Reactive Halogen Species-Mediated Electrocatalytic Oxidation of Arsenite(III).

Electrocatalytic advanced oxidation processes have long been considered among of the most viable ways to remediate aquatic contaminants, including As(III). Although direct electrochemical oxidation of As(III) is thermochemically facile, a high reaction rate is not easily achieved because of the competitive oxygen evolution reaction (OER), particularly at high potentials. This study examines the effect of three halides (Cl-, Br-, and I-) on the electrochemical oxidation of As(III) with nanoparticulate TiO2 electrodes in an aqueous bicarbonate solution at pH 8.7. The halides significantly enhance As(III) oxidation kinetics by >4, >8, and >20 times, respectively, under optimal conditions. Faradaic efficiencies of As(V) production (AsV-FEs) are also enhanced by a maximum of 10 times by the halides, even at high potentials at which the OER occurs. Pre-electrolysis of each halide solution produces reactive halogen species (ClO-, BrO-, and I3-). As(III)-spiking of the pre-electrolyzed halide solutions allows simultaneous concentration changes at near-stoichiometric ratios (R2 > 0.98) between each halogen species and As(V). Among the three halides, iodide imparts the strongest effect on As(III) oxidation owing to its lowest redox potential. Finally, technical considerations of reactive-halogen-species-mediated As(III) oxidation are discussed.

In Situ-Generated Reactive Oxygen Species in Precharged Titania and Tungsten Trioxide Composite Catalyst Membrane Filters: Application to As(III) Oxidation in the Absence of Irradiation.

This study demonstrates that in situ-generated reactive oxygen species (ROSs) in prephotocharged TiO2 and WO3 (TW) composite particle-embedded inorganic membrane filters oxidize arsenite (As(III)) into arsenate (As(V)) without any auxiliary chemical oxidants under ambient conditions in the dark. TW membrane filters have been charged with UV or simulated sunlight and subsequently transferred to a once-through flow-type system. The charged TW filters can transfer the stored electrons to dissolved O2, producing ROSs that mediate As(III) oxidation in the dark. Dramatic inhibition of As(V) production with O2 removal or addition of ROS quenchers indicates an ROS-mediated As(III) oxidation mechanism. Electron paramagnetic spectroscopic analysis has confirmed the formation of the HO2•/O2•- pair in the dark. The WO3 fraction in the TW filter significantly influences the performance of the As(III) oxidation, while As(V) production is enhanced with increasing charging time and solution pH. The As(III) oxidation is terminated when the singly charged TW filter is fully discharged; however, recharging of TW recovers the catalytic activity for As(III) oxidation. The proposed oxidation process using charged TW membrane filters is practical and environmentally benign for the continuous treatment of As(III)-contaminated water during periods of unavailability of sunlight.

Redox-Responsive Covalent Organic Nanosheets from Viologens and Calix[4]arene for Iodine and Toxic Dye Capture.

Owing to their chemical and thermal stabilities, high uptake capacities, and easy recyclability, covalent organic polymers (COPs) have shown promise as pollutant sponges. Herein, we describe the use of diazo coupling to synthesize two cationic COPs, COP1++ and COP2++ , that incorporate a viologen-based molecular switch and an organic macrocycle, calix[4]arene. The COPs form nanosheets that have height profiles of 6.00 nm and 8.00 nm, respectively, based on AFM measurements. The sheets remain morphologically intact upon one- or two-electron reductions of their viologen subunits. MD simulations of the COPs containing dicationic viologens indicate that the calix[4]arenes adopt a partial cone conformation and that, in height, the individual 2D polymer layers are 5.48 Šin COP1++ and 5.65 Šin COP2++ , which, together with the AFM measurements, suggests that the nanosheets are composed of 11 and 14 layers, respectively. Whether their viologens are in dicationic, radical cationic, or neutral form, the COPs exhibit high affinity for iodine, reaching up to 200 % mass increase when exposed to iodine vapor at 70 °C, which makes the materials among the best-performing nanosheets for iodine capture reported in the literature. In addition, the COPs effectively remove Congo red from solution in the pH range of 2-10, reaching nearly 100 % removal within 15 minutes at acidic pH.

