Increase In Adsorption Energy Research Articles

Effect of coexisting trivalent aluminum on the adsorption of hexavalent chromium on sp2 carbon

The analysis of the influence of coexisting ion impurities on the adsorption behavior of Cr6+ on activated carbon at microscopic interfaces should be highlighted. Based on the research background on the adsorption treatment for waste solutions of chromic anhydride, this study reveals that coexisting Al3+ affects the adsorption behavior of Cr6+ on sp2 carbon structure-containing defects, as evidenced by density functional theory calculations. After conducting electronic environment analyses based on isolated Al3+–Cr2O72− coordination and its adsorption models, the Al3+ ion acts as an electron relay station that srapidly transfer the electrons of the 2p orbital of the ortho-carbon atoms to Cr2O72− owing to the saturation of its own p orbital. These findings lead to two conclusions: (i) the facilitated reduction of Cr6+ and its positive charge neutralized by approximately 0.16 Coulomp, and (ii) the increased adsorption energy of Cr2O72− by 3.0 % and 14.6 % on the unelectron-neutralized and electron-neutralized (002) plane of sp2 C-containing defects, respectively, owing to the presence of Al3+. This is attributed to the decreased in 0.089 Hartree Gap value resulting from the energy change of the molecular orbital after Al3+ stable coordination with Cr2O72−. Therefore, the reduced energy barrier facilitates the electron transfer from the 2p orbital of the edge carbon atom to the O–Al–O bridge via the Al3+ bridge.

CaO/SiC alkaline fillers for High-Temperature reduction of mercury (II)

The reduction of Hg2+ to Hg0 through high temperature is a crucial technique for mercury monitoring. However, this application encounters two challenges: suboptimal thermal conditions in the reaction zone leading to incomplete decomposition of Hg2+ and the susceptibility of the decomposed Hg0 to re-oxidation by Cl species. This work proposes a novel alkaline filler with alkaline earth metal oxides (AEMOs) as the active component, which enhances the thermal conditions of the reaction while effectively removing Cl species. DFT reveals increased adsorption energies of AEMOs for HCl and Cl with the growing atomic period. Further comparison of the electronic structures and adsorption behaviors between AEMOs and Cl species indicates a similar trend in electron transfer and electron density at the bond critical points. The frontier molecular orbital analysis shows a positive correlation between orbital energy level difference and adsorption energy. Experimental validation of the DFT results, combined with a comparison of costs and de-HCl performance, identifies CaO as the optimal active component. Subsequently, the CaO is loaded onto SiC, and the impact of precursor and loading ratio on the composite performance is investigated through experiments and characterization. The optimal preparation method involves using calcium acetate monohydrate as the precursor with a loading rate of 50 %. Finally, the developed alkaline filler is tested in a Hg-CEMS for industrial application, it shows errors of below 7 % compared to the EPA Method 30B results, validating its industrial feasibility. This work offers a practical solution for Hg2+ high-temperature reduction in industrial settings.

In situ self-assembled bismuth oxide fractals enabling highly selective electrosynthesis of formate in flow cells at high current densities

In this work, we present a scalable in-situ growth strategy for self-assembling a carbon felt supported Bi2O3 fractal nanostructure (f-Bi2O3/CF), enabling superior performance towards electrocatalytic CO2-to-formate conversion with an optimal Faradaic efficiency of 95.1% at −0.9 V (vs. RHE) in flow cell. More impressively, the current density reaches an industrially relevant 235.7 mA cm−2 and remains a high FEformate of 87.7%. The enhanced catalytic activity of the f-Bi2O3/CF model is attributed to the increased adsorption energy of OCHO* intermediate by changing the surface charge distribution according to DFT calculations. Using the aforementioned method, a series of other CF supported metal oxide catalysts (i.e., CuO, In2O3, and SnO2) are easily obtained. A brief techno-economic analysis (TEA) model demonstrates the economic potential of electrocatalytic hydrogenation of CO2 into formate in flow cell. Our findings offer a promising pathway for the fabrication of stable and accessible fractal structure, applicable to a wide range of scenarios.

