Research On Synthesis And Water Splitting Of Doped In₂O₃

As an excellent n-type semiconductor, indium oxide (In2O3) is good candidate for photocatalysis such as photocatalytic water splitting. To promote photocatalytic activity, narrowing the energy gap (BG) of In2O3 is necessary, and nitrogen-doping has been proved a sound method. Moreover, element doping provides new energy levels or defects, which will significantly affact the recombination of the photogenerated carries as well as the overall photocatalytic efficiency.In this work, we use an In-based organic framework sod-ZMOF as precursor to prepare the N-doped In2O3 and N、Co co-doped In2O3, respectively, and discussed the mechanism of anion doping and anion-canion co-doping for water splitting. Three parts are included:Chapter One:Introduction. The mechanism of water splitting, the species of photocatalyst, characteristic of photocatalyst and their preparation method are systemtically introduced.Chapter Two:N-doped In2O3 from the In-MOF for photocatalytic O2-evolution from water. Sod-ZMOF was employed as precursor to prepare N-doped In2O3 nanocrystalline by thermal decomposition, where the ligand within sod-ZMOF serves as the nitrogen source. Accordingly, the BG is estimated to be 2.9 eV, which is highly reduced relative to 3.7 eV of the pure In2O3. The obtained N-doped In2O3 nanocrystalline bares relatively high BET surface area, which can provide more surface active sites that is benifical for catalytic promotion. Meanwhile, the presence of N-doping effectively prevented the recombination of the photoinduced e- and h+ pair. The overall O2-evolution efficiency is greatly enhanced to 20.48 μmol (204.15 μmol/g) in one hour. The nitrogen-doping mode was investigated in detail based on structure characterization.Chapter Three:N, Co-codoped In2O3 for photocatalytic O2-evolution from water. With the Co doped In-MOF precursor, N and Co are co-doped when the MOF is transformed into metal oxide by calcination. The co-doping leads to the reduction of the BG to 2.65 eV. According to previous reports, Co doping will cause the formation of new band energy adjacent to the conduction band level between the valance band and conduction band of the In2O3. Oxygen evolution reaction (OER) confirmed that the amount of evolved oxygen in four hours for 10% Co doped was 312.52 μmol/g.Innovaion Points of this work:We used a novel method to prepare the N-doped and N, Co co-doped In2O3. In-MOF or Co-doped In-MOF is emplyed as precursor to prepare the doped In2O3 by thermolysis under the optimized condition. N or Co is doped directly without adding the additional species. Meanwhile, In2O3 nanocrystal is obtained with porous structure and high surface area, which are benifical for enhancement of the photocatalysis. O2-evolution rate was estimated, which has rarely been reported before.