Kinetic Results Research Articles

Preparation of MOEAMCl and MAAm Based Hydrogels and Effective Use in Anionic Dye Adsorption

ABSTRACTIn this study, hydrogels based on [2‐(Methacryloyloxy)ethyl]trimethylammonium chloride (MOEAMCl) and methacrylamide (MAAm) were synthesized for the removal of anionic dyes from aqueous solutions. Following detailed characterization, the use of hydrogels for methyl orange (MO) adsorption was investigated. Hydrogels prepared at MOEAMCl‐MAAm monomer feed ratios of 75:25 and 50:50 (HD‐2 and HD‐3) were found to be effective in MO removal. The optimal pH for MO adsorption was determined to be 9, the adsorption time 6 h, and the amount of adsorbent 0.1 g. Under optimal adsorption conditions, dye removal at an MO concentration of 1000 ppm was 89.4% and 90.9% for HD‐2 and HD‐3 hydrogels, respectively, with adsorption capacities of 950 and 994 mg/g. It was observed that MO adsorption on both hydrogels decreased with increasing adsorbent amount and temperature, but was almost unaffected by the medium matrix. Additionally, the Freundlich isotherm was found to be the appropriate isotherm model, and kinetic results indicated that the HD‐3 hydrogel fit all examined kinetic models better than HD‐2. In conclusion, it was determined that these adsorbents could be efficiently used for anionic dye removal.

Controllable Synthesis and “Fast‐charging” Mechanism of Hollow‐Micropencil Co3V2O8 from Perspective of Ion Diffusion in Crystal Structure

AbstractCo3V2O8 as a bimetallic oxide with “fast‐charging” capacity presents some potential advantages, comprising decent theoretical specific capacity, favorable crystal structure, and intrinsic safety. Presently, although extensive research of Co3V2O8 as an anode material are reported, the formed Co° from Co3V2O8 after the initial discharging is not oxidized to CoO during the charging process, and the ion diffusion mechanism are not well clarified. The lithium‐storage process of Co3V2O8 and the diffusion mechanism of lithium ion in Co3V2O8 are studied in detail in this work. A hollow‐micropencil Co3V2O8 prepared through the hydrothermal method without using surfactants or templates demonstrates a high “fast‐charging” capability even at the current densities as high as 1.0–2.0 A g−1. The electrochemical kinetic results illustrate that the hollow‐micropencil Co3V2O8 presents low charge transfer resistance. The distinctive lithium ion storage sites as well as diffusion paths are predicted. The in situ X‐ray diffraction analysis is adopted to confirm that the formed Co° after the initial discharging is not oxidized to CoO during the delithiation process. The work not only helps to understand the lithium insertion mechanisms of Co3V2O8 but also offers new means to develop “fast‐charging” anode material for lithium‐ion batteries with remarkable electrochemical performance.

Dilute Povidone-Iodine Irrigation: The Science of Molecular Iodine (I2) Kinetics and Its Antimicrobial Activity.

Dilute povidone-iodine (polyvinylpyrrolidone iodine [PVP-I]) irrigation in spine surgery and total joint arthroplasty has seen a rapid and substantial increase in its use during the past decade. Yet, most surgeons do not know the chemistry and biochemistry that explain its efficacy in preventing infections. PVP-I forms a complex with molecular iodine (I2), facilitating the delivery of I2 to the membrane of the infectious organism. Here, PVP-I establishes an equilibrium between complexed and noncomplexed (free) I2 in the aqueous solution. The I2 acts at numerous cellular targets of infecting organisms augmenting its role as a biocidal molecule. The paradoxical increase in the concentration of I2 that occurs with dilution of PVP-I is a result of equilibrium kinetics and is associated with an enhanced antimicrobial activity. Cytotoxicity studies have yielded conflicting results, but most endorse diluted concentrations as being less damaging to tissues. Clinical studies have verified notable reductions in surgical site infections with a 3-minute soak of 0.35% dilute povidone-iodine irrigation. Guidelines from the World Health Organization, Centers for Disease Control and Prevention, and International Consensus Meeting on Musculoskeletal Infection support the use of prophylactic incisional wound irrigation with aqueous PVP-I to reduce and prevent surgical site infections.

Mechanism of Ampicillin Hydrolysis by New Delhi Metallo-β-Lactamase 1: Insight From QM/MM MP2 Calculation.