Sunlight-charged heterojunction TiO2 and WO3 particle-embedded inorganic membranes for night-time environmental applications.

A metal oxide-heterojunction photocatalyst is developed to harvest sunlight, store the energy in electrons, and apply the stored energy in water treatment. Light-absorbing nanoparticular and nanotubular TiO2 are hybridized with electron-storing WO3 at different weight ratios of TiO2 to WO3 (e.g., TW25 represents a composite of 25 wt% TiO2 and 75 wt% WO3). The ability of the TW composite to utilize the stored electrons is examined for the reduction of hexavalent chromium (Cr(vi)). In the photoelectrochemical (PEC) tests, irradiation using simulated sunlight (AM 1.5, 100 mW cm-2) leads to a rapid shift in the open-circuit potential (OCP) of the TW electrodes to the negative potential region (photocharging process). The termination of irradiation causes a gradual shift of the OCP to the positive potential region over 20 h (discharging process). Spiked Cr(vi) added to the solution with pre-photocharged TW electrodes is efficiently removed; the kinetics of this process depends on the TW composition (25, 50, or 75 wt%), TiO2 morphology (particular or tubular), initial Cr(vi) concentration (0.125 or 0.25 ppm), and whether the conditions are aerated or non-aerated. Based on this knowledge, TW composite-embedded inorganic membranes are synthesized and charged using sunlight. For Cr(vi) removal, single-pass and continuous circulation filtration systems are employed. The fraction of Cr(vi) removed from the circulation system is ∼30% in 4 h, which is 1.5 times that removed using the single-pass filtration system (∼20%). An X-ray photoelectron spectroscopy analysis of the TW membranes used for Cr(vi) removal reveals that Cr is not sorbed in the membrane. The W(vi) in WO3 is partially reduced to W(6-x)+ upon photocharging and is oxidized during the reduction of Cr(vi), leading to the co-existence of W6+ and W(6-x)+.

Viologen-Based Conjugated Covalent Organic Networks via Zincke Reaction.

Morphology influences the functionality of covalent organic networks and determines potential applications. Here, we report for the first time the use of Zincke reaction to fabricate, under either solvothermal or microwave conditions, a viologen-linked covalent organic network in the form of hollow particles or nanosheets. The synthesized materials are stable in acidic, neutral, and basic aqueous solutions. Under basic conditions, the neutral network assumes radical cationic character without decomposing or changing structure. Solvent polarity and heating method determine product morphology. Depending upon solvent polarity, the resulting polymeric network forms either uniform self-templated hollow spheres (HS) or hollow tubes (HT). The spheres develop via an inside-out Ostwald ripening mechanism. Interestingly, microwave conditions and certain solvent polarities result in the formation of a robust covalent organic gel framework (COGF) that is organized in nanosheets stacked several layers thick. In the gel phase, the nanosheets are crystalline and form honeycomb lattices. The use of the Zincke reaction has previously been limited to the synthesis of small viologen molecules and conjugated viologen oligomers. Its application here expands the repertoire of tools for the fabrication of covalent organic networks (which are usually prepared by dynamic covalent chemistry) and for the synthesis of viologen-based materials. All three materials-HT, HS, and COGF-serve as efficient adsorbents of iodine due to the presence of the cationic viologen linker and, in the cases of HT and HS, permanent porosity.

Photocatalytic H2 production on trititanate nanotubes coupled with CdS and platinum nanoparticles under visible light: revisiting H2 production and material durability.

The photocatalytic production of molecular hydrogen (H2) on ternary composites of Pt, CdS, and sodium trititanate nanotubes (NaxH2-xTi3O7, TNTs) is examined in an aqueous 2-propanol (IPA) solution (typically 5 vol%) at a circum-neutral pH under visible light (λ > 420 nm). The H2 production rates are dependent on the Pt-loading level, and the optimum production rate in the Pt/CdS/TNTs is approximately six times higher than that in Pt/CdS/TiO2. A D2O solution containing 5 vol% IPA leads only to the production of D2 molecules, whereas increasing the IPA amount to 30 vol% leads to the production of DH molecules. This indicates that the Pt/CdS/TNTs composites enable H2 production via true water splitting under our typical experimental conditions. X-ray photoelectron spectroscopy (XPS) analyses of the as-synthesized Pt/CdS/TNTs and those used for 6 and 12 h show that metallic Pt on the CdS/TNTs is less susceptible to oxidation than Pt on CdS/TiO2. In addition, photocorrosion of CdS (i.e., sulfate formation) is significantly inhibited during the photocatalytic H2 production reactions in the Pt/CdS/TNTs because of the efficient charge transfer via the TNTs framework. The Pt/CdS/TNTs samples are thermally more stable than Pt/CdS/TiO2 and CdS/TNTs, effectively inhibiting the formation of CdO during the thermal synthesis. Detailed surface characterizations of the as-synthesized ternary composites are performed using X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, and XPS.