The regulation mechanism of transition metal doping on Hg0 adsorption and oxidation on Ce/TiO2(001) surface: A DFT study

The mercury oxidation performance of Ce/TiO2 catalyst can be further enhanced by transition metal modifications. This study employed density functional theory (DFT) calculations to investigate the adsorption and oxidation mechanisms of Hg0 on Ce/TiO2(001) and its transition metal modified surfaces. According to the calculation results, Ru-, Mo-, Nb-, and Mn-doping increased the affinity of the Ce/TiO2(001) surface towards Hg0 and HCl, thereby facilitating the efficient capture and oxidation of Hg0. The increased adsorption energy (Eads) of the intermediate HgCl on the modified surfaces could promote its conversion to the final product HgCl2. The modification of transition metals impeded the desorption of the final products HgCl2 and HgO, but it did not serve as the rate-determining step. The oxidation of Hg0 by lattice oxygen and HCl followed the Mars-Maessen and Langmuir-Hinshelwood mechanisms, respectively. HCl exhibited higher mercury oxidation ability than lattice oxygen. The reactivity of lattice oxygen could be further improved by doping transition metals, their promotion order was Ru > Nb > Mo > Mn. In a HCl atmosphere, Mn modification could significantly reduce the energy barrier for HCl activation and HgCl2 formation, providing the optimal enhancement for the mercury oxidation ability of Ce/TiO2 catalyst. The screening method of transition metal modified components based on surface adsorption reaction and oxidation energy barrier was proposed in this study, which provided theoretical guidance for the development of CeTi based catalysts with high mercury oxidation activity.

NaNO3-Promoted MgO-Based Adsorbents Prepared from Bischofite for CO2 Capture: Experimental and Density Functional Theory Study.

MgO has broad application potential in CO2 capture at intermedium temperatures. In this paper, the effects of NaNO3 doping on the properties of MgO prepared by using waste bischofite as the raw material were investigated to improve the performance of the CO2 capture. MgO-doped NaNO3 exhibited excellent CO2 capture performance at 320 °C with a maximum adsorption capacity of 36.62 wt %. MgO-doped NaNO3 has good cycling stability after 10 adsorption-desorption cycle experiments. In addition, CO2 adsorption on pure MgO and MgO-NaNO3 surfaces was investigated in accordance with density functional theory. Calculation results show that doping with NaNO3 allows more electrons to be transferred from the MgO substrate to the CO2 molecule. MgO-doped NaNO3 can lead to an increase in adsorption energy, resulting in a more stable structure after adsorption and thereby promoting adsorption. The result of this study provides an effective method for the comprehensive utilization of salt lake resources.

Remarkable enhancement of the adsorption and diffusion performance of alkali ions in two-dimensional (2D) transition metal oxide monolayers via Ru-doping

Transition metal oxides (TMO) are the preferred materials for metal ion battery cathodes because of their high redox potentials and good metal-ion intercalation capacity, which serve as an outstanding replacement for layered sulphide. In this work, using first-principles calculations based on Density functional theory approach, we explored the structural and electronic properties which comprise of adsorption and diffusion behaviour along with the analysis of voltage profile and storage capacity of Ru doped two-dimensional transition metal oxide MnO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$MnO_{2}$$\\end{document}, CoO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$CoO_{2}$$\\end{document}, and NiO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$NiO_{2}$$\\end{document} monolayers. The adsorption of alkali ions (Li, Na) to the surface of TMOs is strengthened by Ru-atom doping. Ru doping enhanced the adsorption energy of Li/Na-ion by 25%/11% for MnO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$MnO_{2}$$\\end{document}, 8%/13% for CoO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$CoO_{2}$$\\end{document}, and 10%/11% NiO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$NiO_{2}$$\\end{document} respectively. The open circuit voltage (OCV) also increases due to the high adsorption capacity of doped Monolayers. Ru doping makes the semiconducting TMOs conduct, which is suitable for battery application. As alkali ion moves closer to the dopant site, the adsorption energy increases. When alkali ions are close to the vicinity of doping site, their diffusion barrier decrease and rises as they go further away. Our current findings will be useful in finding ways to improve the storage performance of 2D oxide materials for application in energy harvesting and green energy architecture.

