Effect of Surface Chemistry on the Electrical Double Layer in a Long-Chain Ionic Liquid.

Room temperature ionic liquids (ILs) can create a strong accumulation of charges at solid interfaces by forming a very thin and dense electrical double layer (EDL). The structure of this EDL has important consequences in numerous applications involving ILs, for example, in supercapacitors, sensors, and lubricants, by impacting the interfacial capacitance, the charge carrier density of semiconductors, as well as the frictional properties of the interfaces. We have studied the interfacial structure of a long chain imidazolium-based IL (1-octyl-3-methylimidazolium dicyanamide) on several substrates: mica, silica, silicon, and molybdenum disulfide (MoS2), using atomic force microscopy (AFM) experiments and molecular dynamics (MD) simulations. We have observed 3 types of interfacial structures for the same IL, depending on the chemistry of the substrate and the water content, showing that the EDL structure is not an intrinsic property of the IL. We evidenced that at a low water content, neutral and apolar (thus hydrophobic) substrates promote a thin layer structure, where the ions are oriented parallel to the substrate and cations and anions are mixed in each layer. In contrast, a strongly charged (thus hydrophilic) substrate yields an extended structuration into several bilayers, while a heterogeneous layering with loose bilayer regions was observed on an intermediate polar and weakly charged substrate and on an apolar one at a high bulk water content. In the latter case, water contamination favors the formation of bilayer patches by promoting the segregation of the long chain IL into polar and apolar domains.

Solvation Environments in Porous Ionic Liquids Determine Selectivity in CO2 Conversion to Cyclic Carbonates.

Porous ionic liquids, which are suspensions of nanoporous particles in ionic liquids that maintain permanent porosity, are effective and selective media for the conversion of styrene oxide into styrene carbonate, absorbing CO2 [Zhou et al. Chem. Commun. 2021, 57, 7922-7925]. Here we elucidate the mechanism of selectivity using polarizable molecular dynamics simulations, which provide a detailed view on the structure of the porous ionic liquid and on the local solvation environments of the reacting species. The porous ionic liquids studied are composed of tetradecyltrihexylphosphonium chloride, or [P66614]Cl, and the ZIF-8 zinc-methylimidazolate metal-organic framework (MOF). The CL&Pol polarizable force field was extended to represent epoxide and cyclic carbonate functional groups, allowing the ionic liquid, the reactants, and the MOF to be all represented by fully flexible, polarizable force fields, providing a detailed description of interactions. The presence of reactant and product molecules leads to changes in the structure of the ionic liquid, revealed by domain analysis. The structure of local solvation environments, namely, the arrangement of charged moieties and CO2 around the epoxide ring of the reactant molecules, clearly indicate ring-opening the reaction mechanism. The MOF acts as a reservoir of CO2 through its free volume. The solute molecules are found in the accessible outer cavities of the MOF, which promotes reaction of the epoxide with CO2 excluding other epoxide molecules, thereby preventing the formation of oligomers, which explains the selectivity toward conversion to cyclic carbonates.

Charge transfer and polarisability in ionic liquids: a case study.

The practical use of ionic liquids (ILs) is benefiting from a growing understanding of the underpinning structural and dynamic properties, facilitated through classical molecular dynamics (MD) simulations. The predictive and explanatory power of a classical MD simulation is inextricably linked to the underlying force field. A key aspect of the forcefield for ILs is the ability to recover charge based interactions. Our focus in this paper is on the description and recovery of charge transfer and polarisability effects, demonstrated through MD simulations of the widely used 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C4C1im][NTf2] IL. We study the charge distributions generated by a range of ab initio methods, and present an interpolation method for determining atom-wise scaled partial charges. Two novel methods for determining the mean field (total) charge transfer from anion to cation are presented. The impact of using different charge models and different partial charge scaling (unscaled, uniformly scaled, atom-wise scaled) are compared to fully polarisable simulations. We study a range of Drude particle explicitly polarisable potentials and shed light on the performance of current approaches to counter known problems. It is demonstrated that small changes in the charge description and MD methodology can have a significant impact; biasing some properties, while leaving others unaffected within the structural and dynamic domains.

Tuning the solvation of indigo in aqueous deep eutectics.

