Adsorbed copper on urea modified activated biochar catalyzed H2O2 for oxidative degradation of sulfadiazine：Degradation mechanism and toxicity assessment.

The combined pollution of heavy metals and organic compounds usually occurs simultaneously and induces high toxicity. The technology of simultaneous removal of combined pollution is lacking and the removal mechanism is not clear. Sulfadiazine (SD), a widely used antibiotic, was used as a model contaminant. Urea modified sludge-based biochar (USBC) was prepared and used to catalyze H2O2 to remove the combined pollution of Cu2+ and sulfadiazine (SD) without causing secondary pollution. After 2 h, the removal rates of SD and Cu2+ were 100 and 64.8%, respectively. Cu2+ adsorbed on the surface of USBC accelerated the activation of H2O2 by the USBC catalyzed by CO bond to produce hydroxyl radical (•OH) and single oxygen (1O2) to degrade SD. Twenty-three intermediate products were detected, most of which were completely decomposed into CO2 and H2O. The toxicity was significantly reduced in the combined polluted system. This study highlights the potential of the low-cost technology based on sludge reuse and its inherent significance in reducing the toxic risk of combined pollution in the environment.

Faster electron injection and higher interface reactivity in g-C3N4/Fe2O3 nanohybrid for efficient photo-Fenton-like activity toward antibiotics degradation.

Two different morphologies of Fe2O3 involving nanodots and nanosheets were deposited on g-C3N4 nanosheets by simple in-situ deposition and impregnation-hydrothermal methods, respectively. Structural effect of Fe2O3 on photo-Fenton-like activity and charge transfer at the interface in these two g-C3N4/Fe2O3 hybrids were studied. Detail characterizations on charge transfer kinetics revealed that g-C3N4/nanodot-Fe2O3 structure showed faster electron injection rate and higher injection efficiency (≈0.084 ns-1 and ≈27.5%) than g-C3N4/nanosheet-Fe2O3 counterpart (≈0.054 ns-1 and ≈19.5%). Stronger intimate junction between g-C3N4 nanosheets and Fe2O3 nanodots was believed to be the reason for faster and more efficient electron injection. In addition, stronger interaction with tetracycline and higher reactivity with H2O2 at the interface were observed for g-C3N4/nanodot-Fe2O3 compared with g-C3N4/nanosheet-Fe2O3. Thereby, under visible light stimulation, g-C3N4/nanodot-Fe2O3 demonstrated higher photo-Fenton-like tetracycline removal efficiency and rate (≈87% and ≈0.037 min-1) than g-C3N4/nanosheet-Fe2O3 (≈57% and ≈0.016 min-1). Furthermore, g-C3N4/nanodot-Fe2O3 junction can remain robust catalytic performance under various conditions (recycle experiment, real environment, different initial pHs and temperatures, anion coexistence, and other contaminants removal) and possible tetracycline degradation pathways were proposed. This study provided deep insights into structure-activity relationship and electron transfer between g-C3N4 and nanostructured Fe2O3, which can open a new avenge to develop Fe2O3-based photo-Fenton catalysts with high efficiencies for antibiotic wastewaters remediation.

Highly efficient adhesion and inactivation of Escherichia coli on visible-light-driven amino-functionalized BiOBr hybrids.

Amino groups are successfully introduced on the surface of BiOBr nanosheets through a facile ammonia functionalization method. The surface morphology of the modified BiOBr hybrids varies on the concentration of applied ammonia solution. The active {001}-facet-exposed feature of nanosheets is well retained after amino-functionalization. With generation of small Bi2O4 nanoparticles on the surface of BiOBr nanosheets, the light adsorption of hybrids gradually shifts to the near infrared range. Compared to pure BiOBr with negligible activity, BOB10 hybrids exhibit superior photocatalytic activity for bacterial inactivation, with 7-log cells reduction in 40 min under LED irradiation. Amino functionalization endows BOB10 hybrids excellent adhesion capability towards surface negatively-charged bacterium Escherichia coli, which can significantly shortened access distance of the predominant •O2- and h+ guaranteeing their inactivation ability on cells membrane, thus leading to remarkable bacterial inactivation performance.

