Utilizing the oxygen-atom trapping effect of Co3O4 with oxygen vacancies to promote chlorite activation for water decontamination

Carbonized nitrogen-containing conjugated microporous polymers: Versatile platforms for high-performance carbon catalytic membranes and their angstrom-confined activation mechanism on peroxymonosulfate

Engineering high-performance N-doped carbon catalysts for peroxymonosulfate (PMS) activation and elucidating their activation mechanism are crucial for the degradation of emerging pollutants. In this study, we propose a novel self-template carbonization strategy (NSCS) based on a N-containing conjugated microporous polymer (NCMP, poly(triphenylamine)) to fabricate high-performance N-doped porous carbon catalysts. Owing to the unique N-mediated catalytic sites within the confined micropores of the NCMP precursor, the NSCS approach enables the investigation of reactive oxygen species evolution and their formation mechanisms as carbonization temperature increases from 200 to 1400 °C. The catalyst carbonized at 1000 °C exhibited high degradation activity (k = 0.170 min-1), driven primarily by O2•- and 1O2, with minor contributions from •OH and SO4•-. Additionally, a PMS self-decomposition and ¹O2 generation mechanism within angstrom-confined spaces was identified. A self-supported carbon catalytic membrane was fabricated from CPTPA-1000 (CPTPA-CNT) due to its high conjugation and thermal stability. This membrane demonstrated efficient removal of organic pollutant (k = 123.54 min-1, 220.3 L m-2 h-1 bar-1, 120 h, 99.4 %), outperforming the carbonized CNT membrane (k = 19.54 min-1, 67.5 L m-2 h-1 bar-1, 120 h, 14.8 %). This work paves an avenue for the design of high-performance carbon-based membranes and gives new insights into the 1O2 generation mechanism in N-doped carbon catalysts.

Spinel-based zinc-doped Co3O4 (ZCO) catalytic membrane for efficient peroxymonosulfate activation and chloroquine phosphate degradation: An atom doping strategy

The degradation of emerging contaminants (ECs) in wastewater remains a significant challenge, primarily due to the low activation efficiency and difficulty in catalyst recovery associated with traditional heterogeneous peroxymonosulfate (PMS) systems. In this study, a zinc (Zn)-doped Co3O4 spinel (ZCO) catalyst was designed via an atom doping strategy and immobilized onto a polyvinylidene fluoride (PVDF) membrane to construct a ZCO@PVDF catalytic membrane, thereby developing an efficient and innovative approach for ECs degradation. The innovation of this study is the Zn doping-induced electron-polarized distribution, which creates electron-rich Co centers and significantly enhances the PMS activation efficiency. The porous structure and confined space of the membrane significantly improved the exposure of active sites, facilitated interfacial mass transfer, and promoted reactant enrichment. Consequently, the ZCO@PVDF membrane/PMS system enabled the efficient filtration-based removal of Chloroquine phosphate, with the pseudo-first-order rate constant K of 0.035 ms-1 for its removal. The system exhibited exceptional catalytic performance, achieving 99.9 % Chloroquine phosphate degradation within 30 min, with the pseudo-first-order rate constant K dominating the reaction (pH = 6.8, PMS = 1.6 mM, Chloroquine phosphate = 10 mg L-1, Catalyst loading = 2.0 mg cm-2). The active species responsible for the degradation of emerging pollutants in the ZCO@PVDF membrane/PMS system was SO4·-, ·OH, and 1O2. The degradation pathway and toxicity evolution of Chloroquine phosphate were identified through molecular orbital calculations, Fukui index analysis, HPLC testing, and T.E.S.T. software predictions. This immobilized catalytic membrane-based AOPs presents an innovative solution to overcome the limitations of conventional heterogeneous catalysis.

Orbital-level band gap engineering of RuO2 for enhanced acidic water oxidation

Developing efficient and stable oxygen evolution reaction electrocatalysts under acidic conditions is crucial for advancing proton-exchange membrane water electrolysers commercialization. Here, we develop a representative strategy through p-orbital atoms (N, P, S, Se) doping in RuO2 to precisely regulate the lattice oxygen-mediated mechanism-oxygen vacancy site mechanism pathway. In situ and ex situ measurements along with theoretical calculations demonstrate that Se doping dynamically adjusts the band gap between the Ru-eg and O-p orbitals during the oxygen evolution reaction process. This modulation accelerates electron diffusion to the external circuit, promotes the lattice oxygen-mediated process, and enhances catalytic activity. Additionally, it facilitates electron feedback and stabilizes oxygen vacancies, thereby promoting the oxygen vacancy site mechanism process and enhancing catalytic stability. The resulting Se-RuOx catalyst achieves efficient proton-exchange membrane water electrolysers performance under industrial conditions with a minimal charge overpotential of 1.67 V to achieve a current density of 1 A cm-2 and maintain long-term cyclability for over 1000 h. This work presents a unique method for guiding the future development of high-performance metal oxide catalysts.

