Adsorption of methyl violet from aqueous solution by halloysite nanotubes

In the paper the clay minerals of halloysite nanotubes (HNTs) were used as adsorbent to remove cationic dye, methyl violet (MV), from aqueous solution. The effects of contact time, initial concentration, adsorbent dose, initial pH, temperature and ionic strength were investigated. The adsorbent exhibited rapid adsorption rate and high adsorption capacity of 113.64 mg/g for MV. Batch kinetic experiments showed that the adsorption fitted pseudo-second-order kinetic model well with correlation coefficients greater than 0.999. The adsorption capacity of the adsorbent increased significantly with the increase of initial concentration, decreased with the increase of ionic strength, and varied little with pH. The equilibrium isotherm data were well described by the Langmuir model. Thermodynamic parameters of ΔG0, ΔH0 and ΔS0 indicated the adsorption process was spontaneous and exothermic. The regeneration of HNTs could be realized by simple calcinations and the recovered HNTs could be used again for MV removal. Due to its low cost, high adsorption capacity, fast adsorption rate and simple regenerated method, HNTs could be used as an effective adsorbent for cationic dye removal.

Research highlights
► Halloysite is an economically viable clay material.
► The adsorbent HNTs exhibited rapid adsorption rate and high adsorption capacity for MV.
► The regeneration of HNTs could be realized by simple calcinations.