Activation Energy Of Adsorption Research Articles

Removal of Pyridine from Aqueous Solutions Using Lignite, Coking Coal, and Anthracite: Adsorption Kinetics

A novel coking wastewater treatment technique is proposed based on the principles of the circular economy. By utilizing coal as an adsorbent for organic pollutants in coking wastewater, the treated coal can be introduced into the coking system after the adsorption and flocculation sedimentation processes. This creates a closed-loop system with zero coking wastewater emissions. We investigated the potential of adsorption for the removal of pyridine. Batch experiments were conducted using lignite, coking coal, and anthracite as adsorbents. Both coking coal and anthracite showed favorable adsorption properties for the chosen contaminants. The experimental data were analyzed utilizing various models, including pseudo-first-order and pseudo-second-order kinetic equations, as well as intraparticle diffusion and Bangham. This study aimed to identify the rate-limiting step in the adsorption process. The results revealed that the adsorption of pyridine onto the three coal types followed pseudo-second-order kinetics. The rate-limiting mechanisms may include both boundary-layer diffusion and intraparticle diffusion. The effect of pH on coal adsorption and the activation energy of pyridine adsorption by coking coal were also examined. Adsorption offers a promising approach in advanced wastewater treatment, with coking coal emerging as a cost-effective adsorbent for addressing persistent organic pollutants during the adsorption process.

Ultra-high temperature suspending stabilizer and cement slurry interface interaction law and mechanism study for ultra-deep well cementing

The high temperature issue that cementing is facing is getting more and more significant as oil and gas extraction is being expanded to deep stratum. In order to increase the sedimentation stability of cement slurry under ultra-high temperature conditions, a suspension stability of cement slurry was created in the study. On the basis of previous research, its mechanism of action was examined from the perspective of interface interaction. The suspension stabilizer's low temperature adsorption behavior was investigated using the Zeta potential test and the total organic carbon (TOC) test. The findings indicate that the suspension stabilizer's apparent adsorption activation energy is 44.667 kJ/mol, which is in the range of chemical adsorption. The XRD test, infrared spectrum test, and Raman spectrum test were used to examine the cement's hydration byproducts. The findings demonstrate that hydrated calcium silicate (C-S-H) is the predominant component of the cement paste's short-term hydration products during ultra-high temperature curing. Ion concentration testing and molecular dynamics modeling were used to examine the interface interaction mechanism between the suspension stabilizer and the hydration products. The findings indicated that a network of chemical interactions, including hydrogen and ionic bonds, interacted between suspension stabilizer and C-S-H. The sedimentation stability of cement slurry is maintained by the persistence of these chemical linkages at extremely high temperatures.

Surface oxidation modification of nitrogen doping biochar for enhancing CO2 adsorption

The purpose of this paper is to demonstrate a surface oxidation modification strategy of nitrogen doping biochar for enhancing CO2 adsorption. The porous structure and surface group distribution of nitrogen doping biochars before and after modification (remarked as TF and OTFs) were characterized. Then the thermodynamic and kinetic characteristics of CO2 adsorption such as adsorption capacity, selectivity and activation energy were systematically investigated. The results indicated that the modified biochars OTFs exhibited high adsorption capacity of CO2 between 5 and 8 mmol·g-1 at 100 kPa and 273 K. The oxidation modification affected CO2 adsorption behaviors by the ways of adjusting surface pore size and surface group distributions. The former decreased the mass transfer diffusion resistance of CO2 from gas phase to biochar surface by transforming some micropores to the mesopores. And the later improved the adsorption selectivity of CO2 to the other gases such as N2 based on the interaction difference enhancement by those oxygen-containing (OFGs) and nitrogen-containing functional groups (NFGs). When the molar ratios of CO2/N2 in gas mixture were 1:1 and 15:85, the modified biochar OTF-10 exhibited the better selectivity, and the maximum selectivities of CO2 to N2 at 273 K were 44.7 and 69.4, respectively. Furthermore, the behavior of CO2 adsorption on the biochars well conformed to the quasi-first-order dynamical model, accompanied by the higher adsorption rate of CO2 and activation energy. The obtained activation energies for TF and OTF-10 were 12.98 and 16.62 kJ·mol-1, respectively. The higher activation energy for OTF-10 meant that the adsorption temperature had a stronger effect on adsorption rate of CO2.

