Local Adsorption Research Articles

On the Relationship between Water Adsorption and Surface Chemistry in Soda-lime Silicate Glasses.

Understanding how the surface structure affects the bioactivity and degradation rate of the glass is one of the primary challenges in developing new bioactive materials. Here, classical and reactive molecular dynamics simulations are used to investigate the relationship between local surface chemistry and local adsorption energies of water on three soda-lime silicate glasses. The compositions of the glasses, (SiO2)65-x(CaO)35(Na2O)x with x=5, 10, and 15, were chosen for their bioactive properties. Analysis of the glass surface structure, compared to the bulk structure, showed that the surface is rich in modifiers and non-bridging oxygen atoms, which were correlated with local adsorption energies. The reactivity of the glasses is found to increase with higher Na2O content, attributed to elevated Na cations and undercoordinated species at the glass surfaces. The current work provides insights into the relationship between the surface structure, chemistry, and properties in these bioactive glasses and offers a step toward their rational design.

Understanding retention and intra-particle diffusivity of alkylsulfobetaine-bonded Ethylene Bridged Particles with different mesopore sizes for hydrophilic interaction liquid chromatography applications

The role of the average pore diameter (APD) of 1.7μm AtlantisTM Premier BEHTM Particles derivatized with a zwitterionic group (propylsulfobetaine) on the efficiency of their 2.1 × 50 mm hydrophilic interaction liquid chromatography (HILIC) packed columns is investigated experimentally. Van Deemter plots for toluene (neutral, hydrophobic), cytosine (neutral, polar), tosylate (negatively charged), bretylium and atenolol (positively charged) were measured on three HILIC columns packed with BEH Z-HILIC Particles having APDs of 95 Å, 130 Å, and 300 Å. The intraparticle diffusivities of the analytes across these three BEH Z-HILIC Particles were measured by the peak parking method.The experimental data reveal that the slope of the C-branch of the van Deemter plots can be reduced by factors of about 15 for toluene, 2.5 for cytosine, 6 for atenolol, 5 for tosylate, and 14 for bretylium with increasing the APD from 95 Å to 300 Å. This observation is explained by: (1) the reduced amount of the highly viscous water diffuse layer and subsequent increase of the amount of acetonitrile-rich eluent in the mesopores, (2) the localized electrostatic adsorption of the retained analytes onto the zwitterion-bonded BEH Particles, and (3) depletion/excess of the analytes into the water diffuse layer. A general model of intraparticle diffusivity was then proposed to account for the impact of the APD of Z-HILIC Particles on the solid-to-liquid mass transfer resistance of small molecules. The model highlights the relevance of the thickness of the water diffuse layer, the access of the bulk eluent into the mesopore, the localized electrostatic adsorption, and the partitioning constant of the retained analyte between the bulk eluent and the water diffuse layer.

Iridium Cluster Anchored onto Cubic Molybdenum Carbide with Strong Electronic Interactions for Robust Hydrogen Oxidation Reaction in Alkaline Medium

AbstractConstructing atomic‐scale dispersed noble metal electrocatalysts holds enormous potential toward alkaline hydrogen oxidation reactions (HOR) owing to the high intrinsic activity and atom utilization. Here, this work shows that Ir clusters anchored on different types of molybdenum carbides (Ir/α‐MoC1‐x, Ir/β‐Mo2C) with tunable electronic interactions display distinct performance in alkaline HOR. Notably, the mass activity of Ir/α‐MoC1‐x with stronger electronic interaction is roughly twice that of Ir/β‐Mo2C. Moreover, the Ir/α‐MoC1‐x has reached an impressive mass‐normalized exchange current density (j0, mass) of 320 mA mg−1metal, making the HOR properties are comparable to those recently reported excellent alkaline HOR Ir‐based electrocatalysts. Both experimental and theoretical calculations have confirmed that the strong metal‐substrate interaction of Ir/α‐MoC1‐x via interfacial Ir‐Mo bonding, leading to a significantly modulated electronic structure and optimized binding energy of H* and OH*, thereby promoting the reaction kinetics of alkaline HOR. This work highlights strong metal‐support interactions can be an effective scheme for regulating the local electronic configuration and adsorption behavior of the catalyst along with an improved intrinsic catalytic activity.

