Synthesis Of Indium Oxide And Tungsten Oxide And Their Formaldehyde Sensing Studies

Formaldehyde(HCHO)is a kind of volatile organic compound with high toxicity and cancerogenicity and broadly used in chemical industry,building and other fields.It is one of the popular research directions to establish a sensitive method for detecting HCHO.Currently,semiconductor metal oxides are popular in gas sensing materials for HCHO detecting.But there are some disadvantages,such as low response,high working temperature,high detection limit and so on.To overcome those disadvantages,indium oxide(In2O3)and tungsten oxide(WO3)were studied in this paper,.The gas sensing performance was enhanced by adjusting the surface properties of materials and element doping.A series of characterization were used to character the morphology,structure and surface properties of materials.And the the gas sensing mechanism was further discussed by combining with the above results.The specific works are as follows:1.A simple and environmentally friendly precipitation method was used to synthesize the precursor of In2O3,and then four kinds of In2O3 nanoparticles with uniform particle size were obtained by adjusting the calcined temperature.The gas sensing test results showed that In2O3-500 exhibited the best sensing performance to HCHO.The response of In2O3-500 to 10 ppm HCHO at the optimum working temperature(100?)is 68.1.Meanwhile,the In2O3-500 aslo have excellent selectivity,stability,reproducibility and ultra-low detection limit(1 ppm).X-ray diffraction(XRD)showed that the four kinds of In2O3 with different calcined temperatures are all cubic phase.Scanning electron microscopy(SEM)and transmission electron microscopy(TEM)demonstrated that all the samples had similar particle-like morphology and the particle size range was 10-25 nm.High resolution transmission microscopy(HRTEM)showed that the lattice plane spacing of(222)was 0.29 nm.X-ray electron spectroscopy(XPS),ultraviolet(UV)and Hall(Hall)characterizations proved that In2O3-500 had the most adsorbed oxygen,the smallest band gap energy and the highest electron mobility,respectively.The coordination of the three facts resulted in the best gas sensing performance of In2O3-500.2.Li doped WO3 nanomaterials with flower-like hierarchical structure formed by self-assembly of nanoplates were obtained by the simple ultrasonic precipitation strategy,and the effect of doping amount of Li on HCHO sensing properties were investigated.The results showed that 3%was the optimum doping amount and WO3/3%Li displayed the highest response(63.3)to 100 ppm HCHO at 175?,which was almost 12 times higher than the pure WO3.SEM,XRD,XPS were used to characterize the morphology,structure and surface state of the materials.The main reason of the enhanced gas sensing performance was that the flower-like hierarchical structure was beneficial for the diffusion and surface reaction of HCHO.Li doping could increase the structural defects of the materials,resulting in the increase of the amounts of adsorbed oxygen and the thickness of electron depletion layer.