Favorable Adsorption Sites Research Articles

Adsorption of molecular hydrogen on Be3Al2(SiO3)6-beryl: theoretical insights for catalysis, hydrogen storage, gas separation, sensing, and environmental applications.

Employing a combination of Density Functional Theory (DFT) calculations and Molecular Dynamics (MD) simulations, the adsorption of molecular hydrogen (H2) on Be3Al2(SiO3)6-beryl, a prominent silicate mineral, has been studied. The crystal structure of beryl, which consists of interconnected tetrahedral and octahedral sites, provides a fascinating framework for comprehending H2 adsorption behavior. Initial investigation of the interaction between H2 molecules and the beryl surface employed DFT calculations. We identified favorable adsorption sites and gained insight into the binding mechanism through extensive structural optimizations and energy calculations. H2 molecules preferentially adsorb on the exposed oxygen atoms surrounding the octahedral sites, producing weak van der Waals interactions with the beryl surface, according to our findings. To further investigate the dynamic aspects of H2 adsorption, MD simulations employing a suitable force field were conducted. To precisely represent interatomic interactions within the Be3Al2(SiO3)6-beryl-H2 system, the force field parameters were meticulously parameterized. By subjecting the system to a variety of temperatures, we were able to obtain valuable information about the stability, diffusion, and desorption kinetics of H2 molecules within the beryl structure. The comprehensive understanding of the H2 adsorption phenomenon on Be3Al2(SiO3)6-beryl is provided by the combined DFT and MD investigations. The results elucidate the mechanisms underlying H2 binding, highlighting the role of surface oxygen atoms and the effect of temperature on H2 dynamics. This research contributes to a fundamental understanding of hydrogen storage and release in beryllium-based silicates and provides valuable guidance for the design and optimization of materials for hydrogen storage, catalysis, gas separation, sensing and environmental applications.

Ultrahigh performance CO2 capture and separation in alkali metal anchored 2D-COF

The development of advanced adsorbents with high CO2 capture and separation performances is essential for decreasing atmospheric CO2 concentration. Herein, grand canonical Monte Carlo and density functional theory were employed to investigate the adsorption and separation properties of CO2, N2, and CH4 in 2D covalent organic framework (COFs) anchored by alkali metal (AMs) Li, Na, and K (UPC-nAMs, n = 3 or 6) at 298 K and 0–1.0 bar. The anchoring of AMs formed favorable adsorption sites, endowing UPC-nAMs with better CO2 capture and separation performances. This effect was more evident with an increase in Li/Na/K concentration. The CO2 adsorption capacity of UPC-6Li/Na/K was ∼ 221.64, 188.28, and 140.50 cm3 cm−3. The smaller atomic size of Li occupied less adsorption space, resulting in the highest CO2 capture capacity of 221.64 cm3 cm−3 with selectivity of 308/206 over N2/CH4 in UPC-6Li at 298 K and 1.0 bar. Structural stability, pore characteristics, isothermal adsorption heat, van der Waals and Coulomb interactions, gas distribution density, adsorption configuration, and gas radial distribution function were analyzed to identify the intrinsic mechanism of anchoring Li/Na/K to improve CO2 capture and separation performances.

Construction of Rh-N4 single atoms and Rh clusters dual-active sites for synergistic heterogeneous hydroformylation of olefins with ultra-high turnover frequency

The design and construction of Rh-based heterogeneous catalysts with excellent catalytic activity and high atom utilization for hydroformylation of olefins is extremely important but still challenging. Herein, we report a robust dual-active sites coupling catalyst containing triphenyl phosphine-coordinated Rh clusters and Rh-N4 single atomic sites (PPh3-RhAC-SA/N-C) for hydroformylation of olefins. The PPh3-RhAC-SA/N-C exhibits ultra-high activity to the hydroformylation of 1-hexene among the reported Rh-based catalysts, achieving the turnover frequency value of 6599 h−1, which is 13-fold higher than that of conventional Wilkinson’s catalyst (508 h−1). Density functional theory calculations reveal that PPh3-coordinated Rh clusters can facilitate the adsorption and activation of olefins and H2. The adjacent Rh-N4 provides a more favorable adsorption site for CO, enabling the easy addition of CO to carbon chain. The incorporated PPh3 increases the electron cloud density of Rh clusters, reduces the energy barriers of hydrogenation step on Rh clusters, and thereby enhancing the activity of catalyst for hydroformylation. Furthermore, PPh3-RhAC-SA/N-C can be applied as a recyclable catalyst without obvious deactivation. This work provides a novel design concept for the construction of dual sites coupling catalyst from the atomic scale for synergistic heterogeneous hydroformylation.