Computational fluid dynamics simulation of Fischer-Tropsch synthesis coupled with a novel reaction kinetics using trimetallic catalyst over a biomass-based support

A mathematical modeling based on the computational fluid dynamics (CFD) was performed in this work. The reactive flow behavior in a tubular reactor was modeled for Fischer-Tropsch synthesis (FTS) using a novel trimetallic catalyst supported on a low-cost and renewable carbonaceous material. The fixed bed reactor was simulated as a porous media using a commercial software package (COMSOL Multiphysics). In this study, major attention has been paid to the species transport and reaction kinetics, as a fundamental stage in CFD simulation of FTS. The reaction kinetics was evaluated using Eley-Rideal theory assuming the molecular adsorption of CO based on the enol mechanism. Furthermore, the products distribution was accounted in the kinetics study by defining a mathematical expression and the kinetics parameters were optimized using genetic algorithm (GA). The activation energy and heat of H2 adsorption were estimated as 62.63 and −29.52 kJ/mol, respectively. The role of operational conditions was critically evaluated on the partial pressure profiles of the species, and the CFD results were validated with the experimental data. While increasing total pressure improved the partial pressure of C5+ hydrocarbons to 1.2 bar, increasing temperature to 310 °C limited the chain growth. The employed modeling and novel catalyst design can provide promising overview of the FTS reaction mechanism and products selectivity in fixed bed reactors.

Application of Metal-Organic Frameworks for Efficient Removal of Doxorubicin Hydrochloride: Removal Process Optimization and Biological Activity.

This study looked at the doxorubicin hydrochloride (DOX) anticancer drug's adsorption characteristics on a silver-based metal-organic framework (Ag-MOF). X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) were used for the characterization of Ag-MOF. The pore volume and surface area of Ag-MOF were determined through Brunauer-Emmett-Teller (BET) testing at 77 K to be 0.509 cm3/g and 676.059 m2/g, respectively. Adsorption at pH 6 was established to be the best for DOX compared to alkaline solution. Ag-MOF has a good capacity for eliminating DOX (1.85 mmol/g), according to adsorption experiments. From the adsorption results, we can find that Langmuir is the most fitted adsorption isotherm model and the pseudo-second order model best fitted the adsorption kinetics. The energy of activation for adsorption, which was determined to be 15.23 kJ/mol, also supported a chemisorption process. The mechanism of adsorption was evaluated, and details of all possible interactions between DOX and Ag-MOF were illustrated. On the other hand, while examining the impact of temperature, we identified the thermodynamic constraints as ΔG°, ΔH°, and ΔS° and confirmed that the reaction was an endothermic one and spontaneous. Even after numerous reuse cycles, the efficiency remained constant. The synthetic adsorbent was remarkably recyclable at a rate of more than 91.6%. By using the MTT assay, the cytotoxicity of the tested Ag-MOF and DOX@Ag-MOF against human breast cancer cells (MCF-7) was evaluated in vitro. The in vitro antimicrobial activity of Ag-MOF and DOX@Ag-MOF was also tested.

Analyzing characteristic and modeling of high-temperature proton exchange membrane fuel cells with CO poisoning effect

High-temperature proton exchange membrane fuel cells (HT-PEMFC) have strong resistance to CO poisoning. However, the published CO poisoning models for HT-PEMFC are based on the finite element analysis method, which are difficult to use for the performance prediction and development of system control strategies due to a large amount of calculation. In the beginning, a semi-empirical model of HT-PEMFC is deduced based on the analysis of the CO poisoning characteristics. Then the key parameters of ohmic impedance and concentration polarization advance correction factor are obtained by fitting the polarization curves, dissociation and adsorption activation energy of H2 and CO are obtained by the calculation, respectively. The slope of the straight line segment in the ohmic polarization interval of the polarization curve is linearly related to ln[H2/CO]. The change of limiting current density is the main factor for the advance of concentration polarization. The fitted ohmic impedance varies with temperature and CO concentration, but changes little above 175 °C. CO coverage depends primarily on dissociation and adsorption activation energy of CO. Subsequently, the proposed model is validated with experimental data and shows high similarity. The model can be used for studying the systematic control strategy development and performance monitoring of HT-PEMFC.