The New Delhi metallo-β-lactamase 1 (NDM-1) can hydrolyze nearly all clinically important β-lactam antibiotics, narrowing the options for effective treatment of bacterial infections. QM/MM MP2 calculations are performed to reveal the mechanism of ampicillin hydrolysis catalyzed by NDM-1. It is found that the rate-determining step is the dissociation of hydrolyzed ampicillin from the NDM-1 active site, which requires a proton transfer from the bridging neutral water molecule to the newly formed carboxylate group. The precedent reaction steps, including the hydroxide nucleophilic addition, CN bond cleavage, and the protonation of the negative lactam N atom by a solvent water molecule, all require insignificant activation free energies. The calculated activation free energy for this rate-determining proton transfer step is 16.0 kcal/mol, in good agreement with experimental values of 13.7 ~ 14.7 kcal/mol. This proton transfer step exhibits a solvent hydrogen-deuterium kinetic isotope effect of 3.4, consistent with several experimental kinetic results.

Improvement of oxidation resistance of the Ti-modified Cr-based coating on Zry-4 by Cr2O3/Cr2TiO5 double oxide layer with coherent interface

The loss of coolant accident (LOCA) has brought great threat to the safety of nuclear power plant. The oxidation resistance of Zircaloy-4(Zry-4) cladding must be improved to prevent the leakage of nuclear fuel. The Ti-modified Cr-based coating with excellent oxidation resistance was deposited on the Zry-4 by magnetron sputtering. The oxidation kinetics and microstructure evolution of the coatings were investigated via isothermal oxidation experiments at 900–1200 °C, respectively. The results of oxidation kinetics shows that the oxidation resistance of the Ti-modified Cr-based coated Zry-4 is significantly improved and the activation energy of the coated Zry-4 is increased by about 25 %. After steam oxidation at 1200 °C, the coating formed a three-layer structure, Cr2TiO5, Cr2O3 and residual Cr layer. The first-principles calculation shows that the diffusion energy of O in Cr2TiO5 is higher than that in Cr2O3. Furthermore, the formed Cr2TiO5 layer is connected to the underlying Cr2O3 layer via a coherent interface, which both improves the bonding of the oxide layer and dissipates the stresses generated during the oxidation.

Reactivity in Friedel-Crafts aromatic benzylation: the role of the electrophilic reactant.

Density functional theory is employed in understanding the reactivity in the TiCl4 catalyzed Friedel-Crafts benzylation of benzene with substituted benzyl chlorides in nitromethane solvent. A series of ten substituted (in the aromatic ring) benzyl chlorides are characterized by theoretical reactivity indices. The theoretical parameters are juxtaposed to experimental relative rates of benzylation. It is established that the carbon-chlorine ionic bond dissociation energy and the Hirshfeld charge at the chlorine atom for the benzyl chlorides reactants - describe quite satisfactorily the reactivity trends. These results provide further insights into the factors governing reactivity in EAS reactions, which so far have been mostly focused on rate variations induced by changes in the structure of the aromatic substrate. The EAS benzylation investigated is quite unusual since, in contrast to most EAS reactions, the latest experimental kinetic results suggest that the aromatic substrate does not participate in the kinetic equation of the process. To shed more light on this unexpected result, we also conducted a theoretical study on the mechanistic pathway by applying M06-2X density functional computations combined with several basis sets: 6-311+G(d,p), 6-311+G(2df,2p), and def2-TZVPP. Because of the well-known difficulties in evaluating realistic free energy barriers for organic reactions, we tested two solvent models in determining the barrier for the TiCl4-catalyzed Friedel-Crafts benzylation of benzene by benzyl chloride. Since all methods employed did not provide satisfactory results for the free energy barriers, we used a combination of theoretically estimated enthalpy barriers and the available (from kinetic experiments) entropy contribution. This approach enabled us to verify that indeed the rate of this EAS reaction does not depend on the nature of the aromatic substrate. The computations revealed the structure and relative energies of the critical structures along the mechanistic pathway. Four intermediates were established along the reaction route.

Theoretical study on the degradation mechanisms, degradation efficiencies, and toxicity evaluation of 2-chlorophenylacetonitrile by hydroxyl radical in the aqueous phase

In this study, the reaction mechanisms and kinetics in the degradation of chlorophenylacetonitrile (2-CPAN) by the UV/H2O2 process were investigated by the theoretical calculation method. A chemical kinetic model was developed to simulate the degradation efficiency of 2-CPAN during the degradation process. In addition, the toxic effects of 2-CPAN and its products on the aquatic environment were assessed. During the initial reactions, the hydrogen atom abstraction reactions of the branched chain was more likely to occur than the ·OH-addition reactions. Kinetic results showed that the total second-order reaction rate increased with increasing temperature in the range of 273–313 K, and the total second-order reaction rate was 5.69 × 107 M−1 s−1 at 298 K. The results of degradation efficiency simulation showed that high concentration of oxidant, long reaction time, low initial concentration of pollutant, and low pH were favorable for improving the degradation efficiency. Toxicity assessment showed that most of the degradation products were less toxic to aquatic organisms than 2-CPAN. A theoretical guidance for the chemical reaction characteristics and kinetic behaviors for the degradation of disinfection by-products by the UV/H2O2 process was provided in this study.

