High Surface Coverage Research Articles

Collectively exhaustive electrochemical hydrogen evolution reaction of polymorphic cobalt selenides derived from organic surfactants modified Co-MOFs

Finding and exploring non-noble metal-based electrocatalysts for the promising power-to-hydrogen fuel technology through water splitting reactions is highly emerging. Herein, we report the preparation of cobalt-based metal-organic frameworks (Co-MOFs) using an oleylamine (OLA) and 1-dodecanethiol (DDT)-modified trimesic acid (TMA), and cobalt precursor. Then, the electrocatalytically active cobalt selenides were derived from the Co-MOFs by a water-organic solvent mixture-assisted single-step selenization process. Interestingly, the cobalt selenide obtained from the DDT-modified Co-MOF shows collectively exhaustive hydrogen evolution reaction (HER) performance with very small overpotentials of ∼161 and ∼206 mV to achieve 10 and 50 mA cm−2, respectively, due to the phase mixing characteristics of cobalt selenide and the synergistic interaction. The fast reaction kinetics were identified at the DDT-Co selenide electrode surface as confirmed by observing the lower charge-transport/interfacial resistance and Tafel slope value due to the high surface coverage of adsorbed hydrogen (Hads) atoms, evidenced by high interfacial chemical capacitance value, as a result of the high electrical conductivity and large electrochemically accessible active sites. The calculated activation energy (Ea) of HER further reveals a low kinetic energy barrier in the HER on the DDT-Co selenide, indicating high intrinsic catalytic activity due to the fast surface diffusion rate of Hads. Furthermore, the obtained cathodic transfer coefficient (αc) value strongly suggested that the HER on the surface of DDT-Co selenide (αc = 2) proceeds in the Langmuir-Hinshelwood reaction mechanism and follows the Volmer-Tafel pathway. The present work provides valuable insights into the modification of Co-MOFs and their impact on HER catalytic activity of cobalt selenide, and also the mechanistic investigation of HER based on electrochemical impedance spectroscopy analysis.

A many-body dissipative particle dynamics parametrisation scheme to study behaviour at air-water interfaces.

In this article, we present a general parametrisation scheme for many-body dissipative particle dynamics (MDPD). The scheme is based on matching model components to experimental surface tensions and chemical potentials. This allows us to obtain the correct surface and mixing behaviours of complex, multicomponent systems. The methodology is tested by modelling the behaviour of nonionic polyoxyethylene alkyl ether surfactants at an air/water interface. In particular, the influence of the number of ethylene oxide units in the surfactant head group is investigated. We find good agreement with many experimentally obtained parameters, such as minimum surface area per molecule; and a decrease in the surface tension with increasing surfactant surface density. Moreover, we observe an orientational transition, from surfactants lying directly on the water surface at low surface coverage, to surfactants lying parallel or tilted with respect to the surface normal at high surface coverage. The parametrisation scheme is also extended to cover the zwitterionic surfactant lauryldimethylamine oxide (LDAO), where we provide good predictions for the surface tension at maximum surface coverage. Here, if we exceed this coverage, we are able to demonstrate the spontaneous production of micelles from the surface surfactant layer.

CO2 coverage on Pd catalysts accelerates oxygen removal in oxy-combustion systems.

Oxy-combustion systems result in enriched CO2 in exhaust gases; however, the utilization of the concentrated CO2 stream from oxy-combustion is limited by remnant O2. CH4 oxidation using Pd catalysts has been found to have high O2-removal efficiency. Here, the effect of excess CO2 in the feed stream on O2 removal with CH4 oxidation is investigated by combining experimental and theoretical approaches. Experimental results reveal complete CH4 oxidation without any side-products, and a monotonic increase in the rate of CO2 generation with an increase in CO2 concentration in the feed stream. Density-functional theory calculations show that high surface coverage of CO2 on Pd leads to a reduction in the activation energy for the initial dissociation of CH4 into CH3 and H, and also the subsequent oxidation reactions. A CO2-rich environment in oxy-combustion systems is therefore beneficial for the reduction of oxygen in exhaust gases.

