  Carbon nitride two-dimensional (2D) materials are among the most attractive
class of nanomaterials, with wide range of application prospects. As a
continuous progress, most recently, two novel carbon nitride 2D lattices of
C3N5 and C3N4 have been successfully experimentally realized. Motivated by
these latest accomplishments and also by taking into account the well-known
C3N4 triazine-based graphitic carbon nitride structures, we predicted two novel
C3N6 and C3N4 counterparts. We then conducted extensive density functional
theory simulations to explore the thermal stability, mechanical, electronic and
optical properties of these novel nanoporous carbon-nitride nanosheets.
According to our results all studied nanosheets were found to exhibit desirable
thermal stability and mechanical properties. Non-equilibrium molecular dynamics
simulations on the basis of machine learning interatomic potentials predict
ultralow thermal conductivities for these novel nanosheets. Electronic
structure analyses confirm direct band gap semiconducting electronic character
and optical calculations reveal the ability of these novel 2D systems to adsorb
visible range of light. Extensive first-principles based results by this study
provide a comprehensive vision on the stability, mechanical, electronic and
optical responses of C3N4, C3N5 and C3N6 as novel 2D semiconductors and suggest
them as promising candidates for the design of advanced nanoelectronics and
energy storage/conversion systems.
