Increasing the Efficiency of Adsorption of Cationic Dyes on Mechanoactivated Montmorillonite

The adsorption of the cationic dyes rhodamine B (RhB) and methylene blue (MB) on natural montmorillonite (MM) and its mechanically activated form (MAMM) has been studied. The mechanical modification of MM was carried out in a planetary mill using zirconium grinding bodies (MM to grinding media mass ratio 7.5 : 1) at a rotor speed of 1500 rpm for 3 min. The adsorption efficiency significantly increases for both dyes in the case of MAMM compared to that of MM: by 26.9% for RhB and 29.8% for MB. The physicochemical properties of adsorbents were compared using small-angle and wide-angle X-ray diffraction; ²⁹Si, ²⁷Al, and ²³Na MAS NMR; scanning electron microscopy; IR spectroscopy; TG-DSC thermal analysis; low-temperature nitrogen adsorption/desorption; and static laser light scattering. The adsorption properties of MAMM were improved due to changes in the structural and textural characteristics during mechanical activation, leading to delamination of aluminosilicate layers, improvement of porometric parameters, and diminishing of clay particles in the aqueous dispersion. In addition, for MAMM, the aluminosilicate layers retained high crystallinity and were partially dehydroxylated; and the ζ potential slightly shifted toward smaller negative values.