Transient FTIR measurements were performed on g-C3N4 at a resolution of a few nsec.
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Variations in peak positions and intensities were observed.
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g-C3N4 prepared at 650 °C revealed strong non-specific absorption after 35 nsec.
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This phenomenon was not observed in g-C3N4 prepared at 510 °C.
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Results are explained based on location and type of defects in the photocatalyst.
Abstract
Transient FTIR measurements were performed on graphitic carbon nitride using a step-scan method, facilitating temporal resolution of a few nanoseconds. Variations in the location and the intensity of specific peaks and emerging of new peaks were observed during the first 170 nanoseconds after excitation. A comparison was made between graphitic carbon nitride prepared at two temperatures: 510 °C and 650 °C. The material prepared at 650 °C revealed very strong non-specific absorption beginning 35 nanoseconds after excitation and lasting for 20 nanoseconds. This phenomenon, termed “IR-blackening” was observed neither in g-C3N4 prepared at 510 °C nor in g-C3N4 prepared at 650 °C that was exposed to hole scavengers (ethanol and benzyl alcohol). In contrast, exposure of material prepared at 650 °C to an electron scavenger (methyl viologen) hardly alter the “IR-blackening” phenomenon. The results were explained by a mechanism, predicting higher reductive activity for materials having imperfect heptazine polymerization, as indeed was found in the photocatalytic degradation of 4-nitrophenol.