Redox-Responsive Viologen-Mediated Self-Assembly of CB[7]-Modified Patchy Particles.

Sulfonated surface patches of poly(styrene)-based colloidal particles (CPs) were functionalized with cucurbit[7]uril (CB[7]). The macrocycles served as recognition units for diphenyl viologen (DPV(2+)), a rigid bridging ligand. The addition of DPV(2+) to aqueous suspensions of the particles triggered the self-assembly of short linear and branched chainlike structures. The self-assembly mechanism is based on hydrophobic/ion-charge interactions that are established between DPV(2+) and surface-adsorbed CB[7]. DPV(2+) guides the self-assembly of the CPs by forming a ternary DPV(2+)⊂(CB[7])2 complex in which the two CB[7] macrocycles are attached to two different particles. Viologen-driven particle assembly was found to be both directional and reversible. Whereas sodium chloride triggers irreversible particle disassembly, the one-electron reduction of DPV(2+) with sodium dithionite causes disassembly that can be reversed via air oxidation. Thus, this bottom-up synthetic supramolecular approach allowed for the reversible formation and directional alignment of a 2D colloidal material.

Ion-imprinted membranes for lithium recovery: A review.

This review critically examines the effectiveness of ion-imprinted membranes (IIMs) in selectively recovering lithium (Li) from challenging sources such as seawater and brine. These membranes feature customized binding sites that specifically target Li ions, enabling selective separation from other ions, thanks to cavities shaped with crown ether or calixarene for improved selectivity. The review thoroughly investigates the application of IIMs in Li extraction, covering extensive sections on 12-crown-4 ether (a fundamental crown ether for Li), its modifications, calixarenes, and other materials for creating imprinting sites. It evaluates these systems against several criteria, including the source solution's complexity, Li+ concentration, operational pH, selectivity, and membrane's ability for regeneration and repeated use. This evaluation places IIMs as a leading-edge technology for Li extraction, surpassing traditional methods like ion-sieves, particularly in high Mg2+/Li+ ratio brines. It also highlights the developmental challenges of IIMs, focusing on optimizing adsorption, maintaining selectivity across varied ionic solutions, and enhancing permselectivity. The review reveals that while the bulk of research is still exploratory, only a limited portion has progressed to detailed lab verification, indicating that the application of IIMs in Li+ recovery is still at an embryonic stage, with no instances of pilot-scale trials reported. This thorough review elucidates the potential of IIMs in Li recovery, cataloging advancements, pinpointing challenges, and suggesting directions for forthcoming research endeavors. This informative synthesis serves as a valuable resource for both the scientific community and industry professionals navigating this evolving field.

Enhancement of Co nucleation on the TaN(x) film surface in Co MOCVD.

In this work, the Co film was deposited by chemical vapor deposition (CVD) on TaN(x)/SiO2/Si substrate at various NH3/H2 gas flow ratio (0, 0.08, 0.11, 0.17, 0.2) to form the continuous layer. It was found that Co film can achieve a low resistivity of 63 microomega-cm, high nucleation density, and a low root-mean-square roughness of 0.79 nm at 0.17 of NH3/H2 gas flow ratio. Moreover, by using fourier transform infrared spectroscopy (FT-IR) analysis, the effect of NH3 gas was confirmed as a reaction catalyst.

Degradation of Organic Methyl Orange (MO) Dye Using a Photocatalyzed Non-Ferrous Fenton Reaction.

