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Developing a 3D material to support α-Fe 2 O 3 nanorods to improve their adsorption performance for Congo Red (CR) is a major challenge. Herein, a novel 3D composite adsorbent was designed, where 2D material Ti 3 C 2 MX and CoFe-LDH stacked on top of each other as the support material of α-Fe 2 O 3 nanorods (α-Fe 2 O 3 @LDH@MX). The specific surface area of the α-Fe 2 O 3 @LDH@MX was increased by 2 times (101.28 m2/g) than original CoFe-LDH@MX, thus more favorable for capturing CR (698.25 mg/g). The results of kinetic studies demonstrate that the effective 3D composite structure enables unhindered movement of CR within the α-Fe 2 O 3 @LDH@MX. The Langmuir model can accurately describe the adsorption process of CR on the α-Fe 2 O 3 @LDH@MX, which means that the process belongs to monomolecular layer chemisorption. Molecular dynamics simulations revealed that the α-Fe 2 O 3 interface primarily interacts with oxygen within the -SO 3 group, achieving an adsorption energy up to E in teraction = −20,375.89 kcal/mol. The results of XPS analysis further revealed that interaction between Fe and O achieved the removal of CR. In this paper, the enhancement of α-Fe 2 O 3 adsorption performance has been successfully achieved through innovative structural design. This significantly advances its potential applications and offers new insights for future material design. [Display omitted] • 3D support improves the exposure of α-Fe 2 O 3 nanorod active sites and promotes rapid response to Congo red. • α-Fe 2 O 3 @LDH@MX has outstanding adsorption capacity for Congo red and excellent anti-interference ability. • Quantum chemistry and molecular dynamics simulations were used to provide in-depth insights into the adsorption mechanism. [ABSTRACT FROM AUTHOR]

Lithium–sulfur (Li–S) batteries are widely regarded as the most promising batteries for the future due to their higher specific capacity and lower prices. Various strategies are utilized to alleviate the shortcomings of Li–S batteries failing to reach theoretical capacity. However, basic research at the molecular level continues to be lacking. Therefore, we use molecular dynamics to study the details of the solvated structure of Li–S batteries electrolyte and the nature of the transport process, revealing the relationship between the solvated structure of the electrolyte of LiPF6 and the organic solvent ethylene carbonate/dimethyl carbonate (EC/DMC). The electrolyte of Li2S4 was first simulated in a pure solvent environment. Then the LiPF6 salt was added to the model to simulate a typical electrolyte for a working Li–S battery. Regarding the rationality of the solvent system, various reference systems such as density, dielectric constant, viscosity and diffusion coefficient of the solvent were used for verification. And the detailed composition of the first solvation shell of the polysulfate ion and the coordination number of the ions are discussed. These results provide new insights into the use of EC/DMC electrolytes in Li–S batteries, while at the same time providing a basis for efficient future predictions of electrolyte structure and transport in complex electrode confinements. The radius of the first solvation shell of each component is the PF 6 − anion at about 0.22–0.28 nm, the DMC solvent at about 0.32–0.36 nm and the EC solvent at about 0.41 nm, respectively. The first solvation shell according to these distributions has a radius of about 0.5 nm. The coordination number in the first solvation shell is plotted, which is about 1.88 for PF 6 − , 1.86 for DMC, and about 0.14 for EC. In conclusion, 3.88 molecules are produced in the first solvation shell of the ion. [ABSTRACT FROM AUTHOR]

