Effect of mesoporous FA-SiO2 extracted from fly ash on the structural and photocatalytic properties of g-C3N4-based materials

To explore high value-added utilization pathways of fly ash, the mesoporous structure of silicon dioxide extracted from fly ash (FA-SiO 2 ) was utilized to restrict the dicyandiamide (DCDA) thermal degradation process. This produced chemically bonded interacting composite photocatalysts of FA-SiO 2 and graphitic-phase carbon nitride (g-C 3 N 4 ). Compared with the spherical silicon dioxide prepared using tetraethyl orthosilicate (TEOS-SiO 2 ), the mesoporous structure of FA-SiO 2 allowed DCDA to react in a smaller space, which facilitated the transformation of DCDA to melamine by the thermal degradation kinetics of FA-SiO 2 /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-C 3 N 4 and FA-SiO 2 , 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-C 3 N 4 . The findings indicate that mesoporous FA-SiO 2 has the potential to improve the structural and photocatalytic properties of g-C 3 N 4 -based materials.