Adsorption of Direct Red 23 dye from aqueous solution by means of modified montmorillonite nanoclay as a superadsorbent: Mechanism, kinetic and isotherm studies

A novel adsorbent of modified nanoclay was synthesized by covering of alum on the montmorillonite nanoclay (Al/nanoclay). Al/nanoclay was applied as an efficient superadsorbent to remove Direct Red 23 (DR23) from colored wastewater. The adsorbent was characterized by Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, and zeta potential analysis. The effects of various operating parameters, such as contact time, initial dye concentration, adsorbent dose, pH and ionic strength on the performance of adsorption, have been studied. The adsorption experiments showed that pH has an obvious effect on the adsorption efficiency and the highest percentage of DR23 dye removal was observed at pH 2. Zeta potential measurement confirmed that the adsorption mechanism is ascribed to electrostatic interaction between sulfonic groups of the anionic dye and the positive surface charge of the adsorbent. The pseudo-second-order kinetic model and the Langmuir isotherm were found to best describe the DR23 adsorption and the maximum monolayer adsorption capacity at the conditions of pH 2 and the adsorbent dose of 0.05 g/L was 2,500 mg/g. The findings recommend that Al/nanoclay can be successfully used for DR23 dye removal from the colored wastewater.