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Recent discovery of vesicle-cloaked virus clusters (i.e., viral vesicles) has greatly challenged the central paradigm of viral transmission and infection as a single virion. To understand the environmental transmission of viral vesicles, we used an in vivo model to investigate their environmental persistence and engineering control by disinfection. Murine rotavirus vesicles maintained both their integrity and infectivity after incubation in filtered freshwater and wastewater for at least 7 days, with 24.5-27.5% of the vesicles still intact at 16 weeks after exposure to both waters. Free chlorine disinfection at a dosage of 13.3 mg min L(−1) did not decompose murine rotavirus vesicles, and it was much less effective in inactivating rotaviruses inside vesicles than free rotaviruses, based on the quantification of rotavirus shedding in mouse stool and rotavirus replication in small intestines. Rotavirus vesicles may be more environmentally transmissible than free rotaviruses regardless of disinfection. Vesicle-mediated en bloc transmission could be responsible for vesicles’ resistance to disinfection, due to an increased multiplicity of infection and/or genetic recombination or reassortment to promote infection. Our work highlights the environmental, biological, and public health significance of viral vesicles, and the findings call for urgent action in advancing disinfection for pathogen control.

Waterborne human pathogenic viruses challenge global health and economy. Viruses were long believed to transmit among hosts as individual, free particles. However, recent evidence indicates that viruses also transmit in populations, so-called en bloc transmission, by either interacting with co-existing bacteria, free-living amoebas, and other higher organisms through endosymbiosis and surface binding, or by being clustered inside membrane-bound vesicles or simply self-aggregating with themselves. En bloc transmission of viruses and virus-microbiome interactions could enable viruses to enhance their infectivity, increase environmental persistence, and resist inactivation from disinfection. Overlooking this type of transmission and virus-microbiome interactions may underestimate the environmental and public health risks of the viruses. We herein provide a critical perspective on waterborne human pathogenic viruses in complex microbial communities to elucidate the environmental implication of virus-microbiome interactions on virus infectivity, persistence, and disinfection. This perspective also provides insights on advancing disinfection and sanitation guidelines and regulations to protect the public health.

The global COVID-19 pandemic has raised great public concern about the airborne transmission of viral pathogens. Virus-laden aerosols with small size could be suspended in the air for a long duration and remain infectious. Among a series of measures implemented to mitigate the airborne spread of infectious diseases, filtration by face masks, respirators, and air filters is a potent nonpharmacologic intervention. Compared with conventional air filtration media, nanofibrous membranes fabricated via electrospinning are promising candidates for controlling airborne viruses due to their desired characteristics, i.e., a reduced pore size (submicrometers to several micrometers), a larger specific surface area and porosity, and retained surface and volume charges. So far, a wide variety of electrospun nanofibrous membranes have been developed for aerosol filtration, and they have shown excellent filtration performance. However, current studies using electrospinning for controlling airborne viruses vary significantly in the practice of aerosol filtration tests, including setup configurations and operations. The discrepancy among various studies makes it difficult, if not impossible, to compare filtration performance. Therefore, there is a pressing need to establish a standardized protocol for evaluating the electrospun nanofibrous membranes' performance for removing viral aerosols. In this perspective, we first reviewed the properties and performance of diverse filter media, including electrospun nanofibrous membranes, for removing viral aerosols. Next, aerosol filtration protocols for electrospun nanofibrous membranes were discussed with respect to the aerosol generation, filtration, collection, and detection. Thereafter, standardizing the aerosol filtration test system for electrospun nanofibrous membranes was proposed. In the end, the future advancement of electrospun nanofibrous membranes for enhanced air filtration was discussed. This perspective provides a comprehensive understanding of status and challenges of electrospinning for air filtration, and it sheds light on future nanomaterial and protocol development for controlling airborne viruses, preventing the spread of infectious diseases, and beyond.

Understanding the transformation of graphitic carbon nitride (g-C3N4) is essential to assess nanomaterial robustness and environmental risks. Using an integrated experimental and simulation approach, our work has demonstrated that the photoinduced hole (h+) on g-C3N4 nanosheets significantly enhances nanomaterial decomposition under •OH attack. Two g-C3N4 nanosheet samples D and M2 were synthesized, among which M2 had more pores, defects, and edges, and they were subjected to treatments with •OH alone and both •OH and h+. Both D and M2 were oxidized and released nitrate and soluble organic fragments, and M2 was more susceptible to oxidation. Particularly, h+ increased the nitrate release rate by 3.37-6.33 times even though the steady-state concentration of •OH was similar. Molecular simulations highlighted that •OH only attacked a limited number of edge-site heptazines on g-C3N4 nanosheets and resulted in peripheral etching and slow degradation, whereas h+ decreased the activation energy barrier of C-N bond breaking between heptazines, shifted the degradation pathway to bulk fragmentation, and thus led to much faster degradation. This discovery not only sheds light on the unique environmental transformation of emerging photoreactive nanomaterials but also provides guidelines for designing robust nanomaterials for engineering applications.

Airborne transmission of SARS-CoV-2 plays a critical role in spreading COVID-19. To protect public health, we designed and fabricated electrospun nanofibrous air filters that hold promise for applications in personal protective equipment and indoor environment. Due to ultrafine nanofibers (∼300 nm), the electrospun air filters had a much smaller pore size compared to the surgical mask and cloth masks (a couple of microns versus tens to hundreds of microns). A coronavirus strain was used to generate aerosols for filtration efficiency tests, which can better represent SARS-CoV-2 than other agents used for aerosol generation in previous studies. The electrospun air filters showed excellent performance by capturing up to 99.9% of coronavirus aerosols, which outperformed many commercial face masks. In addition, since NaCl aerosols have been widely used in filtration tests, we compared the filtration efficiency obtained from the coronavirus aerosols and the NaCl aerosols. The NaCl aerosols were demonstrated as an eligible surrogate for the coronavirus aerosols in the filtration tests, when air filters and face masks with diverse pore sizes, morphologies, and efficiencies were used. Our work paves a new avenue for advancing air filtration by developing electrospun nanofibrous air filters for controlling SARS-CoV-2 airborne transmission. Moreover, the removal efficiency of the NaCl aerosols can be reasonably translated into understanding how air filters capture the coronavirus aerosols. Table of Contents

