Engineering Hybrid Nanomaterials and Their Heterointerfaces for Photocatalysis

Student thesis: Doctoral Thesis

Abstract

Among the common photocatalysts, TiO2 becomes one of the most excellent photocatalysts due to its non-toxicity, low cost, chemical stability and high photocatalytic activity. However, the wide band gap and fast charge recombination limit its applications. The construction of heterojunction has been proven as an effective strategy. Herein, in this work, we design and fabricate several TiO2-based heterojunctions with non-selective and selective methods to enhance the photocatalytic performance of pristine TiO2. The facet junction built between highly-exposed (001) facets and thin (101) facets of anatase TiO2 nanosheets is demonstrated to be more efficient than the heterojunctions (TiO2-rGO and WO3/TiO2 Type II) synthesized by non-selective methods. The lower photocatalytic performance of rGO/TiO2 and WO3/TiO2 is attributed to the decreased active sites on TiO2 (001) facets in the nanocomposites by the random growth of rGO and WO3. An edge-connected MoS2/Au/TiO2 Z-scheme system that combines the facet junction and the interfacial heterojunction was then fabricated to achieve effective long-range charge separation and large reactive surface exposure. The heterostructure is realized by the selective growth of 2D layered MoS2 nanoflakes on the edge-sites of thin TiO2 nanosheets via a Au-promoted photodeposition method. Attributed to the synergetic coupling of the facet junction and the interfacial heterojunction that assures the effective charge separation, and tremendous but physically separated reactive sites offered by layered MoS2 and TiO2 (001) facets respectively, the artificial Z-scheme exhibits an excellent photocatalytic performance in photodegradation tests. The junctional plasmonic Au nanoclusters not only act as electron traps to promote the edge-selective synthesis, but also generate 'hot electrons' to further boost photocatalytic performance. A kinetic model is then derived to study the MB photodegradation with MS/Au/T Z-scheme nanocomposite, which demonstrates a kinetic transition changing from zero-order to first-order with the decrease of MB concentration. Combining in situ characterization, it is found that with the increase of MoS2 mass ratio, the charge transfer mechanism in MS/Au/T changes from pure Z-scheme to a combination of Zscheme and Type II.
Date of AwardMay 2022
Original languageAmerican English

Keywords

  • photocatalysis; facet junction; heterojunction; Z-scheme; kinetics study.

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