The solubility of synthetic indigo dye was measured at room temperature in three deep eutectic solvents (DESs)-1:3 choline chloride:1,4-butanediol, 1:3 tetrabutylammonium bromide:1,4-butanediol, and 1:2 choline chloride:p-cresol-to test the hypothesis that the structure of DESs can be systematically altered, to induce specific DES-solute interactions, and, thus, tune solubility. DESs were designed starting from the well-known cholinium chloride salt mixed with the partially amphiphilic 1,4-butanediol hydrogen bond donor (HBD), and then, the effect of increasing salt hydrophobicity (tetrabutylammonium bromide) and HBD hydrophobicity (p-cresol) was explored. Measurements were made between 2.5 and 25 wt. % H2O, as a reasonable range representing atmospherically absorbed water, and molecular dynamics simulations were used for structural analysis. The choline chloride:1,4-butanediol DES had the lowest indigo solubility, with only the hydrophobic character of the alcohol alkyl spacers. Solubility was highest for indigo in the tetrabutylammonium bromide:1,4-butanediol DES with 2.5 wt. % H2O due to interactions of indigo with the hydrophobic cation, but further addition of water caused this to reduce in line with the added water mole fraction, as water solvated the cation and reduced the extent of the hydrophobic region. The ChCl:p-cresol DES did not have the highest solubility at 2.5 wt. % H2O, but did at 25 wt. % H2O. Radial distribution functions, coordination numbers, and spatial distribution functions demonstrate that this is due to strong indigo-HBD interactions, which allow this system to resist the higher mole fraction of water molecules and retain its solubility. The DES is, therefore, a host to local-composition effects in solvation, where its hydrophobic moieties concentrate around the hydrophobic solute, illustrating the versatility of DES as solvents.

High-Performance Porous Ionic Liquids for Low-Pressure CO2 Capture*.

Porous ionic liquids are non-volatile, versatile materials that associate porosity and fluidity. New porous ionic liquids, based on the ZIF-8 metal-organic framework and on phosphonium acetate or levulinate salts, were prepared and show an increased capacity to absorb carbon dioxide at low pressures. Porous suspensions based on phosphonium levulinate ionic liquid absorb reversibly 103 % more carbon dioxide per mass than pure ZIF-8 at 1 bar and 303 K. We show how the rational combination of MOFs with ionic liquids can greatly enhance low pressure CO2 absorption, paving the way towards a new generation of high-performance, readily available liquid materials for effective low pressure carbon capture.

Extension of the CL&Pol Polarizable Force Field to Electrolytes, Protic Ionic Liquids, and Deep Eutectic Solvents.

The polarizable CL&Pol force field presented in our previous study, Transferable, Polarizable Force Field for Ionic Liquids (J. Chem. Theory Comput. 2019, 15, 5858, DOI: http://doi.org/10.1021/acs.jctc.9b0068910.1021/acs.jctc.9b00689), is extended to electrolytes, protic ionic liquids (PIL), deep eutectic solvents (DES), and glycols. These systems are problematic in polarizable simulations because they contain either small, highly charged ions or strong hydrogen bonds, which cause trajectory instabilities due to the pull exerted on the induced dipoles. We use a Tang-Toennies (TT) function to dampen, or smear, the interactions between charges and induced dipole at a short range involving small, highly charged atoms (such as hydrogen or lithium), thus preventing the "polarization catastrophe". The new force field gives stable trajectories and is validated through comparison with experimental data on density, viscosity, and ion diffusion coefficients of liquid systems of the above-mentioned classes. The results also shed light on the hydrogen-bonding pattern in ethylammonium nitrate, a PIL, for which the literature contains conflicting views. We describe the implementation of the TT damping function, of the temperature-grouped Nosé-Hoover thermostat for polarizable molecular dynamics (MD) and of the periodic perturbation method for viscosity evaluation from non-equilibrium trajectories in the LAMMPS MD code. The main result of this work is the wider applicability of the CL&Pol polarizable force field to new, important classes of fluids, achieving robust trajectories and a good description of equilibrium and transport properties in challenging systems. The fragment-based approach of CL&Pol will allow ready extension to a wide variety of PILs, DES, and electrolytes.

Effect of side chain modifications in imidazolium ionic liquids on the properties of the electrical double layer at a molybdenum disulfide electrode.