Exploring the performance of T-graphene for the anode of Mg-ion and Ca-ion batteries: A first-principles study

Due to the growing need for high-capacity ion storage batteries, researchers are exploring new categories of electrode materials with superior electrochemical properties. In this investigation, a tetragonal symmetry of carbon named T-graphene has been taken into consideration as an anode material for Mg and Ca ion batteries for its superior electrical characteristics. To comprehend the adsorption behavior, charge transfer, and anodic properties of T-graphene, density functional theory has been employed. Initially, the most favorable adsorption sites for Mg/Ca insertion on the T-graphene have been identified and it found that bridge and octagonal hollow sites show high adsorption behavior with energy of about −1.99 and −4.86 eV, respectively. A significant amount of charge (Hirshfeld) about 0.24e and 0.79e transfer from Mg and Ca to T-graphene, respectively. When Mg/Ca is inserted, the electronic structure calculations demonstrate that T-graphene acts metallically. A very high specific capacity is found at about 1737.13 and 1985.30 mAh/g for Mg and Ca ion batteries, respectively. Moreover, the average open-circuit voltages for Mg are 0.65 V and 1.51 V for Ca. Therefore, it is assumed that T-graphene may be used as high-capacity anode material for Mg and Ca ion battery.

Surface functionalization of graphene-like boron arsenide monolayer: a first-principles study

In this work, the effects of hydrogen (H) and oxygen (O) adsorption on the electronic and magnetic properties of graphene-like boron arsenide (BAs) monolayer are investigated using first-principles calculations. Pristine monolayer is a non-magnetic two-dimensional (2D) material, exhibiting direct gap semiconductor character with band gap of 0.75 (1.18) eV as calculated by generalized gradient approximation with Perdew–Burke–Ernzerhof (HSE06) functional. Four high-symmetry adsorption sites are considered, including on-top of B atom (), on-top of As atom (), on-top of hollow site (), and on-top of bridge site (). Using the criterion of adsorption energy, it is found that and sites are favorable adsorption sites for H and O adatom, respectively. The analysis of electronic interactions indicate the charge transfer from host BAs monolayer to both adatoms. H adsorption conducts to the emergence of magnetic semiconductor nature in BAs monolayer with a total magnetic moment of 1.00 . Herein, the magnetism is originated mainly from H adatom and its neighbor As atoms. In contrast, the non-magnetic nature of BAs monolayer is preserved upon absorbing O atoms. In this case, the energy gap exhibits a slight reduction of 4%. Further, the effects of adatom coverage are also analyzed. The presented results suggest an effective modification of ground state electronic properties, as well as induction of new feature-rich properties to make new multifunctional 2D materials from non-magnetic BAs monolayer.

High performance iridium loaded on natural halloysite nanotubes for CO-SCR reaction

Iridium nanocatalysts are ideal candidates for the selective catalytic reduction of NOx by CO (CO-SCR) in excess oxygen. Here, a high-performance Ir nanocatalyst supported on natural halloysite nanotubes (HNTs) was applied for the CO-SCR. The HNTs loaded with only 0.5 wt% Ir achieved 78 % NOx conversion at 250 °C in the presence of 5 % O2, which was the highest among catalysts with varied Ir loadings or reduction temperatures. It also possessed an excellent SO2 and H2O tolerance during longevity tests. An interesting SO2-enhanced CO-SCR long-term stability was observed, which was ascribed to the inhibitory effects of SO2 on the side reaction between CO and O2. The loading amount and the reduction temperature could modulate the size of Ir nanoparticles and the percent of Ir0, which were two key factors determining the CO-SCR activity. DRIFTS characterizations and DFT calculations coherently revealed the favorable adsorption sites of CO (top) and NO (hcp) on Ir nanoparticles. The Ir atoms served as a charge transfer bridge from the C atom of CO to the N atom of NO, leading to the enhanced breakage of N-O bonds. This work provides Ir/HNT as a promising CO-SCR material with high performance and robustness to tackle NOx pollution.

