Adsorption of cationic dye from water using thermo-sensitive colloid composed of methylcellulose and sodium alginate

Abstract

The adsorption behaviors of methylene blue (MB) by a thermo-sensitive colloid composed of sodium alginate and methylcellulose (TSC-SA/MC) have been investigated. The results showed that the dosage of SA had an important effect on the adsorption capability of TSC-SA/MC. The maximum of adsorption capability appeared at m SA/m MC of 0.3:1, and among all the differences in adsorption capability between 30 and 60 °C, 61 mg·g−1 was the maximum adsorption difference appeared at m SA/m MC of 0.3:1. The adsorption capability of TSC-SA/MC increased with pH from 2 to 11, decreased with temperature from 30 to 70 °C. The adsorption data were not well fitted by Langmuir, Freundlich, Temkin, or Dubinin-Radushkevich model, suggesting the adsorption of MB on TSC-SA/MC did not belong to a single adsorption style. The maximum adsorption capacity of adsorption isotherm data was 1098.5 mg·g−1. The adsorption of MB by TSC-SA/MC fitted the pseudo-second-order model, and the main resistances for MB adsorption by TSC-SA/MC involved the external mass transfer, intraparticle mass transfer, and sorption on active site. The ΔH of MB adsorption by TSC-SA/MC was −48.26 kJ·mol−1, and the ΔS was −143.00 J·K−1·mol−1. The ΔG indicated that the adsorption could change from a spontaneous process to a nonspontaneous process with temperature increase. Both physical and chemical adsorption took place in the MB adsorption process. Fourier transform infrared spectroscopy (FTIR) spectra of filter cakes of TSC-SA/MC before and after adsorption of MB showed that the adsorption process for MB by TSC-SA/MC had a quite complicated mechanism, and the successful adsorption involved many chemical groups.