An individual virion was long believed to act as an independent infectious unit in virology, until the recent discovery of vesicle-cloaked virus clusters which has greatly challenged this central paradigm. Vesicle-cloaked virus clusters (also known as viral vesicles) are phospholipid-bilayer encapsulated fluid sacs that contain multiple virions or multiple copies of viral genomes. Norovirus is a global leading causative agent of gastroenteritis, and the reported prevalence of vesicle-cloaked norovirus clusters in stool has raised concerns whether the current disinfection, sanitation, and hygiene practices can effectively control environmental pollution by these pathogenic units. In this study, we have demonstrated that vesicle-cloaked murine norovirus (MNV-1) clusters were highly persistent under temperature variation (i.e., freeze-thaw) and they were partially resistant to detergent decomposition. MNV-1 vesicles were 1.89-3.17-fold more infectious in vitro than their free virus counterparts. Most importantly, MNV-1 vesicles were up to 2.16-times more resistant to UV254 disinfection than free MNV-1 at a low viral load in vitro. Interestingly, with the increase of the viral load, free MNV-1 and MNV-1 vesicles showed equivalent resistance to UV254 disinfection. We show that the increased multiplicity of infection provided by vesicles is in part responsible for these attributes. Our study, for the first time, sheds light on the environmental behavior of vesicle-cloaked virus clusters as unique emerging pathogenic units. Our study highlights the need to revisit current paradigms of disinfection, sanitation, and hygiene practices for protecting public health.

Solar-driven photocatalytic generation of H

To address the challenge of the airborne transmission of SARS-CoV-2, photosensitized electrospun nanofibrous membranes were fabricated to effectively capture and inactivate coronavirus aerosols. With an ultrafine fiber diameter (∼200 nm) and a small pore size (∼1.5 μm), optimized membranes caught 99.2% of the aerosols of the murine hepatitis virus A59 (MHV-A59), a coronavirus surrogate for SARS-CoV-2. In addition, rose bengal was used as the photosensitizer for membranes because of its excellent reactivity in generating virucidal singlet oxygen, and the membranes rapidly inactivated 97.1% of MHV-A59 in virus-laden droplets only after 15 min irradiation of simulated reading light. Singlet oxygen damaged the virus genome and impaired virus binding to host cells, which elucidated the mechanism of disinfection at a molecular level. Membrane robustness was also evaluated, and in general, the performance of virus filtration and disinfection was maintained in artificial saliva and for long-term use. Only sunlight exposure photobleached membranes, reduced singlet oxygen production, and compromised the performance of virus disinfection. In summary, photosensitized electrospun nanofibrous membranes have been developed to capture and kill airborne environmental pathogens under ambient conditions, and they hold promise for broad applications as personal protective equipment and indoor air filters.

To address the challenge of the airborne transmission of SARS-CoV-2, photosensitized electrospun nanofibrous membranes were fabricated to effectively capture and inactivate coronavirus aerosols. With an ultrafine fiber diameter (∼ 200 nm) and a small pore size (∼ 1.5 µm), the optimized membranes caught 99.2% of the aerosols of the murine hepatitis virus A59 (MHV-A59), a coronavirus surrogate for SARS-CoV-2. In addition, rose bengal was used as the photosensitizer for the membranes because of its excellent reactivity in generating virucidal singlet oxygen, and the membranes rapidly inactivated 98.9% of MHV-A59 in virus-laden droplets only after 15 min irradiation of simulated reading light. Singlet oxygen damaged the virus genome and impaired virus binding to host cells, which elucidated the mechanism of disinfection at a molecular level. Membrane robustness was also evaluated, and no efficiency reduction for filtering MHV-A59 aerosols was observed after the membranes being exposed to both indoor light and sunlight for days. Nevertheless, sunlight exposure photobleached the membranes, reduced singlet oxygen production, and compromised the performance of disinfecting MHV-A59 in droplets. In contrast, the membranes after simulated indoor light exposure maintained their excellent disinfection performance. In summary, photosensitized electrospun nanofibrous membranes have been developed to capture and kill airborne environmental pathogens under ambient conditions, and they hold promise for broad applications as personal protective equipment and indoor air filters.SynopsisPhotosensitized electrospun nanofibrous filters with excellent capture-and-kill performance against coronaviruses were designed and implemented to prevent the airborne transmission of COVID-19.Table of Contents

Waterborne pathogenic viruses, with an ultra-small particle size of tens of nanometers, a high risk of causing disease, and strong persistence in natural environment and water treatment processes, pose a serious threat to human health. Here, a new class of metal-free heterojunction photocatalysts was developed by integrating oxygen-doped graphitic carbon nitride microspheres (O-g-C3N4) with hydrothermal carbonation carbon (HTCC) via a facile low-temperature solvothermal-hydrothermal approach for the inactivation of human adenovirus type 2 (HAdV-2). The sample of O-g-C3N4/HTCC-2 with a uniform coverage of HTCC, strong visible light absorption, and a narrow band gap exhibited the higher virucidal activity against highly resistant HAdV-2 under visible light irradiation, compared to HTCC, bulk g-C3N4, and O-g-C3N4. A titer of 105 MPN/mL viruses was completely inactivated within 120 min of photocatalysis, and viral inactivation efficiency was enhanced with the increase of water temperature from 4 to 37 °C, the decrease of pH from 8 to 5, or the presence of salinity (NaCl) and hardness (Ca2+). Furthermore, the effectiveness for HAdV-2 inactivation in real drinking water and excellent photocatalyst stability of O-g-C3N4/HTCC-2 highlighted its promising potential for water disinfection in practice. The mechanism of enhanced virucidal performance of O-g-C3N4/HTCC was revealed, and it was because of enhanced charge separation by the formation of heterojunction in the photocatalyst. Besides, Z-scheme heterojunction was proposed to enable the production of OH as a strong antiviral agent in photocatalysis, in contrast to Type II heterojunction. Interestingly, OH rather than O2− dominated HAdV-2 inactivation, and it led to the rupture, distortion, and hole formation of viral capsid. In addition to the excellent photocatalytic performance of O-g-C3N4/HTCC for HAdV-2 inactivation, the photocatalyst exhibited negligible toxicity to a human cell line, suggesting the material is safe for water purification. Our study not only highlights the promising future of an emerging metal-free visible-light-responsive heterostructure of O-g-C3N4/HTCC for viral disinfection and an effective, sustainable, and safe water purification process, but also sheds light on the key photocatalyst properties and mechanisms that improve photocatalytic performance.

