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Significance Statement
To date, carbon nitride phases are promised to have a great future. This standpoint seems to be shared by a wide number of researchers worldwide according to the abundant dedicated literature. The carbon nitride material (C3N4) which can be described by several polymorphs is thermodynamically stable at ambient conditions under the graphitic form (g-C3N4). This phase exhibits numerous and diverse intrinsic properties among them a non-toxicity, a high thermal and chemical inertia and interesting optoelectronic properties (band gap of 2.7 eV). Based on these interests, the g-C3N4 material has been assessed as a promising photocatalyst in the production of hydrogen by photocatalytic water splitting under visible-light irradiation. This possible application focuses a lot of efforts of the scientific community since hydrogen is seen as a clean energy for a world where decrease the greenhouse gas emission is primordial and vital. In spite of the expectations, the performance of this material was not this exciting – mainly due to the high recombination rate of the photo generated charge carriers and the low specific surface area developed by the material.
Improving surface properties of g-C3N4 material through the concept of nanostructuring can be addressed from soft- or hard-templating methods. The most interesting surface properties were indisputably obtained by using hard templates such as mesoporous silica matrices, alumina membranes and colloidal suspension of silica nanospheres. Although efficient, these templates require the use of fluoride-based reagents for their removal which is hazardous and may be a drawback for the development of an industrial process.
In the present investigation, alternative hard templates are suggested to substitute silica and alumina-templates. These are calcium-containing salts as the calcium carbonate (CaCO3) and calcium phosphate (Ca3(PO4)2), both known as biomaterials. These templates are readily soluble in diluted acid solutions and available on the market at nanometer scale, representing real advantages. Their successful use in designing of nanostructured materials was demonstrated by the improvement of surface properties of the as-synthesized carbon nitride materials. According to us, using these new template agents may offer a viable alternative to conventional templates for the design of large surface materials.
Journal Reference
Microporous and Mesoporous Materials, Volume 219, 2016, Pages 42-47.
P. Gibot, F. Schnell, D. Spitzer
Laboratory of Nanomaterials for Systems Under Extreme Stress, CNRS-ISL-UNISTRA UMR 3208, French-German Research Institute of Saint-Louis (ISL), 5 rue du Général Cassagnou, BP 70034, 68301 Saint-Louis, France
Abstract
A graphitic carbon nitride material with enhanced surface properties has been successfully synthesized from guanidine monohydrochloride used as carbon nitride precursor, and from calcium salts nanoparticles used as templates. The products were characterized by X-ray Diffraction (XRD), chemical analysis, Fourier Transform Infra-Red spectroscopy (FTIR), nitrogen adsorption, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Ultra-Violet Visible spectroscopy (UV-Vis). The results show that the products adopt a graphitic structure with basal planes made of carbon and nitrogen atom species linked together by single and double bonds in an aromatic array (s-triazine, tri-s-triazine ring). As a function of the amount of the calcium-based template, a series of mesoporous materials was prepared which had specific surface areas ranging from 24.0 to 39.4 m2/g and coupled with pore volumes of 0.13 – 0.22 cm3/g. Instead of using the usual silica hard templates, our results show that using CaCO3 and Ca3(PO4)2 nanoparticles appears to be an encouraging solution for developing the surface properties of the carbon nitride. The carbon nitride is a promising candidate in the field of photocatalysis.
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