One electron oxidation-induced degradation of brominated flame retardants in electroactive membrane filtration system: Vital role of dichlorine radical-mediated process.

Reactive chlorine species (RCS) are inevitably generated in electrochemical oxidation process for treating high-salinity industrial wastewater, thereby resulting in the competition with coexisting hydroxyl radicals (•OH) for oxidizing recalcitrant organic compounds. Due to the low redox potentials compared to •OH, the role of RCS has been often overlooked. In this work, we developed an electroactive membrane filtration (EMF) system that had a high removal efficiency (99.1 ± 0.5 %) for tetrabromobisphenol S (TBBPS) at low energy consumption (1.45 kWh m-3). Electron spin resonance spectroscopy and molecular probing tests indicated the predominance of Cl2•-, of which steady-state concentration (2.2 ×10-10 M) was extremely higher than those of ClO• (6.7 ×10-13 M), •OH (0.95 ×10-13 M), and Cl• (2.39 ×10-15 M). The density functional theory (DFT) and intermediate product analysis highlighted that Cl2•- radicals had a higher electrophilic attack efficacy than •OH radicals for inducing changes in the electron density of the carbon atoms around phenolic hydroxyl groups, thus leading to the generation of transition state intermediates and accelerating the degradation of TBBPS. Our work demonstrates the vital role of Cl2•- radicals for pollutant degradation, highlighting the potential of this technology for cost-effective removal of recalcitrant organic compounds from water and wastewater.

Electrochemical oxidation of reverse osmosis concentrate using a pilot-scale reactive electrochemical membrane filtration system: Performance and mechanisms.

Scale-up treatment of real wastewater holds the key to promoting the practical application of electrochemical filtration technology. This work used a pilot-scale Ti/Pd reactive electrochemical membrane (REM) system (12 REM modules with a total REM area of 0.144 m2) to treat high-salinity reverse osmosis concentrate (ROC) from a chemical industry park. The pilot-scale Ti/Pd REM system demonstrated effective electrochemical degradation of ROC wastewater, achieving removal efficiencies of 82.3 ± 1.9% for COD and 46.7 ± 5.6% for TN at a membrane flux of 90 L/(m2·h) and a cell voltage of 5 V, with an energy consumption of 0.045 kWh/g-COD. Singlet oxygen (1O2) and reactive chlorine species were identified as the two primary reactive oxygen species generated in the Ti/Pd REM system. Fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) analysis indicated that the pilot-scale Ti/Pd REM treatment effectively oxidized humic acid-like substance and unsaturated aromatic compounds. Overall, the Ti/Pd REM technology shows a promising application potential for the treatment of high-salinity ROC from the chemical industry.

Selective Synergistic Catalytic Elimination of NOx and CH3SH via Engineering Deep Oxidation Sites against Toxic Byproducts Formation.

NOx and CH3SH as two typical air pollutants widely coexist in various energy and industrial processes; hence, it is urgent to develop highly efficient catalysts to synergistically eliminate NOx and CH3SH. However, the catalytic system for synergistically eliminating NOx and CH3SH is seldom investigated to date. Meanwhile, the deactivation effects of CH3SH on catalysts and the formation mechanism of toxic byproducts emitted from the synergistic catalytic elimination reaction are still vague. Herein, selective synergistic catalytic elimination (SSCE) of NOx and CH3SH via engineering deep oxidation sites over Cu-modified Nb-Fe composite oxides supported on TiO2 catalyst against toxic CO and HCN byproducts formation has been originally demonstrated. Various spectroscopic and microscopic characterizations demonstrate that the sufficient chemisorbed oxygen species induced by the persistent electron transfer from Nb-Fe composite oxides to copper oxides can deeply oxidize HCOOH to CO2 for avoiding highly toxic byproducts formation. This work is of significance in designing superior catalysts employed in more complex working conditions and sheds light on the progress in the SSCE of NOx and sulfur-containing volatile organic compounds.

Efficient removal of neonicotinoid by singlet oxygen dominated MoSx/ceramic membrane-integrated Fenton-like process.