Understanding and Predicting the Spatially Resolved Adsorption Properties of Nanoporous Materials.

Using knowledge from statistical thermodynamics and crystallography, we develop an image-image translation model, called SorbIIT, that uses three-dimensional grids of adsorbate-adsorbent interaction energies as input to predict the spatially resolved loading surface of nanoporous materials over a broad range of temperatures and pressures. SorbIIT consists of a closed-form differential model for loading-surface prediction and a U-Net to generate spatial differential distributions from the energy grids. SorbIIT is trained using the energy grids and adsorbate distributions (obtained from high-throughput simulations) of 50 synthesized and 70 hypothetical zeolites and applied for predicting the adsorption of carbon dioxide, hydrogen sulfide, n-butane, 2-methylpropane, krypton, and xenon in other zeolites from 256 to 400 K. Employing a quadratic isotherm model for the local differentiation, SorbIIT yields mean R2 values of 0.998 for total adsorption and 0.6904 for local adsorption with a resolution of 0.2 Å, and a value of 0.721 for the structural similarity of the local loading distribution.

Dynamic Reconfiguration and Local Polarization of NiFe-Layered Double Hydroxide-Bi2MoO6- x Heterojunction for Enhancing Piezo-Photocatalytic Nitrogen Oxidation to Nitric Acid.

Constructing heterojunctions with vacancies has garnered substantial attention in the field of piezo-photocatalysis. However, the presence of interfacial vacancies can serve as charge-trapping sites, leading to the localization of electrons and hindering interfacial charge transfer. Herein, dual oxygen vacancies in the NiFe-layered double hydroxide and Bi2MoO6- x induced interfacial bonds have been designed for the piezo-photocatalytic N2 oxidation to NO3 -. Fortunately, it achieves sensational nitric acid production rates (7.23mg g-1 h-1) in the absence of cocatalysts and sacrificial agents, which is 6.03 times of pure Bi2MoO6 that under ultrasound and light illumination. Theoretical and experimental results indicate that interfacial bonds act as "charge bridge" and "strain center" to break the carrier local effect and negative effects with piezocatalysis and photocatalysis for promoting exciton dissociation and charge transfer. Moreover, the strong electronic interaction of the interfacial bond induces internal reconstruction under ultrasound for promoting the local polarization and adsorption of N2, which accelerates the fracture of the N≡N bonds and reduces the activation energy of the reaction. The research not only establishes a novel approach for optimizing the combined effects of piezo-catalysis and photocatalysis, but also achieves equilibrium between the synergistic impacts of vacancies and heterojunctions.

Anionic Dye Removal with a Thin Cationic Polyaniline Coating on Cellulosic Biomaterial.

This paper reports the development of novel adsorbent materials using polyaniline (PANI) grafted onto Posidonia (POS) fibers, aimed at efficiently removing phenol red (PSP), an anionic dye, from aqueous solutions. The synthesis involved the copolymerization of aniline grafted on the surface of the POS and aniline monomer in solution, resulting in a chemically bound thin PANI layer on the POS bioadsorbent. Structural characteristics and binding affinities of these adsorbents with PANI under its emeraldine salt (POS@PANI-ES) or emeraldine base (POS@PANI-EB) forms are reported. The rapid adsorption kinetics observed are attributed to enhanced accessibility to PANI adsorption sites on the POS surface. The binding percentages of PSP to POS@PANI-ES and POS@PANI-EB materials were found to be 97 and 50%, respectively, after 15 min of contact time. The Langmuir model for localized adsorption sites and the Volmer model for nonlocalized adsorption as a mobile layer were fitted to the experimental adsorption isotherms of PSP to POS@PANI-EB and POS@PANI-ES, yielding the thermodynamic parameters of adsorption. The adsorption capacities of PSP on POS@PANI-EB and POS@PANI-ES were 37.8 and 71.5 μmol g-1, respectively. The adsorption of PSP remained above 80% at moderate salt concentrations of around 0.1 mol L-1; however, higher concentrations of NaCl and CaCl2 in PSP solutions significantly reduced the adsorption on POS@PANI-ES.

