Atomically thin films of boron carbon oxynitride (BCNO) are an intriguing new form of thin quaternary semiconducting hybrid films that have recently generated tremendous interest in the scientific community. These films are composition-tunable 2D materials which exhibit rich physical, chemical and electronic properties. Herein, a facile atmospheric pressure chemical vapour deposition (APCVD) synthesis and in-depth characterization of BCNO films with tunable composition, in which methane, ammonia and boric acid were used as precursor materials is reported. The different atomic compositions were achieved by adjusting the vaporization temperature of boric acid by varying the distance (i.e. 2 cm to 12 cm) between the boric acid and the growth substrate. From the XPS survey spectra, the atomic compositions of the BCNO films formed varied as follows: C (48–71 at%), B (2.34–12.8 at%), N (1.98–7.9 at%) and O (33–34 at%). Raman spectral analyses showed that the films exhibited vibrational modes from h-BN, B–C, and graphene domains. XPS data corroborated the Raman analyses by indicating that the films consisted of h-BN, B–O–B, and B₂O₂ domains embedded within a graphene-rich BCN matrix. Three band gap energies assigned to h-BN (5.87 ± 0.05–5.66 ± 0.06 eV), h-BCN (5.76 ± 0.01–5.22 ± 0.01 eV) and doped graphene (2.35 ± 0.06–1.74 ± 0.04 eV) domains were observed from the UV-vis spectra of BCNO films as a function of boric acid distance from the growth substrate. The narrowing optical energies were attributed to an increasing C-content with increasing growth distance, thus leading to C-doping in h-BN and h-BCN as well as in the formation of larger graphene domains. Finally, the in-depth analysis of the samples allowed for a mechanism of the BCNO formation to be proposed and hence provided further understanding of the growth of the BCNO films.

In this study, the effect of K₂CO₃ activation on the structural, textural, and electrochemical properties of carbon spheres (CSs) and boron and nitrogen co-doped carbon spheres (BN-CSs) was evaluated. Activation of the CSs and BN-CSs by K₂CO₃ resulted in increased specific surface areas and I_D/I_G ratios. From the X-ray photoelectron spectroscopy (XPS) results, the BN-CSs comprised of 64% pyridinic-N, 24% pyrrolic-N and 7% graphitic-N whereas the activated BN-CSs had 19% pyridinic-N, 40% pyrrolic-N and 22% graphitic-N displaying the effect of activation on the type of N configurations in BN-CSs. A possible BN-co-doping and activation mechanism for the BN-CSs is proposed. Electrochemical analysis of the electrode materials revealed that BN doping, carbon morphology, structure, and porosity played a crucial role in enhancing the capacitive behavior of the CSs. As a proof of concept, a symmetric device comprising the activated BN-CSs displayed a specific power of 800 W kg⁻¹ at a specific current of 1 A g⁻¹ within an operating cell potential of 1.6 V in a 3 M KNO₃ electrolyte. The study illustrated for the first time the role of K₂CO₃ activation in influencing the physical and surface properties of template-free activated BN-CSs as potential electrode materials for energy storage systems.

This study reports on low nitrogen content-doped hollow carbon spheres (N-HCSs) for use as chemical vapour sensors. The N-HCSs were prepared by a template-assisted chemical vapour deposition method followed by nitrogen doping in an ammonia atmosphere. Raman spectroscopy data displayed an increase in the I_D/I_G ratio of the carbons upon N-doping indicating the creation of structural defects in the hollow carbon spheres (HCSs). The XPS results showed the N-HCSs had a very low N content (0.6 at%) comprising predominantly pyridinic-N (35%) and pyrrolic-N (48%) configurations. Annealed HCSs obtained by thermal annealing in Ar exhibited a lower I_D/I_G ratio and higher thermal stability than the N-HCSs. The HCSs-based sensors were exposed to varying concentrations of acetone, water, lactic acid, ammonia, toluene, chloroform and methanol vapours at room temperature. Low detection limits for toluene (15 ppm), lactic acid (12 ppm) and ammonia (6 ppm) were established for the N-HCSs-based sensors. The methanol sensitivity for the N-HCSs was recorded to be 5 times higher than that of related rGO based sensors. This was ascribed to the moderate degree of graphitization, hollow carbon morphology and the electron-rich N-HCS surface. Most importantly, the water dependency for the N-HCSs was lower than that of the un-doped HCSs. This indicated the effect of heat treatment and post-nitrogen doping of the HCSs in significantly lowering the humidity dependency of the carbon. Thus, the results suggested that the N-HCSs nanostructures are potential candidates for humidity-insensitive environmental sensing devices for the detection of various chemical vapours.

Hexagonal boron nitride (h-BN) is nowadays an increasingly attractive material, especially for two-dimensional material applications, due to its intrisic properties. However, its properties are highly dependent on the used synthesis approach. The polymer derived ceramics (PDCs) route allows elaboration of h-BN with tailored textural and structural properties. Here, we demonstrate the interest of the PDCs pathway for the synthesis of h-BN. Growth of h-BN single crystals with crystal sizes of a few microns at relatively low temperature and atmospheric pressure is successfully achieved from borazine precursor using PDCs. The crystallization is improved by additivation of 5 wt% of Li₃N to the pre-ceramic polymer. Furthermore, by coupling PDCs with gas pressure sintering, starting from the same pre-ceramic polymer and 25 wt% of Li₃N, the crystal size is enlarged up to hundreds of microns. The fabricated single crystals of pure h-BN can then be exfoliated into h-BN nanosheets. Finally, by combining PDCs with atomic layer deposition, functional BN nano-/hetero-structures are successfully synthesized from highly structured sensitive templates, making this ALD process a promising alternative for fabricating functional BN nanostructures.

A mechanism showing the role of carrier gas on the N-configuration of the post-N-doped CSs synthesized in the presence of (a) H₂ and (b) Ar, respectively.

Given the challenging task of constructing an efficient nitrogen reduction reaction (NRR) electrocatalyst with enhanced ambient condition performance, properties such as high specific surface area, fast electron transfer, and design of the catalyst surface constitute a group of key factors to be taken into consideration to guarantee outstanding catalytic performance and durability. Thereof, this work investigates the contribution of the 2D/2D heterojunction interface between MoS₂ and reduced graphene oxide (rGO) on the electrocatalytic synthesis of NH₃ in an alkaline media. The results revealed remarkable NRR performance on the MoS₂@rGO 2D/2D hybrid electrocatalyst, characterized by a high NRR sensitivity (faradaic efficiency) of 34.7% with an NH₃ yield rate of 3.98 ± 0.19 mg h^-1 cm^-2 at an overpotential of -0.3 V vs RHE in 0.1 M KOH solution. The hybrid electrocatalysts also exhibited selectivity for NH₃ synthesis against the production of the hydrazine (N₂H₄) byproduct, hindrance of the competitive hydrogen evolution reaction (HER), and good durability over an operation period of 8 h. In hindsight, the study presented a low-cost and highly efficient catalyst design for achieving enhanced ammonia synthesis in alkaline media via the formation of defect-rich ultrathin MoS₂@rGO nanostructures, consisting predominantly of an HER-hindering hexagonal 2H-MoS₂ phase.