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Graphitic carbon nitride (g-CN), as an orderly structured polymer derivative, has been widely concerned for its photocatalytic ability due to its metal-free nature and unique properties. However, the photoelectrochemical (PEC) application of g-CN is still hindered by the difficulty of forming high-quality films with good uniformity and crystallinity. Herein, we studied the rapid thermal vapor condensation (RTVC) for growing g-CN films with improved PEC activity. The polycondensation and polymerization reactions of precursor melamine molecules under the optimized temperature 600 °C and calcination time 20 min resulted in better crystallinity of g-CN films. Remarkably, the growth of g-CN film based on the coalescence of unambiguous hexagonal nanosheets was observed, as corroborated by scanning electron microscopy and transmission electron microscopy. This novel RTVC method offers a fast and easy strategy for improving the crystallinity of g-CN films through controlling the thermal dynamics and kinetics of film growth from temperature and time. [ABSTRACT FROM AUTHOR]

Applications of graphitic carbon nitride (g-CN) in photoelectrochemical and optoelectronic devices are still hindered due to the difficulties in synthesis of g-CN films with tunable chemical, physical and catalytic properties. Herein we present a general method to alter the electronic and photoelectrochemical properties of g-CN films by annealing. We found that N atoms can be removed from the g-CN networks after annealing treatment. Assisted by theoretical calculations, we confirm that upon appropriate N removal, the adjacent C atoms will form new C=C π bonds. Detailed calculations demonstrate that the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are located at the structure unit with C=C π bonds and the electrons are more delocalized. Valence band X-ray photoelectron spectroscopy spectra together with optical absorption spectra unveil that the structure changes result in the alteration of the g-CN energy levels and position of band edges. Our results show that the photocurrent density of the annealed g-CN film is doubled compared with the pristine one, thanks to the better charge separation and transport within the film induced by the new C=C π bonds. An ultrathin TiO2 film (2.2 nm) is further deposited on the g-CN film as stabilizer and the photocurrent density is kept at 0.05 mA cm−2 at 1.23 V versus reversible hydrogen electrode after two-cycle stability assessment. This work enables the applications of g-CN films in many electronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (g-CN) is a unique organic semiconductor that has been widely applied as a visible-light-driven photocatalyst. However, these applications are primarily based on g-CN powders. Applications of g-CN in devices are hindered because of difficulties associated with the synthesis of high-quality g-CN films. This work reviews the latest advances in g-CN films. The deposition methods are summarized and the structural, optical, and electronic properties of g-CN films and their applications in catalysis, solar cells, and light-emitting diodes are outlined. Moreover, the challenges remaining in this field are also discussed. [ABSTRACT FROM AUTHOR]

• Colorful photoelectrode concept was proposed. • Colorful carbon nitride based composite films were prepared. • Multiple-steps thermal vapor condensation (MSTVC) method was adopted to fabricate films. • Hierarchical surface morphologies of colorful films were observed. • The colorful photoelectrodes exhibited photocurrent densities from 13.2 to 96.2 μA cm−2 at 1.23 V versus RHE. Carbon nitride based photoelectrodes for solar water splitting devices have attracted tremendous attention. However, for practical applications, it is desirable to develop a kind of carbon nitride based photoelectrode with a wide range of colors for meeting the demand of aesthetic properties when the light harvesting devices are loaded on buildings. This work first presents an innovative strategy for constructing colorful carbon nitride films by adopting multiple-steps thermal vapor condensation (MSTVC) method. Different monomers and amounts are studied to tailor carbon nitride based photoelectrodes with different colors, including dark brown, iridescence, green, bluish violet, reddish brown, red, crimson, orange, dark yellow and black due to the change of the composition and the evolution of impressive surface hierarchical structure caused by the reaction between the sulfur-rich monomers and fluorine-doped titanium dioxide (FTO) layer. The colorful carbon nitride based photoelectrodes also generate satisfied photocatalytic activity, the photocurrent densities are from 13.2 to 96.2 μA cm−2 at 1.23 V vs. RHE. We expect this work can be of interest not just for the development of carbon nitride photoelectrochemical cells, but also for the fundamental exploration and applications in electronics, photonics, sensors and displays. [ABSTRACT FROM AUTHOR]