Exploring the Diversity of Biofilm Formation by the Food Spoiler Brochothrix thermosphacta.

Brochothrix thermosphacta is considered as a major spoiler of meat and seafood products. This study explores the biofilm formation ability and the biofilm structural diversity of 30 multi-origin B. thermosphacta strains using a set of complementary biofilm assays (biofilm ring test, crystal violet staining, and confocal laser scanning microscopy). Two major groups corresponding to low and high biofilm producers were identified. High biofilm producers presented flat architectures characterized by high surface coverage, high cell biovolume, and high surface area.

Autonomous image background removal for accurate and efficient close-range photogrammetry

Close-range photogrammetry can be used to reconstruct dense point clouds of an object with very high surface coverage, making it useful for manufacturing metrology tasks such as part inspection and validation. However, compared to competing techniques, data processing times can be slow. In this paper we present a method to autonomously remove the background from the images within a photogrammetric dataset. We show that using masked images directly in the reconstruction results in much lower data processing times, with lower memory utilisation. Furthermore, we show that the point density on the object surface is increased while the number of superfluous background points is reduced. Finally, a set of reconstruction results are compared to a set of tactile coordinate measurements. Reconstructions with the background removed are shown to have a standard deviation in the point to mesh distance of up to 30 µm lower than if the background is not removed. This improvement in standard deviation is likely due to the static background, relative to the object on the rotation stage, causing triangulation errors when points are detected and matched on this background data. The proposed approach is shown to be robust over several example artefacts and can, therefore, be implemented to improve the measurement efficiency and measurement results of photogrammetry coordinate measurement systems.

Molecular Factors of Ice Growth Inhibition for Hyperactive and Globular Antifreeze Proteins: Insights from Molecular Dynamics Simulation.

The molecular mechanism behind the ice growth inhibition by antifreeze proteins (AFPs) is yet to be understood completely. Also, what physical parameters differentiate between the AFP and non-AFP are largely unknown. Thus, to get an atomistic overview of the differential antifreeze activities of different classes of AFPs, we have studied ice growth from different ice surfaces in the presence of a moderately active globular type III AFP and a hyperactive spruce budworm (sbw) AFP. Results are compared with the observations of ice growth simulations in the presence of topologically similar non-AFPs using all-atom molecular dynamics simulations. Simulation data suggest that the ice surface coverage is a critical factor in ice growth inhibition. Due to the presence of an ice binding surface (IBS), AFPs form a high affinity complex with ice, accompanied by a transition of hydration water around the IBS from clathrate-like to ice-like. Several residues around the periphery of the IBS anchor the AFP to the curved ice surface mediated by multiple strong hydrogen bonds, stabilizing the complex immensely. In the high surface coverage regime, the slow unbinding kinetics dominates over the ice growth kinetics and thus facilitates the ice growth inhibition. Due to the non-availability of a proper IBS, non-AFPs form a low-affinity complex with the growing ice surface. As a result, the non-AFPs are continuously repelled by the surface. If the concentration of AFPs is low, then the effective surface coverage is reduced significantly. In this low surface coverage regime, AFPs can also behave like impurities and are engulfed by the growing ice crystal.

Electrochemical detection of cystatin C by oriented antibody immobilization on streptococcal protein G–modified ZIF-8-Cu1−xNix(OH)2@Cu core-shell nanostructured electrode

