Photocatalytic Overall Water Splitting Activity of Templateless Structured Graphitic Nanoparticles Obtained from Cyclodextrins

Pyrolysis of α-, β-, and γ-cyclodextrins at 900 °C under Ar forms porous 3D graphitic carbon nanoparticles with remarkable crystallinity, in which the pore dimensions range from 0.74 to 1.1 nm in the ultra/micropore range as determined by N2, Ar, and CO2 adsorption. These materials behave as semiconductors with the potential energy of the conduction and valence bands being remarkably dependent in as much as 0.57 eV on the dimensions of the micropores. The photogeneration of electrons and holes was confirmed by photodeposition of Pt (electrons) and PbO2 (holes) nanoparticles by reduction and oxidation, respectively. Importantly, these 3D porous graphitic carbons generate H2 and O2 from H2O in the absence of any metal cocatalyst. Theoretical calculations at the DFT level confirm in models the influence of the dimensions of the pores, the presence of defects, and residual oxygen on the band energy and that the occurrence of H2O dissociation is favored inside the pores by a confinement effect. Considering the interest in developing metal-free photocatalyst, the present results show the possibility to tune the band alignment of porous carbon semiconductors by appropriate selection of precursors and the convenient generation of defects.