Alpine pasture plant species affect in vitro rumen methane production and kinetics

This study aimed to evaluate the influence of different plant species widespread in alpine pastures on in vitro rumen fermentation parameters and methane kinetic production. A total of 11 plant species were sampled at the beginning of the grazing season and used as substrates in an in vitro batch fermentation system. After 24h of fermentation, plants affected volatile fatty acids profiles, ammonia yield, and dry matter (DM) digestibilities. Carum carvi, Ranunculus. acris and Festuca rubra showed the highest total production of methane per unit of digested DM while Potentilla erecta was the species that produced less methane. In terms of methane as a percentage of the total gas, F. rubra had the highest value (28.9%) while R. acris had the lowest (24.2%). Total gas and methane production were monitored continuously and the percentage of methane in total gas was fitted with the Gompertz model. Plants differed significantly (p < .01) in methane production kinetics, including production rate decline (A), asymptotic methane concentration (B), time to maximum fermentation rate (TMFR), and maximum fermentation rate (MFR). C. carvi, Prunella grandiflora, and R. acris showed high values of MFR and the top values in the production rate decline (A > 0.9). The two grasses (F. rubra and Poa alpina) together with Hypericum maculatum showed an opposite behaviour with low values in MFR, A and a longer TMFR. The results of the methane production kinetics allow for an in-depth evaluation of plant species, adding further information to those registered at the end of fermentation.

A Quantum Chemistry Insight into the Potential Role of the Singlet Oxygen-Acetone System as a Source for Production of Stable Secondary Organic Aerosols through a Multiwell Multipath Reaction.

The high abundance of acetone ((CH3)2C═O), which makes it a good candidate for oxygenated molecules, and the high reactivity of oxygen atoms in the first excited state O(1D) are two well-known facts in the chemistry of the atmosphere. In this research, we prove that the singlet oxygen and acetone system is capable of proceeding through multiwell multipath reactions, leading to the production of several organic aerosols. Hence, the nature of species released by the (CH3)2C═O + O(1D) reaction to air can be clarified by profound attention to the possible routes. To verify this, the singlet potential energy surface (PES) of the acetone + O(1D) reaction is investigated by using various validated quantum chemistry approaches, especially the high-cost BD(TQ) method. By the carefully chosen theoretical methods, we forecast all possible multistep routes with high accuracy for the production of possible adducts in reliable conditions. Also, we use the kinetic results of the well-proven theories (TST and RRKM) to show the importance and atmospheric relevance of the simulated reactions. So, the rate constants of the (CH3)2C═O + O(1D) reaction channels are computed at a large temperature range employing precise energetics and partition functions to show which products have a high percentage of yield. Moreover, the competitive canonical unified statistical (CCUS) model is utilized to show whether pressure influences the products generated by barrierless reactions. In addition, the thermodynamic functions of stationary points (at 298 K) and the rate constants of the found reaction routes demonstrate that the reaction adducts are very stable, so the reverse reactions have less importance compared to the forward reactions. In summary, this study illustrates how designed reaction routes could play a vital role in secondary aerosol formation in the atmosphere.

Unlocking the Catalytic Potential of Anionic Micelles: Insights into the Ce(IV)-Directed Phenylalanine Oxidation Kinetics in Asymmetric Hydrophobic Environments.

