Preparation,structural and photocatalytic activity of Sn/Fe co-doped TiO2 nanoparticles by sol-gel method

Pure and Sn/Fe co-doped (0.2 at.% Sn and 0.6 at.% Fe, 0.6 at.% Sn and 0.2 at.% Fe, 1.0 at.% Sn and 1.0 at.% Fe) TiO₂ nanoparticles were synthesized via a sol-gel method and subsequently calcined at different temperatures. Furthermore, the particles were analyzed by TG-DSC, XRD, TEM, HRTEM, EDS, SAED and UV–Vis for investigating the influences of dopant and calcination temperature on the thermal effect, composition, morphology, energy band gap (E_g) and the degradation efficiency of methyl orange (MO) under various light irradiations respectively. Results indicated that Sn/Fe co-doping inhibited the crystallization transformation from anatase to rutile phase of TiO₂ and decreased the E_g. The increased calcination temperature and Sn/Fe co-doped effect brought about the abnormal grain growth of TiO₂ nanoparticles. 0.6 at.% Sn/0.2 at.% Fe and 1.0 at.% Sn/1.0 at.% Fe co-doped TiO₂ nanoparticles presented better photocatalytic performance than pure and 0.2 at.% Sn/0.6 at.% Fe co-doped TiO₂ nanoparticles under visible light irradiation mainly due to the decreased E_g. On the contrary, 0.2 at.% Sn and 0.6 at.% Fe co-doped TiO₂ nanoparticles calcined at 650 °C showed the most excellent photocatalytic performance under UV light irradiation, which was about twice as large as that of pure TiO₂ possibly due to the formed hybrid structure of anatase and rutile phase as well as the h⁺-mediated decomposition pathway.     

Effects on the crystallite growth behavior of LaPO4 nanopowders and its mechanical properties

The effects of pH of the reaction solution and the concentration of phosphoric acid on the crystal growth behavior of LaPO₄ crystallites were investigated and the mechanical properties of rare-earth phosphates were compared. As a result, the concentration of phosphoric acid of 10% was beneficial to the crystal growth of LaPO₄ nanocrystalline. When the pH value of the reaction solution was 2, the size of LaPO₄ crystallites increased gradually with the increasing reaction temperature, and the smallest crystallite size of 43.27 nm was obtained after heat-treatment at 1000 °C. Simultaneously, the activation energy for crystal growth of LaPO₄ nanocrystalline was relatively lower (26.82 kJ mol⁻¹). With the decreasing radii of rare-earth ions, the hardness, Young's modulus and fracture toughness of the bulk rare-earth phosphates exhibited a reduced tendency, resulted from the increase of porosity under the same preparation process.     

Epitaxial Growth of 2D Materials on High-Index Substrate Surfaces

Recently, the successful synthesis of wafer-scale single-crystal graphene, hexagonal boron nitride (hBN), and MoS₂ on transition metal surfaces with step edges boosted the research interests in synthesizing wafer-scale 2D single crystals on high-index substrate surfaces. Here, using hBN growth on high-index Cu surfaces as an example, a systematic theoretical study to understand the epitaxial growth of 2D materials on various high-index surfaces is performed. It is revealed that hBN orientation on a high-index surface is highly dependent on the alignment of the step edges of the surface as well as the surface roughness. On an ideal high-index surface, well-aligned hBN islands can be easily achieved, whereas curved step edges on a rough surface can lead to the alignment of hBN along with different directions. This study shows that high-index surfaces with a large step density are robust for templating the epitaxial growth of 2D single crystals due to their large tolerance for surface roughness and provides a general guideline for the epitaxial growth of various 2D single crystals.     

Biocompatibility and electron microscopy studies of epitaxial nanolaminate (Al0·5Ti0.5)N/ZrN coatings deposited by Arc-PVD technique

The ability to combine layers with high mechanical strength and additional physicochemical properties, such as biocompatibility, makes the use of multilayer coatings attractive for various applications. The transition from single layer to nanolaminate architecture can improve the mechanical performance of the coatings by increasing the number of interfaces and decreasing the modulation period of the layers. The microstructural study of the nanolaminate (Al_0·5Ti_0.5)N/ZrN coating with a modulation period λ of ≃ 20 nm was carried out using the TEM-HRTEM method. It was found that the coatings of (Al_0·5Ti_0.5)N/ZrN series consisted of two phases: the fcc-(Ti,Al)N solid solution obtained by isomorphic substitution of Ti atoms with Al ones in the TiN crystal lattice and the cubic ZrN phase. ZrN layers had a high texture structure with [111]-preferred growth texture and made a dominant effect on the nucleation and growth of (Al_0·5Ti_0.5)N layers. The epitaxial growth process was the most pronounced for fcc-(Ti,Al)N (111)||fcc-(ZrN) (111) and fcc-(Ti,Al)N (200)||fcc-(ZrN) (200) grains. Finally, the new coating demonstrated high biocompatibility, failure to toxicity and supported U2OS osteogenic cells proliferation within 7 days of cultivation.     

