Pulsed hydraulic-pressure-responsive self-cleaning membrane.

Pressure-driven membranes is a widely used separation technology in a range of industries, such as water purification, bioprocessing, food processing and chemical production1,2. Despite their numerous advantages, such as modular design and minimal footprint, inevitable membrane fouling is the key challenge in most practical applications3. Fouling limits membrane performance by reducing permeate flux or increasing pressure requirements, which results in higher energetic operation and maintenance costs4-7. Here we report a hydraulic-pressure-responsive membrane (PiezoMem) to transform pressure pulses into electroactive responses for in situ self-cleaning. A transient hydraulic pressure fluctuation across the membrane results in generation of current pulses and rapid voltage oscillations (peak, +5.0/-3.2 V) capable of foulant degradation and repulsion without the need for supplementary chemical cleaning agents, secondary waste disposal or further external stimuli3,8-13. PiezoMem showed broad-spectrum antifouling action towards a range of membrane foulants, including organic molecules, oil droplets, proteins, bacteria and inorganic colloids, through reactive oxygen species (ROS) production and dielectrophoretic repulsion.

O2-Independent H2O2 Production via Water-Polymer Contact Electrification.

Hydrogen peroxide (H2O2), as a critical green chemical, has received immense attention in energy and environmental fields. The ability to produce H2O2 in earth-abundant water without relying on low solubility oxygen would be a sustainable and potentially economic process, applicable even to anaerobic microenvironments, such as groundwater treatment. However, the direct water to H2O2 process is currently hindered by low selectivity and low production rates. Herein, we report that poly(tetrafluoroethylene) (PTFE), a commonly used inert polymer, can act as an efficient triboelectric catalyst for H2O2 generation. For example, a high H2O2 production rate of 24.8 mmol gcat-1 h-1 at a dosage of 0.01 g/L PTFE was achieved under the condition of pure water, ambient atmosphere, and no sacrificial agents, which exceeds the performance of state-of-the-art aqueous H2O2 powder catalysts. Electron spin resonance and isotope experiments provide strong evidence that water-PTFE tribocatalysis can directly oxidize water to produce H2O2 under both anaerobic and aerobic conditions, albeit with different synthetic pathways. This study demonstrates a potential strategy for green and effective tribocatalytic H2O2 production that may be particularly useful toward environmental applications.

Centurial Persistence of Forever Chemicals at Military Fire Training Sites.

Drinking water contamination by per- and polyfluoroalkyl substances (PFAS) is widespread near more than 300 United States (U.S.) military bases that used aqueous film-forming foams (AFFF) for fire training and firefighting activities. Much of the PFAS at these sites consist of precursors that can transform into terminal compounds of known health concern but are omitted from standard analytical methods. Here, we estimate the expected duration and contribution of precursor biotransformation to groundwater PFAS contamination at an AFFF-contaminated military base on Cape Cod, Massachusetts, United States, by optimizing a geochemical box model using measured PFAS concentrations from a multidecadal time series of groundwater and a soil survey in the source zone. A toolbox of analytical techniques used to reconstruct the mass budget of PFAS showed that precursors accounted for 46 ± 8% of the extractable organofluorine (a proxy for total PFAS) across years. Terminal PFAS still exceed regulatory limits by 2000-fold decades after AFFF use ceased. Measurements and numerical modeling show that sulfonamido precursors are retained in the vadose zone and their slow biotransformation into perfluoroalkyl sulfonates (half-life > 66 yr) sustains groundwater concentrations of perfluorobutane sulfonate (PFBS) and perfluorohexane sulfonate (PFHxS). The estimated PFAS reservoir in the vadose zone and modeled flux into groundwater suggest PFAS contamination above regulatory guidelines will persist for centuries without remediation.

Nitrifying Microorganisms Linked to Biotransformation of Perfluoroalkyl Sulfonamido Precursors from Legacy Aqueous Film-Forming Foams.

