Novel Hemicellulose–Chitosan Biosorbent for Water Desalination and Heavy Metal Removal

Abstract

Hemicellulose material is an abundant and relatively under-utilized polymeric material present in lignocellulosic materials. In this research, an alkaline treatment was applied to pinewood (PW), switchgrass (SG), and coastal bermuda grass (CBG) in order to extract hemicelluloses to subsequently produce a novel biosorbent. Alkaline extraction at 75 °C recovered 23% of the biomass as a predominantly hemicellulose material with a number average degree of polymerization of ∼450. These hemicelluloses were grafted with penetic acid (diethylene triamine pentaacetic acid, DTPA) and were then cross-linked to chitosan. The effects of hemicellulose–DTPA concentration, reaction time, and temperature of reaction with chitosan on the resulting salt (sodium chloride, NaCl) uptake and weight loss in saline solutions were determined. A maximum salt uptake for the materials was ∼0.30 g/g of foam biosorbent. The foam biosorbent was characterized by FT-IR spectra, porosity, and dynamic mechanical analysis. Batch adsorption equilibrium results suggest that the adsorption process for salt follows a second-order kinetic model. The hemicellulose-DTPA-chitosan foam biosorbent had uptakes of 2.90, 0.95, and 1.37 mg/g of Pb2+, Cu2+, and Ni2+ ions, respectively, from aqueous medium at initial concentrations of 5000 PPB at pH 5. The cross-linked hemicellulose–DTPA–chitosan material has good potential for environmental engineering applications.