Novel one-pot synthesis of mpg-C3N4 with metal/metal oxide nanoparticles
Résumé
Due to many interesting properties such as high thermal and chemical stability polymeric graphitic carbon nitride found numerous applications in many fields of chemistry [1]. Recently, g-C3N4 have been reported to be effective and inexpensive photocatalyst for water splitting under visible light irradiation [2]. The performance of g-C3N4 as a photocatalyst could be improved by modification of textural properties or adjusting the electronic structure of C3N4 via doping with heteroelements. In the present work we have investigated the influence of synthesis route (hard templating method and condensation way of preparation with electron-deficient precursors) and the role of cocatalysts on the photocatalytic activity of mesoporous g-C3N4. Experimental Mesoporous g-C3N4 was prepared by two different strategies. In a hard templating method mesoporous silica KIT-6 was impregnated with cyanamide with the following calcination and removal of silica matrix. H2PtCl6-6H2O and Co(NO3)2-6H2O were introduced in functionalized KIT-6 before the cyanamide impregnation to form the nanoparticles of cocatalysts (Pt and Co3O4) inside the pores of KIT-6. The prepared KIT-6 material containing nanoparticles of cocatalysts with a size limited by the pore openings of KIT-6 was used as a hard template for the formation of mesoporous g-C3N4. The influence of synthesis methods (impregnation conditions, calcination temperature, conditions of cocatalyst incorporation and formation etc.) on crystalline and electronic structure of mpg-C3N4 has been investigated in details. Our second approach consisted in preparation of modified g-C3N4 via condensation of melem or melamine with electron-deficient precursors like pyromellitic dianhydride. This strategy allows to modify the band structure of g-C3N4 toward enhanced photooxidation/photoreduction properties. We systematically investigated the influence of structure of electron-deficient precursors on the electronic structure of g-C3N4. The photocatalytic activities of prepared samples have been determined for methanol dehydrogenation in comparison with Pt/TiO2. The influence of the preparation parameters on the activities will be discussed. Conclusions We developed an original way of preparation of mpg-C3N4 by replication of mesoporous silica KIT-6 containing cocatalyst nanoparticles in the pores of KIT-6. The strategy provides the better dispersion of cocatalyst nanoparticles in the mpg-C3N4 and leads to the creation of highly ordered 3-D materials with large surface area and photooxidation/photoreduction properties for water splitting. The second, "condensation" approach has been demonstrated to tune the band gap of g-C3N4 depending on the structure of electron-deficient precursors.
[1] Q. Li, J. Yang, D. Feng, Z. Wu, Q. Wu, S. S. Park, C.-S. Ha, D. Zhao, Nano Res., 2010, 3, 632-642.
[2] X. Wang, K. Maeda, A. Thomas, K. Takanabe, G. Xin, J.M. Carlsso, K. Domen, M. Antonietti, Nat Mater. 2009, 8(1), 76-80.