Transition metal doped 2D SiC (TM=Ag, Pd and Rh) as a potential candidate for NOx (x = 1,2) and NH3 sensing

To control the nitrogen oxide emissions in large power plants, accurate monitoring NOx and NH3 gases at the outlet of the selective catalytic reduction system is vital to determine the degree of NOx reaction and adjust the amount of injected NH3. In this study, transition-metal (TM) atoms (Ag, Pd and Rh) doped 2D graphene-like SiC monolayers have been designed based on first-principles calculations. The adsorption and detection characteristics of TM-doped 2D SiC monolayers for NOx (x = 1, 2) and NH3 were systematically investigated. It is found that TM-doped 2D SiC monolayers exhibit strong potential in developing chemical sensors capable of detecting NO, NO2 and NH3. With the decoration of TM atoms in SiC monolayers, the adsorption ability of NO, NO2 and NH3 could be enhanced ascribed to the increased adsorption energy and electrical conductivity. In addition, the TM-SiC monolayers exhibit desirable thermostability at 298 K, 498 K and 798 K. By comparing the variations in atom-to-atom distances, plane-averaged charge density differences, charge transfers, density of states, energy gap variation and the recovery times of TM-doped SiC before and after adsorbed NOx and NH3, we found that Pd-SiC, Ag-SiC and Rh-SiC are optimal for the detection and recovery of NO, NO2 and NH3 gases with adsorption energies − 1.82 eV, − 2.17 eV, − 1.10 eV, respectively.

Anisole disproportionation on HZSM-5: The key role of Si/Al ratio on auto-inhibition effect

The conversion of anisole has been studied at 773 K on HZSM-5 zeolites with nine Si/Al ratios ranging from 9 to 201. The influence of the distribution of Brønsted Acid Sites on catalytic activity and reaction products selectivity has been studied experimentally. The adsorption energies for reactant and products on isolated and paired aluminium have been modelled by DFT. The Si/Al ratio does not affect any selectivity. Higher concentration of Brønsted acid sites leads to higher activity from Si/Al = 201 to 29. The shift from mostly isolated to increasingly paired Al strongly inhibits the conversion and initial activity. This is attributed to product desorption becoming the limiting step in the Sabatier volcano plot. This finding is consistent with the significant increase in adsorption energies between isolated and paired sites. When the adsorption energy of gaseous anisole becomes similar to that of its products, an auto-inhibition effect takes place as already known for liquid-phase processes.

Computational analysis of anti-cancer drug hydroxyurea adsorption on nanocages of gold, silver and copper: SERS and DFT assessment

The use of nanostructures in targeted drug delivery is effective in decreasing anticancer drug toxicity. Here, we discuss the theoretically predicted adsorption and interaction behavior of hydroxyurea [HU] with nano metal cages (nmC). HU interact the nmC through the N4 in primary amine with energies of −29.776, −30.684 and −22.105 kcal/mol for Au, Ag and Cu cage, respectively. As a result of reactivity studies, HU complexes with nmC (Au/Ag/Cu) are becoming more electrophilic and this gives the nmC system their bioactivity. It is suggested that nanocage is going to change the FMO's energy levels by means of absorption, so that it is used in drug administration. DOS and MEP were accomplished to gain additional understandings into the reactivity of proposed complexes. Method for improving the Raman signal of biomolecules is surface enhanced Raman scattering (SERS), which uses nanosized metal substrates. Chemical enhancement is evidenced by Mulliken charge distributions of all systems for detection and chemical compositions and exerts a significant role in determining them. In HU complexes containing nmC (Au/Ag/Cu), electron density was detected via ELF and LOL calculations. Based on the results of a non-covalent interaction (NCI) analysis, Van der Waals/hydrogen bonds/repulsive steric – interactions have been found. The title compound will also be analyzed in order to determine its bioactivity and drug likeness parameters, as a result, we will able to create a molecule with a highly favorable pharmacological profile and use the docking method to determine the values of the interaction energies for drug delivery. This study suggests that adsorption of drugs on nanocage surface occurs physically and functionalizing the nanocage has increased adsorption energy.

