Microscopic Adsorption Mechanism Research Articles

Investigation of the impact of micro-nano pore geometry on CH4 adsorption

CH4 is a clean fossil fuel that is widely used in the gas supply of homes and industry, and its energy value is increasingly important. Coal pores provide certain conditions for the storage of CH4. In order to reveal the microscopic adsorption mechanism of CH4 in different pores under high pressure, based on the experimental results, a cross-shaped pore model was proposed, and then molecular simulation was used to construct three kinds of cross-shaped, round and slit pore models for simulation experiment verification. The changes of adsorption parameters, such as adsorption amount, adsorption heat, adsorption energy, adsorption potential and adsorption entropy, were analyzed during the adsorption process. Combined with adsorption and condensation theory, the influence of different geometric pores on the adsorption of CH4 was further verified. The results show that round pore have more adsorption sites, larger adsorption quantity and stronger adsorption capacity, followed by cross pore, while slit pore have the weakest adsorption capacity and least adsorption sites. Under high pressure susaturated adsorption, the interaction force between molecules is stronger, the affinity is higher, the molecules are arranged in order, and the adsorption system is more stable, and the adsorption capacity of slit pore > cross pore > round pore is displayed. This study further verifies the mechanism of the effect of pore geometry on CH4 adsorption, which provides a strong support and theoretical basis for CBM mining engineering.

Multiple modulating energy-efficient nanofiltration membranes during high-quality drinking water towards high mineral/organic matter selectivity

Solving the low mineral/organic matter selectivity of nanofiltration (NF) membranes and realizing high permeability are effective strategies to satisfy the energy-saving production of high-quality drinking water. Controlling the interfacial polymerization (IP) reaction rate at the molecular level is a feasible approach to customize the functionality of NF membranes and simultaneously modulate multiple membrane properties. Here, we selected 1.4-piperazinediethanesulfonic acid (PIPES) as an aqueous-phase additive, and by taking advantage of the hydrogen-bonding, long-range electrostatic, and steric hindrance effects between PIPES and piperazine (PIP)monomers, as well as the reduction of solution pH, we achieved precise molecular-level regulation of the IP reaction rate. This strategy simultaneously enables the integrated tailoring of various membrane properties such as high hydrophilicity, high surface charge density, uniform pore size distribution and roughness reduction. Molecular dynamics (MD) and computational fluid dynamics (CFD) simulations were used to explore the effects of structural and morphological changes of the polyamide layer on the permeation performance, and the microscopic adsorption mechanism of foulants on the membrane was analyzed by a Quartz Crystal Microbalance (QCM). For pacificating natural surface water, the PIPES-0.75 NF membrane exhibited high permeation performance (23.7 LMH/bar), high mineral/organic selectivity (KCa2+/DOM = 16.5), excellent anti-fouling and anti-scaling properties, and reduced CO2 emissions per ton of water produced up to 90 %. In addition, an attempt was made to correlate the physicochemical properties of the membranes with the permselectivity and membrane fouling, and the economic availability of PIPES-conditioned NF membranes was examined, which provides a novel option for achieving NF in drinking water systems from the perspective of cost reduction and efficiency.

A self-assembled surfactant for efficient flotation of cassiterite: Experimental study and DFT calculation

Surfactants of different kinds are important in the flotation of metal oxide ores. In this paper, a combined organic surfactant was formed through self-assembly of salicylhydroxamic acid (SHA) and isopropanolamine dodecylbenzenesulfonate (DBIA). The effects of SHA and DBIA on the flotation behavior of cassiterite were investigated. Density functional theory (DFT) calculations were used to clarify the microscopic adsorption mechanism of SHA and DBIA on the cassiterite surface. The flotation performance of the combined surfactant was investigated to determine the optimum ratio. Subsequently, the self-assembly behavior of the surfactants in aqueous solutions was examined using surface tension tests and molecular dynamics simulations. Flotation experiments and zeta potential, X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), contact angle, and adsorption capacity analyses were used to explore the flotation behavior and adsorption mechanism at the solid–liquid–gas boundary. The maximum flotation recovery of cassiterite were 45.73 % and 71.25 % when SHA and DBIA were used alone. By contrast, with the developed combined surfactant, the flotation recovery at the same reagent concentration was 84.92 %. The SHA/DBIA surfactant co-adsorbed at the aqueous solution interface, which decreased the surface tension of the solution to 4.943 × 10−4 mol/L and resulted in formation of a stable foam layer. These effects altered the surface properties of cassiterite and enhanced its surface hydrophobicity. Overall, this study provides valuable mechanistic insights into the enhanced chelation complexation of self-assembled surface collectors with metal oxides.

