Double perovskite halides are potential materials for the production of renewable energy that could meet the global demands for resolving energy shortage issues. In this study, we systematically investigate the Rb 2 XGaBr 6 (X Na, K) double perovskites using the full-potential linearized augmented plane wave (FP-LAPW+lo) method of density functional theory. The thermodynamic as well as the structural stabilities of the studied materials have been confirmed from the calculated formation energy and Goldsmith tolerance factor (0.89 and 0.92). On the other hand, the calculated Pugh's ratio shows the ductile mechanical nature of the studied materials. The calculated electronic bandgaps of 2.2 eV/1.90 eV for Rb 2 Na/KGaBr 6 lies is in the visible region, which indicated the potential application of these materials in solar cells. The electronic properties of the two compounds are studied using the electronic density of states and the complex dielectric functions are used to evaluate optical properties. Our calculated results clearly indicate the optimum absorption of light in visible regions which depicts the potential of these materials for optoelectronic devices. The thermoelectric properties of the two Rb 2 XGaBr 6 (X Na, K) double perovskites are also studied in terms of thermal and electrical conductivity and the Seebeck coefficient. K E Y W O R D Sdensity functional theory, direct band gap double perovskite, figure of merit, mechanical characteristics, opto-electronic devices

In the present work, TiO2/g-C3N4 nanocomposites were synthesized by using highly crystalline TiO2 nanorods/rice (NRs) and various percentages of g-C3N4 via a facile, scalable, and inexpensive pyrolysis method. The synthesized nanocomposites were characterized by various techniques, e.g., X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), N2 adsorption and desorption analysis (BET), Fourier transform infrared spectroscopy (FTIR), UV–vis diffuse reflectance spectroscopy (DRS), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CA). It was found that biodiesel production by the esterification reaction can be remarkably enhanced by coupling TiO2 with g-C3N4; hereby, it was observed that with increasing percentage of g-C3N4 from 5 to 10 and 15% with respect to TiO2 NRs, the photocatalytic activity rose and the maximum photocatalytic activity with 97% conversion was observed for NC-3, i.e., 15% g-C3N4/TiO2. Moreover, the photoactivity of pristine TiO2 NR aggregates was contrasted with their nanoparticle morphology and was estimated to be slightly better. When applied for photocatalytic Congo red dye degradation, this sample showed a 91% degradation efficiency using only a very small amount of the catalyst. The high catalytic efficiency is attributed to the narrow band gap, exceptionally high surface area, and efficient charge separation properties of the prepared catalysts.

Since the last decade, vegetable oil has received tremendous attention as an alternative lubricant because of worsening state of environmental health and finite resources of mineral oil. However, the use of vegetable oil is restricted due to the poor low temperature fluidity and thermal-oxidative stability. These drawbacks can be enhanced by adding additive into the solution of vegetable oil. Thus, objective of this research is to investigate the influence of adding nanoparticle additive on tribological performance of palm kernel oil. The type of nanoparticle used throughout this study is copper oxide, which serves as anti-wear additive. Palm kernel oil (PKO), palm kernel oil-copper oxide nanoparticle (PKO-CuO), mineral oil (SAE-40), synthetic oil (SAE15W-50) are used as lubricant. Tribological properties if the used lubricants are evaluated using fourball tribotester under standard load and extreme pressure tests. Experimental results showed that the presence of nanoparticles in natural palm kernel oil improved tribological performances of friction and wear. The friction coefficient and wear scar diameter are reduced by approximately 5.0% and 3.5% respectively. The highest enhancement in friction coefficient value of ~20% was obtained under extreme pressure condition. Addition of nanoparticle also is found to improve load carrying capacity of PKO by 15%.

Linearized augmented plane wave plus local orbitals (LAPW + lo) method designed within density functional theory (DFT) has been used in this study to calculate the structural, electronic and thermoelectric properties of XCuOTe (X=Bi, Ce, La). Generalized gradient approximation, Wu-Cohen (GGA-WC) parameterized exchange correlation functional, was used. The structural and electronic calculations have a good agreement with previous study. For thermoelectric calculation, semi empirical Boltzmann approach implemented in BoltzTraP package was used to calculate Seebeck coefficient, electronic conductivity as well as thermal conductivity. By referring to previous studies, the results have good agreement with them. In addition, the Seebeck coefficient of these materials was calculated as a function of the chemical potential at temperatures 300K, 600K, and 900K. Our calculations highlight suitability of these materials for applications in thermoelectric devices.