Herein, we prepared a novel nanostructure involving Cu shell on Zeolitic imidazolate frameworks (ZIF-8) and Cu1−xNix(OH)2 composite (ZIF-8-Cu1−xNix(OH)2@Cu) combining sol-gel and co-precipitation method. The morphology, stoichiometry, and structure of the nanocomposite were elucidated by various physicochemical analyses. A poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) coated indium tin oxide (ITO) was modified with the synthesized ZIF-8-Cu1−xNix(OH)2@Cu nanoparticles (NPs) to obtain an efficient electrode for further antibody immobilization. The ZIF-8-Cu1−xNix(OH)2@Cu/PEDOT:PSS/ITO was applied for the detection of cystatin C, a promising biomarker of chronic kidney disease (CKD). The electrode was functionalized by streptococcal protein G (SPG) to bind the Fc region of anti-cystatin C in an oriented manner. The synergistic catalytic activities, high surface coverage, enhanced electroactive sites, and excellent redox properties of the proposed electrode lead to excellent electrochemical sensing. The proposed sensor obtained a much lower detection limit (33 pg/mL) for a linear range of 0.1 ng/mL to 1,000 ng/mL with high selectivity, stability, and reproducibility compared with bare ZIF-8/PEDOT:PSS/ITO-based immunosensor. The clinical feasibility of the sensor was confirmed by measuring the human serum in the presence of different concentrations of cystatin C. This work demonstrates a new and facile approach to fabricating a metal-organic framework (MOF) –based nanoimmunosensor for cystatin C, which has significant importance in diagnosing the renal failure.

Anion-catalyzed active dissolution model for the electrochemical adsorption of bisulfate, sulfate, and oxygen on gold in H2SO4 solution

The mechanism of the electrochemical adsorption of bisulfate, sulfate, and oxygen on polycrystalline gold in H2SO4 (0.5 M) was modeled using a mechanistic analysis of potentiodynamic polarization and electrochemical impedance spectroscopy data acquired at multiple dc potentials in the electric double-layer and pre-oxide formation region. Electrochemical quartz-crystal microgravimetry and optical ellipsometry provided evidence for the potential-dependent adsorption of solution species on the gold surface. Also, despite the high surface coverages of oxygen on the electrode surfaces, dissolution was observed over the entire the potential region studied. The anion-catalyzed active dissolution model accounts well for the experimentally observed current density and fractional surface coverages.

A Combined Extended X-ray Absorption Fine Structure Spectroscopy and Density Functional Theory Study of Americium vs. Yttrium Adsorption on Corundum (α–Al2O3)

Adsorption reactions on mineral surfaces are influenced by the overall concentration of the adsorbing metal cation. Different site types (strong vs. weak ones) are often included to describe the complexation reactions in the various concentration regimes. More specifically, strong sites are presumed to retain metal ions at low sorbate concentrations, while weak sites contribute to metal ion retention when the sorbate concentration increases. The involvement of different sites in the sorption reaction may, thereby, also be influenced by competing cations, which increase the overall metal ion concentration in the system. To date, very little is known about the complex structures and metal ion speciation in these hypothetical strong- and weak-site regimes, especially in competing scenarios. In the present study, we have investigated the uptake of the actinide americium on corundum (α–Al2O3) in the absence and presence of yttrium as competing metal by combining extended X-ray absorption fine structure spectroscopy (EXAFS) with density functional theory (DFT) calculations. Isotherm studies using the radioactive 152Eu tracer were used to identify the sorption regimes where strong sites and weak sites contribute to the sorption reaction. The overall americium concentration, as well as the presence of yttrium could be seen to influence both the amount of americium uptake by corundum, but also the speciation at the surface. More specifically, increasing the Am3+ or Y3+ concentrations from the strong site to the weak site concentration regimes in the mineral suspensions resulted in a decrease in the overall Am–O coordination number from nine to eight, with a subsequent shortening of the average Am–O bond length. DFT calculations suggest a reduction of the surface coordination with increasing metal–ion loading, postulating the formation of tetradentate and tridentate Am3+ complexes at low and high surface coverages, respectively.

Mechanism of lipid bilayer perturbation by bactericidal membrane-active small molecules

Membrane-active small molecules (MASMs) are small organic molecules designed to reproduce the fundamental physicochemical properties of natural antimicrobial peptides: their cationic charge and amphiphilic character. This class of compounds has a promising broad range of antimicrobial activity and, at the same time, solves some major limitations of the peptides, such as their high production costs and low in vivo stability. Most cationic antimicrobial peptides act by accumulating on the surface of bacterial membranes and causing the formation of defects when a threshold is reached. Due to the drastically different structures of the two classes of molecules, it is not obvious that small-molecule antimicrobials act in the same way as natural peptides, and very few data are available on this aspect. Here we combined spectroscopic studies and molecular dynamics simulations to characterize the mechanism of action of two different MASMs. Our results show that, notwithstanding their simple structure, these molecules act just like antimicrobial peptides. They bind to the membrane surface, below the head-groups, and insert their apolar moieties in the core of the bilayer. Like many natural peptides, they cause the formation of defects when they reach a high coverage of the membrane surface. In addition, they cause membrane aggregation, and this property could contribute to their antimicrobial activity.

