Synthesis and characterization of a novel amphoteric adsorbent coating for anionic and cationic dyes adsorption: Experimental investigation and statistical physics modelling

A new adsorbent (amphoteric adsorbent coating: AAC) based on composite coating with amphoteric functionality was employed to study the adsorption mechanism of Brilliant Green (BG) and Acid Red 1 (AR1) dyes. This adsorbent was prepared as a coating and supported on cotton cloth by application of a facile method, based on the combined use of smectite-based clay powder, acrylic polymer emulsion (APE) and cationic polyelectrolyte. The novel adsorbent coating was characterized by FE-SEM, EDX, zeta potential and FTIR analysis. Subsequently, the equilibrium adsorption isotherms of AR1 and BG dyes were performed and analyzed at different temperatures (from 303 to 343 K) in order to achieve a thorough comprehension of dyes adsorption mechanism. To this aim, a multilayer model with saturation was developed using statistical physics theory and was applied as a sophisticated tool for data interpretation. The correlations of experimental and theoretical results allowed to understand two distinct behaviours for the adsorption of AR1 and of BG dyes, which were related to the formation of two different adsorbed layers and a variable number of layers, respectively. Based on the parameter of the adopted model, the adsorption geometry of dyes has been described at different temperatures. Interestingly, the adsorption process was energetically typified by estimation of the adsorption energies, which indicated that the adsorption of AR1 and BG dyes were exothermic and endothermic, respectively.