Molecular-Level Insight into the Chlorofluorocarbons Adsorption by Defective Covalent Organic Polymers.

Halocarbons have important industrial applications, but because of their contribution to global warming and the fact that they can cause ozone depletion, they are considered highly toxic. Hence, the techniques that can capture and recover the used halocarbons with energy-efficient methods have been recently received greater attention. In this contribution, we report the capture of dichlorodifluoromethane (R12), which has high global warming and ozone depletion potential, using covalent organic polymers (COPs). The defect-engineered COPs were synthesized and demonstrated outstanding sorption capacities, ~226 wt % of R12 combined with linear-shaped adsorption isotherms. We further identified the plausible microscopic adsorption mechanism of the investigated COPs via grand canonical Monte Carlo simulations applied to non-defective and a collection of atomistic models of the defective COPs. The modeling work suggests that significant R12 adsorption performance is attributed to a gradual increment of porosities due to isolated/interconnected micro-/meso-pore channels and the change of the long-range ordering of both COPs. The successive hierarchical-pore-filling mechanism promotes R12 molecular adsorption via moderate van der Waals adsorbate-adsorbent interactions in the micropores of both COPs at low pressure followed by adsorbate-adsorbate interactions in the extra-voids created at moderate to high pressure ranges. This continuous pore-filling mechanism makes defective COPs as promising sorbents for halocarbon adsorption.

Construction of a food waste biochar model and determination of contaminant adsorption sites: Combining experimental characterisation with quantum chemical calculations

Increasing urbanization has made it a serious challenge to deal with food waste (FW) from people and wastewater with pollutants from industry. Biochar from FW pyrolysis(FWB) can be used as an adsorbent to adsorb pollutants from wastewater, but its molecular structure is still unknown, limiting the understanding of its adsorption mechanism and its application in industry. In this paper, a series of combined methods of experimental characterization and quantum chemical calculations, such as solid-state 13C nuclear magnetic resonance spectroscopy (13C NMR), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) were used to investigate and successfully construct a model of the molecular structural features of FWB under the optimal contaminant adsorption preparation conditions. Based on the electrostatic potential distribution and adsorption experiments, the adsorption sites of the pollutants were elucidated. The results showed that the FWB prepared at different temperatures, 450 °C had a variety of oxygen-containing functional groups and polarity favorable for adsorption. In the molecular structure of FWB with the molecular formula C60H49N7O8, oxygen is present in the form of carboxyl, carbonyl, ether, alcohol hydroxyl, and phenol hydroxyl groups with numbers 1, 1, 1, 1, 2, 1, 2. Nitrogen is present in the form of pyridinyl nitrogen, pyrrolidinyl nitrogen, and primary amines with numbers 1, 1, and 5, respectively. In addition, nitrogen-containing and oxygen-containing functional groups are possible adsorption sites for pollutants on FWB, and alcohol hydroxyl and amino groups can bind better to Cu2+, which provides scientific guidance for improving the adsorption performance of biochar. This provides a solid foundation for the study of the microscopic adsorption mechanism of FWB and a method for the modeling of biochar from other biomasses.

Nanoporous Frameworks with High Porosity and Unexpected Rigid Framework Topologies Based on Odd‐Numbered Ring‐Expanded Linkers

Two tetracarboxylic linkers containing seven‐membered rings are synthesized and utilized in metal–organic framework (MOF) syntheses, leading to the two new compounds DUT‐184 and DUT‐193. The introduced odd angles between carboxylates in a new dihydro‐azepine‐containing linker lead to exotic Zn‐based MOFs: a 3D structure based on two catenated sets of 2D nets in DUT‐184 and a cubic structure with so far unknown topology in the DUT‐193 framework. The mesoporous DUT‐193 shows high porosity upon adsorption of N2, Ar, CH4, and CO2 at their standard boiling points. Grand canonical Monte Carlo simulations show good agreement between experimental and theoretical results and shine light on the microscopic adsorption mechanism at low pressure.