Interpreting chemisorption strength with AutoML-based feature deletion experiments

The chemisorption energy of reactants on a catalyst surface, [Formula: see text], is among the most informative characteristics of understanding and pinpointing the optimal catalyst. The intrinsic complexity of catalyst surfaces and chemisorption reactions presents significant difficulties in identifying the pivotal physical quantities determining [Formula: see text]. In response to this, the study proposes a methodology, the feature deletion experiment, based on Automatic Machine Learning (AutoML) for knowledge extraction from a high-throughput density functional theory (DFT) database. The study reveals that, for binary alloy surfaces, the local adsorption site geometric information is the primary physical quantity determining [Formula: see text], compared to the electronic and physiochemical properties of the catalyst alloys. By integrating the feature deletion experiment with instance-wise variable selection (INVASE), a neural network-based explainable AI (XAI) tool, we established the best-performing feature set containing 21 intrinsic, non-DFT computed properties, achieving an MAE of 0.23 eV across a periodic table-wide chemical space involving more than 1,600 types of alloys surfaces and 8,400 chemisorption reactions. This study demonstrates the stability, consistency, and potential of AutoML-based feature deletion experiment in developing concise, predictive, and theoretically meaningful models for complex chemical problems with minimal human intervention.

Observation on Microenvironment Changes of Dynamic Catalysts in Acidic CO2 Reduction.

Electrochemical CO2 reduction reaction (CO2RR) in acid can solve alkalinity issues while highly corrosive and reductive acidic electrolytes usually cause catalyst degradation. Inhibiting catalyst degradation is crucial for the stability of acidic CO2RR. Here, we reveal the microenvironment changes of dynamic Bi-based catalysts and develop a pulse chronoamperometry (CA) strategy to improve the stability of acidic CO2RR. In situ fluorescence mappings show that the local pH changes from neutral to acid, and the in situ Raman spectra reveal the dynamic evolution of interfacial water structures in the microenvironment. We propose that the surface charge properties of dynamic catalysts affect the competitive adsorption of K+ and protons, thereby causing the differences in local pH and CO2RR intermediate adsorption. We also develop a pulse CA strategy to reactivate catalysts, and the stability of acidic CO2RR is improved by 2 orders of magnitude for 100 h operation, which is higher than most reports on the stability of acidic CO2RR. This work gives insights on how microenvironment changes affecting the stability of acidic CO2RR, and provides guidance for designing stable catalysts in acidic electrolytes.

Modulation of hydroxymethyl/aldehyde groups activation on V2O3 decorated CuCo for 5-hydroxymethylfurfural electrooxidation

5-Hydroxymethylfurfural electrooxidation reaction (HMFOR) has attracted increasing attention due to energy conservation and value-added production. It is crucial to design highly active catalysts with fast kinetics and reveal the catalytic mechanism. Herein, the activation of hydroxymethyl/aldehyde groups is tuned on V2O3-modificated CuCo for efficient HMFOR. Experimental and theoretical results reveal that strong electron transfer occurs on the heterointerface between V2O3 and CuCo, endowing its unique electronic structure and conductivity. Meanwhile, CuCo-V2O3 heterostructure facilitates the modulation of local electron density, charge transfer, and adsorption behavior to promote the activation of hydroxymethyl/aldehyde groups. The higher activation of hydroxymethyl groups than that of aldehyde groups over CuCo-V2O3 induces an altered rate-determining step for HMFOR. Consequently, CuCo-V2O3 presents enhanced HMFOR activity (E10, 1.27 VRHE), reaction kinetics (38 mV dec−1), 2,5-furandicarboxylic acid selectivity (99.1%), and stability (40 successive cycles). This work provides a strategy for designing highly active catalysts for synthesizing value-added products.