Effect of Vacancy Defects and Hydroxyl on the Adsorption of Glycine on Mg(0001): A First-Principles Study

Glycine (Gly), as one of the fundamental components of biomolecules, plays a crucial role in functional biomolecular coatings. The presence of structural defects and hydroxyl-containing functional groups in magnesium (Mg) materials, which are commonly used as biomedical materials, significantly affects their biocompatibility and corrosion resistance performance. This study computationally investigates the influence of vacancy defects and hydroxyl groups on the adsorption behavior of Gly on Mg(0001) surfaces. All potential adsorption configurations are considered through first-principles calculations. The findings indicate that stronger chemisorption occurs when Gly is positioned at the edge of the groove, where the surface has a vacancy defect concentration of 1/3. Among the four adsorption locations, the fcc-hollow site is determined to be the most favorable adsorption site for hydroxyl. The adsorption energy of Gly on the Mg(0001) surface containing the hydroxyl (−1.11 eV) is 0.05 eV more than that of on the Mg(0001) surface (−1.16 eV). The adsorption energies, electronic properties, charge transfer, and stable configurations are calculated to evaluate the interaction mechanism between Gly and defective surfaces. Calculated results provide a comprehensive understanding of the interaction mechanism of biomolecules on defective Mg surfaces and also indicate the directions for future experimental research.

Temperature effect on sulphur adsorption on iron surface: A molecular dynamics simulations study

The effect of temperature on the adsorption of a sulphur atom on the Fe(110) surface has been investigated using molecular dynamics simulations at a temperature of 353[Formula: see text]K, 373[Formula: see text]K and 398[Formula: see text]K. The most favorable adsorption site for a sulphur atom on the Fe(110) is found at a hollow site. The perpendicular height of the sulphur atom position is 4.017[Formula: see text]Å above the Fe surface at a temperature of 398[Formula: see text]K. The Fe–S bonding strength was affected by temperature, it becomes weaker with increasing temperature. The adsorption energy is calculated to be −6.640[Formula: see text]eV, −6.579[Formula: see text]eV and −1.841[Formula: see text]eV for the system at a temperature of 353[Formula: see text]K, 373[Formula: see text]K and 398[Formula: see text]K, respectively. This condition is confirmed by experimental results where the corrosion rate of the samples began to appear at 353[Formula: see text]K, with darker physical characteristics of the corrosion.

First-principles study on the adsorption and lithium storage capacities of Hf3C2 and Hf3C2T2(T = O, F, S) MXenes

Based on the theoretical framework of the first principle, the adsorption and theoretical lithium storage capacities of Hf3C2 and surface functionalized Hf3C2T2(T = O, F, S) MXenes were studied. The structural stability of the system and the influence of electrical properties on energy storage properties are analyzed when different functional groups are located in different positions. The formation energy results suggest that the three functional Hf3C2T2(T = O, F, S) structures are energetically stable, and the CCP site is the most stable among the possible sites of HCP, TOP and CCP. By calculating the energy bands and density of states, it is proved that F-functionalized Hf3C2F2 is not conducive to adsorption. During the adsorption process, the lithium intercalation process is carried out in the way of surface adsorption of atoms, in which the HCP site of bare Hf3C2 and the CCP site of functionalized Hf3C2T2 are the most favorable adsorption sites. The storage capacities of bare Hf3C2, Hf3C2O2, and Hf3C2S2 are 287.51 mAhg−1, 271.95 mAhg−1 and 258.00 mAhg−1, respectively. The Hf3C2O2 has a higher lithium storage capacity than Hf3C2S2, so both oxygen functionalized Hf3C2O2 and bare Hf3C2 are promising battery materials.