Drinking water supplies across the United States have been contaminated by firefighting and fire-training activities that use aqueous film-forming foams (AFFF) containing per- and polyfluoroalkyl substances (PFAS). Much of the AFFF is manufactured using electrochemical fluorination by 3M. Precursors with six perfluorinated carbons (C6) and non-fluorinated amine substituents make up approximately one-third of the PFAS in 3M AFFF. C6 precursors can be transformed through nitrification (microbial oxidation) of amine moieties into perfluorohexane sulfonate (PFHxS), a compound of regulatory concern. Here, we report biotransformation of the most abundant C6 sulfonamido precursors in 3M AFFF with available commercial standards (FHxSA, PFHxSAm, and PFHxSAmS) in microcosms representative of the groundwater/surface water boundary. Results show rapid (<1 day) biosorption to living cells by precursors but slow biotransformation into PFHxS (1-100 pM day-1). The transformation pathway includes one or two nitrification steps and is supported by the detection of key intermediates using high-resolution mass spectrometry. Increasing nitrate concentrations and total abundance of nitrifying taxa occur in parallel with precursor biotransformation. Together, these data provide multiple lines of evidence supporting microbially limited biotransformation of C6 sulfonamido precursors involving ammonia-oxidizing archaea (Nitrososphaeria) and nitrite-oxidizing bacteria (Nitrospina). Further elucidation of interrelationships between precursor biotransformation and nitrogen cycling in ecosystems would help inform site remediation efforts.

Prospects of an Electroactive Carbon Nanotube Membrane toward Environmental Applications.

Rapid population growth and industrialization have driven the emergence of advanced electrochemical and membrane technologies for environmental and energy applications. Electrochemical processes have potential for chemical transformations, chloralkali disinfection, and energy storage. Membrane separations have potential for gas, fluid, and chemical purification. Electrochemical and membrane technologies are often used additively in the same unit process, e.g., the chloroalkali process where a membrane is used to separate cathodic and anodic products from scavenging each other. However, to access the maximal potential requires intimate hybridization of the two technologies into an electroactive membrane. The combination of the two discrete technologies results in a range of synergisms such as reduced footprint, increased processing kinetics, reduced fouling, and increased energy efficiency.Due to their high specific surface area, excellent electric conductivity, and desirable robustness, 1D carbon nanotubes (CNTs) hold promise for many applications over a range of industry sectors such as a base material for electrodes and membranes. Importantly, CNT morphology and surface chemistry can be rationally modified and fine-tuning of these CNT physicochemical properties can enhance their functionality toward practical applications. The CNT 1D form allows assembly of a stable thin-film fibrous network by a variety of facile techniques. These CNT networks have pore sizes in the range of 10-500 nm (dpore ∼ 6-8dCNT) and thicknesses of 10-200 µm, both similar to those of classical polymer membranes, thus allowing for straightforward incorporation into commercial membrane devices modified for electroactivity inclusion.In this Account, CNTs and their composites are used as model electroactive porous materials to exemplify the design strategies and environmental applications of emerging electroactive membrane technology. The Account begins with a brief summary of the electroactive membrane design principles and flow processes developed by our groups. After the methodology section, a detailed discussion is provided on the underlying physical-chemical mechanisms that govern the electroactive membrane technology. Then we summarize our findings on the rational design of several flow-through electrochemical CNT filtration systems focused on either anodic oxidation reactions or cathodic reduction reactions. Subsequently, we discuss a recently discovered electrochemical valence-state-regulation strategy that is capable to detoxify and sequester heavy metal ions. Finally, we conclude the Account with our perspectives toward future development of the electroactive membrane technology.

Isolating the AFFF Signature in Coastal Watersheds Using Oxidizable PFAS Precursors and Unexplained Organofluorine.

