Tungsten oxide modified with carbon nanodots: Integrating adsorptive and photocatalytic functionalities for water remediation

We report for the first time the green synthesis of carbon nanodots (g-CDs) from the peels of T. cucumerina by simple hydrothermal route. An in-situ liquid phase process was adopted for the design of the monoclinic tungsten trioxide (m-WO3)- based nanostructure with g-CDs to obtain a bi-functional g-CDs/m-WO3 system. Characterization techniques, such as X- Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Field Emission Scanning Electron Microcsopy (FESEM), Energy Dispersion X-Ray Analysis (EDX), Fourier Transformed Infra-Red (FTIR), Ultra Violet Defuse Reflectance Spectroscopy (UV-DRS) and Photoluminescence Emission Spectroscopy (PLES) were employed for the morphological, dimensional, chemical and optical analysis. The efficiency in the adsorption of the heavy metal, namely Cd2+ ions of the m-WO3 was found improved in the formated nanocomposite with g-CDs to 81%. The detailed adsorption kinetics study through the adsorption isotherms revealed that the reaction mechanism can be described by the pseudo-second-order kinetic model determined by Freundlich isotherms. Furthermore, the photocatalytic degradation efficiency of the crystal violet dye under the visible light was found significantly enhanced to 95% for the studied composite. The photocatalytic ability of the nanocomposite was found remaining almost intact even after four repeated cycles. A study in the presence of different scavengers suggested that the hydroxyl radicals play a crucial role in determining the photocatalytic activity of the nanocomposite. An improvement in the structural stability and charge carrier separation kinetics was achieved by carefully growing the m-WO3 nanostructures in g-CDs. These resultes have revealed the integrated adsorptive and photocatalytic capabilities of the studied nanocomposites for the waste water treatment.