Stability and electronic sensitivity of CunM (M = Co, Mn, Pd, Au and V; n = 3–8) nanoclusters towards HCOOH molecule: a computational study

The stability, electronic and magnetic properties of the Cun + 1 and CunM (M = Co, Mn, Pd, Au and V; n = 3–8) nanoclusters were investigated using the PW91PW91/LANL2DZ/-311G(d,p) level of theory. The electronic sensitivity of these clusters towards the formic acid (FA) has also been evaluated. The results obtained show that the doping of the Cun + 1 with Co, Mn, Pd, Au or V atom has strongly altered their electronic properties. The interaction of HCOOH molecule over the CunM clusters exhibits that the most favourable adsorption site for the molecule is the metal atom dopant, and the calculated adsorption energies (E ads) range from −113.4 to −436.0 kJ mol−1, indicating a great chemisorption between both species. The values of ΔH and ΔG of the formed complexes by the adsorption of the HCOOH onto the CunM clusters are found to be negative, indicating that the adsorption process is regarded as exothermic and thermodynamically realisable at room temperature. The results reveal also that the CunV and CunAu clusters have the greatest sensitivity towards the HCOOH molecule in comparison with the other clusters, suggesting that the two clusters could be proposed as high-performance clusters for the detection of HCOOH molecule.

Co-decoration of WS2 nanosheets with both Au and In2O3-nanoparticles for attaining the CO sensing in self-heating mode

Two-dimensional materials such as WS2 nanosheets (NSs) have unique merits such as high surface area, good conductivity at low temperatures and good chemo-physical stability. In this study, we co-decorated In2O3 and Au NPs on WS2 NSs for CO gas sensing studies. The fabricated sensors were used in self-heating mode of operation at 25 °C, which can significantly decrease the power consumption. It was found that co-decorated gas sensor not only operates at a lower applied voltage, but also exhibits a higher sensing performance (sensitivity and selectivity), relative to bare WS2 NSs. On one hand, generation of In2O3-WS2 heterojunctions acted as notable sources of the resistance modulation and on the other hand, Au with its catalytic effect, significantly enhanced the dissociation of oxygen molecules and also offers many favorable adsorption sites for CO molecules. Therefore, we believe that co-decoration of WS2 is a reliable strategy to enhanced the sensing features in self-heating mode, which is highly demanded for devices with reduced power consumption.

Insights into the structures and elastic properties of Mg-Sn compounds with superconductivity

The CALYPSO crystal structural search in combination with first-principles calculations are performed to explore the crystalline structures and elastic properties, and superconductivity of Mg-Sn compounds. A novel stoichiometry of Mg4Sn with space group Cmmm has been predicted for the first time, which is different from the previously reported structures of Mg3Sn and Mg2Sn. Compared with P63/mmc-Mg3Sn and Mg2Sn, the Mg4Sn and Pm-3m-Mg3Sn possess excellent ductility. Calculated elastic anisotropy index, 3D shear and Young's modulus imply that these four Mg-Sn compounds are anisotropic. More importantly, Mg4Sn and Pm-3m-Mg3Sn can be the potential superconductors. The superconducting transition temperature of Mg4Sn is predicted to be 2.49K at 0 GPa, which is similar to other binary compound of SnSb (below 1.50K) [Phys. Rev. Mater. 3 (2019) 084603], and slightly lower than 5.03K of Pm-3m-Mg3Sn. In addition, the favorable adsorption site for Mg2Sn(001) and Mg4Sn(001) surfaces is hollow site, whereas for Pm-3m-Mg3Sn(001) and P63/mmc-Mg3Sn(001) surfaces is top sites (T1).