Photocatalytic inactivation and destruction of harmful microalgae Karenia mikimotoi under visible-light irradiation: Insights into physiological response and toxicity assessment.

Harmful algal blooms (HABs) caused by Karenia mikimotoi have frequently happened in coastal waters worldwide, causing serious damages to marine ecosystems and economic losses. Photocatalysis has potential to in-situ inhibit algal growth using sustainable sunlight. However, the inactivation and detoxification mechanisms of microalgae in marine environment have not been systematically investigated. In this work, for the first time, visible-light-driven photocatalytic inactivation of K. mikimotoi was attempted using g-C3N4/TiO2 immobilized films as a model photocatalyst. The inactivation efficiency could reach 64% within 60 min, evaluated by real-time in vivo chlorophyll-a fluorometric method. The immobilized photocatalyst films also exhibited excellent photo-stability and recyclability. Mechanisms study indicated photo-generated h+ and 1O2 were the dominant reactive species. Algal cell rupture process was monitored by fluorescent microscope combined with SEM observation, which confirmed the damage of cell membrane followed by the leakage of the intracellular components including the entire cell nucleus. The physiological responses regarding up-regulation of antioxidant enzyme activity (i.e. CAT and SOD), intracellular ROSs level and lipid peroxidation were all observed. Moreover, the intracellular release profile and acute toxicity assessment indicated the toxic K. mikimotoi was successfully detoxified, and the released organic matter had no cytotoxicity. This work not only provides a potential new strategy for in-situ treatment of K. mikimotoi using sunlight at sea environments, but also creates avenue for understanding the inactivation and destruction mechanisms of marine microalgae treated by photocatalysis and the toxicity impacts on the marine environments.

Dramatically enhanced degradation of recalcitrant organic contaminants in MgO2/Fe(III) Fenton-like system by organic chelating agents.

Herein, the application of organic acids as chelating agent, including citric acid (CA), tartaric acid (TA), oxalic acid (OA) and ethylenediaminetetraacetic acid (EDTA), to enhance the degradation performance of MgO2/Fe(III) system was investigated in the terms of chelating agent dosage, Fe(III) dosage, reaction temperature, initial solution pH and inorganic anion. When the molar ratio of MgO2/Fe(III)/chelating agent was 1 : 0.7 : 0.3, the degradation efficiencies of Rhodamine B (RhB) increased from 6.7% (without chelating agent) to 42.3%, 98.5%, 48.9% and 25.8% within 30 min for CA, TA, OA, and EDTA, respectively. The promotion effect was mainly attributed to the chelation between chelating agents and Fe(III), rather than the acidification of chelating agents. The pseudo-first-order kinetic model well fitted RhB degradation in MgO2/Fe(III)/TA system, and the kinetic rate constant reached up to 0.295 min-1. Hydroxyl radical was confirmed to be the dominant active species to degrade organics in the MgO2/Fe(III)/TA system. Notably, the degradation system could work in a broad pH (3-11) and temperature (5-35 °C) range. Moreover, the MgO2/Fe(III)/TA system can also effectively degrade methylene blue, tetracycline and bisphenol A. This work provided a new, efficient and environmentally-friendly Fenton-like system for stubborn contaminant treatment.

Efficient Ammonia Electrosynthesis from Nitrate on Strained Ruthenium Nanoclusters.

