Titanium Oxide Electrocatalytic Membrane Filtration: "Two Faces" of Oxygen Vacancies in Generation and Transformation of Reactive Oxygen Species

Functionalized membrane assembled by iron-based two-dimensional Fenton-like catalyst for ultra-efficient water decontamination: Mechanism and application insights

The design of functionalized membrane-coupled Fenton-like catalysis processes is pivotal for wastewater treatment, providing a promising strategy to enhance peroxide activation and degrade organic contaminants. Herein, a functionalized membrane based on Fe3O4 nanosheets (Fe3O4 NS) was designed, featuring a densely stacked structure with highly exposed reactive sites, creating an optimal environment for efficient Fenton-like catalysis. The Fe3O4 NS membrane achieved nearly complete degradation of target contaminants at a flux of 289.97 L·m-2·h-1, with a pseudo-first-order rate constant of 0.021 ms-1 for Fenton-like catalysis, surpassing previously reported Fenton-like catalytic membrane systems by 6-17 times. Detailed mechanistic experiments and theoretical calculations elucidated the efficient activation of hydrogen peroxide (H2O2) by the Fe3O4 NS membrane from both thermodynamic and kinetic perspectives. Notably, the Fe3O4 NS membrane/H2O2 system significantly reduced the toxicity of target contaminants and their degradation intermediates toward activated sludge, thereby alleviating the subsequent biochemical treatment burden. Moreover, it demonstrated potential for treating actual secondary effluent. The findings of this study advance the design of sustainable and efficient water purification strategies, offering a viable approach to overcoming the technical limitations of traditional Fenton-like catalysis.

Tunable reconstruction of metal-organic frameworks for advanced electrocatalytic degradation of antibiotics: Key role of structural defects and pollutant properties

Although metal-organic frameworks (MOFs) catalysts are appealing for removing emerging contaminants, they are significantly restricted by the activity-stability trade-off effect. This study develops a facile and sustainable strategy to realize the synchronous promotion of stability and activity by utilizing the metastable property of UiO-66 with optimal defect concentration to in-situ reconstruct into more stable and active ZrOOH@UiO-66 heterojunction under working conditions. The crucial role of structural defects and pollutant properties in controlling MOFs reconstruction was unveiled by tracking dynamic structure evolution during electrocatalytic degradation of antibiotics. The mechanism is the selective oxidation of exposed metal active sites on defective UiO-66 during electrocatalysis, forming well-dispersed ZrOOH with rich oxygen vacancies that protected MOFs and reduced activation energy for •OH and •O2- radicals generation. Additionally, lower ionization potential and stronger adsorption of antibiotics restricted reconstruction of defective UiO-66 by inhibiting electron transfer and occupying reconstruction site. Besides, the reconstructed UiO-66 electrocatalytic membrane presented high stability, removing approximately 90 % of tetracycline with efficient self-cleaning and low energy consumption (0.4 mW•h/m3) in surface water remediation over 200 h. This strategy is also feasible for other carboxylate-based MOFs, which provides the guidance for MOFs-based catalysts in emerging contaminants removal from complex water matrices.

Enhanced electro-fenton degradation of tetracycline pharmaceutical wastewater by N-doped carbon modified titanium membrane aeration: Formation of highly selective singlet oxygen

Singlet oxygen (1O2), the lowest excited electronic state of molecular oxygen, plays an important role in advanced oxidation, but how to directionally enhance the generation of 1O2 is a challenge. In this study,we use membrane aeration electrode modified by carbon-nitrogen for the first time to enhance the generation of 1O2 in the EF (Electro-Fenton) system. The carbon-nitrogen supported tubular titanium membrane (TTM@CN) aeration electrode was prepared by a simple dopamine-loaded one-step sintering method. A membrane aeration EF system was designed with TTM@CN as cathode and netted ruthenium-iridium titanium electrode as anode, and the output of 1O2 was greatly improved. The results of quenching experiments show that the main way of singlet oxygen production is 3O2 → H2O2 → 1O2. In addition, the results of density functional theory (DFT) show that the empty orbital of C above Fermi level in heterojunction is obviously filled, and the density of states tends to shift to the depth of valence band. The system with metal Ti as carrier can quickly transfer electrons to the layer of C, which makes the states density of C increase significantly near Fermi level. It can reduce 3O2 to H2O2 more quickly, and H2O2 can be further converted to 1O2. The system showed excellent degradation performance in a wide pH range (1-12) and excellent stability in 20 cycle experiments, which provided a reference significance for promoting the development of sustainable EF technology.