Structural reconfiguration of Al/CaO adsorbent by Ni doping to improve sintering resistance and arsenic removal performance

CaO-based adsorbents have poor adsorption performance due to high temperature sintering. In this study, a trace amount of Ni was added to an Al/CaO adsorbent using the Pechini hydrothermal method and anhydrous grinding method. The modified adsorbent was then used to remove As2O3, and both experimental and theoretical approaches were employed. The experimental results showed that the addition of Ni transformed the surface of the adsorbent from a two-dimensional network structure to a three-dimensional cluster structure, significantly increasing its specific surface area and improving its adsorption capacity for As2O3. The adsorption capacity reached 933.1 mg/kg at 900 °C, which was 3.79 times higher than that of pure CaO and 8.2 times higher than that of Al2O3. Additionally, the presence of nano-scale NiO particles prevented the sintering of CaO grains, allowing the adsorbent to maintain its pore structure even after the reaction. Density functional theory (DFT) calculations showed that NiO was the most active site for As2O3 adsorption on the surface of Al/Ni-CaO. Ni acted as an electron transport bridge, enhancing electron transfer on the material's surface and increasing adsorption energy. These findings are important for future research on high-temperature removal of As2O3 with doped CaO-based adsorbents.

Gas Sensing Properties of Pd-Decorated GeSe Monolayer toward Formaldehyde and Benzene Molecules: A First-Principles Study.

In this study, the gas sensing properties of formaldehyde (HCHO) and benzene (C6H6) adsorbed on two-dimensional (2D) pristine GeSe and Pd-decorated GeSe (Pd-GeSe) monolayers are studied by using first-principles calculations. The adsorption energies, electronic properties, optical properties, sensitivity, and recovery time of the gas adsorption systems have been thoroughly investigated. It is found that the adsorption of C6H6 on two substrate surfaces and the adsorption of HCHO on pristine GeSe are examples of physical adsorption. However, after HCHO adsorption on the Pd-GeSe monolayer, the adsorption system exhibits an increased adsorption energy of -1.21 eV, which is more favorable compared with the other adsorption systems studied. Moreover, the electron localization function and charge transfer from Pd-GeSe to HCHO are significantly enhanced, indicating distinct chemical adsorption behavior. Furthermore, it demonstrates a larger band gap change rate of 18.8% and a significant enhancement of optical absorption upon the adsorption of HCHO on the Pd-GeSe monolayer. Additionally, the appropriate sensitivity and moderate recovery time for the adsorption of HCHO on the Pd-GeSe surface indicate that the Pd-GeSe monolayer possesses an outstanding sensing capability for HCHO gas.

Unraveling the sorption mechanisms of ciprofloxacin on the surface of zeolite 4A (001) in aqueous medium by DFT and MC approaches

The adsorption mechanism of ciprofloxacin (CIP) and its ionic form were investigated using density functional theory (DFT) and molecular dynamics (MD), with the goal of forecasting their adsorption behavior in terms of gap energy, global reactivity descriptors, Fukui functions, adsorption energies, and density of state on the surface of zeolite 4A (001). Quantum chemical parameters related to the adsorption process were calculated, as well as the overall reactivity. According to DFT calculations, the zwetterionic form CIP± are the most stable and reactive and have a greater power of electron transfer compared to the other species. Under aqueous conditions, zeolite can adsorb ciprofloxacin (CIP) and its ionic forms, as revealed by molecular dynamics simulation. Ciprofloxacin in the zwitterionic form (CIP±) were more efficiently adsorbed to the surface of zeolite 4A (001) than the cationic (CIP+), anionic (CIP−), and neutral(CIP) forms; through the evaluation of adsorption energy, probability distribution, interaction, and density of state. The results also demonstrated that the compounds studied were adsorbed via the process of chemical bonding, which was confirmed by the negative values of the interaction energy. Furthermore, the negative adsorption energy values suggest a significant adsorption of all compounds, with electrostatic interactions (physisorption), diffusion into the pores, and n-π bonds (chemisorption) on the zeolite surface. The increase in adsorption energies and the proximity of the molecules studied to the zeolite surface indicate the predominance of chemisorption, and the adsorption of ciprofloxacin was found to be an exothermic and spontaneous process. Molecular dynamics (MD) modeling was in agreement with the DFT results.