The oxidation kinetics of phenylalanine (Phe) by Ce(IV) have been examined in both the absence and presence of aqueous micellar media with asymmetric tails, specifically using sodium dodecyl sulfate (SDS) and sodium tetradecyl sulfate (STS) surfactants. The reaction progress was monitored by observing a decrease in absorbance using UV-vis spectroscopy. Interestingly, the kinetic profile revealed a consistent increase in the observed rate constant values as the concentration of the surfactant increased. The kinetic results have been analyzed by using numerous experimental studies, such as dynamic light scattering (DLS), zeta potential, 1H NMR analysis, FT-IR spectroscopy, conductometry, scanning electron microscopy (SEM), fluorometry, time-correlated single-photon counting (TCSPC), and transmission electron microscopy (TEM). Micellar aggregates maintain their spherical shape in the presence of the substrate, even at higher surfactant concentrations, as revealed by microstructural analysis. The substrate molecules are encapsulated to a greater extent in the inner micellar core of STS micelles on account of the more hydrophobic nature of STS surfactants. Therefore, in STS micellar media, fewer substrate molecules diffuse to the Stern layer compared to the SDS micellar medium, resulting in fewer molecules participating in the oxidative transformation reaction. As a result, the rate enhancement of oxidation kinetics is less pronounced in STS micelles than in SDS micelles. A plausible mechanism that aligns with the kinetic results has been highlighted, along with the interpretation of the Piszkiewicz model, to explain the observed catalytic effect of both micellar mediums.

Preparation of MgAl‐LDH/halloysite composite materials for efficient CO2 adsorption

AbstractBackgroundCO2 emissions have had negative impacts on various aspects of life and the environment, making the development of materials with high CO2 adsorption performance crucial.ResultIn this study, halloysite nanotubes (HNTs) were used as a carrier to prepare MgAl layered double hydroxide (LDH) via a convenient coprecipitation method, resulting in MgAl‐LDH/HNT composite material, which was then evaluated for its CO2 adsorption performance. The physicochemical properties of the composite material were characterized using various methods. Results showed that the 1:1 ratio MgAl‐LDH/HNT composite exhibited superior material structure, with a specific surface area reaching 178.24 m2 g−1. In CO2 adsorption performance tests, the 1:1 MgAl‐LDH/HNT composite showed the best adsorption performance, with a CO2 adsorption capacity of 3.91 mmol g−1. This adsorption process includes physical adsorption and chemical adsorption. Kinetic analysis results indicate that the adsorption process is mainly dominated by physical adsorption. The material also demonstrated good performance in cyclic stability tests, maintaining a regeneration efficiency of over 94% after six cycles.ConclusionThe MgAl‐LDH/HNT material has good properties and stability. This provides an effective pathway and direction for the development of new adsorbents with higher CO2 adsorption performance. © 2024 Society of Chemical Industry (SCI).

Spatial resolution of a velocity-selected ion imaging microscope for surface reaction kinetics mapping.

Experimental validation of complex microkinetic models derived from quantum chemistry is crucial for the advancement of bottom-up approaches to heterogeneous catalysis. State-of-the-art velocity-resolved kinetics experiments have made tremendous progress in this arena but integrate reactivity over centimeter-scale single-crystal catalytic surfaces even when complex spatial phenomena may perturb the kinetic results. We report a new design, optimization, and analysis of an ion imaging microscope that can collect spatially resolved kinetic data from a catalytic surface. In its simplest configuration, gaseous reaction products are ionized by a laser line or sheet above a catalytic surface. The resulting ions are extracted and strongly lensed to an intermediate velocity-mapped plane where a pinhole of radius r only transmits ions produced from reaction products with desorption velocities within a narrow solid angle centered on the surface normal. Transmitted ions re-expand through an electrostatic zoom lens to form a spatial image of the initial reaction product distribution with reduced blur from desorption velocity components parallel to the surface. The ion hits that define the magnified and deblurred spatial image can be used to determine spatiotemporal flux and speed-distributions of gas leaving the catalyst surface. Electrostatic trajectory simulations are performed and verify that transmission is ∝r2/TSurface. However, calculated global point spread functions acting on the magnified image have a width that is ∝r and largely independent of TSurface. Thus, velocity-filtered ion imaging microscopy can deliver a consistent resolution as the TSurface is varied, which is a great advantage because many catalytic reactions require elevated temperatures.

Insight into the Simultaneous Super-Stable Mineralization of AsO4 3-, Cd2+ and Pb2+ Using MgFe-LDHs.