The limitations of the Haber-Bosch reaction, particularly high-temperature operation, have ignited new interests in low-temperature ammonia-synthesis scenarios. Ambient N2 electroreduction is a compelling alternative but is impeded by a low ammonia production rate (mostly <10 mmol gcat-1 h-1), a small partial current density (<1 mA cm-2), and a high-selectivity hydrogen-evolving side reaction. Herein, we report that room-temperature nitrate electroreduction catalyzed by strained ruthenium nanoclusters generates ammonia at a higher rate (5.56 mol gcat-1 h-1) than the Haber-Bosch process. The primary contributor to such performance is hydrogen radicals, which are generated by suppressing hydrogen-hydrogen dimerization during water splitting enabled by the tensile lattice strains. The radicals expedite nitrate-to-ammonia conversion by hydrogenating intermediates of the rate-limiting steps at lower kinetic barriers. The strained nanostructures can maintain nearly 100% ammonia-evolving selectivity at >120 mA cm-2 current densities for 100 h due to the robust subsurface Ru-O coordination. These findings highlight the potential of nitrate electroreduction in real-world, low-temperature ammonia synthesis.

Sterilization of Escherichia coli by Photothermal Synergy of WO3-x/C Nanosheet under Infrared Light Irradiation.

The application of photocatalytic sterilization technology for the sterilization of water has been broadly studied in recent years. However, developing photocatalysts with high disinfection efficiency remains an urgent challenge. Tungsten trioxide with coexisting oxygen vacancies and carbon coating (WO3-x/C) has been successfully synthesized toward the photothermal inactivation of Escherichia coli. Oxygen vacancies and carbon coating bring WO3-x/C strong absorption in the infrared region and enhance the carrier separation efficiency. As a result, a higher sterilization rate is obtained compared to WO3. WO3-x/C can completely inactivate E. coli under infrared light within 40 min through photothermal synergy process. During the process of inactivating bacteria over WO3-x/C, E. coli is killed by the destruction of their cell membrane to decrease the activity of enzymes and release the cell contents, which can be ascribed to the efficient generation of reactive oxygen species (O2•- and •OH) and thermal effect. This work demonstrates a novel approach for engineering efficient and energy-saving catalysts for water sterilization.

Photocatalytic Bacterial Inactivation by a Rape Pollen-MoS2 Biohybrid Catalyst: Synergetic Effects and Inactivation Mechanisms.

A novel and efficient 3D biohybrid photocatalyst, defective MoS2 nanosheets encapsulated carbonized rape pollen, was fabricated and applied to water disinfection. The rape pollen-MoS2 (PM) biohybrid showed excellent dispersibility, high stability, and efficient charge-carrier separation and migration ability, resulting in the highly enhanced photocatalytic inactivation performance toward various waterborne bacteria under different light sources. The inactivation mechanisms were systematically investigated. Reactive species (RSs), including electrons, holes, and reactive oxygen species (•O2- and •OH), played major roles in inactivating bacteria. The antioxidant system of bacteria exhibited a self-protection capacity by eliminating the photogenerated RSs from PM biohybrid at the early stage of inactivation. With the accumulation of RSs, the cell membrane and membrane-associated functions were destroyed, as suggested by the collapse of cell envelope and subsequent loss of cell respiration and ATP synthesis capacity. The microscopic images further confirmed the destruction of the bacterial membrane. After losing the membrane barrier, the oxidation of cytoplasmic proteins and lipids caused by invaded RSs occurred readily. Finally, the leakage of DNA and RNA announced the irreversible death of bacteria. These results indicated that the bacterial inactivation began with the membrane rupture, followed by the oxidation and leakage of intracellular substances. This work not only provided a new insight into the combination of semiconductors with earth-abundant biomaterials for fabricating high-performance photocatalysts, but also revealed the underlying mechanisms of photocatalytic bacterial inactivation in depth.

Protection Mechanisms of Periphytic Biofilm to Photocatalytic Nanoparticle Exposure.

