Date of Award

December 2014

Degree Type

Thesis

Degree Name

Master of Science

Department

Engineering

First Advisor

Ying Li

Committee Members

Junhong Chen, Junjie Niu

Abstract

Photocatalytic conversion of CO2 into value-added solar fuels is a promising approach to simultaneously address the greenhouse gas pollution and energy shortage issues. TiO2, the most widely studied photocatalyst, suffers from drawbacks like fast electron-hole recombination and limited CO2 adsorption. In this study, Ti-containing MgAl layered double hydroxides (MgAl/Ti-LDHs) were designed to provide high activity of CO2 photoreduction by dispersing Ti species over MgAl-LDHs which have been extensively investigated as CO2 adsorbent. This study was the first attempt to apply MgAl/Ti-LDHs for photoreduction of CO2 with water vapor.

MgAl/Ti-LDHs were prepared through coprecipitation (CP) method, the most common technique for LDH synthesis. However, as-prepared MgAl/Ti(CP) sample only contained amorphous Ti species, which was usually considered to be less active than crystalline TiO2 for photoreactions. To crystallize the Ti species, the MgAl/Ti(CP) sample was treated with two different approaches: a). hydrothermal treatment of water dispersions of MgAl/Ti(CP) at 100, 150, or 200 °C. b). calcination of MgAl/Ti(CP) at 400, 500, or 600 °C and then rehydration in water, which was called the reconstruction method. Hydrothermal treatment at 150-200 °C and reconstruction from 600 °C calcination temperature resulted in formation of anatase TiO2 in MgAl/Ti samples.

The MgAl/Ti(CP) sample with amorphous TiO2 resulted in more than three times of CO yield than the commercial P25-TiO2, possibly due to high dispersion of Ti species and the excellent ability to adsorb CO2. The hydrothermal treatment at 150°C lead to the highest CO production as a result of competing effects of TiO2 crystallinity and surface area of the material. However, the sample reconstructed from 600°C calcination did not show improvement in the CO production, although it showed the highest crystallinity of anatase TiO2. The reasons might be greatly decreased surface area of the overall material and anatase particles. The phase transformation of amorphous Ti in LDHs to anatase crystals using hydrothermal treatment technique was for the first time reported and was demonstrated to be effective in improving photocatalysis of Ti-containing LDHs.

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