Generation of a pH-blind/pH-sensitive alternating surface on a hydrophobic resin by mussel-inspired chemistry and investigating the effect of surface modification on the adsorption dynamics of some anionic colorants

Abstract

The effect of a surface modification process known as "mussel-inspired modification" on the adsorption dynamics of hydrophobic adsorbent, namely XAD1180, was studied based on equilibrium adsorption data. In the study, three anionic colorants (i.e., Sunset yellow, SY; Allura red, AR; and Tartrazine, TZ) were used as the model compounds. The role of some experimental parameters, such as pH (4–7), ionic strength (0.01–0.50 mM) and colorant concentration (25–125 mg/L), were investigated to determine optimal conditions leading to the highest adsorption. Equilibrium adsorption data were obtained under optimal conditions by stepwise frontal analysis method (SFA) and modeled on the basis of some common adsorption isotherm models (i.e., Langmuir and Freundlich). The adsorption dynamics of the XAD1180 resin have been found to vary significantly after PD coating. After the PD coating process, it was found that the highly hydrophobic background material, XAD1180, gained a pH-sensitive character, thereby replacing a sharp decrease in the adsorption capacity at pH = 5.0–7.0 with an increase in pH = 4.0. Another dramatic effect of the PD coating was observed with Langmuir monolayer adsorption capacities, so that the PD layer was found to increase the monolayer saturation capacity of the XAD1180 (from 8.0 to 17 µmol/g for SY, from 7.7 to 9.9 µmol/g for AR, and from 5.3 to 9.1 µmol/g for TZ). It was also deduced from the Freundlich isotherm parameter, KF, that there was, in general, a clear increment in the overall effect of adsorption capacity and the average affinity after mussel-inspired surface modification process.