Knowledge of how the molecular structures of ionic liquids (ILs) affect their properties at electrified interfaces is key to the rational design of ILs for electric applications. Polarizable molecular dynamics simulations were performed to investigate the structural, electrical, and dynamic properties of electric double layers (EDLs) formed by imidazolium dicyanamide ([ImX1][DCA]) at the interface with the molybdenum disulfide electrode. The effect of side chain of imidazolium on the properties of EDLs was analyzed by using 1-ethyl-3-methylimidazolium ([Im21]), 1-octyl-3-methylimidazolium ([Im81]), 1-benzyl-3-methylimidazolium ([ImB1]), and 1-(2-hydroxyethyl)-3-methylimidazolium ([ImO1]) as cations. Using [Im21] as reference, we find that the introduction of octyl or benzyl groups significantly alters the interfacial structures near the cathode because of the reorientation of cations. For [Im81], the positive charge on the cathode induces pronounced polar and non-polar domain separation. In contrast, the hydroxyl group has a minor effect on the interfacial structures. [ImB1] is shown to deliver slightly larger capacitance than other ILs even though it has larger molecular volume than [Im21]. This is attributed to the limiting factor for capacitance being the strong association between counter-ions, instead of the free space available to ions at the interface. For [Im81], the charging mechanism is mainly the exchange between anions and octyl tails, while for the other ILs, the mechanism is mainly the exchange of counter-ions. Analysis on the charging process shows that the charging speed does not correlate strongly with macroscopic bulk dynamics like viscosity. Instead, it is dominated by local displacement and reorientation of ions.

Sodium diffusion in ionic liquid-based electrolytes for Na-ion batteries: the effect of polarizable force fields.

Understanding the transport of sodium ions in ionic liquids is key to designing novel electrolyte materials for sodium-ion batteries. In this work, we combine molecular dynamics simulation and experiments to study how molecular interactions and local ordering affect relevant physico-chemical properties. Ionic transport and local solvation environments are investigated in electrolytes composed of sodium bis(fluorosulfonyl)imide, (Na[FSI]), in N,N-methylpropylpyrrolidinium bis(fluorosulfonyl)imide, [C3C1pyr][FSI], at different salt concentrations. The electrolyte systems are modelled by means of molecular dynamic simulations using a polarizable force field. We show that including polarization effects explicitly in the molecular simulations is required in order to attain a reliable description of the transport properties of sodium in the [C3C1pyr][FSI] electrolyte. The validation of the computational results upon comparison with experimental data allows us to assess the suitability of polarizable force fields in describing and interpreting the structure and dynamics of the sodium salt-ionic liquid system, which is essential to enable the application of IL-based electrolytes in novel energy-storage technologies.

Are There Magic Compositions in Deep Eutectic Solvents? Effects of Composition and Water Content in Choline Chloride/Ethylene Glycol from Ab Initio Molecular Dynamics.

Ab initio molecular dynamics simulations at elevated temperature are carried out to investigate the microscopic structure of liquid mixtures (deep eutectic solvents) composed of 1:1 and 1:2 choline chloride:ethylene glycol ([Ch]Cl:EG) and 1:2:1 choline chloride:ethylene glycol:water ([Ch]Cl:EG:water). In the present study, we aim to understand the composition effect on the choline chloride:ethylene glycol deep eutectic solvent and whether there is a specific composition in these solvents with marked special behavior at the microscopic level. The role of hydrogen bonds between all components was investigated through distribution functions. The structures are governed by the balance of hydrogen bond networks and the different populations of the EG molecule conformations. In the water-containing system, water competes for association with the anion. Also, the charge distribution analysis, which is consistent with structural analysis, indicates that the results are not impacted by changing composition. In addition, the charge transfer observed between ions, EG, and water molecules appears to be significant.

Corrigendum: Dispersion and Stabilization of Exfoliated Graphene in Ionic Liquids.

[This corrects the article DOI: 10.3389/fchem.2019.00223.].

Ion pair free energy surface as a probe of ionic liquid structure.