Local Steric Hindrance for CO2 Electroreduction at a Thermodynamic Potential and Wide Working Window

AbstractTo improve the energy‐conversion efficiency and adaptability between a CO2 electroreduction system and intermittent renewable energy, small onset potentials, and wide working windows are highly important. Here, three indium metal–organic frameworks (In‐MOFs) have been projected using different ligands to adjust the local steric hindrance and electronic structure of In nodes, manipulating the whole workflow of CO2 during electroreduction including local CO2 transport, adsorption, activation, hydrogenation, and product desorption. Significantly, a CO2 electroreduction to formate process promoted by 2,5‐TDC In‐MOF shows an onset potential of −0.1 V versus RHE around the therymodynamic potential, over 90% FEforamte in a wide current‐density window from 0.1 to 0.9 A cm−2. Driven by solar cells, the system displays a high solar‐to‐chemical efficiency of 17.39%. In depth mechanism study indicates that the local CO2 transport and adsorption of all In‐MOFs are thermodynamically and kinetically favorable, while the energy barrier of potential‐determine step (*HCOOH desorption) is the lowest for 2,5‐TDC In‐MOF.

In Situ Local Band Engineering of Monolayer Graphene Using Triboelectric Plasma.

Graphene, a promising material with excellent properties, suffers from a major limitation in electronics due to its zero bandgap. The gas molecules adsorption has proven to be an effective approach for band regulation, which usually requires a harsh environment. Here, O2 - ions produced with triboelectric plasma are used for in situ regulation of graphene, and the switching ratio can reach 1010. The O2 - ions physical adsorption will reduce the Fermi-level (EF) of graphene. As the EF of graphene is lower than the lowest unoccupied molecular orbital (LUMO) level of O2-, the adsorption of O2 - changes from uniform physical adsorption to local chemical adsorption, thereby realizing the semiconductor properties of graphene. The local graphene bandgap is calculated to be 83.4meV by the variable-temperature experiment. Furthermore, annealing treatment can restore to 1/10 of the initial conductance. The C─O bond formed by O2 - adsorption has low bond energy and is easy to desorb, while the C═O bond formed by adsorption on defects and edges has higher bond energy and is difficult to desorb. The study proposes a simple in situ method to investigate the microscopic process of O2 - adsorption on the graphene surface, demonstrating a new perspective for local energy band engineering of graphene.

Differential local ordering of mixed crowders determines effective size and stability of ss-DNA capped gold nanoparticle.

Understanding the influence of a crowded intracellular environment on the structure and solvation of DNA functionalized gold nanoparticles (ss-DNA AuNP) is necessary for designing applications in nanomedicine. In this study, the effect of single (Gly, Ser, Lys) and mixture of amino acids (Gly+Ser, Gly+Lys, Ser+Lys) at crowded concentrations is examined on the structure of the ss-DNA AuNP using molecular dynamics simulations. Using the structural estimators such as pair correlation functions and ligand shell positional fluctuations, the solvation entropy is estimated. Combining the AuNP-solvent interaction energy with the solvation entropy estimates, the free energy of solvation of the AuNP in crowded solutions is computed. The solvation entropy favours the solvation free energy which becomes more favourable for larger effective size of AuNP in crowded solutions relative to that in water. The effective size of AuNP depends on the different propensity of the crowders to adsorb on Au surface, with the smallest crowder (Gly) having the highest propensity inducing the least effective AuNP size as compared to other single crowder solutions. In mixed crowded solutions of amino acids of variable size and chemistry, distinctive local adsorption of the crowders on the gold surface is observed that controls the additive or non-additive crowding effects which govern an increase (in Gly+Ser) or decrease (in Gly+Lys) in nanoparticle effective size respectively. The results shed light into the fundamental understanding of the influence of intracellular crowding on structure of ss-DNA AuNP and plausible employability of crowding as a tool to design programmable self-assembly of functionalized nanoparticles.

Regulating the local electron density and adsorption energy of COF-based single copper sites for highly efficient Fenton-like photo-oxidation

Introducing single Cu atoms and electron-donating groups onto ketoenamine-based covalent organic frameworks effectively regulates the local electron density and adsorption energy, thus significantly enhancing Fenton-like photo-oxidation performance.

Enhancing Local CO2 Adsorption by L-histidine Incorporation for Selective Formate Production Over the Wide Potential Window.

