Porous Graphitic Carbon Nitride: A Possible Metal-free Photocatalyst for Water Splitting

Abstract

Hydrogen generation through photocatalytic water splitting with the aid of renewable solar energy is an important step toward the development of sustainable and alternative energy. In the present study, using the first-principles calculations, we have explored the s-triazine based two-dimensional porous graphitic carbon nitride (g-CN) materials as a potential photocatalyst for water splitting. For calculating the band structures more accurately, we have employed hybrid density functionals. The calculated band gap of the single layer g-CN is found to be 2.89 eV, which decreases to ∼2.75 eV in multilayered structure. To improve the visible light activity, the effect of doping with different nonmetals on the electronic structure has been investigated. Among the different dopants studied, phosphorus is found to be more effective to reduce the band gap to 2.31 eV. The band edge potentials obtained from density functional calculations are corrected for vacuum potentials. The band alignments with respect to the water redox levels show that the thermodynamic criterion for the overall water splitting is satisfied. We have also carried out analogous studies on the heptazine based carbon nitride, g-C 3 N 4 , and the calculated band gaps, as well as the position of the valence band maximum, are consistent with the reported experimental results validating the computational method we have used. Based on our theoretical investigations, we can predict that the s-triazine based carbon nitride materials should be a potential photocatalyst for water splitting under visible light.

Reduced graphene oxide supported titanium dioxide nanomaterials for the photocatalysis with long cycling life

“…During the last decade a considerable number of TiO 2 composite materials have been proposed as potential photocatalyist, particularly in the case of solar applications, to extend the absorbance light to a wider range and imporve the stability under irradiation [8, 20,25]. The illustration of the reduced Graphene Oxide (rGO) supported TiO 2 as the photocatalyst was showed in Fig.1.…”

“…In the effort to develop photocatalysts based on TiO 2 , a large number of recent researches have been devoted to investigation of integrated composite TiO 2 catalysts [12][13][14][15][16][17][18][19][20][21]. For example, transition metal doping TiO 2 is effective to improve the Page 6 of 27 A c c e p t e d M a n u s c r i p t photocatalytic activity by decreasing the charge carrier recombination rates [12,13]; and other various non-metal-doped TiO 2 have been widely studied for the visible light photocatalytic activities [11,15,[21][22][23].…”

“…For example, transition metal doping TiO 2 is effective to improve the Page 6 of 27 A c c e p t e d M a n u s c r i p t photocatalytic activity by decreasing the charge carrier recombination rates [12,13]; and other various non-metal-doped TiO 2 have been widely studied for the visible light photocatalytic activities [11,15,[21][22][23]. These composite TiO 2 catalysts can be used as not only an efficient photocatalyst for highly selective oxidation, but also as a multifunctional component designed to promote wider spectrum absorption and separation of electrons and holes, as well as to stabilize photolysis semiconductors [20][21][22]. Among these designs and developments, carbon materials attracted more attention because they could both improve vastly the visible light response and photocatalytic activity [8,10,20].…”

“…These composite TiO 2 catalysts can be used as not only an efficient photocatalyst for highly selective oxidation, but also as a multifunctional component designed to promote wider spectrum absorption and separation of electrons and holes, as well as to stabilize photolysis semiconductors [20][21][22]. Among these designs and developments, carbon materials attracted more attention because they could both improve vastly the visible light response and photocatalytic activity [8,10,20]. Incorporation of various carbon nanomateirals into the TiO 2 matrix has been found to yield composite material with improved optical and photocatalytic properties compared to pure TiO 2 [8,21].…”

“…Incorporation of various carbon nanomateirals into the TiO 2 matrix has been found to yield composite material with improved optical and photocatalytic properties compared to pure TiO 2 [8,21]. The strong and intimate interaction between TiO 2 catalysts and the carbon nanomaterial enables the exploitation of their cooperative effect [20]. The carbon materials have been found to improve the surface area and adsorption capacity of the photocatalyst, and minimize the aggregation of TiO 2 nanoparticles.…”