Optimizing the Local Charge of Graphene via Iron Doping to Promote the Adsorption of Formaldehyde Molecules—A Density Functional Theory Study

Formaldehyde is a colorless, pungent, and highly volatile toxic gas known for its detrimental effects on the brain, respiratory, and nervous systems. The adsorption method emerges as an effective approach for detecting and mitigating formaldehyde gas, with the adsorption material serving as its core component. Graphene, a two-dimensional nanomaterial with remarkable properties, exhibits enhanced adsorption capabilities when subjected to metal doping, which alters its local geometric and charge characteristics. In this investigation, theoretical first-principles density functional technology was employed to optimize the efficiency of Fe-doped graphene in formaldehyde adsorption. The calculated adsorption bond length and energy were used to determine the type of adsorption. Then, the calculated Bader charge, density of states (partial density of states), and differential valence charge density distribution were used to analyze the electron transfer process before and after adsorption. Finally, the theoretical optical properties analysis result was applied to analyze the potential of Fe-doped graphene for formaldehyde detection. The findings indicated that Fe-doped graphene constitutes a viable and stable doping structure, accompanied by a notable shift in valence charge distribution around the doped iron atom. This altered charge distribution facilitated the chemical adsorption process, leading to reduced adsorption spacing and increased adsorption energy. Throughout the chemical adsorption process, there was evident charge transfer between carbon (formaldehyde) and iron atoms, as well as between oxygen (formaldehyde) and iron atoms. The formation of adsorption bonds primarily involved the p-orbital electrons of carbon and oxygen atoms, along with the p- and d-orbital electrons of iron atoms. Ultimately, the Fe-doped graphene material exhibited promising applications in the realm of formaldehyde molecular detection, marked by significant theoretical disparities in optical properties before and after the adsorption process.

Adsorption of SO2 Molecule on Pristine, N, Ga-Doped and -Ga-N- co-Doped Graphene: A DFT Study

SO2 (sulfur dioxide) is a toxic substance emitted into the environment due to burning sulfur-containing fossil fuels in cars, factories, power plants, and homes. This issue is of grave concern because of its negative effects on the environment and human health. Therefore, the search for a material capable of interacting to detect SO2 and the research on developing effective materials for gas detection holds significant importance in the realm of environmental and health applications. It is well known that one of the effective methods for predicting the structure and electronic properties of systems capable of interacting with a molecule is a method based on quantum mechanical approaches. In this work, the DFT (Density Functional Theory) program DMol3 in Materials Studio was used to study the interactions between the SO2 molecule and four systems. The adsorption energy, bond lengths, bond angle, charge transfer, and density of states of SO2 molecule on pristine graphene, N-doped graphene, Ga-doped graphene, and -Ga-N- co-doped graphene were investigated using DFT calculations. The obtained data indicate that the bonding between the SO2 molecule and pristine graphene is relatively weak, with a binding energy of −0.32 eV and a bond length of 3.06 Å, indicating physical adsorption. Next, the adsorption of the molecule on an N-doped graphene system was considered. The adsorption of SO2 molecules on N-doped graphene is negligible; generally, the interaction of SO2 molecules with this system does not significantly change the electronic properties. However, the adsorption energy of the gas molecule on Ga-doped graphene relative to pristine graphene increased significantly. The evidence of chemisorption is increased adsorption energy and decreased adsorption distance between SO2 and Ga-doped graphene. In addition, our results show that introducing -Ga-N- co-dopants of an “ortho” configuration into pristine graphene significantly affects the adsorption between the gas molecule and graphene. Thus, this approach is significantly practical in the adsorption of SO2 molecules.

