Incorporating p‐Phenylene as an Electron‐Donating Group into Graphitic Carbon Nitride for Efficient Charge Separation

Abstract

Low charge‐separation transport efficiency resulting from structural defects largely limits photocatalytic hydrogen production over polymeric graphitic carbon nitride (PCN) photocatalyst. Herein, an electron‐donating group, namely p‐phenylene, is incorporated into PCN by a polycondensation reaction between carbon nitride and p‐phenylenediamine (or p‐benzoquinone) to repair the structural defects. The p‐phenylene‐modified PCN exhibits an almost fivefold increase in H2 evolution, a threefold increase in photocurrent density, and higher nonradiative rate (0.285 ns−1). Spectroscopic studies confirm that p‐phenylene tends to bridge the heptazine‐based oligomers through a polycondensation reaction. Theoretical calculations reveal that anchoring of the heptazine units by p‐phenylene induces localization of h+ and e− on the phenylene and melem moieties, respectively, which effectively separates the charge carriers. This strategy provides an opportunity to overcome structural defects in carbon nitride for efficient photocatalytic solar energy conversion.

Development and Functionalization of Visible-Light-Driven Water-Splitting Photocatalysts

“…Furthermore, for g-C 3 N 4 (BG = 2.7–2.9 eV; Figure 7 and Table 2 ), the CBM is composed of C p z orbitals, and the VBM is composed of N p z orbitals, with band positions suitable for water splitting [ 160 ]. Accordingly, g-C 3 N 4 has attracted significant attention as a next-generation Vis-light-driven water-splitting photocatalyst [ 161 , 162 , 163 , 164 , 165 , 166 , 167 , 168 , 169 , 170 , 171 , 172 , 173 ].…”

Donor Bandgap Engineering without Sacrificing the Reduction Ability of Photogenerated Electrons in Crystalline Carbon Nitride

“…Considering that a relatively high conduction band (CB) position favors thermodynamic proton/water reduction to produce H 2 , it may not be cost‐effective to introduce acceptor into CCN to narrow the bandgap and lower the CB position. Besides, many studies have narrowed the bandgap of CN by introducing acceptor units, containing benzene or heteroaromatic rings [19–22] . However, owing to the enrichment of photogenerated electrons in acceptor sites, these newly introduced units will become the sites for H 2 production.…”

Template-Assisted Surface Hydrophilicity of Graphitic Carbon Nitride for Enhanced Photocatalytic H2 Evolution

“…Consequently, development of efficient, low-cost, sustainable, and eco-friendly photocatalysts is crucial to the application of solar energy. In recent years, a metal-free photocatalyst, known as graphitic carbon nitride (g-C 3 N 4 ), with excellent properties, such as easy synthesis, visible-light absorption, chemical stability, and tunable electronic structure, has attracted the attention of numerous researchers . It is important to point out that the pristine bulk g-C 3 N 4 (BCN) has an infinitely broad prospect in the field of photocatalysis because of the appropriate band gap (2.7 eV). − Unfortunately, the activity of BCN is limited by a small BET surface area and high recombination rate of photogenerated carriers …”

“…Surface functional structure creation was found to be useful for improving the photocatalytic performance of carbon nitride . Especially, various strategies of functional terminal groups were used to improve the active sites of carbon nitride. ,− Plasma treatment in a hydrogen atmosphere, using high-energy particles to bombard the surface of BCN, introduces hydrophilic groups to effectively capture water molecules for increasing active sites and substrate adsorption sites. , Huang et al has introduced functional groups into the precursor by treating with HNO 3 , and the active functional groups of −NH x , −CO/CO, and −OH were successfully grafted onto the surface of g-C 3 N 4 , while a facile hydrothermal posttreatment for pristine BCN can be used to synthesize soluble g-C 3 N 4 nanosheets with hydrophilic groups (−NH 2 , −OH, and −CO) . Interestingly, the cyano group in which C atoms are more polarized (δ++) than other structures was also introduced into g-C 3 N 4 frameworks acting as electron acceptors and thus more unpaired electrons were induced to participate in the photoexcitation process for the photocatalytic reaction. − …”