Adsorption kinetics and thermodynamics of metal complex acid dyes on silk fabric

Abstract

This study reports the adsorption phenomena of metal complex acid dyes onto silk fabric. Two commercial metal complex acid dyes namely Bestalan Yellow SF and Bestalan Navy SF were adsorbed onto degummed silk fabric. The functional properties and surface morphology of silk fabric were investigated with FT-IR spectroscopy and FE-SEM respectively. The typical absorption band of C = O stretching was found at 1620 cm⁻¹ indicating amide I structure and C-N stretching as well as N-H bending vibrations were observed at 1510 cm⁻¹ suggesting the β-sheet crystallites of amide I and amide II silk proteins. The effectiveness of degumming performance was confirmed by SEM images. The adsorption of dyes by silk fabric was investigated with respect to pH, initial dye bath concentration, and contact time. It was found that the adsorption of dye onto silk fabric was highly influenced by the dye bath pH, initial dye concentration, and contact time. The higher dye adsorption was observed at acidic dye bath condition (pH = 3.5). The adsorption of dye was also increased with the increase of the initial dye bath concentration. The dyes adsorption reached at equilibrium condition after 80 min. The adsorption isotherm and kinetics were also evaluated based on the experimental results. The adsorption pattern fitted well to the Langmuir adsorption isotherm with high correlation coefficient (R²>0.97) for both dyes. The kinetic parameters suggested that the pseudo-second-order model is more suitable compare to the pseudo-first-order model considering the higher regression coefficients ($R^2=\sim 0.99).$ The maximum adsorption of Bestalan Yellow SF and Bestalan Navy SF was found to be 232.5 and 222.2 mg/g respectively. The thermodynamic data were studied at 25, 40 and 60 °C. The change of Gibbs free energy of the system was positive indicating the spontaneous nature of the adsorption. The values of ΔH (-4.68 kJ/mole −3.65 kJ/mole) suggested the exothermic environment and the negative values of ΔS (-0.035 and −0.034 kJ/mole/k) advocated the good interaction between the metal complex acid dyes and silk fabric. The Langmuir adsorption model and pseudo-second-order kinetic suggested that the dyeing of metal complex acid dyes on silk fabric was controlled by ion-exchange chemical reaction.

GRAPHICAL ABSTRACT

Keywords:

• Adsorption
• Langmuir isotherm
• dyeing kinetics
• metal complex dyes
• silk fiber

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors are thankful for the financial support of University Grants Commission (UGC) of Bangladesh through the Research Cell of Mawlana Bhashani Science and Technology University for the fiscal year 2021–2022. The specific research grants number is 3631108. The support from the Oriental Giant Dye and Chemical Ind. Corp. through Bangladeshi supplier also gratefully acknowledged for providing the metal complex acid dyes for the study.