Pt Single Atoms Supported on Defect Ceria as an Active and Stable Dual-Site Catalyst for Alkaline Hydrogen Evolution.

This work evaluates the feasibility of alkaline hydrogen evolution reaction (HER) using Pt single-atoms (1.0 wt %) on defect-rich ceria (Pt1/CeOx) as an active and stable dual-site catalyst. The catalyst displayed a low overpotential and a small Tafel slope in an alkaline medium. Moreover, Pt1/CeOx presented a high mass activity and excellent durability, competing with those of the commercial Pt/C (20 wt %). In this picture, the defective CeOx is active for water adsorption and dissociation to create H* intermediates, providing the first site where the reaction occurs. The H* intermediate species then migrate to adsorb and react on the Pt2+ isolated atoms, the site where H2 is formed and released. DFT calculations were also performed to obtain mechanistic insight on the Pt1/CeOx catalyst for the HER. The results indicate a new possibility to improve the state-of-the-art alkaline HER catalysts via a combined effect of the O vacancies on the ceria support and Pt2+ single atoms.

Influence of Bicationic and Catanionic Surfactants Over the Morphology of Mesoporous Nanohydroxyapatite.

In the co-precipitation method, the morphology of nano Hydroxyapatite (HAp) is usually being controlled by parameters like pH, temperature, concentration, and the ratio of the mixed surfactants. In the present work, effective tailoring of morphology has been done by exploiting the electrostatic interaction between surfactants by grouping them as catanionic (Cetrimide and SDS) and bicationic (Cetrimide and CTAB), with weight ratio of 1:1 and total concentration of 0.28 g/100 ml. The prepared samples were subjected to various characterizations like FTIR, XRD, FESEM, HRTEM, TGA/DTA, and BET analysis. The results show that the samples are in HAp phase, nano size and mesoporous in nature. The FESEM images reveal the fact that the catanionic surfactant enhances the growth of particle from sphere to hexagonal rod whereas bicationic mixture suppresses the growth and results in a disk-like HAp. The samples were subjected to AAS test for finding the Ca2+ ion release rate in SBF and were compared with a commercial nanocrystalline HAp sample. The Ca2+ ion release test of the samples shows signs of better bioactivity of disk-like HAp than that of commercial one.

Highly efficient degradation of dyes by carbon quantum dots/N-doped zinc oxide (CQD/N-ZnO) photocatalyst and its compatibility on three different commercial dyes under daylight.

Eco-friendly carbon quantum dots/nitrogen-doped ZnO (CQD/N-ZnO) composites were successfully prepared by a facile one-step method. The various techniques were employed to characterize the phase structure, morphology and optical properties of CQD/N-ZnO composites. The nitrogen doping was confirmed by Raman and X-ray photoelectron spectroscopy. Three commercial dyes, such as malachite green, methylene blue and fluorescein dyes were chosen to investigate the photocatalytic performance of CQD/N-ZnO under daylight irradiation. It was found that the CQD/N-ZnO photocatalyst established a high compatibility to degrade all three commercial dyes within 30-45 min, under daylight irradiation. Also, it remains capable of reusing the CQD/N-ZnO photocatalyst for repeated photocatalytic performance due to anti-photocorrosion offered by CQDs. The synergetic effect of N-doping and CQDs is key to design a new class of photocatalyst for environmental remediation under naturally available daylight source.

Comparison of various surface textured layer in InGaN LEDs for high light extraction efficiency.

The various surface texturing effects of InGaN light emitting diodes (LEDs) have been investigated by comparison of experimented data and simulated data. The single-layer and double-layer texturing were performed with the help of ITO nanospheres using wet etching, where the ITO ohmic contact layer and the p-GaN layer are textured using ITO nanospheres as an etch mask. In case of single-layer texturing, p-type GaN layer texturing was more effective than ITO ohmic contact layer texturing. The maximum enhancement of wall-plug efficiency of double-layered textured LEDs is 40% more than conventional LEDs, after packaging at an injected current of 20 mA. The increase of light scattering at the textured GaN surfaces is a major reason for increasing the light extraction efficiency of LEDs.

Enhanced air-cavity effect of periodically oriented embedded air protrusions for high-efficiency InGaN/GaN light-emitting diodes.

We report on the development of periodically oriented embedded air protrusion (EAP) structures at the GaN-sapphire interface in InGaN/GaN LEDs. A specific SiO(2) mask pattern and a simple wet etching process were utilized for the fabrication of EAP structures. A strong coupling between closely proximate air cavities and the multiple quantum wells promoted spontaneous emission due to the high-index contrast at the GaN-air interface. As a result, the light output power of the EAP LED was 2.2 times higher than that of a conventional LED at an injection current of 20 mA.

The impact of ZnO nanoparticle interlayer on the growth and morphology of broom-like single crystalline gallium nitride.

Broom-like single crystalline gallium nitride (GaN) nanomaterials have been successfully grown on Si (100) substrates through ammoniating the new type of complex precursor hexafluoroammonium gallate [(NH4)3GaF6], under a constant flow of ammonia at 900 degrees C in a quartz tube. This research mainly deals with the effect of zinc oxide (ZnO) interlayer on the growth and morphological changes of GaN nanoparticles. Broom-like GaN nanomaterials were obtained upon the influence of very fine ZnO nanoparticle interlayer in between the silicon substrate and the Ga source complex materials. On the other hand, well organized micron size hexagonal GaN particles were resulted in absence of ZnO interlayer. The transformation of hexagonal to broom-like GaN nanomaterials was predominant due to improved surface compatibility between the Si substrate and Ga source complex by the ZnO interlayer. The starting point for the transformation was indentified by controlling the process time. The structure and morphology changes of the GaN product were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM images demonstrate the difference in their morphological changes of single crystalline GaN upon the ZnO nanoparticles layer deposition.