Removal of recalcitrant organic pollutants by degradation or mineralization from industrial waste streams is continuously being explored to find viable options to apply on the commercial scale. Herein, we propose a titanium nanotube array (based on a non-ferrous Fenton system) for the successful degradation of a model contaminant azo dye, methyl orange, under simulated solar illumination. Titanium nanotube arrays were synthesized by anodizing a titanium film in an electrolyte medium containing water and ethylene glycol. Characterization by SEM, XRD, and profilometry confirmed uniformly distributed tubular arrays with 100 nm width and 400 nm length. The non-ferrous Fenton performance of the titanium nanotube array in a minimal concentration of H2O2 showed remarkable degradation kinetics, with a 99.7% reduction in methyl orange dye concentration after a 60 min reaction time when illuminated with simulated solar light (100 mW cm-2, AM 1.5G). The pseudo-first-order rate constant was 0.407 µmol-1 min-1, adhering to the Langmuir-Hinshelwood model. Reaction product analyses by TOC and LC/MS/MS confirmed that the methyl orange was partially fragmented, while the rest was mineralized. The facile withdrawal and regeneration observed in the film-based titanium nanotube array photocatalyst highlight its potential to treat real industrial wastewater streams with a <5% performance drop over 20 reaction cycles.

Novel LiAlO2 Material for Scalable and Facile Lithium Recovery Using Electrochemical Ion Pumping.

In this study, α-LiAlO2 was investigated for the first time as a Li-capturing positive electrode material to recover Li from aqueous Li resources. The material was synthesized using hydrothermal synthesis and air annealing, which is a low-cost and low-energy fabrication process. The physical characterization showed that the material formed an α-LiAlO2 phase, and electrochemical activation revealed the presence of AlO2* as a Li deficient form that can intercalate Li+. The AlO2*/activated carbon electrode pair showed selective capture of Li+ ions when the concentrations were between 100 mM and 25 mM. In mono salt solution comprising 25 mM LiCl, the adsorption capacity was 8.25 mg g-1, and the energy consumption was 27.98 Wh mol Li-1. The system can also handle complex solutions such as first-pass seawater reverse osmosis brine, which has a slightly higher concentration of Li than seawater at 0.34 ppm.

Thermally assisted efficient electrochemical lithium extraction from simulated seawater.

Extracting lithium electrochemically from seawater has the potential to resolve any future lithium shortage. However, electrochemical extraction only functions efficiently in high lithium concentration solutions. Herein, we discovered that lithium extraction is temperature and concentration dependent. Lithium extraction capacity (i.e., the mass of lithium extracted from the source solutions) and speed (i.e., the lithium extraction rate) in electrochemical extraction can be increased significantly in heated source solutions, especially at low lithium concentrations (e.g., < 3 mM) and high Na+/Li+ molar ratios (e.g., >1000). Comprehensive material characterization and mechanistic analyses revealed that the improved lithium extraction originates from boosted kinetics rather than thermodynamic equilibrium shifts. A higher temperature (i.e., 60 oC) mitigates the activation polarization of lithium intercalation, decreases charge transfer resistances, and improves lithium diffusion. Based on these understandings, we demonstrated that a thermally assisted electrochemical lithium extraction process could achieve rapid (36.8 mg g-1 day-1) and selective (51.79% purity) lithium extraction from simulated seawater with an ultrahigh Na+/Li+ molar ratio of 20,000. The integrated thermally regenerative electrochemical cycle can harvest thermal energy in heated source solutions, enabling a low electrical energy consumption (11.3-16.0 Wh mol-1 lithium). Furthermore, the coupled thermal-driven membrane process in the system can also produce freshwater (13.2 kg m-2 h-1) as a byproduct. Given abundant low-grade thermal energy availability, the thermally assisted electrochemical lithium extraction process has excellent potential to realize mining lithium from seawater.

Tandem Osmotic Engine Based on Hydrogel Particles with Antipolyelectrolyte and Polyelectrolyte Effect Fuelled by Both Salinity Gradient Modes.