Microbial contamination in drinking water is of great concern around the world because of high pathogenic risks to humans. Semiconductor photocatalysis has aroused an increasing interest as a promising environmental remediation technology for water disinfection and microbial control. Among various photocatalysts, graphitic carbon nitride (g-C3N4), as a fascinating two-dimensional conjugated polymer consisting of low-cost, earth-abundant elements, has drawn broad attention as a robust, metal-free, and visible-light-active material in the fields of both environmental remediation and solar energy conversion. Photocatalytic applications of g-C3N4-based nanomaterials for water splitting, hydrogen production, carbon dioxide reduction, and pollutant degradation have been extensively investigated and systematically reviewed. In contrast, their antimicrobial properties have been explored more recently due to the complex structure and unique metabolism of living microorganisms compared with chemicals. The corresponding rapidly increasing research efforts in the last five years have inspired us to conduct the review. This review is the first to comprehensively summarize the progress in design and antimicrobial performance of g-C3N4-based photocatalysts for water disinfection and microbial control, involving not only bacteria but also viruses and microalgae. Moreover, the underlying inactivation mechanisms of photocatalysts for microorganisms are evaluated to provide further understanding of g-C3N4-based advanced disinfection processes. In addition, some exciting future opportunities and challenges at the forefront of this research platform are pointed out. It is expected that this review can pave a new avenue for the development of a facile, cost-effective, environmental-friendly, and sustainable disinfection alternative.

Achieving efficient disinfection of waterborne pathogens with minimized harmful disinfection byproducts demands a facile, cost-effective, and environmentally friendly technology. Recently, photocatalytic water disinfection has attracted an ever-growing worldwide attention due to its powerful oxidative capability and promising potential in solar energy utilization. Among waterborne pathogens, viruses, which have been found with very small sizes, high risks of illness, and resistant to environmental inactivation/decomposition, pose a great threat to public health. Over the past a few decades, efforts have been made to employ photocatalysis to achieve effective viral inactivation. Though photocatalysis has been comprehensively reviewed for bacterial disinfection, photocatalytic disinfection of viruses with quite different compositions, structures, and resistance to oxidative stress compared to bacteria was not systematically documented. Here, we present an overview of antiviral effects of a wide range of photocatalysts, including TiO2-based, metal-containing (other than TiO2), and metal-free photocatalysts. Moreover, the development of photocatalytic reactors for viral inactivation is summarized to promote practical engineering applications for water disinfection. In addition, key mechanisms that determine the performance of photocatalytic viral disinfection are reviewed. Future perspectives of research opportunities and challenges in photocatalytic viral disinfection are also included. This review will shed light on the development and implementation of sustainable disinfection strategies for controlling waterborne viruses in the future.

Solar-energy-enabled photocatalysis is a sustainable process to destruct persistent environmental pollutants via the attack of photogenerated reactive species (e.g., holes, reactive oxygen species such as OH, O2− /HO2 , H2O2, and 1O2). Graphitic carbon nitride (g-C3N4) has emerged as a promising polymeric photocatalyst, and its highly tunable properties allow the material with an enhanced photocatalytic activity for environmental remediation. In this study, by taking advantage of simulation and experimental tools, we systematically evaluated the production of reactive species of undoped and carbon (C)-doped g-C3N4 samples, and identify the role of these species in contaminant oxidation under simulated visible sunlight irradiation (xenon lamp, λ > 400 nm). Both g-C3N4 samples produced negligible OH or triplet-excited states (3g-C3N4*), but the C-doped g-C3N4 sample generated more 1O2, O2− , and H2O2 compared to the undoped counterpart. Surprisingly, all these oxidative species did not contribute substantially for the degradation kinetics of contaminant phenol and atrazine, at least for the initial oxidation of the parent compounds; and the results otherwise highlighted the important role of the holes for contaminant transformation. The surface-mediated hole oxidation of the contaminants, including the adsorption of the contaminants on the photocatalyst surface (quantified by the binding free energy) and electron transfer kinetics from the contaminants to the excited photocatalysts (quantified by the concerted proton-coupled electron transfer (CPCET) rate) were investigated by molecular dynamics (MD) and density functional theory (DFT) simulations. The simulation results indicated that C-doping could favor the binding of atrazine but not of phenol on g-C3N4. The C-doping also significantly decreased the CPCET rate of phenol on g-C3N4 but could have little to no adverse impact for the CPCET rate of atrazine. These simulation and experimental results could explain the selective oxidation of phenol and atrazine on undoped and C-doped g-C3N4 in our previous study, and the results also highlight the dominant role of the holes for contaminant transformation that was largely overlooked before. This study generates mechanistic insights of photocatalytic oxidation, and will provide guidelines for the rational design of g-C3N4 as an effective visible-light-responsive photocatalyst for many applications, including contaminant degradation, chemical synthesis, and beyond.

We provide an efficient, sustainable, low-cost, and potentially scalable method to prepare N-functionalized activated carbon (AC) for Pd-based catalysis with improved performance for water purification. N-functionalized AC supports were realized via “soft nitriding”, that is, low temperature heating of a urea–AC mixture, and Pd nanoparticles with a significantly increased number of surface Pd(0) sites were achieved on the supports. Moreover, Pd nanoparticles were preferentially loaded near the (treated) AC exterior surface. N-functionalization improved nitrite and bromate hydrogenation kinetics but not for chlorite and chlorate, suggesting that different mechanisms determine the reaction activity of these oxyanions.

