Charge Density Difference Research Articles

Density Functional Theory Provides Insights into β-SnSe Monolayers as a Highly Sensitive and Recoverable Ozone Sensing Material.

This study explores the potential of β-SnSe monolayers as a promising material for ozone (O3) sensing using density functional theory (DFT) combined with the non-equilibrium Green's function (NEGF) method. The adsorption characteristics of O3 molecules on the β-SnSe monolayer surface were thoroughly investigated, including adsorption energy, band structure, density of states (DOSs), differential charge density, and Bader charge analysis. Post-adsorption, hybridization energy levels were introduced into the system, leading to a reduced band gap and increased electrical conductivity. A robust charge exchange between O3 and the β-SnSe monolayer was observed, indicative of chemisorption. Recovery time calculations also revealed that the β-SnSe monolayer could be reused after O3 adsorption. The sensitivity of the β-SnSe monolayer to O3 was quantitatively evaluated through current-voltage characteristic simulations, revealing an extraordinary sensitivity of 1817.57% at a bias voltage of 1.2 V. This sensitivity surpasses that of other two-dimensional materials such as graphene oxide. This comprehensive investigation demonstrates the exceptional potential of β-SnSe monolayers as a highly sensitive, recoverable, and environmentally friendly O3 sensing material.

Regulating coordination environment around transition metal (Fe, Co) single atom catalysts for efficient Hg0 adsorption

Elemental mercury (Hg0) is one of the main pollutants released during coal combustion, which is difficult to remove due to its hydrophobicity and volatility, resulting in serious environmental pollution. Therefore, it is urgent to develop a low-cost and high-performance catalyst to remove Hg0. In this work, using first-principles study, the effect of nonmetal (NM = B, C and O) coordination environment on the charge distribution of graphene-supported transition metal single atom catalysts (TM-N4-SAC) has been investigated. It is found that regulating the TM-N4-SAC with NM coordination atoms with fewer valence electrons than N atom can cause TM atoms to lose more electrons, and the charge distribution in the active center to be locally deviated. Moreover, in-depth analysis of the adsorption configuration, charge density difference, charge transfer, adsorption energy and density of state of Hg0 adsorption on NM modified TM-N4-SAC confirmed that the adsorption of Hg0 can be effectively enhanced only when TM atoms lose more electrons. Thus, Fe-N3B- and Co-N3B-SAC have the strongest ability to adsorb Hg0 because they have the most negative adsorption energy of −1.13 and −0.49 eV. This work provides theoretical guidance for the design of SAC for efficient adsorption of Hg0.

Engineering Bis-Pyridine N-Functionalized Cellulose Aerogel for Efficient Extraction of Cu2+ from High-Acidity Wastewaters: Coupling Molecular Scale Interpretation with Experiment.

In order to address the issue of protonation of functional groups and structural instability on the surface of aerogel due to strong acidic wastewater, a three-dimensional bis-pyridine N cellulose aerogel [PEIPD/carboxymethyl cellulose (CMC)] with protonation resistance was prepared in this paper by grafting pyridine onto polyethylenimine. The adsorption capacity for Cu2+ of the as-prepared aerogel is as high as 1.64 mmol/g (pH 5) and is maintained well in high-acidity solutions (1.15 mmol/g at pH = 2). It reveals high selectivity, splendid anti-interference ability, and also reliable on the recycle performance. Through the zeta potential tests, this adsorbent reveals a rather low zero charge point (pHpzc = 2.2). The adsorption of Cu2+ on the adsorbent is consistent with the pseudo-second-order kinetic model and the Langmuir model, suggesting that the adsorption process is dominated by chemisorption in a monolayer. The characterizations by Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy proved pyridine N as responsible binding sites, based on which two possible mechanisms are proposed, including chelation and cation-π interaction. Density functional theory calculations are further used to precisely investigate the pathway. By comparing the binding energies, molecular electrostatic potentials, electron densities, and differential charge densities, the bis-pyridine N functional group is finally determined to be of much higher affinity to Cu2+ following chelation reaction as designated. By integrating bis-pyridine N with the CMC and understanding their crucial roles, this will provide significant insights into the rational design of aerogel adsorbents to enhance the recovery of Cu from strongly acidic wastewaters.

