N-DOPED GRAPHENE FROM MESOPOROUS CHITOSAN AS PHOTOCATALYST FOR HYDROGEN GENERATION

N-DOPED GRAPHENE FROM MESOPOROUS CHITOSAN AS PHOTOCATALYST FOR HYDROGEN GENERATION Cristina Lavorato1,2, Ana Primo1, Raffaele Molinari2 and Hermenegildo Garcia1. 1Instituto Universitario de Tecnología Química, Univ. Politecnica de Valencia, Av. De los Naranjos s/n, 46022 Valencia, Spain. 2Department of Environmental and Chemical Engineering, University of Calabria, Via P. Bucci 44A, 87036 Rende, CS (Italy). E-mail: lavorato.cristina@libero.it We have recently reported an innovative process to convert natural biopolymers into graphene materials1. The whole process, depicted in scheme 1, is based on the preparation of highly porous, large surface area bead of this natural biopolymer. The resulting chitosan aerogels exhibit a very large surface area (450 m2/g) and large mesoporous volume. Figure 1 shows SEM image of the resulting chitosan aerogels after supercritical drying and pyrolysis. Pyrolysis of these chitosan beads at temperature between 600-900 °C leads to undoped graphene according to Raman (1190 and 1350 cm-1 bands) and X-ray spectroscopy (see Figure 1). The resulting N doped graphene exhibited activity as photocatalyst for hydrogen generation from water methanol mixtures. It was observed that the activity for hydrogen evolution strongly depends on the preparation conditions and particularly from the pyrolysis temperatures. This fact can be rationalized considering that pyrolysis temperature strongly influences the quality of the graphene layers and that graphene is a conducting material instead of a semiconductor. It seems that energy of the conduction and valence bands N doped graphene resulting from pyrolysis of chitosan can be considerably modified depending on the quality of the material. Overall, our results constitute a remarkable example of valorization of biomass by converting residue into a photoactive material. Scheme 1. Figure 1. a) Amount of hydrogen evolved during a photocatalytic run using chitosan pyrolysed at different temperature under UV irradiation; b) SEM image of the front of the chitosan graphitized at 900 °C showing domains of very large porosity; c) Spheres of millimetric chitosan aerogel after calcination at 900 °C; d) XPS of N doped graphene. References: 1 Primo, A.; Forneli, A.; Corma, A.; Garcia, H. J. ChemSusChem 2012, 5, 2207–2214.