Experimental Identification of Ultrafast Reverse Hole Transfer at the Interface of the Photoexcited Methanol/Graphitic Carbon Nitride System

An experimental scrutiny of the photoexcited hole dynamics in a prototypical system is presented in which hole-scavenging methanol molecules are chemisorbed on a graphitic carbon nitride (g-C3N4) substrate. A set of comparison and control experiments by means of femtosecond time-resolved transient absorption (fs-TA) spectroscopy were conducted. The elusive reverse hole transfer (RHT) process was identified, which occurs on a timescale of a few hundred picoseconds. The critical role of interfacially chemisorbed methoxy (instead of methanol) as the dominant species responsible for hole scavenging was confirmed by a control experiment using protonated g-C3N4 as the substrate. A hot-hole transfer effect was revealed by implementing different interband photoexcitation scenarios. The RHT rate is the key factor governing the hole-scavenging ability of different hole scavengers.