A simple method to prepare poly(amic acid)-modified biomass for enhancement of lead and cadmium adsorption

A modified biomass of baker's yeast was prepared by grafting poly(amic acid), which was obtained via reaction of pyromellitic dianhydride (PMDA) and thiourea, onto the biomass surface at 50 C for 4 h. This method was simpler than other reported chemical grafting methods. The presence of poly(amic acid) on the biomass surface was verified by FTIR, X-ray photoelectron spectroscopy (XPS) and microscope analyses, and the amount of carboxylate and amide groups in the biomass surface were found to be 1.36 and 0.7 mmol g(-1) through potentiometric titration. Compared with the pristine biomass, the adsorption capacity of the modified biomass increased 15- and 11-fold for Cd2+ and Pb2+, respectively. According to the Langmuir equation, the maximum uptake capacities (q(m)) for lead and cadmium were 210.5 and 95.2 mg g(-1), respectively. The kinetics for cadmium and lead adsorption followed the pseudo-second-order kinetics. FTIR and XPS demonstrated that carboxyl, amide, and hydroxyl groups were involved in the adsorption of lead and cadmium, and the adsorption mechanism for the two metal ions included ion exchange, electrostatic interaction and complexation. (c) 2006 Elsevier B.V. All rights reserved.