Design And Performance Of Formaldehyde Sensor Based On ZnO/CuO

Since formaldehyde has been listed as a carcinogen,long-term exposure to formaldehyde gas will seriously harm human health.Therefore,the timely and effective detection of formaldehyde gas is an urgent need for the development of today’s society.Semiconductor gas sensor has been widely used in the field of gas sensor because of its low cost,simple processing and convenient detection.Zinc oxide(Zn O)is used by most researchers to prepare gas-sensitive sensors,because of its many excellent properties,such as high electron mobility,non-toxicity,good thermal stability and so on,and so on.This article mainly studies the gas sensor based on Zn O material and its sensing mechanism.The main work includes the following two parts:(1)Based on Cu metal particles modified Zn O(CZO),a highly sensitive gas sensor for formaldehyde(HCHO)detection at room temperature was prepared by the sol–gel method,and the sensing mechanism was studied by density functional theory.Calculations indicate that the binding energy of CZO to HCHO is higher than that of pure Zn O when Cu metal occupies the oxygen vacancy on the surface of Zn O,which is beneficial for CZO to capture more HCHO molecules.Moreover,Cu metal splits oxygen molecules in the air to form a large number of oxygen free radicals on the surface of CZO and react with HCHO molecules to produce more conductive ions.The lowest band gap can be obtained when HCHO is adsorbed in CZO compared to other gases,which means CZO has better selectivity in the detection for HCHO.Experiments show that Cu metal can effectively improve the performance of Zn O for HCHO detection.CZO with 3 mol% Cu exhibits short response/recovery times(1.7s/2.9 s)and the limit of detection(LOD)is 0.61 ppm at HCHO concentration of 1 ppm.Moreover,CZO displays the excellent endurance to humidity.(2)Formaldehyde(HCHO)gas sensors based on Zn O/Cu O heterostructure(ZC)were prepared by the sol-gel method,and the sensing mechanism was studied by first-principles calculations.Calculations indicate that the presence of amino and hydroxyl groups on the surface of ZC have strong binding energy to HCHO,which facilitates ZC to capture more HCHO molecules.Furthermore,the band gap of ZC decreases when HCHO is adsorbed on the amino group of ZC,which accelerates oxidation-reduction reaction between HCHO molecules and free oxygen on the surface of ZC.Experiments show that the formation of ZC heterojunction leads to the formation of a large number of free oxygen on the surface and the reaction with HCHO molecules to produce more conductive ions.With the increase of Cu O content,more amino group and hydroxyl groups appeared on the surface of ZC,which is conducive to capturing more HCHO molecules to react with free oxygen on the surface of ZC.ZC2 sensor has excellent selectivity,high sensitivity,low detection limit(0.079 ppm)and fast response/recovery time(1.78/2.90 s)for HCHO detection at room temperature.In addition,ZC2 gas sensor has high resistance to humidity.