Adsorption kinetics and thermodynamic studies of lac dye on polydopamine-coated silk yarn

Abstract

In this study, silk yarn was treated with polydopamine nanoparticles (PDA) formed in situ by oxidation of a dopamine solution in the presence of oxygen. The adsorption kinetics of lac dye on the PDA-coated silk yarn at different temperatures was investigated. The values of the dye adsorption rate constant (k) at different temperature were calculated using the modified Cegarra-Puente equation. The results showed that the dye adsorption rate constant (k) and the diffusion coefficient (D) increased with an increasing temperature, which was consistent with a kinetically controlled diffusion process. The activation energy (Ea) was found to be 51.2 kJ mol–1. The adsorption isotherm of lac dye on the PDA-coated silk yarn at pH 2.50 was studied in a batch system. The findings revealed that the adsorption isotherm could be described by the Langmuir isotherm (R2 > 0.99). The results indicated that the pretreatment of silk yarn with PDA, followed by dyeing with an aqueous solution of lac dye and then post-mordanting with alum, exhibited color fastness to light and washing at rating levels of 4 and 3-4, respectively.