Molecular simulation study of liquid sulfur adsorption and diffusion in calcite nanoscale slits under varying temperature and pressure conditions

In the late stages of extensive development of high-sulfur carbonate gas reservoirs, pressure decline leads to sulfur enrichment, and when the temperature exceeds sulfur's melting point, sulfur precipitates in a liquid form, severely restricting the exploitation of high-sulfur carbonate gas reservoirs. However, the adsorption mechanism of sulfur deposition remains poorly understood. In this study, we investigated the microscopic adsorption mechanism of liquid sulfur in calcite nanopores using molecular simulation methods. Our research revealed that liquid sulfur adsorption in calcite nanopores is primarily influenced by pore size. When the pore size is less than 160 Å, multilayer adsorption dominates, with a single-layer sulfur film thickness of approximately 5 Å. At the nanoscale, 1 g of calcite with a 40 Å nanopore structure exhibits excess adsorption of liquid sulfur ranging from 0.00734 to 0.0279 g. As pressure increases, the adsorption of two or more layers intensifies, while the diffusion coefficient decreases. Conversely, as temperature rises, the density of each layer decreases, and the diffusion coefficient increases. Simultaneously, the diffusion coefficient of liquid sulfur in calcite slits exhibits a power function increase as the pore size enlarges. Under a pressure of 15 MPa, when the temperature increases from 420 K to 480 K, the diffusion coefficient increases from 6.96 × 10−11 m²/s to 3.51 × 10−10 m²/s. This study provides valuable insights into the adsorption and diffusion behavior of liquid sulfur in calcite nanopores, which can inform the development of high-sulfur carbonate reservoirs.

Preparation and properties of modified starch-based low viscosity and high consolidation foam dust suppressant

Aiming at the high-concentration dust pollution in open-pit coal mines, a foam dust suppressant with low viscosity and consolidated coal dust is developed. In order to reduce the limited effect of binder viscosity on the foaming ability and wettability of foam, tapioca starch is oxidized with Cu2+/H2O2 System in this study to reduce the molecular weight of the polymer and prepare materials with high consolidation and low viscosity. The dust suppression performance of the sample is measured, and the microscopic adsorption mechanism of the dust suppressant is investigated by molecular dynamics simulation. The results show that the oxidized starch adhesive solution consists of 20 g tapioca starch, 0.88 ml hydrogen peroxide, 2.4 g sodium hydroxide, and 0.48 g copper sulfate, which need to be diluted to 10 times the original volume, and 1 g of surfactant (sodium fatty alcohol polyoxyethylene ether sulfate/alkyl Glycoside=1:4) is added to prepare a new foam dust suppressant. The viscosity is 2.6 mPa·s, the foaming multiple is 6.25, the contact angle is 13.73° at the first second, the hardness reaches 70.75 HA, and a dust suppression rate of 98.17% for PM10. The dust suppressant can effectively suppress coal dust.

Enhanced adsorption of 3,4-methylenedioxymethamphetamine by magnetic graphene oxide-polydopamine nanohybrid modified zeolitic imidazolate framework-67 and its micro-mechanism: Experiments and calculations

