Combined photocatalytic-adsorptive removal of water contaminants using a biologically prepared CdS-diatomite nanocomposite

Cadmium sulfide nanoparticles smaller than 10 nm were synthesized using Bacillus licheniformis and characterized by X-Ray Diffraction (XRD), Transmission Electron Microscope (TEM), Differential Thermogravimetry (DTG), Differential Scanning Calorimetry (DSC), and Photoluminescence (PL) spectroscopy. The biologically synthesized nanoparticles were stabilized on the purified diatomite powder. The purification process included acidic leaching and calcination steps. Proper fixation of the semiconducting nanoparticles was proved by electron microscope images, and elemental analysis. Maximum immobilization of 19.64 mg/g (nanoparticles/diatomite) was obtained under the determined optimum condition. The combined adsorptive-photocatalytic capability of the manufactured nanocomposite was examined by eliminating methylene blue and chromium (Cr VI) under ultraviolet (UVA)-visible (360–450 nm) radiation. In the absence of light and after the first 30 min, more than 90% of both selected contaminants were adsorbed by the nanocomposite. At pH = 9 and the initial dye concentration of 10 mg/l, 27.7% of the remained methylene blue was degraded due to the photocatalytic activities of the manufactured nanocomposite. Similarly, at pH = 2 and Cr (VI) concentration of 100 mg/l, 76.2% of the remained ions were eliminated. Among the several kinetic models, the pseudo-first-order kinetic model showed the best correlation with the experimental results gained from the photocatalytic-adsorptive processes.