Synthesis of carbon nitrides (CNx) 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 CNx occurred upon refluxing for 1.5 h, producing a biphasic CNx. 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 NH2) was consistent with the Fourier transform infrared, nuclear magnetic resonance, and X-ray photoelectron spectroscopic results. The sample refluxed for 2.0 h (CNx/2.0 h) had the highest surface area of 24.5 m2·g–1 and displayed enhanced adsorption capacities for methylene blue (MB) molecules and heavy metal ions Pb2+ (720 mg·g–1), Cd2+ (480 mg·g–1), and As(V) (220 mg·g–1), which was attributed to the presence of COOH functional groups. CNx 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 CNx/2.0 h toward phenol, a common pollutant in aqueous waste, was also demonstrated and a possible photocatalytic route was proposed
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