Ionic Carbon Nitrides in Solar Hydrogen Production and Organic Synthesis: Exciting Chemistry and Economic Advantages

Abstract

Molecular photoredox complexes from the platinum group paved the way of organic photocatalysis. However, high price and difficulties related to removal and recycling hamper application of such complexes on the larger scale. Carbon nitride semiconductor photocatalysts are deprived at large extent of such limitations. Herein, we summarize application of ionic carbon nitrides in photocatalysis. A salt-like structure of ionic carbon nitrides comprising negatively charged poly (heptazine imide) anion and positively charged alkali metal cations gives rise to a number of unique properties and high activity in photocatalysis. The performance of ionic carbon nitrides in H 2 generation is up to 100 times higher compared with the covalent graphitic carbon nitrides. Eleven photocatalytic reactions mediated by ionic carbon nitrides and their long-lived radicals are reviewed. Economy of using carbon nitride photocatalysts in comparison with the photoredox complexes from the platinum group has been analyzed.

Emerging Concepts in Carbon Nitride Organic Photocatalysis

“…[67] At the same time, application of carbon nitrides in organic photoredox catalysis has been summarized in the dedicated reviews. [68,69,70,71] Recapitulating available literature we conclude that, in general, CN-based photocatalysts of sophisticated structure, such as those featuring heterojunction and exquisite morphology, are employed in water splitting and environmental applications (model reactions), while CNs photocatalysts with large surface area and stoichiometry close to C 3 N 4 are commonly employed in organic synthesis.…”

“…The great ensemble of materials with a general name of carbon nitrides can be divided into two categories: covalent and ionic CNs (Figure 2). [69,91] The crucial difference is that covalent CNs do not have ionic N bonds -they possess only covalent CÀ N bonds or contain equal amount of cations and anions that are delocalized and intercalated between the π-conjugated layers and NÀ H functionality. [92] On the other hand, ionic CNs have negatively charge N atoms, bonded with metal cations.…”

“…Potassium PHI (K-PHI) has been selected as a model material because of its broadly documented application in organic synthesis, and in depth characterization (Figure 2c). [69,[98][99] The structure is highly ordered compared to g-CN, although 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-PHI are constructed from six heptazine units observed as a honeycomb structure in TEM images.…”

Dichloromethylation of enones by carbon nitride photocatalysis

“…1b, c). Our alternative approach uses cheap heterogenous carbon nitride (CN) photocatalysts (1-10 Euro per gram on a gram-scale synthesis) 24 and have a low toxicity 25 .…”

Highly rapid and non-enzymatic detection of cholesterol based on carbon nitride quantum dots as fluorescent nanoprobes

“…Carbon nitride materials, including carbon nitride nanosheets (CNNS) and carbon nitride quantum dots (CNQDs) etc., which a metal-free semiconductor composes of carbon and nitrogen, have attracted extensive interests owing to their excellent advantages of catalysis, cost-effective, good stability, low toxicity and so on. 16 They are widely applied in energy conversion, 17 photocatalysis, 18,19 drug delivery, 20 oxygen reduction 21 and biological imaging. 22 Recently, CNQDs, which not only possess the excellent properties of carbon nitride materials but also have the advantages of quantum dots (stable uorescence, long Stoke shi, anti-photobleaching and so on), have been assessed for various biochemical applications.…”