Novel remediation technologies using macroscopic graphene-based materials for wastewater treatment

Wastewater treatment is not a new concept as water bodies around the world have been polluted since the dawn of industrialisation. With the increase in human activities, including domestic, industrial, and commercial practices, water pollution levels continue to rise due to aqueous contaminants. In addition, rapid industrialisation and recent human progress have given rise to a new form of pollution - emerging contaminants (ECs) - which are highly resistant to biodegradation and can travel across the world. While traditional wastewater treatment methods, such as adsorption, can combat these chemicals, their production of sludge is a major drawback that leads to secondary contaminants. Advanced oxidation processes (AOPs) have emerged as a prominent choice among other wastewater remediation technologies owing to their ability to convert emerging organic pollutants to less toxic compounds through complete oxidation, such as mineral salts, CO2, and H2O. AOPs rely on the generation of reactive radicals to attack pollutants, however, the performance of AOPs for environmental remediation depends on the availability of a suitable catalytic material that can provide sufficient active sites for completing the redox reactions and can be efficiently recovered and reused. Recently, graphene and its derivatives, such as reduced graphene oxide (rGO), have demonstrated high efficiencies for the catalytic oxidation of aqueous pollutants, thanks to their extremely large specific surface area, superior interfacial charge transfer properties, and excellent functional chemistry. The self-assembly of rGO into three-dimensional (3D) macrostructures further enhances its catalytic properties, making it a promising candidate for large-scale operations. Taking advantage of 3D graphene-based materials, this thesis presents novel remediation technologies for wastewater treatment. Macroscopic graphene-based materials were fabricated and modified through various techniques, such as structural manipulation, heteroatom doping and integration with other carbonaceous materials, to enhance their catalytic activity in AOPs. Different facile techniques such as coagulation and cross-linking, freeze-casting and annealing, and hydrothermal and hydraulic pressing were employed to fabricate 3D macrostructures. The physical and chemical properties of the prepared materials were characterised using advanced techniques such as Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, electron microscopy, and Fourier-transform infrared spectroscopy, among others. The catalytic activity of the prepared materials was evaluated by applying them in AOPs using peroxygens (peroxymonosulfate - PMS and peroxydisulfate - PS) to remove 4-hydroxybenzoic acid (HBA) and sulfamethoxazole (SMX) from wastewater. The primary performance indicator in this thesis was the extent of modification, where optimal modification conditions were identified to maintain the best catalytic properties. The influence of various reaction parameters on the reaction kinetics was investigated, and electron paramagnetic resonance coupled with selective radical quenching was used to identify the radical and free radical species generated during the AOPs. The mineralisation ability of the prepared materials was evaluated using ultra-high performance liquid chromatography. The results showed that the prepared macroscopic graphene-based materials exhibited excellent catalytic activity for the removal of ECs from wastewater using AOPs. This PhD study provides a fundamental basis for the development of efficient and sustainable graphene-based materials for real-world applications in wastewater treatment