Design, Preparation, and High Intrinsic Proton Conductivity of Two Highly Stable Hydrazone-Linked Covalent Organic Frameworks.

Assembling crystalline materials with high stability and high proton conductivity as a potential alternative to the Nafion membrane is a challenging topic in the field of energy materials. Herein, we concentrated on the creation and preparation of hydrazone-linked COFs with super-high stability to explore their proton conduction. Fortunately, two hydrazone-linked COFs, TpBth and TaBth, were solvothermally prepared by using benzene-1,3,5-tricarbohydrazide (Bth), 2,4,6-trihydroxy-benzene-1,3,5-tricarbaldehyde (Tp), and 2,4,6-tris(4-formylphenyl)-1,3,5-triazine (Ta) as monomers. Their structures were simulated by Material Studio 8.0 software and confirmed by the PXRD pattern, demonstrating a two-dimensional framework with AA packing. The presence of a large number of carbonyl groups as well as -NH-NH2- groups on the backbone is responsible for their super-high water stability as well as high water absorption capacity. AC impedance tests demonstrated a positive correlation between the water-assisted proton conductivity (σ) of the two COFs and the temperature and humidity. Under 100 °C/98% RH, the highest σ values of TpBth and TaBth can reach 2.11 × 10-4 and 0.62 × 10-5 S·cm-1, which are among the high σ values of the reported COFs. Their proton-conductive mechanisms were highlighted by structural analyses as well as N2 and H2O vapor adsorption data and activation energy values. Our systematic research affords ideas for the synthesis of proton-conducting COFs with high σ values.

Novel Imine-Tethering Cationic Surfactants: Synthesis, Surface Activity, and Investigation of the Corrosion Mitigation Impact on Carbon Steel in Acidic Chloride Medium via Various Techniques.

Novel imine-tethering cationic surfactants, namely (E)-3-((2-chlorobenzylidene)amino)-N-(2-(decyloxy)-2-oxoethyl)-N,N-dimethylpropan-1-aminium chloride (ICS-10) and (E)-3-((2-chlorobenzylidene)amino)-N,N-dimethyl-N-(2-oxo-2-(tetradecyloxy)ethyl)propan-1-aminium chloride (ICS-14), were synthesized, and the chemical structures were elucidated by various spectroscopic approaches. The surface properties of the target-prepared imine-tethering cationic surfactants were investigated. The effects of both synthesized imine surfactants on carbon steel corrosion in a 1.0 M HCl solution were investigated by weight loss (WL), potentiodynamic polarization (PDP), and scanning electron microscopy (SEM) methods. The outcomes show that the inhibition effectiveness rises with raising the concentration and diminishes with raising the temperature. The inhibition efficiency of 91.53 and 94.58 % were attained in the presence of the optimum concentration of 0.5 mM of ICS-10 and ICS-14, respectively. The activation energy (Ea) and heat of adsorption (Qads) were calculated and explained. Additionally, the synthesized compounds were investigated using density functional theory (DFT). Monte Carlo (MC) simulation was utilized to understand the mechanism of adsorption of inhibitors on the Fe (110) surface.

Anticorrosive properties of aqueous Cichorium intybus seeds extract as a sustainable-green inhibitor for aluminum corrosion in hydrochloric acid solution: An experimental and DFT/MC/MD theoretical approach

The inhibitory effect of Cichorium intybus seeds (C. Intybus) on the corrosion behavior of Al 7075 alloy was evaluated in a 1 M HCl acid solution using chemical and electrochemical methods. The adsorption process was proved using FTIR, UV-Vis, Fluorescence, SEM, EDX, AFM, and contact angle measurements. The results reflect that C. Intybus provided excellent protection, and all measurements showed that the inhibition performance of extracts increased by increasing the concentration to reach 93.67% at 12% v/v. Furthermore, this substance functioned as a mixed-type inhibitor to obstruct the anodic and cathodic active sites on the surface of the metal. The study outcomes matched the monolayer Langmuir isotherm, and the calculated adsorption free energy and activation energy reflect that the inhibition mechanism featured the physisorption process. The computational studies were used to provide further confirmation of the adsorption mechanism and to find out how organic inhibitor molecules interact with metal surface using Density Functional Theory (DFT) with Lee/Yang/Parr (B3LYP) level, 6–311 + + G(d,p) as the basis function set calculation, Monte Carlo (MC), and Molecular Dynamic (MD) simulations. The findings showed good agreement with both the experimental and theoretical results. One of the important findings of this work is the possibility of using C. Intybus as a greener alternative and environmentally friendly resource for corrosion inhibition in an acidic medium.

