Preparation, Doping And Gas-sensing Properties Of Indium Oxides

Indium oxide (In₂O₃) is an n-type semiconductor that shows t a wide band-gap and a low resistance and good catalysis. In₂O₃ nanometer materials, is an interesting material with excellent properties in applications such as solar cells, liquid crystal displays, gas sensor, Nowadays, zinc based composite oxides materials have become a hot topic in research and development. Composite oxide gas sensor can be applied to many aspects, such as agriculture, biological process, construction, and so on.In₂O₃ nano-powder was prepared by several methods. Its size, phase and morphology were analyzed by XRD, SEM and TEM. The results show that the morphology of the In₂O₃ prepared by the room temperature solid-phase synthesis, hydrothermal method and chemical co-precipitation method were nanorods. The gas-sensing properties of the materials were tested in static state. The results show that theIn₂O₃ nano-powder has high sensitivity to Cl₂. The In₂O₃ nano-powder prepared by homogeneous-precipitation method has a highest sensitivity as high as 1175 to 100ppm Cl₂ at lower working temperature 110℃. The sensor based on In₂O₃ also has satisfactory selectivity, quickly response and short recover time.In₂O₃ nano–powder was prepared by hydrothermal methods with Polyethylene glycol (PEG) 400/600/1000/2000 and series of EO (Textlo). The results show In₂O₃ nanorods can successfully prepared by a one–step hydrothermal method with PEG–600. In₂O₃ nanobelts were successfully synthesized by a one-step hydrothermal method. The average length of the nanorods reaches 150 nm, and the width 20 nm, giving an aspect ratio of a few hundreds. The In₂O₃ sensor has a high sensitivity up to 32.2 to 10 ppm NO₂ at lower working temperature 175℃. The sensor based on In₂O₃ also has satisfactory selectivity, quickly response and recover times. Using Textlo138 as surfactant, In₂O₃ nanobelts were synthesized by a one–step hydrothermal method. The average length of the nanobelts reaches 200 nm, and the width 10 nm. The results demonstrated that the In₂O₃ sensor has a high sensitivity up to 10.6 to 10 ppm Cl₂ at the working temperature 290℃. The response time to 10 ppm Cl₂ was about 8s, and the recovery time was about 1s. In order to improve the sensitivity of In₂O₃, doping is an effective way. In this work, metal elements were doped to In₂O₃in our work, such as Fe, Co, Ni. The result show that doped with metal elements, the sensitivity to NO₂ and Cl₂ increased significantly. The sensor In₂O₃ doped with 7 wt% Fe(NO₃)₃ has the best gas-sensing capability. So was the sensor In₂O₃ doped with 5wt% Co(NO₃)2 and 7wt% Ni(NO₃)₃. Take Ni(NO₃)₃ as an example, the sensor In₂O₃ doped with 7wt% Ni(NO₃)₃ has the best gas-sensing capability, its sensitivity to 100ppm Cl₂ can reach 843.1 at the working temperature 350℃.When the Cl₂ concentration is 10ppm, the gas response is 28.5, so the sensors can test Cl₂ concentration of even lower than 10ppm. The sensor based on In₂O₃ also has satisfactory selectivity, quickly response and short recover time.Rare earth elements were also doped to In₂O₃, such as La, Ce, Pr, Nd. The result show that doped with rare earth elements, the sensitivity to NO₂ and Cl₂ increased significantly. The sensor In₂O₃ doped with 7wt% rare earth elements La(NO₃)₃ has the best gas-sensing capability. The sensor In₂O₃ doped with 3wt% Ce(NO₃)₃, 7wt% Pr6O11, 7wt% Nd(NO₃)₃ has the best gas-sensing capability, too. Take La as an example, the sensor In₂O₃ doped with 7wt% La(NO₃)₃ has the best gas-sensing capability, its sensitivity to 100ppm Cl₂ can reach 1665.667 at lower working temperture110℃, and also has satisfactory selectivity; quickly response and short recover time.