Exploring the structure-dependent adsorption mechanism of contaminants in wastewater is beneficial to high-efficiency adsorbents design and environmental remediation. In this study, emerging porous material of zeolitic imidazolate framework-67 (ZIF-67) has been modified by the magnetic graphene oxide-polydopamine nanohybrid (mGOP) to obtain three-dimensional ZIF-67/mGOP through an in-situ growth strategy, which was applied to adsorb 3,4-methylenedioxymethamphetamine (MDMA, “ecstasy”) in wastewater. A combination of characterizations, experiments (pH, humic acid and ion strength effect) and quantum chemical calculations revealed the microscopic adsorption mechanism involves each single component, of which the hydrogen bond (O/N…HO) and π–π electron donor acceptor (π–π EDA) interactions of mGOP endowed favourable adsorption of ZIF-67/mGOP, and mechanisms of the pore filling and Co-O chelation of ZIF-67 played synergistic effect. Such nanocomposite as a ZIFs-based adsorbent exhibited ultra-high porosity (total pore volume = 0.4033 cm3/g) and specific surface area (995.22 m2/g), revealed the heterogeneity and multilayer adsorption properties, and obtained a theoretical maximum adsorption capacity of 159.845 μg/g which higher than that of mZIF-67 alone. Overall, this work provided an effective strategy for rationally modulate ZIFs-based composites and exploration of adsorption mechanism.

π-π electron-donor-acceptor (EDA) interaction enhancing adsorption of tetracycline on 3D PPY/CMC aerogels

In this work, a hydrophilic polypyrrole carboxymethyl cellulose aerogel (PPY/CMC) with a 3D structure was prepared via in-situ polymerization of pyrrole monomers with carboxymethyl cellulose as the substrate. The adsorption experiments showed that tetracycline can be effectively removed in a wide range of pH (4–10), and the adsorption capacity was 689.39 mg/g when the pH value was 6. The pseudo-second-order kinetic and Langmuir models better fitted the kinetic and isotherm data, which revealed that the adsorption was homogeneous and dominated by chemisorption. The experiment of adsorption thermodynamics showed that the adsorption process was spontaneous and endothermic. Zeta potential, FT-IR and XPS results indicated that the adsorption mechanism included π-π EDA interaction, hydrogen bonding and electrostatic interaction. Through Density Functional Theory (DFT) and Frontier Orbital Theory (FOT) simulation, the microscopic adsorption mechanism was further explored on the molecular and electronic scales. It is confirmed that TC was adsorbed onto PPY/CMC aerogels mainly through π-π EDA interaction in sandwich (S) configuration and parallel-displaced (PD) configuration, thus ensuring high adsorption efficiency. Compared with various adsorbent materials reported recently, the PPY/CMC aerogels have the advantages of higher adsorption capacity, excellent pH buffering capacity, simple preparation process and quickly removal of pollutants.

High-efficiency removal of methcathinone from water using a novel DES modified magnetic biochar nanocomposite

Deep eutectic solvent (DES), an environmentally friendly solvent, has drawn the growing interest of the academic community due to its distinctive physicochemical properties and widespread applications. In this work, magnetic biochar modified with DES (DES-MBC) has been fabricated and utilized to efficiently remove methcathinone from water. Batch experiments and density functional theory (DFT) simulations were utilized to explore the adsorption performance and mechanism of DES-MBC. Under optimal conditions, the removal rates of DES-MBC were highly remarkable with 93.26% and 95.85% in water containing methcathinone of 0.5 mg·L−1 and 1.0 mg·L−1, respectively. DFT simulations revealed that DES incorporation lowered the HOMO-LUMO energy gap (ΔEgap) and introduced additional reaction sites (e. g. hydroxyl groups and quaternary amino groups) which could react with methcathinone to increase the adsorption capacity of DES-MBC. Combining the results of experiments and simulations, the main removal mechanism between methcathinone and DES-MBC were electrostatic interaction, hydrogen bond and π-π interaction. In conclusion, DES modification was an effective strategy to enhance the adsorption capacity for methcathinone from water in practical applications. This study will contribute to the deep and extensive understanding of the microscopic adsorption mechanism so as to help optimize and develop more excellent adsorbents.