F-doped carbon derived from asphalt by mechanochemical approach: More effective toward selective CO2 capture

Porous carbon materials are a preferred choice for CO2 capture and separation owing to unique physical and chemical properties. Here, mechanochemical synthesis of porous carbon (high surface area, up to 1188 m2g−1) and in situ fluorine doping have been accomplished with asphalt as carbon source and Teflon (PTFE) as porogen and fluorine-doped precursors. Ball milling treatment are indispensable for the subsequent carbonization process of asphalt-PTFE mixture. The particle mixing and surface activation in the solid state are promoted by the input of mechanical energy and reaction mixtures are exposed to mechanical force impact. Meanwhile, the micropores and polar functional groups rich in the as-prepared carbon materials both conduce to higher CO2 capture and increase in adsorption energy based on DFT calculation. As evidence, the CO2 uptake capacity reached to 4.1 mmol g−1 for F-C-30# at 273 K, 1 bar. The CO2/N2 selectivity could reach up to 54 under ambient conditions, thereby reflecting a highly competitive CO2-adsorption capacity.

Cation Defect-Engineered Boost Fast Kinetics of Two-Dimensional Topological Bi2 Se3 Cathode for High-Performance Aqueous Zn-Ion Batteries.

The challenge with aqueous zinc-ion batteries (ZIBs) lies in finding suitable cathode materials that can provide high capacity and fast kinetics. Herein, two-dimensional topological Bi2 Se3 with acceptable Bi-vacancies for ZIBs cathode (Cu-Bi2-x Se3 ) is constructed through one-step hydrothermal process accompanied by Cu heteroatom introduction. The cation-deficient Cu-Bi2-x Se3 nanosheets (≈4nm) bring improved conductivity from large surface topological metal states contribution and enhanced bulk conductivity. Besides, the increased adsorption energy and reduced Zn2+ migration barrier demonstrated by density-functional theory (DFT) calculations illustrate the decreased Coulombic ion-lattice repulsion of Cu-Bi2-x Se3 . Therefore, Cu-Bi2-x Se3 exhibits both enhanced ion and electron transport capability, leading to more carrier reversible insertion proved by in situ synchrotron X-ray diffraction (SXRD). These features endow Cu-Bi2-x Se3 with sufficient specific capacity (320mAhg-1 at 0.1Ag-1 ), high-rate performance (97mAhg-1 at 10Ag-1 ), and reliable cycling stability (70mAhg-1 at 10Ag-1 after 4000 cycles). Furthermore, quasi-solid-state fiber-shaped ZIBs employing the Cu-Bi2-x Se3 cathode demonstrate respectable performance and superior flexibility even under high mass loading. This work implements a conceptually innovative strategy represented by cation defect design in topological insulator cathode for achieving high-performance battery electrochemistry.

Structure of bound water layer on montmorillonite surface: The role of trans- and cis- vacant sites

Bound water on the surface of clay minerals determines the nature of a wide class of phenomena, from the diffusion of interlayer cations to synthesizing prebiotic macromolecules during the early Earth. However, the nature of forming the bound water layer's spatial structure and properties has yet to be fully investigated. Many factors, including peculiarities of structural charge distribution, surface adsorption centers, and OH-groups of the octahedral sheet of the clay minerals, can affect it in natural clays. In this work the role of hydroxyl ligands and isomorphic substitutions of the octahedral sheet in trans- and cis- vacant sites in the formation of the bound water layer structure on the basal surface of montmorillonite was studied by the Density Functional Theory. It was found out that in the case of single isomorphic substitution in the octahedral sheet OH-groups in the cis-vacant sites provide higher adsorption energy of water molecules on the basal surface as compared to OH-groups in the trans-vacant sites. The double isomorphic substitution in the octahedral sheet creates a mutual enhancement effect due to the difference in the structural arrangement of the OH-groups. This leads to an increase in the interaction with adsorbed water molecules. The maximum increase in adsorption energy is observed for the case with isomorphic substitutions of Mg-cis and Fe-trans in the octahedral sheet. The results of the theoretical study contribute to explaining the experimental data available in the literature.