Water supplies for millions of U.S. individuals exceed maximum contaminant levels for per- and polyfluoroalkyl substances (PFAS). Contemporary and legacy use of aqueous film forming foams (AFFF) is a major contamination source. However, diverse PFAS sources are present within watersheds, making it difficult to isolate their predominant origins. Here we examine PFAS source signatures among six adjacent coastal watersheds on Cape Cod, MA, U.S.A. using multivariate clustering techniques. A distinct signature of AFFF contamination enriched in precursors with six perfluorinated carbons (C6) was identified in watersheds with an AFFF source, while others were enriched in C4 precursors. Principal component analysis of PFAS composition in impacted watersheds showed a decline in precursor composition relative to AFFF stocks and a corresponding increase in terminal perfluoroalkyl sulfonates with < C6 but not those with ≥ C6. Prior work shows that in AFFF stocks, all extractable organofluorine (EOF) can be explained by targeted PFAS and precursors inferred using Bayesian inference on the total oxidizable precursor assay. Using the same techniques for the first time in impacted watersheds, we find that only 24%-63% of the EOF can be explained by targeted PFAS and oxidizable precursors. Our work thus indicates the presence of large non-AFFF organofluorine sources in these coastal watersheds.

Dependence of Graphene Oxide (GO) Toxicity on Oxidation Level, Elemental Composition, and Size.

The mass production of graphene oxide (GO) unavoidably elevates the chance of human exposure, as well as the possibility of release into the environment with high stability, raising public concern as to its potential toxicological risks and the implications for humans and ecosystems. Therefore, a thorough assessment of GO toxicity, including its potential reliance on key physicochemical factors, which is lacking in the literature, is of high significance and importance. In this study, GO toxicity, and its dependence on oxidation level, elemental composition, and size, were comprehensively assessed. A newly established quantitative toxicogenomic-based toxicity testing approach, combined with conventional phenotypic bioassays, were employed. The toxicogenomic assay utilized a GFP-fused yeast reporter library covering key cellular toxicity pathways. The results reveal that, indeed, the elemental composition and size do exert impacts on GO toxicity, while the oxidation level exhibits no significant effects. The UV-treated GO, with significantly higher carbon-carbon groups and carboxyl groups, showed a higher toxicity level, especially in the protein and chemical stress categories. With the decrease in size, the toxicity level of the sonicated GOs tended to increase. It is proposed that the covering and subsequent internalization of GO sheets might be the main mode of action in yeast cells.

Synthesis and Physicochemical Transformations of Size-Sorted Graphene Oxide during Simulated Digestion and Its Toxicological Assessment against an In Vitro Model of the Human Intestinal Epithelium.

In the last decade, along with the increasing use of graphene oxide (GO) in various applications, there is also considerable interest in understanding its effects on human health. Only a few experimental approaches can simulate common routes of exposure, such as ingestion, due to the inherent complexity of the digestive tract. This study presents the synthesis of size-sorted GO of sub-micrometer- or micrometer-sized lateral dimensions, its physicochemical transformations across mouth, gastric, and small intestinal simulated digestions, and its toxicological assessment against a physiologically relevant, in vitro cellular model of the human intestinal epithelium. Results from real-time characterization of the simulated digestas of the gastrointestinal tract using multi-angle laser diffraction and field-emission scanning electron microscopy show that GO agglomerates in the gastric and small intestinal phase. Extensive morphological changes, such as folding, are also observed on GO following simulated digestion. Furthermore, X-ray photoelectron spectroscopy reveals that GO presents covalently bound N-containing groups on its surface. It is shown that the GO employed in this study undergoes reduction. Toxicological assessment of the GO small intestinal digesta over 24 h does not point to acute cytotoxicity, and examination of the intestinal epithelium under electron microscopy does not reveal histological alterations. Both sub-micrometer- and micrometer-sized GO variants elicit a 20% statistically significant increase in reactive oxygen species generation compared to the untreated control after a 6 h exposure.

Recent advances in nanomaterials for water protection and monitoring.

The efficient handling of wastewater pollutants is a must, since they are continuously defiling limited fresh water resources, seriously affecting the terrestrial, aquatic, and aerial flora and fauna. Our vision is to undertake an exhaustive examination of current research trends with a focus on nanomaterials (NMs) to considerably improve the performance of classical wastewater treatment technologies, e.g. adsorption, catalysis, separation, and disinfection. Additionally, NM-based sensor technologies are considered, since they have been significantly used for monitoring water contaminants. We also suggest future directions to inform investigators of potentially disruptive NM technologies that have to be investigated in more detail. The fate and environmental transformations of NMs, which need to be addressed before large-scale implementation of NMs for water purification, are also highlighted.

