Photobase effect for just-in-time delivery in photocatalytic hydrogen generation

Abstract

Carbon dots (CDs) are a promising nanomaterial for photocatalytic applications. However, the mechanism of the photocatalytic processes remains the subject of a debate due to the complex internal structure of the CDs, comprising crystalline and molecular units embedded in an amorphous matrix, rendering the analysis of the charge and energy transfer pathways between the constituent parts very challenging. Here we propose that the photobasic effect, that is the abstraction of a proton from water upon excitation by light, facilitates the photoexcited electron transfer to the proton. We show that the controlled inclusion in CDs of a model photobase, acridine, resembling the molecular moieties found in photocatalytically active CDs, strongly increases hydrogen generation. Ultrafast spectroscopy measurements reveal proton transfer within 30 ps of the excitation. This way, we use a model system to show that the photobasic effect may be contributing to the photocatalytic H2 generation of carbon nanomaterials and suggest that it may be tuned to achieve further improvements. The study demonstrates the critical role of the understanding the dynamics of the CDs in the design of next generation photocatalysts.

Perylenetetracarboxylic acid nanosheets with internal electric fields and anisotropic charge migration for photocatalytic hydrogen evolution

“…The rate of D 2 evolution can reach 33.95 mmol g −1 h −1 under the full spectrum (Fig. 6c ), indicating that the origin of H 2 is aqueous protons 82 . The presence of the H/D isotope effect decreases the photocatalytic HER 83 , but in principle, it does not harm our inferences about the source of H 2 in the reaction systems.…”

Carbon Nanodots for All-in-One Photocatalytic Hydrogen Generation

“…*­(pCNDs) abstract a proton from the solvent. Such a protonated species undergoes electron transfer with an electron donor and produces CND-bound hydrogen radicals . In line with the assumption that a proton transfer from the solvent occurs on the picosecond time scale, fsTAS of our CND materials at a different pH was performed (Figures S27–S32).…”

“…The photobasic effect could not be corroborated in any of the cases. Nevertheless, it should be noted that only subtle spectral changes are expected for a proton transfer to CND . It is hard to unambiguously determine if the proton transfer occurs before, after, or concomitant with the electron transfer (step 2).…”

Catalytic Acetalization and Hydrogenation of Furfural over the Light‐Tunable Phosphated TiO2 Catalyst

“…On the other hand, with the enriched photogenerated carriers, the surface acid sites on the catalyst may change dramatically. [8] However, this phenomenon and its correlation to catalytic performance are often overlooked. MacFarlane et al [9] indicated that the decoration of hydrogensulfate on the carbon quantum dots endows the catalyst with the photoinduced acidity, promoting the acid-catalyzed ring-opening reaction of epoxides.…”

“…On the other hand, with the enriched photogenerated carriers, the surface acid sites on the catalyst may change dramatically [8] . However, this phenomenon and its correlation to catalytic performance are often overlooked.…”