Numerous combinations of cations and anions are possible for the production of ionic liquids with fine-tuned properties once the correlation with the molecular structure is known. In this sense, computer simulations are useful tools to explain and even predict the properties of ionic liquids. However, quantum mechanical methods are usually restricted to either small clusters or short time scales so that parameterized force fields are required to study the bulk liquids. In this work, a method is proposed to enable a comparison between the quantum mechanical system and both polarizable and nonpolarizable force fields by means of the calculation of free energy surfaces for the translational motion of the anion around the cation in gas phase. This method was tested for imidazolium-based cations with 3 different anions, [BF4]-, [N(CN)2]-, and [NTf2]-. Better agreement was found with the density functional theory calculations when polarizability is introduced in the force field. In addition, the ion pair free energy surfaces reproduced the main structural patterns observed in the first coordination shell in molecular dynamics simulations of the bulk liquid, proving to be useful probes for the liquid phase structure that can be computed with higher level methods and the comparison with forcefields can indicate further improvements in their parameterization.

Kinetic analysis of microwave-enhanced cellulose dissolution in ionic solvents.

Cellulose dissolution in mixtures of the ionic liquid 1-ethyl-3-methylimidazolium acetate with dimethylsulfoxide, [C2C1Im][OAc] + DMSO, have been kinetically compared using conventional heating and microwave heating in a single-mode cavity with a semiconductor generator. Microwaves led to enhancements in the dissolution rate between 21 and 57% under different conditions of temperature and concentration of ionic liquid. Rate enhancement by microwaves prominently occurred at temperatures above 60 °C. Based on an Arrhenius plot and wide-band dielectric measurements we advance the hypothesis that the faster dissolution is caused by ionic motion induced by microwaves in the timescale of formation and breaking of hydrogen bonds between cellulose chains and acetate anions.

Transferable, Polarizable Force Field for Ionic Liquids.

A general, transferable, polarizable force field for molecular simulation of ionic liquids (ILs) and their mixtures with molecular compounds is developed. This polarizable model is derived from the widely used CL&P fixed-charge force field that describes most families of ILs, in a form compatible with OPLS-AA, one of the major force fields for organic compounds. Models for ILs with fixed, integer-ionic charges lead to pathologically slow dynamics, a problem that is corrected when polarization effects are included explicitly. In the model proposed here, Drude-induced dipoles are used with parameters determined from atomic polarizabilities. The CL&P force field is modified upon inclusion of the Drude dipoles to avoid double-counting of polarization effects. This modification is based on first-principles calculations of the dispersion and induction contributions to the van der Waals interactions using symmetry-adapted perturbation theory (SAPT) for a set of dimers composed of positive, negative, and neutral fragments representative of a wide variety of ILs. The fragment approach provides transferability, allowing the representation of a multitude of cation and anion families, including different functional groups, without the need to reparametrize. Because SAPT calculations are expensive, an alternative predictive scheme was devised, requiring only molecular properties with a clear physical meaning, namely, dipole moments and atomic polarizabilities. The new polarizable force field, CL&Pol, describes a broad set of ILs and their mixtures with molecular compounds and is validated by comparisons with experimental data on density, ion diffusion coefficients, and viscosity. The approaches proposed here can also be applied to the conversion of other fixed-charge force fields into polarizable versions.

Self-assembled nanostructures in ionic liquids facilitate charge storage at electrified interfaces.

Driven by the potential applications of ionic liquids (ILs) in many emerging electrochemical technologies, recent research efforts have been directed at understanding the complex ion ordering in these systems, to uncover novel energy storage mechanisms at IL-electrode interfaces. Here, we discover that surface-active ILs (SAILs), which contain amphiphilic structures inducing self-assembly, exhibit enhanced charge storage performance at electrified surfaces. Unlike conventional non-amphiphilic ILs, for which ion distribution is dominated by Coulombic interactions, SAILs exhibit significant and competing van der Waals interactions owing to the non-polar surfactant tails, leading to unusual interfacial ion distributions. We reveal that, at an intermediate degree of electrode polarization, SAILs display optimum performance, because the low-charge-density alkyl tails are effectively excluded from the electrode surfaces, whereas the formation of non-polar domains along the surface suppresses undesired overscreening effects. This work represents a crucial step towards understanding the unique interfacial behaviour and electrochemical properties of amphiphilic liquid systems showing long-range ordering, and offers insights into the design principles for high-energy-density electrolytes based on spontaneous self-assembly behaviour.

On the Regular Behavior of a Binary Mixture of Ionic Liquids.