An individual virion was long believed to act as an independent infectious unit in virology, until the recent discovery of vesicle-cloaked virus clusters which has greatly challenged this central paradigm. Vesicle-cloaked virus clusters (also known as viral vesicles) are phospholipid-bilayer encapsulated fluid sacs that contain multiple virions or multiple copies of viral genomes. Norovirus is a global leading causative agent of gastroenteritis, and the reported prevalence of vesicle-cloaked norovirus clusters in stool has raised concerns whether the current disinfection, sanitation, and hygiene practices can effectively control environmental pollution by these pathogenic units. In this study, we have demonstrated that vesicle-cloaked murine norovirus (MNV-1) clusters were highly persistent under temperature variation (i.e., freeze-thaw) and they were partially resistant to detergent decomposition. MNV-1 vesicles were 1.89-3.17-fold more infectious in vitro than their free virus counterparts. Most importantly, MNV-1 vesicles were up to 2.16-times more resistant to UV

We prepared a single-atom Fe catalyst supported on an oxygen-doped, nitrogen-rich carbon support (SAFe-OCN) for degrading a broad spectrum of contaminants of emerging concern (CECs) by activating peroxides such as peroxymonosulfate (PMS). In the SAFe-OCN/PMS system, most selected CECs were amenable to degradation and high-valent Fe species were present for oxidation. Moreover, SAFe-OCN showed excellent performance for contaminant degradation in complex water matrices and high stability in oxidation. Specifically, SAFe-OCN, with a catalytic center of Fe coordinated with both nitrogen and oxygen (FeNxO4-x), showed 5.13-times increased phenol degradation kinetics upon activating PMS compared to the catalyst where Fe was only coordinated with nitrogen (FeN4). Molecular simulations suggested that FeNxO4-x, compared to FeN4, was an excellent multiple-electron donor and it could potential-readily form high-valent Fe species upon oxidation. In summary, the single-atom Fe catalyst enables efficient, robust, and sustainable water and wastewater treatment, and molecular simulations highlight that the electronic nature of Fe could play a key role in determining the activity of the single-atom catalyst.

Photocatalysis holds promise for inactivating environmental pathogens. Visible-light-responsive composites of carbon-doped graphitic carbon nitride and chitosan with high reactivity and processability were fabricated, and they can control pathogenic biofilms for environmental, food, biomedical, and building applications. The broad-spectrum biofilm inhibition and eradication of the photocatalytic composites against Staphylococcus epidermidis, Pseudomonas aeruginosa PAO1, and Escherichia coli O157: H7 under visible light irradiation were demonstrated. Extracellular polymeric substances in Escherichia coli O157: H7 biofilms were most resistant to photocatalytic oxidation, which led to reduced performance for biofilm removal. 1O2 produced by the composites was believed to dominate biofilm inactivation. Moreover, the composites exhibited excellent performance for inhibiting biofilm development in urine, highlighting the promise for inactivating environmental biofilms developed from multiple bacterial species. Our study provides fundamental insights into the development of new photocatalytic composites, and elucidates the mechanism of how the photocatalyst reacts with a microbiological system.

Waterborne pathogens, especially bacteria and viruses, pose significant health risks to the public, calling for the development of a sustainable, efficient, and robust disinfection strategy with reduced energy footprint and minimized byproduct formation. Here, we developed a sustainable photocatalytic composite for antimicrobial applications by integrating visible-light-responsive graphitic carbon nitride (g-C3N4) with low-density porous expanded perlite (EP) mineral, and g-C3N4/EP-520 showed a high specific surface area of 45.3 m2/g and optimum performance for disinfection. g-C3N4/EP-520 achieved 8-log inactivation of E. coli and MS2 under 180 and 240 min visible-light irradiation without stirring, respectively. Water quality parameters were found to influence the disinfection performance of g-C3N4/EP-520: MS2 inactivation was promoted with the increase of dissolved oxygen (DO), proton concentration, salinity (NaCl), and hardness (Ca2+). Importantly, g-C3N4/EP-520 could fully inactivate MS2 in a real source water sample with prolonged light irradiation, and negligible activity loss was observed in recycle use, demonstrating its viability and robustness for waterborne pathogen removal. Antimicrobial mechanisms of g-C3N4/EP-520 were systemically evaluated by radical scavenger addition, and revealed that the inactivation behavior was dependent on the type of microorganisms. Microscopic analyses confirmed that the destruction of bacterial cells and viral particles, leading to the inactivation of microorganisms.

Photocatalytic membrane filtration has emerged as a promising technology for water purification because it integrates both physical rejection and chemical destruction of contaminants in a single unit, and also largely mitigates membrane fouling by natural organic matter (NOM). In this study, we evaluated the performance of a photocatalytic membrane system for mitigating fouling by a humic acid, which is representative NOM, and identified critical properties of the humic acid that determined membrane fouling. We prepared a partially oxidized humic acid (OHA) through the photocatalysis of a purified humic acid (PHA), and the OHA showed reduced fouling for polyvinylidene fluoride (PVDF) ultrafiltration membranes compared to PHA. Molecular-level characterizations indicated that OHA had a reduced molecular size, an increased oxygen content, and increased hydrophilicity. OHA also formed smaller aggregates on the fouled membrane surfaces than PHA. The introduction of oxygen-containing, hydrophilic functional groups, e.g., -OH and -COOH, to the humic acid and the depolymerization or mineralization of the humic acid in photocatalysis could result in the reduction of the foulant-membrane and foulant-foulant interactions, as characterized by atomic force microscopy (AFM), thereby mitigating membrane fouling. Foulant-membrane adhesion forces were always larger than foulant-foulant adhesion forces in our study, irrespective of the humic acid before or after photocatalytic oxidation, which may suggest that the reduction of foulant-membrane interactions is critical for membrane fouling control. In summary, this study sheds light into humic acid fouling in a photocatalytic membrane system through a systematic and comprehensive research approach, and provides insights for the design of novel membrane materials and processes with improved performance for water purification.