Photodegradation of PCB-209 on suspended particles: Discrepancy in mechanism of direct dechlorination and active species-mediated indirect dechlorination reactions

While the reaction mechanism of direct photochemical dechlorination has been extensively studied, significant knowledge gaps remain regarding the specific roles of reactive species in governing dechlorination pathways during indirect photodegradation. By integrating mass spectrometry analysis, probe experiments and theoretical calculations, we propose for the first time an indirect dechlorination reaction mechanism for PCB-209 involving active species commonly found in DOM photosensitive systems, which differs significantly from that of direct photodegradation. Due to the lower bond energy of the CCl bond at the position opposite the carbon bridge, PCB-209 primarily yielded PCB-208 in direct dechlorination systems. However, our study revealed that active species (3DOM*, •O2- and 1O2) can specifically weaken the meta-positioned CCl bond at the carbon bridge through electron transfer and cycloaddition mechanisms, thereby fundamentally altering the regioselectivity of dechlorination. Remarkably, our results confirm the indirect degradation of PCB-209 through DOM photosensitization to form dechlorination products dominated by PCB-207, a previously unrecognized transformation pathway in natural photochemical processes. This study refines the mechanism of indirect dechlorination mediated by reactive species and provides a predictive framework for the environmental fate of halogenated pollutants in real complex environmental systems.

Defect Engineering in Wüstite: Unlocking Control Over Iron Morphologies in Gas-Solid Reduction

Hydrogen-based direct reduction (HyDR) technology has emerged as a promising pathway for sustainable steelmaking. However, the efficiency and stability of HyDR are critically influenced by the microstructure evolution of iron during gas-solid reduction reactions. Despite significant research on the reduction mechanisms of hydrogen (H2) and carbon monoxide (CO) with iron oxides, key aspects of the interplay between internal defects, pore dynamics, and reduction chemistry remain unresolved. In this study, the morphological evolution of iron during reduction with H2 and CO across a full concentration range at 900 °C is explored, establishing a direct link between lattice distortions in wüstite (FexO) and the resultant iron microstructure. Complementary analyses reveal that the concentration of defects in FexO governs these distortions. Specifically, low CO concentrations (< 80%) induce limited large-scale defects, leading to single-point nucleation and the growth of filament-shaped iron whiskers. Conversely, H₂ and high CO concentrations (> 80%) create a high density of large-scale defects, promoting multi-point nucleation and the aggregation of tumor-shaped iron structures. This work provides a multiscale perspective on how defect engineering in FexO modulates the morphologies of iron during reduction, offering valuable insights into optimizing reaction pathways to enhance efficiency and sustainability in materials processing.

Oxygen vacancies in piezo-photocatalysts: synthesis, characterization, effect mechanism and application

The escalating consumption of fossil fuels and the worsening of environmental pollution have rendered the advancement of sustainable clean energy conversion technologies an urgent priority. Piezo-photocatalytic technology, which integrates piezoelectric and photoexcited properties, provides an efficient means of converting chemical energy by utilizing mechanical and solar energy. Oxygen vacancies (OVs), as a critical type of defect structure, play a significant role in enhancing piezo-photocatalytic performance by modifying the band structure, improving polarization effects, and providing additional active sites. This review comprehensively examines the formation methods and characterization techniques of OVs, alongside their mechanistic roles in piezo-photocatalytic technology. We discuss how OVs influence the band structure, dipole moments, and local electronic configurations. Furthermore, we summarize the applications of OVs in various fields, including water pollution degradation, hydrogen production, nitrogen fixation, and CO2 reduction. Finally, we outline future research directions for OVs, focusing on precise synthesis methods, the development of novel piezoelectric materials, enhancement of stability, and the investigation of interactions between OVs and other local structures. We hope that this review will provide valuable insights for the continued development and application of OVs in piezo-photocatalysis.

