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Based on the first-principles density-functional theory, formation energies, transition energy levels of M (M = Mo, W) doped α-BiNbO4 systems are studied. The calculation results show that the donor defects form easily under Bi-rich condition. Of these, the Wint (W interstitial) and Moint (Mo interstitial) are the two main defects that lead to n-type conductivity. Then, the electronic structures of M-mono-doped and M/Ovac (O vacancy)-codoped α-BiNbO4 were investigated. Our results show that the band gap of Wint/Ovac-codoped α-BiNbO4 is reduced by 0.43 eV, and the conduction band minimum and valence band maximum are reduced by 0.20 and 0.23 eV, respectively, compared to pure α-BiNbO4, with less driving force required for the redox reaction process and then an increased redox rate. The α-BiNbO4 with Wint+Ovac defects with n-type conductivity has good photocatalytic activity in water splitting. [ABSTRACT FROM AUTHOR]

A new fluorine-containing chalcohalide, Ba4GaS4F3, has been synthesized by conventional high-temperature solid-state reaction. The compound crystallizes in the centrosymmetric space group I41/a with a = b = 16.628 (5) Å, c = 17.139 (10) Å, Z = 16. Experimental and theoretical results confirm that Ba4GaS4F3 is a direct band gap compound with an experimental band gap of about 3.13 eV, and the band gap is mainly determined by the Ba-5p, F-2p and S-3p orbitals. What's more, different from the many newly discovered chalcohalides in the Ba3AM4Q (A = Ga, In; M = S, Se; Q = Cl, Br, I) family, Ba4GaS4F3 is the first reported compound in the Ba4AM4D3 (A = Ga, In; M = chalcogen; D = halogen) family. The results enrich the structural diversity of metal chalcohalides. [ABSTRACT FROM AUTHOR]

Porous carbon has attracted extensive attention as an electrode material for various energy storage devices considering its advantages such as high theoretical capacitance/capacity, high conductivity, low cost and earth abundance. However, there still exist limitations hindering its practical applications, such as the tedious fabrication process, limited metal-ion transport kinetics and undesired structural deformation under harsh electrochemical conditions. Herein, we report a facile strategy, with calcium gluconate as the carbon source, to fabricate ultrathin porous carbon nanosheets. The as-prepared Ca-900 electrode delivers excellent K-ion storage performance including high reversible capacity (413.7 mA h g−1), superior rate capability (161.8 mA h g−1 at an ultrahigh current density of 5.0 A g−1) and ultra-stable long-term cycling stability (a high capacity retention ratio of ∼75.0% after 5500 cycles at 5.0 A g−1). Similarly, when being applied in Zn-ion hybrid capacitors, the Ca-900 electrode exhibits a high energy density of 75.22 W h kg−1, illustrating the application potential. Moreover, the origin of the fast and smooth metal-ion storage is also revealed by carefully designed consecutive CV measurements. Both K-ion/Zn-ion storage mechanisms are preliminarily revealed through ex situ measurements. Overall, considering the facile preparation strategy, unique structure, application flexibility and in-depth mechanistic investigations, it can be seen that this work will deepen the fundamental understanding of potassium-ion batteries and serve as a reference for the development of porous carbon materials for other highly efficient energy storage devices. [ABSTRACT FROM AUTHOR]

The Z-scheme Se/BiVO4 photocatalysts were successfully prepared by chemical reduction and hydrothermal methods. Ethanol had the effect of solubilizing a-Se and insoluble t-Se during aging, which was critical for the rapid growth of t-Se rods. Compared with pure Se rods and BiVO4, the Z-scheme Se/BiVO4 exhibits enhanced photocatalytic activity for rhodamine B (RhB) degradation under visible-light irradiation. The photoluminescence detection technology of terephthalic acid spectra shows that ·OH is the major active radical in the degradation of RhB by Se/BiVO4. Based on the transient photocurrent measurements and band structures, it can be concluded that the Z-scheme structure of Se/BiVO4 not only enhances the photogenerated electrons and holes migration rates but also to provide higher redox ability. With the enhanced photocatalytic performance, Se/BiVO4 can be potentially applied for the environmental remediation. [ABSTRACT FROM AUTHOR]

One type of nonlinear optical crystal Na3VO2B6O11 (NVB) with noncentrosymmetry was synthesized and shows extraordinary UV-visible light driven photocatalytic activity in the dechlorination of 2,4-DCP under UV-vis (λ ＞ 320 nm) light irradiation. The obtained dechlorination efficiency is 90 times higher than that of the commercial P25 TiO2 catalyst under the same conditions. The noncentrosymmetric structure of NVB gives rise to an intrinsic large polarization effect as evidenced by Kelvin probe force microscopy, and the polarization promotes separation of photogenerated electron–hole pairs, leading to efficient cleavage of chlorophenols into phenol series fragments and dissociative Cl− anions. A possible reaction pathway for 2,4-DCP dechlorination by NVB upon UV-vis light irradiation is proposed. Hydrodechlorination was found to be the major reaction pathway for 2,4-DCP dechlorination which could react with hydroxyl radicals to produce 1,4-benzoquinone and ocatechol. This work further advances the understanding of nonlinear optical materials, which opens up a new route to the design and synthesis of highly efficient photocatalysts by using nonlinear optical materials. [ABSTRACT FROM AUTHOR]

