Singlet oxygen: Properties, generation, detection, and environmental applications

Size-optimized Prussian blue and oxygen-doped carbon nanotubes encapsulation: A catalyst in electro-Fenton for antibiotic degradation

The Electro-Fenton (EF) process has been identified as a potentially effective solution for the treatment of antibiotic wastewater. However, challenges related to catalyst activity and stability persist as significant obstacles. In this study, we developed a bifunctional catalyst that has demonstrated stability in practical applications. A systematic investigation was conducted into the influence of Prussian Blue (PB) particle size (350-950 nm) on Fe3+/Fe2+ conversion efficiency, and it was identified that 592 nm PB was optimal, achieving the highest conversion rate of 0.162 min-1. To further enhance Fe3+/Fe2+ cycling, PB was encapsulated within oxidized carbon nanotubes (OCNT), forming an interconnected OCNT/PB catalyst that exhibited a remarkable 204.8 % synergistic enhancement. The superior performance of the catalyst can be attributed to three key factors: (i) The presence of dual active sites for the oxygen reduction reaction (ORR) and Fenton reaction, separated by an atomic-scale distance of 2.352 Å, facilitating both hydrogen peroxide (H2O2) generation and its subsequent activation into reactive radicals. (ii) OCNT functioning as an electron-transfer bridge between the cathode and PB, effectively overcoming PB's inherent low conductivity. (iii) Fe complexation on the PB surface with oxygen-containing functional groups, which significantly accelerates Fe3+/Fe2+ redox cycling. Quantitatively, the coupling of ORR and Fenton sites accounts for 46.6 % of the catalytic activity, the electron-transfer bridge contributes 21.8 %, and Fe complexation enhances activity by 31.5 %. This study offers novel insights into the design of high-performance EF catalysts and presents an innovative strategy for the efficient degradation of organic pollutants in water.

Enhanced aquatic antibiotic removal via dual piezoelectric photocatalyst CdS/BiFeO3 S-scheme heterojunction: Mechanism, degradation pathway, and toxicity evaluation

Piezo-photocatalysis represents an effective and eco-friendly strategy for water purification, wherein singlet oxygen (1O2) serves as a crucial reactive oxygen species due to its exceptional selectivity and remarkable oxidative capacity in wastewater degradation processes. Herein, we elaborately designed a dual piezoelectric photocatalyst, the Cadmium sulfide/Bismuth ferrite (CdS/BiFeO3) step-scheme (S-scheme) heterojunction to synergistically enhance generation pathways of 1O2 for efficient removal of antibiotic contaminants. In this study, under the combination of ultrasonic vibration and visible light irradiation, the optimized CdS/BiFeO3-10 % exhibited a reaction rate constant of 0.200 min-1 for ciprofloxacin (CIP) degradation, which was 9.52 and 5.88 times higher than that of individual piezocatalysis and photocatalysis, respectively. The synergistic effect of the interfacial electric field and the vibration-induced piezoelectric field significantly promoted charge carrier separation, as supported by detailed experimental and theoretical results. Through quenching experiment and Electron spin resonance (ESR), 1O2 and holes (h+) played major roles in CIP degradation. Furthermore, the toxicity and degradation pathways of CIP intermediates were systematically evaluated. The CdS/BiFeO3 composite also demonstrated outstanding reusability and cycle stability, making it suitable for practical wastewater treatment applications. This work highlights the potential of CdS/BiFeO3 with piezoelectric effect-assisted S-scheme heterojunction for highly efficient antibiotic wastewater remediation, offering a novel and effective strategy for water purification.

Z-Scheme MIL-88A(Fe)/LaFeO3 Heterostructured Photocatalyst: Boosting Photo-Fenton Activity for Enhanced Organic Pollutant Detoxification

A series of MIL-88A(Fe)/LaFeO3 were prepared by mechanical ball-milling method for boosted photo-Fenton ofloxacin (OFX) degradation under visible light irradiation. The optimized M160L40/photo-Fenton system accomplished complete degradation of 5.0 mg/L OFX within 10 min, attributed to synergistic enhancement of mass transfer efficiency and photogenerated carriers separation. Environmental adaptability was demonstrated through pH robustness (3.0-9.0), interference resistance to coexisting ions, and stable performance under natural sunlight in real water matrices, while 95.0% activity retention after five cycles confirmed practical durability. Mechanistic investigations combining radical trapping, ESR spectroscopy, photodeposition, and DFT calculations revealed a direct Z-scheme charge transfer pathway between MIL-88A(Fe) and LaFeO3, enabling simultaneous preservation of strong redox potentials and efficient carrier separation. Biotoxicity assessment via bacterial growth inhibition assays showed significant reduction in ecotoxicity of degradation intermediates. This work establishes a new paradigm for designing MOF/perovskite hybrid systems in advanced oxidation processes while offering mechanistic insights into Z-scheme photocatalysis for environmental remediation.

Degradation of Indomethacin in Wastewater: Removal with Sodium Hypochlorite and Analysis of Degradation Byproducts

Over the years, the frequent and continuous use of drugs has led to a high presence of emerging micropollutants in wastewater, increasing environmental and health concerns. Among these chemicals, Indomethacin (IND), a widely used anti-inflammatory drug, has been detected up to 150 ng/L in water bodies. Its presence in aquatic environments causes increasing concerns due to its high persistence, limited biodegradability, and resistance to conventional treatment processes. This study examined the degradation of IND via oxidation with sodium hypochlorite (NaClO) and the characterization of the degradation byproducts (DPs) generated by this process. Based on NMR spectroscopy studies and mass spectrometry analysis, thirteen DPs were identified, seven of which were previously unpublished (DP1: 2-(3-Chloro-1-(4-chlorobenzoyl)-2-hydroxy-5-methoxy-2-methylindolin-3-yl)acetic acid, DP3: 2-(3,4-Dichloro-1-(4-chlorobenzoyl)-2-hydroxy-5-methoxy-2-methylindolin-3-yl)acetic acid, DP5: (3-Chloro-5-methoxy-2-methyl-1H-indol-1-yl)(4-chlorophenyl)methanone, DP6: (4-Chlorophenyl)(5-methoxy-3-(methoxymethyl)-2-methyl-1H-indol-1-yl)methanone, DP7: 2-(2-(4-Chlorobenzamido)-5-methoxyphenyl)-2- oxoethyl acetate, DP8: 2-(5-Methoxy-2-methyl-1H-indol-3-yl)acetic acid, DP9: 4-Chloro-N-(4-methoxyphenyl)benzamide), and a degradation mechanism was proposed. These results show how the degradation of Indomethacin leads to the generation of new byproducts that may persist in the environment, obtaining DP1 in far larger quantities than the other byproducts. Given Indomethacin's degradation rate of over 90% but not its complete mineralization, it is fundamental to study not only IND but also the byproducts generated to assess their potential environmental impact.

Zn-Driven AgI Anchoring on Ti-MOF for Photocatalytic Singlet Oxygen Generation in Imidacloprid Removal

Utilizing metal-organic frameworks (MOFs) to facilitate the formation of AgI and construct novel heterojunction material is a promising strategy for water remediation. However, achieving strong connections at the active sites of MOFs and improving charge transfer processes remain a challenge. Herein, we proposed a Zn-driven approach to anchor AgI on Zn-doped NH2-MIL-125(Ti) (ZTNML), which exhibited 6.7 times and 5.3 times higher imidacloprid degradation efficiencies than that of AgI and NH2-MIL-125(Ti), respectively. Density functional theory calculations revealed that the Zn sites in ZTNML played a critical role in anchoring AgI, facilitated by strong I- adsorption and Ag+ binding. This unique Zn-I interaction significantly enhanced charge transfer from ZTNML to AgI, promoting the separation of photogenerated electron-hole pairs through a Z-scheme mechanism, induced by both the difference in work functions and strong interfacial interactions. As derived from Fukui function analysis and liquid chromatography-mass spectrometry (LC-MS) data, a potential degradation pathway for imidacloprid driven by superoxide radicals and singlet oxygen species was proposed. Furthermore, QSAR modeling was employed to predict the toxicity of degradation intermediates, providing an assessment of environmental safety. Our work converts heavy metal ions while constructing heterojunctions and efficiently eliminating organic pollutants, providing a sustainable approach to environmental protection.