Infrared Reflection-Absorption Spectroscopy of α-Hydroxyacids at the Water-Air Interface.

Organic molecules, including α-hydroxyacids, are ubiquitous in the natural environment. Often found at water-air interfaces, organic molecules can alter the structure of the interface or participate in interfacial chemistry. Despite their prevalence in the environment, the structure and ordering of α-hydroxyacids have not been widely investigated at water-air interfaces, and the impact of the hydrophobic tail length on structure has not been explored. Here, for the first time, we use infrared reflection-absorption spectroscopy to assess the vibrational structure of α-hydroxyacids at a water surface as a function of surface partitioning and surface coverage. We study lactic acid, 2-hydroxyoctanoic acid, and 2-hydroxystearic acid, which have 1 carbon, 6 carbon, and 16 carbon tails, respectively. Vibrational features compared across the set of α-hydroxyacids studied here are used to determine the interaction of the polar headgroup with the water subphase and the ordering of the hydrophobic tail. We find that the carbonyl and α-hydroxyl groups participate in a complex hydrogen-bonding motif at the water-air interface that can be affected by the hydrophobic tail length and places the polar headgroup in or below the water-air interface. Furthermore, molecular ordering increases with the tail length or the surface coverage. The presence of the α-hydroxyl group causes the α-hydroxyacids to maintain a tilted orientation with respect to the surface normal even at high surface coverages. A combination of polar headgroup and hydrophobic tail effects dictates the overall orientation of α-hydroxyacids and can thus affect their ability to participate in chemistry and alter organic coatings on water surfaces.

Controlling Product Distribution of CO2 Reduction on CuO‐Based Gas Diffusion Electrodes by Manipulating Back Pressure

The electrochemical reduction reaction of CO2 (CO2RR) is a promising avenue toward the renewable energy‐driven transformation of a greenhouse gas toward fuels and value‐added chemicals. While copper uniquely can catalyze this reaction to longer carbon chains, Cu‐based electrodes continue to face numerous challenges, including low selectivity toward desired products and poor stability. To unlock its potential for large‐scale industrial implementation, great interest is shown in tackling these challenges, primarily focusing on catalyst and electrode modifications and thereby leaving a research gap in the effects of operation conditions. Herein, back pressure application is introduced in CO2 electrolyzers at industrially relevant current densities (200 mA cm−2) in order to steer selectivity toward C2+ products. The back pressure adjusts CO2 availability at the electrode surface, with a high CO2 surface coverage achieved at ΔP = 130 mbar suppressing the competing hydrogen evolving reaction for 72 h and doubling of stable ethylene production duration. Faradaic efficiency of 60% for C2+ products and overall C2+ conversion efficiency of 19.8% are achieved with the easily implementable back pressure operation mode presented in this study. It is proven to be a promising tool for product selectivity control in future upscaled Cu‐based CO2 electrolysis cells.

Rapid electrochemical detection of levodopa using polyaniline-modified screen-printed electrodes for the improved management of Parkinson's disease

A portable test to rapidly determine levels of levodopa, the drug used to treat Parkinson's disease, can improve clinical management of the disease. In this study, screen-printed electrodes (SPEs) were modified with polymers to facilitate the electrochemical detection of levodopa. Cyclic voltammetry was used to deposit a thin layer of polyaniline on the electrode surface. Scanning electron microscopy revealed high surface coverage, which did not impact the electrode's conductivity. Differential pulse voltammetry measurements with the polyaniline-modified electrodes enabled the measurement of levodopa at physiologically relevant concentrations with discrimination between a common interferent (ascorbic acid) and a structurally similar compound (l-tyrosine). However, the use of the polymer layer did not permit differentiation between levodopa and dopamine; the only difference in these molecules is that levodopa has an amino acid moiety whereas dopamine has a free amine group. Density functional theory calculations demonstrated that aniline formed a hydrogen bond between the amino group of the monomer and the meta-hydroxyl group, which is present in both levodopa and dopamine, with similar binding energies (−53.36 vs −50.08 kJ mol−1). Thus, the polymer-functionalised SPEs are a valuable tool to measure compounds important in Parkinson's disease, but further refinement is needed to achieve selective detection.