Two ternary metal chalcogenides, Ba2In2 Q5 ( Q = S, Se) were successfully synthesized by solid-state reactions. They are isostructural and crystallize in the orthorhombic space group Pbca (no. 61). Both of them have a similar three-dimensional (3D) framework structure, which is composed of [In Q4] ( Q = S, Se) tetrahedra that are alternatingly connected on layer in the ab plane, with Ba2+ cations arranged between In-S or In-Se layers for electric charge balance. The measured Raman and IR spectra show that title compounds have broad transparency range up to 20 μm. From the UV/Vis/NIR diffuse reflectance spectra, it can be seen that the bandgaps of Ba2In2S5 and Ba2In2S5 are 2.47 eV and 2.12 eV, which are larger than these of the calculation values (Ba2In2S5, 2.362 eV and Ba2In2Se5, 1.908 eV), respectively. The calculated partial densities of states indicate that the bandgaps are determined by the interaction of S-3p and In-5s (Ba2In2S5) or Se-4p and In-5s (Ba2In2Se5), respectively. The calculated birefringences (Δ n) are about 0.03 (Ba2In2S5) and 0.05 (Ba2In2Se5) as the wavelength above 1 μm, respectively. [ABSTRACT FROM AUTHOR]

Abstract: The electronic and optical properties of Al-doped SnO2 without and with O vacancies are investigated by means of first-principles calculations. Our results indicate that Al-doped SnO2 is of p-type conductivity character and its band gap decreases compared with undoped SnO2. The accompanied oxygen vacancies can introduce localized gap states below the bottom of the conduction band and lead to the conductivity character translating to n-type from p-type in Al-doped SnO2. The localized gap states are contributed by the hybridizing of Sn 5s, 5p, O 2p, and Al 3p states and the density of these states becomes much stronger with oxygen vacancies increasing. Meanwhile, Fermi level shifts upward, showing a stronger n-type conductive character. With respect to the optical properties, Al-doped SnO2 has a weak absorption peak at about 2.73eV in the visible region, while the presence of oxygen vacancies reinforces the absorption in the visible light region. [Copyright &y& Elsevier]

Abstract: The electronic structures and related properties of N- and M (M = Cr, Mo) doped BiVO4 are investigated by means of first-principles calculations. The synergistic codoping effects of N and M on photocatalytic O2 evolution in BiVO4 are studied. Our results demonstrate that the band gap of N/Cr- and N/Mo-codoped BiVO4 are reduced by about 0.34 and 0.15 eV compared with undoped system, respectively, with the redox potential still locating at a level suitable for O2 evolution, which results in the response of visible light enhancement and the production of O2 evolution improvement of BiVO4 under visible light. The energy calculations indicate that the introduction of M in BiVO4 favors incorporation of N and the codoped material is more stable. [Copyright &y& Elsevier]

Abstract: To understand the photocatalytic activity of Bi2WO6 for water splitting, the electronic structures of N- and Mo-monodoped and N/Mo-codoped Bi2WO6 are investigated based on first-principles calculations. Our results indicate that the band gap of N/Mo-codoped Bi2WO6 reduces by 0.19eV and the smaller driving force is required for the water-splitting oxidation process. The calculated binding energy of the defect pairs shows that N/Mo-codoping in Bi2WO6 is more feasible than mono-doping, indicating N/Mo-codoped Bi2WO6 is a potential candidate for the photocatalytic water splitting. [Copyright &y& Elsevier]

Abstract: The electronic properties of Bi2 MO6 (M=Mo and W) are studied by using the first-principles calculations. It is attributed to its smaller electron effective mass that Bi2WO6 has higher photocatalytic activity than Bi2MoO6. The oxygen vacancy in Bi2 MO6 serves as a trapping center of photogenerated electrons and thus is in favor of the photocatalytic efficiency. Nitrogen-doping induces localized structure distortion and thus improves the separation of photogenerated electron-hole pairs. Moreover, band gaps decrease obviously with doping concentration increasing, therefore the photoabsorption edges will give rise to a redshift in Bi2 MO6. [Copyright &y& Elsevier]

Two new diamond-like (DL) chalcogenides, Li2MgGeSe4 and Li2MgSnSe4, have been successfully synthesized using a conventional high-temperature solid-state method. The two compounds crystallize in the non-centrosymmetric space group Pmn21 with a = 8.402 (14) Å, b = 7.181 (12) Å, c = 6.728 (11) Å, Z = 2 for Li2MgSnSe4, and a = 8.2961 (7) Å, b = 7.0069 (5) Å, c = 6.6116 (6) Å, Z = 2 for Li2MgGeSe4. The calculated results show that the second harmonic generation (SHG) coefficients of Li2MgSnSe4 (d33 = 12.19 pm/v) and Li2MgGeSe4 (d33 = −14.77 pm/v), mainly deriving from the [MSe4] (M = Ge, Sn) tetrahedral units, are close to the one in the benchmark AgGaS2 (d14 = 13.7 pm/V). The calculated band gaps for Li2MgSnSe4 and Li2MgGeSe4 are 2.42 and 2.44 eV, respectively. Moreover, the two compounds are the first series of alkali and alkaline-earth metal DL compounds in the I2-II-IV-VI4 family, enriching the structural diversity of DL compounds. [ABSTRACT FROM AUTHOR]

Abstract: Atomic Cu adsorption on SrTiO3(001) surface was studied via the first-principles calculations. On TiO2-terminated(001) surface, Cu prefers to be adsorbed at a 4-hold hollow site and covalently bonds four oxygen atoms. Work function is lowered due to the charge transfer from Cu to SrTiO3. On SrO-termination, Cu is adsorbed over an oxygen atom and intra-unit charge polarization mainly contributes to the bonding. It has been identified that Cu plays as an electron trapping center and a mediating role in charge transfer from photon excited SrTiO3 to target compounds. The photogenerated electron–hole pairs can be separated effectively. [Copyright &y& Elsevier]