A facile strategy for fabrication of nano-ZnO/yeast composites and their adsorption mechanism towards lead (II) ions

Highlights: • Nano-ZnO/yeast composites were fabricated by alkali hydrothermal method. • Nano-ZnO was in-situ achieved and anchored on the yeast surface. • Alkali and hydrothermal process cause more exposed funcitional groups on yeast. • Nano-ZnO/yeast composites show higher Pb²⁺ adsorption ability than pristine yeast. • Nano-ZnO and exposed functional groups synergistically participate in adsorption. - Abstract: Nano-ZnO/yeast composites were successfully fabricated by one-step alkali hydrothermal method, and their adsorption properties for Pb²⁺ ions were also evaluated. Various influencing parameters of nano-ZnO/yeast composites, such as initial pH, contact time and initial Pb²⁺ concentration were investigated, respectively. The maximum adsorption capacity of nano-ZnO/yeast composites for Pb²⁺ (31.72 mg g⁻¹) is 2.03 times higher than that of pristine yeast (15.63 mg g⁻¹). The adsorption mechanism of nano-ZnO/yeast composites was studied by a series of techniques. Scanning electron microscopy (SEM) showed that nano-ZnO is evenly deposited on yeast surface. Atomic force microscopy (AFM) analysis exhibited that the yeast surface is rougher than that of pristine yeast. Energy dispersive X-ray detector (EDX) and X-ray diffraction (XRD) indicated the existence of nano-ZnO on yeast surface. Additionally, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) measurements further illustrated that alkali hydrothermal method causes not only the generation and anchorage of nano-ZnO on yeast surface but also the exposure of more functional groups (such as amino, carboxyl groups etc.) on yeast surface, both of which could adsorb Pb²⁺ via synergistic effect.