Enhanced visible light photocatalytic performance of Sr0.3(Ba,Mn)0.7ZrO3 perovskites anchored on graphene oxide

In search of better materials for visible light photocatalytic performance, perovskite Sr0.3(Ba/Mn)0.7ZrO3 nanopowders anchored on graphene oxide were synthesized for the evaluation of their photocatalytic activity against methylene blue (MB). The chemical coprecipitation method was used to synthesize SrZrO3 (SZO) and a series of doped derivatives having a nominal composition of Sr1-x(Ba,Mn)xZrO3 (x = 0.1–0.9) at an annealing temperature of 700 °C for 12 h. However, Sr0.3(Ba,Mn)0.7ZrO3 with a bandgap value of 3.50 eV was further processed for the formation of composite with graphene oxide (GO) owing to its lowest bandgap value in the synthesized series. The inclusion of larger Ba2+ cations in the lattice resulted in the redistribution of cations creating antisite defects which were evident from the shrinkage of the lattice. The incorporation of Mn2+ resulted in the hybridization of Mn2+ (3d) orbitals with the split Zr4+ (4d) orbitals. This reduced the bandgap and composite formation with GO further enhancing the delocalization of excited electrons to GO hence, reducing electron-hole recombination. Adsorption assisted photocatalysis under a 100 W tungsten lamp was performed using the designed catalysts for the removal/degradation of MB. The π-π conjugation and the ionic interactions were found responsible for the adsorption of MB at the GO surface. High surface coverage, initial dye concentrations, heterogeneous catalyst surface, weak van der Waals interactions, pH and availability of •OH radicals were found to be the decisive factors for the removal/degradation process. Improved charge separation enhances the generation of •OH and better performance of the GO composites as opposed to the pristine strontium zirconate perovskites.

Mechanistic Insight into Hydrocarbon Synthesis via CO2 Hydrogenation on χ-Fe5C2 Catalysts.

Converting CO2 into value-added chemicals and fuels is one of the promising approaches to alleviate CO2 emissions, reduce the dependence on nonrenewable energy resources, and minimize the negative environmental effect of fossil fuels. This work used density functional theory (DFT) calculations combined with microkinetic modeling to provide fundamental insight into the mechanisms of CO2 hydrogenation to hydrocarbons over the iron carbide catalyst, with a focus on understanding the energetically favorable pathways and kinetic controlling factors for selective hydrocarbon production. The crystal orbital Hamiltonian population analysis demonstrated that the transition states associated with O-H bond formation steps within the path are less stable than those of C-H bond formation, accounting for the observed higher barriers in O-H bond formation from DFT. Energetically favorable pathways for CO2 hydrogenation to CH4 and C2H4 products were identified which go through an HCOO intermediate, while the CH* species was found to be the key C1 intermediate over χ-Fe5C2(510). The microkinetic modeling results showed that the relative selectivity to CH4 is higher than C2H4 in CO2 hydrogenation, but the trend is opposite under CO hydrogenation conditions. The major impact on C2 hydrocarbon production is attributed to the high surface coverage of O* from CO2 conversion, which occupies crucial active sites and impedes C-C couplings to C2 species over χ-Fe5C2(510). The coexistence of iron oxide and carbide phases was proposed and the interfacial sites created between the two phases impact CO2 surface chemistry. Adding potassium into the Fe5C2 catalyst accelerates O* removal from the carbide surface, enhances the stability of the iron carbide catalyst, thus, promotes C-C couplings to hydrocarbons.

Supramolecular Self-Assembly of Dipalmitoylphosphatidylcholine and Carbon Nanotubes: A Dissipative Particle Dynamics Simulation Study.

