Porous AlN films grown on C-face SiC by hydride vapor phase epitaxy

We report the growth of porous AlN films on C-face SiC substrates by hydride vapor phase epitaxy(HⅤPE).The influences of growth condition on surface morphology,residual strain and crystalline quality of Al N films have been investigated.With the increase of theⅤ/Ⅲratio,the growth mode of Al N grown on C-face 6H-SiC substrates changes from step-flow to pit-hole morphology.Atomic force microscopy(AFM),scanning electron microscopy(SEM)and Raman analysis show that cracks appear due to tensile stress in the films with the lowestⅤ/Ⅲratio and the highestⅤ/Ⅲratio with a thickness of about 3μm.In contrast,under the mediumⅤ/Ⅲratio growth condition,the porous film can be obtained.Even when the thickness of the porous Al N film is further increased to 8μm,the film remains porous and crack-free,and the crystal quality is improved.

Density functional theory calculations on 2H-MoS_(2) monolayer for HCHO degradation:Piezoelectric-photocatalytic synergy

Formaldehyde(HCHO)is a common indoor gaseous pollutant,and long-term exposure to it may cause serious damage to the human immune system.Photocatalytic degradation of HCHO is a promising technique.However,most photocatalysts have the disadvantage of rapid recombination of photo-generated electron-hole pairs.In this work,the recombination of photogenerated electron holes was proposed to inhibit through the piezoelectric effect.A two-dimensional(2D)piezoelectric material,2H-MoS_(2),was selected to investigate the catalytic performance for HCHO degradation by the synergy of the piezoelectric and photocatalysis properties.The results show that the piezoelectric effect can induce the polarization in 2H-MoS_(2) and inhibit the recombination of photogenerated electron-hole pairs,thus improving the photogeneration of hydroxyl radicals for HCHO degradation.Therefore,the piezoelectric-photo-catalysis synergistic effect based on density functional theory(DFT)calculation was proposed to elucidate the HCHO degradation performance.This work could provide important guidance for the development of effective catalysts for HCHO degradation and the application of 2D piezoelectric materials.

Deactivation and regeneration of the commercial Cu/ZnO/Al_(2)O_(3) catalyst in low-temperature methanol steam reforming

Cu-based catalysts with excellent activity at low temperatures are widely used for methanol steam reforming(MSR)but suffer from deactivation problems.The present work aims to elucidate the deactivation and regeneration mechanisms of the commercial Cu/ZnO/Al_(2)O_(3) catalyst in low temperature MSR.By employing a series of(quasi)in situ characterization methods,it is found that the deactivation of the catalyst at a high weight hourly space velocity(WHSV)and a low reaction temperature is mainly due to the poisoning of Cu species associated with surface-oxygenated species with less Cu sintering,rather than carbon deposition,and strong metal-support interaction(SMSI).An in situ regeneration method was developed for the deactivated commercial Cu/ZnO/Al_(2)O_(3) catalyst via the simultaneous supply of O_(2).It is shown that the addition of O_(2)(≥1 vol%)can reverse the deactivation caused by surface-oxygenated poisoning due to the weak interaction between formed surface copper oxide and surface-oxygenated species,facilitating their desorption,but not deactivation caused by sintering,thereby partially restoring the catalytic activity.

Density functional theory investigation on selective adsorption of VOCs on borophene

In the field of volatile organic compounds(VOCs)pollution control,adsorption is one of the major control methods,and effective adsorbents are desired in this technology.In this work,the density functional theory(DFT)calculations are employed to investigate the adsorption of typical VOCs molecules on the two-dimensional material borophenes.The results demonstrate that both structure ofχBorophene;2D material;Volatile organic compounds(VOCs);Selective adsorption;Electronic structure andβ12 borophene can chemically adsorb ethylene and formaldehyde with forming chemical bonds and releasing large energy.However,other VOCs,including ethane,methanol,formic acid,methyl chloride,benzene and toluene,are physically adsorbed with weak interaction.The analysis of density of states(DOS)reveals that the chemical adsorption changes the conductivity of borophenes,while the physical adsorption has no distinct effect on the conductivity.Therefore,bothχ^(3)andβ_(12) borophene are appropriate adsorbents for selective adsorption of ethylene and formaldehyde,and they also have potential in gas sensor applications due to the obvious conductivity change during the adsorption.