Wrinkling and Periodic Folding of Graphene Oxide Monolayers by Langmuir-Blodgett Compression.

Crumples, wrinkles, and other three-dimensional topographical features in graphene oxide (GO) have been of recent interest as these features have improved material performance for a variety of applications. However, wrinkling of monolayer GO films has yet to be reported. Herein, we demonstrate wrinkling and folding of monolayer GO using the Langmuir-Blodgett technique for the first time. First, cetyltrimethylammonium bromide (CTAB) and GO are deposited on the air-water interface and uniaxially compressed to form a monolayer. CTAB enhances in-plane rigidity of the monolayer through hydrophobic tail aggregation, preventing GO-GO in-plane sliding behavior. Overcompression of the GO monolayer results in the out-of-plane periodic nanoscale wrinkling and in turn generates folds that are stable during deposition onto a substrate and GO chemical reduction. Furthermore, we investigate one potential application of this material by constructing a 3D electrode of the stacked nanofolded GO-CTAB layers that exhibits superior volumetric capacitance compared to commercial devices and comparable volumetric capacitance compared to high-performing recently reported devices. The high volumetric capacitance is attributed to the electrolyte-accessible channels generated by the nanofolds which are similar in size to the hydrated ions.

Role of Oxygen Functionalities in Graphene Oxide Architectural Laminate Subnanometer Spacing and Water Transport.

Active research in nanotechnology contemplates the use of nanomaterials for environmental engineering applications. However, a primary challenge is understanding the effects of nanomaterial properties on industrial device performance and translating unique nanoscale properties to the macroscale. One emerging example consists of graphene oxide (GO) membranes for separation processes. Thus, here we investigate how individual GO properties can impact GO membrane characteristics and water permeability. GO chemistry and morphology were controlled with easy-to-implement photoreduction and sonication techniques and were quantitatively correlated, offering a valuable tool for accelerating characterization. Chemical GO modification allows for fine control of GO oxidation state, allowing control of GO architectural laminate (GOAL) spacing and permeability. Water permeability was measured for eight GOALs characterized by different GOAL chemistry and morphology and indicates that GOAL nanochannel height dictates water transport. The experimental outputs were corroborated with mesoscale water transport simulations of relatively large domains (thousands of square nanometers) and indicate a no-slip Darcy-like behavior inside the GOAL nanochannels. The experimental and simulation evidence presented in this study helps create a clearer picture of water transport in GOAL and can be used to rationally design more effective and efficient GO membranes.

Interlaced CNT Electrodes for Bacterial Fouling Reduction of Microfiltration Membranes.

Interlaced carbon nanotube electrodes (ICE) were prepared by vacuum filtering a well-dispersed carbon nanotube-Nafion solution through a laser-cut acrylic stencil onto a commercial polyvinylidene fluoride (PVDF) microfiltration (MF) membrane. Dead-end filtration was carried out using 107 and 108 CFU mL-1 Pseudomonas fluorescens to study the effects of the electrochemically active ICE on bacterial density and morphology, as well as to evaluate the bacterial fouling trend and backwash (BW) efficacy, respectively. Finally, a simplified COMSOL model of the ICE electric field was used to help elucidate the antifouling mechanism in solution. At 2 V DC and AC (total cell potential), the average bacterial log removal of the ICE-PVDF increased by ∼1 log compared to the control PVDF (3.5-4 log). Bacterial surface density was affected by the presence and polarity of DC electric potential, being 87-90% lower on the ICE cathode and 59-93% lower on the ICE anode than that on the PVDF after filtration, and BW further reduced the density on the cathode significantly. The optimal operating conditions (2 V AC) reduced the fouling rate by 75% versus the control and achieved up to 96% fouling resistance recovery (FRR) during BW at 8 V AC using 155 mM NaCl. The antifouling performance should mainly be due to electrokinetic effects, and the electric field simulation by COMSOL model suggested electrophoresis and dielectrophoresis as likely mechanisms.

