Sorption of tartrate, citrate, and EDTA onto chitosan and its regeneration applying electrolysis

摘要

The equilibrium isotherm data obtained by the sorption of tartrate, citrate, and EDTA onto chitosan were analyzed using Langmuir and Freundlich equations. The process fits best the Langmuir equation. Kinetic investigations showed that the sorption process obeys the pseudo-second-order kinetic equation. Sorption and desorption peculiarities, FTIR investigations, and measurements of molecular weight enable one to hypothesize that sorption proceeds along with the electrostatic interaction between the positively charged -NH3+ groups of chitosan and the negatively charged -COO- of carboxylic acids in the formation of amide bonds between the -NH2 groups of chitosan and the -COOH groups of the carboxylic acid. Electrolysis under galvanostatic conditions in a mixture of chitosan with a 0.1 mol L-1 Na2SO4 solution enables one to destroy the amide bonds in the cathode compartment of the electrochemical cell and to anodize organics in the anodic compartment. The choosing of relevant conditions of electrolysis enables one to obtain chitosan with properties (deacetylation degree, molecular weight, and sorption ability) similar to those of initial chitosan. After electrolysis the regenerated chitosan possesses the same or even higher ability for sorption of the carboxylic acids as the initial chitosan. (C) 2008 Elsevier Ltd. All rights reserved.