Multiple-heavy-metal contamination in soil, such as the simultaneous presence of AsO4 3-, Cd2+ and Pb2+, which can reduce crop yields and damage human health, is a serious issue to be addressed. Herein, the MgFe-LDHs (layered double hydroxides) intercalated with carbonate and nitrate (MgFe-CO3 and MgFe-NO3) were synthesized by Separate Nucleation and Aging Steps and ion-exchange method, respectively. The MgFe-CO3 demonstrated the maximum saturation adsorption capacity of 55.86, 543.48 and 1597.4 mg g-1 for single AsO4 3-, Cd2+ and Pb2+ in aqueous solution, while MgFe-NO3 exhibited 92.50, 387.59 and 869.56 mg g-1, respectively. Kinetic and thermodynamic results for mineralization of single AsO4 3-, Cd2+ and Pb2+ fitted well with the pseudo-second-order kinetic model and Langmuir isotherm model, indicating the occurrence of chemisorption and monolayer adsorption for both MgFe-CO3 and MgFe-NO3. Furthermore, simultaneous mineralization of AsO4 3-, Cd2+ and Pb2+ with >99.0 % efficiency in 240 min in aqueous solution and >81.1 % efficiency in 14 days in soil can be achieved by both MgFe-CO3 and MgFe-NO3. Preliminary red bean seedlings cultivation experiments indicated that the released Mg2+ ions from MgFe-CO3 and MgFe-NO3 were capable to promote the emergence and growth of red bean seedlings. Detailed XRD and XPS results demonstrated that the AsO4 3- anions were adsorbed on the laminate of LDHs, whereas the Pb3(OH)2(CO3)2 was the mineralization product for both MgFe-CO3 and MgFe-NO3. In terms of Cd2+, CdCO3 was obtained as a mineralization product for MgFe-CO3, while CdCO3 and Cd(OH)2 can be detected due to the slow transformation of MgFe-NO3 to MgFe-CO3 in air.

Toxicity of microplastics and nano-plastics to coral-symbiotic alga (Dinophyceae Symbiodinium): Evidence from alga physiology, ultrastructure, OJIP kinetics and multi-omics.

Corals are representative of typical symbiotic organisms. The coral-algal (Symbiodinium spp.) symbiosis drives the productivity of entire coral reefs. In recent years, microplastics (MPs) and nano-plastics (NPs) have been shown to disrupt this symbiosis, leading to coral bleaching. However, how MPs/NPs affect the Symbiodinium spp. is less thoroughly explored. In this work, Dinophyceae Symbiodinium was employed as a model to study the toxicity effects of MPs and NPs with different concentrations (covering environment-related concentration) toward algae in terms of cellular responses, ultrastructure, OJIP kinetics curve and multi-omics. MPs and NPs caused adverse effects on algae growth throughout whole growing phase, with only slight differences observed in the maximal inhibition ratio. In addition to cell surface shrinkage, holes and plate sutures shedding of algae, the presence of distorted thylakoids, plasmolysis and expanded vesicle volume were observed due to the oxidative stress and physical damage caused by MPs/NPs. The results of OJIP kinetics and JIP-test revealed that MPs/NPs-induced deactivation of oxygen-releasing complex (OEC) centers, reduced electron transfer (photosystem II, PSII), and inefficient energy conversion of antenna proteins were the primary factors for photosynthesis reduction. Weighted correlation network analysis (WGCNA) showed that the impairment of photosynthesis further induces metabolic disturbances, including reactive oxygen species (ROS) generation and nucleotide metabolism dysregulation, thereby exacerbating DNA damage in the algae. Proteomics further validate the accuracy of our results and underscore the significance of the phosphatidylinositol (PI) signaling system in algae responding to MP/NPs acclimation. Collectively, our findings provide comprehensive insights into the ecotoxicity of NPs/MPs on symbiotic algae.

Three-dimensional, multi-functionalized nanocellulose/alginate hydrogel for efficient and selective phosphate scavenging: Optimization, performance, and in-depth mechanisms.

Challenges in developing adsorbents with sufficient phosphate (P) adsorption capacity, selectivity, and regeneration properties remain to be addressed. Herein, a multi-functionalized high-capacity nanocellulose/alginate hydrogel (La-NCF/SA-PEI [La: lanthanum, NCF: nanocellulose fiber, SA: sodium alginate, PEI: polyethyleneimine]) was prepared through environmentally friendly methods. The La-NCF/SA-PEI hydrogel, featuring a 3D porous structure with interwoven functional groups (amino, quaternary ammonium, and lanthanum), demonstrated a maximum P adsorption capacity of 78.0mg/g, exceeding most La-based hydrogel adsorbents. The kinetic and isotherm fitting results confirmed the multilayer chemisorption process. Comprehensive experimental results, instrumental analysis, and computational results revealed that the ammonium phosphate complex (NH3+-O-P) and the inner-sphere complex (La-O-P) formed by La(OH)3 dominated the selective P adsorption process. Density-functional theory (DFT) was employed to calculate the bond length between phosphate and each component of the La-NCF/SA-PEI. The calculation results revealed the double-bridge adsorption between the N (apex) atom on La-NCF/SA-PEI and the O (apex) atomic site in phosphate, including electrostatic adsorption and two hydrogen bonds (bond lengths 1.001 and 1.008Å) between the O of PO43- and the H+ of the protonated amino group. Except the remarkable P adsorption performance (both municipal sewage and aquaculture tail water), the La-NCF/SA-PEI hydrogel's high selectivity toward P, environmental compatibility, and easy separability from water underscore its significant potential for phosphate-contaminated water remediation. The multi-functionalized La-NCF/SA-PEI demonstrate promising potential for P removal applications and advanced the development of sustainable, biomass-based adsorbents design.

