Modified Clays as an Efficient Adsorbent for Brilliant Green, Ethyl Violet and Allura red Dyes: Kinetic and Thermodynamic Studies

Clay minerals can effectively adsorb contaminants from aqueous effluents due to their good adsorption and high cation exchange capacity. However, naturally occurring clay materials possessing hydrophilic features are not especially effective for the removal of organic pollutants. Therefore, in the present work the issue of hydrophilicity is tackled by modification of the clay (Pakistan origin) to prepare organoclays. Hexadecylpyridinium chloride, cetyltrimethylammonium bromide, and sodium dodecyl sulfate were used as clay modifiers. Changes in the basal spacing of clay layers after modification with surfactants were determined through XRD analysis. Chemical compositions of the clay and organoclays were determined by FTIR spectroscopy. Surface morphology of the as-prepared organoclays was assessed from SEM analysis. The modified clays (organoclays) were tested for their ability as potential adsorbents for three dyes from water: brilliant green, ethyl violet and allura red. All three modified clays showed high adsorption characteristics by removing (>90 %) of all three dyes with an adsorption capacity ranging from 35 to 85 mg/g. The time-dependent adsorption experiments showed that the rates of adsorption of dyes on organoclays were fast, adsorbing maximum amounts of dyes ranging from 15 to 80 mins of contact time. The adsorption kinetic study revealed that the dye removal process is mainly governed by a pseudo-1st order mechanism. Thus, surfactant-modified clays are an excellent choice as cost-effective and efficient adsorbents for the purification of water from dye contaminants.