Thermal stability studies of plasma deposited hydrogenated carbon nitride nanostructures

Thermally stable carbon nitride nanostructures have potential applications in surface coatings and automotive fields. In this work, hydrogenated nitrogen-rich carbon nitride nanoparticles have been synthesised via low-pressure low-power plasma vapour deposition technique from methane/nitrogen gas mixture in a dry process. Thermal stability of the initially prepared hydrogenated carbon nitride structures has been analysed by near-edge X-ray absorption fine-structure spectroscopy (NEXAFS, in-situ), Raman spectroscopy, scanning and transmission electron microscopy and nuclear reaction analysis (NRA). Thermal studies reveal the excellent stability of the material and nitrogen-rich characteristics (N/C ratio 0.5–0.2 ± 0.01). The obtained results suggest transformation of sp3-rich as-deposited carbon nitride into sp2-carbon phase with more graphitic features upon thermal annealing. Such in-situ thermal studies of plasma deposited carbon nitrides confirm the conversion of sp3-rich phase to sp2-rich carbon phase at the critical temperature (about 450 K), without a huge loss in nitrogen content. The analysis revealed that the material is a stable plasma deposit after this critical temperature up to >1100 K. Additionally, super hydrophilic carbon nitride nanostructure transforms into a hydrophobic surface after thermal annealing. These thermally stable hydrophobic carbon nitride nanoparticles could be used as a promising material for the hydrophobic coatings for various applications, especially for harsh conditions. [Display omitted] •Plasma-assisted deposition technique used to synthesise hydrogenated carbon nitride (a-C: H–N) nanostructures.•Thermal stability of the a-C: H–N nanospheres analysed by near-edge x-ray absorption fine structure spectroscopy.•In-situ thermal stability studies reveal the improvement in graphitic characteristic of a-C: H–N upon thermal annealing.•Surface properties of a-C: H–N nanospheres changes from hydrophilic to hydrophobic after the thermal annealing.