Controllable Synthesis Of Al Doped ZnO And Study Of Its Gas Sensing And Photocatalysis Properties

Al doped ZnO?AZO?showed excellent electrical and optical performances and is widely used in thermoelectricity,solar cells,gas sensors and photocatalysis.In this work,AZO with exposed specific crystal face and different morphologies were solvothermally synthesized by designing experimental program reasonably.The crystal growth and morphology evolution mechanism of AZO have been revealed.The theoretical basis and technical assistance have been provided for AZO controllable synthesis.Gas sensors based on AZO have been fabricated.The internal ralationship between morphology and gas sensing properties has been studied.The gas-sensing mechanism model has been established.Based on energy band matching theory,metal phthalocyanine complex sensitized AZO photocatalysts have been designed and synthesized.The photocatalytic degradation mechanism has been revealed.The main research content is as follows:AZO were solvothermally synthesized from zinc acetate,aluminum nitrate and HMT by adjusting the reactant concentrations,the ratio of water and ethanol in mixed solvent,additives,the mixing amount of aluminum,additives,the mixing amount of aluminum,reaction temperature and reaction time.The crystal structures,morphologies and chemical constitutions were characterized by XRD,SEM,TEM and HRTEM,XPS and IR respectively.The AZO powders were obtained with seven kinds of morphologies exposed?0001?crystal facet.These morphologies were plates,flowers,dumbbells,cactus,ball-flowers,rice and rods respectively.The as-synthesized AZO powder exposed mainly?0001?plane.According to density functional theory of first-principles the surface energy of AZO was calculated by means of CASTEP software.The results indicated that?0001?surface energy of AZO after reacting with H2 O molecules decreased,and then the law of crystal growth and morphology evolution have been discussed.The indirectly heated gas sensors based on AZO powders have been fabricated.The results revealed that the optimum working temperature is 332 ?.This kind of AZO gas sensor showed high selectivity and good response-recovery time to ethanol.The influences of morphology and aluminum doping amount on the gas sensitivity have been further studied.The AZO nanoplates exposed more?0001?planes showed excenllent gas sensitivity to ethanol.The AZO nanoplates with 3 at.% Al doping showed good response to ethanol.It's also found that AZO nanoplates provided most?0001?crystal facets to adsorb maximum ethanol by calculation of CASTEP software of density functional theory in the first principles,thereby AZO gas sensor with plates morphology showed the best selectivity and sensitivity.This is consistent with the experimental results.In order to explore the gas-sensing mechanisms,the research on dynamics has been carried out and the rate equation of gas-sensing reaction has been set up.The reaction order is determined as the first order reaction.The form of oxygen adsorption is O2-.The relationship between AZO sensitivity and the grain size has been discussed.The surface depletion layer model is set up.Better use ratio of visible light and develop efficient photocatalytic material are hot topics in photocatalysis field at present.Energy level matched sensitized AZO photocatalysts were desgined and synthesized in this work.Firstly,Cu Pc?iso-PeO?₈,CoPc?iso-PeO?₈,Ni Pc?iso-Pe O?₈ and Pb Pc?iso-PeO?₈ metal phthalocyanine complex sensitizers and sensitized AZO photocatalysts were synthesized.The photocatalytic performances of sensitized AZO powders in degradation methylene blue have been studied,then it was found that absorption wavelength was red shifted 21 nm after sensitization and the degradation efficiency of sensitized AZO improved by 30%.The influence of sensitizers,morphologies,and the doping amounts of Al on photocatalytic activity were studied respectively.The results indicated that AZO sensitized by PbPc?iso-Pe O?₈,AZO flowers and AZO with 3 at.% Al dopant exhibited better degradation efficiency.In order to explore mechanism of photocatalysis of the sensitizied AZO.The dynamic experiment has been designed.The photocatalytic reaction in degradation methylene blue is confirmed as the pseudo first order reaction.The speed constants are 0.08653 min-1 for flower-like,0.0590 min-1 for plates and 0.0517 min-1 for dumbbell-like,respectively.The spectral analysis of sensitizied AZO indicated that it has type II alternating energy band structure,the light carrier sepa ration has been improved effectively and recombination has been inhibited,a series of degradation reactions triggered by ROS can be realized.