Water‐Soluble Polymeric Carbon Nitride Colloidal Nanoparticles for Highly Selective Quasi‐Homogeneous Photocatalysis

Abstract

Heptazine‐based polymeric carbon nitrides (PCN) are promising photocatalysts for light‐driven redox transformations. However, their activity is hampered by low surface area resulting in low concentration of accessible active sites. Herein, we report a bottom‐up preparation of PCN nanoparticles with a narrow size distribution (ca. 10±3 nm), which are fully soluble in water showing no gelation or precipitation over several months. They allow photocatalysis to be carried out under quasi‐homogeneous conditions. The superior performance of water‐soluble PCN, compared to conventional solid PCN, is shown in photocatalytic H2O2 production via reduction of oxygen accompanied by highly selective photooxidation of 4‐methoxybenzyl alcohol and benzyl alcohol or lignocellulose‐derived feedstock (ethanol, glycerol, glucose). The dissolved photocatalyst can be easily recovered and re‐dissolved by simple modulation of the ionic strength of the medium, without any loss of activity and selectivity.

Heteroatom Dopants Promote Two‐Electron O2 Reduction for Photocatalytic Production of H2O2 on Polymeric Carbon Nitride

“…This indicates that the introduction of NaOH in the AKMT synthesis facilitated the formation of these new functional groups. [34] For example, the NaOHinduced alkalization process seemed to deprotonate the terminal C-NH 2 groups forming -CN groups at one apex of the melon structure, which is in agreement with the FTIR and…”

Dichloromethylation of enones by carbon nitride photocatalysis

“…Using flow approach, 2a was obtained with 57% yield. Considering convenience of K-PHI suspension pumping through thin FEP tubing along with easiness of the photocatalyst recovery, the entire system enables quasihomogeneous photocatalysis in flow 39 .…”

“…Due to the advantages of flow reactors 34,35 , several types of such photoreactors employing carbon nitrides have been reported -packed bed photoreactor 36 , serial micro batch photoreactors 2 , and triphasic flow photoreactor 37 . Due to relatively small particle size (average diameter 100 nm) and highly negative zeta-potential (−40 mV) 38 , K-PHI gives stable colloidal solution and has been used in quasi-homogeneous catalysis 39 . Due to these features colloidal solution of K-PHI can be used in simple plug-flow photoreactors that are designed for homogeneous reaction mixtures.…”

Sol–Gel Processing of Water-Soluble Carbon Nitride Enables High-Performance Photoanodes

“…We have recently developed a novel synthetic procedure yielding fully water-soluble and stable nanoparticles (10 nm size) of alkali metal poly(heptazine imide) (PHI), 55 a promising member of the PCN family. [56][57][58][59][60] As our synthetic strategy avoids the use of aggressive exfoliating or oxidizing agents that might impair the material's structural integrity, the water-soluble PHI exhibited excellent photocatalytic activity in alcohol oxidation and concurrent H2O2 production without any apparent deactivation.…”

“…[56][57][58][59][60] As our synthetic strategy avoids the use of aggressive exfoliating or oxidizing agents that might impair the material's structural integrity, the water-soluble PHI exhibited excellent photocatalytic activity in alcohol oxidation and concurrent H2O2 production without any apparent deactivation. 55 Notably, as the presence of hydrophilic oxygenated (mainly cyamelurate) moieties on the nanoparticle surface is highly beneficial in view of effective attachment to the surface of conductive substrates, such as fluorine-doped tin oxide (FTO), and since the water-soluble PHI can be gelled, 55 we anticipated that our water-soluble carbon nitride might be a promising candidate for fabrication of high-quality photoelectrode via sol-gel processing (Figure 1). Herein, we demonstrate, for the first time, the fabrication of binder-free, mechanically robust and photoelectrochemically stable PHI photoanodes via an aqueous sol-gel technique with water-soluble PCN using various and versatile protocols based on electrodeposition, doctor-blading, and spray pyrolysis.…”