Carbon-based nanomaterials have shown great promise in regenerative medicine because of their unique electrical, mechanical, and biological properties; however, it is still difficult to engineer 2D pure carbon nanomaterials into a 3D scaffold while maintaining its structural integrity. In the present study, we developed novel carbon nanofibrous scaffolds by annealing electrospun mats at elevated temperature. The resultant scaffold showed a cohesive structure and excellent mechanical flexibility. The graphitic structure generated by annealing renders superior electrical conductivity to the carbon nanofibrous scaffold. By integrating the conductive scaffold with biphasic electrical stimulation, neural stem cell proliferation was promoted associating with upregulated neuronal gene expression level and increased microtubule-associated protein 2 immunofluorescence, demonstrating an improved neuronal differentiation and maturation. The findings suggest that the integration of the conducting carbon nanofibrous scaffold and electrical stimulation may pave a new avenue for neural tissue regeneration.

In this work, we demonstrate the production of reactive, robust, sustainable catalysts for water treatment created through Natural Fiber Welding (NFW) of lignocellulose-supported palladium-indium (Pd-In) nanoparticles onto linen yarns. First, Pd-In catalysts were synthesized by incipient wetness onto ball-milled powders of linen. Our process preserved the lignocellulose, yielding small (5–10 nm), near-spherical crystalline nanoparticles of Pd-In alloy and a uniform Pd-In metal composition throughout the fibers. Nitrate reduction tests identified the existence of an optimum Pd-In catalyst composition (5 wt% Pd and 1.2 wt% In with respect to lignocellulose) for maximum reactivity; the most reactive Pd-In catalyst was 10 times more reactive than the best performing Pd-Cu nanoparticles deposited on lignocellulose using the same approach. This improved performance was most likely due to more uniform distribution of alloyed Pd-In nanoparticles throughout the support. Nitrate reduction tests and X-ray photoelectron spectroscopy depth profiling of aged Pd-In catalysts showed that they remained stable and lost no reactivity during extended storage in air at room temperature. Next, the optimized Pd-In catalyst was fiber-welded onto linen yarns, using a custom-built yarn-coating system and a novel, scalable process that controlled catalyst loading, delivering a Pd-In catalyst coating onto the yarn surface. This fiber-welded Pd-In catalyst yarn was integrated into a novel water treatment reactor and evaluated during four months and more than 180 h of nitrate reduction tests in ultrapure water. During this evaluation, the fiber-welded catalysts maintained their reactivity with negligible metal leaching. When tested in raw or (partially) treated drinking water and wastewater, the fiber-welded catalysts were robust and stable, and their performance was not significantly impacted by constituents in the complex waters (e.g. alkalinity, organic matter). Our research demonstrates an innovative, scalable approach through NFW to design and implement robust, sustainable lignocellulose-supported catalysts with enhanced reactivity capable of water purification in complex water chemistries.

Continuous photocatalysis via photo-charging and dark-discharging presents a paradigm shift in conventional photocatalysis with the requirement of continuous illumination to maintain the catalytic activity. This is expected to meet the ever-increasing demand for sustainable development of energy and environment driven by natural day-night cycles. Substantial advances in continuous photocatalysis for various environmental applications under light-dark cycles have been witnessed during the last decade. However, there lacks a systematic and critical review on basic but important information of continuous photocatalysis for environmental remediation, challenging robust scientific progress of this technology towards potential practical use. Here, the general description of continuous photocatalysis involving energy storage mechanisms (hole and electron storage) and characterizations (electron storage behaviors, release behaviors and storage capacity) has been first introduced. Importantly, the remediation performance and mechanism of continuous photocatalysis for environmental applications are qualitatively and quantitatively demonstrated, including chemical pollutant oxidation and reduction, microbial pathogen inactivation, and multifunctional treatment. In addition, key factors influencing its remediation performance are analyzed, for the first time, from both operational and environmental views. The ample opportunities in the field of continuous photocatalysis for sustainable environmental remediation are also pointed out, calling for more efforts to fill current knowledge gaps in the future.

Novel Pd-based catalysts (i.e., Pd and Pd–Cu) supported on graphitic carbon nitride (g-C3N4) were prepared for nitrite and nitrate hydrogenation. The catalysts prepared by ethylene glycol reduction exhibited ultrafine Pd and Pd–Cu nanoparticles (∼2 nm), and they showed high reactivity, high selectivity toward nitrogen gas over byproduct ammonium, and excellent stability over multiple reaction cycles. The unique nitrogen-abundant surface, porous structure, and hydrophilic nature of g-C3N4 facilitates metal nanoparticle dispersion, mass transfer of reactants, and nitrogen coupling for nitrogen gas production to improve catalytic performance.

Catalytic reduction of 4-nitrophenol (4-NP) by palladium-resin catalysts is promising for 4-NP detoxification, in situ regeneration of the catalysts, and recycling of the products. In this study, we examined the catalytic reduction of 4-NP by Pd 0 -based catalysts supported on three neutral resins and two anion exchange resins, using hydrogen gas as the electron donor. The reduction kinetics followed the same trend as the adsorption kinetics, i.e., faster adsorption and reduction were observed at acidic pHs for the neutral resins and at basic pHs for the anionic resins (4-NP pK a = 7.15). The Langmuir-Hinshelwood model based on surface reaction as the rate determining step fitted the kinetic data well. These findings point to the significant role of adsorption in the overall catalytic reaction. Cl − inhibited the reactivity of the neutral resins less than that of the anion exchangers due to the hydrophobic nature of the former. The longevity of the catalysts was examined in two tests: (1) 1 mM 4-NP was repeatedly spiked into the same catalysts for eight times, where the accumulation of 4-NP and the sole reduction product (4-aminophenol) on the resin surfaces resulted in the gradual loss in the catalytic activity, which was largely restored after regeneration, and (2) the catalysts were subjected to fresh influent in each adsorption and catalytic reduction cycle for seven times, where the catalysts sustained their reactivity through the seven cycles, significantly eliminating the need for frequent regeneration.

