Waste-to-microporous framework: Al/Si fractionation of coal fly ash coupled with waste PET conversion for separated synthesis of high-porosity MIL-53(Al) and ZSM-5 toward efficient dyes and CO2 capture

This study demonstrates a sustainable strategy for synthesizing MIL-53(Al) and ZSM-5 zeolite through dual-waste synergy using coal fly ash (CFA) and waste polyethylene terephthalate (PET). A sequential alkaline fusion-acid leaching protocol selectively fractionated CFA into aluminum-rich solutions and silica residues, while alkaline hydrolysis of PET liberated terephthalic acid (PTA) as organic ligands. The Al 3+ -PTA coordination under solvothermal conditions produced MIL-53(Al)(CFA-PET) exhibiting well-defined 1D rhombic channels with a high BET surface area (1303 m 2 ·g −1 ), whereas hydrothermal crystallization of silica residues yielded ZSM-5(CFA), which formed spherical aggregates composed of 100 nm nanosheets with 89.9 % yield and a surface area of 311 m 2 ·g −1 . Structural advantages were evidenced by exceptional adsorption performance: MIL-53(Al)(CFA-PET) achieved 96.24 % methylene blue removal at pH 7 (250 mg·L −1 ), outperforming rhodamine B (30.8 %) and methyl orange (66.4 %), as well as reagent-synthesized MIL-53(Al) Che (91.99 %). Both materials demonstrated exceptional CO 2 capture capacities (4.23 mmol·g −1 for MIL-53(Al)(CFA-PET) vs. 2.37 mmol·g −1 for ZSM-5(CFA) at 273 K/1 bar), attributable to MIL-53′s flexible framework enabling dynamic pore adjustment and ZSM-5′s rigid microporous channels favoring molecular sieving. This work establishes a closed-loop strategy for converting industrial and plastic wastes into functionally differentiated porous materials through element-targeted process design.