Abstract
Organic π-conjugated polymers are promising heterogeneous photocatalysts that involve photoredox or energy transfer processes. In such settings, the materials are usually applied in the form of dispersion in liquid medium, which is bound to certain technological limits of applicability. Herein, we present an innovative approach using carbon nitride thin films prepared via chemical vapor deposition at different vessel walls and using them as batch and microfluidic photoreactors. This approach allows us not only to fabricate technologically relevant and reusable devices but also to improve photophysical properties of carbon nitride, such as the singlet–triplet energy gap and lifetime of triplet excited states, when the material is assembled in thin films. These morphological changes are employed to maximize the performance of the materials in photocatalytic reactions, in which the carbon nitride thin films show at least 1 order of magnitude higher activity per area unit compared to photocatalysis using suspended particles.
Highlights
Photoredox catalysis enables unique reaction pathways to high value-added products that are not available with classical thermal activation of the molecules.[1−4] Recently, visible light photocatalysis has gained high momentum, in academic research and in the chemical industry as a new synthetic tool,[5,6] in the preparation of fine chemicals and active pharmaceutical ingredients.[7−10]In general, photoredox catalysis can be divided into homogeneous and heterogeneous catalyses, both effectively mediating a number of photochemical transformations.[11]
We coated standard 4 mL glass vials that are used by many research groups working in the field of automated photoredox catalysis across the world, with the Carbon nitride (CN) thin film using chemical vapor deposition (CVD) similar to the earlier reported procedure.[35,36]
Deposition of the CN film on the reactor wall after the CVD is seen with naked eye by its typical yellowish color, photonic reflections, and the deep blue fluorescence when the visible batch wall reactors (Vis-BWR) is exposed to UV light (Figure 1b).[50]
Summary
Photoredox catalysis enables unique reaction pathways to high value-added products that are not available with classical thermal activation of the molecules.[1−4] Recently, visible light photocatalysis has gained high momentum, in academic research and in the chemical industry as a new synthetic tool,[5,6] in the preparation of fine chemicals and active pharmaceutical ingredients.[7−10]. Semiconductor photocatalysis offers multiple engineering solutions.[25] For example, coating of the photoreactor wall with semiconductor particles is an appealing feature in combination with flow technology.[26] In this regard, Wang et al recently reported on a fixed-bed flow system employing CN supported on glass fibers and beads.[27] backscattering. Rich experimental data of using CN particulates in photocatalysis, as well as unique opportunities offered by this class of materials in combination with the CVD, enabled us to explore the highly homogeneous thin and transparent CN film as active coating in photoreactors. The glassware with the photocatalytically active layer is tested in the oxidation of benzyl alcohols under light irradiation
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