Characterization Of Modified Baker's Yeast And Its Adsorption Behavior For Heavy Metals And Dyes

Using some materials, including glutaraldehyde, amino acid and poly(amic acid) to modify the surface of baker's yeast, the adsorption capacity of modified biomass were increased and showed different selectivity. In this paper, the modified biomass surface was characterized by FTIR, XPS and microscope. The effect of pH, adsorption time, initial concentration and temperature on adsorption capacity was tested. The regenerated capacity of the modified biomass and adsorption mechanism of the pollution in wastewater were also studied.1. The adsorbent, which is prepared by glutaraldehyde and baker's yeast, showed that the aggregation of cells was increased with the increase of glutaraldehyde concentration. The adsorption capacity for Cd2+ of the cross-linked biomass, which was prepared by different concentration of glutaraldehyde, was investigated. The cross-linked biomass, which was prepared with 1.0% glutaraldehyde is the best chosen. At 25℃, pH 6.0~7.0, the adsorption equilibrium of Cd2+ was carried out after 30min, and the metal adsorption data were fitted with the Langmuir isotherm. The maximum adsorption capacity of the cross-linked biomass was 8.59mg·g-1,which was 2.16 times of baker's yeast.2. At 50°C, in anhydrous DMF, cross-linked biomass was grafted with poly(amic acid) which was prepared via reaction of pyromellitic dianhydride and arginine. The product treated with NaOH solution was noted as poly(amic acid) modified biomass(Ⅰ). The results of FTIR, XPS and microscope indicated that the hydroxyl groups in the biomass surface and poly(amic acid) were involved by the graft reaction. The results of the metal adsorption showed that the adsorption equilibriums of Ni2+ and Pb2+ were carried out after 30min among pH6.0~7.0. The metal adsorption data were fitted with the Langmuir and Freundlich isotherms, and the former one had a better fit. In Langmuir adsorption isotherm, the maximum adsorption capacity of Ni2+ and Pb2+ were found to be 49.78 and 202.8mg·g-1 respectively, which were about 9.80 and 10.7 times of the cross-linked biomass. The loaded biomass was regenerated by EDTA solution. When the modified biomass was used repeatedly, the loss of adsorption capacity <10 %, and the recovery of Pb2+ is more than 90 %. In the simulated wastewater, the recovery of Ni2+ and Pb2+ were more than 90%.3. Using arginine and glutaraldehyde to modify Baker's yeast, and the presence of arginine on the modified biomass surface was verified by XPS and microscope. The graft reaction was only aggregated the cells and did not change the form of the cells. The adsorption system of sunset yellow and tartrazine by the arginine modified biomass were endothermic and spontaneously, and the adsorption capacity increased with the decrease of pH, the increase of dyes concentration, adsorption time and temperature, respectively. At 25℃, pH2.0, the adsorption capacity of modified biomass for sunset yellow and tartrazine is 362.8 and 269.3mg·g-1, respectively. In pH6.0, the equilibriums of biomass were carried out after 40h and the constant v0 in kinetics was changed from 10.45 and 16.01 to 65.6 and 86.6mg·g-1·h-1 after modified, the adsorption isotherms of modified biomass obeyed Langmuir model and the maximum adsorption capacity were found to be 146.4 and 107.1mg·g-1, respectively. At 25℃,ΔG°of the modified biomass for sunset yellow and tartrazine adsorption system were calculated -4.70 and -5.11KJ·mol-1. The adsorption systems of sunset yellow and tartrazine were mainly chemically adsorbed by arginine modified biomass, the reaction was via theδ-guanidino on the lateral chain of arginine with positive charge and the chromophoric groups with negative charge.4. The XPS spectra of poly(amic acid) modified biomass(Ⅱ) shows the hydroxyl groups in the biomass surface and the anhydride groups in poly(amic acid) were involved in the graft reaction, and a large number of carboxylate and amide groups were introduced to the biomass surface. The image of SEM indicated that this modified method was not changed the biomass surface greatly. And the potentiometric titration showed the concentration of carboxylate and amide groups in the biomass were 1.36 and 0.7mmol·g-1, respectively. The results of basic magenta and methylene blue adsorption showed that the adsorption systems were endothermic and spontaneously, adsorption capacity is steady among pH4.0~11.0 and decreased with the increase of ion strength. The equilibriums were carried out after 40 and 20min respectively, the adsorption isotherms obeyed Langmuir model and the maximum adsorption capacity were found to be 335.9 and 694.2mg·g-1, respectively. Poly(amic acid) modified biomass(Ⅱ) adsorb methylene blue which was not affect by butylrhodamine B, but adsorb with basic magenta simultaneous.