Geochemical and Hydrologic Factors Controlling Subsurface Transport of Poly- and Perfluoroalkyl Substances, Cape Cod, Massachusetts.

Growing evidence that certain poly- and perfluoroalkyl substances (PFASs) are associated with negative human health effects prompted the U.S. Environmental Protection Agency to issue lifetime drinking water health advisories for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) in 2016. Given that groundwater is a major source of drinking water, the main objective of this work was to investigate geochemical and hydrological processes governing the subsurface transport of PFASs at a former fire training area (FTA) on Cape Cod, Massachusetts, where PFAS-containing aqueous film-forming foams were used historically. A total of 148 groundwater samples and 4 sediment cores were collected along a 1200-m-long downgradient transect originating near the FTA and analyzed for PFAS content. The results indicate that unsaturated zones at the FTA and at hydraulically downgradient former domestic wastewater effluent infiltration beds both act as continuous PFAS sources to the groundwater despite 18 and 20 years of inactivity, respectively. Historically different PFAS sources are evident from contrasting PFAS composition near the water table below the FTA and wastewater-infiltration beds. Results from total oxidizable precursor assays conducted using groundwater samples collected throughout the plume suggest that some perfluoroalkyl acid precursors at this site are transporting with perfluoroalkyl acids.

Semiquantitative Performance and Mechanism Evaluation of Carbon Nanomaterials as Cathode Coatings for Microbial Fouling Reduction.

In this study, we examine bacterial attachment and survival on a titanium (Ti) cathode coated with various carbon nanomaterials (CNM): pristine carbon nanotubes (CNT), oxidized carbon nanotubes (O-CNT), oxidized-annealed carbon nanotubes (OA-CNT), carbon black (CB), and reduced graphene oxide (rGO). The carbon nanomaterials were dispersed in an isopropyl alcohol-Nafion solution and were then used to dip-coat a Ti substrate. Pseudomonas fluorescens was selected as the representative bacterium for environmental biofouling. Experiments in the absence of an electric potential indicate that increased nanoscale surface roughness and decreased hydrophobicity of the CNM coating decreased bacterial adhesion. The loss of bacterial viability on the noncharged CNM coatings ranged from 22% for CB to 67% for OA-CNT and was dependent on the CNM dimensions and surface chemistry. For electrochemical experiments, the total density and percentage of inactivation of the adherent bacteria were analyzed semiquantitatively as functions of electrode potential, current density, and hydrogen peroxide generation. Electrode potential and hydrogen peroxide generation were the dominant factors with regard to short-term (3-h) bacterial attachment and inactivation, respectively. Extended-time electrochemical experiments (12 h) indicated that in all cases, the density of total deposited bacteria increased almost linearly with time and that the rate of bacterial adhesion was decreased 8- to 10-fold when an electric potential was applied. In summary, this study provides a fundamental rationale for the selection of CNM as cathode coatings and electric potential to reduce microbial fouling.

Carbon nanotube membrane stack for flow-through sequential regenerative electro-Fenton.

