processing capacity (3600 t/month). Furthermore, the high scalability, material durability, and catalytic activity of LFCO@CFC under various realistic environmental conditions prove the potential ability for large-scale applications.

A sequencing electroreduction-electrooxidation system driven by atomic hydrogen for enhancing 2,4-dichloronitrobenzene removal from wastewater

The sequencing electroreduction-electrooxidation process has emerged as a promising approach for the degradation of the chloronitrobenzenes (CNBs) due to its elimination of electro-withdrawing groups in the reduction process, facilitating further removal in the subsequent oxidation process. Herein, we developed a cathode consisting of atom Pd on a Ti plate, which enabled the electro-generation of atomic hydrogen (H*) and the efficient electrocatalytic activation of H2O2 to hydroxyl radical (•OH). Cyclic voltammetry (CV) curves and electron spin resonance (ESR) spectra verified the existence of H* and •OH. The electroreduction-electrooxidation system achieved 94.7% of 20 mg L-1 2,4-DCNB removal with a relatively low H2O2 addition (5 mM). Moreover, the inhibition rate of Photobacterium phosphoreum in the effluent decreased from 95% to 52% after the sequencing electroreduction-electrooxidation processes. It was further revealed that the H* dominated the electroreduction process and triggered the electrooxidation process. Our work sheds light on the effective removal of electron-withdrawing groups substituted aromatic contaminants from water and wastewater.

MOF-derived Fe/Ni@C marigold-like nanosheets as heterogeneous electro-Fenton cathode for efficient antibiotic oxytetracycline degradation

The widespread occurrence of organic antibiotic pollution in the environment and the associated harmful effects necessitate effective treatment method. Heterogeneous electro-Fenton (hetero-EF) has been regarded as one of the most promising techniques towards organic pollutant removal. However, the preparation of efficient cathode still remains challenging. Herein, a novel metal-organic framework (MOF)-derived Fe/Ni@C marigold-like nanosheets were fabricated successfully for the degradation of oxytetracycline (OTC) by serving as the hetero-EF cathode. The FeNi3@C (Fe/Ni molar ratio of 1:3) based hetero-EF system exhibited 8.2 times faster OTC removal rate than that of anodic oxidation and possessed many advantages such as excellent OTC degradation efficiency (95.4% within 90 min), broad environmental adaptability (satisfactory treatment performance for multiple antibiotics under various actual water matrixes), good stability and reusability, and significant toxicity reduction. The superior hetero-EF catalytic performance was mainly attributed to: 1) porous carbon and Ni existence were both conducive to the in-situ generation of H2O2 from dissolved O2; 2) the synergistic effects of bimetals together with electron transfer from the cathode promoted the regeneration of ≡ FeII/NiII, thereby accelerating the production of reactive oxygen species; 3) the unique nanosheet structure derived from the precursor two-dimensional Fe-Ni MOFs enhanced the accessibility of active sites. This work presented a promising hetero-EF cathode for the electrocatalytic treatment of antibiotic-containing wastewaters.

Controllable Pyridine N-Oxidation-Nucleophilic Dechlorination Process for Enhanced Dechlorination of Chloropyridines: The Cooperation of HCO4- and HO2. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2024;58:4438-4449. [PMID: 38330552 DOI: 10.1021/acs.est.3c09878] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Dechlorination of chloropyridines can eliminate their detrimental environmental effects. However, traditional dechlorination technology cannot efficiently break the C-Cl bond of chloropyridines, which is restricted by the uncontrollable nonselective species. Hence, we propose the carbonate species-activated hydrogen peroxide (carbonate species/H2O2) process wherein the selective oxidant (peroxymonocarbonate ion, HCO4-) and selective reductant (hydroperoxide anion, HO2-) controllably coexist by manipulation of reaction pH. Taking 2-chloropyridine (Cl-Py) as an example, HCO4- first induces Cl-Py into pyridine N-oxidation intermediates, which then suffer from the nucleophilic dechlorination by HO2-. The obtained dechlorination efficiencies in the carbonate species/H2O2 process (32.5-84.5%) based on the cooperation of HCO4- and HO2- are significantly higher than those in the HO2--mediated sodium hydroxide/hydrogen peroxide process (0-43.8%). Theoretical calculations confirm that pyridine N-oxidation of Cl-Py can effectively lower the energy barrier of the dechlorination process. Moreover, the carbonate species/H2O2 process exhibits superior anti-interference performance and low electric energy consumption. Furthermore, Cl-Py is completely detoxified via the carbonate species/H2O2 process. More importantly, the carbonate species/H2O2 process is applicable for efficient dehalogenation of halogenated pyridines and pyrazines. This work offers a simple and useful strategy to enhance the dehalogenation efficiency of halogenated organics and sheds new insights into the application of the carbonate species/H2O2 process in practical environmental remediation.

Degradation of Nitrobenzene by Mackinawite through a Sequential Two-Step Reduction and Oxidation Process

Mackinawite (FeS) has gained increasing interest due to its potential application in contaminant removal by either reduction or oxidation processes. This study further demonstrated the efficiency of FeS in degrading nitrobenzene (ArNO2) via a sequential two-step reduction and oxidation process under neutral conditions. In the reduction stage, FeS rapidly reduced ArNO2 to aniline (ArNH2), with nitrosobenzene (ArNO) and phenylhydroxylamine (ArNHOH) serving as the intermediates. X-ray photoelectron spectroscopy (XPS) analysis indicated that both Fe(II) and S(II) in FeS contributed electrons to the reduction of ArNO2. In the subsequent oxidation stage with oxygen, by addition of 0.5 mM tripolyphosphate (TPP), ArNH2 generated in the reduction process could be effectively oxidized to aminophenols by hydroxyl radicals (•OH), which would undergo eventual mineralization via ring-cleavage reactions. TPP exerted a favorable role in enhancing •OH production for ArNH2 degradation by promoting the formation of the dissolved Fe(II)-TPP complex, thus enhancing the homogeneous Fenton reaction. Additionally, TPP adsorption inhibited the surface oxidation reactivity of FeS due to the change of Fe(II) coordination. Finally, the effective degradation of ArNO2 by FeS in actual groundwater was demonstrated by using this sequential reduction and oxidation approach. These research findings provide a theoretical basis for a new FeS-based remediation approach, offering an alternative way for comprehensive removal of ArNO2.

