Abstract
Carbon nitrides encompass a class of transition-metal-free materials possessing numerous advantages such as low cost (few Euros per gram), high chemical stability, broad tunability of redox potentials and optical bandgap, recyclability, and a high absorption coefficient (>105 cm-1 ), which make them highly attractive for application in photoredox catalysis. In this Review, we classify carbon nitrides based on their unique properties, structure, and redox potentials. We summarize recently emerging concepts in heterogeneous carbon nitride photocatalysis, with an emphasis on the synthesis of organic compounds: 1) Illumination-Driven Electron Accumulation in Semiconductors and Exploitation (IDEASE); 2) singlet-triplet intersystem crossing in carbon nitride excited states and related energy transfer; 3) architectures of flow photoreactors; and 4) dual metal/carbon nitride photocatalysis. The objective of this Review is to provide a detailed overview regarding innovative research in carbon nitride photocatalysis focusing on these topics.
Highlights
Verschueren and Borggraeve indicated the shared attributes of these approaches,[7] but they possess unique features.For example, a photoredox approach functions better in overall redox neutral reactions, due to the fact that oxidation and reduction steps are executed by the same species, while electrocatalysis offers a greater tolerance to functional groups due to precise control over electrolysis parameters, namely voltage or current
The structure is highly ordered compared to g-Carbon nitrides (CNs), still possessing a large amount of structural defects such as unit cell distortions, faults in the sequences of CN-layer stacking, edge and screw dislocations as well as rippling of CN-layers.[99b]. The ordered motifs of K-poly (heptazine imide)s (PHIs) are constructed from six heptazine units observed as a honeycomb structure in transmission electron microscopy (TEM) images
Jeschke, Reisner and co-workers found that during the dark phase, once charged with electrons during irradiation in presence of benzylic alcohol, CN materials enable hydrogen evolution reaction (HER) with the aid of colloidal Pt (Figure 6b).[99n]. Thanks to this work, it is possible to brand photocatalytic net reductive reactions, in which photocatalyst turnover is accomplished in dark, with the name “Dark Photocatalysis”
Summary
Verschueren and Borggraeve indicated the shared attributes of these approaches,[7] but they possess unique features. Photocatalyst redox potentials as well as the energy and intensity of incident light utilized for energy transfer in photocatalyic systems,[9] multiphoton/chromoselective catalysis,[10] and proton coupled multielectron transfer.[11]. To properly explore these and other concepts in photocatalysis, we would like to give a brief overview of materials used as photocatalysts, their key features, and advantages. Catalytic redox approaches are more material efficient compared to purely chemical approaches, as they ideally require only energy which can be derived from renewable sources and the catalyst These approaches come with some drawbacks, such as the employment of sacrificial agents, and degradation of electrodes. License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited
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