Dissipative particle dynamics simulations were performed to investigate the self-assembly of dipalmitoylphosphatidylcholine (DPPC) as a model lipid membrane on the surface of carbon nanotubes (CNTs). The influence of surface curvature of CNTs on self-assembly was investigated by performing simulations on solutions of DPPC in water in contact with CNTs of different diameters: CNT (10, 10), CNT (14, 14), CNT (20, 20), and CNT (34, 34). DPPC solutions with a wide range of concentrations were chosen to allow for formation of lipid structures of various surface densities, ranging from a submonolayer to a well-organized monolayer and a CNT covered with a lipid monolayer immersed in a planar lipid bilayer. Our results are indicative of a sequence of phase-ordering processes for DPPC on the surface of CNTs. At low surface coverages, the majority of hydrocarbon tail groups of DPPC are in contact with the CNT surface. Increasing the surface coverage leads to the formation of hemimicellar aggregates, and at high surface coverages close to the saturation limit, an organized lipid monolayer self-assembles. An examination of the mechanism of self-assembly reveals a two-step mechanism. The first step involves densification of DPPC on the CNT surface. Here, the lipid molecules do not adopt the order of the target phase (lipid monolayer on the CNT surface). In the second step, when the lipid density on the CNT surface is above a threshold value (close to saturation), the lipid molecules reorient themselves to form an organized monolayer around the tube. Here, the DPPC molecules adopt stretched conformations normal to the surface, the end hydrocarbon groups adsorb on the surface, and the head groups occupy the outermost part of the monolayer. The saturation density and the degree of lipid ordering on the CNT surface depend on the surface curvature. The saturation density increases with increased surface curvature, and better-ordered structures are formed on less curved surfaces.

Influence of Counter Surface Roughness and Lay on the Tribological Behaviour of Self-Lubricating Bearing Materials in Dry Sliding Conditions at High Contact Pressures

In Kaplan turbines, the most critical components are the self-lubricating polymer composite bearings used to control the guide vanes and the turbine blades. Reducing the sliding wear and friction of these bearings can benefit both the economy and the environment, including longer useful life, lower operational costs, and higher efficiency. In this study, the influence of stainless-steel counter surface roughness and lay on the tribological behaviour of three bearing materials used in hydropower applications were investigated using a linear reciprocating flat-on-flat configuration under high contact pressure and low sliding speed. The surface roughness was measured using white light interferometry. SEM and EDS analysis were used to investigate the worn surfaces. Results from this study show that overly smooth surfaces result in higher friction and wear of the counter surface, while rougher surfaces have a negative effect on the wear of the polymers. Highest surface coverage using protective transfer layers is found on the steel surfaces with the perpendicular lay and is accompanied with a lower coefficient of friction compared to the parallel lay. The dominant wear mechanism of the bearing materials changes from delamination wear to abrasive wear between the lowest and the intermediate roughness for steel surfaces with the parallel lay. It can be concluded that counter surface topography has a significant influence on the tribological behaviour of these bearing materials and that the effect differs between the self-lubricating polymer composites.

Adsorptive Removal of Naproxen from Water Using Polyhedral Oligomeric Silesquioxane (POSS) Covalent Organic Frameworks (COFs).

