Optimization of Toluidine Blue removal from aqueous solution by iron terephthalate metal-organic framework

Dyes are one of the larger group of pollutants discharged into the water bodies, making it unsuitable for drinking, irrigation, and industrial usages. Toluidine blue dye (TB), a cationic thiazine dye, is widely used as a colorant in textile industry, medical science and biotechnology. It has harmful effects on living organisms and environment. Hence, removing the dye contents from effluents before disposal is essential. In the current work, the removal of TB dye was investigated by the stable iron terephthalate metal-organic framework (MOF-235). Metal-organic framework (MOF), a highly crystalline organic- inorganic hybrid solid material, due to large surface area, tunable pore size, and excellent chemical stability is showing great promise for adsorption of different water pollutants. MOF-235 was synthesized hydrothermally and used for removing TB dye from aqueous solution. Resulting sample was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and FT-IR analysis. A Box–Behnken design was used to identify the effective factors on the removal efficiency of TB (R%). Experimental results indicated that MOF-235 can remove more than 98 % of TB under optimum conditions of a dosage of 0.0125 g MOF-235, pH 4.5, initial dye concentration of 150 mg L-1). The adsorption data was analyzed by using the Langmuir, Freundlich and Dubinin-Radushkevich isotherm models and was found to give better results with respect to Langmuir equation. The maximum monolayer adsorption amount (qmax) was about 180.44 mg g-1. Moreover, the adsorption kinetic data were analyzed according to the first and second-order models. kinetic studies show that adsorption of TB onto MOF-235 was fitted to the second-order adsorption model with two-step diffusion process