Researchers are devoting great effort to combine photocatalytic nanoparticles (PNPs) with biological processes to create efficient environmental purification technologies (i.e., intimately coupled photobiocatalysis). However, little information is available to illuminate the responses of multispecies microbial aggregates against PNP exposure. Periphytic biofilm, as a model multispecies microbial aggregate, was exposed to three different PNPs (CdS, TiO2, and Fe2O3) under xenon lamp irradiation. There were no obvious toxic effects of PNP exposure on periphytic biofilm as biomass, chlorophyll content, and ATPase activity were not negatively impacted. Enhanced production of extracellular polymetric substances (EPS) is the most important protection mechanism of periphytic biofilm against PNPs exposure. Although PNP exposure produced extracellular superoxide radicals and caused intracellular reactive oxygen species (ROS) accumulation in periphytic biofilm, the interaction between EPS and PNPs could mitigate production of ROS while superoxide dismutase could alleviate biotic ROS accumulation in periphytic biofilm. The periphytic biofilms changed their community composition in the presence of PNPs by increasing the relative abundance of phototrophic and high nutrient metabolic microorganisms (families Chlamydomonadaceae, Cyanobacteriacea, Sphingobacteriales, and Xanthomonadaceae). This study provides insight into the protection mechanisms of microbial aggregates against simultaneous photogenerated and nanoparticle toxicity from PNPs.

Photocatalytic defluorination of perfluorooctanoic acid by surface defective BiOCl: Fast microwave solvothermal synthesis and photocatalytic mechanisms.

There is an urgent need for developing cost-effective methods for the treatment of perfluorooctanoic acid (PFOA) due to its global emergence and potential risks. In this study, taking surface-defective BiOCl as an example, a strategy of surface oxygen vacancy modulation was used to promote the photocatalytic defluorination efficiency of PFOA under simulated sunlight irradiation. The defective BiOCl was fabricated by a fast microwave solvothermal method, which was found to induce more surface oxygen vacancies than conventional solvothermal and precipitation methods. As a result, the as-prepared BiOCl showed significantly enhanced defluorination efficiency, which was 2.7 and 33.8 times higher than that of BiOCl fabricated by conventional solvothermal and precipitation methods, respectively. Mechanistic studies indicated that the defluorination of PFOA follows a direct hole (h+) oxidation pathway with the aid of •OH, while the oxygen vacancies not only promote charge separation but also facilitate the intimate contact between the photocatalyst surface and PFOA by coordinating with its terminal carboxylate group in a bidentate or bridging mode. This work will provide a general strategy of oxygen vacancy modulation by microwave-assisted methods for efficient photocatalytic defluorination of PFOA in the environment using sunlight as the energy source.

Enhanced Visible-Light-Driven Photocatalytic Bacterial Inactivation by Ultrathin Carbon-Coated Magnetic Cobalt Ferrite Nanoparticles.

Ultrathin hydrothermal carbonation carbon (HTCC)-coated cobalt ferrite (CoFe2O4) composites with HTCC coating thicknesses between 0.62 and 4.38 nm were fabricated as novel, efficient, and magnetically recyclable photocatalysts via a facile, green approach. The CoFe2O4/HTCC composites showed high magnetization and low coercivity, which favored magnetic separation for reuse. The results show that the close coating of HTCC on CoFe2O4 nanoparticles enhanced electron transfer and charge separation, leading to a significant improvement in photocatalytic efficiency. The composites exhibited superior photocatalytic inactivation toward Escherichia coli K-12 under visible-light irradiation, with the complete inactivation of 7 log10 cfu·mL-1 of bacterial cells within 60 min. The destruction of bacterial cell membranes was monitored by field-effect scanning electron microscopy analysis and fluorescence microscopic images. The bacterial inactivation mechanism was investigated in a scavenger study, and •O2, H2O2, and h+ were identified as the major reactive species for bacterial inactivation. Multiple cycle runs revealed that these composites had excellent stability and reusability. In addition, the composites showed good photocatalytic bacterial inactivation performance in authentic water matrices such as surface water samples and secondarily treated sewage effluents. The results of this work indicate that CoFe2O4/HTCC composites have great potential in large-scale photocatalytic disinfection operations.

A New Concept of Promoting Nitrate Reduction in Surface Waters: Simultaneous Supplement of Denitrifiers, Electron Donor Pool, and Electron Mediators.