Oxygen vacancies-mediated the peracetic acid activation to selectively generate 1O2 for water decontamination

As a pre-oxidation unit, developing non-radical pathway-dominant advanced oxidation processes (AOPs) with remarkably-efficient oxidation, superior environmental robustness, and ecological safety is essential in actual water pollution control. Herein, using Co3O4 as an example, we present an oxygen vacancies (OVs)-mediated peracetic acid (PAA) activation process, thereby predominantly generating singlet oxygen (1O2) for degrading contaminants. In-situ monitoring of PAA activation by OVs-rich Co3O4 (Co3O4-OVs) reveals that surface oxygen-containing intermediates (e.g., *OH and *O) are the precursors of 1O2. Theoretical calculations show that the selective adsorption of terminal oxygen atoms (ATO) in PAA serves as an activity descriptor for 1O2 generation. OVs can induce electron redistribution, triggering the ATO-dominated PAA adsorption to form the Co3O4-OVs-PAA* complex, followed by O-O bond breakage to yield *OH. Concurrently, OVs modulate the Co d-band center, lowering the energy barrier for 1O2 formation. The system enables ultra-fast catalytic performance (kobs = 1.17 min-1) for degrading sulfamethoxazole, outperforming pristine Co3O4 by 11.64-fold. The high-selectivity towards non-radical pathway endows the Co3O4-OVs/PAA system with remarkable stability in complex environment backgrounds and continuous-flow microreactor. This work not only provides a broad perspective on the modulation of non-radical pathways via defect engineering, but also advances the development of PAA-based AOPs for water decontamination.

Coordination Anions Dimensionality-Engineered Dual-Atom Catalysts for Enhanced Fenton-Like Reactions: 3D Coordination Induced Spin-State Transition

Dual-atom catalysts (DACs) have shown significant application potential in Fenton-like reactions. However, effectively modulating their electronic structure and fully understanding the mechanisms driving their high catalytic activity remain challenging. Herein, we propose a coordination anions dimensionality engineering strategy to synthesize biomass-derived dual-atom FeCo-N4O1C catalysts, in which Fe and Co atoms are bridged by two-dimensional planar N atoms and a three-dimensional (3D) axial O atom. Experimental data and theoretical calculations reveal that the 3D coordination structure of FeCo-N4O1C induces the spin state of Fe undergo a transition from a low spin state to an intermediate spin state compared with single-atom Fe-N4O1C, resulting in moderate adsorption and desorption of intermediates, thus reducing the energy barriers for generating more singlet oxygen and high-valent cobalt-oxo species during peroxymonosulfate activation. The electron transfer from Co atoms to neighboring Fe atoms through N atoms and 3D axial O atoms can effectively prevent the poisoning of active species. Benefiting from the 3D coordination structure and the synergistic effects of multiple active sites, the catalyst-dose normalized reaction rate constant reaches 14.5 L min-1 g-1 under low peroxymonosulfate concentrations─an improvement of 1 ∼ 2 orders of magnitude over most reported catalysts. The practical applicability of FeCo-N4O1C is demonstrated through nearly 100% pollutant removal during 7 days of continuous operation in a membrane filtration system. This study provides deep insights into the relationship between electronic structure and catalytic performance through spin-state regulation of DACs, and introduces a promising approach for large-scale synthesis of low-cost, highly efficient DACs for Fenton-like reactions.

Oxygen Vacancy Formation Energy Determines the Phase-Activity Relationship of MnO2 Laccase Nanozymes

Although manganese dioxide (MnO2) has been explored as a powerful laccase nanozyme for pollutant oxidation in wastewater treatment, the phase-activity relationship of multiphase MnO2 remains ambiguous and controversial. Herein, the experimental studies show that the laccase-like activities and aerobic catalytic oxidation toward tetracycline antibiotics of the six types of MnO2 are in the following order: β- > λ- > γ- > α- > ε- > δ-MnO2. Density functional theory (DFT) calculations revealed that the catalytic activities are inversely proportional to the oxygen vacancy formation energies of the different MnO2 materials. Further investigation of surface oxygen species with reactivity demonstrated that rich oxygen vacancies boost the oxygen mobility and catalytic efficiency of MnO2 nanozymes, which is in good agreement with both experimental and DFT results. Hence, this study reveals the decisive role of the crystal phase in the oxygen vacancy generation, which elucidates the laccase-like catalytic mechanism of MnO2 nanozymes and is valuable for the future design and synthesis of MnO2 nanocatalysts.

