Advanced treatment of wastewater effluents by multi-functional carbon nanotube-TiO2 nanotube membranes

Abstract

Recently, the coupling of TiO2-photocatalysis with a membrane separation process has been perceived as a powerful tool for the recycling of wastewater effluents. While the membrane has the simultaneous task of supporting the photocatalyst as well as acting as a selective barrier for the species to be degraded, the photocatalyst degrades the organic compounds with the added advantage of mitigating membrane fouling. The focus of this thesis is to combine the specific features of TiO2 nanotubes with the unique properties of CNTs to design a multi-functional membrane for the enhanced removal of effluent organic matters (EfOMs) in wastewater effluents. Firstly, the kinetics of photocatalytic degradation of model organic compounds by TiO2 NPs were studied, and the experimental conditions for the enhancement of photocatalytic degradation efficiency were optimised. The photocatalytic reactivity and stability of TiO2 NPs were affected in the presence of natural organic matter (NOM). Secondly, TiO2 nanotube arrays (TNAs) were successfully fabricated via anodic oxidation of Ti substrates and their geometrical characteristics were optimised by controlling the synthesis parameters for enhancement of the photocatalytic removal efficiency of model organic compounds. Finally, multi-functional CNT/TiO2 nanotube membranes were fabricated via chemical vapour deposition (CVD) and anodic growth of TNAs on a porous Ti sheet. The performance of the hybrid CNT/TiO2 nanotube membrane (CNT/TNM) for removal of 4CBA was experimentally evaluated in a continuous filtration system under UV-A irradiation. The surface properties and the performance of the TNM were notably influenced by incorporation of CNTs. The CNT/TNM showed enhanced performance in removal of model compound compared to the TNM, which was attributed to the higher adsorption capacity of well-incorporated CNT/TNM.