Polymeric resins have been widely used for the removal of halogenated compounds, however, the sustainability of resin adsorption is compromised by frequent resin regeneration and further treatment/disposal of concentrated brine. Palladium (Pd)-based catalytic hydrogenation is promising to treat various classes of contaminants, including halogenated compounds, and the development of Pd-polymeric resin composites is advantageous because the composites can convert halogenated compounds to less toxic chemicals in situ and mitigate challenges associated with resin regeneration. In this work, three neutral resins (MN200, MN100, and XAD4) and two anion exchange resins (IRA910 and IRA96) were used as Pd supports to evaluate 4-chlorophenol (4-CP) hydrodechlorination reactivity. Similar 4-CP adsorption and reduction kinetics were observed, i.e., adsorption and reduction were both faster at acidic pHs for the neutral resins but faster at basic pHs for the anionic resins. The developed Langmuir–Hinshelwood kinetic model based on surface reaction as the rate determining step also suggested an enhancing effect of adsorption on the catalytic reactivity. When adsorption was constant, the reactivity of the catalysts increased with increasing solution pH. This is because higher pH mitigates the adverse impacts of the dehalogenation products (i.e., H + and Cl − ) on the catalytic reaction. The inhibition effect of Cl − was more pronounced on IRA910 than on MN200. IRA910 with anion exchange functional groups facilitates Cl − adsorption and promotes the production of PdCl 3 − and PdCl 4 2− species, which are inactive for catalytic reduction. The accumulation of phenol, the dominant product in 4-CP reduction, on resin resulted in catalytic activity loss over eight cycles when 4-CP was repeatedly spiked into the same reactor; the catalytic activity was largely restored after resin regeneration.

Graphitic carbon nitride (g-C3N4) is an emerging visible-light-responsive photocatalyst that has been explored since 2009. This photocatalyst has highly tailorable structures and properties that enable potential utilization of a large portion of solar energy. This material is also synthesized from earth-abundant precursors, is chemically and thermally stable, and is biocompatible with no reported toxicity to date. The merits and pioneering performance evaluation of g-C3N4 indicate that this photocatalyst holds promise for the degradation of persistent and emerging contaminants, including chemicals and pathogens, for sustainable water purification with reduced energy and chemical footprint. In this perspective, we propose and answer five questions that are most relevant to the development and application of g-C3N4 for photocatalytic water purification, including both benefits and current barriers, from molecular-scale mechanistic understanding of g-C3N4 properties and photocatalytic performance to industrial-scale photoreactor design for g-C3N4 implementation in practice.

The challenge to achieve effective water disinfection of pathogens, especially viruses, with minimized harmful disinfection byproducts calls for a cost-effective and environmentally benign technology. Here, polymeric graphitic carbon nitride (g-C3N4), as a metal-free robust photocatalyst, was explored for the first time for its ability to inactivate viruses under visible light irradiation. MS2 with an initial concentration of 1 × 108 PFU/mL was completely inactivated by g-C3N4 with a loading of 150 mg/L under visible light irradiation of 360 min. g-C3N4 was a robust photocatalyst, and no decrease in its virucidal performance was observed over five cycles of sequential MS2 photocatalytic inactivation. The reactive oxygen species (ROSs) were measured by a range of scavengers, and photo-generated electrons and its derived ROSs (O- 2) were found to be the leading contributor for viral inactivation. TEM images indicated that the viral particle shape was distorted and the capsid shell was ruptured after photocatalysis. Viral surface proteins, particularly replicase proteins and maturation proteins, were damaged by photocatalytic oxidation. The loss of proteins would result in the leakage and rapid destruction of interior components (four main types of RNA genes), finally leading to viral death without regrowth. Our work opens a new avenue for the exploration and applications of a low-cost, high-efficient, and robust metal-free photocatalyst for green/sustainable viral disinfection.

Biofilms are a cluster of bacteria embedded in extracellular polymeric substances (EPS) that contain a complex composition of polysaccharides, proteins, and extracellular DNA (eDNA). Desirable mechanical properties of the biofilms are critical for their survival, propagation, and dispersal, and the response of mechanical properties to different treatment conditions also sheds light on biofilm control and eradication in vivo and on engineering surfaces. However, it is challenging yet important to interrogate mechanical behaviors of biofilms with a high spatial resolution because biofilms are very heterogeneous. Moreover, biofilms are viscoelastic, and their time-dependent mechanical behavior is difficult to capture. Herein, we developed a powerful technique that combines the high spatial resolution of the atomic force microscope (AFM) with a rigorous history-dependent viscoelastic analysis to deliver highly spatial-localized biofilm properties within a wide time-frequency window. By exploiting the use of static force spectroscopy in combination with an appropriate viscoelastic framework, we highlight the intensive amount of time-dependent information experimentally available that has been largely overlooked. It is shown that this technique provides a detailed nanorheological signature of the biofilms even at the single-cell level. We share the computational routines that would allow any user to perform the analysis from experimental raw data. The detailed localization of mechanical properties in space and in time-frequency domain provides insights on the understanding of biofilm stability, cohesiveness, dispersal, and control.

Pathogenic biofilms raise significant health and economic concerns, because these bacteria are persistent and can lead to long-term infections in vivo and surface contamination in healthcare and industrial facilities or devices. Compared with conventional antimicrobial strategies, photocatalysis holds promise for biofilm control because of its broad-spectrum effectiveness under ambient conditions, low cost, easy operation, and reduced maintenance. In this study, we investigated the performance and mechanism of Staphylococcus epidermidis biofilm control and eradication on the surface of an innovative photocatalyst, graphitic carbon nitride (g-C3N4), under visible-light irradiation, which overcame the need for ultraviolet light for many current photocatalysts (e.g., titanium dioxide (TiO2)). Optical coherence tomography and confocal laser scanning microscopy (CLSM) suggested that g-C3N4 coupons inhibited biofilm development and eradicated mature biofilms under the irradiation of white light-emitting diodes....