Electronic and vacancy engineering of ruthenium doped hollow-structured NiO/Co3O4 nanoreactors for low-barrier electrochemical urea-assisted energy-saving hydrogen production

Discovering a valid approach to achieve a novel and efficient water splitting catalyst is essential for the development of hydrogen energy technology. Herein, unique hollow-structured ruthenium (Ru)-doped nickel-cobalt oxide (Ru-NiO/Co3O4/NF) nanocube arrays are fabricated as high-efficiency bifunctional electrocatalysts for hydrogen evolution reaction (HER)/urea oxidation reaction (UOR) through combined electronic and vacancy engineering. The structural characterization and experimental results indicate that the doping of Ru can not only effectively modulate the electronic structure of Ru-NiO/Co3O4/NF, but also increase the content of oxygen vacancies in the structure of Ru-NiO/Co3O4/NF to stabilize the existence of oxygen vacancies during the catalytic process. This can optimize the adsorption and desorption of the reactive intermediates on the surface of Ru-NiO/Co3O4/NF and dramatically accelerate the HER and UOR kinetics. As a result, the Ru-NiO/Co3O4/NF hollow structure nanocube arrays exhibit overpotentials of 21 and 60 mV for HER, as well as potentials of 1.36 and 1.42 V for UOR at 10 and 100 mA cm-2, respectively. Furthermore, the coupled HER and UOR system requires only 1.59 V of cell voltage to drive a current density of 100 mA cm-2, which is approximately 240 mV lower than conventional water electrolysis. This work provides a tremendous promise for the development of novel and high-activity electrocatalysts in future energy conversion applications.

Constructing Tandem Fenton-like Reaction Systems Based on Structure Adaption to Boost Water Contaminant Mineralization Efficiency

Mineralization of emerging contaminants by using advanced oxidation processes (AOPs) is a desirable option to ensure water safety, but still challenged by the excessive chemical and/or energy input. Here, we conceptually proposed the tandem reaction system (TRS) of different reactive oxygen species (ROS) based on structure adaption of target contaminants. To construct a model TRS, we first realized highly selective generation of three classical ROS (1O2, HO⋅ and SO4⋅-) by peroxymonosulfate activation in an electrochemical Fenton-like system, where three replaceable Fe-centered cathodes were rationally designed as electronic mediator. The 1O2+SO4⋅--TRS exhibited nearly 100 % mineralization of sulfamethoxazole (SMX), whereas only 34.2 %, 56.2 % and 60.8 % for each of the single 1O2/HO⋅/SO4⋅--AOP systems. Mechanism exploration of SMX degradation in TRS evidenced that the initial reaction with 1O2 selectively destructed the sulfonamide bridge of SMX to form p-aminobenzenesulfonic acid, which will be vulnerable to sequent SO4⋅- attack to facilitate mineralization. Successful extendibility of 1O2+SO4⋅--TRS to other sulfonamide antibiotics and 1O2+HO⋅-TRS to phenolic and arylcarboxylic compounds, as well as the demonstration of 1O2+SO4⋅--TRS in treatment of three actual pharmaceutical wastewaters strongly support that TRS is a powerful and sustainable strategy to enhance the mineralization of emerging contaminants in water.

Support work-function dependent Fenton-like catalytic activity of Co single atoms for selective cobalt(IV)=O generation

In Fenton-like reactions, high-valent cobalt-oxo (CoIV=O) has attracted increasing interests due to high redox potential, long lifetime, and anti-interference properties, but its generation is hindered by the electron repulsion between the electron rich oxo- and cobalt centers. Here, we demonstrate CoIV=O generation from peroxymonosulfate (PMS) activation over cobalt single-atom catalysts (Co-SACs) using in-situ Co K-edge X-ray absorption spectra, and discern that CoIV=O generation is dependent on the support work-function (WF) due to the strong electronic metal-support interaction (EMSI). Supports with a high WF value like anatase-TiO2 facilitate the binding of PMS-terminal oxo-ligand to Co sites by extracting Co-d electrons, thus decreasing the generation barrier for the critical intermediate (Co-OOSO32-). The Co atoms anchored on anatase-TiO2 (Co-TiO2) exhibited enhanced CoIV=O generation and superior activity for sulfamethoxazole (SMX) degradation during PMS activation. The normalized steady-state concentration of CoIV=O in Co-TiO2/PMS system was three orders of magnitude higher than that of free radicals, and 1.3- to 11-fold higher than that generated in other Co-SACs/PMS systems. Co-TiO2/PMS sustained efficient removal of SMX with minimal Co2+ leaching under continuous flow operation, suggesting its attractive water purification potential. Overall, these results underscore the significance of support selection for enhanced generation of high-valent metal-oxo species and efficient PMS activation in supported metal SACs.

