Graphene p-n junctions have important applications in the fields of optical interconnection and low–power integrated circuits. Most current research is based on the lateral p-n junction prepared by chemical doping and other methods. Here, we report a new type of pure graphene oxide (pGO) vertical p-n junctions which do not dope any other elements but only controls the oxygen content of GO. The I–V curve of the pGO vertical p–n junction demonstrates a remarkable rectification effect. In addition, the pGO vertical p–n junction shows stability of its rectification characteristic over long-term storage for six months when sealed and stored in a PE bag. Moreover, the pGO vertical p–n junctions have obvious photoelectric response and various rectification effects with different thicknesses and an oxygen content of GO, humidity, and temperature. Hall effect test results show that rGO is an n–type semiconductor; theoretical calculations and research show that GO is generally a p–type semiconductor with a bandgap, thereby forming a p–n junction. Our work provides a method for preparing undoped GO vertical p–n junctions with advantages such as simplicity, convenience, and large–scale industrial preparation. Our work demonstrates great potential for application in electronics and highly sensitive sensors.

Effectively removal of air pollutants using adsorbents is one of the most important methods to purify the air. In this work, we proposed for the first time that PtN3-CNT is an effective adsorbent for air purification. Its air purification performance was studied by calculating the adsorption behaviors and electronic structures of 12 gas molecules, including the main components of air (N2, O2, H2O, CO2) and the most common air pollutants (NO, NO2, SO3, SO2, CO, O3, NH3, H2S), on the surface of PtN3-CNT using first-principles calculations. The results showed that these gases were adsorbed stably via the coordination between Pt and the coordinated atoms (C, N, O, and S atoms) in the gas molecules, and the adsorption energies vary in the range of −0.81∼−4.28 eV. The obvious chemical interactions between PtN3-CNT and the adsorbed gas molecules are mainly determined by the apparent overlaps between the Pt 5d orbitals and the outmost p orbitals of the coordination atoms. PtN3-CNT has strong adsorption capacity for the toxic gas molecules, while relatively weaker adsorption performance for the main components of the air except oxygen. The recovery time of each adsorbed molecule calculated at different temperatures showed that, CO2, H2O, and N2 can be desorbed gradually at 298∼498 K, while the toxic gases are always adsorbed stably on the surface of PtN3-CNT. Considering the excellent thermal stability of PtN3-CNT at up to 1000 K proved by AIMD, PtN3-CNT is very suitable to act as an adsorbent to remove toxic gases to achieve the purpose of air purification. Our findings in this report would be beneficial for exploiting possible carbon-based air purification adsorbents with excellent adsorbing ability and good recovery performance.

Helium (He) is widely used in many scientific and industrial fields, and 9 the shortage of He resources and the growing demand make He 10 separation extremely important. In this paper, the He separation 11 performance of a series of graphanes containing crown ether nanopores 12 (crown ether graphane, CG-n, n=3, 4, 5, 6) was studied by first-principles 13 calculations. At first, the minimum energy paths of He and other 10 gas 14 molecules (Ne, Ar, H₂, CO, NO, NO₂, N₂, CO₂, SO₂ and CH₄) passing 15 through CG-n membranes were calculated, and the factors affecting the 16 energy barriers were also investigated. The calculated results show that 17 He was the easiest to pass through all the CG-n membranes with energy 18 barriers of 4.55 eV, 1.05 eV, 0.53 eV and 0.01 eV, respectively. He can be 19 separated by CG-5 and CG-6 with very low energy barriers, and the 20 energy barrier of He passing through CG-6 is the lowest so far as we 21 know. Moreover, all gas molecules can pass through CG-6 with low energy barriers, including many molecules with large kinetic diameters, such as CO (0.13 eV) and N₂ (0.16 eV). Therefore, CG-6 is also expected to be used in the screening field of other gas molecules. In addition, it was found that the energy barriers of gas molecules passing through CG-n were synergistically affected by the sizes of the crown ether nanopores, the kinetic diameters and the types of the gas molecules. Secondly, the diffusion rates of gas molecules passing through CG-5 and CG-6 and the He selectivity towards other 10 gases of CG-5 and CG-6 at different temperatures were calculated. It was found that CG-5 exhibited extremely high He selectivity at a wide temperature range (0-600 K). In summary, crown ether graphanes CG-5 and CG-6 can act as excellent He separation membranes with high He selectivity. This work is expected to inspire experimentalists to develop other graphene-based two-dimensional separation membranes for the separation of He and other gas molecules.