Birnessite enhanced Cr(III) oxidation during subsurface geochemical processes: Role of Mn(III)-induced nonphotochemical reactive oxygen species

Cr(III) oxidation by birnessite was the dominant geologic source of Cr(VI), which increases the environmental mobility and toxicity of Cr, threatening ecological safety. Photochemically hydroxyl radical (•OH) generated by birnessite was widely accepted to be the dominant reactive oxygen species (ROS) oxidating Cr(III). However, birnessite and Cr mainly co-exist in dark subsurface soils, with contribution of nonphotochemical ROS remaining unclear. In this work, free-radical quenching experiments, electrochemistry method and density functional theory (DFT) calculations were performed to elucidate ROS generation mechanisms during Cr(III) oxidation in simulated light-deprived environment. The results indicated that •OH was completely suppressed and nonphotochemical O2•- still accelerated Cr(III) oxidation in dark aerobic conditions with the contribution of 15.3%-19.1%. Moreover, DFT calculations proved that O2•- was produced by O2 molecules adsorbed on oxygen vacancies in the structure, thus being generated spontaneously in the dark. The oxidation contribution of O2•- was undetectable after extracting Mn(III), indicating that electron transfer occurred between Mn(III) and O2 to generate O2•-. Additionally, intervention of Cd2+ (for occupying oxygen vacancies) did not reduce participation of •OH, but resulted in suppression of electron transport which greatly reduced the production of O2•-, thereby affecting Cr(III) oxidation process. The above findings provide new insights on Cr(III) oxidation by manganese oxides and is able to have profound significance for predicting the fate of Cr in subsurface environments.

Oxygen vacancy-dependent synergistic disinfection of antibiotic-resistant bacteria by BiOBr nanoflower induced H2O2 activation

Antibiotic-resistant bacteria (ARB) and antibiotic-resistant genes (ARGs) pose a significant threat to both ecosystems and human health. Owing to the excellent catalytic activity, eco-safety, and convenience for defect engineering, BiOBr with oxygen vacancies (OVs) of different density thus were fabricated and employed to activate H2O2 for ARB disinfection/ARGs degradation in present study. We found that BiOBr with OVs of appropriate density induced via ethanol reduction (BOB-E) could effectively activate H2O2, achieving excellent ARB disinfection and ARGs degradation efficiency. Moreover, this disinfection system exhibited remarkable tolerance to complex water environments and actual water conditions. In-situ characterization and theoretical calculations revealed that OVs in BOB-E could effectively capture and activate aqueous H2O2 into HO· and O2·-. The generated reactive oxygen species combined with electron transfer could damage the cell membrane system and degrade genetic materials of ARB, leading to effective disinfection. The impressive reusability, high performance achieved in two immobilized reaction systems (packed column and baffled ditch reactor), excellent degradation of emerging organic pollutants supported the feasibility of BOB-E/H2O2 system towards practical water decontamination. Overall, this study not only provides insights into fabrication of bismuth-based catalysts for efficient ARB disinfection/ARGs degradation via OVs regulation, but also paves the way for their practical applications.

Micro/nanomotors for neuromodulation

Micro-nanomotors (MNMs) are micro/nanoscale intelligent devices with vast potential in the fields of drug delivery, precision medicine, biosensing, and environmental remediation. Their primary advantage lies in their ability to convert various forms of external energy (such as magnetic, ultrasonic, and light energy) into their own propulsive force. Additionally, MNMs offer high controllability and modifiability, enabling them to navigate in the microscopic world. Importantly, recent research has harnessed the unique advantages of MNMs to synergize their capabilities in neuromodulation. This mini-review presents the significant progress and pioneering achievements in the use of MNMs for neuromodulation, with the aim of inspiring readers to explore the broader biomedical applications of these MNMs. Through continuous innovation and diligent exploration, MNMs show promise to have a profound impact on the field of biomedicine.

Synergistic strategy of solute environment and phase control of Pb-based anodes to solve the activity-stability trade-off

The contradiction between the activity and stability of metal anodes exists extensively, especially in acid electrooxidation under industrial-level current density. Although the anode modification enhanced the initial activity of anodes, its long-term activity is limited by anode slime accumulation. Herein, a synergistic strategy, coupling the solute environment with the phase control of anodes, is proposed to achieve the trade-off between activity and stability of Pb-based anodes in concentrated sulfuric acid electrolysis. Non-exogenous Mn2+ motivated a series of positive behaviours of reactive-oxygen-species capture, anode reconstruction and corrosion-dependent activity alleviation. The synergistic effects, which are crystal phase-dependent, mainly benefit from the continuous self-healing ability of the specific crystal phase of MnO2 on the anodes by the coexisted Mn2+. Compared with Mn2+/α-MnO2, Mn2+/γ-MnO2 exhibited outperformed activity and stability in boosting oxygen evolution reaction (OER) and reducing hazardous pollutants, which resulted from the energy difference in the rate-determining step of OER and in the selectivity priority of Mn2+/MnO2 oxidation pathway. Interestingly, the pre-coated γ-MnO2 on the anode also presents excellent inheritance, guaranteeing the unchanged crystal phase of MnO2 and the high performance in ultra-low hazardous slime generation in subsequent Mn2+ oxidation. The sustainability of Mn2+/γ-MnO2 was proved in the operating hydrometallurgy conditions on Pb-based anodes. This strategy offers a promising approach for this common issue in electrooxidation-related areas.