Electrochemical carbon dioxide reduction reaction (CO2 RR) to produce valuable chemicals is a promising pathway to alleviate the energy crisis and global warming issues. However, simultaneously achieving high Faradaic efficiency (FE) and current densities of CO2 RR in a wide potential range remains as a huge challenge for practical implements. Herein, we demonstrate that incorporating bismuth-based (BH) catalysts with L-histidine, a common amino acid molecule of proteins, is an effective strategy to overcome the inherent trade-off between the activity and selectivity. Benefiting from the significantly enhanced CO2 adsorption capability and promoted electron-rich nature by L-histidine integrity, the BH catalyst exhibits excellent FEformate in the unprecedented wide potential windows (>90 % within -0.1--1.8 V and >95 % within -0.2--1.6 V versus reversible hydrogen electrode, RHE). Excellent CO2 RR performance can still be achieved under the low-concentration CO2 feeding (e.g., 20 vol.%). Besides, an extremely low onset potential of -0.05 VRHE (close to the theoretical thermodynamic potential of -0.02 VRHE ) was detected by in situ ultraviolet-visible (UV-Vis) measurements, together with stable operation over 50 h with preserved FEformate of ≈95 % and high partial current density of 326.2 mA cm-2 at -1.0 VRHE .

Mixture Adsorption in Nanoporous Zeolite and at Its External Surface: In-Pore and Surface Selectivity.

Using toluene, ethylene, and water as gas compounds with different representative molecular interactions, we perform atom-scale simulations for their mixtures to investigate the selectivity of the core nanoporosity and external surface in a prototypical zeolite. As expected, the overall behavior suggests that increasing the pressure of a given component promotes the desorption of the coadsorbing species. However, for water-toluene mixtures, we identify that the pseudohydrogen bonding between water and toluene leads to beneficial coadsorption as toluene adsorption in the low-pressure range promotes water adsorption. Moreover, when the zeolite is completely filled with water, toluene adsorption does not occur due to steric repulsion, and ethylene shows oversolubility as the amount of ethylene per water molecule is significantly larger than in bulk water. The underlying oversolubility mechanism is found to be due to localized ethylene adsorption in the density minima arising from the layering of water in nanoconfinement. Despite these specific effects, the relatively weak coadsorption effects in the zeolite nanoporosity, which are found to be reasonably captured using the ideal adsorbed solution theory, arise from the fact that adsorption of these gases having different molecular sizes occurs in distinct pore regions (channel type, channel intersection). Finally, in contrast to confinement in the nanoporosity, mixture adsorption at the external surface does not show coadsorption effects as it mostly follows the Henry regime. These results show that selectivity is mostly governed by the confinement effects as the external surface leads to a selectivity loss.

Preparation of nano-scale ferric hexacyanoferrate using coal ash by microwave-assisted hydrothermal process for cesium removal

The removal of radioactive cesium (Cs+) has received considerable attention owing to its chemotoxicity and radiotoxicity. This study presents a method for producing ferric hexacyanoferrate nanoparticles (Prussian blue, PB), using recycled magnetic coal ash (M-CA) as an effective and selective adsorbent for Cs+ removal. A microwave-assisted hydrothermal technique was employed to recover the Fe solution from M-CA and a simple sol–gel technique was used to synthesize PB nanoparticles. The PB nanoparticles exhibited cubic cluster structures with an average size of 20.67 nm. Their Cs+ adsorption capacity reached 213.061 mg/g, significantly surpassing the capacities of absorbents reported in previous studies. Cs+ was observed to be associated with localized adsorption sites on the PB surfaces, with minimal internal diffusion. In addition, the hydrated radius of Cs+ emerged as a critical factor influencing its adsorption onto PB surfaces, enabling the efficient removal of Cs+ even in the presence of competing ions. These findings offer valuable insights for the straightforward synthesis of highly efficient and selective adsorbents for radioactive substances, as well as the recovery of valuable materials from industrial solid waste.