First-principles study of beryllium substituted borophene as an anode material for Li/Na-ion batteries

In this work, we predict the effects of beryllium (Be) doping on β12 borophene as an electrode material for lithium-ion batteries (LIBs) and sodium-ion batteries (NIBs) by using first principles methods. The optimized Li and Na adsorption sites are identified, and we found that Be doping enhances a single Li/Na ion adsorption on β12 borophene with increased adsorption energy (−2.174/−1.765 eV for Li/Na). Before to and following adsorption of Li/Na, the electrical conductivity of Be-doped borophene was revealed by the finite density of states at the Fermi level. Be-doped borophene provides adequate open circuit voltages (0.84/0.80 V for LIBs/NIBs). Besides these advantages, most remarkably, BeB19 has an extremely high theoretical specific capacity of 2869/2087 mA h g−1 for LIBs/NIBs which is several times higher than the other discovered 2D materials. Our results support that Be doping has a positive effect on β12 borophene and can be used to create anodes with excellent electrochemical properties for both LIBs and NIBs.

Achieving smartphone-based colorimetric assay for Hg2+ with a bimetallic site strategy based on Hg2+-triggered oxidase-like catalytic activity of NSC/Co6Ni3S8 nanocomposite

Modulation of the nanozyme's catalytic activity is crucial for its real applications in detecting target analytes. Herein, we fabricated the nanocomposite (NSC/Co6Ni3S8) of N, S co-doped carbon and Co6Ni3S8 by a facile sol-gel approach. Compared to NSC/Ni9S8, NSC/Co6Ni3S8 with bimetallic active sites displayed better enzyme-mimetic activity. This nanocomposite could catalyze O2 to form ·O2− and oxidize colorless 3, 3′, 5, 5′-tetramethylbenzidine (TMB) into blue oxTMB. The other two free radicals (h+ and ·OH) played minor roles during the catalytic reaction. Hg2+ could integrate with S2− to form HgS and the surface charges of O2 were transferred to Hg2+ to promote O2 adsorption. DFT theoretical calculations highlight that the main reasons for the enhancing effect of Hg2+ on color development results from electron transfer and increased adsorption energy of O2 molecules onto the surface of NSC/Co6Ni3S8. By employing the oxidase-like activity of NSC/Co6Ni3S8 and Hg2+-triggered promoting effect, a colorimetric sensing platform was established for Hg2+ assay with a linear range of 10–200 μg/L and detection limit of 3 μg/L. Through integration with a smartphone-based APP “Thing Identify” software, a visual colorimetric assay for Hg2+ was constructed with a detection limit of 5 μg/L. Compared to the data detected by the mercury vapor meter, the relative recoveries of 92.4–108.1% evidenced the higher accuracy of this smartphone-based visual detection. Overall, the NSC/Co6Ni3S8-based colorimetric assay is convenient, rapid, and visual, and can be applied for routine monitoring of Hg2+ in real-world waters under outdoor conditions.

First-principles study of graphene intercalation in h-BN based resistance random access memory

Graphene intercalation between metal electrode and resistance layers has attracted extensive experimental and theoretical research because of its capability to manipulate the electronic structure and properties of hexagonal boron nitride based resistance random access memory. Herein, the interface characteristic, adsorption and migration behavior of Ti on pristine and defective graphene intercalation have been systematically investigated by utilizing the density functional theory method, which could help accurately preset defects and regulate the permeation process. Analysis of the interfacial contact form showed that Ohmic-type contact occurs between intercalation and resistance layer interface due to the heavy doping effect caused by charge accumulation on the h-BN layer surface upon introduction of intercalation. Ti metal adsorption at hollow site on defective graphene containing grain boundary with double vacancies was more energetically favorable than that on pristine graphene without vacancy or with single vacancy, whereas the increase of adsorption energy caused by grain boundary defects that represented by pentagons and heptagons and double vacancies were very limited. Migration barrier calculations with defect distribution and vacancy indicated that the critical factor controlling ion penetration in the whole intercalation process is the presetting of single vacancy defect rather than the varying number of vacancies and the existence of grain boundary defect. This finding provides a new perspective aiding understanding and design of the defect-assisted graphene intercalation mechanism.