Enhanced photocatalytic alkane production from fatty acid decarboxylation over sulfide-modified TiO2 under mild conditions

Photocatalytic decarboxylation of fatty acids derived from biomass is considered a sustainable approach for alkane production. In this study, a series of NiS2 co-catalyst-modified TiO2 (NiS2/TiO2) composites were successfully synthesized and employed for the photocatalytic decarboxylation of fatty acids. Under mild conditions, the optimized NiS2/TiO2 composite exhibited conversion of 60.2% and selectivity of 72.6% for converting chondritic acid to pentadecane, which was 6.56 times to single TiO2. The incorporation of the co-catalyst led to red shift of the absorption edge, and decrease in photoluminescence (PL) intensity, indicating enhanced light absorption and efficient separation of photogenerated charge in NiS2/TiO2. The lower work function of NiS2 compared with TiO2 and the differential charge density indicated that electrons tended to migrate from the S-atom to the O-atom, thus creating a built-in electric field that accelerated the reaction. The study on biofuel synthesized from biomass offered insights that can help mitigate future energy crises.

Activation of efficient hydrogen evolution on 1T-VS2 nanoribbons by low-cost transition metals: A first-principles study

Electrocatalytic water splitting is a very important energy conversion technology that utilizes renewable energy sources to produce hydrogen for sustainable energy development. In this work, the catalytic performance of 1T-VS2 (1T phase of vanadium disulfide) nanoribbons in the hydrogen evolution reaction (HER) was investigated based on first-principles calculations. It was found that 1T-VS2 nanoribbons have a Gibbs free energy (ΔGH*) of 0.05 eV, demonstrating its excellent HER performance. Moreover, some transition metal substitutions can further improve this performance (e.g. the ΔGH* of the Ti/Fe-1T-VS2 are as low as −0.02/0.04 eV). The mechanism of the performance enhancement is thoroughly investigated. The improved catalytic performance of HER is mainly promoted by hybridization between the V-d and TM-d-orbitals. The crystal orbital Hamiltonian population (COHP) and integral crystal orbital Hamiltonian habitation (ICOHP) calculations show that the HER properties are closely related to the filling of bonding and antibonding states. The differential charge density indicates that the adsorption of H results in an effective charge transfer at the interface and an increase in the conductivity, leading to an increase in the HER. The HER activity of the TM-1T-VS2 (TM stands for transition metal) nanoribbons is also related to the proximity of the adsorption site to the edge. Our work suggests that the TM-1T-VS2 nanoribbons are expected to be low cost and highly efficient catalysts.

Towards first-principles predict of doped α-Ga2O3 based structural and electrical properties

The α-Ga2O3 holds significant research value on high power device applications for its superior breakdown voltage performance. However, research concerning the doping of α-Ga2O3 remains scant, and the optimal dopant remains unidentified. To identify a potential n-type dopant, a theoretical study of the effects of group IV atoms (Si, Ge, Sn) on doped α-Ga2O3 was evaluated through the first principles calculations. We have systematically explored the lattice deformation, band structure, density of state, charge density difference and electron localization functions. The electron mobility is then evaluated by the deformation potential theory. The lowest formation energy of the Si-doped system suggests it forms the most readily. Meanwhile, Si loses approximately 1.5 times more electrons than Ge and Sn in the doped α-Ga2O3, as evidenced by the charge density difference and electron localization functions. Furthermore, our results reveal that Si is a superior dopant over Ge and Sn. It is owing to a small interaction between the Si 3 s state and the Ga 4 s generated host CBM, resulting in a minimal effect on the CBM even at high doping levels. The findings of this study have important consequences for improving the doping process of α-Ga2O3 and achieving the development of optoelectronic devices.

Gas-Sensing Performance of Metal Oxide Heterojunction Materials for SF6 Decomposition Gases: A DFT Study.

