Mechanistic study of cationic dye interactions with clay-polymer dispersions via metachromatic effect, aggregation, and surface charge



Interactions for a series of aqueous dispersions of a clay, Laponite, and nonionic difunctional triblock copolymer, Pluronic L62, with two cationic dyes, crystal violet and brilliant green, are studied using UV–vis spectroscopy, dynamic light scattering (DLS), and electrophoretic mobility (EPM) to better understand the adsorption mechanisms. Different concentrations for clay, 0.1–2.0 g/L, mixed with polymer, 0.125–0.5 g/L to produce an organoclay, were tested with a fixed dye concentration, 2.0 × 10−5 mol/L. The aggregation states of the cationic dyes interacting with the clay–polymer dispersions were characterized by UV–vis absorbance. The dyes changed aggregation states from monomer to dimer and higher aggregate states upon addition to varying Laponite–polymer dispersion concentrations. DLS was used to understand the adsorbed polymer and dye interactions on the clay particle showing longer relaxation times for the largest aggregates observed from UV–vis absorbance. The EPM was used to characterize the surface charge of the clay relative to the polymer–dye interactions, which showed that the surface charge approached zero as the dyes interacted with clay–polymer dispersions. The most significant changes occurred with a reduction in light scattering intensity and longer relaxation decay at 0.1 g/L Laponite and 0.5 g/L Pluronic L62 concentrations in the presence of cationic dyes. The study of the clay–polymer–dye interactions help to better understand and design chemical templates for removal of contaminates in waste-water treatment. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40141.