Removal of Cr6+ in water by superoxide anion-mediated redox reaction assisted by lignin-rich kiwifruit twig biochar: Application of DFT calculation.

This research aims to investigate the role of reactive oxygen species (ROS) in the adsorption and reduction of Cr6+ on lignin-rich biochar under dark conditions and under various oxygen treatment conditions. The research found that under aerobic conditions, the reduction content of Cr6+ (0.38 mg) and the production content of ·O2- (20.36 × 10-6 mg·L-1) are the highest, followed by untreated conditions (0.32 mg, 15.03 × 10-6 mg·L-1), and the lowest under anaerobic conditions (0.21 mg, 5.14 × 10-6 mg·L-1). Compared with anaerobic conditions, the reduction content of Cr6+ increased by 1.52 times under untreated conditions. Meanwhile, under anaerobic conditions, ·O2- disappeared, indicating that ·O2- had played an important role in the reduction of Cr6+. Kinetic results showed that the role of ·O2- in the reduction of Cr6+ mainly occurred in liquid solution. DFT calculations confirmed that C-OH was the main electron supplier in the reduction process of Cr6+, and there was a positive correlation between the production content of ·O2- and the content of C-OH in liquid solution. The present research is expected to provide a scientific basis for the transformation of Cr6+ on lignin-rich biochar in liquid solution.

Functional ZnONPs‐modified biochar derived from Funtumia elastica husk as an efficient adsorbent for the removal of sulfamethoxazole from wastewater

Funtumia elastica husk was employed as an efficient and economically viable adsorbent to supplement traditional treatment methods in the removal of sulfamethoxazole from wastewater by converting it into usable material. The purpose of this study was to make biochar (FHB) from Funtumia elastica husk through the pyrolysis process and further modify the biochar using zinc oxide nanoparticles (ZnONPs) to a nanocomposite (FBZC). The antioxidant and antimicrobial characteristics as well as the potential of FBZC and FHB to sequester sulfamethoxazole from wastewater were investigated. Uptake capacities of 59.34 mg g−1 and 26.18 mg g−1 were attained for the monolayer adsorption of SMX onto FBZC and FHB, respectively. SEM and FTIR spectroscopic techniques were used to determine the surface morphology and chemical moieties of adsorbents, respectively. Brunauer–Emmett–teller (BET) surface analysis was used to assess the specific surface area of FHB (0.5643 m2 g−1) and FBZC (1.2267 m2 g−1). The Elovich and pseudo-first-order models are both well-fitted by the experimental data for FHB and FBZC, according to kinetic results. Nonetheless, the equilibrium data for FHB and FBZC were better explained by the Freundlich and Langmuir isotherm models, respectively. The pHPZC values of 6.83 and 5.57 were determined for FBZC and FHB respectively. Optimum solution pH, dosage, and contact time of 6, 0.05 g, and 120 min were estimated for FHB and FBZC. In conclusion, these findings demonstrate the strong potential of FBZC to simultaneously arrest the spread of pathogenic microbes and sequester sulfamethoxazole from wastewater.

Design Strategies for Oxygen Evolution Reaction Catalysts: Insights from a Kinetic Perspective via Constrained Ab Initio Molecular Dynamics