The efficiency of biological nitrate reduction depends on the community composition of microorganisms, the electron donor pool, and the electron mediators participating in the biological reduction process. This study aims at creating an in situ system comprising of denitrifiers, electron donors, and electron mediators to reduce nitrate in surface waters. The ubiquitous periphytic biofilm in waters was employed to promote in situ nitrate reduction in the presence of titanium dioxide (TiO2) nanoparticles (NPs). The nitrate removal rate in the periphytic biofilm and TiO2 NPs system was significantly higher than the control (only periphytic biofilm or TiO2 NPs). TiO2 NPs optimized the community composition of periphytic biofilm for nitrate reduction by increasing the relative abundance of four dominant denitrifying bacteria. Periphytic biofilm showed a substantial increase in extracellular polymeric substance, especially the humic acid and protein content, due to the presence of TiO2 NPs. The synergistic action of humic acid, protein, denitrifying bacteria of the periphytic biofilm, and TiO2 NPs contributed to 80% of the nitrate reduction. The protein and humic acid, acting as electron mediators, facilitated the transfer of exogenous electrons from photoexcited TiO2 NPs to periphytic biofilm containing denitrifiers, which enhanced nitrate reduction in surface waters.

Gas-Permeable Membrane-Based Conductivity Probe Capable of In Situ Real-Time Monitoring of Ammonia in Aquatic Environments.

Aquatic ammonia has toxic effects on aquatic life. This work reports a gas-permeable membrane-based conductivity probe (GPMCP) developed for real-time monitoring of ammonia in aquatic environments. The GPMCP innovatively combines a gas-permeable membrane with a boric acid receiving phase to selectively extract ammonia from samples and form ammonium at the inner membrane interface. The rate of the receiving phase conductivity increase is directly proportional to the instantaneous ammonia concentration in the sample, which can be rapidly and sensitively determined by the embedded conductivity detector. A precalibration strategy was developed to eliminate the need for an ongoing calibration. The analytical principle and GPMCP performance were systematically validated. The laboratory results showed that ammonia concentrations ranging from 2 to 50 000 µg L-1 can be detected. The field deployment results demonstrated the GPMCP's ability to obtain high-resolution continuous ammonia concentration profiles and the absolute average ammonia concentration over a prolonged deployment period. By inputting the temperature and pH data, the ammonium concentration can be simultaneously derived from the corresponding ammonia concentration. The GPMCP embeds a sophisticated analytical principle with the inherent advantages of high selectivity, sensitivity, and accuracy, and it can be used as an effective tool for long-term, large-scale, aquatic-environment assessments.

Dual Roles of Capsular Extracellular Polymeric Substances in Photocatalytic Inactivation of Escherichia coli: Comparison of E. coli BW25113 and Isogenic Mutants.

The dual roles of capsular extracellular polymeric substances (EPS) in the photocatalytic inactivation of bacteria were demonstrated in a TiO2-UVA system, by comparing wild-type Escherichia coli strain BW25113 and isogenic mutants with upregulated and downregulated production of capsular EPS. In a partition system in which direct contact between bacterial cells and TiO2 particles was inhibited, an increase in the amount of EPS was associated with increased bacterial resistance to photocatalytic inactivation. In contrast, when bacterial cells were in direct contact with TiO2 particles, an increase in the amount of capsular EPS decreased cell viability during photocatalytic treatment. Taken together, these results suggest that although capsular EPS can protect bacterial cells by consuming photogenerated reactive species, it also facilitates photocatalytic inactivation of bacteria by promoting the adhesion of TiO2 particles to the cell surface. Fluorescence microscopy and scanning electron microscopy analyses further confirmed that high capsular EPS density led to more TiO2 particles attaching to cells and forming bacterium-TiO2 aggregates. Calculations of interaction energy, represented by extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) potential, suggested that the presence of capsular EPS enhances the attachment of TiO2 particles to bacterial cells via acid-base interactions. Consideration of these mechanisms is critical for understanding bacterium-nanoparticle interactions and the photocatalytic inactivation of bacteria.

