Synthesis And Properties Of Nanostructured Indium Oxide Films

Indium oxide is an important n-type semiconductor material, whose band gap is2.8-3.6 eV, which was widely used in many fields such as gas-sensor, photo-device and solar energy conversion. In recent years, low dimensional indium oxide nanostructures, such as nanowires, nanorods, nanobelt, have been successfully achieved. In2O3 octahedrons, as a type of advanced material promising being used in gas sensor, field emission, and so on, however, was not reported so much. Moreover,up to now the reported syntheses of the In2O3 octahedrons were mainly based on the chemical vapor deposition method.This article focused on exploring mild liquid routes to prepare In2O3 octahedrons and then carried out the studies on the novel properties of these octahedrons based on their microstructures. The specific research contents include:1. Preparation of In2O3 octahedron films on glass substrates and their gas sensing properties.The preparation of nanostructured In2O3 films on glass was based on a sol-gel technique. We first studied the factors that affected the sol quality, which included the concentration of InCl3·4H2O(indium source), C2H5COOH(solvent), the additives like HOC2H4 OH and C6H8O7·H2O. It was found that the optimal conditions for forming high quality of sol included 8.0 g of In Cl3·4H2O, 1.2 g of C6H8O7·H2O, 10 mL of C2H5 COOH, 2 mL of HOC2H4 OH, 5 mL of C2H5 OH, 3 mL of H2 O and a refluxing process operated at 500?C for 2.5 h. Then, the gel films were fabricated by using spin-coating and dip-coating methods, respectively. In dip-coating, the withdrawing speed was set as 90 mm·min-1. In the spin-coating, two steps were applied: a low speed coating at 5000 rpm for 50 s and a high speed coating at 6500 rpm for 20 s. The final In2O3 films were obtained by annealing the gel films at 500?C for 4 h. It was found that the nanoplate-like In2O3 crystals were formed in the former route and the In2O3 octahedrons were obtained in the latter case.We used the two kinds of In2O3 films as gas sensors to test their gas sensitivity at room temperature. It was found that, compared to the nanoplate-like In2O3 films, the In2O3 octahedron films possessed much enhanced gas sensing performance to NO2 gas, with a detect limit of 100 ppb. In addition, the sensors composed of In2O3 octahedrons showed good selectivity toward NO2 gas.2. N-doped In2O3 octahedron films on FTO substrates enhancing the photoelectrochemical water splitting.In2O3 octahedron films on FTO substrates were also fabricated by using the spin-coating technique. In addition to adding 0.08 g of urea, the components of the sol were identical with those of the sol described above. The spin-coating process included a low speed coating at 4500 rpm for 50 s and a high speed coating at 5000 rpm for 20 s. After annealing at 500?C for 4 h, the final In2O3 octahedron films on FTO substrates were obtained. As a control, the un-doped In2O3 films on FTO substrates were also fabricated using the same sol just without adding urea. Using the N-doped In2O3 octahedron films as the working electrode, the photoelectrochemical water splitting experiments were conducted. It was found that under AM 1.5G illumination at 100 mW·cm-2, the photocurrent of the N-doped In2O3 film can reach0.17 mA·cm-2, without noticeable decay during the 30 min of experiment process.Whereas, the un-doped In2O3 film could only achieve a 0.03 mA·cm-2 photocurrent in the same photoelectrochemical water splitting experiment.