An investigation of the adsorption of organic dyes onto organo-montmorillonite

Adsorption of organic dyes, crystal violet (CV), orange II (OR), and phenol red (PR), onto organo-clay was investigated in a batch type reactor at 25 degreesC. The organo-clay was obtained by modifying montmorillonite with a cationic surfactant, cetylpyridinium (CP), and used as an adsorbent. We conducted experiments to find out the effect of pH and solvent on the adsorption affinity of organic dyes for the modified montmorillonite. From the results, we observed that the adsorption capacity on the organo-montmorillonite decreased in the order CV > OR > PR at all pH values examined (pH 3, pH 7, and pH 11). It mostly resulted from the difference in solubility and the molecular weight of the solutes. In a 30-V/V % methanol/water cosolvent solution the adsorption capacity of the dyes decreased compared to that in aqueous solution. In addition, the adsorption capacities of OR and PR on CV-montmorillonite were lower than those on CP-montmorillonite. These results might show that partitioning by CP was superior to the adsorption by CV to hold the solute molecules on the surface of montmorillonite. The Langmuir and Redlich-Peterson (RP) models were used to represent the adsorption equilibria of the organic dyes.