BACKGROUND: Copper is a heavy metal that is widely available in nature and has attracted people's attention because of its toxicity and difficult biodegradability. Using modified montmorillonite to adsorb copper ions (Cu2+) was widely adopted because of its simple operation, high efficiency, and easy availability. RESULTS: Na‐montmorillonite (Na‐Mt) was modified through a Gemini surfactant (containing four ammonium cations) to explore the adsorption capacity for Cu2+ in aqueous media. The resulting product is called G‐Mt. FT‐IR XRDBET results indicated that Gemini surfactant has significantly intercalated into the montmorillonite interlayers. The results ofbatch adsorption experiments presented that the amount of adsorbed (qe) depend on pH value and qe (G‐Mt) can reach to 29.30 mg/g, which was greater than that of Na‐Mt (25.30 mg/g) when pH is 6.0 and initial Cu2+ concentration is 75 mg/L. The experimental data matched well with Langmuir isotherm. The thermodynamic analysis implied that adsorption of Cu2+ was endothermic and a spontaneous process. Molecular dynamics (MD) models were carried out to investigate the microstructure and kinetic information of Gemini cations in the interlayer of G‐Mt. The results elucidated that the distribution and interaction characteristic of ammonium cations of Gemini surfactant including four ammonium cations were completely different from that of the quaternary ammonium salts containing asingle ammonium cation. CONCLUSION: Generally, considering the comprehensive performances, polyamine Gemini surfactant to modify montmorillonite can improve its ability to adsorb Cu2+. The micro environment in the interlayer space and adsorption properties of G‐Mt on Cu2+, which will improve the potential utilization of G‐Mt in soil remediation or wastewater treatment. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Thecrystal morphology of the energetic material cyclotrimethylenetrinitramine (also known as RDX) influenced by the solvent effectwas investigated via molecular dynamics simulation. The modified attachmentenergy (MAE) model was established by incorporating the growth parameter–solventterm. The adsorption interface models were used to study the adsorptioninteractions between solvent and RDX surfaces. The RDX crystal morphologygrown from the cyclohexanone (CYC) solvent as a case investigationwas calculated by the MAE model. The calculation results indicatedthat, due to the effect of CYC solvent, (210) and (111) faces hadthe greatest morphological importance on the final RDX crystal, whilethe morphological importance of (020), (002), and (200) faces werereduced. The predicted RDX morphology was in reasonable agreementwith the observed experiment result. [ABSTRACT FROM AUTHOR]

In this work, a molecular dynamics investigation was performed to study the effect of the solvents acetone and cyclohexanone on the crystal habits of hexogen. The results show that the adsorption energies of hexogen polar faces such as the (002), (210), (111), and (200) faces are larger than that of the nonpolar (020) face. The adsorption interactions of hexogen surfaces with acetone are stronger than those with cyclohexanone. The adsorption interactions consist of van der Waals and electrostatic interactions. The effect of solvents on the crystal growth of hexogen is discussed by comparing the adsorption energy of each crystal face. It may qualitatively predict that if hexogen crystallizes from polar solvents (acetone and cyclohexanone), the morphological importance of polar faces increases, especially in acetone solvent, while the importance of the nonpolar (020) face probably diminishes, even disappears. The theoretical prediction properly explains the different crystal morphologies of hexogen observed experimentally in these two solvents. [ABSTRACT FROM AUTHOR]

Highlights: [•] Crystal morphology of ANPyO in vacuum and solvent was predicted by attachment energy. [•] Crystal shape becomes very close to a flake in trifluoroacetic acid solvent. [•] Interaction energies include hydrogen bond, Coulomb and Van der Waals forces. [•] Analysis of solvent self-diffusion coefficient shows stirring affects crystal habit. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations have been performed to investigate the effect of acetone solvent on the crystal morphology of RDX. The results show that the growth morphology of RDX crystal in vacuum is dominated by the (111), (020), (200), (002), and (210) faces using the BFDH laws, and (111) face is morphologically the most important. The analysis of surface structures of RDX crystal indicates that (020) face is non-polar, while (210), (111), (002), and (200) faces are polar among which (210) face has the strongest polarity. The interaction between acetone solvent and each RDX crystal face is different, and the order of binding energy on these surfaces is (210) > (111) > (002) > (200) > (020). The analysis of interactions among RDX and acetone molecules reveal that the system nonbond interactions are primary strong van der Waals and electrostatic interactions containing π-hole interactions, the weak hydrogen bond interactions are also existent. The effect of acetone on the growth of RDX crystal can be evaluated by comparing the binding energies of RDX crystalline faces. It can be predicted that compared to that in vacuum, in the process of RDX crystallization from acetone, the morphological importance of (210) face is increased more and (111) face is not the most important among RDX polar surfaces, while the non-polar (020) face probably disappears. The experimentally obtained RDX morphology grown from acetone is in agreement with the theoretical prediction. [ABSTRACT FROM AUTHOR]