Saliva-acquired pellicle inspired multifunctional gargle with wet adhesion, photodynamic antimicrobial, and In situ remineralization properties for dental caries prevention

Dental caries is primarily caused by cariogenic bacteria metabolizing carbohydrates to produce acidic substances that erode the dental hard tissues. Traditional remineralization treatments often have limited efficacy due to their lack of antibacterial activity. According to the Interrupting Dental Caries (IDC) theory, ideal caries-preventive materials should possess both antibacterial and remineralizing properties. Furthermore, effective adhesion to dental surfaces is crucial. Inspired by the wet adhesion properties of the salivary acquired pellicle, we developed a multifunctional gargle named Ce6@PDN-SAP (CP-SAP). This formulation employed peptide dendrimer nanogels (PDN) as a carrier for the photosensitizer Ce6, further functionalized with saliva-acquired peptide (SAP) to confer wet adhesion properties. CP-SAP rapidly adhered to the dental surface and remained effective for extended periods. Upon laser irradiation, Ce6 generated reactive oxygen species (ROS), disrupting bacterial outer membrane integrity, causing protein leakage, and reducing ATP levels, thereby achieving potent antibacterial effects. Following this, PDN and SAP acted as nucleation templates to promote in situ remineralization of demineralized dental hard tissues. In vivo studies using rat models demonstrated that CP-SAP provided significantly superior caries-preventive effects compared to chlorhexidine gargle. In conclusion, CP-SAP, as an innovative approach grounded in the IDC theory, holds great promise for the prevention and treatment of dental caries.

New insight of surface water disinfection by Fe2+-SPC: Important role of carbonate radical and the influence of carbonate/bicarbonate ions on free radicals balance

Waterborne viruses significantly endanger public health during water treatment. To explore green, efficient solutions, we compared Fe2+-H2O2 and Fe2+-SPC (sodium percarbonate, solid synthesis of H2O2 and Na2CO3) treatment for virus-laden water (MS2 bacteriophage as the viral model). The Fe2+-SPC system proved more effective in virus elimination at 45 μmol/L and offered sustained disinfection within 24 h. Free radicals: HO•, CO3-•, O2•- contributed 27.62 %, 23.89 %, 11.78 %, respectively to virus removal in the system. Non-radical contributions (1O2) and adsorption & coagulation were 17.87 % and 18.85 %. CO3-• with higher stability and longevity leading to superior virus elimination and prolonged disinfection. HCO3- and CO32- are crucial for producing CO3-• and can convert HO• into CO3-•. 1 μmol/L HCO3- can boost virus removal from 5.35 LRV to 5.41 LRV with 30 μmol/L Fe2+-SPC and shorten virus elimination time to 18 h. CO32- excessively converts HO• into CO3-•, disrupting the system's free radical balance due to high hydrolysis constant and reaction rate, resulting in a poor virus removal enhancement. This study provides a potentially economical method for virus-laden water treatment and explores the contribution and transformation mechanism of free radicals in the Fe2+-SPC system. It also provides insights into optimizing virus removal in the presence of HCO3- and CO32-.

Visible-light-driven copper(II) catalysis for 2,3-disubstituted quinazolinone synthesis via Ullmann N-arylation and C-H oxidative amidation

A novel visible-light-driven method for the synthesis of 2,3-disubstituted quinazolinones has been developed, employing copper(II) as a catalyst in a sequential Ullmann N-arylation and C-H oxidative amidation process. This methodology utilizes o-iodo-N-substituted benzamides and benzylamines as substrates, with molecular oxygen sourced from ambient air functioning as the oxidant. The reaction is conducted under mild conditions, utilizing cost-effective copper(II) chloride as the catalytic agent and Eosin Y as a photosensitizer, facilitated by blue LED irradiation. A broad compatibility with various substrates is demonstrated, yielding products in the range of 30% to 84%. Additionally, mechanistic studies elucidate a single-electron transfer pathway that incorporates aryl radical intermediates. This research presents a sustainable and efficient strategy for the synthesis of quinazolinones, with considerable synthetic and mechanistic implications.

Singlet oxygen presenting a higher detoxification potential on enrofloxacin than sulfate and hydroxyl radicals

With the aid of radical and non-radical reactive species (RS), advanced oxidation processes can efficiently degrade emerging organic contaminants including antibiotics but may generate toxic transformation products (TPs). However, the detoxification capacity of popular RS has not been well elucidated. This study compared the detoxification of enrofloxacin (ENR) with three RS-dominated systems: 1O2, SO4•-+•OH, •OH. The toxicity of ENR TPs generated from those systems was evaluated with multiple methods. It was found that the 1O2-dominated system detoxified ENR more effectively than the other systems in terms of microbial respiratory inhibition, developmental toxicity in zebrafish embryos, and three typical molecular biomarkers, including reactive oxygen species (ROS), and lactate dehydrogenase (LDH), and glutathione S-transferase (GST). Based on their chemical structures of ENR TPs projected with UPLC-QTOF-MS/MS, the toxicity prediction tool (T.E.S.T) revealed that the 1O2-dominated system led to more harmless TPs than the others. The results of this study underscore the great potential of 1O2-dominated system in the detoxification of organic contaminants.

Protonation of Nitrogen-Containing Covalent Organic Frameworks for Enhanced Catalysis

Covalent organic frameworks (COFs) are a class of porous crystalline materials with ordered structures and tunable properties, which have been widely explored in catalysis, sensing, gas storage, and separation. Among various post-synthetic modifications, protonation emerges as a simple yet effective strategy to fine-tune the properties of nitrogen-containing COFs, thereby enhancing their catalytic performance. This concept article highlights the contribution of protonation on the mass transfer kinetics, charge distribution, photo-response, charge transfer, and other properties related to photocatalysis and electrocatalysis. The applications of protonated COFs are explored in catalytic processes including hydrogen evolution, CO2 reduction, H2O2 synthesis, and singlet oxygen generation. We also emphasize the necessity of considering the protonation process when nitrogen-containing COFs are applied in acidic environments to accurately reveal the structure-activity relationship. By analyzing recent advancements in protonated COFs, this article underscores the potential and challenges of protonation as a powerful tool for advancing COF-based catalytic systems.

Modification of iron-containing silicate tailings with oxalic acid to develop a long-efficacy utilization peroxymonosulfate-based system for the efficient decomplexation and removal of Cr(III)-ethylenediamine tetraacetic acid

Ferrous oxalate (FeC2O4)-based composite has been recognized as an eminent catalyst for Cr(III)-ethylenediamine tetraacetic acid (Cr(III)-EDTA) decomplexation. However, their practical application has been limited by low cycling capacity and an ambiguous mechanism. In this research, a composite catalyst consisting of biotite loaded with nano FeC2O4 (CFS90) was prepared directly from iron-containing silicate tailing. The removal efficiency (91.3 %, kobs = 0.0185 min-1) of Cr(III)-EDTA by CFS90/peroxymonosulfate (PMS) system was remarkably higher than that of other typical systems. The Si site in biotite lost electrons while the electron cloud density around the Fe atom in FeC2O4 increased, which facilitates the activation of PMS and the generation of reactive oxygen species (ROS). In this system, abundant singlet oxygen (1O2) was primarily produced via interactions between carbon-centered radicals (CO2·-) and dissolved oxygen (DO), rather than through oxygen vacancies (Ovs) in CFS90. Both CO2·- and Fe(II) provided reducing conditions, preventing the released Cr(III) from being re-oxidized. Notably, the released Cr(III) was effectively precipitated by elevating the solution pH with NaOH, therefore endowing superior stability and deactivation capacity of CFS90 to enable its removal rate of Cr(III)-EDTA to remain above 84.1 % for 18 h in a fix-bed reactor. These findings provide an in-depth analysis of the enhanced Cr(III)-EDTA removal mechanism and highlight the environmental remediation potential of iron-containing silicate tailings.

