Ya Fei Zhao

Adjustable electronic performances and redox ability of a g-C3N4 monolayer by adsorbing nonmetal solute ions: a first principles study

During the process of hydrogen generation via photocatalytic water splitting, solute ions may be adsorbed on the surface of the graphitic carbon nitride (g-C3N4) monolayer, modifying its electronic and optical performances, as well as its redox ability due to chemical bond relaxation. With the aid of first principles calculations, we investigated the properties of a g-C3N4 monolayer with a series of nonmetal (NM) ions adsorbed on its surface. The obtained results revealed that the adsorbed solute ions can form NM–N or NM–C bonds with the g-C3N4 monolayer and result in bond relaxation, altering the valence band maximum and conduction band minimum synchronously. The small coverage rate of Br, Cl and I ions enhances the redox ability of g-C3N4 synchronously, while the adsorption of the other solute ions enhances the oxidizability and weakens the reducibility. In addition, the adsorption of solute ions can alter the active sites by impacting the distribution of the highest occupied molecular orbital and the lowest unoccupied molecular orbital. Therefore, we can adjust the electronic, optical performances and redox ability of a g-C3N4 monolayer by selecting the suitable type and quantity of solute ions, e.g., the photocatalytic efficiency of g-C3N4 can be enhanced by H ions plus B, N, Si, O, P and As ions with high coverage rates plus halogen ions with low coverage rates while it is suppressed by C, S, Se and Te ions.

The effects of nonmetal dopants on the electronic, optical, and catalytic performances of monolayer WSe2 by a first-principles study

Doping modifies the electronic, optical, and catalytic behavior of materials through the newly formed chemical bonds and the localized electrons. With the aid of first-principles calculations, the electronic, optical, and catalytic performances of the nonmetal (NM = H, B, C, N, O, F, Si, P, S, Cl, As, Br, Te, or I)-doped monolayer WSe2 were investigated. The results showed that the NM dopants substitute preferentially for Se under a W-rich condition and H, F, Cl, Br, and I atoms are willing to locate at the interstitial site. The electron-clouds around the dopants and nearby W or Se atoms were altered by the newly formed W–NM or Se–NM bonds, with the differences determined by the bonding strength between them. The band gap, optical absorption edge, and intensities were altered or shifted by less than 0.08 eV, 32 nm, and 9.5%, respectively. The H, F, P, Cl, As, Br, and I dopants were conductive to separating the photogenerated e−/h+ pairs, whereas the B, C, Si, and Te dopants became recombination centers for the photogenerated e−/h+ pairs. Compared with pristine monolayer WSe2, NM atoms with odd free electrons reduced the reduction potential by 0.39–0.71 eV and enhanced the oxidation potential by 0.45–0.75 eV. Thus, we can adjust the redox potentials of monolayer WSe2 by introducing different kinds of NM impurities for various catalytic reactions, and the H-, F-, P-, Cl-, As-, Br-, and I-doped specimens have excellent photocatalysis capability.

The common effects of surface and internal bonds on the electronic structure of Bi2Te3 nano-films by first-principles calculation

The effects of external stress on Bi2Te3 nano-films have been investigated by first-principles calculation, including stability, electronic structure, crystal structure, and bond order. It is found that the critical thickness of nano-film is sensitive to the stress in Bi2Te3 nano-film while the band gap is near constant. The critical thickness decreases under tensile stress, whereas it increases under compressive stress. The band gap and band order of Bi2Te3 film has been affected collectively by the surface and internal crystal structures, the contraction ratio between surface bond length of nano-film and the corresponding bond length of bulk decides the band order of Bi2Te3 film.