The online monitoring of GIS equipment can be realized through detecting SF6 decomposition gasses. Metal oxide heterojunctions are widely used as gas-sensing materials. In this study, the structural and electrical properties of In2O3-ZnO and TiO2-ZnO heterojunctions were analyzed based on density functional theory calculations. After heterojunction structural optimization, the electrical conductivity of these two heterojunctions was enhanced compared to each intrinsic model, and the electrical conductivity is ranked as follows: In2O3-ZnO heterojunction > TiO2-ZnO heterojunction. The gas-sensing response of these two heterojunctions to four SF6 decomposition gasses, H2S, SO2, SOF2, and SO2F2, was investigated. For gas adsorption systems, the adsorption energy, charge transfer, density of states, charge difference density, and frontier molecular orbitals were calculated to analyze the adsorption and gas-sensing performance. For gas adsorption on the In2O3-ZnO heterojunction surface, the induced conductivity changes are in the following order: H2S > SO2F2 > SOF2 > SO2. For gas adsorption on the TiO2-ZnO heterojunction surface, H2S and SOF2 increase conductivity, and SO2 and SO2F2 decrease conductivity.

Joule heating for structure reconstruction of hard carbon with superior sodium ion storage performance

Hard carbon anode for sodium ion batteries still remains many challenges including insufficient cycling life and initial Coulombic efficiency (ICE), weak rate capability and poor compatibility in common ester electrolytes. Here, we propose a Joule heating post-treatment including multifield sintering method to reconstruct the structure of hard carbon from thick graphene layers to more disordered vortex layer structure composed of thin and curved graphite-like domains. The molecular dynamics simulation and differential charge density distribution demonstrate the crucial effect of electric field in strengthening the interaction between the polar molecule groups and the graphene layer, leading to the distortion and expanding of graphene layer. This is a universal and highly efficient strategy to modify various hard carbons within minutes. The optimized hard carbon anode exhibits exceptional rate capability and cycling stability with a high retention rate of 88.4% after 15,000 cycles at 10C in ether electrolyte. It also displays remarkably improved reversible capacity, initial Coulombic efficiency ICE of 89.5% and cycling stability in ester electrolyte. It is revealed by in-situ electrochemical impedance spectroscopy and atomic force microscopy that the spontaneous formation of a thin, stable and inorganic substance-rich solid electrolyte interface layer with significantly improved mechanical property is largely responsible for the outstanding sodium-ion transport kinetics and long lifespan.

A frugal machine-intelligent paper sensor for quantification of glucose through standalone desktop application: A computational and experimental approach

A paper-based electrochemical sensor utilizing MoS2 as sensing material is developed to quantitatively estimate glucose in a complex extracellular fluid matrix. The contribution of MoS2 as sensing material is substantiated in the context of density functional theory formalism. The molecular modelling of MoS2 and glucose interaction is elucidated through the theoretical estimation of non-covalent interactions and charge density difference plots. The charge transfer phenomenon during the oxidation of glucose molecule in electrochemical experiments is verified through electronic band structure analysis and frontier orbital theory. The electrochemical responses indicate that the sensor exhibits an average accuracy of nearly 96%, with a quantification limit of 100 nM. Furthermore, the chronoamperometric measurements highlight the superior sensitivity of the device in presence of various perturbing molecules. The obtained DPV responses were integrated with a robust machine learning-driven standalone app GluQuantify. This app precisely predicts the glucose concentrations in serum samples. The utilization of GluQuantify substantially elevates the overall accuracy of the sensing platform to 99% and automates the detection process. The application also enhances the resolution of the sensor to 0.01 µM, which mitigates the sensor resolution-related issues in manual estimation.

Structural evolutions and tribological properties of laser cladded FeCoNiCrMo high-entropy alloy coating by laser remelting and tempering process: TEM and DFT calculations

A laser cladded FeCoNiCrMo high-entropy alloy (HEA) coating was treated by laser remelting and tempering process in sequence to improve its tribological properties. The morphologies, phases and nanostructures of obtained coatings were analyzed using a scanning electron microscope, X-ray diffraction and transmission electron microscope. The effects of laser remelting and tempering process on the tribological properties were investigated by a ball-on-disc wear tester, and the wear mechanism was revealed with the density functional theory calculation. The results show that the main crystal planes of laser cladded, laser remelted and tempering processed HEA coatings are transformed from (200) and (220) to (111), and the reduced free energy and differential charge density of crystal plane (111) contribute to the improvement of tribological properties on the HEA coatings.