Novel millimeter-sized honeycomb-like Fe/Fe3C@HBC from waste cotton textiles towards rapid degradation of ofloxacin via activation of H2O2

Although multiphase catalysts with large sizes exhibit excellent recyclability and low toxicity in heterogeneous Fenton reactions, their reactivity, reusability and storage stability for degradation of organic contaminants still need improvement, which is essential for treating complex wastewater and ensuring environmental sustainability. In this study, the waste cotton textiles were firstly used as the carbon source to generate a novel millimeter-sized catalyst (Fe/Fe3C@HBC) with a honeycomb-like structure, which could effectively activate H2O2 to realize rapid removal of ofloxacin (OFL) (100% in 10 min). It achieved remarkable removal performance across a broad temperature range (4-40 °C) and high-concentration OFL. It even demonstrated excellent removal towards other typical contaminants (Tetracycline, Ciprofloxacin, Methylene Blue, Rhodamine B, Malachite Green), showing outstanding storage stability, physical structural stability, reusability and separation characteristics. Whereafter, its removal mechanism was also explored, showing that it was entirely dependent on the degradation by the reactive oxygen species (ROS), including •OH, O2•- and 1O2, as well as the persistent free radicals from the catalyst. Moreover, the honeycomb-like structure promoted the effective utilization of H2O2, facilitated the generation of •OH and expedited the accumulation of OFL on the catalyst surface. Fe/Fe3C (inside of the catalytic instead of in the reaction solution) was essential for the degradation. Finally, the OFL degradation pathways and toxicity predictions were also proposed. Overall, this innovation supports cleaner water resources and enhances public health, demonstrating a significant step forward in environmental remediation technologies.

Photodegradation of Chlorinated Persistent Organic Pollutants (Cl-POPs) in Pearl River Suspended Particulate Matter-Water Systems: Kinetics, Quantitative Structure-Activity Relationship (QSAR) Development, and Mechanism

Chlorinated persistent organic pollutants (Cl-POPs) are highly hydrophobic and are easily adsorbed to solid particulate matter after being released into the water column, thus affecting the transformation process and environmental fate. This study investigated the photodegradation behavior of 16 Cl-POPs in the Pearl River suspended particulate matter (SPM)-water system. The photodegradation rates of polychlorinated biphenyls (PCBs) were generally higher than those of dioxins and increased with substitution numbers of Cl atoms. A QSAR model correlating photodegradation rate constants of Cl-POPs and their structural parameters was established by using multiple linear regression (MLR) analysis and machine learning. The model results showed that soil-water partition coefficient (KOC), morgan fingerprint (mf_1747), and nucleophilicity index (NI) were the main factors affecting the photodegradation of Cl-POPs, confirming that the photodegradation of Cl-POPs with higher hydrophobicity and larger nucleophilic reactivity proceeded faster. According to the quenching experiment and theoretical calculation results, •O2- in the hydrophobic region contributed more to the strongly hydrophobic Cl-POPs, while the contribution of •OH was mainly concentrated in the weakly hydrophobic Cl-POPs. This study provided valuable insights into photolysis-related environmental persistence and fate of Cl-POPs in the SPM-water system.

Carbonaceous materials in structural dimensions for advanced oxidation processes

Carbonaceous materials have attracted extensive research and application interests in water treatment owing to their advantageous structural and physicochemical properties. Despite the significant interest and ongoing debates on the mechanisms through which carbonaceous materials facilitate advanced oxidation processes (AOPs), a systematic summary of carbon materials across all dimensions (0D-3D nanocarbon to bulk carbon) in various AOP systems remains absent. Addressing this gap, the current review presents a comprehensive analysis of various carbon/oxidant systems, exploring carbon quantum dots (0D), nanodiamonds (0D), carbon nanotubes (1D), graphene derivatives (2D), nanoporous carbon (3D), and biochar (bulk 3D), across different oxidant systems: persulfates (peroxymonosulfate/peroxydisulfate), ozone, hydrogen peroxide, and high-valent metals (Mn(VII)/Fe(VI)). Our discussion is anchored on the identification of active sites and elucidation of catalytic mechanisms, spanning both radical and nonradical pathways. By dissecting catalysis-related factors such as sp2/sp3 C, defects, and surface functional groups that include heteroatoms and oxygen groups in different carbon configurations, this review aims to provide a holistic understanding of the catalytic nature of different dimensional carbonaceous materials in AOPs. Furthermore, we address current challenges and underscore the potential for optimizing and innovating water treatment methodologies through the strategic application of carbon-based catalysts. Finally, prospects for future investigations and the associated bottlenecks are proposed.

Nanotherapies Based on ROS Regulation in Oral Diseases

Oral diseases rank among the most prevalent clinical conditions globally, typically involving detrimental factors such as infection, inflammation, and injury in their occurrence, development, and outcomes. The concentration of reactive oxygen species (ROS) within cells has been demonstrated as a pivotal player in modulating these intricate pathological processes, exerting significant roles in restoring oral functionality and maintaining tissue structural integrity. Due to their enzyme-like catalytic properties, unique composition, and intelligent design, ROS-based nanomaterials have garnered considerable attention in oral nanomedicine. Such nanomaterials have the capacity to influence the spatiotemporal dynamics of ROS within biological systems, guiding the evolution of intra-ROS to facilitate therapeutic interventions. This paper reviews the latest advancements in the design, functional customization, and oral medical applications of ROS-based nanomaterials. Through the analysis of the components and designs of various novel nanozymes and ROS-based nanoplatforms responsive to different stimuli dimensions, it elaborates on their impacts on the dynamic behavior of intra-ROS and their potential regulatory mechanisms within the body. Furthermore, it discusses the prospects and strategies of nanotherapies based on ROS scavenging and generation in oral diseases, offering alternative insights for the design and development of nanomaterials for treating ROS-related conditions.

Enhanced visible-light-driven photocatalytic antibacterial activity by in-situ synthesized NH2-MIL-101(Al)/AgI heterojunction and mechanism insight

Photocatalytic antibacterial technology has the potential to prevent the formation of biofilms and microbial corrosion of metals by rapidly eliminating microorganisms in a short period. In this study, novel NH2-MIL-101(Al)/AgI is in-situ synthesized at ambient temperature, revealing enhanced photocatalytic antibacterial activity and cyclic stability in seawater. A low dosage of 0.1 mg mL-1 NH2-MIL-101(Al)/AgI sterilizes almost all Staphylococcus aureus within 60 min, and all Pseudomonas aeruginosa within 20 min upon visible light irradiation. Microscopic characterizations, photoelectrochemical experiments, and finite element method simulation indicate that the uniform dispersion of AgI nanoparticles and the formation of NH2-MIL-101(Al)/AgI Z-type heterojunction enhance the visible light absorption of NH2-MIL-101(Al), suppress the recombination of the photogenerated carriers, and improve the transfer efficiency. The photocatalytic antibacterial mechanism is also proposed based on the generation of h+, e⁻, and reactive oxygen species (especially 1O2) which induced the rupture of cell structures. Hence, the NH2-MIL-101(Al)-related material is introduced for photocatalytic antibacterial applications and offers insights for protecting metals from microbial corrosion in marine environments.

Dual Pathways of Photorelease Carbon Monoxide via Photosensitization for Tumor Treatment

Carbon monoxide (CO) gas therapy, as an emerging therapeutic strategy, is promising in tumor treatment. However, the development of a red or near-infrared light-driven efficient CO release strategy is still challenging due to the limited physicochemical characteristics of the photoactivated carbon monoxide-releasing molecules (photoCORMs). Here, we discovered a novel photorelease CO mechanism that involved dual pathways of CO release via photosensitization. Specifically, the photosensitizer Chlorin e6 (Ce6) sensitized oxygen to produce singlet oxygen (1O2) and oxidized photoCORM Mn2(CO)10 to release CO in an air-saturated solvent under red light (655 nm, 50 mW/cm2) irradiation. Furthermore, Ce6 and Mn2(CO)10 could undergo multistep photochemical reactions to release CO, as well as the degradation of the photosensitizer Ce6 in an oxygen-depleted solution. As a proof of concept, we demonstrated the feasibility and tumor inhibition of this CO release strategy both in vitro and in vivo. These results provide a robust platform for the development of new approaches to CO-mediated modulation of signaling pathways and further facilitate the practical use of gas therapeutic methods in tumor therapy in vivo.