Fenton-like membrane reactor assembled by electron polarization and defect engineering modifying Co3O4 spinel for flow-through removal of organic contaminants

The application of Fenton-like membrane reactors for water purification offers a promising solution to overcome technical challenges associated with catalyst recovery, reaction efficiency, and mass transfer typically encountered in heterogeneous batch reaction modes. This study presents a dual-modification strategy encompassing electron polarization and defect engineering to synthesize Al-doped and oxygen vacancies (OV)-enriched Co3O4 spinel catalysts (ACO-OV). This modification empowered ACO-OV with exceptional performance in activating peroxymonosulfate (PMS) for the removal of organic contaminants. Moreover, the ACO-OV@polyethersulfone (PES) membrane/PMS system achieved organic contaminant removal through filtration (with a reaction kinetic constant of 0.085 ms-1), demonstrating outstanding resistance to environmental interference and high operational stability. Mechanistic investigations revealed that the exceptional catalytic performance of this Fenton-like membrane reactor stemmed from the enrichment of reactants, exposure of reactive sites, and enhanced mass transfer within the confined space, leading to a higher availability of reactive species. Theoretical calculations were conducted to validate the beneficial intrinsic effects of electron polarization, defect engineering, and the confined space within the membrane reactor on PMS activation and organic contaminant removal. Notably, the ACO-OV@PES membrane/PMS system not only mineralized the targeted organic contaminants but also effectively mitigated their potential environmental risks. Overall, this work underscores the significant potential of the dual-modification strategy in designing spinel catalysts and Fenton-like membrane reactors for efficient organic contaminant removal.

Sulfur Vacancies in Pyrite Trigger the Path to Nonradical Singlet Oxygen and Spontaneous Sulfamethoxazole Degradation: Unveiling the Hidden Potential in Sediments

Pharmaceutical residues in sediments are concerning as ubiquitous emerging contaminants. Pyrite is the most abundant sulfide minerals in the estuarine and coastal sediments, making it a major sink for pharmaceutical pollutants such as sulfamethoxazole (SMX). However, research on the adsorption and redox behaviors of SMX on the pyrite surface is limited. Here, we investigated the impact of the nonphotochemical process of pyrite on the fate of coexisting SMX. Remarkably, sulfur vacancies (SVs) on pyrite promoted the generation of nonradical species (hydrogen peroxide, H2O2 and singlet oxygen, 1O2), thereby exhibiting prominent SMX degradation performance under darkness. Nonradical 1O2 contributed approximately 73.1% of the total SMX degradation. The SVs with high surrounding electron density showed an advanced affinity for adsorbing O2 and then initiated redox reactions in the sediment electron-storing geobattery pyrite, resulting in the extensive generation of H2O2 through a two-electron oxygen reduction pathway. Surface Fe(III) (hydro)oxides on pyrite facilitated the decomposition of H2O2 to 1O2 generation. Distinct nonradical products were observed in all investigated estuarine and coastal samples with the concentrations of H2O2 ranging from 1.96 to 2.94 μM, while the concentrations of 1O2 ranged from 4.63 × 10-15 to 8.93 × 10-15 M. This dark-redox pathway outperformed traditional photochemical routes for pollutant degradation, broadening the possibilities for nonradical species use in estuarine and coastal sediments. Our study highlighted the SV-triggered process as a ubiquitous yet previously overlooked source of nonradical species, which offered fresh insights into geochemical processes and the dynamics of pollutants in regions of frequent redox oscillations and sulfur-rich sediments.

Humic substances mediated superior photochemical pollutant conversion on defective TiO2 in environmentally relevant matrices: The key roles of oxygen vacancy in surface interactions, oxidant activation and radical generation

Ubiquitous humic substances usually exhibit strong interfering effects on target pollutant removal in advanced water purification. This work aims to develop a photochemical conversion system on the nonstoichiometric TiO2 for pollutant removal in environmentally relevant matrices. In this synergistic reaction system, the redox-reactive humic substances and defective oxygen vacancies can serve as the organic electron transfer mediator and the key surface reactive sites, respectively. This system achieves a superior pollutant degradation in real surface water at low oxidant concentrations. Reactive oxygen vacancies on the TiO2 surface and sub-surface are of considerable interest for this photochemical reaction system. By engineering defective oxygen vacancies on high-energy {001} polar facet, the surface and electronic interactions between tailored TiO2 and humic substances are greatly strengthened for the promoted electron transfer and oxidant activation. Rendered by the strong surface affinity and molecular activation, defective oxygen vacancies thermodynamically and dynamically promote reactive chain reactions for free radical formation, including the selective O2 reduction to ·O2- and the H2O2 activation to ·OH. Our findings take new insights into environmental geochemistry, and provide an effective strategy to in-situ boost the humic substances-mediated water purification without secondary pollution. ENVIRONMENTAL IMPLICATION: Humic substances are widely distributed in aquatic environment, thus playing important roles in environmental geochemistry. For example, humic substances can achieve good surface adsorption through electrostatic adsorption, ligand exchange and electronic interactions with typical TiO2 to form reactive ligand-metal charge transfer complexes for pollutant degradation. Inspired by the unique properties of surface and sub-surface oxygen vacancies, the defective TiO2 was designed to refine the humic substances-mediated photochemical reactions. A superior reactivity was measured for pollutant degradation. Our findings provide an effective strategy to boost naturally photochemical decontamination in environmentally relevant matrices.