Formic acid assisted fabrication of Oxygen-doped Rod-like carbon nitride with improved photocatalytic hydrogen evolution.

Rod-like carbon nitrides synthesized by calcinating supramolecular precursors prepared from acid (or alkali) and melamine have attracted great attention because they have large surface area and abundant accessible active sites. However, they are highly inefficient in separating charges, which limits their photocatalytic activity. Here, we prepared porous, rod-shaped carbon nitrides doped with oxygen by calcinating the precursors prepared from melamine and formic acid. The porous O-doped g-C3N4 nanorods have a large surface area of 81.4 m2 g-1. In particular, the oxygen doped into the catalyst enables it to have high efficiency in utilizing light in a range of 420-600 nm, and significantly improves its ability to separate photogenerated carriers. Under light irradiation (λ ≥ 420 nm), the prepared catalyst exhibits high photocatalytic activity with a hydrogen production rate of 12,766 µmol g-1h-1, which is 18.3 times that of pure carbon nitride. This research provides a novel way of preparing highly active non-metallic photocatalysts.

Which kind of nitrogen chemical states doped carbon dots loaded by g-C3N4 is the best for photocatalytic hydrogen production.

Recently, g-C3N4 (CN) loaded N-doped carbon dots (NCDs) have been widely studied as promising metal-free photocatalysts due to their impressive performance in hydrogen production. However, deep understanding of the effect of nitrogen chemical states on photocatalytic activity is still lacked. In this work, NCDs doped with pyrrole nitrogen, graphite/pyrrole nitrogen, and pyrrole/pyridine nitrogen were prepared and hybridized with g-C3N4. The characterizations revealed that, incorporation of pyrrole N-doped CDs into g-C3N4 (CN/NCDs-en) effectively enhanced the visible light absorption, facilitated electron-hole separation, and promoted the participation of photoexcited electrons in H2 evolution reaction. Moreover, theoretical calculation showed that, compared with graphite N and pyridine N, pyrrole N has the most appropriate H adsorption ability, which is conducive to the H2 formation. Under visible light irradiation, the CN/NCDs-en exhibited the best hydrogen evolution of 3028 µmol h-1 g-1. These results shed a light on the design and optimization of N-doped metal-free photocatalysts for H2 evolution reaction.