In the pursuit of sustainable energy, the efficient production of green hydrogen through electrochemical water splitting has emerged as a promising strategy.1 Central to this process is the optimization of the Oxygen Evolution Reaction (OER), where the necessity for a high overpotential at the anodic electrode poses a significant barrier. Among the myriad of catalysts studied, iridium oxides (IrOx) have garnered attention for their superior catalytic activity and stability in acidic environments.2 Yet, the quest for unlocking the full potential of IrOx catalysts necessitates a deeper dive into their operational mechanisms under OER conditions, a challenge that traditional Density Functional Theory (DFT) methodologies have struggled to meet due to their limited representation of the dynamic electrochemical environment intrinsic to OER catalysis.3 Addressing these challenges, our research introduces a novel approach by integrating constant Fermi-level ab initio molecular dynamics (AIMD) simulations with slow-growth kinetic analysis. This methodological innovation captures the complex electrochemical environment of OER catalysis, unveiling reaction pathways and energy barriers with close to actual electrochemical reaction. Through this approach, we explore the impact of the oxygen 2p orbital, Ir–O bond strength, and proton affinity on the Lattice Oxygen Mechanism (LOM) and Adsorbate Evolution Mechanism (AEM), establishing new paradigms for catalyst evaluation and design.A focal point of our study is the detailed analysis of the elemental phases of LOM and AEM, which provides a granular understanding of the catalytic actions within these mechanisms. In the case of LOM, our focus is on the dynamics and electronic state of lattice oxygen, which play pivotal roles in defining the energy barriers distinct to each elemental phase. This analysis identifies the electronic structure of lattice oxygen and the robustness of Ir–O bonds as key determinants of LOM activity. Similarly, the phase of AEM process is characterized by the sequential proton transfer of water molecules and surface proton, highlighting the importance of the structural arrangement of surface hydrogen and the proton affinity of lattice oxygen in determining AEM activation stages.Subsequent to the mechanism phase analysis, we present the validation of our theoretical insights through the suggestion and evaluation of E–IrTaO2, a lattice-elongated Ir-Ta bimetallic oxide catalyst designed to enhance LOM selectivity. The design of E–IrTaO2 is informed by kinetic analysis, with its activity evaluation underpinned by kinetic results that consider the thermodynamic energy diagram, including pathways through metastable states. This departure from conventional DFT methodologies signals a paradigm shift towards a kinetic-driven approach, crucial for unraveling the intricate behaviors of IrOx in OER processes and laying the groundwork for the development of sophisticated catalysts.This study not only provides an in-depth understanding of the catalytic mechanisms in OER processes but also introduces a programmable strategy for catalyst design, paving the way for the rational development of high-performance OER catalysts. References Taibi, E., Miranda, R., Carmo, M. & Blanco, H. Green hydrogen cost reduction. (2020).King, L. A. et al. A non-precious metal hydrogen catalyst in a commercial polymer electrolyte membrane electrolyser. Nature nanotechnology 14, 1071-1074 (2019).Mefford, J. T. et al. Water electrolysis on La1− x Sr x CoO3− δ perovskite electrocatalysts. Nature communications 7, 11053 (2016) Figure 1

Exploring Reference Electrodes in Polymer Electrolyte Membrane Water Electrolysis: Analysis of Design Challenges and Review of Characterization Results for Oxygen and Hydrogen Evolution Reaction Kinetics

Clean hydrogen from renewable energy sources via proton exchange membrane water electrolyzers (PEMWE) has great potential to decarbonize various sectors and integrate intermittent renewables into the energy mix (1). However, its large-scale deployment faces significant hurdles, mainly due to the high cost of materials like platinum and iridium used as electrocatalysts (2). Improving the characterization of catalyst layers in PEMWE helps to address this, as a better understanding of the efficiency and durability of the catalyst layers drives research advancements and facilitates cost-reduction efforts.Current characterization tools have limitations in providing realistic insights into catalyst performance in PEMWE. This contribution explores using reference electrodes (REs) to address this gap. REs offer the advantage of measuring the proton potential within the system, which helps to optimize performance and understand degradation mechanisms. However, integrating REs into PEM cells presents challenges, such as the impact of the RE device on the cell or its accuracy (3–5).This study presents the integration of two reference electrode (RE) setups, a salt bridge RE (SBRE) and a dynamic hydrogen RE (DHE), into a standardized PEMWE test cell. The focus is on overcoming design optimization challenges and mitigating performance impacts. Among these challenges is the influence of ionomer treatment of the porous transport layer (PTL), an integral part of the SBRE design, which affects cell performance. The impregnation of the PTL can result in increased ohmic, mass transport and other losses (5). The Figure below shows the full cell polarization curve for both pristine PTLs and PTLs subject to various degrees of impregnation. A clear pattern can be observed where lower impregnation volumes result in cell performance closer to that of the unimpregnated counterpart. An optimal impregnation volume of 1 µL of a 5 wt% electrolyte solution is identified. This adjustment minimizes the impact on cell performance while ensuring the necessary ionic connectivity is maintained.Additionally, another challenge lies in electrochemical impedance measurements (EIS) for half-cells. This is addressed by integrating improved EIS settings that strategically avoid high frequencies prone to inductance, enabling accurate HFR measurements in half-cells for subsequent kinetic analyses. In addition to these challenges, further obstacles, such as potential gradient across the salt bridge and RE precision, are also addressed. These challenges are thoroughly analyzed both theoretically and experimentally, and corresponding solutions are presented.Building on the thorough analysis of the RE setups and the implemented solutions and enhancements, experimental investigation and kinetic analysis are carried out. An overview of the findings is given, which includes OER and HER kinetic parameters, investigates temperature effects on kinetics, and elucidates aspects of degradation. In addition, the application of the Arrhenius equation to analyze the temperature dependence of the exchange current density provides insight into the activation energies for half-cell reactions.References U.S. Department of Energy, Hydrogen Production Processes, https://www.energy.gov/eere/fuelcells/hydrogen-production-processes.S. Krishnan, V. Koning, M. Theodorus de Groot, A. de Groot, P. G. Mendoza, M. Junginger and G. J. Kramer, International Journal of Hydrogen Energy, 48(83), 32313–32330 (2023).L. V. Bühre, A. J. McLeod, P. Trinke, B. Bensmann, M. Benecke, O. E. Herrera, W. Merida and R. Hanke-Rauschenbach, J. Electrochem. Soc. (2023).A. J. McLeod, L. V. Bühre, B. Bensmann, O. E. Herrera and W. Mérida, Journal of Power Sources, 589, 233750 (2024).L. V. Bühre, S. Bullerdiek, P. Trinke, B. Bensmann, A.-L. Deutsch, P. Behrens and R. Hanke-Rauschenbach, J. Electrochem. Soc. (2022). Figure 1

