Fusion-Assisted Hydrothermal Synthesis of Technogenic-Waste-Derived Zeolites and Nanocomposites: Synthesis, Characterization, and Mercury (II) Adsorption

Abstract

This study presents the synthesis of zeolites derived from coal fly ash (CFA) using the fusion-assisted alkaline hydrothermal method. The zeolites were synthesized by combining CFA and NaOH at a molar ratio of 1:1.2 under fusion temperatures of 500, 600, and 700 °C. Subsequently, the obtained zeolites were subjected to further modifications through the incorporation of magnetic (Fe3O4) and silver (Ag0) nanoparticles (NPs). The Fe3O4 NPs were introduced through co-precipitation of Fe(NO3)2 and FeCl3 at a molar ratio of 1:1, followed by thermal curing at 120 °C. On the other hand, the Ag0 NPs were incorporated via ion exchange of Na+ with Ag+ and subsequent reduction using NaBH4. The synthesized porous materials exhibited the formation of zeolites, specifically analcime and sodalite, as confirmed by X-ray diffraction (XRD) analysis. Additionally, the presence of Fe3O4 and Ag0 NPs was also confirmed by XRD analysis. The elemental composition analysis of the synthesized nanocomposites further validated the successful formation of Fe3O4 and Ag0 NPs. Nitrogen porosimetric analysis revealed the formation of a microporous structure, with the BET surface area of the zeolites and nanocomposites ranging from 48.6 to 128.7 m2/g and pore sizes ranging from 0.6 to 4.8 nm. The porosimetric characteristics of the zeolites exhibited noticeable changes after the modification process, which can be attributed to the impregnation of Fe3O4 and Ag0 NPs. The findings of this research demonstrate the effectiveness of the fusion-assisted method in producing synthetic zeolites and nanocomposites derived from CFA. The resulting composites were evaluated for their potential application in the removal of mercury ions from aqueous solutions. Among the samples tested, the composite containing Ag0 NPs exhibited the highest adsorption capacity, reaching 107.4 mg of Hg2+ per gram of composite. The composites modified with Fe3O4 NPs and Ag/Fe3O4 nanocomposites displayed adsorption capacities of 68.4 mg/g and 71.4 mg/g, respectively.