Adsorption of hazardous dyesindigo carmine and acid red on nanofiber membranes

Abstract

Through an electrospinning process, thiol-functionalized polyvinyl alcohol (PVA)/SiO₂ composite nanofiber membranes were synthesized as adsorbents. The adsorption of indigo carmine and acid red onto the nanofiber membranes was investigated. The effect of contact time, initial concentration, pH, dosage, temperature, the adsorption equilibrium and thermodynamic parameters were studied. The adsorption equilibrium was reached within 20 min. The initial concentration, pH and the temperature played important roles on the adsorption capacity onto the nanofiber membranes. Increase of the initial concentration could effectively increase the adsorption capacity. The best adsorption pH was 2 for indigo carmine and acid red. Higher temperatures were favourable for the adsorption. The maximum indigo carmine adsorption capacity was 266.77 mg g⁻¹ for 500 mg L⁻¹ indigo carmine and 211.74 mg g⁻¹ for 315 mg L⁻¹ acid red at pH 2 and 25 °C. The adsorption isotherm studies showed that the adsorption of the two dyes fitted well with Langmuir, Freundlich, and Redlich–Peterson adsorption models, while the Redlich-Peterson model achieved the best results. The kinetic adsorption shows that the pseudo-second-order model fits the adsorption process of indigo carmine while the pseudo-first-order model fits the adsorption process of acid red.