Abstract
In this work, ZnO nanoparticles, synthesized by the sol-gel process, are immobilized on the external surface of raw kaolinite particles and kaolinite activated by different treatments: heat treatment at 600, 700 and 800 °C; treatment in a dimethyl sulfoxide (DMSO) medium; hot acid treatment (HCl, 6M) under reflux conditions or heat treatment at 800 °C followed by acid treatment. Characterization confirmed the successful immobilization of the nanocrystalline ZnO particles in the hexagonal structure of the different clay matrices. Measurement of the zeta potential showed a sudden inversion of the nature of the surface charge of certain composite materials obtained, through zeta potential values ranging from −31 mV before doping with ZnO to +36 mV after doping. The raw kaolinite and certain composites obtained were tested in batch mode for the adsorption in aqueous solution of three anionic azo textile dyes: a monozoic (Mordant Red 19, MR19), diazoic (Direct Blue 53, DB53) and a triazoic (Direct Green 1, DG1) dye. Compared to raw kaolinite, a linear and rapid increase in the quantity of dye adsorbed is observed during the first 5 min with retention rates around 95% for the best composite materials. The adsorption efficiency strongly depends on the zeta potential of the material: the higher the latter is towards positive values, the better the adsorption capacities of the samples towards these anionic textile dyes.
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