Covalent organic frameworks are porous crystalline compounds made up of organic material bonded together by strong reversible covalent bonds (these are novel types of materials which have the processability of extended or repeated structures with high performance, like those of thermosets and thermoplastics that produce high surface coverage). These have a long-term effect on an arrangement’s geometry and permeability. These compounds are entirely made up of light elements like H, B, C, N, O and Si. Pharmaceuticals and personal care products (PPCPs) have emerged as a new threatened species. A hazardous substance known as an “emerging toxin,” such as naproxen, is one that has been established or is generated in sufficient amounts in an environment, creating permanent damage to organisms. COF-S7, OAPS and 2-methylanthraquionone(2-MeAQ), and COF-S12, OAPS and terephthalaldehyde (TPA) were effectively synthesized by condensation (solvothermal) via a Schiff base reaction (R1R2C=NR′), with a molar ratio of 1:8 for OAPS to linker (L1 and L2), at a temperature of 125 °C and 100 °C for COF-S7 and COF-S12, respectively. The compounds obtained were assessed using several spectroscopy techniques, which revealed azomethine C=N bonds, aromatic carbon environments via solid 13C and 29Si NMR, the morphological structure and porosity, and the thermostability of these materials. The remedied effluent was investigated, and a substantial execution was noted in the removal ability of the naproxen over synthesized materials, such as 70% and 86% at a contact time of 210 min and 270 min, respectively, at a constant dose of 0.05 g and pH 7. The maximum adsorption abilities of the substances were found to be 35 mg/g and 42 mg/g. The pH result implies that there is stable exclusion with a rise in pH to 9. At pH 9, the drop significance was attained for COF-S7 with the exception of COF-S12, which was detected at pH 11, due to the negative Foster charge, consequent to the repulsion among the synthesized COFs and naproxen solution. From the isotherms acquired (Langmuir and Freundlich), the substances displayed a higher value (close to 1) of correlation coefficient (R2), which showed that the substances fit into the Freundlich isotherm (heterogenous process), and the value of heterogeneity process (n) achieved (less than 1) specifies that the adsorption is a chemical process. Analysis of the as-prepared composites revealed remarkable reusability in the elimination of naproxen by adsorption. Due to its convenience of synthesis, significant adsorption effectiveness, and remarkable reusability, the as-synthesized COFs are expected to be able to be used as potential adsorbents for eliminating AIDs from water.

Redox-Induced Lipid Vesicle Fusion Onto Electroactive Self-Assembled Monolayers

Supported lipid bilayers (SLBs) are popular model systems to study cell membrane functionalities and various biomolecular interaction forces. A key advantage of SLBs on metallic surfaces, is the application of spectroscopic, electrochemical, and surface plasmon resonance techniques for biomolecular recognition studies. The most common method for forming SLBs is vesicle fusion, which involves the adsorption, deformation, and rupture of small unilamellar vesicles (SUVs) of lipids from aqueous suspension to the substrate surface.1 The formation of continuous single bilayers by vesicle fusion can be problematic due to the many experimental parameters influencing vesicle rupture and bilayer spreading (i.e., lipid and vesicle properties, physicochemical characteristics of the surface, temperature, and solvent environment)1. Vesicle fusion typically works only with smooth hydrophilic surfaces, such as glass, silica, and mica. Although approaches have been developed to form bilayers on technologically relevant surfaces such gold (e.g., surface functionalization with hydrophilic organic films,2 solvent-assisted lipid bilayer formation3 or the addition of a vesicle-destabilizing agent4), there remains a need for active strategies that are fast, versatile, and scalable.We present a redox-induced approach for the formation of single bilayers on gold functionalized with electroactive self-assembled monolayers (SAMs) of ferrocenylalkanethiolates. The electrochemical oxidation of the SAM-bound ferrocene (Fc) to ferrocenium (Fc+) involves coupled electron transfer and ion pairing reactions. Counteranions from solution pair with the ferroceniums to stabilize the oxidized cations and neutralize the excess positive charge at the SAM/aqueous interface. The surface-confined redox reaction triggers the formation of single bilayer membranes from SUVs of anionic or zwitterionic phospholipids onto gold surfaces modified with the electroactive SAM. The ion pairing association of the charged lipid head groups with the electrogenerated ferroceniums drives the assembly of the phospholipids on the SAM surface to produce solid-supported bilayers of high surface coverage (≳ 90%) from gel- or fluid-phase forming phospholipids within minutes at room temperature. The redox-mediated strategy reported in this work is a conceptual advance in the preparation of solid-supported lipid bilayers. It is fast, insensitive to the phase state of the phospholipid in the vesicle precursor, and not limited to hydrophilic surfaces. References Richter, R. P.; Bérat, R.; Brisson, A. R., Formation of Solid-Supported Lipid Bilayers: An Integrated View. Langmuir 2006, 22 (8), 3497-3505.Silin, V. I.; Wider, H.; Woodward, J. T.; Valincius, G.; Offenhausser, A.; Plant, A. L., The Role of Surface Energy on the Formation of Hybrid Bilayer Membranes. J. Am. Chem. Soc. 2002, 124, 14676-14683.Ferhan, A. R.; Yoon, B. K.; Park, S.; Sut, T. N.; Chin, H.; Park, J. H.; Jackman, J. A.; Cho, N.-J., Solvent-Assisted Preparation of Supported Lipid Bilayers. Nat. Protoc. 2019, 14 (7), 2091-2118.Cho, N.-J.; Cho, S.-J.; Cheong, K. H.; Glenn, J. S.; Frank, C. W., Employing an Amphipathic Viral Peptide to Create a Lipid Bilayer on Au and TiO2. J. Am. Chem. Soc. 2007, 129 (33), 10050-10051. Figure 1