Augmented CO2 utilization for acidic industrial-level CO2 electroreduction to near-unity CO

Electrochemical reduction of CO2 represents an environmental-friendly process that could alleviate the environmental and energy crisis by eliminating greenhouse gasses and generating value-added chemicals. However, industrial-level CO2 reduction to CO suffers from low CO2-conversion efficiency. To address this issue, this work proposes to use acidic electrolytes to avoid carbonate/bicarbonate salt precipitation, and shell for local CO2 adsorption to improve its utilization and thus facilitate electroconversion. An Ag-based metal-organic framework (MOF) is hybridized with Ag, which exhibits near-unity selectivity to CO at an industrial-level current density (500 mA cm−2) in acidic media, robust electrochemical stability (100 h) and more importantly, high CO2 conversion efficiency of 42.5 %. Fundamentally, CO2 molecules are activated by Ag-MOF via atop adsorption of *CO after uptake by the porous organic complexes. The extraordinary performance originates from multi-scale regulation of CO2 transport from the gas-diffusion layer to the local CO2 adsorption shell near the atomic Ag active center of Ag-MOF.

Microwave Regenerable Nickel, Zinc Co-doped Nitrogen-Coordinated Porous Carbon Catalyst for Nitrogen Fixation.

More than 90% of the global NH3 synthesis is dominated by the Haber-Bosch process, which consumes 2% of the worldwide energy and generates 1.44% of the global carbon emission. The electrochemical N2 reduction reaction (NRR) is regarded as an attractive alternative route to produce NH3 under mild reaction conditions, but the electrocatalysts suffer from the difficulty of N≡N cleavage. In this work, we report a leaf-like MOF-derived Ni/Zn bimetallic co-doped nitrogen-coordinated porous carbon (Ni/Zn-NPC) as a cost-effective NH3 synthesis electrocatalyst. The resultant electrocatalyst achieved a high NH3 production rate of 22.68 μg h-1 mgcat-1 at -1.0 V vs a reversible hydrogen electrode (RHE) in a 0.1 M Na2SO4 electrolyte. The Ni/Zn-NPC material can be called a microwave regenerable catalyst because microwave treatment has proven to be a crucial part of the multi-field coupling to detoxify and make the catalyst reactive, further improving its stability. Density functional theory (DFT) was chosen to explore the mechanism of Ni/Zn-NPC for NRR, providing a profound prediction of the structure of the active site and related reaction pathways and revealing that trace Ni doping optimizes the local coordination environment and N2 adsorption of Zn atoms.

Effector-dependent structural transformation of a crystalline framework with allosteric effects on molecular recognition ability

Structurally flexible porous crystals that combine high regularity and stimuli responsiveness have received attracted attention in connection with natural allostery found in regulatory systems of activity and function in biological systems. Porous crystals with molecular recognition sites in the inner pores are particularly promising for achieving elaborate functional control, where the local binding of effectors triggers their distortion to propagate throughout the structure. Here we report that the structure of a porous molecular crystal can be allosterically controlled by local adsorption of effectors within low-symmetry nanochannels with multiple molecular recognition sites. The exchange of effectors at the allosteric site triggers diverse conversion of the framework structure in an effector-dependent manner. In conjunction with the structural conversion, it is also possible to switch the molecular affinity at different recognition sites. These results may provide a guideline for the development of supramolecular materials with flexible and highly-ordered three-dimensional structures for biological applications.

Adsorption and dyeing properties of acid dye on bio-based polyamide 11 fibers

The dyeing mechanism of bio-based polyamide 11 fibers with acid dyes was explored in order to provide a theoretical foundation for the dyeing properties of polyamide 11 fibers. The surface morphology and diameters of polyamide 11 fibers and polyamide 6 fibers were compared. Both polyamide 11 fibers and polyamide 6 fibers were dyed with acid dye Isolan blue NHF-S, and the effects of the initial dye concentration, pH values, dyeing temperature and time on the dyeing properties were investigated. The effects of the dyeing kinetics and thermodynamic model of Isolan blue NHF-S on polyamide 11 fibers were analyzed, and the corresponding parameters were calculated. It was found that the dyeing properties of polyamide 11 fibers were not comparable to those of polyamide 6 fibers, while the washing and rubbing fastness were more or less the same. The dyeing mechanism of Isolan blue NHF-S on polyamide 11 was a combination of localized and non-localized adsorption, which conformed to the pseudo-second-order kinetic model and the Redlich–Peterson thermodynamic model. Increasing dyeing temperature could shorten the half-dyeing time and improve the average diffusion coefficient and affinity between the dye and polyamide 11 fibers.