Construction of g-C₃N₄/Al₂O₃ hybrids via in-situ acidification and exfoliation with enhanced photocatalytic activity

Highlights: • Ultrathin g-C₃N₄/Al₂O₃ hybrids are prepared via in-situ reaction. • The structure modification role of in-situ formed HNO₃ for g-C₃N₄ is found. • The ultrathin g-C₃N₄ nanosheets are formed by the acidified melamine and Al(OH)₃. • In-situ calcination of melamine and Al(OH)₃ benefits the contact of C₃N₄ and Al₂O₃. • The activity of g-C₃N₄/Al₂O₃ is 16.6 times that of pristine g-C₃N₄ in degrading RhB. - Abstract: Homogeneous ultrathin g-C₃N₄ nanosheets/Al₂O₃ heterojunctions are synthesized using melamine and Al(NO₃)₃ via in-situ reaction and the following thermal polymerization approach. The in-situ reaction between melamine and Al(NO₃)₃ results in the existence of HNO₃-acidified melamine and Al(OH)₃ aggregates via the hydrolysis of Al(NO₃)₃. After thermal polymerization, the aggregates are converted to g-C₃N₄/Al₂O₃ composites. The thermal polymerization of acidified melamine and the support effect of aluminum hydroxide for g-C₃N₄ during the calcination process lead to highly dispersed amrophous Al₂O₃ on ultrathin g-C₃N₄ nanosheets, which is beneficial for the separation of photogenerated electron-hole pairs in the heterojunction. The degradation rate for Rhodamine B (RhB) over the most activie sample is 16.6 times than that of pristine g-C₃N₄ under visible light irradiation, which can be attributed to the high specific surface area, highly dispersion of amorphous Al₂O₃ on ultrathin g-C₃N₄ nanosheet, and the effective electrons transfer from g-C₃N₄ to the amorphous Al₂O₃.