Biosynthesis, characterization of zinc oxide nanoparticles and investigation of cadmium removal potential

In this thesis, new biopolymer beads were produced and the synthesized biopolymeric beads were functionalized and used to remove cadmium (Cd2+) from aqueous solutions, which is one of the important causes of environmental pollution. For this purpose, firstly, zinc oxide (ZnO) nanoparticles (ZnO-NP) were obtained by the green synthesis method using basil plant extract. The produced nanoparticles were characterized by ultraviolet visible region (UV-GB) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). Then, a new biopolymer bead was developed by coating the nanoparticles with sodium alginate (ZnO-NP@ALJ), thus improving the performance and stability of ZnO nanoparticles and sodium alginate. The biosynthesized beads were further functionalized by using ethylenediamine tetraacetic acid (EDTA) and tannic acid. The adsorption abilities of three different beads obtained in this way were compared. The central composite design (CCD) method combined with the surface response methodology (RSM) was used to optimize the adsorption parameters. This method determined optimum levels for independent variables such as pH, temperature, and amount of adsorbent affecting the adsorption processalyses were performed and determined that the obtained regression coefficients were high. The validation of the methods used was carried out with Fisher and t-tests. Langmuir, Temkin, and Freundlich models from isotherm equilibrium studies were used to elucidate the adsorption nature of the ZnO doped polymeric composite material in the removal of Cd2+ ions. Pseudo-first order, pseudo-second order, and intraparticle diffusion models were used to evaluate the kinetic data. It was determined that the most suitable model for the removal of Cd2+ ions was the pseudo-second order model. Because of thermodynamic studies, it was concluded that adsorption occurs spontaneously. The optimum conditions for the three composite materials produced were determined as 5 for pH, 32.5 °C for temperature and 5 mg for adsorbent amount. In these optimum conditions, (ZnO-NP@ALJ)-TA was found to be the material with the highest adsorption capacity with 35.9 mg g-1.