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A novel up-conversion luminescence tetranuclear sodium complex [Na4(5-(carboxymethyl 2-oxo-propyl) amino isophthalic acid)(H2O)9] is synthesized by a solvothermal reaction, and its crystal structure is determined by single-crystal X-ray diffraction. The title complex crystallizes as a triclinic system with the P 1 ¯ space group and exists as an isolated tetranuclear complex. Numerous intermolecular hydrogen bonds and van der waals forces form a three-dimensional supramolecular network. Solid-state diffuse reflectance data show that there is a wide optical band gap of 2.91 eV. The solid-state photoluminescence spectrum reveals that the complex shows an up-conversion emission in the blue region of the light spectrum. Time-dependent density functional theory calculations reveal that this emission can be attributed to ligand-to-ligand charge transfer. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H2S) and sulfur dioxide (SO2) are two typical decomposition byproducts of sulfur hexafluoride (SF6), commonly used as an insulating medium in electrical equipment; for instance, in gas circuit breakers and gas insulated switchgears. In our work, fiber-like p-CuO/n-ZnO heterojunction gas sensing materials were successfully prepared via the electrospinning method to detect the SF6 decomposition byproducts, H2S and SO2 gases. The sensing results demonstrated that p-CuO/n-ZnO nanofiber sensors have good sensing performance with respect to H2S and SO2. It is noteworthy that this fiber-like p-CuO/n-ZnO heterojunction sensor exhibits higher and faster response–recovery time to H2S and SO2. The enhanced sensor performances can probably be attributed to the sulfuration–desulfuration reaction between H2S and the sensing materials. Moreover, the gas sensor exhibited a high response to the low exposure of H2S and SO2 gas (below 5 ppm). Towards the end of the paper, the gas sensing mechanism of the prepared p-CuO/n-ZnO heterojunction sensors to SO2 and H2S is discussed carefully. Calculations based on first principles were carried out for Cu/ZnO to construct adsorption models for the adsorption of SO2 and H2S gas molecules. Information on adsorption energy, density of states, energy gap values and charge density were calculated and compared to explain the gas-sensitive mechanism of ZnO on SO2 and H2S gases. [ABSTRACT FROM AUTHOR]

Recent years have witnessed a surge of research in using graphitic carbon nitride (g-C 3 N 4) as a metal-free photocatalyst for hydrogen production. Experiments showed an enhanced catalytic performance in g-C 3 N 4 by introducing intrinsic defects, but the physical mechanism remains elusive. Herein, via first-principles calculations with hybrid functional, we investigated the structural, energetic, electronic and optical properties of g-C 3 N 4 with C and N vacancies. We identified the most stable configurations with the lowest formation energies, and found that the vacancy induced defect state resides inside the energy gap of g-C 3 N 4 , leading to enhanced optical absorption in the visible light region. Interestingly, spatially separated conduction and valence band edge states can be observed, which may contribute to suppressed recombination of photo-generated electron-hole pairs. Detailed analyses on band alignment with reference to normal hydrogen electrode potential reveal the superior photocatalytic properties of g-C 3 N 4 with vacancy. We further discussed strain effects on the formation energies of C/N vacancies in g-C 3 N 4. These results not only provide physical insight into available experimental results, but also shed new light on synthesizing novel and high-efficiency photocatalyst for energy applications. Unlabelled Image • Structural and optoelectronic properties of g-C 3 N 4 with intrinsic defects are explored by first-principles hybrid functional calculations. • C/N vacancy induces defect state residing inside the energy gap, leading to enhanced visible-light absorption. • Spatially separated conduction and valence band edges are observed, beneficial for suppressed recombination of excited electron-hole pairs. • Strain-engineered vacancy formation is demonstrated. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Heterovalent doping of all-inorganic perovskite CsPbI 3 is explored by first-principles calculations. • Both p -type and n -type doping can be achieved, with energy gap efficiently tuned from 1.2 to 0.4 eV. • Optical absorption can be enhanced at visible light region. • Stability of the doped systems is evaluated that agrees well with experimental results. Abstract Via first-principles calculations, we investigate heterovalent doping of all-inorganic perovskite CsPbI 3 with In, Sb, Tl and Bi, focusing on the electronic, optical and energetic properties. Results show that p -type doping can be achieved by replacing Pb with In and Tl, while Sb and Bi make CsPbI 3 n -type doped. Energy gap of CsPbI 3 can be tuned from 1.2 to 0.4 eV, leading to enhanced optical absorption at visible light region. Furthermore, we show that In, Sb and Bi are much easier to be doped, which explains available experiments. These findings may shed light on fabrication of optoelectronic devices based on perovskites. [ABSTRACT FROM AUTHOR]

