Synthesis and characterization of alumina/talc nanocomposite by sol-gel method and its application for removal of bromocresol green from aqueous solution

In this research, alumina/talc nanocomposite was synthesized for the first time and used to remove bromocresol green as a dye pollutant from aqueous solution. The synthesized nanocomposite was identified and confirmed by Fourier transform infrared spectroscopy, X-ray diffraction analysis, scan electron microscopy, energy dispersive X-ray spectroscopy and nitrogen adsorption and desorption isotherm. The adsorption experiments of bromocresol green dye on alumina/talc nanocomposite were designed and performed based on the design of experiment software by response surface method and central cube design. In the design of experiments, factors including pH, initial concentration of bromocresol green, alumina/talc nanocomposite dose, contact time and temperature were investigated. The maximum adsorption percentage obtained 98.43% at optimal conditions: pH = 2.06; in the initial concentration, 8.83 mg/L; adsorbent dose, 0.035 g; contact time, 32 min; and temperature, 25 °C. Among Langmuir, Freundlich and Temkin isotherms, the desired adsorption followed the Langmuir isotherm model with a regression coefficient of 0.9955 and the maximum adsorption capacity of 147.06 mg/g. The thermodynamic investigation of the adsorption process indicated that all three quantities of Gibbs free energy, enthalpy, and entropy changes were negative and therefore, the process was spontaneity, exothermic, and reducing disorder, respectively, especially at 25 °C. In addition, among four kinetic models, zero order, pseudo first order, pseudo second order and Higuchi model, the most appropriate kinetic model is the pseudo-second order model with a regression coefficient of 0.9992.