Electro-Fenton is a promising advanced oxidation process for water treatment consisting a series redox reactions. Here, we design and examine an electrochemical filter for sequential electro-Fenton reactions to optimize the treatment process. The carbon nanotube (CNT) membrane stack (thickness ∼ 200 µm) used here consisted of 1) a CNT network cathode for O2 reduction to H2O2, 2) a CNT-COOFe(2+) cathode to chemical reduction H2O2 to (•)OH and HO(-) and to regenerate Fe(2+) in situ, 3) a porous PVDF or PTFE insulating separator, and 4) a CNT filter anode for remaining intermediate oxidation intermediates. The sequential electro-Fenton was compared to individual electrochemical and Fenton process using oxalate, a persistent organic, as a target molecule. Synergism is observed during the sequential electro-Fenton process. For example, when [DO]in = 38 ± 1 mg L(-1), J = 1.6 mL min(-1), neutral pH, and Ecell = 2.89 V, the sequential electro-Fenton oxidation rate was 206.8 ± 6.3 mgC m(-2) h(-1), which is 4-fold greater than the sum of the individual electrochemistry (16.4 ± 3.2 mgC m(-2) h(-1)) and Fenton (33.3 ± 1.3 mgC m(-2) h(-1)) reaction fluxes, and the energy consumption was 45.8 kWh kgTOC(-1). The sequential electro-Fenton was also challenged with the refractory trifluoroacetic acid (TFA) and trichloroacetic acid (TCA), and they can be transferred at a removal rate of 11.3 ± 1.2 and 21.8 ± 1.9 mmol m(-2) h(-1), respectively, with different transformation mechanisms.

Degradation of the Common Aqueous Antibiotic Tetracycline using a Carbon Nanotube Electrochemical Filter.

In this work, a carbon nanotube (CNT) electrochemical filter was investigated for treatment of aqueous antibiotics using tetracycline (TC) as a model compound. Electrochemical filtration of 0.2 mM TC at a total cell potential of 2.5 V and a flow rate of 1.5 mL min(-1) (hydraulic residence time <2 s) resulted in an oxidative flux of 0.025 ± 0.001 mol h(-1) m(-2). Replacement of the perforated Ti cathode with a CNT cathode increased the TC oxidative flux by 2.3-fold to 0.020 ± 0.001 mol h(-1) m(-2) at a total cell potential of 1.0 V. Effluent analysis by liquid chromatography-mass spectrometry and disk agar biocidal diffusion tests indicate that the electrochemical filtration process can degrade the TC molecular structure and significantly decrease its antimicrobial activity, respectively. Addition of dissolved natural organic matter (NOM) negatively affected the TC electrooxidation because of competition for CNT sorption and electrooxidation sites. At 2.0 V total cell potential, TC spiked (0.2 mM) into drinking water reservoir and wastewater treatment plant effluent samples had an oxidative flux of 0.015 ± 0.001 and 0.022 ± 0.001 mol h(-1) m(-2), respectively, and an energy requirement of 0.7 kWh kgCOD(-1) or 0.084 kWh m(-3). These results indicate a CNT electrochemical filter may have potential to effectively and efficiently treat antibiotics in water and wastewater effluent.

Titanium dioxide-coated carbon nanotube network filter for rapid and effective arsenic sorption.

In this study, a TiO2-coated carbon nanotube (CNT) network filter was prepared via a simple filtration­steam hydrolysis method and evaluated with respect to aqueous arsenic removal. The TiO2 coating was 5.5 ± 2.7 nm thick, completely covered the CNT network surface, and had a specific surface area of 196 m(2) g(­1), which was ∼2-fold greater than that of the CNT network. The TiO2­CNT As sorption kinetics increased with both increasing flow rate and cell potential, with increasing flow rate having a significantly stronger effect. At 6 mL min(­1) in the absence of potential and in recirculation mode, the first-order As sorption rate constants were 4.3 and 4.4 s(­1) for As(III) and As(V), respectively. The TiO2­CNT electro-assisted equilibrium sorption capacities at a cell potential of 2 V for effluent [As] = 10 ppb in single-pass mode were 1.8 and 1.3 mg g(­1) for As(III) and As(V), respectively. The enhanced TiO2­CNT filter As sorption kinetics and capacity result from increased mass transport due to internal convection and pore radius range, improved sorption site accessibility due to porosity and TiO2 dispersion, and reduced TiO2 negative surface charge due to anodic capacitance. Groundwater samples containing 44 ppb As were treated by single-pass filtration, and 12,500 bed volumes (residence time of 4.5 s; 127 L m(­2) h(­1); 5.8 mg m(­2) h(­1)) were filtered prior to the effluent As level reaching >10 ppb. A spent TiO2 filter was successfully regenerated by 5 mM NaOH for both As(III) and As(V).

