Considerable attention has been focused on layered double hydroxides (LDHs) for their applications in solar energy storage and conversion recently, but the in-depth investigation on the semiconducting properties of LDHs is limited. Herein, the electronic properties (band structure, density of states (DOS), surface energy, and band edge placement) of 14 kinds of MIInMIII/IV–A–LDHs (MII = Mg, Co, Ni, Cu, Zn; MIII = Cr, Fe; MIV = Ti; n = 2, 3, 4; A = Cl–, NO3–, CO32–) which contain transition-metal cations as well as their thermodynamic reaction mechanism toward the oxygen evolution reaction (OER) were studied using a density functional theory plus U (DFT + U) method. The calculation results indicate that the (003) plane is the most preferably exposed surface, and all these calculated LDHs are visible light responsive. The OER driving force and overpotential for these LDHs were obtained via their band edge placement and thermodynamic mechanism, and the results show that 10 of the calculated 12 LDHs (Ni2Ti–Cl–, Cu2Ti–Cl–, Zn2Ti–Cl–, Ni2Cr–Cl–, Zn2Cr–Cl–, Co2Fe–Cl–, Ni2Cr–NO3–, Ni2Cr–CO3–, Ni3Cr–Cl–, and Ni4Cr–Cl–LDHs) can overcome the reaction barriers by virtue of their driving force of photogenerated hole. Experimental observations further prove that NinCr–A–LDHs (n = 2, 3, 4; A = Cl–, NO3–, CO32–) are efficient OER photocatalysts, among which Ni2Cr–Cl–LDH shows the most active photocatalytic OER performance (O2 generation rate 1037 μmol h–1 g–1). In the meantime, Mg2Cr–Cl–LDH has no OER activity, agreeing well with the theoretical prediction. This work provides theoretical insight into the photocatalytic OER performance of LDHs materials which contain transition-metal cations with semiconducting property, which would show potential application in optical/optoelectronic field.

Recently, layered double hydroxides (LDHs) have attracted extensive attention in the field of energy storage and conversion, and an in-depth understanding of their semiconducting properties is rather limited. In this work, the electronic properties (band structure, density of states (DOS), and band edge placement) of MIIMIII-LDHs (MII = Mg, Co, Ni and Zn; MIII = Al and Ga) were studied in detail. The thermodynamic mechanism toward oxygen evolution reaction (OER) was investigated by using the density functional theory plus U (DFT + U) method. The calculation results of band structure indicate that Mg and Zn-based LDHs (band gap energies larger than 3.1 eV) are ultraviolet responsive, while Co and Ni-based LDHs are responsive to visible light (band gap energies less than 3.1 eV). The DOS calculations reveal that the photogenerated hole localizes on the surface hydroxyl group of LDHs, facilitating the oxidization of a water molecule without a long transportation route. The band edge placements of MIIMIII-LDHs show that NiGa-, CoAl-, ZnAl-, and NiAl-LDHs have a driving force (0.965 eV, 0.836 eV, 0.667 eV, and 0.426 eV, respectively) toward oxygen evolution. However, the thermodynamic mechanism of these four LDHs reveal that only CoAl-LDH can overcome the reaction barrier (0.653 eV) via the driving force of photogenerated hole (0.836 eV). Experimental observations of MgAl-, CoAl-, and ZnAl-LDHs further prove that only CoAl-LDH is an efficient oxygen evolution photocatalyst (O2 generation rate: 973 μmol h–1 g–1), agreeing well with the theoretical prediction. Therefore, this work provides an effective theoretical and experimental combined method for screening possible photocatalysts, which can be extended to other semiconductor materials in addition to LDHs.

Catalytic hydrogenation of CO2 or CO to chemicals/fuels is of great significance in chemical engineering and the energy industry. In this work, density functional theory (DFT) calculations were carried out to investigate the hydrogenation of CO2 and CO on Ru(0001) surface to shed light on the understanding of the reaction mechanism, searching new catalysts and improving reaction efficiency. The adsorption of intermediate species (e.g., COOH, CHO and CH), reaction mechanisms, reaction selectivity and kinetics were systematically investigated. The results showed that on Ru(0001) surface, CO2 hydrogenation starts with the formation of an HCOO intermediate and produces adsorbed CHO and O species, followed by CHO dissociation to CH and O; while CO hydrogenation occurs via either a COH or CHO intermediate. Both the hydrogenation processes produce active C and CH species, which subsequently undergoes hydrogenation to CH4 or a carbon chain growth reaction. The kinetics study indicates that product selectivity (methane or liquid hydrocarbons) is determined by the competition between the two most favorable reactions: CH + H and CH + CH. Methane is the predominant product with a high H2 fraction at normal reaction pressure; while liquid hydrocarbons are mainly produced with a large CO2/CO fraction at a relatively high pressure.