Design and Fabrication of MoCuOx Bimetallic Oxide Electrodes for High-Performance Micro-Supercapacitor by Electro-Spark Machining

Transition metal oxides, distinguished by their high theoretical specific capacitance values, inexpensive cost, and low toxicity, have been extensively utilized as electrode materials for high-performance supercapacitors. Nevertheless, their conductivity is generally insufficient to facilitate rapid electron transport at high rates. Therefore, research on bimetallic oxide electrode materials has become a hot spot, especially in the field of micro-supercapacitors (MSC). Hence, this study presents the preparation of bimetallic oxide electrode materials via electro-spark machining (EM), which is efficient, convenient, green and non-polluting, as well as customizable. The fabricated copper-molybdenum bimetallic oxide (MoCuOx) device showed good electrochemical performance under the electrode system. It provided a high areal capacity of 50.2 mF cm-2 (scan rate: 2 mV s-1) with outstanding cycling retention of 94.9% even after 2000 cycles. This work opens a new window for fabricating bimetallic oxide materials in an efficient, environmental and customizable way for various electronics applications.

Enhanced the removal of norfloxacin by oxalated zero-valent iron with rich surface Fe(II) sites activating the chlorite

Oxalic acid-modified ball-milled zero-valent iron (OA-ZVIbm) was employed to activate sodium chlorite (ClO2-) for the removal of norfloxacin (NOR). The complete removal of 20 mg/L NOR was achieved within 60 min by the OA-ZVIbm/ClO2- process. Compared with the ZVIbm/ClO2- process which was the ball-milled zero-valent iron (ZVIbm) activate sodium chlorite, the reaction activity of the OA-ZVIbm/ClO2- process was increased by 102.6 times. Through scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electrochemical testing, and density functional theory (DFT) calculations, which has been confirmed that the introduction of oxalic acid can significantly increase the surface Fe(II) content of OA-ZVIbm, and accelerate the electron transfer rate of iron nuclei, thereby improve the efficiency of ClO2- activation for the removal of NOR. The role of various active species in NOR removal, which were •O2-, 1O2, Fe(IV), ClO2, and •OH, was elucidated through free radical quenching experiments, electron paramagnetic resonance (EPR) spectroscopy, and quantitative detection of active species. These active species all participated in the reaction, while •O2- played a dominant role in the reaction because it could transform into other active species, such as (•OH, 1O2). Inorganic anions and natural organic matter have no significant effect on the removal of NOR in the OA-ZVIbm/ClO2- process. The protonation of oxalic acid ensured its good pH applicability range (pH = 2-11), thus exhibiting excellent performance in NOR removal in real water bodies. This further demonstrates that OA-ZVIbm prepared by oxalic acid ball milling modification is an efficient ClO2- activator, offering promising prospects for antibiotic removal technology.

Picolinic acid-mediated Mn(II) activated periodate for ultrafast and selective degradation of emerging contaminants: Key role of high-valent Mn-oxo species

The utilization of periodate (PI, IO4-) in metal-based advanced oxidation processes (AOPs) for the elimination of emerging contaminants (ECs) have garnered significant attention. However, the commonly used homogeneous metal catalyst Mn(II) performs inadequately in activating PI. Herein, we exploited a novel AOP technology by employing the complex of Mn(II) with the biodegradable picolinic acid (PICA) to activate PI for the degradation of electron-rich pollutants. The performance of the Mn(II)-PICA complex surpassed that of ligand-free Mn(II) and other Mn(II) complexes with common aminopolycarboxylate ligands. Through scavenger, sulfoxide-probe transformation, and 18O isotope-labeling experiments, we confirmed that the dominant reactive oxidant generated in the Mn(II)-PICA/PI system was high-valent manganese-oxo species (Mn(V)=O). Due to its reliance on Mn(V)=O, the Mn(II)-PICA/PI process exhibited remarkable selectivity and strong anti-interference during EC oxidation in complex water matrices. Nine structurally diverse pollutants were selected for evaluation, and their lnkobs values in the Mn(II)-PICA/PI system correlated well with their electrophilic/nucleophilic indexes, EHOMO, and vertical IP (R2 = 0.79-0.94). Additionally, IO4- was converted into non-toxic iodate (IO3-) without producing undesired iodine species such as HOI, I2, and I3-. This study provides a novel protocol for metal-based AOPs using PI in combination with chelating agents and high-valent metal-oxo species formation during water purification.

