Sorption of Aromatic Organic Contaminants by Biopolymers: Effects of pH, Copper (II) Complexation, and Cellulose Coating

Sorption of hydrophobic organic compounds (HOCs) (i.e., pyrene, phenanthrene, naphthalene, and 1-naphthol) by original and coated biopolymers was examined. Lignin yielded nonlinear isotherms due to its glassy character. Except for pyrene, cellulose showed linear isotherms for other compounds, indicating a partitioning dominant mechanism. Sorption of 1-naphthol by lignin decreased with increasing pH, attributed to both the increased pi e theta-pi e theta repulsion and weakened hydrogen bonds, while the affinity reduction of cellulose for 1-naphthol with increasing pH resulted from only the decrease in H-bonding due to its absence of benzene ring. Complexation of lignin with Cu2+ increased the sorption affinity for phenanthrene (2.6 times) and slightly enhanced its isotherm nonlinearity. For 1-naphthol, lignin-Cu2+ complex had a much higher sorption capacity (7 times)than the original lignin, accompanied bythe increased isotherm nonlinearity. Cellulose-coated lignin showed increased sorption affinity and more pronounced nonlinearity for 1-naphthol than the lignin-Cu2+ complex. In comparison, cellulose coating exhibited little effect on sorption affinity for phenanthrene relative to the lignin-Cu2+ complex. Isotherm nonlinearity of coated lignins increased with increasing cellulose coating, indicating more condensed domains produced, supported by an increase (from 68.9 degrees C for the original lignin to 82.4 degrees C for the highest cellulose coating level) in glass transition temperature (Tg). Results of this study highlightthe importance of structure, polarity, surface O-containing functional groups, and surface charges of biopolymers in controlling HOC sorption.