In this study, we propose a new approach to attain energy by salinity gradient engines with pistons based on hydrogels possessing polyelectrolyte and antipolyelectrolyte effects in a tandem arrangement, providing energy in each salinity gradient mode in a repeatable manner. The swelling of hydrogel with a polyelectrolyte effect and shrinking of hydrogel particles possessing an antipolyelectrolyte effect in desalinated water, and subsequent shrinking of hydrogel with polyelectrolyte and swelling of hydrogel antipolyelectrolyte effect in saline water, generate power in both increasing and decreasing salinity modes. To investigate the energy recovery, we scrutinized osmotic engine assemblies by a setup arrangement of pistons with hydrogel particles, with polyelectrolyte and antipolyelectrolyte effects, in tandem. The energy recovery from the tandem engine setup (calculated based on dry form for each polyelectrolyte polyacrylate-based hydrogel-SPA) and antipolyelectrolyte-sulfobetaine-based gel with methacrylate polymeric backbone-SBE) up to 581 J kg-1 and a mean power of 0.16 W kg-1 was obtained by the tandem setup of SPA and SBE hydrogel containing 3% crosslinking density and particle size of 500 microns with an external load of 3.0 kPa. Exchange of sulfobetaine with methacrylamide (SBAm), the main polymer backbone, revealed a positive increase in energy recovery of 670 J kg-1 with a mean power of 0.19 W kg-1 for the tandem system operating under the same parameters (SPA@SBAm). The energy recovery can be controlled, modulated and tuned by selecting both hydrogels with antipolyelectrolyte and polyelectrolyte effects and their performing parameters. This proof of concept provides blue energy harvesting by contributing both polyelectrolyte and antipolyelectrolyte effects in a single tandem setup; together with easy accessibility (diaper-based materials (SPA)) and known antibiofouling, these properties offer a robust alternative for energy harvesting.

Thermo-osmosis-Coupled Thermally Regenerative Electrochemical Cycle for Efficient Lithium Extraction.

Lithium (Li) production based on the soda evaporation process is time-consuming and unsustainable. The emerging electrochemical Li extraction is time-efficient but requires high-concentration Li sources and significant electrical energy input. Here, we demonstrate a fast, energy-saving, and environment-friendly Li production process by coupling a thermally regenerative electrochemical cycle (TREC) using lithium manganese oxide (LMO) and nickel hexacyanoferrate (NiHCF) electrodes with poly(vinylidene fluoride) membrane-based thermo-osmosis (denoted as TO-TREC). The characterization of LMO and NiHCF electrodes confirmed that the relatively high temperature of TO-TREC has negligible adverse effects on the ion intercalation in LMO and NiHCF electrodes. The LMO/NiHCF pair has a positive temperature coefficient of 0.843 mV K-1. In the TO-TREC process, Li ions are selectively extracted from a Li-containing brine warmed by low-grade heat and then released into a room-temperature recovery solution such as LiCl with a production rate of 50-60 mmol Li+ m-2 h-1. Li source solutions are concentrated by thermo-osmosis simultaneously, making it possible to utilize previously unusable Li-containing sources, such as concentrated brines from desalination plants and industrial effluents. Besides, the TREC harvests thermal energy from the heated brine, saving >20% of electrical energy compared to conventional electrochemical methods. The new process shows the potential to meet the growing global Li demands for many applications.

Ion-Enhanced Conversion of CO2 into Formate on Porous Dendritic Bismuth Electrodes with High Efficiency and Durability.

Facile synthesis of efficient electrocatalysts that can selectively convert CO2 to value-added chemicals remains a challenge. Herein, the electrochemical synthesis of porous Bi dendrite electrodes and details of their activity toward CO2 conversion to formate in aqueous solutions of bicarbonate are presented. The as-synthesized multilayered, porous, dendritic Bi electrodes exhibit a faradaic efficiency (FE) of approximately 100 % for formate production. Added halides and cations significantly influence the steady-state partial current density for formate production JFM (Cl- >Br- ≈I- ; Cs+ >K+ >Li+ ). DFT calculations revealed that the reaction pathway involving the species *OCOH occurs predominantly and the presence of both Cs+ and Cl- makes the overall reaction more spontaneous. Photovoltaic-cell-assisted electrocatalysis produced formate with an FE of approximately 95 % (JFM ≈10 mA cm-2 ) at an overall solar conversion efficiency of approximately 8.5 %. The Bi electrodes maintain their activity for 360 h without a change in the surface states.

