title: Heterostructured Metaloxide Photocatalytic (Copper Oxide and Titanium Oxide) for Degradation and Removal of Water Organic Pollutants
Creators: name: Chandrabose, Gauthaman
Publisher: name: The Open University
Year: 2022

description: Metal oxides with favourable light absorption properties and charge transport characteristics play wide application as a photocatalyst. Titanium oxide and Copper oxide are the two major earth abundant metal oxides, and this dissertation is aimed to synthesize the heterostructured copper oxide and titanium oxide for the application of water treatment by enhancing their photocatalytic activity. Metal oxides are treated with atmospheric pressure plasma or by altering the structural level in nano size region to enhance the photocatalytic activity. <br><br> Cupric oxide (CuO) thin film has found widespread application as a low-cost material for photo catalytic applications. High surface wettability is a key factor to achieve enhanced efficiency in these catalytic applications. Here, we report a fast and environment friendly route to fabricate super hydrophilic CuO thin films using a low power (5–10 W) atmospheric pressure plasma jet (APPJ). With APPJ treatment for 5 min, the CuO surface transforms from hydrophobic to super-hydrophilic with increase in catalytic activity. APPJ introduces anisotropy in the crystal structure and creates unique three-dimensional surface morphology with distinct surface chemical and electronic features. The treated films exhibited a higher rate of photo degradation of Methylene Blue and phenol indicating efficient charge separation. <br><br> An environment friendly alternative to epitaxially grown process of copper oxide nanowires (NWs) on copper substrates using single step atmospheric pressure plasma jet assisted oxidation is used. NWs of average length 300 nm are grown rapidly in 5 minutes along with transforming the surface to superhydrophilic. This method introduces defects in the nanowire structure which is otherwise difficult to achieve due to the highly isotropic nature of nanowire growth. High resolution transmission electron microscopy reveals vacancies and structural defects such as lattice twinning and kinks. Copper oxide NWs have an excellent degradation activity towards organic pollutants Methylene Blue. <br><br> Two-dimensional (2D) Molybdenum disulfide (MoS<sub>2</sub>) has become one of the most exciting areas of research for adsorbents due to its high surface area and abundant active sites. Mainly, 2D MoS<sub>2</sub> show promising removal of textile dye pollutants by adsorption process, but it shows high affinity for anionic type of dyes, that limits its performance in mixed dye pollutants treatment. Herein, we demonstrate an integrated approach to remove mixed dye pollutants (anionic and cationic) concurrently by combining adsorption and photocatalysis process. We synthesize MoS<sub>2</sub>/TiO<sub>2</sub> nanocomposites for different weight percentages 2.5, 5, 10, 20, 30 and 50 wt% of pre-synthesized flower-like MoS<sub>2</sub> nanoparticle by a two-step hydrothermal method. We demonstrate a new process of two-stage adsorption / photocatalysis using high wt% of MoS<sub>2</sub> (Stage-I) and low wt% of MoS<sub>2</sub> (Stage-II) nanocomposites. The proposed two-stage integrated adsorption and photocatalysis process using 50% and 2.5% of MoS<sub>2</sub> coated TiO<sub>2</sub>, respectively showed complete removal of methylene blue dye ~5 times faster than conventional single-stage (adsorption or photocatalysis) water treatment process. Furthermore, the feasibility of the proposed two stage method in mixed dye pollutants removal (anionic and cationic) showed excellent performance even in doubling the dye pollutant concentration. This work brings a deeper insight into understanding the morphology and concentration of 2-D MoS<sub>2</sub> in MoS<sub>2</sub>/TiO<sub>2</sub> nanocomposite in tackling mixed dye pollutants and the possibilities of applying in textile dyeing industries wastewater treatment plants.