EVALUATION OF PHOTOCATALYTIC GEOPOLYMERS FOR GASOUES α-PINENE AND AQUEOUS METHYLENE BLUE DEGRADATION

: (Alternative Format Thesis)

Abstract

A demand for sustainable materials for the abatement of gaseous and aqueous pollutants has led to the development of photocatalytic geopolymers. Synthesised from the alkali activation of aluminosilicate sources, geopolymer matrices are able to support functional materials, such as photocatalysts. This thesis investigates how the microstructure, optical properties and photocatalytic activity of geopolymer composites are impacted by the incorporation of titanium dioxide (TiO2), zinc oxide (ZnO) and tungsten trioxide (WO3).

Geopolymer composites with Si/Al molar ratios of 1 and 2, and photocatalyst-to-aluminium molar loadings (PC/Al) of 0.10, 0.15 and 0.20 were systematically investigated. X-ray diffraction (XRD), Fourier transform infrared (FTIR), solid-state aluminium nuclear magnetic resonance (27Al NMR), nitrogen adsorption-desorption with Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH) models applied to understand the microstructure. The optical properties were studied using UV-Vis spectroscopy to find relative shifts in the bandgaps and in-situ irradiated x-ray photoelectron spectroscopy (ISI-XPS) to understand underlying photocatalytic mechanisms. The photocatalytic activity was evaluated using the decolourisation of aqueous methylene blue dye, monitored via UV-Vis spectroscopy. The degradation of gaseous α-pinene was evaluated using a novel flow cell and thermal desorption – gas chromatography mass spectroscopy (TD-GCMS).

It was observed that in general photocatalyst loading decreased the BET surface area and the BJH pore volume, whilst increasing the average pore size, regardless of photocatalyst type. ZnO had the lowest impact on the relative band gap energies of the composites, whereas significant shifts were observed for the WO3 loaded geopolymers due to the complete conversion of WO3 into sodium tungstate (Na2WO4) in the alkaline conditions. A deeper understanding of the role of the geopolymer structure on the photocatalytic reaction was achieved using ISI-XPS, which showed the movement of photoinduced electrons from the titanium centres towards aluminium and silicon centres. The pristine geopolymer samples, without photocatalyst loading, displayed the highest photocatalytic activity due to the natural inclusion of TiO2 within the aluminosilicate feedstock and large BET surface areas. The ZnO-geopolymer composites generally outperformed the WO3-geopolymer composites in the degradation of α-pinene, with an Si/Al ratio of 2 being more active than a Si/Al ratio of 1, attributed to better adsorption of the pollutant.

Due to the consistency of the synthesis and evaluation methods used throughout the thesis, a comparative and statistical analysis was performed to better understand structure-function relationships. It was shown that there is a significant correlation (p < 0.05) between both the BET surface area and BJH pore volume with the methylene blue decolourisation. These finding highlight the complex relationships between geopolymer gel chemistry, photocatalyst loading and photocatalytic activity. This work has significantly improved the understanding of photocatalyst-geopolymer interactions and demonstrates the potential of these advanced materials for environmental remediation.

Date of Award	22 Apr 2026
Original language	English
Awarding Institution	University of Bath
Supervisor	Xinyuan Ke (Supervisor), Richard Ball (Supervisor) & Dan Maskell (Supervisor)