Fluorine-fluorine interaction-driven colorimetric sensor for PFOA-sensitive detection using F-functionalized Ce-UiO-66-NH2 MOF with oxidase-like activity

A novel colorimetric sensor was designed for sensitive perfluorooctanoic acid (PFOA) detection based on a fluorine-functionalized Ce-metal-organic framework (F-Ce-UiO-66-NH2) with oxidase-like activity, using 3,3',5,5'-tetramethylbenzidine (TMB) as the chromogenic substrate. This F-Ce-UiO-66-NH2 was synthesized through ligand exchange and post-modification with pentafluorobenzaldehyde (PFBA) on the basis of Ce-terephthalic acid (Ce-UiO-66), incorporating pentafluorophenyl groups that enhance the material's affinity for PFOA, leading to a more sensitive absorbance change in the presence of PFOA. Experimental and computational assays revealed that oxidase-like activity of F-Ce-UiO-66-NH2 primarily arises from hydroxyl radicals (•OH) generated through the conversion of superoxide radicals (•O2-). Furthermore, PFOA molecules were shown to undergo self-aggregation on the F-Ce-UiO-66-NH2 surface via fluorine-fluorine (F-F) interactions between PFOA molecules and the pentafluorophenyl groups as well as between PFOA themselves, blocking the active Ce sites and hindering the interaction of O2 and TMB with F-Ce-UiO-66-NH2, thereby diminishing its oxidase-like activity. Owing to these sophisticated mechanisms, this colorimetric sensor demonstrated a broad linear detection range from 0.5 to 210 µM with a low detection limit of 0.41 µM for PFOA, enabling precise quantification of PFOA concentrations in real environmental water samples. This work introduces a new strategy for constructing field-deployable colorimetric sensors based on F-F interaction, offering very valuable insights into the design and operational principle for PFAS detection.

Surface-Enhanced Raman Spectroscopy for the Detection of Reactive Oxygen Species

Reactive oxygen species (ROS) play fundamental roles in various biological and chemical processes in nature and industries, including cell signaling, disease development and aging, immune defenses, environmental remediation, pharmaceutical syntheses, metal corrosion, energy production, etc. As such, their detection is of paramount importance, but their accurate identification and quantification are technically challenging due to their transient nature with short lifetimes and low steady-state concentrations. As a highly sensitive and selective analytical technique, surface-enhanced Raman spectroscopy (SERS) is promising for detecting ROS in real-time, enabling in situ monitoring of ROS-involved electrochemical and biochemical events with exceptional resolution. This review provides a comprehensive analysis of the state-of-the-art in the SERS-based detection of ROS. Herein, the principles and ROS sensing mechanisms of SERS have been critically evaluated, highlighting their emerging applications in direct and indirect ROS monitoring in electrochemical and biological systems. The developments and reaction schemes of selective SERS probes for superoxide (•O2-), hydroxyl radicals (•OH), nitric oxide (•NO), peroxynitrite (ONOO-), and hypochlorite (OCl-) are presented. Finally, technical challenges and future research directions are discussed to guide the design of SERS for ROS analysis.

A high-valence bismuth(V) nanoplatform triggers cancer cell death and anti-tumor immune responses with exogenous excitation-free endogenous H2O2- and O2-independent ROS generation

Reactive oxygen species with evoked immunotherapy holds tremendous promise for cancer treatment but has limitations due to its dependence on exogenous excitation and/or endogenous H2O2 and O2. Here we report a versatile oxidizing pentavalent bismuth(V) nanoplatform (NaBiVO3-PEG) can generate reactive oxygen species in an excitation-free and H2O2- and O2-independent manner. Upon exposure to the tumor microenvironment, NaBiVO3-PEG undergoes continuous H+-accelerated hydrolysis with •OH and 1O2 generation through electron transfer-mediated BiV-to-BiIII conversion and lattice oxygen transformation. The simultaneous release of sodium counterions after endocytosis triggers caspase-1-mediated pyroptosis. NaBiVO3-PEG intratumorally administered initiates robust therapeutic efficacies against both primary and distant tumors and activates systemic immune responses to combat tumor metastasis. NaBiVO3-PEG intravenously administered can efficiently accumulate at the tumor site for further real-time computed tomography monitoring, immunotherapy, or alternative synergistic immune-radiotherapy. Overall, this work offers a nanomedicine based on high-valence bismuth(V) nanoplatform and underscores its great potential for cancer immunotherapy.

Tungsten phosphide nanoparticles anchored on ultrathin carbon nanosheets for efficient oxidative desulfurization: Pivotal roles and generation pathways of singlet oxygen

Singlet oxygen (1O2) is an excellent reactive oxygen species for the selective oxidation of organic compounds. Therefore, its application in oxidative desulfurization (ODS) of fuels is theoretically promising, while this has rarely been systematically investigated. Herein, a novel ultrathin carbon nanosheet (CN)-supported tungsten phosphide (WP) catalyst (WP/CN) was devised and employed to activate hydrogen peroxide (H2O2) for the efficient 1O2 generation in ODS. The turnover frequency of WP/CN for the oxidation of dibenzothiophene was as high as 32.7 h-1 at 60 °C, surpassing that of most reported ODS catalysts. More importantly, benefiting from the high selectivity of 1O2, the WP/CN-H2O2 system exhibited exceptional interference resistance and achieved complete ODS of real diesels at a molar ratio of H2O2 to S of 4:1 (the theoretical value is 2:1), outperforming reported ODS systems. The results of experiments and density functional theory calculations demonstrated that the most reasonable reaction pathway for the formation of 1O2 was H2O2→H2O2*→2OH*→O*→2O*→1O2*. The present findings may provide new insights into the development of high-performance and energy-saving ODS processes.

Degradation mechanisms and toxicity determination of bisphenol A by FeOx-activated peroxydisulfate under ultraviolet light

Ultraviolet light (UV)-assisted advanced oxidation processes (AOPs) are commonly used to degrade organic contaminants. However, this reaction system's extensive comprehension of the degradation mechanisms and toxicity assessment remains inadequate. This study focuses on investigating the degradation mechanisms and pathways of bisphenol A (BPA), generation of reactive oxygen species (ROS), and toxicity of degradation intermediates in UV/PDS/ferrous composites (FeOx) systems. The degradation rate of BPA gradually increased from the initial 11.92% to 100% within 120 min. Sulfate radicals (SO 4 . - ), hydroxyl radicals (.OH), superoxide anions (O 2 . - ), and singlet oxygen (1O2) were the primary factors in the photocatalytic degradation of BPA in the UV/PDS/FeOx systems. The main reactions of BPA in this system were deduced to be β-bond cleavage, hydroxyl substitution reaction, hydrogen bond cleavage, and oxidation reaction. A trend of decreasing toxicity for the degradation intermediates of BPA was observed according to the toxicity investigations. The efficient degradation of BPA in UV/PDS/FeOx systems provided theoretical data for AOPs, which will improve the understanding of organic contaminants by FeOx in natural industry wastewater.

Applying molecular oxygen for organic pollutant degradation: Strategies, mechanisms, and perspectives

Molecular oxygen (O2) is an environmentally friendly, cost-effective, and non-toxic oxidant. Activation of O2 generates various highly oxidative reactive oxygen species (ROS), which efficiently degrade pollutants with minimal environmental impact. Despite extensive research on the application of O2 activation in environmental remediation, a comprehensive review addressing this topic is currently lacking. This review provides an informative overview of recent advancements in O2 activation, focusing on three primary strategies: photocatalytic activation, chemical activation, and electrochemical activation of O2. We elucidate the respective mechanisms of these activation methods and discuss their advantages and disadvantages. Additionally, we thoroughly analyze the influence of oxygen supply, reactive temperature, and pH on the O2 activation process. From electron transfer and energy transfer perspectives, we explore the pathways for ROS generation during O2 activation. Finally, we address the challenges faced by researchers in this field and discuss future prospects for utilizing O2 activation in pollution control applications. This detailed analysis enhances our understanding and provides valuable insights for the practical implementation of organic pollutant degradation.

Effects of chemically reactive species generated in plasma treatment on the physico-chemical properties and biological activities of polysaccharides: An overview

Plasma technology as an advanced oxidation technology, has gained increasing interest to generate numerous chemically reactive species during the plasma discharge process. Such chemically reactive species can trigger a chain of chemical reactions leading to the degradation of macromolecules including polysaccharides. This review primarily summarizes the generation of various chemically reactive species during plasma treatment and their effects on the physico-chemical properties and biological activities of polysaccharides. During plasma treatment, the type of chemically reactive species that play a major role is related to equipment, working gases and types of polysaccharides. The primary chain structure of polysaccharides did not changed much during the plasma treatment, other physico-chemical properties might be changed, such as molecular weight, solubility, hydrophilicity, rheological properties, gel properties, crystallinity, elemental composition, glycosidic bonding, and surface morphology. Additionally, the biological activities of plasma-treated polysaccharides including antibacterial, antioxidant, immunological, antidiabetic activities, and seed germination promotion activities in agriculture could be improved. Therefore, plasma treatment has the potential application in preparing polysaccharides with enhanced biological activities.