Red Phosphorus: An Earth-Abundant Elemental Photocatalyst for "Green" Bacterial Inactivation under Visible Light.

Earth-abundant red phosphorus was found to exhibit remarkable efficiency to inactivate Escherichia coli K-12 under the full spectrum of visible light and even sunlight. The reactive oxygen species (•OH, •O2(-), H2O2), which were measured and identified to derive mainly from photogenerated electrons in the conduction band using fluorescent probes and scavengers, collectively contributed to the good performance of red phosphorus. Especially, the inactivated-membrane function enzymes were found to be associated with great loss of respiratory and ATP synthesis activity, the kinetics of which paralleled cell death and occurred much earlier than those of cytoplasmic proteins and chromosomal DNA. This indicated that the cell membrane was a vital first target for reactive oxygen species oxidation. The increased permeability of the cell membrane consequently accelerated intracellular protein carboxylation and DNA degradation to cause definite bacterial death. Microscopic analyses further confirmed the cell destruction process starting with the cell envelope and extending to the intracellular components. The red phosphorus still maintained good performance even after recycling through five reaction cycles. This work offers new insight into the exploration and use of an elemental photocatalyst for "green" environmental applications.

Advances in photocatalytic disinfection of bacteria: Development of photocatalysts and mechanisms.

Photocatalysis has attracted worldwide attention due to its potential in solar energy conversion. As a "green" advanced oxidation technology, it has been extensively used for water disinfection and wastewater treatment. This article provides a review of the recent progress in solar energy-induced photocatalytic disinfection of bacteria, focusing on the development of highly efficient photocatalysts and their underlying mechanisms in bacterial inactivation. The photocatalysts are classified into TiO2-based and non-TiO2-based systems, as TiO2 is the most investigated photocatalyst. The synthesis methods, modification strategies, bacterial disinfection activities and mechanisms of different types of photocatalysts are reviewed in detail. Emphasis is given to the modified TiO2, including noble metal deposition, non-metal doping, dye sensitization and composite TiO2, along with typical non-TiO2-based photocatalysts for bacterial disinfection, including metal oxides, sulfides, bismuth metallates, graphene-based photocatalysts, carbon nitride-based photocatalysts and natural photocatalysts. A simple and versatile methodology by using a partition system combined with scavenging study is introduced to study the photocatalytic disinfection mechanisms in different photocatalytic systems. This review summarizes the current state of the work on photocatalytic disinfection of bacteria, and is expected to offer useful insights for the future development in the field.

Systematic approach to in-depth understanding of photoelectrocatalytic bacterial inactivation mechanisms by tracking the decomposed building blocks.

A systematic approach was developed to understand, in-depth, the mechanisms involved during the inactivation of bacterial cells using photoelectrocatalytic (PEC) processes with Escherichia coli K-12 as the model microorganism. The bacterial cells were found to be inactivated and decomposed primarily due to attack from photogenerated H2O2. Extracellular reactive oxygen species (ROSs), such as H2O2, may penetrate into the bacterial cell and cause dramatically elevated intracellular ROSs levels, which would overwhelm the antioxidative capacity of bacterial protective enzymes such as superoxide dismutase and catalase. The activities of these two enzymes were found to decrease due to the ROSs attacks during PEC inactivation. Bacterial cell wall damage was then observed, including loss of cell membrane integrity and increased permeability, followed by the decomposition of cell envelope (demonstrated by scanning electronic microscope images). One of the bacterial building blocks, protein, was found to be oxidatively damaged due to the ROSs attacks, as well. Leakage of cytoplasm and biomolecules (bacterial building blocks such as proteins and nucleic acids) were evident during prolonged PEC inactivation process. The leaked cytoplasmic substances and cell debris could be further degraded and, ultimately, mineralized with prolonged PEC treatment.

Adenovirus inactivation by in situ photocatalytically and photoelectrocatalytically generated halogen viricides.