Constructing physical and chemical synergistic effect of graphene aerogels regenerated from spent graphite anode of lithium ion batteries achieves high efficient adsorption of lead in wastewater

The treatment and disposal of lead in wastewater is deeply troubled in industry due to the limitations of physical adsorption and exclusivity of chemical adsorption methods. Herein, an unique graphene aerogel (GA) structure, rich in active functional groups such as sulfur, carboxyl and hydroxyl, etc., is designed and synthesized from the waste graphite anode of lithium ion batteries in our work. Through the physical adsorption of the porous structure of graphene itself, combined with the chemical adsorption of special functional groups, the synergistic effect can achieve high efficiency absorption of lead in wastewater, reaching the maximum of 152.70 mg/g. The best conditions for the adsorption of lead-containing wastewater are using 50 mg of GAs for adsorbing at 30 °C for 1 h when the initial concentration is 50 mg/L. The adsorption process conforms to the Langmuir isothermal adsorption model, the adsorption dynamics conform to the quasi-secondary kinetic equation, and the adsorption activation energy is 47.29 kJ/mol, confirming that the adsorption is controlled by the chemical reaction. Owing to the superiority of waste recycling, our research provides a novel idea for the combined physical adsorption and chemical adsorption of heavy metals in wastewater.

Adsorption and Dissociation of R-Methyl p-Tolyl Sulfoxide on Au(111).

Sulfur-based molecules producing self-assembled monolayers on gold surfaces have long since become relevant functional molecular materials with many applications in biosensing, electronics, and nanotechnology. Among the various sulfur-containing molecules, the possibility to anchor a chiral sulfoxide to a metal surface has been scarcely investigated, despite this class of molecules being of great importance as ligands and catalysts. In this work, (R)-(+)-methyl p-tolyl sulfoxide was deposited on Au(111) and investigated by means of photoelectron spectroscopy and density functional theory calculations. The interaction with Au(111) leads to a partial dissociation of the adsorbate due to S-CH3 bond cleavage. The observed kinetics support the hypotheses that (R)-(+)-methyl p-tolyl sulfoxide adsorbs on Au(111) in two different adsorption arrangements endowed with different adsorption and reaction activation energies. The kinetic parameters related to the adsorption/desorption and reaction of the molecule on the Au(111) surface have been estimated.

Surface stability and H adsorption and diffusion near surfaces of W borides: a first-principles study

Understanding the behavior of tungsten boride (W x B y ) surfaces in a fusion reactor environment is an important topic since boronization is a common wall conditioning method used in fusion Tokamaks. We report the results of density functional theory calculations that investigate the surface stability of W x B y (tetragonal I41/amd-WB, hexagonal P63/mmc-WB2 and tetragonal I4/m-W2B) with low-index orientations, as well as hydrogen (H) energetics near W x B y surfaces. For single element terminated W x B y surfaces, B terminated surfaces are more energetically stable than W terminated as a result of significant reconstruction of B. The H surface adsorption energy and activation energy of H diffusion penetration below W x B y surfaces are mainly related to the outer termination. Specifically, the WB(001) surface terminated with two B layers, referred to as WB(001)-TBB, has higher H adsorption affinity and lower H diffusivity on this surface than other terminations, which is controlled by the significant charge transfer from B to H. However, B atoms on the WB2(0001)-TBB surface decrease both H adsorption and diffusivity on the surface, but enhance H diffusion below the surface in comparison to W terminated WB2(0001) surface. H would be trapped and diffuse within atomic surface gaps on the WB2() surface, while H below the surface layer would jump along the [0001] direction rather than diffuse into bulk. The surface diffusion activation energy of H on the W2B(001) surface slightly varies with terminations. Once H crosses the surface layer of W2B(001) with either termination, it prefers to diffuse into the bulk, or back towards the surface, rather than move parallel to the surface. Interestingly, WB2(0001) and WB2() surfaces will have relatively higher H retention than the other W x B y surfaces evaluated in this work.