Fabrication of Low Loading Ag Electrodes for CO2 Reduction Reaction in Zero-Gap Electrolyzer

In recent years, there has been intense effort directed towards catalyst development and electrode design for electrochemical carbon dioxide reduction reaction (CO2RR) with an objective of achieving high production rate (current density) of desirable products including CO, CH3OH, CH4 and C2+ hydrocarbons. Silver electrocatalyst is reported to exhibit remarkable CO selectivity and high current density, both of which are requisite parameters for CO2RR electrolyzer scale up. Silver is still moderately priced and reduction of Ag loading in CO2RR electrode is one of the technological goals for electrolyzer development.Most of the prior studies on Ag electrodes for CO2RR have utilized Ag nanoparticles, which are typically spray coated on a substrate from Ag or Ag-ionomer suspension resulting in high-Ag loading (> 1 mg/cm2 loading) and hence low mass specific activity (MSA) < 150 mA.mg-1 Ag. In this work, we developed a combined approach for Ag deposition using pulse electrodeposition (PE) and spray coating (SC) with an aim of decreasing Ag loading and increasing MSA. Such electrodes were found to exhibit high current densities and CO selectivity even with low Ag loading (< 0.5 mg/cm2).Specifically, several different gas diffusion electrodes (GDE) prepared by pulse electrodeposition of silver, spray coating of Ag nanoparticles, and combination of the two were prepared by coating of Sigracet gas diffusion layer (GDL). Commercial IrO2 electrode and the fabricated silver electrode were utilized as the anode and cathode, respectively. The anode and the cathode were separated by a polymer electrolyte membrane, which was Sustainion® X37-50 Grade 60- an anion exchange membrane. 10 mM KHCO3 electrolyte was re-circulated at the anode using a pump while humidified CO2 gas was flowed through the cathode. CO2RR tests are performed in a zero-gap electrolyzer setup, at a temperature of 25 °C.The main findings are summarized in the Figure below. The electrode prepared by pulse electrodeposition (PE) exhibits a low areal current density (~30 mA/cm2) but high mass-specific activity of 302 mA.mg-1 Ag. However, the selectivity for CO is low. On the other hand, spray coated (SC) electrodes yield higher CO selectivity and higher areal current density but mass specific activity is lower. By depositing silver sequentially, either pulse electrodeposition (PE) followed by spray coating (SC), i.e. the SC+PE electrode, or SC followed by PE (PE+SC electrode), both the mass-specific and areal current density increased drastically while CO selectivity remained high (99%). In particular, the current densities of the PE and SC electrodes are improved by 2 and 4.5 times, respectively, from 31 and 70 mA.cm-2 up to 136 mA.cm-2 on the SP+PE electrode, at the cell voltage of -3 V. Also, the CO selectivity of the electrodes is improved from 25 % (PE sample) and 81 % (SC sample) up to 99 % on the SC+PE electrode. The optimized electrode provided a catalyst layer with high surface coverage of silver on the GDL substrate at low Ag loadings (<0.5 mg/cm2). Further optimization of electrode is underway including modification of silver deposition and incorporation of ionomer to increase current density while maintaining the CO selectivity and durability of GDE. Details of the electrode fabrication and characterization as well as performance evaluation will be presented at the meeting. Figure 1