This study investigates and compares the virucidal performances of photocatalytic (PC) and photoelectrocatalytic (PEC) treatments in the presence and absence of halides, such as Br- and Cl-, under comparable experimental conditions. The results confirm that the PC virucidal efficiency can be enhanced in the presence of low halide concentrations (e.g., X = Br- or Cl-) and further enhanced by applying potential bias onto the photoanode in a PEC system. The PEC treatment in the presence of 1.0 mM Br (PEC-Br) shows the highest virucidal efficiency, enabling complete inactivation of a ∼1000 TCID50 replication-deficient recombinant adenovirus (RDRADS) population within 31.7 s. The superior virucidal performances of PEC-X treatments can be attributed to the increased production of active oxygen species and additional viricides resulting from the PEC halide oxidation, as well as prolonged lifetime of photoholes (h+ ) for direct inactivation. The findings of this work confirm that new forms of active species generated in situ via a PC or PEC process are effective for viruses.

Mechanism of antibiotic resistance spread during sub-lethal ozonation of antibiotic-resistant bacteria with different resistance targets.

The increase and spread of antibiotic-resistant bacteria (ARB) in aquatic environments and the dissemination of antibiotic resistance genes (ARGs) greatly impact environmental and human health. It is necessary to understand the mechanism of action of ARB and ARGs to formulate measures to solve this problem. This study aimed to determine the mechanism of antibiotic resistance spread during sub-lethal ozonation of ARB with different antibiotic resistance targets, including proteins, cell walls, and cell membranes. ARB conjugation and transformation frequencies increased after exposure to 0-1.0 mg/L ozone for 10 min. During sub-lethal ozonation, compared with control groups not stimulated by ozone, the conjugative transfer frequencies of E. coli DH5α (CTX), E. coli DH5α (MCR), and E. coli DH5α (GEN) increased by 1.35-2.02, 1.13-1.58, and 1.32-2.12 times, respectively; the transformation frequencies of E. coli DH5α (MCR) and E. coli DH5α (GEN) increased by 1.49-3.02 and 1.45-1.92 times, respectively. When target inhibitors were added, the conjugative transfer frequencies of antibiotics targeting cell wall and membrane synthesis decreased 0.59-0.75 and 0.43-0.76 times, respectively, while that for those targeting protein synthesis increased by 1-1.38 times. After inhibitor addition, the transformation frequencies of bacteria resistant to antibiotics targeting the cell membrane and proteins decreased by 0.76-0.89 and 0.69-0.78 times, respectively. Cell morphology, cell membrane permeability, reactive oxygen species, and antioxidant enzymes changed with different ozone concentrations. Expression of most genes related to regulating different antibiotic resistance targets was up-regulated when bacteria were exposed to sub-lethal ozonation, further confirming the target genes playing a crucial role in the inactivation of different target bacteria. These results will help guide the careful utilization of ozonation for bacterial inactivation, providing more detailed reference information for ozonation oxidation treatment of ARB and ARGs in aquatic environments.

Graphene and g-C3N4 nanosheets cowrapped elemental α-sulfur as a novel metal-free heterojunction photocatalyst for bacterial inactivation under visible-light.

A new class of metal-free heterojunction photocatalysts was prepared by wrapping reduced graphene oxide (RGO) and g-C3N4 (CN) sheets on crystals of cyclooctasulfur (α-S8). Two distinctive structures were fabricated by wrapping RGO and CN sheets in different orders. The first was RGO sheets sandwiched in heterojunction of CN sheets and α-S8 (i.e., CNRGOS8), while the second structure was the other way around (i.e., RGOCNS8). Both structures exhibited antibacterial activity under visible-light irradiation. CNRGOS8 showed stronger bacterial inactivation than RGOCNS8 in aerobic conditions. However, RGOCNS8 was more active than CNRGOS8 under anaerobic condition. A possible mechanism was proposed to explain the differences between photocatalytic oxidative inactivation and reductive inactivation. As a proof-of-concept, this work could offer new inroads into exploration and utilization of graphene sheets and g-C3N4 sheets cowrapped nanocomposites for environmental applications.