Periodic DFT study on heavy metals Cu(II) and Pb(II) atoms adsorption on Na-montmorillonite (010) edge surface

Heavy metal (HM) pollution is of great concern currently because it has been recognized as a potential threat to air, water,and soil. Adsorption is one of the most effective strategies for removing heavy metals. Montmorillonite as the adsorbent with a low cost and high thermal stability has received much attention. The adsorption of heavy metal Copper [Cu(II)] and Plumbum [Pb(II)] atoms on Na-montmorillonite hydroxylated (010) edge surface was analyzed using the generalized gradient approximation and density functional theory in the supercell technique. The coverage dependence of the adsorption structure and energetics was systematically investigated for a wide range of coverage from 0 to 1.0 monolayer (ML). Among all the possible adsorption sites, the most stable adsorption site for Cu(II) atom was a three-fold hollow site while the most favorable adsorption site for Pb(II) atom was a three-fold hollow site and followed by a two-fold bridge site. The adsorption energy increased with increasing coverage of Pb(II) atoms, indicating higher stability of surface adsorption and a tendency for the formation of adsorbate island clusters with increasing coverage. However, the adsorption energy of Cu(II) atoms decreased with increasing coverage. In the coverage range of 0 < Θ ≤ 0.5 ML the recovery capacity of the Na-montmorillonite for the heavy metal atoms was in the order of Cu(II)>Pb(II), while the recovery capacity of the Na-montmorillonite in the coverage range of 0.5 < Θ ≤ 1 ML was in the order of Pb(II)>Cu(II). The other aspects of the Cu(II) and Pb(II)/Na-montmorillonite (010) systems, including adsorption geometry, differential charge distribution, and electronic density of states were also studied and discussed in detail.

Engineering Pore Environments of Sulfate-Pillared Metal-Organic Framework for Efficient C2 H2 /CO2 Separation with Record Selectivity.

Engineering pore environments exhibit great potential in improving gas adsorption and separation performances but require specific means for acetylene/carbon dioxide (C2 H2 /CO2 ) separation due to their identical dynamic diameters and similar properties. Herein, a novel sulfate-pillared MOF adsorbent (SOFOUR-TEPE-Zn) using 1,1,2,2-tetra(pyridin-4-yl) ethene (TEPE) ligand with dense electronegative pore surfaces is reported. Compared to the prototype SOFOUR-1-Zn, SOFOUR-TEPE-Zn exhibits a higher C2 H2 uptake (89.1 cm3 g-1 ), meanwhile the CO2 uptake reduces to 14.1 cm3 g-1 , only 17.4% of that on SOFOUR-1-Zn (81.0 cm3 g-1 ). The high affinity toward C2 H2 than CO2 is demonstrated by the benchmark C2 H2 /CO2 selectivity (16 833). Furthermore, dynamic breakthrough experiments confirm its application feasibility and good cyclability at various flow rates. During the desorption cycle, 60.1 cm3 g-1 C2 H2 of 99.5% purity or 33.2 cm3 g-1 C2 H2 of 99.99% purity can be recovered by stepped purging and mild heating. The simulated pressure swing adsorption processes reveal that 75.5 cm3 g-1 C2 H2 of 99.5+% purity with a high gas recovery of 99.82% can be produced in a counter-current blowdown process. Modeling studies disclose four favorable adsorption sites and dense packing for C2 H2 .

Li-phobicity of polyvinyl alcohol for the control of Li electrodeposition in Li-secondary batteries

As various types of new electrode designs for Li-secondary batteries are researched, development of technologies to control the electrodeposition of Li is required. Herein, the Li affinity of polyvinyl alcohol (PVA) is investigated to examine its applicability as a coating material for the control of Li plating position in battery anodes, via first-principle simulation and experimental studies. The simulation indicates that the oxygen ions in the PVA provide favorable adsorption sites for Li at the initial stage of Li deposition, but the sites are readily passivated because Li is combined with multiple O ions. Therefore, the binding force for the subsequent Li becomes weak and the PVA surface generally exhibits Li-phobic characteristics. The experiment of a patterned PVA coating on the Li-ion battery anode demonstrates the anti-Li-plating function of the PVA. From the investigation results, it is concluded that PVA is Li-phobic, and can be utilized for guiding the Li plating in the future design of Li-secondary battery anodes.

