Publication Date

Spring 2016

Advisor(s) - Committee Chair

Dr. Yan Cao (Director), Dr. Banbo Yan, Dr. Darwin Dahl.

Degree Program

Department of Chemistry

Degree Type

Master of Science

Abstract

This study focuses on the visible light response of hetero-structures of TiO2-graphene- MoS2 for solar energy harvestings. The commercial P25 TiO2 nano-particles, and selfprepared layered reduced graphene oxides (RG) and MoS2 were assembled for the targeted hetero-structure materials as visible-light responsible solar harvesting cocatalysts. The hydrothermal method was applied for nano-material synthesis, the reduction of graphene oxides, and bonding formation. Multiple characterization methods (SEM-TEM, XRD, XPS, UV-VIS, PL, FT-IR, TGA) have been applied to understand the electron-hole pair separation and recombination, and performance tuning in their visible-light photo-catalysis rhodamine B (Rh.B) degradations process

Compared to TiO2, an obvious red shift of light absorption (from 3.1 eV to 2.6 eV) of the as-prepared RG-TiO2 was observed by UV-vis analysis, and an enhanced photocatalytic degradation of the Rhodamine B (Rh.B) using the as-prepared RG-TiO2 was also observed in a Xe lamp exposure test. The explication of these two approaches to photocatalytic improvements were concluded as the energy gap changing, the formation of Ti-O-C chemical bonds between TiO2 and RG for charge transfer and the reduction of the band gap, as well as a likelihood of up-conversion photoluminescence mechanism (UCPL). The synthesis temperature was found to be critical factor to control binding formation and agglomeration of nano-materials. The lower and higher temperatures induced ineffective formations of preferable bonding structures and the significant agglomeration. The optimal synthesis temperature was found to be within 120 ℃-150 ℃ in the TiO2-RG system. For better understanding of the Ti-O-C bonding, a heterostructure of TiO2 nanotube arrays with GO (TNA-GO) was synthesized using the Langmuir-Blodgett (LB) assembly method. The band gap of this assemble was very close to the previous TiO2-RG synthesized below 120 ℃, which is very close to that of TiO2 nano-particles. This lead to the conclusion on the significance of the Ti-O-C bonding in the visible-light-responsible photo-catalysis solar harvestings.

This study revealed the fundamental mechanisms on the bonding formations and the significant visible-light-response of hetero-structcures between commercial-available, inexpensive and non-toxic TiO2 and layered materials, such as the zero-band-gap graphene and the smaller-band-gap MoS2. This mechanisms understanding will greatly sustain applications of economical-effective and environmental-safe TiO2.

Disciplines

Materials Chemistry | Nanoscience and Nanotechnology

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