Hydrothermal-Assisted Fabrication of Eco-Friendly ZnO/Tapioca Nanocomposite Films with Enhanced Structural and Optical Properties

The growing demand for environmentally sustainable materials has encouraged the development of biodegradable polymer nanocomposites with improved functional properties. In the present study, ZnO/tapioca starch nanocomposite films were fabricated by combining hydrothermally synthesized ZnO nanoparticles with a tapioca starch matrix through a solution-casting process. The influence of ZnO incorporation on the structural, morphological, chemical, and optical characteristics of the films was investigated using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, UV-Visible spectroscopy, and photoluminescence (PL) analysis. XRD analysis confirmed the formation of crystalline hexagonal ZnO in the nanocomposite films. The average crystallite size decreased from 60 nm for pristine ZnO to 39 nm and 33 nm for ZnTp1 and ZnTp2, respectively, suggesting that the starch matrix restricted crystal growth during film formation. FESEM images revealed a corresponding reduction in particle size and a more uniform particle distribution with increasing tapioca content. FTIR spectra showed the characteristic absorption bands of both ZnO and tapioca starch without the appearance of new chemical bonds, indicating that the interaction between the inorganic nanoparticles and the polymer matrix was predominantly physical and governed by hydrogen bonding. The optical behaviour of the nanocomposite films was influenced by the incorporation of ZnO nanoparticles. UV-Visible measurements showed enhanced absorption in the ultraviolet region together with a slight decrease in the optical band gap from 3.56 to 3.49 eV. Photoluminescence spectra exhibited characteristic near-band-edge emission along with visible defect-related emission associated with intrinsic ZnO defects, indicating changes in the defect structure after incorporation into the starch matrix. Overall, the results demonstrate that hydrothermal synthesis combined with solution casting provides an effective route for preparing biodegradable ZnO/tapioca nanocomposites films with improved structural and optical characteristics.