Development of a photocatalytic titanium dioxide/chitosan nanocomposite for the potential treatment of textile wastewater

Abstract

Unsustainable human progress is driving rising water consumption, moreover our actions are heavily polluting vital global water sources, endangering life on Earth. A major contributor to the global problem of water pollution is the textile industry. This industry pollutes water systems with dyes that have detrimental effects on aquatic life, to the ecosystems as well as humans. Unfortunately, conventional wastewater treatments have certain limitations that lower their effectiveness whilst being costly. This research was driven by the motivation a more cost-effective solution for water treatment. A photocatalytic nanocomposite consisting of Titanium Dioxide TiO2 nanomaterial (NM) immobilised in a chitosan matrix was identified as such a solution to this global problem. The aim was to develop a photocatalytic efficient TiO2/Chitosan nanocomposite to decolourise the textile dye. The development process involved determining which TiO2 NM size and TiO2 loading concentration achieved the best photocatalytic performance against methylene blue dye. Six TiO2 NM sizes were tested. Three were purchased from Nanograin (NG1, NG2, and NG3) and the other three were produced by sol-gel synthesis (1X, 3X, and 8X). The sol-gel technique also involved varying the water content to determine if this influenced the size of the final TiO2 NM. The shape and phase composition of all TiO2 NM samples were the near-spherical and anatase to reduce variable factors in the development process. The phase composition was chosen to be anatase for most effective photocatalytic performance as highlighted in literature and previous studies. For this study, characterisation techniques such as scanning electron microscopy, X-ray diffraction, dynamic light scattering, and ultraviolet-visible spectroscopy were used to determine the best combination of TiO2 NM sample and TiO2 concentration and understand why the nanocomposite had the highest photocatalytic performance. From the analysis and data recorded, the most effective TiO2/chitosan nanocomposite was found to be the NG2 TiO2 NM sample, a 0.2 w/v% TiO2 loading concentration, and an energy bandgap of 3.26 eV as it achieved the best photocatalytic performance against multiple textile dyes. This was due to multiple factors such as size, phase and light penetration that allowed for effective photocatalysis initiation by UV-A illumination. This nanocomposite also had good photocatalytic durability for longer-use application against multiple textile dyes such as Congo red, methylene blue, methyl orange and bromocresol green.