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Graphene nanoribbons with mixed edge structures are promising candidate materials for the next generation of nanoelectronics due to their unique and peculiar physical and chemical properties, as well as their interesting and tunable electronic structures. Here, we designs and calculates a series of periodic edge N-doped ZGNRs using first principles calculations based on density functional theory. The band gap of these ZGNRs can be adjusted from metal to semiconductor, by the periodic length of the nanobands, and the number and interval distance of N atom doping. Among them, 6-ZGNR-(1,3) is a metallic, 6-ZGNR-(1,4) and 6-ZGNR-(2,4) are half-metallic, 6-ZGNR-(2,5) and 6-ZGNR-(3,5) are SGS, and 6-ZGNR-(3,6) is a magnetic semiconductor. We projected band structures into p x orbitals of edge C and N atoms separately, and found that the energy near the Fermi level in 6-ZGNR-(1,4) is mainly contributed by edge C atoms, while 6-ZGNR-(3,5) is contributed by edge N atoms. This indicates that N atom doping plays a major role in the transition of spin polarization properties. Our studies suggest that it will have significant theoretical significance and practical value in the application of spintronic devices. [ABSTRACT FROM AUTHOR]

• Photocatalytic water splitting on type-II semiconductor heterojunction. • Band edges straddle the redox potential in both ph = 0 and 7. • Efficiently driving HER and OER, separating photogenerated electron-hole pairs. • High optical absorption and high solar power conversion efficiency. • Outstanding optoelectronic properties under vertical and in-plane strain. Two-dimensional (2D) van der Waals (vdW) materials have been widely adopted as photocatalysts in water splitting. Based on the first-principles calculations within screened hybrid functional of Heyd-Scuseria-Ernzerhof (HSE), we find that Janus group-III chalcogenide based vdW heterojunction (SeGa 2 Te/SeIn 2 Se) is a promising visible-light-driven photocatalyst regardless on the stacking configuration. The SeGa 2 Te/SeIn 2 Se in AA stacking satisfy the requirement for the band gap under both pH = 0 and pH = 7 according to standard water-splitting mechanism. The notable intrinsic electric field (v-EF) in the AB stacking of SeGa 2 Te/SeIn 2 Se alter the band alignment and enhance the overpotentials of the photogenerated carriers to efficiently drive the redox reaction. In both stacking, the type-II band alignment, suitable direct band gaps, high optical absorbance and high power conversion efficiency promote the photocatalytic efficiency. Furthermore, outstanding photocatalytic ability and efficiency are maintained under both vertical and in-plane strains, guaranteeing the application under natural environment. [ABSTRACT FROM AUTHOR]