High-Performance Coral Reef-like Carbon Nitrides: Synthesis and Application in Photocatalysis and Heavy Metal Ion Adsorption

Synthesis of carbon nitrides (CN x ) by refluxing under nitrogen exhibited mixed growth mechanisms of oriented attachment and Ostwald ripening, leading to the formation of coral reef-like microstructures from spherical agglomerates. Some phase transformation from β-phase to α-phase CN x occurred upon refluxing for 1.5 h, producing a biphasic CN x . The N content relative to C was determined from CHN elemental analysis, and the presence of C═N and terminal groups (i.e., COOH and NH 2 ) was consistent with the Fourier transform infrared, nuclear magnetic resonance, and X-ray photoelectron spectroscopic results. The sample refluxed for 2.0 h (CN x /2.0 h) had the highest surface area of 24.5 m 2 ·g –1 and displayed enhanced adsorption capacities for methylene blue (MB) molecules and heavy metal ions Pb 2+ (720 mg·g –1 ), Cd 2+ (480 mg·g –1 ), and As(V) (220 mg·g –1 ), which was attributed to the presence of COOH functional groups. CN x samples had a negative surface charge that electrostatically attracted the cationic heavy metal ions as well as MB molecules for subsequent photodecomposition under visible-light illumination. The photocatalytic activity of CN x /2.0 h toward phenol, a common pollutant in aqueous waste, was also demonstrated and a possible photocatalytic route was proposed.