Facile preparation of MnO2 functionalized baker's yeast composites and their adsorption mechanism for Cadmium

Nano-MnO2 functionalized baker's yeast composites (yeast-MnO2) were prepared by direct oxidation of baker's yeast with KMnO4 in acidic condition. The obtained yeast-MnO2 composites were utilized as adsorbents to adsorb Cd2+ in aqueous solution. Various influencing parameters on Cd2+ adsorption by yeast-MnO2 composites, such as initial pH, contact time and initial Cd2+ concentration, were studied. The mechanism of Cd2+ binding by yeast-MnO2 composites was investigated by a number of techniques. SEM, EDX and AFM tests revealed that the yeast cell walls were destructed and the nano-MnO2 particles were successfully deposited on yeast surface. XRD measurement showed the nano-MnO2 particles were at a non-stoichiometric and amorphous phase. Zeta potential analysis showed that KMnO4 treatment resulted in the change of yeast surface charge. Evidence from FTIR spectra confirmed that the exposed functional groups (such as hydroxyl, amino, carboxyl and phosphate groups) and nano-MnO2 particles on yeast surface could be available for synergetic adsorption of Cd2+. Besides, XPS analysis further demonstrated that the Mn2+ ions attached on yeast-MnO2 composites surface were also involved in the adsorption of Cd2+ via ion-exchange behavior.