Abstract: Molecular dynamics (MD) simulations were employed to investigate the interactions between polyether polyamino methylene phosphonate (PAPEMP) with different degrees of polymerization (n=1–7) and (010), (020) crystal surfaces of anhydrite. An aqueous environment was added through the introduction of water in the simulation cell. The results showed that PAPEMP molecules attach to the surfaces rather than remain in the bulk water and the interactions of the same PAPEMP molecule with the two surfaces show small differences; under the same mass of PAPEMP (n=1–7), the order of the binding energy E m of PAPEMP is as follows: PAPEMP (n=3)>PAPEMP (n=2)>PAPEMP (n=1)>PAPEMP (n=4)>PAPEMP (n=6)>PAPEMP (n=5)>PAPEMP (n=7). The number of the functional groups and the stereo-hindrance effect are two main factors influencing the interactions between PAPEMP and anhydrite. When n≤3, the former is the main factor; while n>3, the latter is the main factor. The binding energies are mainly provided by the ionic bond and the non-bonding interaction. The structures of the polymers are deformed during the combining processes. Simulation results provide theoretical guidance to judge the performance of scale inhibitors, and synthesize new highly effective scale inhibitor. [Copyright &y& Elsevier]

The interaction of seven pamidronate bisphosphonate (Pami-BPs) and its analogs with the hydroxyapatite (HAP) (100) surface was studied using density functional theory (DFT) and molecular dynamic (MD) methods. Partial Mulliken oxygen atomic charges in protonated structures were calculated at the level of B3LYP/6-31G*. The MD simulation was performed using the Discover module of Material Studio by compass force field. The results indicate the abilities of donating electrons of the oxygen atoms of the phosphate groups that are closely associated with the antiresorptive potency. The binding energies, including vdw and electrostatic, are used to discuss the mechanism of antiresorption. The results of calculations show that the strength of interaction of the HAP (100) face with the bisphosphonates is N > N > N > N > N > N > N according to their experimental pIC values. [ABSTRACT FROM AUTHOR]

Two gemini surfactants propylbis (dodecyldimethyl) ammonium chloride (12−3−12) and propylbis (octadecyldimethyl) ammonium chloride (18–3-18) with different chain lengths were used to modify Ca- montmorillonite (Ca-Mt). XRD results showed that the arrangement of surfactants was mainly paraffin-type and with additional minor lateral-bilayer in the interlayer space of montmorillonite. Batch adsorption tests indicated that the modified organo-montmorillonite (G 12 -Mt and G 18 -Mt) had better removal effect on three benzotriazole emerging contaminants (ECs) than that of original Ca-Mt, and the sequence of adsorption capacity was 1-Hydroxybenzotriazole (OHBTA) > benzotriazole (BTA) >5-methylbenzotriazole (TTA). Molecular dynamics simulation was carried out to reveal the arrangement, conformation and behavior of Gemini surfactants in the interlayer of Mt. at atomic level. The results suggested that one of the two long alkyl chains was erected in a paraffin-type arrangement, the other long alkyl chain accompanying with the positively charged N head groups & the propyl spacer were parallel to the Mt. (001) plane and was fixed near the top and bottom surfaces with the arrangement of lateral-bilayer, which was agreement with the XRD data. BTA molecules located at the aggregate organic phase formed by the alkyl chain, while Cl− ions preferred to appear in the middle area of the interlayer of montmorillonite. Meanwhile, Multiwfn wavefunction program was applied to quantitatively analysis the molecular surface area in different electrostatic potential (ESP) intervals, the ESP minimum & maximum values on the three ECs molecular vdW surface, integrating with color-filled ESP planar maps and VMD program to insight the electrostatic interaction and magnitude order between Gemini surfactants modified Ca-Mt and three pollutants. The adsorption mechanisms of Gemini surfactants modified Mt. to three benzotriazole emerging contaminants involved electrostatic interaction and hydrophobic partitioning effect. [Display omitted] • ESP distribution was used to quantitatively assess the electrostatic interaction. • MD simulation was used to reveal the dynamics of interlayer species. • The adsorption effects of different gemini surfactants modified Mts were compared. • The adsorption micromechanisms were uncovered. [ABSTRACT FROM AUTHOR]