Influence of impurities on adsorption of hydrated Y3+ ions on the kaolinite (001) surface

The adsorption behavior of hydrated Y3+ ions on the outer and inner layers of the kaolinite (001) aluminum hydroxyl surface is studied by density functional theory. The bonding mechanism and the effect of common impurities (Mg, Ca and Fe) on the inner layer adsorption behavior are investigated. The results shows that the hydrated Y3+ ions retain the original number of coordinated water molecules and adsorb on the outer layer of the surface of kaolinite through hydrogen bonding, with an adsorption energy of − 262.66 kJ·mol−1. When the inner layer is adsorbed, the number of coordinated water molecules of the hydrated Y3+ ions decreases obviously due to the steric hindrance effect and they are adsorbed on the Ou site of the surface mainly through Y-Os covalent bonds. The electrons are transferred from the 5 s and 4p orbitals of the Y ions to the 2p orbital of the Os ions on the surface. The adsorption energy (−744.52 kJ·mol−1) is much lower than that for the outer layer. These results indicate that the inner layer adsorption of hydrated Y3+ ions occurs preferentially on the kaolinite (001) aluminum hydroxyl surface. The internal adsorption configurations and adsorption energies of hydrated Y3+ ions on the kaolinite surface are significantly affected by Mg, Ca and Fe doped at the Al sites, respectively. The adsorption of hydrated Y3+ ions on kaolinite surface becomes stronger with the increase of doping ion concentration with Mg, Ca and Fe doping, respectively, and the Ca and Mg impurities therefore significantly promote the adsorption of hydrated Y3+ ions. These results are helpful in revealing the microscopic adsorption mechanism of rare earth elements on ion-adsorbed rare earth minerals.

Magnetic powdery acrylic polymer with ultrahigh adsorption capacity for atenolol removal: Preparation, characterization, and microscopic adsorption mechanism

Contamination of pharmaceutically active ingredients (PhACs) in water has attracted the attention of the scientific community. Magnetic powdery acrylic polymer (MPAP) was prepared and used to adsorb atenolol (ATL) in aqueous solution for the first time. Adsorption kinetics results showed that the adsorption of ATL on MPAP reached equilibrium within 30 min, and the removal efficiency of ATL (100 mL, 500 mg·L−1) with 0.05 g MPAP was 86.8%. Adsorption isotherms showed that the maximum adsorption capacity was 2.82 × 103 mg·g−1 at 323 K. The positive △H0 (9.94 KJ·mol−1) indicated that the increase of temperature was beneficial to the adsorption. The positive △S0 (90.5 J·mol−1·K−1) indicated the increase of randomness of the adsorbent-solution interface. Cations in solution decreased the adsorption capacity of ATL by competing for the active sites on MPAP. The adsorption amount of ATL decreased with the decrease of solution pH. The hydrogen bonding adsorption mechanism was proposed and verified by the theoretical calculations. The adsorption of ATL on MPAP was more efficient under alkaline conditions, which could be explained by the loss of H from the carboxyl group being more favourable for the adsorption of protonated ATL. The degree of electron sharing between H-bond donors and H atoms decreased after the formation of H-bonds, which was reflected in the increase of bond length and the decrease of vibrational frequency. MPAP has high adsorption capacity and short adsorption equilibrium time, which is a promising adsorbent for removal of PhACs containing amide groups.

Study on Adsorption Behavior of a New Type Gemini Surfactant Onto Quartz Surface by a Molecular Dynamics Method

The adsorption mechanism of the branched quaternary ammonium salt Gemini surfactant (Gemini C3) at the water-surfactant-quartz interfaces for both neutral and negatively charged quartz surfaces was studied by a molecular dynamics (MD) method. Initial and final configurations, distributions of the surfactant and its interaction with surfaces, the radial distribution function (RDF) of water molecules, and the mean square displacement (MSD) of the surfactant in bulk phase have been elucidated at the molecular level. The results showed that the adsorption of Gemini surfactants onto the hydrophilic quartz surface was driven by electrostatic interaction, which increased the hydrophobicity of the solid surface when the surfactant concentration was lower than critical micelle concentration (CMC). However, the contact angle only slightly increased since the surface tension decreased simultaneously with growing concentration. Monolayers were formed during the adsorption process of Gemini C3 molecules on the quartz surface rather than a double layer when the concentration reached the CMC, indicating a gradual transformation of an extended monolayer adsorption configuration into a more compact one. The solid-liquid interfacial tension increased with the surfactant concentration and led to a significant increase of the contact angle. The simulation results were consistent with the experiments, which further revealed the microscopic adsorption mechanism of the Gemini C3 surfactant onto the quartz surface, and provided theoretical guidance for controlling the wetting properties and surface modification of the rock.