Binary mixtures of the ionic liquids 1-ethyl-3-methylimidazolium dicyanamide and tributyl(methyl)ammonium dicyanamide, [C2C1im]x[N4441](1-x)[N(CN)2], are studied by means of their excess properties (enthalpy and volume), their viscosity, and their Raman spectra. The mixtures exhibit positive values of excess volume VE and excess enthalpy HE. The plot of the logarithm of viscosity as a function of composition is consistent with the finding HE > 0. The excess thermodynamic properties of the ionic liquid mixtures are compared with well-known results for binary mixtures of (high-temperature) molten salts. The asymmetry of the curve HE versus composition is reproduced by considering the volumetric fraction of the [C2C1im]x[N4441](1-x)[N(CN)2] mixtures according to basic results of the theory of regular solutions. The anion totally symmetric stretching mode νs(C≡N) was used to probe the local environment around the anion in a Raman spectroscopy investigation of the [C2C1im]x[N4441](1-x)[N(CN)2] mixtures as a function of the composition. The Raman band shape (peak frequency and bandwidth) of the νs(C≡N) mode changes as expected from the fluctuation of concentration around the probe oscillator according to models for vibrational spectroscopy of liquid mixtures. This thermodynamic and spectroscopic study leads to the classification of the [C2C1im]x[N4441](1-x)[N(CN)2] mixture as a regular solution. The application of the regular solution equation for HE to other ionic liquid binary mixtures is discussed.

Dispersion and Stabilization of Exfoliated Graphene in Ionic Liquids.

The liquid-phase exfoliation of graphite is one of the most promising methods to increase production and commercial availability of graphene. Because ionic liquids can be easily obtained with chosen molecular structures and tuneable physicochemical properties, they can be use as media to optimize the exfoliation of graphite. The understanding of the interactions involved between graphite and various chemical functions in the solvent ions will be helpful to find liquids capable of dissociating and stabilizing important quantities of large graphene layers. After a step of sonication, as a mechanical precursor, samples of suspended exfoliated graphene in different ionic liquids have been characterized experimentally in terms of flake size, number of layers, total concentration and purity of the exfoliated material. Nine different ionic liquids based on imidazolium, pyrrolidinium and ammonium cations and on bis(trifluoromethylsulfonyl)imide, triflate, dicyanamide, tricyanomethanide, and methyl sulfate anions have been tested. UV-vis, Raman and X-ray photoelectron in addition to high resolution transmission electron and atomic force microscopy have been selected to characterize suspended exfoliated graphene in ionic liquids. The number of layers in the flakes exfoliated, the size and concentration depend of the structure of the ionic liquid selected. In order to obtain large flake sizes, ionic liquids with bis(trifluoromethylsulfonyl)imide anions and a cation with an alkyl chain of medium length should be selected. Smaller cation and anion favors the exfoliation of graphene. The exfoliation caused the formation of C-H bonds and the oxidation of the graphitic surface.

Using hydrogenated and perfluorinated gases to probe the interactions and structure of fluorinated ionic liquids.

After studying the properties of a mixture of hydrogenated and fluorinated ionic liquids we have measured the solubility of perfluoromethane, perfluoroethane and perfluoropropane in 1-alkyl-3-methylimidazolium based ionic liquids with hydrogenated or fluorinated alkyl side-chains: 1-octyl-3-methylimidazolium bis[trifluoromethylsulfonyl]amide ([C8C1Im][NTf2]), 1-octyl-3-methylimidazolium bis[pentafluoroethylsulfonyl]amide ([C8C1Im][BETI]), 1-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl)-3-methylimidazolium bis[trifluoromethylsulfonyl]amide ([C8H4F13C1Im][NTf2]), and 1-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl)-3-methylimidazolium bis[pentafluoroethylsulfonyl]amide ([C8H4F13C1Im][BETI]). The ionic liquids expand on mixing and mix endothermally with a relatively high enthalpy of mixing (ΔmixH for [C8C1Im]x[C8H4F13C1Im](1-x)[NTf2] of ca. 0.85 kJ mol-1 for x = 0.5) when compared with other ionic mixtures. The solubility of the perfluorinated gases is larger in the fluorinated ionic liquids when compared with that of their hydrogenated counterparts and follows the order [C8H4F13C1Im][BETI] > [C8H4F13C1Im][NTf2] > [C8C1Im][BETI] > [C8C1Im][NTf2], a behaviour explained by a slightly more favourable enthalpy of solvation. The fluorinated ionic liquids nevertheless do not dissolve larger quantities of perfluorinated gases than their hydrogenated equivalents, as observed by comparing the results herein for perfluoroethane to those measured previously for ethane in the same ionic liquids. By using molecular simulations to study the microscopic structure of the solutions, we could show that the gases, hydrogenated and fluorinated, are always preferentially solvated in the apolar domains of the ionic liquids, and the hydrogenated hydrocarbon gases are always more soluble, independent of the fluorination of the ionic liquid.