Ion-Enhanced Conversion of CO2 into Formate on Porous Dendritic Bismuth Electrodes with High Efficiency and Durability.

Invited for this month's cover is the group of Prof. Hyunwoong Park at the Kyungpook National University. The image shows the high-efficiency CO2 conversion to formate using multilayered porous dendrite Bi electrocatalysts. The Full Paper itself is available at 10.1002/cssc.201902581.

Ti3C2Tx MXene-Based Light-Responsive Hydrogel Composite for Bendable Bilayer Photoactuator.

Soft actuators based on hydrogel materials, which can convert light energy directly into mechanical energy, are of the utmost importance, especially with enhancements in device development. However, the hunt for specific photothermal nanomaterials with distinct performance remains challenging. In this study, we successfully fabricated a bilayer hydrogel actuator consisting of an active photothermal layer from incorporated Ti3C2Tx MXene in poly(N-isopropylacrylamide) p(NIPAm)hydrogel structure and a passive layer from the N-(2-hydroxylethylpropyl)acrylamide (HEAA) hydrogel structure. The uniform and effective incorporation of MXene into the NIPAm hydrogel structures were characterized by a battery of techniques. The light responsive swelling properties of the MXene-embedded NIPAm-based hydrogel demonstrated fully reversible and repeatable behavior in the light on-off regime for up to ten consecutive cycles. The effect of MXene loading, the shape of the actuator, and the light source effects on the bilayer NIPAm-HEAA hydrogel structure were investigated. The bilayer hydrogel with MXene loading of 0.3% in the NIPAm hydrogel exhibited a 200% change of the bending angle in terms of its bidirectional shape/volume after 100 s exposure to white light at an intensity of 70 mW cm-2. Additionally, the bending behavior under real sunlight was evaluated, showing the material's potential applicability in practical environments.

Efficient fouling control using outer-selective hollow fiber thin-film composite membranes for osmotic membrane bioreactor applications.

This paper investigates the efficiency of fouling mitigation methods using a novel outer selective hollow fiber thin-film composite forward osmosis (OSHF TFC FO) membrane for osmosis membrane bioreactor (OMBR) system treating municipal wastewater. Two home-made membrane modules having similar transport properties were used. Two operation regimes with three different fouling mitigation strategies were utilized to test the easiness of membrane for fouling cleaning. These two membrane modules demonstrated high performance with high initial water flux of 14.4 LMH and 14.1 LMH and slow increase rate of mixed liquor's salinity in the bioreactor using 30 g/L NaCl as draw solution. OMBR system showed high removals of total organic carbon and NH4 + -N (>98%). High fouling cleaning efficiency was achieved using OSHF TFC FO membrane with different fouling control methods. These results showed that this membrane is suitable for OMBR applications due to its high performance and its simplicity for fouling mitigation.

Modification of Nanofiber Support Layer for Thin Film Composite forward Osmosis Membranes via Layer-by-Layer Polyelectrolyte Deposition.

Electrospun nanofiber-supported thin film composite membranes are among the most promising membranes for seawater desalination via forward osmosis. In this study, a high-performance electrospun polyvinylidenefluoride (PVDF) nanofiber-supported thin film composite (TFC) membrane was successfully fabricated after molecular layer-by-layer polyelectrolyte deposition. Negatively-charged electrospun polyacrylic acid (PAA) nanofibers were deposited on electrospun PVDF nanofibers to form a support layer consisted of PVDF and PAA nanofibers. This resulted to a more hydrophilic support compared to the plain PVDF nanofiber support. The PVDF-PAA nanofiber support then underwent a layer-by-layer deposition of polyethylenimine (PEI) and PAA to form a polyelectrolyte layer on the nanofiber surface prior to interfacial polymerization, which forms the selective polyamide layer of TFC membranes. The resultant PVDF-LbL TFC membrane exhibited enhanced hydrophilicity and porosity, without sacrificing mechanical strength. As a result, it showed high pure water permeability and low structural parameter values of 4.12 L m-2 h-1 bar-1 and 221 µm, respectively, significantly better compared to commercial FO membrane. Layer-by-layer deposition of polyelectrolyte is therefore a useful and practical modification method for fabrication of high performance nanofiber-supported TFC membrane.