Synthesis And Gas Sensing Properties Of Nano Zn-Al-O Materials

The problem of atmospheric environment is becoming more and more serious,the research and preparation of gas sensor become one of the the research hotspot.Nano-semiconductor metal oxide sensors are an important class of gas sensors with the preparation of simple,small size,low cost and many other advantages.However,the sensitivity and selectivity of single metal oxide sensor still have some limitations.Although the metal doping will improve its gas-sensing properties,the vast majority of doping are precious metals,whose the disadvantage is high cost and will pollute the environment.It has been found that the composite oxide gas sensor can improve the gas sensitivity by forming heterojunctions or synergistic effects.Therefore,it is of great practical value to find a composite gas-sensing material with good shape,high sensitivity,high selectivity and good stability.In this paper,Zn-Al LDH/ZnO composite?Zn-Al Layered Double Hydroxide?precursors with excellent homogeneity were prepared on the substrate of porous anodic aluminum oxide?AAO?by sol-hydrothermal method.The ZnAl₂O₄/ZnO composite was obtained by annealing.The effects of annealing temperature on the gas sensing properties of ZnAl₂O₄/ZnO were studied.The main contents and conclusions of this paper are as follows:Firstly,AAO was prepared by using anodic acid method in the oxalic acid solution with high purity aluminum as raw material.The experimental results show that the AAO film with better orderliness and consistency is prepared when the oxidation time is 2h,the oxidation voltage is 40V,the film removal time is 2h and the reaming time is 1h.Secondly,Zn-Al LDH/ZnO composite films were prepared on the AAO substrate by sol-hydrothermal method with zinc acetate and hexamethylenediamine as the reaction solution.The effects of solution concentration,reactant concentration ratio,reaction temperature and time on the morphology and structure of the films were analyzed.The results show that the Nano-sized flower-like spherical film of Zn-Al LDH/ZnO composite with large area continuity are prepared at 60?,5h,zinc acetate concentration of 0.005mol/L,zinc acetate and hexamethylenediamine concentration ratio of 1:10.Thirdly,Zn-Al LDH/ZnO composite films were used as precursors,and the effects of precursor concentration ratio and annealing temperature were studied by annealing.The results show that ZnAl₂O₄/ZnO composite oxide with better crystallinity is prepared after annealing at 600?with zinc acetate and hexamethylenediamine concentration ratio of 1:10.Finally,the gas sensitivity of ZnAl₂O₄/ZnO composite oxide to methanol,ethanol and acetone was tested and analyzed.It was found that the sensitivity of ZnAl₂O₄/ZnO composite oxide gas sensitive material to methanol,ethanol and acetone was higher with the increase of annealing temperature.The ZnAl₂O₄/ZnO composite oxide prepared by annealing at 600? had a higher sensitivity of ethanol than that of 500? or 400?.