Influence of the hydrophilic/hydrophobic nature of polyetheramines on the interaction between amine–alcohol–silicate hybrids and anionic dyes for effective water cleaning

Abstract

This work reports on the preparation of cross-linked amine–alcohol–silicate hybrid matrixes with tunable hydrophilic/hydrophobic domains from end-group functionalized polyetheramines (PEO and PPO) and 3-glycidoxypropyl-trimethoxysilane (GPMS) by the sol–gel route as efficient adsorbents for retaining anionic species; the resulting hybrid matrixes were designated as PEO500-GPMS and PPO400-GPMS, respectively. This work also discusses how the nature and swelling properties of the polyethers PEO and PPO, investigated by small-angle X-ray scattering (SAXS) and in situ SAXS measurements, affect the way PEO500-GPMS and PPO400-GPMS interact with the anionic dye, Rose Bengal (RB). The use of polyetheramines of different polyether nature afforded hybrid matrixes with distinct capacity and mechanisms of anionic species adsorption. Compared with the literature and PPO400-GPMS, PEO500-GPMS had higher RB adsorption capacity, which indicated that the latter matrix is a highly efficient adsorbent and good candidate in the field of anion binding for applications in water treatment. The in situ UV-vis spectroscopy results and the pseudo-first order, pseudo-second order, and Morris–Weber intraparticle diffusion models allowed us to propose a three-step mechanism for RB adsorption onto PEO500-GPMS. The first step is short-range diffusion of RB molecules to the external surface of PEO500-GPMS, followed by water uptake (hydrogel behavior) by the matrix which accelerated the adsorption and diffusion process, and finally a dynamic equilibrium stage leading to the higher adsorption capacity. The thermodynamic studies provided information about the inherent energetic changes taking place in PEO500-GPMS and PPO400-GPMS during RB adsorption. The use of a distribution coefficient (D) helped to define the strength of the interaction between the hybrid matrixes and the dye in water. Comparative DSC studies showed that the presence of RB in the hybrid matrixes increased the rigidity of the polymeric backbone. We demonstrated that hybrid xerogels efficiently remove a series of anionic dyes such as Congo Red, Ponceau S, Indigo Carmine, Eosin Y, Brilliant Green and Fluorescein. The excellent water uptake, swelling behavior and the impressive anionic binding ability of PEO500-GPMS make it a highly efficient adsorbent for water purification and treatment.