Alginate/PAMAM dendrimer - Halloysite beads for removal of cationic and anionic dyes.

The alginate beads have been widely used for dye removal. However, most of the systems described in literature refer to one type of dyes and the adsorbents of cationic ones are dominant. In this study, the composite alginate beads were prepared and characterized. The system was obtained by encapsulation of polyamidoamine - functionalized halloysite nanotubes in alginate (Alg/Hal_PAMAM beads). The adsorptive properties of the beads towards model dyes - cationic methyl green (MG) and anionic sunset yellow FCF (SY) - were investigated with reference to pH, adsorbent dose, time, dye concentration and temperature. The adsorption capacities were improved compared to pure alginate beads. The kinetic data were best correlated to the pseudo-second-order model. The intraparticle diffusion model showed two (MG) or one (SY) adsorptive steps of mass transport. The Freundlich isotherm model was suitable for describing the adsorption process thus the composite beads were characterized by heterogeneous sites. The thermodynamic parameters indicated the spontaneous and endothermic nature of the adsorption process. It was also found that the process was favorable. Additionally, the beads could be reused with satisfactory removal efficiency in several cycles. Therefore, Alg/Hal_PAMAM beads could be considered as promising material for simultaneous removal of cationic and anionic dyes.