Decontamination of water polluted with recalcitrant chemicals, such as phenolic and aromatic substances, for which conventional wastewater treatment processes are largely not effective, remains a major challenge all over the world. The simultaneous combination of photocatalytic and biological processes in a single system, either with or without the support of porous carriers, exhibits superior synergistic performance for removing refractory contaminants with the advantages of both photocatalysis and biotransformation. This promising emerging alternative, defined as simultaneous coupling here, has attracted increased attention and has been substantially developed over the last five years. To our best knowledge, this is the first critical review systematically focusing on the simultaneous coupling of photocatalytic and biological processes in enhancing decontamination of recalcitrants from water. The current review includes not only the synergy for pollutant oxidation/reduction removal and corresponding key factors affecting coupled systems, but also the underlying mechanisms of two different couplings in the interaction view of photocatalytic and biological responses. Last but not least, the challenges and opportunities faced by the coupling are pointed out. This review can provide useful information on the design and application of the synergistic coupling of chemical and biological processes for efficient and complete decontamination of recalcitrant compounds in water.

In our study, lignocellulose yarns were fabricated via natural fiber welding (NFW) into a robust, free-standing, sustainable catalyst for water treatment. First, a series of powder catalysts were created by loading monometallic palladium (Pd) and bimetallic palladium–copper (Pd–Cu) nanoparticles onto ball-milled yarn powders via incipient wetness (IW) followed by a gentle reduction method in hydrogen gas that preserved the natural fiber while reducing the metal ions to their zerovalent state. Material characterization revealed Pd preferentially reduced near the surface whereas Cu distributed more uniformly throughout the supports. Although no chemical bonding interactions were observed between the metals and their supports, small (5–10 nm), near-spherical crystalline nanoparticles were produced, and a Pd–Cu alloy formed on the surface of the supports. Catalytic performance was evaluated for each Pd-only and Pd–Cu powder catalyst via nitrite and nitrate reduction tests, respectively. Next, the optimized Pd...

We report a facile synthesis method for carbon nanofiber (CNF) supported Pd catalysts via one-pot electrospinning and their application for nitrite hydrogenation. A mixture of Pd acetylacetonate (Pd(acac)2), polyacrylonitrile (PAN), and nonfunctionalized multiwalled carbon nanotubes (MWCNTs) was electrospun and thermally treated to produce Pd/CNF-MWCNT catalysts. The addition of MWCNTs with a mass loading of 1.0-2.5 wt % (to PAN) significantly improved nitrite reduction activity compared to the catalyst without MWCNT addition. The results of CO chemisorption confirmed that the addition of MWCNTs increased Pd exposure on CNFs and hence improved catalytic activity.

Efficient algal harvesting, cell pretreatment and lipid extraction are the major steps challenging the algal biofuel industrialization. To develop sustainable solutions for economically viable algal biofuels, our research aims at devising innovative reactive electrochemical membrane (REM) filtration systems for simultaneous algal harvesting and pretreatment for lipid extraction. The results in this work particularly demonstrated the use of the Ti4O7-based REM in algal pretreatment and the positive impacts on lipid extraction. After REM treatment, algal cells exhibited significant disruption in morphology and photosynthetic activity due to the anodic oxidation. Cell lysis was evidenced by the changes of fluorescent patterns of dissolved organic matter (DOM) in the treated algal suspension. The lipid extraction efficiency increased from 15.2 ± 0.6 g-lipidg-algae(-1) for untreated algae to 23.4 ± 0.7 g-lipidg-algae(-1) for treated algae (p

The mechanistic understanding of the fate, transport, and transformation of contaminants in natural and engineered water systems is of great importance for environmental remediation. Recently, atomic force microscopy (AFM) has emerged as a promising tool to provide insights on the properties and interactions of materials, chemicals, and microorganisms. This article highlights three studies using AFM to understand the molecular mechanism of membrane fouling for water and wastewater treatment, to characterize biofilm properties that influence the accumulation and release of pathogens in drinking water distribution systems, and to evaluate the nucleation and growth of manganese (Mn) (hydr)oxide for remediating Mn-contaminated environmental systems.

Maintaining drinking water safety from treatment to point-of use is a critical health priority. Growth and proliferation of opportunistic pathogens in premise plumbing is a well-known concern that can be mitigated by controlling water heater temperatures and water stagnation patterns. However, there is growing evidence that upstream processes, beginning with choice of treatment methods, have significant influences on premise plumbing microbial communities. Here, we highlight four papers that explore the roles of microbial communities in drinking water quality, and how design and treatment choices shape these roles.

Photocatalysis holds great promise for sustainable water treatment due to the generation of reactive radicals for efficient contaminant removal, minimized chemicals consumption, and the utilization of renewable, inexhaustible solar energy (DOI: 10.1021/cr00033a004, DOI: 10.1021/cr00018a003). The most widely used photocatalyst for water treatment, titanium dioxide (TiO2), requires UV excitation. However, UV only accounts for 4% of solar energy, and the dependence of current photocatalysts on UV compromises the efficiency and feasibility of solar powered water treatment. Disinfection, an important water treatment process for the inactivation of pathogenic microorganisms, also requires UV radiation with a wavelength of 250–260 nm. Therefore, the development of novel photocatalysts, and photophysical and photochemical processes for the use of optical radiation with a longer wavelength, such as visible light that accounts for 40% of solar energy, would present a major breakthrough for solar powered water treatment. A unique photoluminescence process, upconversion, has recently drawn attention for its ability to convert low energy photons (e.g., visible light) into high energy photons (e.g., UV light) for antimicrobial purposes (DOI: 10.1021/es200196c, DOI: 10.1021/es405229p). In this research highlight, we discuss three innovative materials used in photocatalysis and photoluminescence for water treatment applications, including graphitic carbon nitride (g-C3N4), red phosphorus, and upconversion phosphors (Y2SiO5 doped with Pr and Li).