Previous work has demonstrated that cointercalation of luminescent dyes and surfactants into layered double hydroxides (LDHs) is an efficient approach to inhibit the aggregation of dye and therefore enhance its photoluminescence behavior. In this work, molecular dynamics simulations are performed on different ZnAl-LDHs cointercalated with dye (fluorescein or 1-anilinonaphthalene-8-sulfonate) and alkylsulfonate with different alkyl chain length (CnH2n+1SO3, n = 5, 6, 7, 10 and 12, respectively), together with dye–alkylsulfonate solutions for comparison. The structure, binding energy and the thermal motion characterized by the diffusion coefficient of each dye are analyzed. In the dye–alkylsulfonate/LDHs, the diffusion coefficient and the binding energy of the dye show a minimum when the dye is cointercalated with heptanesulfonate (HPS, n = 7), whose size is the closest to that of the dye. While in the case of dye–alkylsulfonate solutions, the diffusion coefficient and the binding energy vary monotonously with the increasing alkylsulfonate size. Furthermore, it is found that the increase of Al3+ content in LDH matrix in dye–HPS/LDHs is favorable for the restriction of the dye motion. These results indicate that the dye–alkylsulfonate/LDH system is more effective in restraining both the thermal motion and the aggregation of the dye than that of dye–alkylsulfonate solutions due to the confined microenvironment provided by the LDH matrix. Therefore, it is possible to inhibit the aggregation of the dye in dye/LDHs by two aspects: choosing a surfactant with a size close to that of the dye as the cointercalant and increasing the content of trivalent cations in the LDH matrix.

Density functional theory (DFT) calculations were carried out to study the nucleation and growth mechanism of Ru clusters on the TiO2(101) surface by using supported Run (n = 1–10, 20, 22) cluster models to understand the metal–support interaction and the resulting catalytic performance toward CO oxidation. The results show that the Run cluster prefers a 3D geometry when n ≥ 4 and that the Ru–TiO2 interface is predominantly composed of Ru–O and Ti–O bonds. Calculation studies based on the density of states (DOS), Hirshfeld charge analysis, and electron deformation density (EDD) demonstrate that the electronic interaction is mainly localized at the Ru–TiO2 interface through the electron transfer via the Ru–O bond. Additionally, the investigation on catalytic behavior of Run/TiO2 toward CO oxidation reveals the largely enhanced catalytic activity of the supported Run clusters, which originates from the significant reduction of the activation barrier as a result of the electron transfer from Ru to TiO2.

A valence force field named LDHFF was systematically developed for the layered double hydroxide (LDH) materials. Its potential function was referred from the polymer consistent force field (PCFF) by introducing a double-well potential to describe the oxygen–metal–oxygen (O–M–O) bending in the octahedral host sheets. The bonded (intramolecular) parameters, including the bond stretching constants, angle bending coefficients, as well as cross terms, were obtained from density function theory (DFT) calculations on the simplified but representative cluster models [MII2MIII(OH2)9(OH)4]3+ and [MIII3(OH2)9(OH)4]5+ (MII2MIII = Mg2Al, Zn2Al, Co2Al, Ni2Al, Cu2Al, Mg2Fe, Zn2Fe, Ni2Fe, Mg2Cr, Zn2Cr, Cu2Cr, Co2Cr; MIII = Al, Fe, Cr). In the case of nonbonded potential, the van der Waals parameters were obtained by fitting them to the cluster models mentioned above. The partial charges used to calculate the Coulombic interactions were assigned as Mulliken charge from density functional theory (DFT) calculation. To validate these potential parameters, a series of molecular dynamics (MD) simulations were subsequently employed for 24 LDH models, and the resulting structures, vibrational frequencies, as well as binding energies are in high accordance with the experimental findings. Using LDHFF, stable octahedral host structures were maintained over 2 ns in molecular dynamics simulations. These results demonstrate that LDHFF works effectively and accurately for MD studies of LDH materials, which provides a theoretical insight for understanding the structural property and exploiting the fabrication of functional LDH and related materials.