Ionic liquids at the surface of graphite: Wettability and structure.

The aim of this work is to provide a better understanding of the interface between graphite and different molecular and ionic liquids. Experimental measurements of the liquid surface tension and of the graphite-liquid contact angle for sixteen ionic liquids and three molecular liquids are reported. These experimental values allowed the calculation of the solid/liquid interfacial energy that varies, for the ionic liquids studied, between 14.5 mN m-1 for 1-ethyl-3-methylimidazolium dicyanamide and 37.8 mN m-1 for 3-dodecyl-1-(naphthalen-1-yl)-1H-imidazol-3-ium tetrafluoroborate. Imidazolium-based ionic liquids with large alkyl side-chains or functionalized with benzyl groups seem to interact more favourably with freshly peeled graphite surfaces. Even if the interfacial energy seems a good descriptor to assess the affinity of a liquid for a carbon-based solid material, we conclude that both the surface tension of the liquid and the contact angle between the liquid and the solid can be significant. Molecular dynamics simulations were used to investigate the ordering of the ions near the graphite surface. We conclude that the presence of large alkyl side-chains in the cations increases the ordering of ions at the graphite surface. Benzyl functional groups in the cations lead to a large affinity towards the graphite surface.

Investigation of Li+ Cation Coordination and Transportation, by Molecular Modeling and NMR Studies, in a LiNTf2-Doped Ionic Liquid-Vinylene Carbonate Mixture.

To increase the safety and stability of lithium-ion batteries, the development of electrolytes based on ionic liquids (ILs) has gained a lot of attention in recent years. However, with graphite electrodes, neat ILs afford weak cycling performance in the absence of organic additives (e.g., vinylene carbonate, VC). The potential formation of a [Li+]-OVC interaction/coordination could have a major influence on the observed electrochemical behavior of Li-ion batteries. On a specific electrolyte, 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C1C6Im][NTf2] in association with Li[NTf2] (1 mol L-1) and VC, we performed NOESY, {1H-7Li} HOESY correlations, and pulsed field gradient spin-echo NMR measurements, combined with molecular dynamics simulations to determine whether such an interaction/coordination between VC and Li+ ions is noticeable. {7Li-1H} HOESY experiment shows the vicinity of VC with [Li+] cation, and strong correlations and association between [Li+] and VC are observed in intense first peaks in radial distribution functions and quantified by the coordination numbers in the first solvation shell between [Li+] and the carbonyl oxygen atom of VC.

New solvent-stabilized few-layer black phosphorus for antibacterial applications.

Discovering highly efficient, environmentally friendly, and low-cost exfoliating media that can both disperse and protect black phosphorus (BP) remains a challenge. Herein, we demonstrate such a new molecule, N,N'-dimethylpropyleneurea (DMPU), for effective exfoliation and dispersion of two-dimensional BP nanosheets. A very high exfoliation efficiency of up to 16% was achieved in DMPU, significantly surpassing other good solvents. Exfoliated flakes are free from structural disorder or oxidation. Nanosheets retain high stability in DMPU even after addition of 25 vol% of common solvents. The solvation shell appears to protect the nanosheets from reacting with water and air, more remarkably than the best solvent N-cyclohexyl-2-pyrrolidone reported so far. Molecular dynamics simulations of the exfoliation process show that DMPU is among the effective solvents, although energetically it does not appear as favorable as some other amides. We also demonstrate that our exfoliated BP nanosheets exhibit excellent antimicrobial activities against both Escherichia coli and Staphylococcus aureus, outperforming other common two-dimensional materials of graphene and MoS2, suggesting promise in biomedical applications.