Removal of neonicotinoids (NEOs) from contaminated water is of great importance for both ecological environment and human health. However, conventional Fenton process might be insufficient for NEOs removal due to short lifetime for generated HO• and limited Fe3+/Fe2+ redox cycle. Advancing Fenton process to produce singlet oxygen can be an effective route to improve its efficacy for NEOs removal. Herein, we developed a molybdenum sulfide modified ceramic membrane-integrated Fenton-like system to achieve efficient catalytic removal of NEOs. The reduced Mo0 and Mo4+ could promote the reduction process of Fe3+ to Fe2+, improving the activation efficiency of hydrogen peroxide (H2O2) and the generation of superoxide radical (O2•-). Consequently, the coexisting Mo6+ reacted with O2•- to generate 1O2. The membrane enabled the pollutants to adequately contact oxidants due to the enhanced convective mass transfer. The functionalized membrane exhibited stable catalytic performance for clothianidin (CLO, a kind of NEOs, 10 mg/L) removal (degradation efficiency > 85%). The presence of 1O2 enabled the dechlorination and hydroxylation of CLO and thus reduced the toxicity of wastewater. Our work sheds light on the use of functionalized ceramic membrane integrated catalytic Fenton system for effective environmental remediation.

A comprehensive review on reactive oxygen species (ROS) in advanced oxidation processes (AOPs).

In this account, the reactive oxygen species (ROS) were comprehensively reviewed, which were based on electro-Fenton and photo-Fenton processes and correlative membrane filtration technology. Specifically, this review focuses on the fundamental principles and applications of advanced oxidation processes (AOPs) based on a series of nanomaterials, and we compare the pros and cons of each method and point out the perspective. Further, the emerging reviews regarding AOPs rarely emphasize the involved ROS and consider the convenience of radical classification and transformation mechanism, such a review is of paramount importance to be needed. Owing to the strong oxidation ability of radical (e.g., •OH, O2•-, and SO4•-) and non-radical (e.g., 1O2 and H2O2), these ROS would attack the organic contaminants of emerging concern, thus achieving the goal of environmental remediation. Hopefully, this review can offer detailed theoretical guidance for the researchers, and we believe it able to offer the frontier knowledge of AOPs for wastewater treatment plants (WWTPs).

Efficient removal of micropollutants from low-conductance surface water using an electrochemical Janus ceramic membrane filtration system.

Electrochemical membrane filtration (EMF) technology is effective to remove the micropollutant in the wastewater but its efficacy is drastically compromised in treating the surface water having a typically low conductivity. In this work, a Janus Fe-Pt electrochemical ceramic membrane (ECM) was fabricated by depositing a thin Fe layer on the side of a ceramic membrane facing feed (cathode) and Pt layer on the other side facing permeate (anode). The low Fe-Pt electrode distance (∼1 mm) ensured a decent conductance of the EMF system even in the low-salinity surface water and thereby maintained the removal efficiency of the micropollutant. It was identified that hydroxyl radicals (•OH) generated via anodic water oxidation and cathodic heterogenous Fenton process on bilateral sides of ECM were the dominant reactive oxygen species. The EMF system not only achieved 74% removal of atrazine (ATZ) from the low-conductance synthetic surface water with a low energy consumption (3.6 Wh per gATZ or 7.2 Wh m - 3), but also realized a stable removal of ATZ from real surface water over a continuous filtration experiment of 168 h. The theoretical computations and experimental analysis identified the degradation pathway, i.e., the dechlorination and dealkylation of ATZ in the EMF system. This study highlights the great potential of the Janus ECM in removing micropollutants from low-conductance surface water and wastewater.

Novel Fenton process of Co-catalyst Co9S8 quantum dots for highly efficient removal of organic pollutants.

