Sorption of organic contaminants by biopolymer-derived chars

Sorption of phenanthrene and naphthalene by chitin and cellulose, as well as these biopolymer-derived chars, was examined. Carbon contents were much higher in the chars than their respective biopolymers, and nitrogen was dramatically accumulated in the chitin-derived chars. After charring, sorption of these two compounds was greatly increased, which was attributed to the newly created surface area, porosity, and aromatic components. The aromatic carbon content of the biopolymer chars increased with an increase in the charring temperature. Sorption of phenanthrene and naphthalene to chitin and cellulose was dominated by partitioning. However, after charring, sorption of these two compounds became much more of an adsorption process, because of the newly created surfaces and micropores. The maximum mass sorption capacity of phenanthrene and naphthalene by the original biopolymers and their chars was positively correlated with their surface areas, suggesting that active sorption sites were largely on the surfaces of chars. At low solute concentrations, sorption of phenanthrene and naphthalene by biopolymer chars was dominated by the micropore-filling mechanism; with an increase in the solute concentration, sorption of these two compounds by biopolymer chars shifted to a surface-sorption-dominant process. The maximum mass sorption capacity and K-OW normalized sorption amount of phenanthrene were lower than those of naphthalene by the biopolymers and their chars, showing the influence of molecular dimension on sorption. This study demonstrates the significantly enhanced sorption of hydrophobic organic compounds by highly polar biopolymers through charring and the joint roles of surface area, porosity, and surface functionalities of biopolymer-derived chars in governing sorption.