Enhanced lithium-ion adsorption by recyclable lithium manganese oxide-sepiolite composite microsphere from aqueous media: Fabrication, structure, and adsorption characteristics

A novel spherical structure, hydrogen-substituted lithium manganese oxide (LMO)-sepiolite (HMO-SEP) composite assembled from nanorods was fabricated via hydrothermal method combined with solid-phase method. The structure and composition of the as-prepared HMO-SEP was analyzed by a series of characterization techniques, and its adsorption behavior and characteristics for Li+ adsorption from aqueous media and recyclability were investigated in detail. The as-prepared HMO-SEP showed a typical IV-type gas adsorption isotherm with H3-type hysteresis loop at high P/P0, with a specific surface area of 46.49 m2/g and a pore size of 18.31 nm. The isotherm adsorption data of Li+ adsorption by HMO-SEP conform well to the Langmuir model, and the maximum adsorption capacity of Li+ reached 52.41 mg/g at 298 K. Kinetic studies showed that the adsorption process complies well with the pseudo-second-order model, reaching adsorption equilibrium within 8 h. The adsorption of Li+ by the resulting HMO-SEP is a spontaneous endothermic process with increasing entropy, with an adsorption ΔH of 21.9432 kJ/mol and an adsorption activation energy of 19.8092 kJ/mol. A suitable amount of SEP could improve the microstructure of the HMO-SEP through the interface effect between SEP and LMO. Such effect could enlarge the specific surface area and pore volume and improve the ion transport channels, thus enhancing the adsorption capacity towards Li+, stability, and recycling performance. The resulting HMO-SEP possesses excellent selective adsorption performance for Li+, even under high concentrations of Na+, K+, Ca2+, and Mg2+, stability, and regeneration–recycling performance. It has excellent potential for efficient use in the extraction of Li+ from aqueous media.

Investigation on the Sulfadiazine Schiff Base Adsorption Ability of Y(III) Ions from Nitrate Solutions, Kinetics, and Thermodynamic Studies

ABSTRACT Sulfadiazine Schiff base (SDSB) was prepared using an inexpensive technique by modification of sulfadiazine drug (SD) to be used as an adsorbent material for recovery of Y(III) ions from aqueous solutions. Chemical and physical characterizations of SDSB were performed using different techniques. The maximum static adsorption capacity of the modified SD was 0.9 mmolg−1 for Y(III) ions and at pH 5.0. The kinetics results revealed that the sorption of Y(III) ions upon the synthesized SDSB followed the pseudo-second-order with R2 of >0.999. Temkin, Dubinin – Radushkevich, Freundlich, and Langmuir models accurately described the adsorption isotherm data. The activation energy (Ea) for adsorption was 17.52 kJmol−1, indicating the process is to be chemisorption. Thermodynamic characteristics with ΔHo of 11.33 kJmol−1 and a ΔSo 110.2 Jmol−1K−1. Using FT-IR and EDAX analysis proved the yttrium adsorption upon the SDSB. The desorption process for Y(III) ions was successfully achieved using 1 M HNO3 and it reduced from 95% to 70% after five consecutive cycles. A pre-concentration process for yttrium ions presented in a waste solution was achieved using SDSB adsorbent with a pre-concentration factor of about 10. As a result, it is regarded as a promising adsorbent for Y(III) ions in a variety of industrial applications.

Revealing the correlation between adsorption energy and activation energy to predict the catalytic activity of metal oxides for HMX using DFT

Traditional selection of combustion catalysis is time-consuming and labor-intensive. Theoretical calculation is expected to resolve this problem. The adsorption energy of HMX and O atoms on 13 metal oxides was calculated using DMol3, since HMX and O are key substances in decomposition process. And the relationship between the adsorption energy of HMX, O on metal oxides (TiO2, Al2O3, PbO, CuO, Fe2O3, Co3O4, Bi2O3, NiO) and experimental T30 values (time required for the decomposition depth of HMX to reach 30%) was depicted as volcano plot. Thus, the T30 values of other metal oxides was predicted based on their adsorption energy on volcano plot and validated by previous experimental data. Further, the adsorption energy of HMX on ZrO2 and MnO2 was predicted based on the linear relationship between surface energy and adsorption energy, and T30 values were estimated based on volcano plot. The apparent activation energy data of HMX/MgO, HMX/SnO2, HMX/ZrO2, and HMX/MnO2 obtained from DSC experiments are basically consistent with our predicted T30 values, indicating that it is feasible to predict the catalytic activity based on the adsorption calculation, and it is expected that these simple structural properties can predict adsorption energy to reduce the large quantities of computation and experiment cost.