Advanced oxidation processes (AOPs) have been widely accepted as an efficient and promising strategy for treating organic pollutants, is mainly dominated by hydroxyl radicals (•OH); however, its further practical application has been hindered by its low decomposition rate of H2O2. Hence, for the first time, we propose an eco-friendly and facile synthesis methodology synthesize water-soluble Co9S8 quantum dots (QDs) derived from commercial cobalt disulfide (CoS2), which can serve as excellent co-catalysts to dramatically enhance the decomposition rate of H2O2. It is demonstrated that the conversion rate of H2O2 into •OH is ca. 80.02% promoted by Co9S8 QDs, whereas the conventional Fenton process is ca. 34.9%. The result shows that unsaturated edged S atoms on the surface of Co9S8 play a pivotal role in this enhancement, where the number of protons will react with sulfur atoms to form H2S and expose reductive metallic active sites to accelerate the Fe3+/Fe2+ conversion. In addition, to tackle the issue for difficult recovery of liquid quantum dots, the magnetic Co9S8 QDs/Fe3O4 nanoparticles are particularly synthesized, which show excellent performance for degradation of 20 mg/L Rhodamine B (RhB). Moreover, the TOC degradation rate can remain stable at 80% even after five cycles. It is expected that this work will provide a new pathway of thinking in the Fenton process and impulse the usage of liquid quantum dots in practical AOPs application.

Hollow Fe3O4/carbon with surface mesopores derived from MOFs for enhanced lithium storage performance.

Hollow metal-organic frameworks (MOFs) and their derivatives have attracted more and more attention due to their high specific surface area and perfect morphological structure, which determine their large potential application in energy storage and catalysis fields. However, few researchers have carried out further modification on the outer shell of hollow MOFs, such as the perforation modification, which will endow hollow nanomaterials derived from MOFs with multifunctionality. In this paper, hollow MOFs of MIL-53(Fe) with perforated outer surface are successfully synthesized by using SiO2 nanospheres as the template via a self-assembly process induced by the coordination polymerization. The tightly packed mesopore structure makes the carbon outer shell of MOFs thinner, thus realizing the in-situ transformation from MOFs to hollow Fe3O4/carbon, which exhibits perfect capacity approaching 1270 mA h g-1 even after 200 cycles at 0.1 A g-1, as an anode material in lithium ion batteries (LIBs) application. This research provides a new strategy for the design and preparation of MOFs and their derivatives with multifunctionality for the energy applications.

Mo0 and Mo4+ bimetallic reactive sites accelerating Fe2+/Fe3+ cycling for the activation of peroxymonosulfate with significantly improved remediation of aromatic pollutants.

In Fe2+/peroxymonosulfate (PMS) activation system, the slow cycle rate of Fe3+/Fe2+ has been considered to be the limiting step in the remediation of organic contaminants. In this paper, commercial molybdenum (Mo) powder is employed as the cocatalyst in Fe2+/PMS system, which can significantly accelerate the Fe3+/Fe2+ cycling efficiency by the exposed bimetallic active sites of Mo4+ and Mo0, and the process is accelerated as the amount of Mo powder increased. The Mo cocatalytic Fe2+/PMS system exhibits an enhanced performance for the activation of PMS and the removal of different aromatic pollutants including dyes, phenolic pollutants and antibiotics, in a wide pH range of 4.0-9.0. Importantly, Mo powder exhibits excellent cycle performance in the PMS activation system, and rhodamine B (RhB) can be removed within 10 min even after 5 cycles. Electron paramagnetic resonance (EPR) prove that the sulfate radicals (SO4-) is the major reactive oxides species in the PMS activation, the increase of Fe2+ content induced by the cocatalytic effect of Mo powder can effectively promote the production of SO4- and increase the utilization of PMS. In addition, to observe the process of pollutant removal more intuitively, HPLC-MS is used to analyze the decomposing pathway of RhB and sulfadiazine in Mo+FeSO4+PMS system. It is believed that this research provides a new idea for the efficient activation of PMS by iron ions in a wide initial pH range, which is expected to be applied to the treatment of large-scale industrial wastewater.

Singlet Oxygen Triggered by Superoxide Radicals in a Molybdenum Cocatalytic Fenton Reaction with Enhanced REDOX Activity in the Environment.