Understanding the poisoning mechanisms of Si and Zr atoms on L12 Al3Ti (111) surface: A first-principles investigation

In order to reveal the poisoning mechanism, the adsorption and diffusion of Si and Zr atoms on the L12 Al3Ti (111) surface have been investigated using first-principles calculations. Based on the results of adsorption energy and work function, the most favorable adsorption sites for Si and Zr atoms are H4 and T1 of L12 Al3Ti (111) surface, respectively. It is revealed from electron density differences, density of states and Mulliken population that the Ti–Si covalent bonds in Si@Al3Ti(111) system the hybridization of Si 3p and Ti 3d orbitals while the Ti–Zr ionic bond in Zr@Al3Ti(111) system is come from the contribution of Ti 3d and Zr 4d orbitals. By calculating formation energy, it is found that the Si and Zr atoms prefer to incorporate the Al site of the first layer and Ti site of the second layer of L12 Al3Ti (111) surface, respectively. The energy barriers of Si and Zr atoms diffusion on or into L12 Al3Ti (111) surface are also evaluated.

Growth morphology and magnetic properties of Gd adatoms on h-BN template: From single atom to small cluster and monolayer

Atomic assembly of surface-supported nanostructures with high structural stability, large magnetic moment and magnetic anisotropy energy (MAE) hold great potential applications in spintronic and magnetic storage devices. With the changes of deposition coverage of Gd adatoms on the hexagonal boron nitride (h-BN) template, we systemically investigate the low-lying structures and magnetic properties of Gdn (n=1–19) clusters and monolayers (1ML-Gd and 2ML-Gd) by combining various theoretical methods including the spin–orbital coupling (SOC) density functional theory (DFT), abinitio molecular dynamics (AIMD) simulations and lattice dynamical calculations. Favorable adsorption sites and preferable orientations as well as distinguishing electronic structures have been thoroughly explored to reveal the bonding characteristics and growth models of Gd clusters and thin films. We demonstrate that the planar Gd clusters/monolayers deposited on h-BN surface can exhibit the energetically, dynamically, thermally, and thermomagnetically stable at high temperature of 500 K. The Gd-B covalent and ionic bonding interactions instead of Gd-N interactions give the synergetically contributions for stabilizing small clusters on planar h-BN sheet via the hybridizations of Gd-5d and B-2pz orbitals, while Gd-N covalent bonds participate in additionally bonding interaction for the depositions of large clusters on corrugated h-BN sheet due to the transformations from B/N-sp2 to B/N-sp3 hybridizations. Robust ferromagnetic (FM) couplings with large spin magnetic moments about 7.6 μB per Gd atoms are always found to be the ground states. Orbital magnetic moments of −0.10∼−0.37 μB per atom and large MAEs in few meV are primarily contributed by Gd-5d electrons. We propose that the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction mediated by 5d electrons determines the long-term FM coupling between Gd atoms, and we estimate the Curie temperatures ranging from 150 K to 60 K for different Gd deposited systems. The excellent structural and magnetic stability as well as large magnetic moment and MAEs therefore facilitate Gd cluster and thin film the promising candidates for spintronic applications.

First-principles study of 2H-Mo2C-based MXenes under biaxial strain as Li-battery anodes.

