Abstract: To explore high value-added utilization pathways of fly ash, the mesoporous structure of silicon dioxide extracted from fly ash (FA-SiO₂) was utilized to restrict the dicyandiamide (DCDA) thermal degradation process. This produced chemically bonded interacting composite photocatalysts of FA-SiO₂ and graphitic-phase carbon nitride (g-C₃N₄). Compared with the spherical silicon dioxide prepared using tetraethyl orthosilicate (TEOS-SiO₂), the mesoporous structure of FA-SiO₂ allowed DCDA to react in a smaller space, which facilitated the transformation of DCDA to melamine by the thermal degradation kinetics of FA-SiO₂/DCDA. This ultimately boosted the formation of an N-atom-removed triazine ring structure and a multistage structure combining lumps and rods in the composite photocatalysts of g-C₃N₄ and FA-SiO₂, which led to a higher visible-light utilization efficiency, a suitable valence-band position, and the photocatalytic activity for methylene blue reaching 3.56 times that of g-C₃N₄. The findings indicate that mesoporous FA-SiO₂ has the potential to improve the structural and photocatalytic properties of g-C₃N₄-based materials.

Key words: Fly ash (FA); FA-SiO₂; g-C₃N₄-based materials; Structural and photocatalytic properties

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