Metal oxide semiconductor(MOS)is a promising material for gas sensing.A single MOS material has problems such as poor selectivity,high operating temperature and low sensitivity.The construction of heterojunction is an effective strategy to improve MOS gas-sensitive performance.In this paper,we take the construction of heterojunctions as the starting point to reduce the operating temperature and prepare three kinds of heterojunction composites,g-C3N4/Co3O4,CeO2-Co3O4 and g-C3N4/Bi2WO6,using metal oxide Co3O4 and composite metal oxide semiconductor Bi2WO6 as substrates,respectively,to investigate the effect of different heterojunction strengthening methods on the gas-sensitive performance of the materials.The specific research works are as follows.First,hollow dodecahedral Co3O4 particles with rich pore structure were prepared by pyrolytic metal organic frameworks(MOFs)method,and g-C3N4/Co3O4composites with heterojunction were prepared by compounding them with two-dimensional graphitic phase carbon nitride(g-C3N4)for the sensing detection of acetone gas to investigate the relationship between the composition,structural characteristics and gas sensing of the materials.The results showed that 0.04 g g-C3N4/Co3O4 exhibited a sensitivity response value of 140 for 50 ppm acetone at an operating temperature of 200℃.The material has a detection limit of 700 ppb for acetone and exhibits good stability and selectivity.The composite of two-dimensional g-C3N4 and Co3O4 forms a depletion layer,which hinders the diffusion of carriers and reduces the probability of electron-hole complexation,so that more carriers on the surface of the material participate in the redox reaction between the material and the target gas,resulting in a significant improvement of the gas-sensitive performance.This method provides a new idea for the construction of heterojunctions between MOS and g-C3N4 derived from MOFs method,and may also provide an important reference for the application of acetone gas sensors in environmental monitoring and medical diagnosis.Second,the CeO2-Co3O4 porous caged composites with p-n heterojunctions were successfully prepared by the pyrolysis method.The composition,structural characteristics and sensing capability of the materials were systematically investigated.The results show that the response value of 7%CeO2-Co3O4 to 50ppm acetone gas at 180℃is 170,which is 3.2 times higher than that of pure Co3O4,and shows good stability and selectivity.p-n heterojunction and Ce4+/Ce3+interconversion enable more electrons to be released to the surface of the material to contact with oxygen,thus generating more adsorbed oxygen to contact with acetone molecules contact.In addition,the hollow and porous structure gives the material a larger specific surface area(103.92 m2/g)and an abundant pore structure,which provides more adsorption sites for acetone,resulting in a more adequate redox reaction.It provides an important reference for the application of acetone gas sensors in environmental monitoring and medical diagnosis.Third,flower-like g-C3N4/Bi2WO6 composites with S-scheme heterogeneous structure self-assembled from thin nanosheets were prepared by oxidative etching and hydrothermal methods for photoinduced room-temperature detection of ethanol gas.It was shown that the 0.01 g g-C3N4/Bi2WO6-based sensor exhibited a response value of 164 for 50 ppm ethanol gas with a response time of 36 s and a recovery time of 199 s under 375 nm Illumination at room temperature.The excellent gas-sensitive performance is attributed to(1)the effective suppression of the electron-hole pair complexation by the S-scheme heterojunction.(2)g-C3N4and Bi2WO6 are excited by light to generate photogenerated electron-hole,and the cyclic reaction between photogenerated electrons and holes with O2 and O2-prolongs the electron lifetime and provides more adsorbed oxygen ions for reaction with ethanol gas.This work provides a feasible solution to achieve a highly sensitive room temperature photoinduced ethanol gas sensor. |