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Date of Award
2014
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Environmental Engineering (PhD)
College, School or Department Name
Department of Civil and Environmental Engineering
First Advisor
David Hand
Abstract
Sol-gel method was used to synthesize N-doped solid solution mixed oxide photocatalysts. N-doped GaZn mixed oxide photocatalyst, N-doped Zn0.75Cd0.25O2 photocatalyst, and N-doped CdIn2O4 photocatalysts were synthesized and characterized. Preliminary work was conducted for the screening of the photocatalysts to determine which photocatalyst material is capable of absorbing visible light while producing hydrogen through water splitting. Photocatalytic activities were conducted in a pure water reaction solution and in the presence of sacrificial electron donors. Sacrificial electron donors are used to donate electrons, thus prevent the photocatalyst from being photodegraded. A plexiglass gas-tight batch reactor was used for the photocatalytic water to produce hydrogen. Two 15-W LED lamps were used as the light source.
XRD patterns showed that the photocatalyst materials consist of well crystalline structure. The diffraction peaks of the materials shifted to higher angels indicating that the crystal structure obtained were not a physical mixture of In2O3 and CdO phases but a CdIn2O4 solid solution. The photocatalytic activity of the photocatalyst increase when small amounts of In2O3 and CdO coexist in the structure of the N-doped CdIn2O4 photocatalyst.
XRD patterns showed that the photocatalyst materials consist of well crystalline structure. The diffraction peaks of the materials shifted to higher angels indicating that the crystal structure obtained were not a physical mixture of In2O3 and CdO phases but a CdIn2O4 solid solution. The photocatalytic activity of the photocatalyst increase when small amounts of In2O3 and CdO coexist in the structure of the N-doped CdIn2O4 photocatalyst.
Preliminary results showed that N-doped CdIn2O4 photocatalyst produced more hydrogen and worked well without the sacrificial electron donors. The effect of urea was examined to determine if urea impacts the crystal structure of the photocatalysts. The results showed that the concentration of urea had an effect on the crystal structure of the photocatalyst and the photocatalytic activity. The photocatalyst particles consist of high crystallite structure as the concentration of urea increases. However, an increase in urea concentration affects the size of the particles. The particle size increases as the urea concentration increases. N-doped CdIn2O4 photocatalysts were synthesized at different sintering temperatures to determine the effects on the photocatalytic water splitting. The particle size of the photocatalyst is increased with increasing sintering temperature. A larger particles size, 900 °C catalysts, has a low photocatalytic hydrogen production. The photocatalyst sintered at 800 °C yielded more hydrogen compared to other photocatalysts sintered at 600 °C, 700 °C, and 900 °C. The hydrogen production rate of 800 °C was 154.27 μmol/h and the apparent quantum yield was 8.3 %, at approximately 450 nm. Nitrogen doping modified the band gap of CdIn2O4 and enhanced absorption of visible light.
The photocatalyst was loaded with Pt to enhance the photocatalytic hydrogen production; however the production rate of Pt/N-doped CdIn2O4 photocatalyst was lower than that of 800 °C photocatalyst. The hydrogen production rate of Pt (2 wt. %)-loaded was 117.24 μmol/h with an apparent quantum yield of 6.1%. The stability of the photocatalyst was examined with 800 °C photocatalyst without sacrificial electron donors. The physicochemical stability of the photocatalyst was assessed during three reaction cycles. The results showed that the photocatalyst is stable and does not photo-degrade. The hydrogen production rate of reaction cycle 2 was 195.24 μmol/h and the apparent quantum yield was 10% (~465 nm).
The photocatalytic hydrogen production was enhanced by loading CuO nano-size clusters on N-doped CdIn2O4 photocatalyst. The hydrogen production rate was 234.87 μmol/h and the apparent quantum yield was 12.2%.
Recommended Citation
Leswifi, Taile Y., "Synthesis and Photochemical Study of N-doped Mixed Oxide Solid Solution Photocatalyst for Hydrogen Production under Visible Light Irradiation", Dissertation, Michigan Technological University, 2014.