[Display omitted] • The novel ampholytic surfactant was firstly used to modify acidified Na-Mt. • Cationic panthenol modified Na-AMt had a higher adsorption capacity to two pollutants. • The arrangement of different components in the interlayer of Mt was revealed. • The bonding characteristics and dynamic behavior of different species were explored. • The electrostatic interaction and hydrophobic partitioning were demonstrated. A novel ampholytic surfactant (cationic panthenol, CP) modified montmorillonite (CPMMt) was firstly prepared and investigated its removal effect and mechanism for a class of emerging pollutants such as benzothiazole (BTH) and 2-hydroxybenzothiazole (2-OH-BTH) in water. Batch experiments were conducted to probe the effects of various conditions on the adsorption. The results showed CPMMt-1.0 had greater adsorption performance for BTH and 2-OH-BTH than Na-AMt (acidified Na-Mt), and the maximum equilibrium adsorption capacities of CPMMt-1.0 for BTH and 2-OH-BTH were three times that of Na-AMt. Zeta potential analysis, the effect experiments of solution pH combined with Multiwfn wave function program were carried out to inspect the electrostatic interaction. Furthermore, molecular dynamics simulation was applied to investigate the dynamics behavior of cationic panthenol (CP) and BTH or 2-OH-BTH in the interlamellar of montmorillonite. The results demonstrated that CP molecules presented a lateral bilayer structure, which was in good agreement with XRD experimental data, and the interaction between BTH and the surface of montmorillonite was stronger than that of 2-OH-BTH, which implies that the CPMMt-1.0 had better adsorption performance for BTH than 2-OH-BTH, which was consistent with the experimental results. The adsorption mechanism involved electrostatic interaction and hydrophobic partitioning. [ABSTRACT FROM AUTHOR]

In order to understand the mechanism of the effect of solvent on the crystal morphology of explosives, and be convenient for the choice of crystallization solvent, the attachment energy (AE) model was performed to predict the growth morphology and the main crystal faces of 1,3,3-trinitroazetidine (TNAZ) in vacuum. The molecular dynamics simulation was applied to investigate the interactions of TNAZ crystal faces and ethanol solvent, and the growth habit of TNAZ in ethanol solvent was predicted using the modified AE model. The results indicate that the morphology of TNAZ crystal in vacuum is dominated by the six faces of [0 2 1], [1 1 2], [0 0 2], [1 0 2], [1 1 1] and [0 2 0], and the crystal shape is similar to polyhedron. In ethanol solvent, The binding strength of ethanol with TNAZ faces changes in the order of [0 2 1] > [1 1 2] > [0 0 2] > [1 0 2] > [1 1 1] > [0 2 0], which causes that [1 1 1] and [0 2 0] faces disappear and the crystal morphology becomes more regular. The radial distribution function analysis shows that the interactions between solvent and crystal faces mainly consist of coulomb interaction, van der Waals force and hydrogen bonds. [ABSTRACT FROM AUTHOR]

Abstract: The interaction of organic phosphonates with mineral surfaces is of interest owing to their use as scale inhibitors. Molecular dynamic (MD) simulations have been employed to study the adsorption of four phosphonic acids, i.e. amino tris(methylene phosphonic acid) (ATMP), ethylene-diamine tetra(methylenephosphonic acid) (EDTMP), hexamethylene-diamine tetra(methylenephosphonic acid) (HDTMP), and diethylene-triamine penta(methylenephosphonic acid) (DTPMP) onto the stepped calcite (011) surface. It has been found that the phosphonate molecules can energetically interact well with the (011) face on the stepped dihedral nook. Furthermore, the strength of adsorption is DTPMP>HDTMP>EDTMP>ATMP based on the binding energy including vdw and electrostatic interaction, in agreement with the pHCM experiment. The results indicate that the phosphonic group number and the length of the backbone methylene chain play an important role in inhibitor effectiveness. [Copyright &y& Elsevier]

