Design And Synthesis Of Light Activated Sensitive Materials

Energy crisis and environmental degradation are two major problems that restrict the human development and social progress. Recently, the environmental pollution problem has presented the trend of globalization. It is time for the portable detection sensors to appear to construct the routine examination of poisonous or harmful gases. Gas sensors withadvantages of low cost, portability and quick response for harmful gases detection, has been widely applied in the industry, agriculture, national defense, electronic, information and other fields related to human life. Gas sensing materialsare the key part for high performance gas sensors, among which metal oxide gas sensors have been widely used in gas detection systems due to their high sensitivities, low costs, portability and simplicities of synthesis. However, their working temperatures are inevitably high, whichseverely limitstheir application. Focusing on the general problem that the metal oxide gas sensors for gas detection often have high working temperatures, the assistance approach of light irradiation has been conducted in our work, specific work is as follows:1. ZnO/ZnFe₂O₄ composites with a hexagonal nanostructure were synthesized by calcination of Zn, Fe layered double hydroxides ?Zn2Fe-LDH? at certain temperatures. Under the light irradiation, the gas sensing measurementswere employed at the working temperature of 80?. Typically, the sample calcined at 600? performs impressive TEA sensing behaviors with advantages of good sensitivity, satisfactorystability and high selectivity, the detection limit is as low as 5ppm. The present finding clearly demonstrates that light excitation is greatly helpful to improve thesensitivity of metal oxide gas sensors and lower the operatingtemperature.The large response under light irradiationcaused by the enhancedactivity of adsorbed oxygen, which shifts the equilibrium of the reactions and facilitate a higher rate of reaction between TEA and adsorbed oxygen molecules. In addition, illumination often influences the gas adsorption rate and the activation energy. Thus, the responses of the ZnO/ZnFe₂O₄ sensor for TEA are greatly improved.2. Novelhierarchical Zn/In metal oxides nanostructures constructed withsmall secondary nanosheets grown on primary tertrahedroid bottom were fabricated by codepositing mixed-metal ?Zn and In? nitrates followed bycalcination in air. The subsequent characterizations prove that the hierarchical structure of Zn/In metal oxides isactually indiumdoped ZnO. More rough surface andlarger specific surface area make their excellent gas sensitive performance. The formation process of hierarchical structure through experimental design was further discussed.The factor such as indium content on the properties of hierarchical metal oxides materials was explored.The product prepared by codepositing mixed-metal ?Zn and In? nitrates withthe ratio of 4:1 obtains best gas sensitive performance. At a working temperature close to room temperature, the response of hierarchical Zn/In metal oxidesto 500 ppm ethanol is around 87 under visible light excitation, which has transcended the response values of many oxide materials for ethanol at the working temperature of 300-400?. With the aid of visible light excitation, high sensing performance response at room temperaturehas been achieved.In conclusion, light activated gas sensors will have broad application prospects in the future.