The Dye-Contaminated Water Treatment Efficiency of Two Types of Geopolymers: A Comparative Study of Structural, Microstructural and Adsorption Properties

This research presents a comprehensive comparative study between two types of geopolymers differentiated by their adopted aluminosilicate precursors concerning mechanical performance, dye removal efficiency from aqueous media, and structural and morphological properties. Compressive strength measurements were performed to evaluate the mechanical properties of the geopolymers studied. At the same time, their efficiency in removing crystal violet (CV) dye was tested by applying batch-mode adsorption as a water treatment technique. The structural and microstructural properties of the aluminosilicate precursors used and their derived geopolymer samples were characterized by several physicochemical analysis techniques. Mechanical tests highlighted that the fly ash-based geopolymer (FA-GP) possessed approximately twice the compressive strength of the metakaolin-based geopolymer (MK-GP). In contrast, tests of the adsorbents’ efficiency in removing the CV dye from an aqueous medium revealed that MK-GP removed the dye somewhat more effectively than FA-GP. The findings of the analytical characterization pointed to the formation of a sodium aluminosilicate hydrate gel as the principal binder phase in both geopolymer matrices. Microstructural and textural properties explained the difference in mechanical and adsorption performance between the two geopolymers, as both matrices were mainly formed of an amorphous geopolymer gel with a different meso-type porous nature for FA-GP, in contrast to MK-GP, which is characterized by larger pore sizes. The kinetic and isothermal readings for CV-dye adsorption by MK-GP and FA-GP fit well, respectively, with the pseudo-second-order, Langmuir, and Temkin models. Overall, this comparative study brings added value to construction and contaminated water treatment applications, with excellent results in terms of mechanical performance, efficiency in removing organic contaminants, and low synthesis costs.