Research on Organic Nanopore Adsorption Mechanism and Influencing Factors of Shale Oil Reservoirs

The adsorption properties of shale oil are of great significance to the development of shale oil resources. This study is aimed at understanding the microscopic adsorption mechanism of shale oil in organic nanopores. Thus, a molecular model of organic micropore walls and multicomponent fluids of CO2, C4H10, C8H18, and C12H26 is constructed to investigate the adsorption pattern of multicomponent fluids in organic nanopores under different temperature and pore size conditions. The quantity and heat of adsorption are simulated with the Monte Carlo method, which has been used in previous studies for single-or two-component fluids. The results demonstrate that the ability of CO2 to displace various alkanes is different. Specifically, medium-chain n-alkanes are slightly weaker than light alkanes in competitive sorption, and long-chain n-alkanes are less conducive to competitive sorption. The higher the CO2 sorption ratio, the more the sorption sites occupied by CO2. Thus, it is the best replacement for shale oil. The adsorption quantity of carbon dioxide, n-butane, and n-octane in organic nanopores first increases and then decreases as temperature rises. Meanwhile, the adsorption quantity of n-dodecane decreases firstly and then increases. With the increase in the pore size, the adsorption quantity of carbon dioxide, n-butane, and n-octane in organic nanopores increases while the adsorption quantity of n-dodecane first increases and then decreases. Besides, the model with larger pore sizes is more sensitive to pressure changes in the adsorption of carbon dioxide and n-butane than the model with smaller pore sizes. The heat of adsorption is CO2, C12H26, C8H18, and C4H10 in descending order. All are physical adsorption. Moreover, the adsorption quantity of all four components mixed fluid in the organic matter nanopores is positively correlated with the heat of adsorption.

Graphene oxide effectively removes polyacrylamide from aqueous solution: Molecular dynamics simulation and experimental analysis

In this paper, graphite oxide (GO) was used to remove polyacrylamide (PAM) from aqueous solution. The micro-interaction between PAM and GO was studied through experiments combined with molecular dynamics simulation (MD). It was found that PAM molecules can be adsorbed on GO flakes and quickly precipitate out of the water phase. The optimal removal concentration was MGO: MPAM= 1:10. The MD simulation results revealed the adsorption mechanism by investigating morphology, diffusion rate and radial distribution function of PAM-GO systems. The main conclusions include three aspects: 1. the dense hydrogen bond network between the amide group of PAM and the oxygen-containing group of GO is the main reason for the formation of PAM-GO; 2. The carboxyl group of GO has the strongest binding ability with the PAM; 3. High temperature is not conducive to the combination of GO and PAM. Our research better explains the microscopic adsorption mechanism of GO and PAM, and provides a theoretical basis for the wider application of GO and PAM-GO.

From wastes to functions: preparation of layered double hydroxides from industrial waste and its removal performance towards phosphates.

To control eutrophication and recover phosphate from wastewater, a calcium carbide slag and red mud composite material (CR-LDH) was prepared using industrial waste as raw material for phosphorus adsorption. The morphology and structure of synthesized CR-LDH were characterized by FT-IR, SEM, EDS, and XRD measurements. Bath adsorption test results showed that the optimal dosages of adsorbent and pH for phosphate were 5 g·L-1 and pH of 7, respectively. The experimental data could be well described by pseudo-second-order kinetic and Langmuir isotherm models, suggesting that the adsorption process of CR-LDH with respect to phosphate was a chemical and monolayer process. The theoretical maximum adsorption capacity obtained by Langmuir isotherm model was 16.06 mg·g-1 at 25 °C. The intra-particle diffusion model fitting results indicated that the adsorption of phosphate by CR-LDH was controlled by both liquid membrane diffusion and intra-particle diffusion. Phosphate was bound to CR-LDH via synergistic effect of physical adsorption, ion exchange, anion intercalation, and chemical precipitation as evidenced from a combination of microscopic analysis and adsorption mechanism study. The actual phosphate-containing wastewater investigation showed that CR-LDH not only exhibited good removal effect on phosphate, but also could greatly reduce turbidity, COD, and ammonia nitrogen, which was suitable for disposal of practical wastewater. The COD, turbidity, and NH4+-N could be reduced by 42.39%, 77.20%, and 20.71%, respectively. These results indicate that CR-LDH can be considered as potential adsorbent for the treatment of phosphate-containing wastewater, which will be helpful to achieve the goal of "treating waste with waste and turning waste into treasure".