MXenes, a family of superior 2D materials, have been intensively investigated because they have many promising properties, particularly high-performance energy storage and high flexibility. To approach the expected critical benchmarks of such materials, the strain dependence of the atomic structure is widely considered for tuning the related properties. In this work, by means of density functional theory, we demonstrate the potential application of the strained 2H phase of Mo2C-based MXenes (Mo2C and Mo2CO2) as anode materials for lithium-ion batteries (LIBs). Adsorption and diffusion of Li on the surfaces of both materials and the impact of biaxial strain (εb) in the range of -4% to 4% are insightfully investigated. The lowest adsorption energy of Mo2C is -0.96 eV, and that of Mo2CO2 is -3.13 eV at εb = 0%. The diffusion of Li ions, considering the pathway between the first two most favorable adsorption sites, reveals that the biaxial strain refinement under compressive strain decreases the energy barrier, but the induction of tensile strain increases it in both MXenes. The ranges of the energy barriers of Li-ion adsorption on the surfaces of Mo2C and Mo2CO2 are 31-57 meV and 177-229 meV, respectively. Interestingly, the storage capacity of Li can reach three layers corresponding to a comparably high theoretical capacity of 788.61 mA h g-1 for Mo2C and 681.64 mA h g-1 for Mo2CO2. The atomic configurations are stable, as verified by the negative adsorption energy as well as the slightly distorted structures, by using ab initio molecular dynamics (AIMD) simulations at 400 K. Moreover, average open circuit voltages (OCVs) of 0.35 V and 0.63 V (at εb = 0%) are reported for Mo2C and Mo2CO2, respectively. Furthermore, the tensile strain results in an increase in the OCVs, while compression has the opposite effect. These computational results provide some basic information on the behaviors of Li-ion adsorption and diffusion on Mo2C-based MXenes upon tuning biaxial strain. They also give a guideline on what conditions are appropriate for practically implementing these MXenes as electrode materials in LIBs.

Highly sensitive and lower detection-limit NO[formula omitted] gas sensor based on Rh-doped ZnO nanofibers prepared by electrospinning

As a kind of toxic gas, NO2 can cause damages to the environment and threaten the health of human beings. To develop highly sensitive NO2 gas sensor is necessary. Here, the Rh-doped ZnO nanofibers were prepared by electrospinning. The Rietveld refinements results of XRD patterns have proved the successful doping of Rh into the crystal lattice of ZnO. The XPS spectra reveals the existence of large amounts of surface oxygen vacancy defects, which are beneficial to the enhancement of the sensitivity. The morphology and crystal lattice of the nanofibers were investigated by SEM and HRTEM, respectively. The highly sensitive NO2 gas sensor based on 1% Rh-doped ZnO nanofibers, with the experimental detection limit of 50 ppb (or 18.6 ppb, theoretical signal-to-noise ratio ¿ 3) was fabricated. At the optimal operating temperature of 150 °C, its response values (Rg/Ra) are 1.04 and 36.17, with the corresponding response time of 45 s and 32 s, towards 50 ppb and 10 ppm NO2, respectively. The sensor also exhibits good selectivity, repeatability and linearity between the relative humidity and the response values. The doping of Rh introduces large amounts of surface oxygen vacancy defects. The defects are more favored adsorption sites for NO2. The reasons for the ultrasensitivity of the sensor are as followings: (1) The binding energy between NO2 and ZnO with surface oxygen vacancy defects is about 1.5 times stronger than that for adsorption on the stoichiometric surface; (2) The surface oxygen vacancies of ZnO can have a reaction with NO2 to produce NO inducing the charge transfer; (3) The catalytic activities of Rh towards NO2 and H2O.

Effect of Cu Vacancy on Cu3Si(001) Surface for the Synthesis of SiHCl3 by Hydrogenation of SiCl4:A DFT Study

AbstractIn this paper, the effect of Cu vacancy of Cu3Si(001) surface for the hydrogenation of silicon tetrachloride was systematically studied by density functional theory (DFT). The favorable adsorption sites and stable configurations of reaction species are obtained and three possible reaction paths of SiHCl3 formation were achieved by transition state search. For the perfect Cu3Si(001) surface(P), Path1 is the most favorable, with a reaction barrier of 158.15 kJ mol−1. For both the single Cu‐vacancy(SV) and double Cu‐vacancy Cu3Si(001) surface(DV), Path2 is the most favorable, with the reaction barriers of 130.07 kJ mol−1 and 124.81 kJ mol−1, respectively. The results reflect that the activation energy of the reaction decreased significantly with the increase of Cu‐vacancy on the Cu3Si(001) surface, which may be the reason for the higher catalytic activity of Cu3Si catalysts with smaller Cu−Si stoichiometric ratios. This study can provide a reasonable explanation for previously experimental observation and provide a guidance for future catalyst design.