Solar-energy-enabled photocatalysis is promising for sustainable water purification. However, photoreactor design, especially immobilizing nano-sized photocatalysts, remains a major barrier preventing industrial-scale application of photocatalysis. In this study, we immobilized photocatalytic graphitic carbon nitride on chitosan to produce g-C3N4/chitosan hydrogel beads (GCHBs), and evaluated GCHB photoreactivity for degrading phenol and emerging persistent micropollutants in a 3D printed compound parabolic collector (CPC) reactor. The CPC photocatalytic system showed comparable performance with slurry reactors for sulfamethoxazole and carbamazepine degradation under simulated sunlight, and it maintained the performance for contaminant removal in real water samples collected from water/wastewater treatment plants or under outdoor sunlight irradiation. Global drinking water production was estimated for the CPC system, and it holds promise for small-scale sustainable water treatment, including, but not limited to, the production of high-quality potable water for single houses, small communities, rural areas, and areas impacted by natural disasters in both developed and developing countries.

Natural Fiber Welding (NFW) is a green engineering process that uses Ionic Liquids (IL) to prepare functional biocomposites for applications including water purification, energy storage, sensing, and thermal enhancement. The composition of the welding solution can significantly impact welding efficiency as well as the structure and composition of fiber-welded biocomposites. This study evaluates how NFW solvent composition influences metal leaching from lignocellulose fiber-supported Pd–In nanoparticles. Solutions were prepared from pure, dry 1-ethyl-3-methylimidazolium acetate, and controlled amounts of IL contaminants (water, acetic acid), and one molecular co-solvent (acetonitrile). Lignocellulose fibers with embedded Pd–In nanoparticles were welded in each solution and reconstituted in water; the recovered precipitates/filtrates were evaluated using ICP-MS to determine how much palladium and indium leached from each catalyst into the welding solvent. Our data show how excess acetic acid in the NFW solvent causes indium metal to dealloy from Pd–In nanoparticles. Because Pd–In nanoparticles are proven hydrogenation catalysts for water purification, nitrate reduction tests were performed with each fiber-welded product and compared to unwelded control samples. These data show how preferential leaching of indium directly impacted the catalysts nitrate reduction reactivity, and provide insight into how one might control this phenomenon to optimize development of fiber-welded catalyst systems.

Trihalomethanes (THMs) and haloacetonitriles (HANs), most common disinfection by-products in drinking water, pose adverse environmental impacts and potential risks to human health. There is a pressing need to develop innovative, economically feasible, and environmentally benign processes to control these persistent contaminants. In this paper, visible-light-responsive graphitic carbon nitride (g-C3N4) samples were synthesized to degrade the THMs and HANs and the photocatalytic degradation mechanism was explored. The results indicated that a carbon-doped g-C3N4 with an optimum dopant content (MCB0.07) displayed the best photocatalytic activity for the total trihalomethanes (TTHM) and total haloacetonitriles (THAN), with the reaction rate constant of 11.6 and 10.4 (10−3 min−1), respectively. MCB0.07 demonstrated a high THMs and HANs removal efficiency under visible light irradiation and could be reused. According to scavenger tests of the selected reactive species and X-ray photoelectron spectroscopy, holes play a dominant role for both THMs and HANs degradation on the MCB0.07. The degradation of HANs by holes proceeded mainly through breakage of the C C bond in the C C N group. The THMs degradation was achieved through hydrogen abstraction or/and dehalogenation. The brominated-THMs/HANs were more photosensitive than their chlorinated analogous and were less stable than bromo-chloro-THMs/HANs. This study sheds light on the mechanism of the photocatalytic degradation of THMs and HANs under visible light irradiation by carbon-doped g-C3N4. Furthermore, it could provide insights for engineering applications and contaminant control in drinking water purification.

Microbial contamination in drinking water is of great concern around the world because of high pathogenic risks to humans. Semiconductor photocatalysis has aroused an increasing interest as a promising environmental remediation technology for water disinfection and microbial control. Among various photocatalysts, graphitic carbon nitride (g-C

We highlight the effects of treated and untreated wastewater on antibiotic resistance genes (ARGs) in the environment, attenuation of ARGs following land application of wastewater solids, and a quantitative model for natural transformation.

We highlight recent studies about monitoring and promoting the growth of anammox bacteria in mainstream wastewater treatment.

Graphitic carbon nitride (g-C3N4) has recently emerged as a promising visible-light-responsive polymeric photocatalyst; however, a molecular-level understanding of material properties and its application for water purification were underexplored. In this study, we rationally designed nonmetal doped, supramolecule-based g-C3N4 with improved surface area and charge separation. Density functional theory (DFT) simulations indicated that carbon-doped g-C3N4 showed a thermodynamically stable structure, promoted charge separation, and had suitable energy levels of conduction and valence bands for photocatalytic oxidation compared to phosphorus-doped g-C3N4. The optimized carbon-doped, supramolecule-based g-C3N4 showed a reaction rate enhancement of 2.3–10.5-fold for the degradation of phenol and persistent organic micropollutants compared to that of conventional, melamine-based g-C3N4 in a model buffer system under the irradiation of simulated visible sunlight. Carbon-doping but not phosphorus-doping improved re...

This Highlight article covers several unconventional precursors and sources for disinfection byproduct formation from recent studies.

Catalytic reduction with Pd has emerged as a promising technology to remove a suite of contaminants from drinking water, such as oxyanions, disinfection byproducts, and halogenated pollutants, but low activity is a major challenge for application. To address this challenge, we synthesized a set of shape- and size-controlled Pd nanoparticles and evaluated the activity of three probe contaminants (i.e., nitrite, N-nitrosodimethylamine (NDMA), and diatrizoate) as a function of facet type (e.g., (100), (110), (111)), ratios of low- to high-coordination sites, and ratios of surface sites to total Pd (i.e., dispersion). Reduction results for an initial contaminant concentration of 100 μM show that initial turnover frequency (TOF0) for nitrite increases 4.7-fold with increasing percent of (100) surface Pd sites (from 0% to 95.3%), whereas the TOF0 for NDMA and for diatrizoate increases 4.5- and 3.6-fold, respectively, with an increasing percent of terrace surface Pd sites (from 79.8% to 95.3%). Results for an in...