Polymeric Carbon Nitrides: Semiconducting Properties and Emerging Applications in Photocatalysis and Photoelectrochemical Energy Conversion

As an analogue of graphite, graphitic carbon nitride polymers also possess a stacked two-dimensional structure, which could be regarded as N-substituted graphite in a regular manner. The history of carbon nitride polymers could trace back to 1834 when Liebig firstly prepared "melon," a carbon nitride derivative, but their potential applications have only emerged in the very recent years. As an organic semiconductor, carbon nitrides have several interesting features as follows. Firstly, both of carbon and nitrogen are among the most abundant elements in our planet, and it is facile for mass-preparation with a very competitive prices of order of several $/Kg, which is always preferred. Secondly, because of intrinsic organic nature, it is easy to chemical functionalize/doping, thus manipulating their electronic band-gap strucutres. Thirdly, distinct to many other organic semiconductors, carbon nitrides have a high stability against oxidation up to 500 degrees C in air, making handling them in air possible. Here we briefly review the proof-of-concept applications of polymeric carbon nitrides for photovoltaic and photocatalytic fields in the past several years, and the performance optimization by morphology and electronic band gap engineering.