Uranium removal by novel graphene oxide-immobilized Saccharomyces cerevisiae gel beads

To evaluate its ability to absorb dissolved uranium (VI), the waste biomass of Saccharomyces cerevisiae was immobilized using different agents, including Ca-alginate (Ca-SA), Ca-alginate with graphene oxide (GO), polyvinyl alcohol (PVA, 5% or 10%, w/v)-SA-GO in CaCl2-boric acid solution. The experimental results showed that graphene oxide at 0.01% (w/v) could enhance the performance of the immobilized cells. The yeast gel beads prepared with 5% PVA-1% SA-2% yeast-0.01% GO-2% CaCl2-saturated boric acid (4#) generally showed the better physical-chemical properties such as higher tolerance to the unfavorable environmental conditions. Moreover, the 4# gel beads exhibited more stable capacity for U(VI) sorption and desorption at various conditions, such as pH in the range of 3-9. A pseudo second-order kinetic model could describe the kinetics of U(VI) sorption onto the 4# gel beads (R-2 = 0.96). The Langmuir, Freundlich, Tempkin and Sips models could be used to describe U(VI) sorption by the 4# gel beads, with the R2 being 0.90, 0.83, 0.96, 0:97, respectively. The Sips maximum capacity of 4# gel beads was 24.4 mg U/g dry weight. The desorption efficiency of U(VI) adsorbed onto the 4# gel beads was 91%, 73% and 40% by 0.1 M HNO3, 0.1 M HCl and 0.1 M NaOH, respectively. However, the 4# gel beads exhibited lower U(VI) sorption capacity than the raw yeast cell (Sips maximum capacity of 35.6 mg U/g). The immobilized Saccharomyces cerevisiae using SA, PVA and/or GO showed obvious changes in the molecular vibration of functional groups such as carboxyl, amide and hydroxyl groups compared with the raw yeast cells, according to FTIR analysis. The SEM-EDX analysis showed that U(VI) was adsorbed unevenly on the cellular surface. Carboxyl and hydroxyl.groups may be involved in U(VI) binding by yeast cells. (C) 2016 Elsevier Ltd. All rights reserved.