Sustainable photocatalytic hydrogen peroxide production over octonary high-entropy oxide

The direct utilization of solar energy for the artificial photosynthesis of hydrogen peroxide (H2O2) provides a reliable approach for producing this high-value green oxidant. Here we report on the utility of high-entropy oxide (HEO) semiconductor as an all-in-one photocatalyst for visible light-driven H2O2 production directly from H2O and atmospheric O2 without the need of any additional cocatalysts or sacrificial agents. This high-entropy photocatalyst contains eight earth-abundant metal elements (Ti/V/Cr/Nb/Mo/W/Al/Cu) homogeneously arranged within a single rutile phase, and the intrinsic chemical complexity along with the presence of a high density of oxygen vacancies endow high-entropy photocatalyst with distinct broadband light harvesting capability. An efficient H2O2 production rate with an apparent quantum yield of 38.8% at 550 nm can be achieved. The high-entropy photocatalyst can be readily assembled into floating artificial leaves for sustained on-site production of H2O2 from open water resources under natural sunlight irradiation.

A "Two-Pronged" Strategy to Boost Hydrogen Evolution Kinetics on NiFe-Based (Oxy)hydroxides via Oxygen Deficient Ni-Mo-Fe Coordinate Structures for Ultra-Stable Ampere-Level Alkaline Overall Water Splitting

NiFe (oxy)hydroxides have been regarded as one of the state-of-the-art catalysts for oxygen evolution reaction (OER). Unfortunately, the sluggish hydrogen evolution reaction (HER) kinetics limit its application as bifunctional electrocatalyst for alkaline overall water splitting (OWS). Herein, a "two-pronged" strategy is proposed to construct highly active oxygen deficient Ni-Mo-Fe coordinate structures in NiFe (oxy)hydroxide (NFM-OVR/NF), which simultaneously reduces the energy barrier of Volmer and Heyrovsky steps during alkaline HER process and significantly accelerate the reaction kinetics. Consequently, NFM-OVR/NF delivers overpotentials as low as 25 and 234 mV to achieve 10 and 1000 mA cm-2 in 1.0 M KOH, respectively. Furthermore, benefiting from excellent HER and OER activity, NFM-OVR/NF exhibits a remarkable OWS activity with cell voltages of 1.44 V and 1.77 V at 10 and 1000 mA cm-2 in 1.0 M KOH, and displays ultralong-term stability for 600 h at 500 mA cm-2, while remaining durable for 300 h in an alkaline water electrolyzer in 30% KOH at 80 °C. The calculated price per gallon of gasoline equivalent for the produced H2 is $ 0.92, which is much lower than 2026 U.S. Department of Energy target ($ 2.00), demonstrating feasibility and practicability of NFM-OVR/NF for industrial applications.

In-Situ Anchoring of Co Single-Atom Synergistically with Cd Vacancy of Cadmium Sulfide for Boosting Asymmetric Charge Distribution and Photocatalytic Hydrogen Evolution

In the context of reshaping the energy pattern, designing and synthesizing high-performance noble metal-free photocatalysts with ultra-high atomic utilization for hydrogen evolution reaction (HER) still remains a challenge. In a streamlined synthesis process, in-situ single atom anchoring is performed in parallel with HER by irradiating a precursory defect-state CdS/Co suspension (Co-DCdS-Ss) system under simulated sunlight and the in-situ synthesizing single-atom Co photocatalyst (Co5:DCdS) exhibits further improved catalytic performance (60.10 mmol g-1 h-1) compared with Co-DCdS-Ss (18.09 mmol g-1 h-1), reaching an apparent quantum yield of 57.6% at 500 nm and a solar-chemical energy conversion efficiency (SCC) of 6.26% at AM 1.5G. In-depth characterization tests and density functional theory (DFT) calculations prove that the anchoring of Co single atom deepens the asymmetric charge distribution of the two-coordination S atom adjacent to the cadmium vacancy (VCd). The synergy between electron delocalization VCd and Co single atom on the catalyst surface is constructed, which bifunctional sites responsible for boosting water adsorption-dissociation and hydrogen evolution. This study advances the understanding of the underlying mechanisms of synergy between surface defects and metal single atoms and opens a new horizon for the development of advanced materials in the field of photocatalysis.

Heterointerface engineering of MXene: Advanced applications in environmental remediation

