Enhancement of the graphitic carbon nitride surface properties from calcium salts as templates

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.

Enhancement of the graphitic carbon nitride surface properties from calcium salts as templates. Advances in Engineering

About the author

Dr. Pierre Gibot is currently CNRS researcher at the NS3E laboratory of Nanomaterials for Systems under Extreme Stress UMR 3208 CNRS/ISL/UNISTRA, Saint-Louis, France. His research activities are focussed on the synthesis of nanosized ceramic materials (oxides, nitrides) by detonation and soft chemistry and the development of safer reactive nanothermites. Before joining this position, he held two Attached Temporary Teaching and Research contracts (School of Chemistry, Mulhouse and University of Picardie Jules Verne, Amiens) and two postdoctoral contracts on the synthesis of materials for magnetic and electrochemical applications (University of Pierre and Marie Curie, Paris and University of Picardie Jules Verne, Amiens). He received his Ph. D degree in chemistry at the University of Haute Alsace in 2002 for a scientific research dedicated to the synthesis of ceramics (oxides, carbides) with controlled and specific morphology. This work was achieved at the Institute of Science of Materials of Mulhouse, France (IS2M CNRS UMR 7361) under the supervision of Dr. Cathie Vix-Guterl. He is author of more than 30 articles/proceedings, 2 patents and 50 international/national communications.

 

About the author

Fabien Schnell is an expert technician of the French Centre National de la Recherche Scientifique (CNRS). Specialized on scientific instrumentation, he has worked in various laboratories at CNRS and at the University of Strasbourg (UNISTRA), where he was responsible for operating analytical devices and for developing adapted protocols for research. His main field of experience focus on X-Ray Diffraction (XRD), Small-angle X-ray scattering (SAXS) and Scanning Electron Microscope (SEM), for innovative materials research and for the characterization at the nanoscale. He is also in charge of health and safety organization for pyrotechnical activities in laboratory environment. He is co-author of more than 20 articles and 30 communications in both peer reviewed international journals and large recognized international conferences.

About the author

Denis Spitzer (Dr. Habil. Ing.) is a confirmed scientist and the founding-director of the NS3E laboratory (Nanomatériaux pour les Systèmes Sous Solicitations Extrêmes). He received his PhD. in chemistry from the University Louis Pasteur of Strasbourg in 1993. His main research activity is the continuous nanocrystallization of explosives and pharmaceuticals. He patented several processes, the investigation of ultra-sensitive explosive detection systems, and imaging of energetic materials with high resolution microscopy (STM and AFM). He is author of more than a hundred publications within peer-reviewed journals and technical reports. Moreover, he is author of 15 patents and more than 50 abstracts presented on national and international conferences. In 2013 he obtained the first price of “Strategic Thinking” on bio-inspired explosive detection that he received from the former French Minister of Interior, Manuel Valls. For his main results on nanocrystallization, synthesis by detonation and also detection studies he recently (2015) received the “Grand Prix Lazare Carnot” from the French “Académie des Sciences” »

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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