Photocatalytic degradation of methyl orange using modified mesoporous TiO2 and Au9 clusters

Author: Anahita Motamedisade

Motamedisade, Anahita, 2023 Photocatalytic degradation of methyl orange using modified mesoporous TiO2 and Au9 clusters, Flinders University, College of Science and Engineering

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Au nanoclusters (Au NCs) exhibit intriguing size-dependent catalytic, electronic, and optical properties. This thesis uncovers the pivotal role of Au NCs in enhancing the photocatalytic efficiency of titanium dioxide (TiO2) through improved charge separation.

As the catalytic efficiency of these NCs is closely linked to their size, preventing Au9 NCs' agglomeration becomes essential to enhance catalytic activity, particularly following heat treatment aimed at ligand removal. The study focuses on designing novel systems capable of adsorbing high levels of ultra-small Au9 NCs and preventing their agglomeration during deposition and annealing processes.

The first approach to achieving this aim involves the preparation of mesoporous TiO2 (MTiO2) with a high density of surface defects, a high specific surface area, and a 3D pore network. These structures provide anchoring sites for the adsorption of Au9 NCs, curbing their mobility and suppressing the tendency to aggregate. Another strategy involves introducing functional groups on the mesoporous TiO2 surface through N or S functionalisation. These chemically modified MTiO2 surfaces can potentially establish a more robust bond between the Au9 NCs and the MTiO2 substrate, preventing agglomeration.

Comprehensive characterisation techniques, including X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), Near-edge X-ray absorption fine structure (NEXAFS), Energy-Dispersive X-ray Spectroscopy (EDS), High-Resolution Transmission Electron Microscopy (HRTEM), and Scanning Transmission Electron Microscopy (STEM), provide detailed insights into the properties of the nanocomposites such as the phase type of TiO2, surface morphology and chemistry, and elemental composition, as well as size and dispersity of the Au9 NCs immobilised onto the substrate surface.

A comprehensive investigation into the relative impacts of surface modification and functionalisation strategies on enhancing the loading of Au9 NCs while mitigating agglomeration is conducted using XPS. Subsequently, the most promising photocatalyst system is identified, and an in-depth analysis of its photocatalytic efficiency in the degradation of methyl orange dye is conducted. Reaction parameters are systematically examined, and their interrelationships are established by applying response surface methodology (RSM).

In this study, the deposition of Au9 NCs onto S-functionalised mesoporous TiO2 (SMTiO2) is studied to produce efficient photocatalysts. The SMTiO2 substrates prevent the agglomeration of Au9 NCs and enhances the overall loading. Furthermore, nanocomposites of N-functionalised mesoporous TiO2 (NMTiO2) embedded with Au9 NCs are created using a chitosan-assisted soft templating method. The study evaluates the influence of the calcination atmosphere on substrate properties and the adsorption of Au9 NCs. The black NMTiO2 surfaces enhance loading and prevent agglomeration of Au9 NC even after heating, leading to improved photocatalytic effectiveness.

Transitioning to more sustainable industrial processes is crucial for addressing global challenges. This study focuses on clean drinking water scarcity, specifically addressing hazardous run-offs from chemical industries. Methyl orange (MO) dye, a common environmental pollutant, is chosen as a model compound for studying photocatalytic degradation. The study emphasizes the examination of diverse parameters affecting the degradation of MO dye and study their relationship using Response Surface Methodology (RSM).

In conclusion, the abstract encapsulates the objectives, methodologies, and key findings of the study, providing a comprehensive overview of the research conducted on Au9 NCs and their role in enhancing the photocatalytic efficiency of TiO2. In this comprehensive journey, our thesis elevates the art of surface modification, where science and creativity come together, opening new possibilities across various materials and systems.

Keywords: Au nanoclusters, photocatalyst, functionalised mesoporous TiO2, water treatment, dye degradation, response surface methodology (RSM), data analysis

Subject: Chemistry thesis

Thesis type: Doctor of Philosophy
Completed: 2023
School: College of Science and Engineering
Supervisor: Professor Gunther Andersson