Contemporary global industrialization, coupled with the relentless growth of the population, has led to a persistent escalation in the emission and accumulation of various toxic and harmful chemicals in the environment, severely disrupting the ecological balance. The development of efficient environmental cleanup materials is a crucial scientific and technological concern. Since the groundbreaking work on Ti3C2Tx in 2011, there has been a huge growing interest in MXene-based composites developed through heterointerface engineering due to its high surface area, hydrophilicity, eco-friendliness, biocompatibility, easy functionalization, excellent thermal/mechanical properties, metal conductivity and rich electronic density. In the area of environmental remediation, MXene-based composites obtained through heterointerface engineering strategies have the ability to effectively remove and systematically monitor contaminants in comparison to virgin MXene, thanks to the synergistic effects and complementary benefits. Heterointerface engineering strategy increases specific surface area, introduces catalytic sites, constructs heterojunctions/Schottky junctions, and facilitates carrier migration and electron-hole separation. These novel MXene-based composites represent significant advances in MXene research and deserve a comprehensive review. Although several excellent reviews and perspectives on the application of MXene-based composites in environmental remediation have been published, there is still a scarcity of comprehensive and systematic assessments on the reliable data and mechanisms of various MXene-based composite materials for pollutant removal and monitoring. In this focused review, the first part briefly introduces the common preparation strategies and characterization methods of single MXene and MXene-based composites, and the second part details the innovative application of MXene-based composites (involving the amalgamation of MXene with metal oxides, metal sulfide, g-C3N4, layered double hydroxides, metal-organic frameworks, single atom/quantum dots, polymers, etc.) in the field of environmental remediation, including carbon dioxide reduction, nitrogen monoxide and volatile organic compounds removal, antibiotic and heavy metal ions degradation, summarizing the relevant performance and mechanisms. Furthermore, the recent advancements in the utilization of MXene-based composites for the sensing of emerging environmental contaminants (antibiotic and antibiotic resistance genes) are summarized. Finally, an outline of the existing challenges and future prospects on this exciting field was narrated for plausible real-world use. This review will help to inspire the diverse design of MXene-based composites and to advance research related to their application in the environmental sector.

Engineering Water-Lotus-like Iridium-Cobalt Carbonate Hydroxides on Plasma-Treated Carbon Fibers for Enhanced Electrocatalytic Oxygen Evolution

The sluggish kinetics of the oxygen evolution reaction (OER) in alkaline water electrolysis remains a significant challenge for developing high-efficiency electrocatalytic systems. In this study, we present a three-dimensional, micrometer-sized iridium oxide (IrO2)-decorated cobalt carbonate hydroxide (IrO2-P-CoCH) electrocatalyst, which is engineered in situ on a carbon cloth (CC) substrate pretreated with atmospheric-pressure dielectric barrier discharge (DBD) plasma (PCC). The electrocatalyst features petal-like structures composed of nanosized rods, providing abundant reactive areas and sites, including the oxygen vacancy caused by the air-DBD plasma. As a result, the IrO2-P-CoCH/PCC electrocatalyst demonstrates an outstanding OER performance, with overpotentials of only 190 and 300 mV required to achieve current densities of 10 mA cm-2 (j10) and 300 mA cm-2 (j300), respectively, along with a low Tafel slope of 48.1 mV dec-1 in 1.0 M KOH. Remarkably, benefiting from rich active sites exposed on the IrO2-P-CoCH (Ir) heterostructure, the synergistic effect between IrO2 and CoCH enhances the charge delivery rates, and the IrO2-P-CoCH/PCC exhibits a superior electrocatalytic activity at a high current density (300 mV/j300) compared to the commercial benchmarked RuO2/PCC (470 mV/j300). Furthermore, the IrO2-P-CoCH/PCC electrocatalyst shows exceptional OER stability, with a mere 1.3% decrease with a current density of j10 for 100 h testing, surpassing most OER catalysts based on CC substrates. This work introduces a novel approach for designing high-performance OER electrocatalysts on flexible electrode substrates.

Qualitative and quantitative analysis of electrons donated by pollutants in electron transfer-based oxidation system: Electrochemical measurement and theoretical calculations

In order to gain a profound understanding of the fate of pollutants in advanced oxidation processes (AOPs), this study analyzed the electron contribution of pollutants qualitatively and quantitatively which rarely reported before. The rich electron transfer system was constructed by mesoporous carbon nitride (MCN) coupling with persulfate (PS) driven by visible light and the sulfanilamide antibiotics (SULs) were used as target contaminants. Firstly, the qualitative analysis of electron transfer in the system was confirmed systematically. The electron flow direction tested by i-t curves indicated that PS absorbed electrons, while SULs released electrons. The flow rate of electrons was also accelerated after the addition of SULs. The fitting curve between the kinetics and the peak potential difference tested by CV curve showed that the larger potential difference, the slower rate of oxidative degradation. Secondly, the quantification of electron transfer was achieved through theoretical calculations to simulate the interactions of the 'catalyst-oxidant-antibiotic' system. After the addition of SULs, the adsorption energy of the 'catalyst-oxidant-antibiotic' system was enhanced and the bond length of the peroxide bond was stretched. Notably, the electron transfer analysis results showed that the charge of SULs was around 0.032-0.056e, indicating that SULs pollutants played the role of electron contributors in the system. The oxidative degradation pathway included the direct cracking of S-N bond, shedding of marginal groups, ring-opening and hydroxyl addition reaction. This study clarified the electronic contribution of SULs in the oxidation system, providing necessary theoretical supplement for the analysis of the transformation of pollutants in AOPs.

