Preparation Of Bio-adsorbents Nanocomposites Based On Yeast And Chitosan And Their Application In Cd²⁺ And Methylene Blue Treatment

A severe water resource crisis exists due to a large amount of water contaminated by heavy metals and dyes, which results from the striking development of some industries in our country such as electroplateing, steel production, dyeing and printing industry etc.. The wastewater, contained heavy metals and dyes, is a big threat to the environment as well as the humans. Therefore, researchers have paid more attention to the research on disposing heavy metal ions and dye molecules in wasterwater. However, the conventional methods are sometimes restricted by some factors such as the technique, economy and secondary pollution. Recently, the utilization of biomass materials and nanometer metal oxides with the function of adsorption and magnetism for wastewater treatment has been a research hotspot.In this paper, 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 Cd2in 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.A novel adsorbent, ethylenediaminetetraacetic dianhydride (EDTAD)-modified magnetic chitosan (EMC), was fabricated using glutaraldehyde as a cross-link agent. The obtained EMC was characterized by SEM, XRD, potentiometric titration and FTIR. The results showed that nano-Fe3O4 with granular morphology were steadily integrated with chitosan and EDTAD was successfully modified on the surface of chitosan. The adsorption properties of EMC for methylene blue were then evaluated. Factors affecting the uptake behavior such as pH, contact time, initial concentration of methylene blue and temperature were investigated. The optimal adsorption conditions were determined as pH 6.0, methylene blue concentration 300 mg L-1, contact time 30 min. The adsorption capacity in the optimal condition was 113.257 mg g-1. The adsorption process followed the Sips isotherm model and the pseudo-second-order kinetic model.