Synthesis Of Nickel Oxide Porous Composites And Its Gas Sensing Studies

Nickel oxide(NiO),as an important p-type semiconductor nanomaterial,is widely used in gas sensing research due to its excellent chemical properties.However,a single NiO has many disadvantages such as relatively poor gas sensing performance,low response,and high detection temperature.Therefore,it is still a chanllenge for researchers to improve the gas sensitivity of NiO materials through material modification.Based on p-type and n-type metal oxides,the most.effective way to combine individuals with different physical and chemical properties is to make nanocomposites.In this paper,NiO-based porous composites were prepared by hydrothermal method.The effects of the morphology and chemical composition of the materials on the gas sensing properties and corresponding mechanisms were investigated in detail.The details are as follows:1.A series of different Ni/Fe molar ratios ?-Fe2O3/NiO nanocomposites were prepared by one-step hydrothermal method and their gas sensitivity to acetone was studied.Compared with pure NiO,the gas sensing properties of?-Fe2O3/NiO composites were improved,significantly.The material with a molar ratio of Ni/Fe of 2(NiFe-2)exhibited the best gas sensing properties.The response of ?-Fe2O3/NiO composites was 290 for 100 ppm acetone at the optimum work temperature of 280?,which was 103 times higher than that of pure NiO.Besides,the ?-Fe2O3/NiO composites also exhibited the fast response/recovery time(28 s/40 s),the good selectivity(higher response to acetone than other gas)and the long-term stability(responses were almost unchanged within 30 days).The results demonstrated that we successfully synthesized the ?-Fe2O3/NiO p-n heterojunction nanocomposites.By compounding different types of semiconductors,the p-n heterojunction was formed between p-type NiO and n-type ?-Fe2O3.The existence of heterojunction increased the amount of oxygen vacancies and the adsorbed oxygen of ?-Fe2O3/NiO composites,also formed an internal electric field and accelerated carrier mobility,which enhanced the gas sensing properties.2.Hierarchical In doped NiO nanomaterials with different proportions were synthesized by a facile hydrothermal method and their gas sensitivity to HCHO was studied.The results showed that it will improve the gas sensitivity of NiO nanomaterials to formaldehyde by doping the proper amount of In element.The response of 5%In-NiO nanomaterial was 23.6 for 100 ppm HCHO at the optimum work temperature of 240? and the response/recovery time is 89 s/41 s.In doping will cause more defects in NiO material.Meanwhile,high valence can provide more free electrons for NiO,which lead to an increase in the number of active sites and increased the number of chemical adsorption oxygen content of the material surface,improving the gas sensing properties.