Non-radical oxidation driven by iron-based materials without energy assistance in wastewater treatment

Chemical oxidation is extensively utilized to mitigate the impact of organic pollutants in wastewater. The non-radical oxidation driven by iron-based materials is noted for its environmental friendliness and resistance to wastewater matrix, and it is a promising approach for practical wastewater treatment. However, the complexity of heterogeneous systems and the diversity of evolutionary pathways make the mechanisms of non-radical oxidation driven by iron-based materials elusive. This work provides a systematic review of various non-radical oxidation systems driven by iron-based materials, including singlet oxygen (1O2), reactive iron species (RFeS), and interfacial electron transfer. The unique mechanisms by which iron-based materials activate different oxidants (ozone, hydrogen peroxide, persulfate, periodate, and peracetic acid) to produce non-radical oxidation are described. The roles of active sites and the unique structures of iron-based materials in facilitating non-radical oxidation are discussed. Commonly employed identification methods in wastewater treatment are compared, such as quenching, chemical probes, spectroscopy, mass spectrometry, and electrochemical testing. According to the process of iron-based materials driving non-radical oxidation to remove organic pollutants, the driving factors at different stages are summarized. Finally, challenges and countermeasures are proposed in terms of mechanism exploration, detection methods and practical applications of non-radical oxidation driven by iron-based materials. This work provides valuable insights for understanding and developing non-radical oxidation systems.

Biomaterials based on advanced oxidation processes in tooth whitening: fundamentals, progress, and models

The increasing desire for aesthetically pleasing teeth has resulted in the widespread use of tooth whitening treatments. Clinical tooth whitening products currently rely on hydrogen peroxide formulations to degrade dental pigments through oxidative processes. However, they usually cause side effects such as tooth sensitivity and gingival irritation due to the use of high concentrations of hydrogen peroxide or long-time contact. In recent years, various novel materials and reaction patterns have been developed to tackle the issues related to H2O2-based tooth whitening. These can be broadly classified as advanced oxidation processes (AOPs). AOPs generate free radicals that have potent oxidizing properties, which can thereby increase the oxidation power and/or reduce the exposure time and can probably minimize the side effects of tooth bleaching. While there have been several reviews on clinical tooth whitening and the application of novel nanomaterials, a review based on the concept of AOPs in tooth bleaching application has not yet been conducted. This review describes the common types and mechanisms of AOPs, summarizes the latest research progress of new tooth bleaching materials based on AOPs, and proposes a model for tooth bleaching and a rate control step at the molecular level. The paper also reviews the shortcomings and suggests future development directions.

Efficient Energy and Electron Transfer Photocatalysis with a Coulombic Dyad

Photocatalysis holds great promise for changing the way value-added molecules are currently prepared. However, many photocatalytic reactions suffer from quantum yields well below 10%, hampering the transition from lab-scale reactions to large-scale or even industrial applications. Molecular dyads can be designed such that the beneficial properties of inorganic and organic chromophores are combined, resulting in milder reaction conditions and improved reaction quantum yields of photocatalytic reactions. We have developed a novel approach for obtaining the advantages of molecular dyads without the time- and resource-consuming synthesis of these tailored photocatalysts. Simply by mixing a cationic ruthenium complex with an anionic pyrene derivative in water a salt bichromophore is produced owing to electrostatic interactions. The long-lived organic triplet state is obtained by static and quantitative energy transfer from the preorganized ruthenium complex. We exploited this so-called Coulombic dyad for energy transfer catalysis with similar reactivity and even higher photostability compared to a molecular dyad and reference photosensitizers in several photooxygenations. In addition, it was shown that this system can also be used to maximize the quantum yield of photoredox reactions. This is due to an intrinsically higher cage escape quantum yield after photoinduced electron transfer for purely organic compounds compared to heavy atom-containing molecules. The combination of laboratory-scale as well as mechanistic irradiation experiments with detailed spectroscopic investigations provided deep mechanistic insights into this easy-to-use photocatalyst class.

Self-Assembly of Nanovesicles for Enhanced Adsorption and Efficient Photodegradation of 2,4,6-Trichlorophenol

The compound 2,4,6-trichlorophenol poses significant risks to both the aquatic environment and human health. Its inherent persistence and stability present challenges in achieving complete purification, thus warranting its inclusion as a priority pollutant. The present study reports the development of an amphiphilic small-molecule compound that self-assembles into nanovesicles exhibiting remarkable adsorption and photodegradation capabilities. Through the synergistic effects of hydrogen bonding, van der Waals forces, π-π interactions, and electrostatic interactions, these vesicles efficiently adsorb 2,4,6-trichlorophenol from aqueous solutions within 1 min while demonstrating exceptional environmental stability and broad applicability. Upon self-assembly into vesicles, not only are more adsorption sites exposed, but charge separation and migration within the vesicles are also facilitated. Through the synergistic effects of adsorption and photodegradation, complete removal of 2,4,6-trichlorophenol in aqueous solution can be achieved within 8 h while exhibiting excellent recycling capability. This approach offers a viable strategy for designing and synthesizing pure organic photodegradable materials.

pH modulates efficiency of singlet oxygen production by flavin cofactors

Flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) are frequently used interchangeably in the catalysis of various reactions as part of flavoenzymes because they have the same functional component, the isoalloxazine ring. However, they differ significantly in their conformational properties. The inclusion of two planar rings in the structure of FAD greatly increases the range of possible conformations compared to FMN. An exemplary instance of this is the remarkable disparity in singlet oxygen efficiency production, Φ Δ, between FMN and FAD. Under neutral pH conditions, FAD has low photosensitizing activity with Φ Δ ∼ 0.07 while FMN demonstrates high photosensitizing activity with Φ Δ ∼ 0.6. Both adenine rings and isoalloxazine in FAD contain pH titratable groups. Through comprehensive analysis of the kinetics of the transient absorbance of the triplet state and the phosphorescence of singlet oxygen from FAD and FMN, we determined the correlation between different conformational states and the pH-dependent generation of singlet oxygen. Based on our findings, we may deduce that within the pH range of pH 2 to pH 13, only two out of the five potential structural states of FAD are capable of efficiently producing singlet oxygen. There are two open conformations: (i) an acidic FAD conformation with a protonated adenine ring, which is around 10 times more populated than the neutral open FAD conformation, and (ii) a neutral pH FAD conformation, which is significantly less populated. The FAD conformer with a protonated adenine ring at acidic pH generates singlet oxygen with approximately 50% efficiency compared to the constantly open FMN at neutral pH. This may have implications for singlet oxygen synthesis in acidic environments.

Hierarchical Anion Exchange and Reverse Electron Transfer in Layered Double Hydroxides/Peroxymonosulfate System for Roxarsone Elimination

Roxarsone (ROX) is the main form of arsenic pollution in the world, and developing effective methods for its elimination is beneficial to human health and the ecological environment. Herein, we report glutaraldehyde cross-linked chitosan-encapsulated CoCe-LDH (layered double hydroxides) as an outstanding catalyst for the advanced oxidation of ROX and the efficient adsorption of inorganic arsenic. 100% of ROX and more than 98.5% of As(III)/As(V) were eliminated, and over 99.3% of remaining inorganic arsenic was oxidized to low-toxicity As(V) in the peroxymonosulfate (PMS) activation system, and some specific properties of LDH are considered the main reasons. The hierarchical anion exchange has been confirmed to be beneficial for constructing a high-concentration PMS interlayer microenvironment. The unique reverse electron transfer process induced 100% selective production of singlet oxygen. This work not only develops an advanced ROX removal method but also provides a new understanding of the LDH-based advanced oxidation process.

Treatment and nutrient recovery from landfill leachate by sequential persulfate oxidation and struvite precipitation: An evaluation of technical feasibility

The technical feasibility of advanced oxidation process, in particular persulfate (PS) oxidation followed by struvite precipitation for landfill leachate treatment and nutrient recovery has been depicted in the current study. Furthermore, the impact of activation of PS with thermal and ultraviolet (UV) irradiation techniques on COD removal efficiency is also investigated. A maximum COD removal efficiency of 96% is accomplished at 65 °C together with supply of UV irradiation. The impact of persulfate dose, pH, and PS/65 °C/UV system on COD and biodegradability is also illustrated in the current study. Additionally, decomposition rate constant values are also ascertained in the present study. Afterwards, nutrient recovery using struvite precipitation is carried out for sustainable utilization of resources. Preliminary treatment of leachate with PS/65 °C/UV system is greatly conducive to recovering high quality struvite crystals. Besides, 94.9%, 83.5%, and 91.3% of PO43- - P, NH4+ - N, and Mg2+ recovery efficiency attained respectively at pH 9.5 and 1.2:1:1 molar ratio of Mg2+: NH4+ - N: PO43- - P. Additionally, all the nutrient recovery studies are validated using chemical equilibrium model Visual MINTEQ. Later, bioavailable fraction of PO43- - P in the recovered struvite is also investigated for utilization as fertilizer. The presence of Cu and Zn in the recovered struvite precipitate enhanced its economic value as a fertilizer. Since Cu and Zn are vital micronutrients for growth of plants. The low soluble values of recovered struvite precipitate confirmed its utilization as slow releasing fertilizer.

