Biological sequestration and retention of cadmium as CdS nanoparticles by the microalga Scenedesmus-24

Biological sequestration of cadmium (Cd) and retention of adsorbed cadmium as cadmium sulphide (CdS) nanoparticles inside the cell by a lipid-producing green algae Scenedesmus-24 is reported. The microalga was able to grow in the growth media containing 30 mg L-1 of cadmium without any growth inhibition. Adsorption of Cd(II) was dependent on the pH of the medium, initial concentration of cadmium, density of algal biomass (biosorbent dose), and contact time. The adsorption follows Langmuir isotherm pattern with an estimated maximum cadmium adsorption capacity at 50 mg g(-1). The kinetics of adsorption followed Lagergren's pseudo-second-order model. FTIR analysis revealed the presence of different functional groups on the algal biomass which may be responsible for adsorption of Cd(II). After adsorption, the bound metal ions were retained in the microalgal biomass as CdS nanoparticles. Presence of CdS nanoparticle was confirmed by XRD and TEM analysis. The results of the present study conclusively demonstrate that the microalga Scenedesmus-24 may be a promising candidate for sequestration of cadmium from cadmium polluted water and also its recovery as precious CdS nanoparticles.