Adsorption at Organic Surfaces IV—Adsorption of Sulphonated Azo Dyes by Chitin from Aqueous Solution

Lobster‐shell chitin has been used in quantitative adsorption studies with sulphonated azo dyes in aqueous solutions, mainly under acid conditions. The extent of adsorption has been correlated with the dye structures. The mechanism of adsorption appears to be largely one of physical association between the aromatic residues of the dye and the molecular chains of the chitin, hydrogen bonding in acid solutions being unimportant. When inorganic acid is present, one sulphonate group in the dye anion takes part in ion exchange with inorganic anions at the cationic centres in chitin. Additional sulphonate groups appear to remain uncombined with the substrate and to reduce the affinity of the dye.