Solar-driven abnormal evaporation of nanoconfined water.

Intrinsic water evaporation demands a high energy input, which limits the efficacy of conventional interfacial solar evaporators. Here, we propose a nanoconfinement strategy altering inherent properties of water for solar-driven water evaporation using a highly uniform composite of vertically aligned Janus carbon nanotubes (CNTs). The water evaporation from the CNT shows the unexpected diameter-dependent evaporation rate, increasing abnormally with decreasing nanochannel diameter. The evaporation rate of CNT10@AAO evaporator thermodynamically exceeds the theoretical limit (1.47 kg m-2 hour-1 under one sun). A hybrid experimental, theoretical, and molecular simulation approach provided fundamental evidence of different nanoconfined water properties. The decreased number of H-bonds and lower interaction energy barrier of water molecules within CNT and formed water clusters may be one of the reasons for the less evaporative energy activating rapid nanoconfined water vaporization.

Insulated Interlaced Surface Electrodes for Bacterial Inactivation and Detachment.

Effective and stable antibiofouling surfaces and interfaces have long been of research interest. In this study, we designed, fabricated, and evaluated a surface coated with insulated interlaced electrodes for bacterial fouling reduction. The electrodes were printed Ag filaments of 100 µm width and 400 µm spacing over an area of 2 × 2 cm2. The insulating Ag electrode coating material was polydimethylsiloxane (PDMS) or thermoplastic polyurethane (TPU) with a thickness of 10 to 40 µm. To evaluate the antibiofouling potential, E. coli inactivation after 2 min contact with the electrified surface and P. fluorescens detachment after 15 and 40 h growth were examined. The extent of bacterial inactivation was related to the insulating material, coating thickness, and applied voltage (magnitude and AC vs DC). A high bacterial inactivation (>98%) was achieved after only 2 min of treatment at 50 V AC and 10 kHz using a 10 µm TPU coating. P. fluorescens detachment after 15 and 40 h incubation in the absence of applied potential was completed with simultaneous cross-flow rinsing and AC application. Higher AC voltages and longer cross-flow rinsing times resulted in greater bacterial detachment with bacterial coverage able to be reduced to <1% after only 2 min of rinsing at 50 V AC and 10 kHz. Theoretical electric field analysis indicated that at 10 V the field strength penetrating the aqueous solution is nonuniform (∼16,000-20,000 V m-1 for the 20 µm TPU) and suggests that dielectrophoresis plays a key role in bacterial detachment. The bacterial inactivation and detachment trends observed in this study indicate that this technique has merit for future antibiofouling surface development.

A General Strategy to Synthesize Fluidic Single Atom Electrodes for Selective Reactive Oxygen Species Production.

Fine-tuning the geometric and electronic structure of catalytic metal centers via N-coordination engineering offers an effective design for the electrocatalytic transformation of O2 to singlet oxygen (1O2). Herein, we develop a general coordination modulation strategy to synthesize fluidic single-atom electrodes for selective electrocatalytic activation of O2 to 1O2. Using a single Cr atom system as an example, >98% 1O2 selectivity can be achieved from electrocatalytic O2 activation due to the subtle engineering of Cr-N4 sites. Both theoretical simulations and experimental results determined that "end-on" adsorption of O2 onto the Cr-N4 sites lowers the overall activation energy barrier of O2 and promotes the breakage of Cr-OOH bonds to form •OOH intermediates. In addition, the flow-through configuration (k = 0.097 min-1) endowed convection-enhanced mass transport and improved charge transfer imparted by spatial confinement within the lamellar electrode structure compared to that of batch reactor (k = 0.019 min-1). In a practical demonstration, the Cr-N4/MXene electrocatalytic system exhibits a high selectivity toward electron-rich micropollutants (e.g., sulfamethoxazole, bisphenol A, and sulfadimidine). The flow-through design of the fluidic electrode achieves a synergy with the molecular microenvironment that enables selective electrocatalytic 1O2 generation, which could be used in numerous ways, including the treatment of environmental pollution.