Adsorption and photocatalytic splitting of water on graphitic carbon nitride: a combined first principles and semiempirical study

Abstract

Graphitic carbon nitride, g-C3N4, is a promising organic photo-catalyst for a variety of redox reactions. In order to improve its efficiency in a systematic manner, however, a fundamental understanding of the microscopic interaction between catalyst, reactants and products is crucial. Here we present a systematic study of water adsorption on g-C3N4 by means of density functional theory and the density functional based tight-binding method as a prerequisite for understanding photocatalytic water splitting. We then analyze this prototypical redox reaction on the basis of a thermodynamic model providing an estimate of the overpotential for both water oxidation and H(+) reduction. While the latter is found to occur readily upon irradiation with visible light, we derive a prohibitive overpotential of 1.56 eV for the water oxidation half reaction, comparing well with the experimental finding that in contrast to H2 production O2 evolution is only possible in the presence of oxidation cocatalysts.

Mechanistic insight into the water photooxidation on pure and sulfur-doped g-C3N4 photocatalysts from DFT calculations with dispersion corrections

“…In addition, the listed vibrational frequencies in Table 1, although not discussed in this section, will provide important information for the future experiments. The adsorption energies for the relevant species except OH* are consistent with those derived by Wirth et al [39] The side and top views of the adsorption configurations on g-C 3 N 4 and S-C 3 N 4 are also displayed in Figs. 2 and 3, respectively.…”

“…The adsorption energy is found to be −3.29 eV, lower than that (−2.73 eV) obtained in the previous report [39]. However, the calculated distance of …”

“…The calculated H N distances in the hydrogen bonds are between 2.10 and 2.40 Å. The adsorption energy is computed to be −0.62 eV, lower than that by a periodic first-principles (PBE) study and in good agreement with the other two previous theoretical reports with correction for dispersion interaction [39,40]. Due to its physisorption characteristic, the H 2 O* molecule almost keeps intact with its H O bond lengths of 0.98 Å and the angle H O H of 101.46 • .…”

The role of the defect on the adsorption and dissociation of water on graphitic carbon nitride

“…However, the information about the interaction between water and g-C 3 N 4 is very little. The adsorption of water on g-C 3 N 4 sheet induces a severe buckle structure of g-C 3 N 4 sheet [38][39][40]. Especially, making defect is a common way to improve the water dissociation [10,41,42].…”

Modelling materials for solar fuel synthesis by artificial photosynthesis; predicting the optical, electronic and redox properties of photocatalysts

“…This arises from the fact that the activation energy of an elementary step is often directly related to the thermodynamic driving force for the same step through a Brönsted-Evans-Polyani relationship. An example of the application of this approach to a photocatalyst is the recent work of Wirth and co-workers on the required overpotential for water oxidation on graphitic carbon nitride [150]. …”