Adsorption of Formaldehyde from Aqueous Solutions Using Metakaolin-Based Geopolymer Sorbents

摘要

Geopolymer samples prepared through alkali activation of metakaolin under varying conditions of synthesis (100 degrees C (14 h); 130 degrees C (3 h); clinoptilolite filler) are employed as formaldehyde sorbents from aqueous solutions. The structure and physicochemical properties of geopolymer sorbents are studied using XRD, XRF, SEM, N-2 adsorption-desorption, and chemical methods. Zeolite A is the main component among the structural components in the synthesized specimens (zeolite ?, hydroxysodalite, and quartz). Addition of the clinoptilolite filler in the synthesis of geopolymers has resulted in a slight increase in their specific surface and pore volume. Geopolymer sorbent specimens display strong adsorption ability in relation to sorbate molecules in aqueous solutions of formaldehyde (0.064-0.366 M). The cation-exchange capacity of the geopolymers, which is 2-3 times as large as that of the natural clinoptilolite specimen, is the probable reason of their strong adsorption capacity to formaldehyde. The nature of the exchanged cation (Na+, Cu2+) determines the magnitude and the predominant mechanism of sorption uptake of formaldehyde (physical adsorption, chemisorption, and complexation). Higher adsorption values of formaldehyde are obtained in the case of - and Cu2+-forms of geopolymer sorbents compared to the Na+-form.