Atomic-scale tribological behavior of pressure-induced MoO3(0 1 0)/Ag(1 1 1) heterogeneous sliding interface

The atomic-scale tribological properties of the MoO3(010)/Ag(111) heterogeneous sliding interface were studied by first-principles calculation method. The interface binding energy, sliding potential energy, friction force, charge density difference, partial density of states, Mulliken bond population and HiRshfeld charge were analyzed, and the essence of the friction was revealed. The results show that the sliding potential energy and friction exhibit anisotropy for the pressure-induced MoO3(010)/Ag(111) heterogeneous sliding interface. The friction force can be described by the change of the sliding potential energy, and the charge redistribution between interface atoms is the intrinsic reason for the change of tribological properties. This work provides atomic and electronic level insights for understanding the tribological characteristics between two-dimensional materials and soft metals.

Rigid Phase Formation and Sb3+ Doping of Tin (IV) Halide Hybrids toward Photoluminescence Enhancement and Tuning for Anti-Counterfeiting and Information Encryption.

Multi-excitonic emitting materials in luminescent metal halides are emerging candidates for anti-counterfeiting and information encryption applications. Herein, ATPP2SnCl6 (ATPP=acetonyltriphenylphosphonium) phase was designed and synthesized by rationally choosing emissive organic reagent of ATPPCl and non-toxic stable metal ions of Sn4+, and Sb3+ was further doped into ATPP2SnCl6 to tune the photoluminescence with external self-trapped excitons emission. The derived non-toxic ATPP2SnCl6 shows multi-excitonic luminescent centers verified by optical study and differential charge-density from density functional theory calculations. Incorporation of Sb3+ dopants and the increasing concentrations induce the efficient energy transfer therein, thus enhancing photoluminescence quantum yield from 5.1 % to 73.8 %. The multi-excitonic emission inspires the creation of information encryption and decryption by leveraging the photoluminescence from ATPPCl to ATPP2SnCl6 host and ATPP2SnCl6 : Sb3+. This study facilitates the anti-counterfeiting application by employing solution-processable luminescent metal halides materials with excitation-dependent PL properties.

Indazole-5-amine (AIA) as competing corrosion coating to Benzotriazole (BTAH) at the interface of Cu: A DFT and BOMD case study

This study compares three organic compounds—benzotriazole (BTAH), imidazole (IM), and indazole-5-amine (AIA)—as corrosion inhibitors for copper substrates. Using Density Functional Theory (DFT) and Born-Oppenheimer Molecular Dynamics (BOMD) calculations, it identifies AIA as a promising and cost-effective alternative to the toxic BTAH. The adsorption strength on Cu(100) surfaces is ranked AIA>BTAH>IM for both neutral and deprotonated forms. These findings are supported by electronic parameter studies, including Bader charge analysis, density of states (DOS), charge density differences (CDD), and frontier molecular orbital analysis. AIA shows the best adsorption in a parallel orientation at the top site. Packing studies reveal that hydrogen bonding stabilizes the interaction energies within self-assembled AIA aggregates. Organometallic complexation studies reveal that deprotonated BTAH exhibits higher interaction energy with a single Cu atom compared to AIA when bonded through the carbon end, consistent with the findings from BOMD studies. However, on periodic Cu surfaces, AIA outperforms BTAH molecules as seen from adsorption energies. This investigation highlights AIA’s potential as a superior and more economical corrosion inhibitor for copper.