Many studies have proved that montmorillonite (Mt) has good adsorption properties for some antibiotic pharmaceuticals, but the detailed research on the microscopic sorption mechanism is very limited from the atomic level. In the present work, Mt was chosen as an adsorbent for common emerging contaminant-ciprofloxacin (CIP) to investigate the essence of the interaction between Mt and different CIP species at different pH. X-ray diffraction (XRD) and Fourier Transform Infrared spectroscopy (FTIR) characterization after adsorption under different pH were utilized to explore the difference of adsorption mechanism with the changed pH. Especially outstanding, for the first time, Molecular dynamics simulation (MD) was carried out to investigate the arrangement and dynamic behavior of cationic CIP in the interlayer of Mt, Multiwfn wave function analysis program was performed to quantitatively analyze the molecular surface electrostatic potential (ESP) distribution of different CIP species to evaluate the electrostatic interaction. Furthermore, for the first time, Hirshfeld surface analysis and independent gradient model (IGM) analysis were applied to probe and visualize the interaction sits between Mt and CIP zwitterion(CIP+/−) or CIP anion (CIP-), which can reveal the adsorption mechanism of Mt for CIP+/− and CIP- from the atomic level microscopic perspective. [ABSTRACT FROM AUTHOR]

• MD simulations reveal the interaction essence of deprotonated HEDP and HAP in presence of water. • The uptake of Cu2+ by single nano-hydroxyapatite and HEDP-HAP-0.5 hybrid system was 40.32 and 171.8 mg/g, respectively. • The adsorption mechanisms of HEDP-HAP hybrid system on Cu2+ involve the formation of surface complexes and ion exchange. The adsorption capacities of different ratios of 1-hydroxyethylidene-1, 1-diphosphonic acid (HEDP) and nano-hydroxyapatite (HAP) hybrid systems on Cu2+ were probed. The FTIR, XRD, SEM and EDS analyses showed that HEDP with Cu2+ adsorbed on the surface of HAP and a new crystal phase appeared. The content of adsorbed Cu2+ were 4.4% and 21.8% on the surface of single HAP and HEDP-HAP-0.5 hybrid system, respectively, and later was 4.94 times that of the former. Conversely, the Ca/P (mol) ratio decreased from 1.40 to 0.61, indicating more Ca2+ were replaced by Cu2+. Meanwhile, molecular dynamics (MD) simulations results showed that HEDP and water molecules both formed ordered adsorption layer with similar concentration profiles, but the former preferred to gather on the HAP surface than the latter. The electrovalence bonds between the phosphonic acid functional groups of HEDP and Ca2＋ of HAP surface played the dominant role in their adsorption. The adsorption results showed that the maximum adsorption capacity of single hydroxyapatite for Cu2+ was 40.32 mg/g, while the maximum adsorption capacities reached 99.11, 171.8 and 147.27 mg/g for HEDP-HAP-0.2, HEDP-HAP-0.5 and HEDP-HAP-1.0 hybrid systems, respectively. The study illustrated that the adsorption process accorded with the pseudo-second-order kinetic and Langmuir isotherm model. [ABSTRACT FROM AUTHOR]

The carboxymethyl-chitosan-montmorillonite (CMC-MMT) organic-inorganic hybrid material was applied to adsorb Pb(II) and Congo red (CR) anionic dye from aqueous solution. Molecular dynamics(MD) simulation was carried out to reveal the mechanism of CMC hybrid MMT. The results suggested that CMC has been adsorbed on the interlayer space and surface of MMT, hydrogen bonds had been formed between hydroxyl & carboxyl groups of CMC with the surface of MMT, Van der Waals interaction was also existed, while amino groups of CMC hadn't obvious interaction with the surface of MMT. Batch experiments were executed to investigate the adsorption effect of CMC-MMT was compared with Na-MMT and CMC. The results showed that CMC-MMT exhibited the higher adsorption capacity than Na-MMT and CMC, The OH and COOH or NH 2 groups of CMC chains may serve as electrostatic interaction active sites and coordination sites, which improved the adsorption performance of CMC-MMT on Pb(II)，and the insertion of CMC enlarged the inter-layer space of MMT, resulting in more surface active sites in the CMC-MMT hybrid composite, which increased the adsorption of organic pollutant CR. The kinetic and isotherm studies indicated that the pseudo-second-order and the Langmuir model well described the adsorption equilibrium of Pb(II) and CR on CMC-MMT. Unlabelled Image • Molecular dynamics (MD) simulation was carried out to reveal the mechanism of carboxymethyl chitosan (CMC) hybrid montmorillonite (MMT). • The hydroxyl groups of CMC molecules interacted most strongly with MMT by hydrogen bond and van der Waals forces, the carboxyl groups had a weak hydrogen bond with the surface of MMT, and the effect of the amino groups was not obvious. • CMC-MMT organic-inorganic hybrid composite exhibited the higher adsorption capacity on Pb(II) and Congo Red (CR) than Na-MMT and CMC alone. • The insertion of CMC enlarged the inter-layer space of MMT, resulting in more surface active sites in the CMC-MMT hybrid composite, which increased the adsorption of organic pollutant CR. • The OH and COOH or NH2 groups of CMC chains may serve as electrostatic interaction active sites and coordination sites, which improved the adsorption performance of CMC-MMT on Pb(II) [ABSTRACT FROM AUTHOR]