Adsorption mechanism of polyacrylamide on kaolinite surface in the presence of Ca2+: Insights from DFT calculation

The microscopic adsorption mechanism of polyacrylamide (PAM) on kaolinite surface in the presence of Ca2+ was investigated by using density functional theory (DFT). The PAM model was constructed firstly, and the optimal adsorption configurations and adsorption mechanism were examined, with adsorption configurations, bond populations and adsorption energy analyzed. Calculation results demonstrated that the adsorption of PAM on kaolinite (001) surface was dominated by three strong hydrogen bonds between the amide groups of PAM and hydroxyl groups of kaolinite (001) surface. And the PAM adsorbed on the kaolinite (00–1) surface through non-bonding interaction. Ca2+ was selected to explore the influence of metal cations on the adsorption of PAM on kaolinite surface. The results suggested that the adsorption of PAM on the kaolinite (001) surface was promoted in the presence of Ca2+, while the adsorption of PAM on the kaolinite (00–1) surface was inhibited.

Preparation of composite high-efficiency dust suppressant and relevant molecular dynamics simulation for wetting coal surface

A new type of high-efficiency dust suppressant for mines was synthesised by graft copolymerisation, with carboxymethyl chitosan serving as the matrix, and the microscopic adsorption mechanism of this dust suppressant was studied by molecular dynamics simulation. Four optimum conditions were determined by a single-factor experiment, namely, the amount of 2-acrylamide-2-methylpropanesulfonic acid was 5 g, the amount of initiator was 2.0% monomer, the amount of crosslinking agent was 0.2 g, and the optimum reaction temperature was 50 °C. The results of the water absorption test show that the product has strong water absorption, and the water absorption rate can reach 138 g/g, The results of the molecular dynamics simulation show that the structure and morphology of the dust suppressant do not change during water absorption; only the diffusion of water molecules in the molecular gap of the dust suppressant changes. The experimental results of the dust suppression performance show that the product can cover the surface of coal dust and form a colloidal film, which can effectively inhibit the spread of coal dust. The results of molecular dynamics simulation show that the dust suppressant acts primarily on the coal/water interface, which promotes the diffusion of water molecules on the coal surface. With the progress of the reaction, the dust suppressant molecules combine with each other and move and permeate towards the coal seam, with one end facing the coal seam and the other facing the water phase, thereby attracting water molecules to migrate towards the coal seam.

Molecular simulation of the competitive adsorption characteristics of CH4, CO2, N2, and multicomponent gases in coal

The microscopic mechanism of the competitive adsorption of CH4, CO2 and N2 in coal is the theoretical basis for enhancing coal seam gas recovery by injecting CO2 (CO2-ECBM). Based on this principle, this work used Grand Canonical Monte Carlo and Molecular Dynamics to investigate the microscopic adsorption mechanism of single, binary, and ternary component gases in Wiser bituminous coal molecules. The adsorption mechanism was explored by changing gas composition and concentration. The comparison of adsorption separation coefficients suggested that CO2 had the highest adsorption capacity, whereas N2 had the lowest capacity. When the CO2 concentration in the gas mixture was high, the adsorption amount was large and the adsorption separation coefficient was small. This finding indicated that high concentrations of CO2 had negative effects on competitive adsorption. Energy changes were also evaluated. The potential energy between CO2 and the framework was the strongest among the two other gases. The inhibition of CH4 adsorption intensified with decreasing molar fraction of CO2. This phenomenon was explained from the perspective of heat of adsorption. As the molar fraction of CO2 in the adsorption system decreased, the heat of the isotherm adsorption increased. Meanwhile, the adsorption system became unstable and the capacity of CH4 adsorption on the framework weakened. Results provide a theoretical basis for the use of CO2-ECBM.