Superior adsorption and removal of doxorubicin from aqueous solution using activated carbon via thermally treated green adsorbent: isothermal, kinetic, and thermodynamic studies

ABSTRACT Activated carbon from apricot seeds (ASAC) was successfully made using a low-cost, straightforward synthesis process. With the use of various instruments, including XRD, XPS, FT-IR, SEM, and TEM, the adsorbent was demonstrated. The surface area of the ASAC that was given was also shown to be 436.8 m2/g. It was discovered that the synthesized ASAC has a fantastic capacity to absorb the anti-cancer medication doxorubicin hydrochloride (DOX). Based on changes in temperature, pH, and DOX concentration, The DOX adsorption behaviour's mechanism was evaluated. The adsorption capacity of ASAC for DOX was greater at pH 6.0, according to experimental data as the adsorption capacity was discovered to be 951.13 mg/g. Adsorption equilibrium analysis revealed that, when compared to the other models, the Langmuir adsorption provided the best fit to the data that were collected. Additionally, The ASAC has validated the DOX activation energy of adsorption as a chemisorption technique. The kinetics of adsorption were shown to be fitted to pseudo-second-order kinetic model. The reaction was endothermic and spontaneous, according to thermodynamic data. Innvestigation the removal efficiency of ASAC to remove DOX from real watrer sample (tap water, effluent wastewater, and impact wastewater). It was suggested by the results that ASAC was a viable option for treating wastewater and adsorbing DOX. The synthesized ASAC has noteworthy cyclability and reusability characteristics due to its high efficiency (up to five cycles) and low cost (around 86 percent).

A Theoretical Description of the Ignition Conditions for TC17 Alloy in Oxygen-Enriched Atmospheres

ABSTRACT Titanium alloys can be ignited under extreme conditions including high pressure, high temperature, and high-speed friction. A theoretical description of the ignition conditions for titanium alloys is critical for their safe use in aerospace industries. In this study, a chemical-absorption-controlled ignition model for bulk TC17 alloy in oxygen-enriched atmospheres was developed based on Semenov’s thermal ignition theory. The adsorption coefficient, reaction order, and activation energy for the ignition of TC17 alloy were obtained by fitting the model with the experimental critical oxygen pressure and critical ignition temperatures. The fitting results showed that the chemical-absorption-controlled ignition model fitted better with the experimental data compared with the diffusion-controlled ignition model, implying that the ignition process was controlled by chemical absorption rather than oxygen diffusion through the oxidation layer. Moreover, the activation energy for the ignition of TC17 alloy bars was obtained to be 50.01 kJ/mol, which was only less than one-fourth of that of non-isothermal oxidation (231.98 kJ/mol), indicating that the ignition requires much lower activation energy than oxidation. The chemical-absorption-controlled ignition model successfully predicted the ignition temperature of TC17 alloy bars with different diameters with the relative error within 4.41%, demonstrating the validity of the model.

Oxygen Vacancies Engineering in Thick Semiconductor Films via Deep Ultraviolet Photoactivation for Selective and Sensitive Gas Sensing

AbstractRoom‐temperature detection of volatile organic compounds in particle‐per‐billion concentrations is critical for the development of wearable and distributed sensor networks. However, sensitivity and selectivity are limited at low operating temperatures. Here, a strategy is proposed to substantially improve the performance of semiconductor sensors. Tunable oxygen vacancies in thick 3D networks of metal oxide nanoparticles are engineered using deep ultraviolet photoactivation. High selectivity and sensitivity are achieved by optimizing the electronic structure and surface activity while preserving the 3D morphology. Cross‐sectional depth analysis reveals oxygen vacancies present at various depths (≈24% at a depth of 1.13 µm), with a uniform distribution throughout the thick films. This results in ≈58% increase in the sensitivity of ZnO to 20‐ppb ethanol at room temperature while ≈51% and 64% decrease in the response and recovery times, respectively. At an operating temperature of 150 °C, oxygen‐vacant nanostructures achieve a lower limit of detection of 2 ppb. Density functional theory analysis shows that inducing oxygen vacancies reduces activation energy for ethanol adsorption and dissociation, leading to improved sensing performance. This scalable approach has the potential for designing low‐power wearable chemical and bio‐sensors and tuning the activity and band structure of porous, thick oxide films for multiple applications.

