Adsorption of malachite green and methyl violet 2B by halloysite nanotube: Batch adsorption experiments and Box-Behnken experimental design

Abstract

Dyes constitute a significant part of the pollutants in industrial wastewater. In this study, halloysite nanotube (HNT) was used for adsorption of malachite green and methyl violet 2B dyes from the solution. Using batch adsorption experiments and response surface method, parameters affecting adsorption have been optimized. As a consequence of the batch experiments, after 60 min, the adsorption equilibrium state was achieved at 3 g L−1 HNT dosage, 125 mg L−1 dye concentration and natural solution pH. Temperature did not significantly affect the adsorption. The adsorption equilibrium data can be said to have fitted the Langmuir, Freundlich, Dubinin-Radushkevich and Temkin isotherms well for the both dyes. The Langmuir maximum monolayer malachite green and methyl violet 2B adsorption capacities (As) of HNT are 74.95 mg g−1 and 67.87 mg g−1, respectively. Adsorption processes are more consistent with the pseudo-second-order kinetic model. In addition, both intra-particle diffusion and film diffusion are effective as rate-determining steps in adsorption. Thermodynamic calculations showed that the adsorption is exothermic and spontaneous. The regeneration of HNT after adsorption was confirmed in five cycles. By using the Box-Behnken response surface method, the parameters affecting the adsorption process were modeled, the effects of these parameters on the adsorption efficiency were expressed mathematically and the optimum operating parameters were determined.