A new route to fabricate high-efficient porous silicate adsorbents by simultaneous inorganic-organic functionalization of low-grade palygorskite clay for removal of Congo red

Abstract

Abstract A series of porous quaternized silicate (QS) adsorbents with superior adsorption capabilities for anionic dye Congo Red (CR) were prepared by synchronous inorganic and organic functionalization of natural low-grade palygorskite (Pal) via a facile one-pot hydrothermal process. The Pal and its associated minerals were restructured as new porous silicate adsorbents under the action of the inorganic salts of sodium silicate and magnesium sulfate, and simultaneously the quaternary ammonium groups were in-situ introduced into the silicates using cetyltrimethylammonium bromide (CTAB) or dodecyltrimethylammonium bromide (DTAB) as donors of quaternary ammonium groups. The adsorption capacities of the QS adsorbents enhanced as the increment of quaternization degree until equilibrium is reached. The silicate adsorbents with the organification degree of 16.46% (for CTA-QS-1.2) and 13.32% (for DTA-QS-1.2) showed the best adsorption capacities of 664.29 ± 3.92 mg/g and 684.01 ± 8.50 mg/g for CR, respectively, which are far away higher than that of raw Pal (51.22 ± 2.85 mg/g), the magnesium silicate adsorbents without quaternization (78.69 ± 0.54 mg/g), and the CTAB-modified Pal prepared by commonly used method (145.10 ± 3.61 mg/g). The fitting results of thermodynamics and kinetic models revealed that the adsorption process of the silicate adsorbents for CR obeys Freundlich and pseudo-second-order models very well, which suggests a chemical interaction and multilayer adsorption mechanism. In addition, the electrostatic attraction and hydrogen-bonding interaction contribute more to the adsorption capability than specific surface area. This paper provides a new route to fabricate high-efficient silicate adsorbent by restructure of naturally abundant low-cost Pal clay for deep decontamination of anionic dye-polluted water.