In Situ Synthesis and Characterization of Graphitic Carbon Nitride/Metakaolin Composite Photocatalysts Using a Commercial Kaolin

Abstract

Kaolin-based graphitic carbon nitride (g-CNx) composite photocatalysts were synthesized from a urea precursor using a commercial kaolin. Structural characterization by X-ray diffraction and infrared spectroscopy (FTIR) verified the successful thermal polycondensation of g-CNx along the thermal dehydroxylation of kaolinite to metakaolin at 550 °C. The g-CNx content of the composites were estimated by thermogravimetry and CHN analysis, ranging from ca. 87 m/m% to ca. 2 m/m% of dry mass. The addition of kaolin during the composite synthesis was found to have a significant effect: the yield of in situ formed g-CNx drastically decreased (from ca. 4.9 m/m% to 3.8–0.1 m/m%) with increasing kaolin content. CHN and FTIR indicated the presence of nitrogen-rich g-CNx, having a specific surface area of 50 m2/g, which synergistically increased after composite synthesis to 67–82 m2/g. Estimated optical band gaps indicated the affinity to absorb in the visible light spectrum (λ < 413 nm). Photocatalytic activity upon both UV and artificial sunlight irradiation was observed by hydroxyl radical evolution, however, without the synergistic effect expected from the favorable porosity.