Exploring the viability of peracetic acid-mediated antibiotic degradation in wastewater through activation with electrogenerated HClO

Electrochemical advanced oxidation processes (EAOPs) face challenging conditions in chloride media, owing to the co-generation of undesirable Cl-disinfection byproducts (Cl-DBPs). Herein, the synergistic activation between in-situ electrogenerated HClO and peracetic acid (PAA)-based reactive species in actual wastewater is discussed. A metal-free graphene-modified graphite felt (graphene/GF) cathode is used for the first time to achieve the electrochemically-mediated activation of PAA. The PAA/Cl- system allowed a near-complete sulfamethoxazole (SMX) degradation (kobs =0.49 min-1) in only 5 min in a model solution, inducing 32.7- and 8.2-fold rise in kobs as compared to single PAA and Cl- systems, respectively. Such enhancement is attributed to the occurrence of 1O2 (25.5 μmol L-1 after 5 min of electrolysis) from the thermodynamically favored reaction between HClO and PAA-based reactive species. The antibiotic degradation in a complex water matrix was further considered. The SMX removal is slightly susceptible to the coexisting natural organic matter, with both the acute cytotoxicity (ACT) and the yield of 12 DBPs decreasing by 29.4 % and 37.3 %, respectively. According to calculations, HClO accumulation and organic Cl-addition reactions are thermodynamically unfavored. This study provides a scenario-oriented paradigm for PAA-based electrochemical treatment technology, being particularly appealing for treating wastewater rich in Cl- ion, which may derive in toxic Cl-DBPs.

Gold(I) complexes as powerful photosensitizers - a visionary frontier perspective

Singlet oxygen production and its reactivity have significant implications in fields ranging from polymer science to photodynamic therapy. Extensive research has focused on the development of organic-based materials and heavy metal complexes, including Ru(II), Rh(III), Ir(III) and Pt(II). However, metal complexes containing Au(I) have been scarcely explored and warrant further investigation. This review provides a comprehensive analysis of reported compounds, classified based on the ligands coordinated to the gold(I) centre. Additionally, future directions in photosensitizer development and singlet oxygen applications are discussed.

Overview of the environmental risks of microplastics and their controlled degradation from the perspective of free radicals

Owing to the significant environmental threat posed by microplastics (MPs) of varying properties, MPs research has garnered considerable attention in current academic discourse. Addressing MPs in river-lake water systems, existing studies have seldom systematically revealed the role of free radicals in the aging/degradation process of MPs. Hence, this review aims to first analyze the pollution distribution and environmental risks of MPs in river-lake water systems and to elaborate the crucial role of free radicals in them. After that, the study delves into the advancements in free radical-mediated degradation techniques for MPs, emphasizing the significance of both the generation and elimination of free radicals. Furthermore, a novel approach is proposed to precisely govern the controlled generation of free radicals for MPs' degradation by interfacial modification of the material structure. Hopefully, it will shed valuable insights for the effective control and reduction of MPs in river-lake water systems.

Dissolved Black Carbon Facilitates the Photodegradation of Microplastics via Molecular Weight-Dependent Generation of Reactive Intermediates

Photodegradation of microplastics (MPs) induced by sunlight plays a crucial role in determining their transport, fate, and impacts in aquatic environments. Dissolved black carbon (DBC), originating from pyrolyzed carbon, can potentially mediate the photodegradation of MPs owing to its potent photosensitization capacity. This study examined the impact of pyrolyzed wood derived DBC (5 mg C/L) on the photodegradation of polystyrene (PS) MPs in aquatic solutions under UV radiation. It revealed that the photodegradation of PS MPs primarily occurred at the benzene ring rather than the aliphatic segments due to the fast attack of hydroxyl radical (•OH) and singlet oxygen (1O2) on the benzene ring. The photosensitivity of DBC accelerated the degradation of PS MPs, primarily attributed to the increased production of •OH, 1O2, and triplet-excited state DBC (3DBC*). Notably, DBC-mediated photodegradation was related to its molecular weight (MW) and chemical properties. Low MW DBC (<3 kDa) containing more carbonyl groups generated more •OH and 1O2, accelerating the photodegradation of MPs. Nevertheless, higher aromatic phenols in high MW DBC (>30 kDa) scavenged •OH and generated more O2•-, inhibiting the photodegradation of MPs. Overall, this study offered valuable insights into UV-induced photodegradation of MPs and highlighted potential impacts of DBC on the transformation of MPs.

Discerning the Relevance of Singlet Oxygen in Pollutant Degradation in Peroxymonosulfate Activation Processes

Significant efforts have recently been exerted toward construction of singlet oxygen (1O2)-dominated catalytic oxidation systems for selective removal of organic contaminants from wastewater, with peroxides serving as the chemical source. However, the relevance of 1O2 in the removal of pollutants remains ambiguous and requires elucidation. In this study, we scrupulously exclude the significant role of 1O2 in contaminant degradation in various peroxymonosulfate (PMS) activation systems. Multiple experimental results indicate that the activation of PMS catalyzed by CuO, MnO2, Fe-doped g-C3N4 (Fe-CN), or N-doped graphite does not predominantly follow the 1O2 pathway. More importantly, the reactivity of 1O2 is remarkably overestimated in the literature, given its inferior capacity in degradation of a range of heterocyclic contaminants and aromatic compounds possessing electron-withdrawing groups. In addition, the strong physical quenching effect of water, coupled with the low oxidizing ability of 1O2, would notably reduce the utilization efficiency of peroxide, which is particularly apparent in the degradation of micropollutants. We reckon that this study is expected to end the long-running dispute associated with the relevance of 1O2 in pollutant removal.

Vanadium as a Ti-like mediator boosting electronic transmission in Fe-based MOFs for photocatalytic sterilization

Efficient metal-organic frameworks (MOFs) photocatalytic bactericidal catalysts are urgently needed in water purification. Herein, a Fe-MOF (MIL-88B-NH2(V1Fe5) with promoted electron transport was achieved by vanadium (V) ions doping and V/Fe ratio optimization, showing excellent photocatalytic bactericidal activity againstE. coliunder visible light irradiation (99.92%). The efficient antibacterial mechanism, V as a Ti-like mediator boosting electronic transmission in MIL-88B-NH2(V1Fe5), was revealed by its band structure, transient photocurrent, electrochemical impedance spectroscopy, and scavenger quenching experiments. The enhancement of photocatalytic bactericidal performance of Fe-MOFs by V-ion-doping was confirmed by two other Fe-MOFs, MIL-53-NH2(V1Fe5) and MIL-101-NH2(V1Fe5), with the same metal ions and ligands, both of which have higher performance than the corresponding undoped MOFs. Among them, MIL-88B-NH2(V1Fe5) exhibits the highest photocatalytic bactericidal activity due to its suitable metal clusters ([M(μ3-O)] cluster) and topological structure (three-dimensional rhomboid network structure). This work demonstrated the amplification effect of V ion doping on electron transport in Fe-MOFs photocatalysts.

Sandwich-structured continuous ZIF-8/Ti3C2 MXene/ZIF-8 for efficient sterilization: Enhanced photocatalytic activity, photothermal effect, and environmental safety

The development of effective water purification systems is crucial for controlling and remediating environmental pollution, especially in terms of sterilization. Herein, we demonstrate elaborately designed composite nanosheets with a sandwich structure, composed of two-dimensional (2D) Ti3C2 MXene nanosheet core and conformal ZIF-8 ultrathin outer layers, and their potential applications in photocatalytic sterilization. The study results indicate that the conformal ZIF-8-MXene nanosheet exhibits an expanded light absorption range (826 nm), improved photothermal conversion efficiency (6.2 °C s-1), and photocurrent response, thus boosting photocatalytic sterilization efficiency (6.63 log10 CFU mL-1) against Escherichia coli under simulated sunlight within 90 min. Interestingly, 2D ZIF-8 layers exhibit positive zeta potential (19 mV), good hydrophilicity (40.6°), and local photogenerated-hole accumulation, possessing efficient bacteria-trapping efficiency. Membrane filters fabricated from optimized composite nanosheets exhibit an outstanding bacteria-trapping and sterilization efficiency (almost 100 %) against Escherichia coli under simulated sunlight within 30 min of the flow photocatalytic experiments. This work not only presents a rational structural design of the conformal and ultrathin anchoring of ZIF-8 onto a 2D conductive material for bacteria-trapping and sterilization, but also opens new opportunities for using metal-organic frameworks in photocatalytic disinfection of drinking water.

