Effect of Synthesis Temperature on Transient Photoconductivity of g-C3N4 from Urea

Graphitic carbon nitride (g-C3N4) is a material that has been at the forefront of heterogeneous photocatalysis. Many factors, such as the synthesis temperature, have a drastic effect on the photocatalytic ability of g-C3N4. In this study, we utilize terahertz (THz) spectroscopy, an ultrafast probe of transient photoconductivity, to understand the effect the synthesis temperature has on the photoconductivity of g-C3N4. Samples were synthesized at seven different temperatures traditionally used to prepare g-C3N4. X-ray diffraction shows that the number of layers increases with an increasing synthesis temperature. IR spectroscopy shows that as the synthesis temperature increases, the structure begins to resemble the idealized g-C3N4 structure. Optical characterization shows that synthesis temperatures of >600 °C begin to disrupt the structure. THz photoconductivity is the largest for the sample synthesized at 600 °C which is corroborated with the greatest photocatalytic CO2 reduction. This study shows the power that THz spectroscopy has in understanding the fundamental properties in these emerging materials for photocatalysis.