Silica functionalized with 1-propyl-3-methylimidazolium chloride as an efficient adsorbent for the removal of Eosin Yellow and Reactive Blue 4

• Silica modified with methylimidazolium cations demonstrates the high affinity to anionic dyes.
• Binding of dyes Eosin Yellow and Reactive Blue 4 occurs due to the ion exchange.
• Adequate models of the dye binding have been found and verified.
• Examined adsorption systems are involved but can be described by the Langmuir model.

Silica chemically modified with ionic liquid 1-propyl-3-methylimidazolium chloride has been examined as the material for the removal of anionic dyes Eosin Yellow (EY) and Reactive Blue 4 (RB4) from solutions. The material has the specific surface area 220 m2/g and average pore diameter 12.4 nm. Equilibrium and kinetics of the dye binding have been studied at 293–313 K using the batch mode measurements. Adsorption systems attain equilibrium within ∼40–50 min. The maximum adsorption occurs from mildly acidic (EY) and neutral (RB4) solutions, effective sorption capacities reach 2 × 10−5 mol/g. The binding has been shown to proceed according to the ionic exchange mechanism. The adequate equilibrium models involve fixation of dye anions predominating in solutions at studied pH values. The model fitting parameters have been determined by the non-linear regression. The models have been verified by independent measurements of the dyes adsorption from solutions with varied concentrations of strong electrolytes. The dye adsorption is spontaneous and favored by the decrease of temperature. Kinetics of the binding corresponds to the pseudo-first-order model; the intraparticle diffusion is not the rate-limiting step. The high degrees of the dye removal can be easily reached, and the adsorbent is regenerated in a simple way. The obtained results demonstrate that silica modified with 1-propyl-3-methylimidazolium chloride is a promising material for the removal of anionic dyes.

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