Adsorption of crystal violet using thiazolium ionic liquid-crosslinked alginate hydrogels: Modelling using...

An effective green hydrogel adsorbent was synthesized through a single-step, one-pot blending and crosslinking of sodium alginate with a novel thiazole-based ionic liquid (tris (2-amino-1,3-thiazolium) hydrogen sulphate sulphate monohydrate) and assessed for its ability to remove cationic dye crystal violet (CV). The Box-Behnken experimental design is used to model CV adsorption onto ImS@Alg hydrogels and to evaluate the interactions among critical process parameters: initial dye concentration (A:50-600 mg/L), solution pH (B:3-10), and temperature (C:298-323 K). Optimal conditions-600 mg/L, pH 10 and 321 K-yielded a theoretical maximum capacity of 565.2 mg/g. ImS@Alg reached equilibrium rapidly within 60 mins, with CV adsorption best described by the pseudo-second-order model. At low concentrations and temperatures, hydrogels fit the Langmuir model best, but at higher concentrations and temperatures, the Temkin isotherm provided a superior fit. The maximum Langmuir adsorption capacities were 296, 360 and 405 mg/g at 298, 310.5 and 323 K, respectively. CV adsorption was endothermic and spontaneous, and it was driven by a combination of electrostatic attraction, π-cation and π-π interactions, with repulsive electrostatic forces also playing a notable role. With its high capacity and short equilibrium time, the green-engineered ImS@Alg holds a great potential for CV adsorption.