The Contributions of Catalyst Layer Resistance on Overall Overpotentials in Anion Exchange Membrane Water Electrolyzers

Anion exchange membrane water electrolyzers (AEMWE) combine the benefits of traditional liquid alkaline (LAWE) and proton exchange membrane water electrolyzers (PEMWE), producing H2 at high current densities while allowing the use of low-cost, low-criticality PGM-free materials for catalysts and hardware. Advances in AEMWE performance have risen rapidly in recent decades, and research on AEMWEs has increased dramatically.1 However, despite significant component-level advances in catalysts and membranes,2,3 gaps remain to achieve performance parity with PEMWEs and the relative overpotentials of AEMWE remain high. Strategies are thus needed to understand, diagnose, and quantify the origins of overpotentials in AEMWEs and help bridge the gap between AEMWE and PEMWE performance.By utilizing Tafel analysis and electrochemical impedance spectroscopy, voltage breakdown analyses can be performed to decouple the origins of high overpotentials in electrolyzers. While such methods are used frequently in the literature to determine kinetic and Ohmic losses, voltage breakdown analyses are rarely performed beyond these contributions, even though other losses can often account for 100s of mVs (20-30% of non-thermodynamic losses). Recent works have demonstrated that catalyst layer resistances can be quantified in electrolyzers using transmission line theory for porous electrodes.4 To the best of our knowledge, however, this method has not yet been adapted to AEMWEs. Furthermore, differences in cell operation and performance (e.g., use of supporting electrolyte, high hydrogen evolution reaction overpotentials) leads to differences in the expected nature of catalyst layer resistances for these two technologies. There is therefore a need for AEMWE-specific methods to diagnose and quantify catalyst layer resistance.In this work, a method for determining catalyst layer resistance from transmission line theory for porous electrodes4 is adapted to AEMWE and applied to four anode catalyst materials tested in single-cell MEAs. Changes to the catalyst layer thickness, ionomer content, and electrolyte concentration reveal trends about the origins of catalyst layer resistances in AEMWE cells. Investigations of the anode transport layer show that this component introduces significant impedance, which thus must be considered for AEM diagnostics and performance optimization. Furthermore, the results suggest that discontinuities in electronic and ionic transport networks in the catalyst layer may explain discrepancies between idealized kinetic results from rotating disc electrode testing and those observed for MEAs. These results then inform the development of a model to understand and differentiate contributions from anode and cathode catalyst layers in AEMWEs. These results will ultimately allow for the design of more efficient catalyst layers, reducing overpotentials and facilitating AEM deployment commercially.[1] Volk, E. K. et al., EES Catalysis 2024, [2] Chen, N. et al., Trends Chem. 2022, [3] Plevová, M. et al., J. Power Sources 2021, [4] Padgett, E. et al., J. Electrochem. Soc. 2023