Dual Defective K-Doping and Cyano Group Sites on Carbon Nitride Nanotubes for Improved Hydrogen Photo-Production

In this work, dual defective potassium (K) doping and cyano group sites have been introduced into carbon nitride (CN) with various morphologies by a co-condensation method for highly efficient photocatalytic hydrogen production. The photocatalysts with potassium doping and inserted cyano groups display higher photocatalytic activity of hydrogen evolution under visible light irradiation in contrast to undoped bulk CN, CN nanosheets, and CN nanotubes. Potassium-doped CN nanotubes present the greatest hydrogen generation yield of 2.11 mmol g–1 h–1 with an apparent quantum efficiency of 5.28% at 420 nm, which is about 2.0 and 40 times that of K-incorporated bulk CN and the bare CN nanotubes, respectively. Benefiting from uniformly distributed potassium ions, the introduction of cyano groups, and the one-dimensional tubular structure of CN nanotubes, the resultant K-doped CN nanotubes have new charge transfer paths between potassium ions and adjacent heptazine units, accelerating photogenerated carrier transfer and enhanced photoreduction ability, thereby improving the photocatalytic performance. This study presents a reliable method for element doping of CN with various morphologies to photocatalytic hydrogen evolution through water splitting.