Removal of cationic and anionic dyes from aqueous solution with magnetite/pectin and magnetite/silica/pectin hybrid nanocomposites: kinetic, isotherm and mechanism analysis

Abstract

Novel adsorbents, magnetite nanoparticles modified with pectin shell and silica/pectin double shell, were fabricated and tested for single dye and dye mixture adsorption from water samples. Cationic dyes methylene blue (MB) and crystal violet (CV) and anionic dyes methyl orange (MO) and Eriochrome black T (EBT) were employed to assess dye removal efficiency. The influence of pH, amount of adsorbent, initial dye concentration and contact time was investigated. Results indicated that the optimum pH for removing cationic dyes was 8.0 and 2.0 for anionic dyes. The kinetic studies showed rapid sorption dynamics following a second-order kinetic model. Dye adsorption equilibrium data were fitted well to the Sips isotherm for cationic and anionic dyes. The maximum monolayer capacity, (q_max) for MB, CV, EBT and MO was calculated from Sips as 197.18, 180.29, 65.35 and 26.75 mg g⁻¹ respectively for magnetite/silica/pectin NPs and 168.72, 140.49, 72.35 and 27.22 mg g⁻¹ respectively for magnetite/pectin nanoparticles. For dye mixture adsorption, a new HPLC assay was proposed for quantitation of dyes in treated samples. The results came in accordance with that of single dye adsorption where the magnetite/pectin NPs showed preferred adsorption to anionic dyes while the magnetite/silica/pectin NPs had more affinity to cationic dyes. Thus, our proposed NPs can be used as cheap and efficient adsorbents for removal of cationic and anionic dyes from aqueous solutions.