The Effects of Modified Fly Ash on the Structure and Photocatalytic Performance of G-C3N4-based Materials

Graphical The fly ash was treated with Ca(OH) 2 lead to a more complex surface structure. It can regulate the polymerization reaction of dicyandiamide, leading to the formation of the CaFA-CN catalyst with more amino groups and fewer carbon–nitrogen heterocycles. The photocatalytic activity of the obtained CaFA-CN is 4.03 times higher than that of the original g-C 3 N 4 . Regulating the polymerization of graphitic carbon nitride (g-C 3 N 4 ) precursor is regarded as a desirable pathway to boost its photocatalytic activity. However, the current has been seldomly concerned in adjusting the polymerization of g-C 3 N 4 precursor based on the structural characteristics of fly ash (FA). This study manipulates the polymerization reaction of dicyandiamide through alkali treatment of fly ash (KOH-FA, CaOH-FA and NaOH-FA), yielding three g-C 3 N 4 -based composite photocatalysts (CaFA-CN, KFA-CN, and NaFA-CN) with varying degrees of polymerization. Compared to the zeolite structures of fly ash treated with potassium hydroxide (KOH) and sodium hydroxide (NaOH), the fly ash treated with calcium hydroxide (Ca(OH) 2 ) developed calcium silicate hydrate, leading to a more complex surface structure. Isotherm adsorption model analysis revealed that Ca(OH) 2 -FA's adsorption of methylene blue fits the Freundlich model, indicating uneven distribution of active sites. This unevenness results in an uneven collision probability during the high-temperature polymerization of dicyandiamide, leading to incomplete polymerization and the formation of the CaFA-CN catalyst with more amino groups and fewer carbon-nitrogen heterocycles. This incomplete polymerization enabled CaFA-CN to achieve a 55.3% degradation efficiency of methylene blue within 60 minutes. The photocatalytic activity of CaFA-CN is 4.03 times that of the original g-C 3 N 4 (19.4%).