Amphichdiral enhancement on singlet oxygen generation and stable thallium immobilization using iron-driven copper oxide

Thallium (Tl) as a prominent priority contaminant in aquatic environment necessitates rigorous regulation. However, limited horizon devotes the impact of selective oxidation on the process of thallium purification. In this study, selective active radical of singlet oxygen (1O2) was continually generated for Tl(Ⅰ) oxidation accomplished with efficient Tl(Ⅲ) immobilization using iron-driven copper oxide (CuFe)/peroxymonosulfate (PMS). Fe-doping changed the active center of electronic structure for enhancing the catalytic and adsorptive reactivities, and installed magnetism for solid-liquid separation. Rapid reaction rate (0.253 min-1) coupled with vigorous elimination efficiency (98.32%) relied on electrostatic attraction, surface complexation, and H-bond interaction. EPR and XPS analyses demonstrated that the synergistic effects of ≡ Cu(Ⅰ)/≡Cu(Ⅱ) and ≡ Fe(Ⅲ)/≡Fe(Ⅱ) redounded to the sustained generation of 1O2 through the pathway of PMS → •O2- → 1O2, and 1O2 exploited an advantage to selectively oxidize Tl(Ⅰ) to Tl(Ⅲ). 3D isosurface cubic charts revealed that the immobilizing ability of Tl(Ⅲ) hydrate for CuFe was notably superior to that of Tl(Ⅲ) hydrate for CuO and Tl(Ⅰ) hydrate for CuO/CuFe, which further attested surface reactivity promoted stable immobilization form. This work develops the continuous generation of 1O2 and stable immobilization with the goal of efficiently cleansing Tl-containing wastewater.

Atomic-Level Engineered Cobalt Catalysts for Fenton-Like Reactions: Synergy of Single Atom Metal Sites and Nonmetal-Bonded Functionalities

Single atom catalysts (SACs) are atomic-level-engineered materials with high intrinsic activity. Catalytic centers of SACs are typically the transition metal (TM)-nonmetal coordination sites, while the functions of coexisting non-TM-bonded functionalities are usually overlooked in catalysis. Herein, the scalable preparation of carbon-supported cobalt-anchored SACs (CoCN) with controlled Co─N sites and free functional N species is reported. The role of metal- and nonmetal-bonded functionalities in the SACs for peroxymonosulfate (PMS)-driven Fenton-like reactions is first systematically studied, revealing their contribution to performance improvement and pathway steering. Experiments and computations demonstrate that the Co─N3C coordination plays a vital role in the formation of a surface-confined PMS* complex to trigger the electron transfer pathway and promote kinetics because of the optimized electronic state of Co centers, while the nonmetal-coordinated graphitic N sites act as preferable pollutant adsorption sites and additional PMS activation sites to accelerate electron transfer. Synergistically, CoCN exhibits ultrahigh activity in PMS activation for p-hydroxybenzoic acid oxidation, achieving complete degradation within 10 min with an ultrahigh turnover frequency of 0.38 min-1, surpassing most reported materials. These findings offer new insights into the versatile functions of N species in SACs and inspire rational design of high-performance catalysts in complicated heterogeneous systems.

Novel Insights into Sb(III) Oxidation and Immobilization during Ferrous Iron Oxygenation: The Overlooked Roles of Singlet Oxygen and Fe (oxyhydr)oxides Formation

Reactive oxygen species (ROS) produced from the oxygenation of reactive Fe(II) species significantly affect the transformation of metalloids such as Sb at anoxic-oxic redox interfaces. However, the main ROS involved in Sb(III) oxidation and Fe (oxyhydr)oxides formation during co-oxidation of Sb(III) and Fe(II) are still poorly understood. Herein, this study comprehensively investigated the Sb(III) oxidation and immobilization process and mechanism during Fe(II) oxygenation. The results indicated that Sb(III) was oxidized to Sb(V) by the ROS produced in the aqueous and solid phases and then immobilized by formed Fe (oxyhydr)oxides via adsorption and coprecipitation. In addition, chemical analysis and extended X-ray absorption fine structure (EXAFS) characterization demonstrated that Sb(V) could be incorporated into the lattice structure of Fe (oxyhydr)oxides via isomorphous substitution, which greatly inhibited the formation of lepidocrocite (γ-FeOOH) and decreased its crystallinity. Notably, goethite (α-FeOOH) formation was favored at pH 6 due to the greater amount of incorporated Sb(V). Moreover, singlet oxygen (1O2) was identified as the dominant ROS responsible for Sb(III) oxidation, followed by surface-adsorbed ·OHads, ·OH, and Fe(IV). Our findings highlight the overlooked roles of 1O2 and Fe (oxyhydr)oxide formation in Sb(III) oxidation and immobilization during Fe(II) oxygenation and shed light on understanding the geochemical cycling of Sb coupled with Fe in redox-fluctuating environments.

Efficient electro-Fenton degradation of organic pollutants via the synergistic effect of 1O2 and •OH generated on single FeN4 sites

The electro-Fenton with in situ generated 1O2 and •OH is a promising method for the degradation of micropollutants. However, its application is hindered by the lack of catalysts that can efficiently generate 1O2 and •OH from electrochemical oxygen reduction. Herein, N-doped stacked carbon nanosheets supported Fe single atoms (Fe-NSC) with FeN4 sites were designed for simultaneous generation of 1O2 and •OH to enhance electro-Fenton degradation. Due to the synergistic effect of 1O2 and •OH, a variety of contaminants (phenol, 2,4-dichlorophenol, sulfamethoxazole, atrazine and bisphenol A) were efficiently degraded with high kinetic constants of 0.037-0.071 min-1 by the electro-Fenton with Fe-NSC as cathode (-0.6 V vs Ag/AgCl, pH 6). Moreover, the superior performance for electro-Fenton degradation was well maintained in a wide pH range from 3 to 10 even with interference of various inorganic salt ions. It was found that FeN4 sites with pyridinic N coordination were responsible for its good performance for electro-Fenton degradation. Its 1O2 yield was higher than •OH yield, and the contribution of 1O2 was more significant than •OH for pollutant degradation.

Nanoconfinement steers nonradical pathway transition in single atom fenton-like catalysis for improving oxidant utilization

The introduction of single-atom catalysts (SACs) into Fenton-like oxidation promises ultrafast water pollutant elimination, but the limited access to pollutants and oxidant by surface catalytic sites and the intensive oxidant consumption still severely restrict the decontamination performance. While nanoconfinement of SACs allows drastically enhanced decontamination reaction kinetics, the detailed regulatory mechanisms remain elusive. Here, we unveil that, apart from local enrichment of reactants, the catalytic pathway shift is also an important cause for the reactivity enhancement of nanoconfined SACs. The surface electronic structure of cobalt site is altered by confining it within the nanopores of mesostructured silica particles, which triggers a fundamental transition from singlet oxygen to electron transfer pathway for 4-chlorophenol oxidation. The changed pathway and accelerated interfacial mass transfer render the nanoconfined system up to 34.7-fold higher pollutant degradation rate and drastically raised peroxymonosulfate utilization efficiency (from 61.8% to 96.6%) relative to the unconfined control. It also demonstrates superior reactivity for the degradation of other electron-rich phenolic compounds, good environment robustness, and high stability for treating real lake water. Our findings deepen the knowledge of nanoconfined catalysis and may inspire innovations in low-carbon water purification technologies and other heterogeneous catalytic applications.