Structural,optical, and electrical properties of tin iodide-based vacancy-ordered-double perovskites synthesized via mechanochemical reaction

Over the recent past, lead-based halide perovskite materials have drawn significant attention due to their excellent optical and electrical properties for solar cells and optoelectronics applications. However, the toxicity of lead elements and instability under ambient conditions leads to develop alternative compositions. Herein, we report a novel mechanochemical synthesis of tin iodide-based double perovskites (A₂SnI₆; A = Rb⁺, Cs⁺, methylammonium, and formamidinium), and their structural, optical, and electrical properties are investigated. Importantly, we found that the hydrogen iodide (HI) addition during the ball-milling process minimizes secondary phase formation in the synthesized A₂SnI₆ powders. The effects of HI addition and the A-site substitution are investigated with respect to the lattice parameters, optical bandgaps, and electrical properties of the synthesized perovskite materials. Our results demonstrate essential information to improve the understanding of halide perovskite materials and develop efficient lead-free perovskite photoelectric devices.     

Enhanced electrochemical performance of LiNi0.8Co0.1Mn0.1O2 via titanium and boron co-doping

Titanium and boron are simultaneously introduced into LiNi_0.8Co_0.1Mn_0.1O₂ to improve the structural stability and electrochemical performance of the material. X-ray diffraction studies reveal that Ti⁴⁺ ion replaces Li⁺ ion and reduces the cation mixing; B³⁺ ion enters the tetrahedron of the transition metal layers and enlarges the distance of the [LiO₆] layers. The co-doped sample has spherical secondary particles with elongated and enlarged primary particles, in which Ti and B elements distribute uniformly. Electrochemical studies reveal the co-doped sample has improved rate performance (183.1 mAh·g^-1 at 1 C and 155.5 mAh·g^-1 at 10 C) and cycle stability (capacity retention of 94.7% after 100 cycles at 1 C). EIS and CV disclose that Ti and B co-doping reduces charge transfer impedance and suppresses phase change of LiNi_0.8Co_0.1Mn_0.1O_2.     

A thermal perspective of flash sintering: The effect of AC current ramp rate on microstructure evolution

In flash sintering experiments, the thermal history of the sample is key to understanding the mechanisms underlying densification rate and final properties. By combining robust temperature measurements with current-ramp-rate control, this study examined the effects of the thermal profile on the flash sintering of yttria-stabilized zirconia, with experiments ranging from a few seconds to several hours. The final density was maximized at slower heating rates, although processes slower than a certain threshold led to grain growth. The amount of grain growth observed was comparable to a similar conventional thermal process. The bulk electrical conductivity correlated with the maximum temperature and cooling rate. The only property that exhibited behavior that could not be attributed to solely the thermal profile was the grain boundary conductivity, which was consistently higher than conventional in flash sintered samples. These results suggest that, during flash sintering, athermal electric field effects are relegated to the grain boundary.     

Nitrogen-doped cobalt sulfide as an efficient electrocatalyst for hydrogen evolution reaction in alkaline and acidic media

The enhancement in intrinsic catalytic activity and material conductivity of an electrocatalyst can leads to promoting HER activity. Herein, a successful nitrogenation of CoS₂ (N–CoS₂) catalyst has been investigated through the facile hydrothermal process followed by N₂ annealing treatment. An optimized N–CoS₂ catalyst reveals an outstanding hydrogen evolution reaction (HER) performance in alkaline as well as acidic electrolyte media, exhibiting an infinitesimal overpotential of ?0.137 and ?0.097 V at a current density of ?10 mA/cm² (?0.309 and ?0.275 V at ?300 mA/cm²), corresponding respectively, with a modest Tafel slope of 117 and 101 mV/dec. Moreover, a static voltage response was observed at low and high current rates (?10 to ?100 mA/cm²) along with an excellent endurance up to 50 h even at ?100 mA/cm². The excellent catalytic HER performance is ascribed to improved electronic conductivity and enhanced electrochemically active sites, which is aroused from the synergy and mutual interaction between heteroatoms that might have varied the surface chemistry of an active catalyst.     

Grain orientation evolution and multi-scale interfaces enhanced thermoelectric properties of textured Sr0.9La0.1TiO3 based ceramics

Sr_0.9La_0.1TiO₃ based textured ceramics (SLTT-S3T) with a texture fraction of 0.81 are successfully fabricated by the reactive template grain growth method, in which Sr_0.9La_0.1TiO₃/20 wt%Ti was used as matrix and 10 wt% plate-like Sr₃Ti₂O₇ template seeds were used as templates. The phase transition, microstructure evolution, and the anisotropic thermoelectric properties of SLTT-S3T ceramics were investigated. The results show that the ceramics are mainly composed of Sr_0.9La_0.1TiO₃ and rutile TiO₂ phases. Grains grow with a preferred orientation along (h00). A maximum ZT of 0.26 at 1073 K was achieved in the direction perpendicular to the tape casting direction. The low lattice thermal conductivity of 1.9 W/(m K) at 1073 K was obtained decreased by 34%, 40%, and 38% compared with non-textured, SrTiO₃ and Sr_0.9La_0.1TiO₃ ceramics prepared by the same process, can be attributed to the enhanced phonon scattering by the complex multi-scale boundaries and interfaces. This work provides a strategy of microstructural design for thermoelectric oxides to decrease intrinsic lattice thermal conductivity and further regulate thermoelectric properties via texture engineering.