Selective oxidation decontamination in cobalt molybdate activated Fenton-like oxidation via synergic effect of cobalt and molybdenum

In this study, cobalt molybdate (CoMoO4) activated peracetic acid (PAA) was developed for water purification. CoMoO4/PAA system could remove 95% SMX with pseudo-first-order reaction rate constant of 0.15410 min-1, which was much higher than CoFe2O4/PAA, FeMoO4/PAA, and CoMoO4/persulfate systems. CoMoO4/PAA system follows a non-radical species pathway dominated by the high-valent cobalt (Co(IV)), and CH3C(O)OO• shows a minor contribution to decontamination. Density functional theory (DFT) calculation indicates that the generation of Co(IV) is thermodynamically more favorable than CH3C(O)OO• generation. The abundant Co(IV) generation was attributed to the special structure of CoMoO4 and effect of molybdenum on redox cycle of Co(II)/Co(III). DFT calculation showed that the atoms of SMX with higher ƒ0 and ƒ- values are the main attack sites, which are in accordance with the results of degradation byproducts. CoMoO4/PAA system can effectively reduce biological toxicity after the reaction. Benefiting from the selective of Co(IV) and CH3C(O)OO•, the established CoMoO4/PAA system exhibits excellent anti-interference capacity and satisfactory decontamination performance under actual water conditions. Furthermore, the system was capable of good potential practical application for efficient removal of various organics and favorable reuse. Overall, this study provides a new strategy by CoMoO4 activated PAA for decontamination with high efficiency, high selectivity and favorable anti-interference.

Oxygen-Centered Organic Radicals-Involved Unified Heterogeneous Self-Fenton Process for Stable Mineralization of Micropollutants in Water

Removing organic micropollutants from water through photocatalysis is hindered by catalyst instability and substantial residuals from incomplete mineralization. Here, a novel water treatment paradigm, the unified heterogeneous self-Fenton process (UHSFP), which achieved an impressive 32% photon utilization efficiency at 470 nm, and a significant 94% mineralization of organic micropollutants-all without the continual addition of oxidants and iron ions is presented. In UHSFP, the active species differs fundamentally from traditional photocatalytic processes. One electron acceptor unit of photocatalyst acquires only one photogenerated electron to convert into oxygen-centered organic radical (OCOR), then spontaneously completing subsequent processes, including pollutant degradation, hydrogen peroxide generation, activation, and mineralization of organic micropollutants. By bolstering electron-transfer capabilities and diminishing catalyst affinity for oxygen in the photocatalytic process, the generation of superoxide radicals is effectively suppressed, preventing detrimental attacks on the catalyst. This study introduces an innovative and cost-effective strategy for the efficient and stable mineralization of organic micropollutants, eliminating the necessity for continuous chemical inputs, providing a new perspective on water treatment technologies.

Interface Defects and Carrier Regulation in MOF-Derived Co3O4/In2O3 Composite Materials for Enhanced Selective Detection of HCHO

Gas sensors for real-time monitoring of low HCHO concentrations have promising applications in the field of health protection and air treatment, and this work reports a novel resistive gas sensor with high sensitivity and selectivity to HCHO. The MOF-derived hollow In2O3 was mixed with ZIF-67(Co) and calcined twice to obtain a hollow Co3O4/In2O3 (hereafter collectively termed MZO-6) composite enriched with oxygen vacancies, and tests such as XPS and EPR proved that the strong interfacial electronic coupling increased the oxygen vacancies. The gas-sensitive test results show that the hollow composite MZO-6 with abundant oxygen vacancies has a higher response value (11,003) to 10 ppm of HCHO and achieves a fast response/recovery time (11/181 s) for HCHO at a lower operating temperature (140 °C). The MZO-6 material significantly enhances the selectivity to HCHO and reduces the interference of common pollutant gases such as ethanol, acetone, and xylene. There is no significant fluctuation of resistance and response values in the 30-day long-term stability test, and the material has good stability. The synergistic effect of the heterostructure and oxygen vacancies altered the formaldehyde adsorption intermediate pathway and reduced the reaction activation energy, enhancing the HCHO responsiveness and selectivity of the MZO-6 material.