Polymeric graphitic carbon nitride materials exhibit exotic properties superior to graphene which are promising for applications in energy conversion, environment protection, and spintronics devices. We propose a two-dimensional (2D) framework of graphene-like carbon nitride composing of C9N7 units connected by nitrogen atoms. From first-principles, we demonstrate that this 2D carbon nitride has a spin-polarized ground state and exhibits metallic electronic properties, in contrast to commonly studied graphitic carbon nitrides which are nonmagnetic semiconductors. Additionally, half-metallicity can be achieved in this framework by applying tensile strain. The realization will be beneficial for spintronics as a candidate material for a spin-current generator. More importantly, this provides a feasible way to realize half-metallicity in experiments.

Photocatalytic water splitting is a new technology for the conversion and utilization of solar energy and has a potential prospect. One important aspect of enhancing the photocatalytic efficiency is how to improve the electron-hole separation. Up to now, there is still no ideal strategy to improve the electron-hole separation. In this article, for metal-free organic photocatalysts, we propose a good strategy- forming heterojunction, which can effectively improve the electron-hole separation. We provide a metal-free organic photocatalyst g-C12N7H3 for water splitting. The stability of g-C12N7H3 has been investigated, the X-ray diffraction spectra has been simulated. Using first-principles calculations, we have systematically studied the electronic structure, band edge alignment, and optical properties for the g-C12N7H3. The results demonstrated that g-C12N7H3 is a new organocatalyst material for water splitting. In order to enhance the photocatalytic efficiency, we provided four strategies, i.e., multilayer stacking, raising N atoms, forming g-C9N10/g-C12N7H3 heterojunction, and forming graphene/g-C12N7H3 heterojunction. Our research is expected to stimulate experimentalists to further study novel 2D metal-free organic materials as visible light photocatalysts. Our strategies, especially forming heterojunction, will substantially help to enhance the photocatalytic efficiency of metal-free organic photocatalyst.

With a first-principles method based on density functional theory, the effect of the alloying element titanium ( Ti ) on the thermodynamic stability and electronic structure of hydrogen ( H ) in pure vanadium ( V ) is investigated. The interactions between H and the vacancy and the defect solution energies in a dilute V – Ti binary alloy are calculated. The results show that: (i) a single H atom prefers to reside in a tetrahedral interstitial site in dilute V – Ti binary alloy systems; (ii) H atoms tend to bond at the vacancy sites; a mono-vacancy is shown to be capable of trapping three H atoms; and (iii) the presence of Ti in pure V can increase the H trapping energy and reduce the H trapping capability of the vacancy defects. This indicates that doping with Ti to form dilute V – Ti binary alloys can inhibit the solution for H , and thus suppress the retention of H . These results provide useful insight into V -based alloys as a candidate structural material in fusion reactors.

We studied the energetic behaviors of interstitial and substitution carbon (C)/nitrogen (N) impurities as well as their interactions with the vacancy in vanadium by first-principles simulations. Both C and N impurities prefer the octahedral site (O-site). N exhibits a lower formation energy than C. Due to the hybridization between vanadium-d and N/C-p, the N-p states are located at the energy from −6.00 eV to −5.00 eV, which is much deeper than that from −5.00 eV to −3.00 eV for the C-p states. Two impurities in bulk vanadium, C-C, C-N, and N-N can be paired up at the two neighboring Osites along the 111 direction and the binding energies of the pairs are 0.227 eV, 0.162 eV, and 0.201 eV, respectively. Further, we find that both C and N do not prefer to stay at the vacancy center and its vicinity, but occupy the O-site off the vacancy in the interstitial lattice in vanadium. The possible physical mechanism is that C/N in the O-site tends to form a carbide/nitride-like structure with its neighboring vanadium atoms, leading to the formation of the strong C/N-vanadium bonding containing a covalent component.