Multi-scale design of MOF-based membrane separation for CO2/CH4 mixture via integration of molecular simulation, machine learning and process modeling and simulation

Metal-organic framework (MOF) membranes have demonstrated high efficiency for CO2 capture due to their wide range of pore sizes, high surface area, high porosity, and open metal sites. In this work, we propose a multi-scale design framework of MOF-based membrane separation for CO2/CH4 mixture via integration of molecular simulation, machine learning, and process modelling and simulation. The GCMC and MD molecular simulation is first used to evaluate adsorption isotherms, isosteric adsorption heat, self-diffusivity, activation energy, permeability, and selectivity of a MOF-based membrane (e.g., IRMOF-1) for CO2/CH4 separation at different operating conditions. It is found that the simulated isotherms at 298 K are consistent with experimental results. CO2 permeability can range from 4.090 × 104 to 3.818 × 105 barrer with variation in operating conditions. The same phenomenon is also reflected in the selectivity. We then establish prediction models of adsorption capacity and self-diffusivity using machine learning methods such as artificial neural network (ANN), which are used to calculate the permeability. The mean squared error is 0.0086, and the coefficient of determination is 0.9822. The proposed ANN models are integrated with the tanks-in-series model of a hollow fiber membrane separation process, which is simulated using the finite volume method. Three case studies illustrate the feasibility and superiority of the proposed integrated framework.

Mechanistic understanding of N2 activation: a comparison of unsupported and supported Ru catalysts.

N2 dissociative adsorption is commonly the rate-determining step in thermal ammonia synthesis. Herein, we performed density functional theory (DFT) calculations to understand the N2 dissociation mechanism on models of unsupported Ru(0001) terraces, Ru B5 sites, and polar MgO(111)-supported Ru8 cluster mimicking a B5 site geometry, denoted (Ru8(B5-like)/MgO(111)). The activation energy of N2 dissociative adsorption on the Ru8(B5-like)/MgO(111) model (Ea = 0.33 eV) is much lower than that on the unsupported Ru(0001) terrace (Ea = 1.74 eV) and Ru B5 (Ea = 0.62 eV) models. The lower N2 dissociation barrier on Ru B5 sites is facilitated by the enhanced σ donation and π* back-donation between N2(σ, π*) and Ru(d) orbitals resulting in the stronger activation of the molecular side-on N2* dissociation precursor. The Ru8(B5-like)/MgO(111) also exhibits enhanced σ donation because of the B5-like cluster geometry. Furthermore, the Ru cluster of the bare Ru8(B5-like)/MgO(111) model is positively charged. This induced an unusual π donation from N2(π) to Ru(d) orbitals as revealed by analyses of the density of states and partial charge densities. The combined σ and π donation resulted in an increased synergistic π* back-donation. The total interactions between N2(σ, π, π*) and Ru(d) resulted in an overall electron transfer to the adsorbed N2 from the Ru atoms in the B5-like site with no direct involvement of the MgO(111) substrate. Analyses of bond stretching vibrations and bond lengths show that the N2(σ, π, π*) and Ru(d) interactions lead to a weaker N-N bond and stronger Ru-N bonds. These correspond to a lower barrier of N2 dissociation on the Ru8(B5-like)/MgO(111) model, where the highest red-shift of N-N vibration and the longest N-N bond length were observed after side-on N2* adsorption. These results demonstrate that an electron-deficient Ru catalyst are not always inhibited from donating electrons to adsorbed N2. Rather, this study shows that the electron deficiency of Ru can promote π* back-donation and N2 activation. These new insights may therefore open new avenues to design supported Ru catalysts for nitrogen activation.