Maleic acid modified cellulose for scavenging lead from water

Macro, micro and nano fibrillary cellulose with sodium maleate groups was synthesized by the reaction of cellulose with maleic anhydride followed by sodium exchange of protons. In the present work, we demonstrate that these carboxylic groups act as chemisorbants towards toxic heavy metal ions present in contaminated water. The effects of the operating parameters such as resident time, temperature, pH, ion concentration and ion nature on chemisorbability were estimated for a given cellulose carboxylate. The kinetic results for the chemisorption of Pb²⁺ ion were indicative of an intra particle diffusion model and pseudo second order reaction. The chemisorption is well explained by a Freundlich isotherm model showing a multilayer chemisorption, heterogeneous surface and interaction between chemisorbed molecules. The chemisorption capability was enhanced upon decreasing the dimension of the cellulose fibril. The efficiency depended also on the nature of metal ions, dictated by the stability of the geometry of the resultant complex. The maximum chemisorption capacities of macro, micro and nano forms of sodium cellulose-maleate for Pb²⁺ were 20 mg/g, 40 mg/g and 115 mg/g, respectively at pH of 5.5. The ion exchanged nano-cellulose maleate could be regenerated by sodium chloride solution without loss of efficiency even after 7 cycles.