Enhanced Hydrosaturation Selectivity and Electron Transfer for Electrocatalytic Chlorophenols Hydrogenation on Ru Sites

Electrocatalytic hydrogenation is acknowledged as a promising strategy for chlorophenol dechlorination. However, the widely used Pd catalysts exhibit drawbacks, such as high costs and low selectivity for phenol hydrosaturation. Herein, we demonstrate the potential and mechanism of Ru in serving as a Pd substitute using 2,4,6-trichlorophenol (TCP) as a model pollutant. Up to 99.8% TCP removal efficiency and 99% selectivity to cyclohexanol, a value-added compound with an extremely low toxicity, were achieved on the Ru electrode. In contrast, only 66% of TCP was removed on the Pd electrode, with almost no hydrosaturation selectivity. The superiority of Ru over Pd was especially noteworthy in alkaline conditions or the presence of interfering species such as S2-. The theoretical simulation demonstrates that Ru possesses a hydrodechlorination energy barrier of 0.72 eV, which is comparable to that on Pd. Meanwhile, hydrosaturation requires an activation energy of 0.69 eV on Ru, which is much lower than that on Pd (0.92 eV). The main reaction mechanism on Ru is direct electron transfer, which is distinct from that on Pd (indirect pathway via atomic hydrogen, H*). This work thereby provides new insights into designing cost-effective electrocatalysts for halogenated phenol detoxification and resource recovery.

Fabricating Amorphous Zero-Valent Iron for Cr(VI) Efficient Reduction: Unveiling the Effect of Ethylenediamine on Physicochemical Properties

Amorphous zero-valent iron (AZVI) has attracted wide attention due to its high-efficiency reduction ability. However, the effect of different EDA/Fe(II) molar ratios on the physicochemical properties of the synthesized AZVI requires further investigation. Herein, series of AZVI samples were prepared by changing the molar ratio of EDA/Fe(II) to 1/1 (AZVI@1), 2/1 (AZVI@2), 3/1 (AZVI@3), and 4/1 (AZVI@4). When the EDA/Fe(II) ratio increased from 0/1 to 3/1, the Fe⁰ proportion on the AZVI surface increased from 26.0 to 35.2% and the reducing ability was enhanced. As for AZVI@4, the surface was severely oxidized to form a large amount of Fe₃O₄, and the Fe⁰ content was only 74.0%. Moreover, the removal ability of Cr(VI) was in the order AZVI@3 > AZVI@2 > AZVI@1 > AZVI@4. The isothermal titration calorimetry results revealed that the increase of the molar ratio of EDA/Fe(II) would lead to the stronger complexation of EDA with Fe(II), which resulted in the gradual decrease of the yield of AZVI@1 to AZVI@4 and the gradual deterioration of water pollution after the synthesis. Therefore, based on the evaluation of all indicators, AZVI@2 was the optimal material, not only because its yield was as high as 88.7% and the secondary water pollution level was low, but most importantly, the removal efficiency of Cr(VI) by AZVI@2 was excellent. Furthermore, the actual Cr(VI) wastewater with the concentration of 14.80 mg/L was treated with AZVI@2, and the removal rate of 97.0% was achieved after only a 30 min reaction. This work clarified the effect of different ratios of EDA/Fe(II) on the physicochemical properties of AZVI, which provided insights for guiding the reasonable synthesis of AZVI and is also conducive to investigating the reaction mechanism of AZVI in Cr(VI) remediation.

Oxyanion-modified zero valent iron with excellent pollutant removal performance

Oxyanion-modified zero valent iron (OM-ZVI), including oxyanion-modified microscale ZVI (OM-mZVI) and nanoscale zero valent iron (OM-nZVI), has attracted growing interest in recent years for their excellent pollutant removal performance. This feature article summarizes the recent progress of OM-ZVI materials, including their synthesis, characterization, enhanced pollutant removal performance, and structure-property relationships. Generally, OM-ZVI could be synthesized with wet chemical and mechanochemical (ball-milling) methods and then characterized with state-of-the-art characterization techniques (e.g., X-ray-based spectroscopy, electron microscopy) to reveal their structure and physicochemical properties. We found that phosphate modification could form iron-phosphate on the nZVI surface, facilitating Cr(VI) removal, while the phosphorylation process could induce tensile hoop stress to produce numerous radial nanocracks in the structurally-dense spherical nZVI for enhanced Ni(II) removal via a boosted Kirkendall effect. Oxalate modification could trigger electron delocalization to increase electron cloud density and surface-bound Fe(II) of mZVI for enhanced Cr(VI) removal, while oxalated mZVI exhibited more efficient Cr(VI) removal performance via an in situ formed FeC₂O₄·2H₂O shell of high proton conductivity, favoring Cr(VI) reduction. Differently, the mechanochemical treatment of mZVI with B₂O₃ could exert tensile strain on it through interstitial boron doping, thereby promoting the release and transfer of electrons from its Fe(0) core to its iron oxide shell for dramatic Cr(VI) reduction. This article aims to demonstrate the potential of OM-ZVI for pollution control and environmental remediation.