As an important reactive oxygen species (ROS) with selective oxidation, singlet oxygen (1O2) has wide application prospects in biology and the environment. However, the mechanism of 1O2 formation, especially the conversion of superoxide radicals (·O2-) to 1O2, has been a great controversy. This process is often disturbed by hydroxyl radicals (·OH). Here, we develop a molybdenum cocatalytic Fenton system, which can realize the transformation from ·O2- to 1O2 on the premise of minimizing ·OH. The Mo0 exposed on the surface of molybdenum powder can significantly improve the Fe3+/Fe2+ cycling efficiency and weaken the production of ·OH, leading to the generation of ·O2-. Meanwhile, the exposed Mo6+ can realize the transformation of ·O2- to 1O2. The molybdenum cocatalytic effect makes the conventional Fenton reaction have high oxidation activity for the remediation of organic pollutants and prompts the inactivation of Staphylococcus aureus, as well as the adsorption and reduction of heavy metal ions (Cu2+, Ni2+, and Cr6+). Compared with iron powder, molybdenum powder is more likely to promote the conversion from Fe3+ to Fe2+ during the Fenton reaction, resulting in a higher Fe2+/Fe3+ ratio and better activity regarding the remediation of organics. Our findings clarify the transformation mechanism from ·O2- to 1O2 during the Fenton-like reaction and provide a promising REDOX Fenton-like system for water treatment.

Graphene modified mesoporous titania single crystals with controlled and selective photoredox surfaces.

Sandwich structured graphene modified TiO2 mesoporous single crystals (GR-MSCs) were obtained by using the graphene embedded silica spheres as the hard template, via a hydrothermal treatment. The selective photocatalysis of TiO2 can be achieved by controlling the location of graphene in TiO2 mesoporous single crystals. The sandwich structured graphene-TiO2 composite has a photooxidation surface, and the core-shell structured TiO2@graphene has a photoreduction surface. It provides a new pathway to realize the selectivity of photocatalysis by controlling the location of graphene in TiO2 MSCs for the first time.

Selective synthesis of TiO2 single nanocrystals and titanate nanotubes: a controllable atomic arrangement approach via NH4TiOF3 mesocrystals.

Nanostructured titania and titanate have been considered as very important materials used in photocatalysis, photovoltaics, gas sensing and other electronic industries. In principle, their common structural feature is that the precursor phase involving TiO6 octahedra or similar building units may be converted to any of the nanostructured titania and titanate forms in a controllable way. Based on the atomic arrangement of ionic liquid-mediated NH4TiOF3 mesocrystals, TiO2 nanocrystals and titanate nanotubes were selectively obtained in H3BO3 and NaOH media, respectively, by using a simple hydrothermal method. Interestingly, the titanate nanotubes were successfully formed by extraction of NH4(+) and F from NH4TiOF3 in a milder alkaline environment as low as 1 M NaOH, rather than conventional treatment of TiO2 in 10 M NaOH. The as-prepared TiO2 nanocrystals with exposed {001} facets exhibit a high photocatalytic activity and sedimentation rate as compared to commercial TiO2. Upon further doping or ion-exchange, the newly prepared TiO2 nanocrystals will show potential applications in the environment.

Chiral Carbonaceous Nanotubes Modified with Titania Nanocrystals: Plasmon-Free and Recyclable SERS Sensitivity.

Chiral carbonaceous nanotubes (CNT) were successfully used in plasmon-free surface-enhanced Raman scattering (SERS) for the first time. Further modification of TiO2 nanocrystals on the chiral CNTs successfully realized the recycling of SERS substrate as chiral CNT/TiO2 hybrids. The high SERS sensitivity of methylene blue (MB) over the chiral CNT/TiO2 hybrids is ascribed to the laser-driven birefringence induced by the helical structure, which provides much more opportunities for the occurrence of Raman scattering. The TiO2 nanocrystals highly dispersed on the surface and inside the hollow cavity of chiral CNTs can completely degrade the MB under the solar light irradiation, leading to the self-cleaning of SERS substrate. The present research opens a new way for the application of chiral inorganic materials in plasmon-free SERS detection.