Electronic structure, bonding, and mechanical strength at the [formula omitted]-Al2O3 (0001)/L12-Al3Zr (111) interface by first-principles calculations

The interface adhesion energy, interfacial energy, charge density difference, local density of states, and first-principles computational tensile test of α-Al2O3 (0001)/L12-Al3Zr (111) interface were investigated by first-principles calculations. The dominant factors affecting the interfacial bond strength are the type of chemical bonds and the number of electronic orbital hybrids at the interface. The first-principles computational tensile test demonstrates that Al-fcc and Al2-hcp configurations fracture at the interface, while the O-fcc configuration fractures at the Al3Zr slab rather than at the interface and has the best tensile strength. The proposed interface bonding criteria were based on the analysis of the Al2O3/Al3Zr interface bonding data. These criteria will guide the establishment of the interface model. These results will provide theoretical guidance for understanding the failure mechanism of the Al2O3/Al3Zr interface and designing new interfaces.

Acetylene and Ethylene Adsorption during Floating Fe Catalyst Formation at the Onset of Carbon Nanotube Growth and the Effect of Sulfur Poisoning: a DFT Study.

Here, we investigated the adsorption of acetylene and ethylene on iron clusters and nanoparticles, which is a crucial aspect in the nascent phase of carbon nanotube growth by floating catalyst chemical vapor deposition (FCCVD). The effect of sulfur on adsorption was also studied due to its indispensable role in the process and its commonly known impact on metal catalyst poisoning. We performed systematic density functional theory (DFT) computations, considering numerous adsorption configurations and iron particles of various sizes (Fen, n = 3-10, 13, 55). We found that acetylene binds significantly more strongly than ethylene and prefers different adsorption sites. The presence of sulfur decreased the adsorption strength only in the immediate proximity of the adsorbate, suggesting that the effect of sulfur is mainly of steric origin while electronic effects play only a minor role. Higher sulfur coverage of the catalyst surface significantly weakened the binding of acetylene or ethylene. To further investigate this interaction, Bader's atoms in molecules (AIM) analysis and charge density difference (CDD) were used, which showed electron transfer from iron clusters or nanoparticles to the adsorbate molecules. The charge transfer exhibited a decreasing trend as sulfur coverage increased. These results can also contribute to the understanding of other iron-based catalytic processes involving hydrocarbons and sulfur, such as the Fischer-Tropsch synthesis.

Influence of Ga doped CoMo/Al2O3 catalysts on the selective hydrogenation performance of polycyclic aromatic hydrocarbons

It is a challenge to effectively control the intermediate ring hydrogenation products in tricyclic aromatic hydrocracking reactions in order to further increase the selectivity of BTX. A series of doped gallium modified CoMo/Al2O3 catalysts were prepared, the effect of gallium on the catalyst's physicochemical properties, active phase structure and hydrogenation reaction pathway was studied. The study revealed that the doping of gallium species promoted the sulfidation of Mo species and improved the catalytic activity of the catalyst. The 1 % Ga-modified catalyst showed the best selective hydrogenation performance, in which the conversion rate of phenanthrene was up to 83.75 % and the selectivity for dihydrophenanthrene reached 28.60 %. In addition, DFT calculations show that the introduction of Ga into the active phase between the Co and Mo atoms results in a higher differential charge density in the middle ring, which is more conducive to hydrogen adsorption.

First principles study on toxic gas adsorption of PtSe2/GaN heterostructure modified by Cu-group elements

Monitoring and identifying toxic gases is essential due to their detrimental effects on human health and the environment. Consequently, developing high-efficiency sensors for the detection of these harmful gases is of paramount importance. Herein, we present a theoretical study on the adsorption and sensing properties of toxic gases CO, NO and NO2 on intrinsic and Cu, Ag and Au atom-decorated PtSe2/GaN van der Waals (vdW) heterostructures, based on first principles calculation investigations. The adsorption energy, charge transfer, band structures, density of states, charge density difference, electron localization functions and recovery time are analyzed. The findings reveal that the intrinsic system demonstrates weak adsorption capabilities. However, when the surface is modified with elements from the Cu-group, there is a significant improvement in the behavior related to gas adsorption. Particularly, the Ag-decorated system demonstrates optimal gas adsorption performance. Incorporating Ag atoms notably enhances the adsorption energy and the quantity of charge transfer for CO, NO and NO2, thereby promoting a shift from physical to chemical adsorption. This alteration significantly boosts the efficiency of adsorption processes for these gases. As for the recovery time, the decorated systems indicate potential application in gas detection devices and gas adsorbers at various temperatures.