Antiscalants commonly used are difficult to be degraded and research of new antiscalants still relies on experiments. Therefore, molecular dynamics was applied to simulate interactions of five different molar ratios of poly(itaconic acid- co -epoxysuccinic acid) (PIA- co -ESA) copolymers with calcite surfaces in aqueous solution. On the basis, PIA- co -ESA which shows excellent antiscaling performance was screened out, synthesized and characterized, and the optimal synthesis condition was obtained by single factor experiments. The crystal morphology of calcite was observed by SEM. The results indicate that when monomer ratio (n IA : n ESA ) is 4:1, dosage of initiator is 11%, reaction temperature is 85 °C and reaction time is 4 h, PIA- co -ESA possesses the largest binding energy and exhibits excellent scale inhibition performance, in agreement with experiment result. Scale inhibition efficiency increases as increase of PIA- co -ESA concentration, reaching to 100% at a level of 18 mg·L −1 agent, which was determined with the static scale test method. The analysis of radial distribution function verified that binding energy originates from ionic bond and hydrogen bond, PIA- co -ESA retards the growth rate of crystal surfaces and results in changes of crystal morphology, according well with SEM results. The results provide theoretical and experimental data for antiscale mechanism study and synthesis of antiscalant. [ABSTRACT FROM AUTHOR]

The maximum adsorption capacities of threonine-montmorillonite (Thr–Mt) composite to Pb2+ and Cu2+ in aqueous solution were higher than that of original sodium-montmorillonite (Na–Mt). Molecular dynamics (MD) simulation and Multiwfn wavefunction program based on density functional theory (DFT) were exploited to probe the interaction and mechanism between threonine-montmorillonite composite and Pb2+ or Cu2+. Moreover, for the first time, Independent Gradient Model (IGM) analysis was utilized to decode the interaction essence among Thr, Mt. and Pb2+ or Cu2+ to reveal the removal mechanism of Thr-Mt to Pb2+ and Cu2+. MD results indicated that the arrangement of Thr+ presented a preferred almost vertical orientation, which was consistent with the X-ray diffraction (XRD) result. There was hydrogen bonding between carboxyl group or hydroxy group of Thr+ and Mt. surface. Multiwfn calculation implied that the minimum points of ESP and ALIE were located near the O atoms of hydroxyl group and carboxyl group, which were most likely providing the lone pair electron to form a complex with the metal ion,which was accordance with the result of basin analysis. IGM analysis vividly revealed that O atoms of carboxyl group and hydroxyl group were binding sites, and the interaction between Pb2+ and Na–Mt or Pb2+ and Thr-Mt was stronger than that of Cu2+, which was well consistent with the experimental conclusion. Unlabelled Image • Environmentally friendly threonine-montmorillonite composite was prepared. • Molecular dynamics simulation was used to reveal the intercalation mechanism of Thr+. • Multiwfn program was applied to quantitatively analyze the Thr+ molecule surface. • The microscopic mechanism of Thr-Mt on Pb2+ and Cu2+ were probed via IGM analysis. [ABSTRACT FROM AUTHOR]