Here, we reported the synthesis of pure CoSn(OH) 6 and Fe-doped CoSn(OH) 6 nanocubes for gas sensing application by hydrothermal method. The extensive characterizations determined the crystal structure, morphology and chemical composition of the samples, such as, XRD, SEM, XPS, etc. Compared with the pure CoSn(OH) 6 , the gas sensing performance of 5Fe-CoSn(OH) 6 to N-butyl alcohol is improved significantly. The 5Fe-CoSn(OH) 6 based sensor presented high gas response of 60.309 toward 30 ppm N-butyl alcohol at relatively low operating temperature of 200 °C. Moreover, the 5Fe-CoSn(OH) 6 based sensor also exhibited excellent stability, selectivity and humidity resistance to N-butyl alcohol. The gas sensing properties of 5Fe-CoSn(OH) 6 is greatly improved due to the large specific surface area, narrow band gap, sufficient oxygen vacancies and quickly separation efficiency of electrons-hole pairs. The results demonstrate that the doping of Fe3+ is an effective way to improve the gas sensing properties of CoSn(OH) 6 sensors to detect N-butyl alcohol. [Display omitted] • The pure CoSn(OH)6 and Fe-doped CoSn(OH)6 were successfully synthesized by a hydrothermal method. • The sensing properties of the pure CoSn(OH)6 and Fe-doped CoSn(OH)6 to N-butyl alcohol were investigated for the first time. • 5Fe-CoSn(OH)6 exhibits the most remarkable gas sensing performance to N-butyl alcohol at 200 ℃. • The doping of Fe3 + is a promising approach for achieving an excellent gas sensing performance for the development of CoSn(OH)6 gas sensors to detect N-butyl alcohol. [ABSTRACT FROM AUTHOR]

In this paper, we explored the adsorption behavior of four kinds of characteristic gases dissolved in oil on Cr doped GaN monolayer. The results show that the Cr-GaN monolayer exhibits satisfactory adsorption performance for H 2 , CO, C 2 H 4 and C 2 H 2 molecules. The adsorption energies of H 2 (−0.326 eV), CO (−0.7 eV), C 2 H 4 (−0.893 eV) and C 2 H 2 (−0.751 eV) manifest the adsorptions can occur spontaneously. According to Hirshfeld charge analysis, Cr-GaN monolayer as an electron donor loses electrons of 0.124, 0.287, 0.243 and 0.244 e when interacting with H 2 , CO, C 2 H 4 and C 2 H 2. The dramatic changes of molecules can be observed after adsorption, indicating the strong interaction between molecules and Gr-GaN monolayer. Besides, the presence of significant overlaps between Cr atom and those molecules in the PDOS analysis verify the interaction is caused by chemisorption. The calculation of the band gap based on the frontier orbital theory shows that there is a significant difference in the conductivity of Cr-GaN before and after adsorption. Therefore, Cr-GaN based material could be used as resistance transducer to detect CO and C 2 H 2. This preliminary research provides a supplement to the study of the physicochemical properties of the transition metal modified GaN monolayer, and provides a first look of the potential application of the Cr-GaN monolayer in the field of gas sensors. [ABSTRACT FROM AUTHOR]

Through Density functional theory and Boltzmann transport theory, the ideal strength, electronic structure, elastic constants and thermoelectric performance of cubic phase PbTe are investigated. When the compressive strain is applied, both band gap and Seebeck coefficient decrease, while the electrical conductivity, power factor, thermal conductivity and ZT increase. According to the ZT of PbTe, the thermoelectric performance of p type is superior to that of n type. The optimal ZT value of p type could reach 3.88 at 0.5% strain, while the optimal ZT value of n type could reach 3.05 at 2.0% strain. Compared to the thermoelectric performance without strain, the thermoelectric performance under strain could be significantly improved, indicating that the strain engineering could be an effective strategy to improve the thermoelectric performance of PbTe. [Display omitted] • The electronic structure of PbTe is calculated, including density of states (DOS), relaxation time, mobility of carrier and effective mass. • The thermoelectric property of p type is found to be significantly better than that of n type. • For n type, the largest ZT value of 3.05 could be obtained at 2.0% strain and 850 K. • For p type, the largest ZT value of 3.88 could be obtained at 0.5% strain and 850 K. • The strain engineering could be an effective strategy to improve the thermoelectric performance of PbTe. [ABSTRACT FROM AUTHOR]