DFT-based adsorption studies of CNCl, HCN, and NH3 on metal-doped diamane

Density functional theory was used to comprehensively investigate the adsorption of cyanogen chloride (CNCl), hydrogen cyanide (HCN), and ammonia (NH3) by metal-doped diamanes. Because the weak gas adsorption ability of pure diamane renders it unsuitable for use as a gas sensor, the adsorption performance thereof was enhanced by doping with alkaline earth and transition metals. The adsorption capacities of monometallic-doped diamanes improved significantly for CNCl, HCN, and NH3. Notably, Be-doped diamane (BeD) delivered the highest adsorption performance for CNCl and HCN, whereas the addition of Au, Ag, and Cu, respectively, to diamane as dopants (AuD, AgD, and CuD) demonstrated enhanced adsorption effects for NH3. The adsorption capacities of the bimetallic co-doped diamanes for CNCl, HCN, and NH3 were significantly enhanced. In particular, diamane co-doped with Cu and Ag (Cu-AgD) exhibited superior adsorption for HCN and NH3, whereas Au and Cu co-doped diamane (Au-CuD) and Au and Ag co-doped diamane (Au-AgD) demonstrated improved adsorption effectiveness for NH3. The charge transfer, band gap, density of states, and charge density differences of these adsorption systems were investigated. Finally, recovery time analysis identified AuD, AgD, CuD, Au-CuD, Au-AgD, and Cu-AgD as potential candidates for reusable sensors.

Cryogenic Photoelectron Spectroscopic and Theoretical Study of the Electronic and Geometric Structures of Undercoordinated Osmium Chloride Anions OsCln- (n = 3-5).

A series of anionic transition metal halides, OsCln- (n = 3-5), have been investigated using a newly developed, home-constructed, cryogenic anion cluster photoelectron spectroscopy. The target anionic species are generated through collision-induced dissociation in a two-stage ion funnel. The measured vertical detachment energies (VDEs) are 3.48, 4.54, and 4.81 eV for n = 3, 4, and 5, respectively. Density functional theory calculations at the B3LYP-D3(BJ)//aug-cc-pVTZ(-pp) level predict the lowest energy structures of the atomic form of OsCln- (n = 3-5) to be a quintet triangle, quartet square, and quintet square-based pyramid, respectively. The CCSD(T)-calculated VDEs and corresponding adiabatic detachment energies agree well with our experimental measurements. Analysis of the corresponding frontier molecular orbitals and charge density differences suggests that the d-orbitals of the transition metal Os play a primary role in the single-photon detachment processes, and the detached electrons originating from different molecular orbitals are distinguishable.

Understanding the Adsorption Mechanism of BTPA, DEPA, and DPPA in the Separation of Malachite from Calcite and Quartz: DFT and Experimental Studies

The relationship between the structure of bis (2,4,4-trimethylpentyl) phosphinic acid (BTPA), diethyl phosphinic acid (DEPA), and diphenyl phosphinic acid (DPPA) on the flotation performance of malachite was investigated. Through a series of flotation experiments, density functional theory (DFT) calculations, and surface analysis methods, we aimed to deeply understand the microscopic mechanism of the interactions between these collectors and the malachite surface. The experimental results showed that BTPA exhibited excellent selectivity and flotation performance for malachite in the pH range of 5.0–11.0, significantly better than DEPA and DPPA. Surface analysis evidence from X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) further confirmed the chemical adsorption characteristics of BTPA on the malachite surface. DFT calculations revealed that the adsorption capacity of BTPA on the malachite surface exceeds that of DEPA and DPPA. Electron transfer analysis, especially through frontier molecular orbital theory, differential charge density, PDOS, and COHP analysis, indicated that the charge transfer process from the s orbitals of oxygen atoms in the collectors to the d orbitals of copper atoms on the mineral surface is the decisive factor for the adsorption strength.