Optimized safranin adsorption onto poly(vinylidene fluoride)-based nanofiber via response surface methodology

Abstract

This study is a comparative work on the surface interactions and adsorptive properties of poly(vinylidene fluoride) nano-fibers (PVDF NFs) and UiO-66/PVDF NFs prepared by using the electro-spinning method. X-ray diffraction (XRD), fourier transform infrared (FT-IR), scanning electron microscope (SEM), thermogravimetric analysis (TGA), and energy-dispersive X-ray (EDX) have been applied to confirm and determine physicochemical changes during preparing and to modify PVDF NFs. The results of XRD, FT-IR, SEM, TGA, and EDX show significant changes in porosity that happened on the surface of adsorbents. The PVDF NFs and UiO-66/PVDF NFs have been applied to remove safranin O (SO) dye in aqueous solution as a cationic azo dye. Three essential factors of the initial concentration of SO, contact time, and pH were optimized by using the Box-Behnken response surface methodology (BBRSM). By using PVDF NFs, the maximum equilibrium adsorption capacity of 28.201 mg g−1 is obtained at optimal adsorption parameters of a contact time of 117.972 min, initial concentration of dye 34.896 mg L−1and pH of 9.975. And also by applying UiO-66/PVDF NFs, the maximum equilibrium adsorption capacity of 25.896 mg g−1 is achieved at optimal parameters of a contact time of 58.47 min, initial concentration of 34.83 mg L−1 and pH of 7.2, which clearly shows that the addition of metal-organic frameworks (MOFs) to the PVDF NFs is reduced the contacted time by half. The adsorptive experimental data were correlated by the famous isotherm and kinetic models. The extrapolated data showed that the SO dye adsorption on the PVDF NFs and UiO-66/PVDF NFs follow better the Langmuir isotherm and the pseudo-second-order kinetic model. Moreover, the thermodynamics result of the nano-fibers shows that, the adsorption process is exothermic and spontaneous. The high efficiency and adequate adsorption ability in the SO removal suggest that the UiO-66/PVDF NFs could be effectively applied as a good applicant in the water filtration of azo dyes.