Efficient degradation of tetracycline via peroxymonosulfate activation by phosphorus-doped biochar loaded with cobalt nanoparticles

The accumulation of tetracycline hydrochloride (TCH) threatens human health because of its potential biological toxicity. Carbon -based materials with easy isolation and excellent performance that can activate peroxymonosulfate (PMS) to generate reactive oxygen species for TCH degradation are essential, but the development of such materials remains a significant challenge. In this study, based on the idea of treating waste, tricobalt tetraoxide loaded P-doped biochar (Co NP-PBC) was synthesised to activate PMS for the degradation of TCH. Possible degradation pathways and intermediate products of TCH were identified using High performance liquid chromatography tandem mass spectrometry (HPLC-MS) detection and density functional theory analysis. Toxicity analysis software was used to predict the toxicity of the intermediate products. Compared to catalysts loaded with Fe and Mn and other Co-based catalysts, Co NP-PBC exhibited an optimal performance (with a kinetic constant of 0.157 min-1 for TCH degradation), and over 99.0% of TCH can be degraded within 20 min. This mechanism demonstrates that the non-free radical oxidation of 1O2 plays a major role in the degradation of TCH. This study provides insights into the purification of wastewater using BC-based catalysts.

Investigation of singlet oxygen and superoxide radical produced from vortex-based hydrodynamic cavitation: Mechanism and its relation to cavitation intensity

Presently, the hydroxyl radical oxidation mechanism is widely acknowledged for the degradation of organic pollutants based on hydrodynamic cavitation technology. The presence and production mechanism of other potential reactive oxygen species (ROS) in the cavitation systems are still unclear. In this paper, singlet oxygen (1O2) and superoxide radical (·O2-) were selected as the target ROS, and their generation rules and mechanism in vortex-based hydrodynamic cavitation (VBHC) were analyzed. Computational fluid dynamics (CFD) were used to simulate and analyze the intensity characteristics of VBHC, and the relationship between the generation of ROS and cavitation intensity was thoroughly revealed. The results show that the operating conditions of the device have a significant and complicated influence on the generation of 1O2 and ·O2-. When the inlet pressure reaches to 4.5 bar, it is more favorable for the generation of 1O2 and ·O2- comparing with those lower pressure. However, higher temperature (45 °C) and aeration rate (15 (L/min)/L) do not always have positive effect on the 1O2 and ·O2- productions, and their optimal parameters need to be analyzed in combination with the inlet pressure. Through quenching experiments, it is found that 1O2 is completely transformed from ·O2-, and ·O2- comes from the transformation of hydroxyl radicals and dissolved oxygen. Higher cavitation intensity is captured and shown more disperse in the vortex cavitation region, which is consistent with the larger production and stronger diffusion of 1O2 and ·O2-. This paper shed light to the generation mechanism of 1O2 and ·O2- in VBHC reactors and the relationship with cavitation intensity. The conclusion provides new ideas for the research of effective ROS in hydrodynamic cavitation process.

Electrocatalytic Generation of Singlet Oxygen via ROS-Mediated Redox Chain Reaction for Efficient Disinfection

The risk of harmful microorganisms to ecosystems and human health has stimulated exploration of singlet oxygen (1O2)-based disinfection. It can be potentially generated via an electrocatalytic process, but is limited by the low production yield and unclear intermediate-mediated mechanism. Herein, we designed a two-site catalyst (Fe/Mo-N/C) for the selective 1O2 generation. The Mo sites enhance the generation of 1O2 precursors (H2O2), accompanied by the generation of intermediate •HO2/•O2-. The Fe site facilitates activation of H2O2 into •OH, which accelerates the •HO2/•O2- into 1O2. A possible mechanism for promoting 1O2 production through the ROS-mediated chain reaction is reported. The as-developed electrochemical disinfection system can kill 1 × 107 CFU mL-1 of E. coli within 8 min, leading to cell membrane damage and DNA degradation. It can be effectively applied for the disinfection of medical wastewater. This work provides a general strategy for promoting the production of 1O2 through electrocatalysis and for efficient electrochemical disinfection.

Switching reactive oxygen species reactions derived from Mn-Pt anchored zeolite for selective catalytic ozonation

Rationally switching reactive oxygen species (ROS) reactions in advanced oxidation processes (AOPs) is urgently needed to improve the adaptability and efficiency for the engineering application. Herein we synthesized bimetallic Mn-Pt catalysts based on zeolite to realize the switching of ROS reactions in catalytic ozonation for sustainable degradation of organic pollutants from water. The ROS reactions switched from singlet oxygen (1O2, 71.01%) to radical-dominated (93.79%) pathway by simply introducing defects and changing Pt/Mn ratios. The oxygen vacancy induced by anchoring Mn-Pt species from zeolite external surface (MnPt/H-Beta) to internal framework (MnPt@Si-Beta) exposes more electron-rich Pt2+/Pt4+ redox sites, accelerating the decomposition of O3 to generate •OH via electron transfer and switching ROS reactions. The Mn site acted as a bridge plays a critical role in conducting electrons from organic pollutants to Pt sites, which solidly solves the electron loss of catalysts, facilitating the efficient degradation of pollutants. A 34.7-fold increase in phenol degradation compared with the non-catalytic ozonation and an excellent catalytic stability are achieved by MnPt@Si-Beta/O3. The 1O2-dominated ROS reaction originated from MnPt/H-Beta/O3 exhibits superior performances in anti-interference for Cl-, HCO3-, NO3-, and SO4-. This work establishes a novel strategy for switching ROS reactions to expand the targeted applications of O3 based AOPs for environmental remediation.

Voltammetric Detection of Singlet Oxygen Enabled by Nanogap Scanning Electrochemical Microscopy

Despite the significance of singlet oxygen (1O2) in several biological, chemical, and energy storage systems, its voltammetric reduction at an electrode remains unreported. We address this issue using nanogap scanning electrochemical microscopy (SECM) in substrate-generation/tip-collection mode. Our investigation reveals a reductive process on the SECM tip at -1.0 V (vs Fc+/Fc) during the breakdown of the Li2CO3 substrate in deuterated acetonitrile. Notably, this value is approximately 0.9 V more positive than the reduction potential of triplet oxygen (3O2), consistent with thermodynamic estimates for the energy of the formation of 1O2. This finding holds significant implications for understanding the reaction mechanisms involving 1O2 in nonaqueous media.

Photo-thermal activation of persulfate for the efficient degradation of synthetic and real industrial wastewaters: System optimization and cost estimation

The photo-thermal activation of persulfate (PS) was carried out to degrade various pollutants such as reactive blue-222 (RB-222) dye, sulfamethazine, and atrazine. Optimizing the operating parameters showed that using 0.90 g/L of PS at pH 7, temperature of 90 °C, initial dye concentration of 21.60 mg/L, and reaction time of 120 min could attain a removal efficiency of 99.30%. The degradation mechanism was explored indicating that hydroxyl and sulfate radicals were the prevailing reactive species. The degradation percentages of 10 mg/L of sulfamethazine and atrazine were 83.30% and 70.60%, respectively, whereas the mineralization ratio was 63.50% in the case of real textile wastewater under the optimal conditions at a reaction time of 120 min. The treatment cost per 1 m3 of real wastewater was appraised to be 1.13 $/m3 which assured the inexpensiveness of the proposed treatment system. This study presents an effective and low-cost treatment system that can be implemented on an industrial scale.

Copper-decorated strategy based on defect-rich NH2-MIL-125(Ti) boosts efficient photocatalytic degradation of methyl mercaptan under sunlight

Photocatalysis has received significant attention as a technology that can solve environmental problems. Metal-organic frameworks are currently being used as novel photocatalysts but are still limited by the rapid recombination of photogenerated carriers, low photogenerated electron migration efficiency and poor solar light utilization rate. In this work, a novel photocatalyst was successfully constructed by introducing Cu species into thermal activated mixed-ligand NH2-MIL-125 (Ti) via defect engineering strategy. The constructed defect structure not only provided 3D-interconnected gas transfer channels, but also offered suitable space to accommodate introduced Cu species. For the most effective photocatalyst 0.2Cu/80%NH2-MIL-125 (300 °C) with optimized Cu content, the photocatalytic degradation rate of CH3SH achieved 4.65 times higher than that of pristine NH2-MIL-125 under visible light (λ > 420 nm). At the same time, it showed great degradation efficiency under natural sunlight, 100 ppm CH3SH was completely removed within 25 min in full solar light illumination. The improved catalytic efficiency is mainly due to the synergistic effect of the integrated Schottky junction and rich-defective NH2-MIL-125, which improved the bandgap and band position, and thus facilitated the separation and transfer of the photo-generated carriers. This work provided a facile way to integrate Schottky junctions and rich-defective MOFs with high stability. Due to its excellent degradation performance under sunlight, it also offered a prospective strategy for rational design of high-efficiency catalysts applied in environmental technologies.