Thesis
Resorcinol-formaldehyde/titania (RFTi) gel composites for wastewater treatment
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2023
- Thesis identifier
- T16565
- Person Identifier (Local)
- 201885931
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- Increasing levels of water pollution, together with the appearance of emerging pollutants, necessitates the development of efficient new techniques for water remediation. Conventionally, adsorption and environmental catalysis can effectively respond to this demand, and these methods can be enhanced by developing new materials and processes to deliver on the needs of an increasingly industrialised society. A combination of adsorption and photodegradation has been proven effective in targeting a wide range of pollutants, and research into materials development pertinent to the integration of both processes is ongoing. Previous studies have recognised the synergistic effects of carbon and Titanium (IV) oxide or Titania in various applications. Within water remediation, carbon has been utilised in in several forms, such as activated carbon, graphene, carbon nanotubes, and fullerenes, for integration with TiO2. This work focuses on employing a new type of organic carbon gel, which are carbon nanospheres, to host TiO2 photocatalysts. This organic carbon gel is derived from a sol-gel process via polycondensation of resorcinol-formaldehyde (RF), yielding unique properties that are ideal for use as an adsorbent for water treatment. TiO2 was successfully incorporated into the RF matrix during the polycondensation reaction of RF, to produce a chemically crosslinked, stable structure. The integration of carbon and TiO2 improves the photocatalytic activity by several means: (i) modification of the electronic structure of TiO2 to lower its band gap for visible-light absorption, (ii) reduction of the recombination rate, and (iii) facilitation of pollutant adsorption. The highly porous carbon gel, with a large surface area, facilitated dispersion of TiO2, enhancing pollutant adsorption. The chemical complexes formed between both phases increase the number of active sites, and interactions between the pollutant and disinfectant, while the carbon phase facilitates charge transfer and minimises the recombination of charge carriers on the TiO2 surface. These combined properties make the composite materials efficient materials for adsorption photodegradation remediation of contaminated water. The relative composition of RF and TiO2 phase in an integrated material is crucial in determining the ultimate adsorption-photodegradation performance; therefore, a suite of RFTi gels was synthesised, moving from pure RF to pure TiO2 in 10% steps, to understand the structure-property relationship, and its impact on the final application, as well as to determine the optimal composition. Extensive analysis of the materials was conducted to determine their textural, chemical, thermal, and optical properties. Firstly, the compositional analysis validated the experimentally deposited theoretical compositions of both phases. The analysis of the results demonstrated the composition-dependent properties of RFTi. The micrographs showed a homogenous distribution of TiO2 in the three dimensional porous RF network for samples up to 30% TiO2, beyond which TiO2 tended to start aggregating. The surface area analysis was in agreement with the micrographs, demonstrating that the aggregates blocked the pores of the RF network, resulting in a decrease in surface area and poor textural properties. Furthermore, the optical properties revealed that the electronic structure of TiO2 was successfully modified, with a narrowed bandgap observed and a shift of the absorption edge to the visible region of the electromagnetic spectrum; hence, the material was capable of activation upon visible light irradiation. RFTi30 and RFTi40 (30% and 40% TiO2 in RF) showed the lowest bandgaps with broadened UV-Vis spectra covering almost the entire visible region. Characterisation of the materials was followed by application tests performed against a model pollutant dye, methylene blue (MB). The experimentally obtained data for the adsorption capacity for MB reduction correlated with the physiochemical properties of the respective samples. The equilibrium adsorption data were extensively studied to elucidate adsorbent-adsorbate interactions by applying kinetic and isotherm models to the adsorption data, and most of the samples showed a combination of physisorption and chemisorption phenomena. The effect of temperature showed that the reactions were thermodynamically feasible, and temperature-dependent adsorption depended on the nature of the RFTi sample. The synergy of RF and TiO2 was corroborated by an observed enhancement in dye reduction upon visible light irradiation, demonstrating > 95% dye reduction for RFTi30 and RFTi40, owing to their optimal physiochemical and optical properties. The antimicrobial performance, evaluated against the reduction of indicator microorganisms (total and faecal coliform and Escherichia coli) was in agreement with the results obtained through adsorption analysis, with no bacterial colonies found after treatment. The synthesised sample was reusable for four repeated cycles without significant loss of performance, as demonstrated for RFTi30. This work not only highlights the potential of RFTi gels for water remediation applications, but also proposes the possibility of their application in various other fields such as thermoelectric applications.
- Advisor / supervisor
- Fletcher, Ashleigh
- Resource Type
- DOI
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