Emilia Alwin

Expression of concern for ‘ In situ growth of N-doped carbon nanotubes from the products of graphitic carbon nitride etching by nickel nanoparticles’ by Mariusz Pietrowski et al. , Nanoscale Adv. , 2024, 6 , 1720–1726, https://doi.org/10.1039/D3NA00983A.

The products of g-C ₃ N ₄ etching are CH ₄ , NH ₃ , and HCN, which are used as building materials for N-doped carbon nanotubes without any external source of carbon or nitrogen.

Pt, Ru, and Ir were introduced onto the surface of graphitic carbon nitride (g-C₃N₄) using the wet impregnation method. A reduction of these photocatalysts with hydrogen causes several changes, such as a significant increase in the specific surface area, a C/N atomic ratio, a number of defects in the crystalline structure of g-C₃N₄, and the contribution of nitrogen bound to the amino and imino groups. According to the X-ray photoelectron spectroscopy results, a transition layer is formed at the g-C₃N₄/metal nanoparticle interphase, which contains metal at a positive degree of oxidation bonded to nitrogen. These structural changes significantly enhanced the photocatalytic activity in the production of hydrogen through the water-splitting reaction. The activity of the platinum photocatalyst was 24 times greater than that of pristine g-C₃N₄. Moreover, the enhanced activity was attributed to significantly better separation of photogenerated electron–hole pairs on metal nanoparticles and structural distortions of g-C₃N₄.

Elucidating the layered structure of the g-C ₃ N ₄ nanomaterials using X-ray photoelectron spectroscopy and X-ray powder diffraction techniques is possible.

Graphitic carbon nitride (g-C₃N₄) was obtained by thermal polymerization of dicyandiamide, thiourea or melamine at high temperatures (550 and 600 °C), using different heating rates (2 or 10 °C min⁻¹) and synthesis times (0 or 4 h). The effects of the synthesis conditions and type of the precursor on the efficiency of g-C₃N₄ were studied. The most efficient was the synthesis from dicyandiamide, 53%, while the efficiency in the process of synthesis from melamine and thiourea were much smaller, 26% and 11%, respectively. On the basis of the results provided by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–vis), thermogravimetric analysis (TGA), elemental analysis (EA), the best precursor and the optimum conditions of synthesis of g-C₃N₄ were identified to get the product of the most stable structure, the highest degree of ordering and condensation of structure and finally the highest photocatalytic activity. It was found that as the proton concentration decreased and the degree of condensation increased, the hydrogen yields during the photocatalytic decomposition of water–methanol solution were significantly enhanced. The generation of hydrogen was 1200 µmol g⁻¹ and the selectivity towards hydrogen of more than 98%.

Results of the first research on structural and surface properties of binary fluorides MgF₂–CoF₂ are presented.