| Graphene has caused great interests in the scientific community because of the unique quantum effect. As a kind of zero band gap semiconductor, the two-dimensional single atomic layer has a high electrical conductivity, which otherwise limits its applications in the microwave absorbing field. However, the band gap of graphene can be easily tuned by doping boron and/or nitrogen, and then the optical and electrical properties are also expected to be tunable. This is a kind of B-C-N hybrid material. The so-called hybrid material is a composite that consists of two component mixed at the molecular or nanometer level. In addition to the intermediate characteristics between the two components, hybrid materials may also have some other new features.Graphene oxide(GO) is one of the most important graphene-derived materials. It has many hydroxyl, carboxyl and other active groups on its surface and edges, which greatly enhance its reactivity. It can be used as the 2D substrate to react with boron and nitrogen to obtained B-C-N hybrid materials. We prepared well-oxidated(34 At.%) and high water-soluble GO from graphite by the modified Hummers method. The solution is bright brown in which GO disperses as monolayer of a thickness of about 1 nm.A kind of B-C-N hybrid material was prepared from GO template using boric acid and urea as the reagents. Boron and nitrogen atoms were incorporated by co-annealing, which was revealed from the distinctive hexagonal structure of h-BN in graphene. After further ammonia treatment, the band gaps of the doped graphene were opened and adjusted. The ammonia treatment increased the spacing or doping defects, and makes the microwave absorbing properties greatly improved. Before the ammonia treatment, the minimum value of-28.0 dB was observed at 11.28 GHz with a thickness of 1.8 mm; After ammonia treatment, the a minimum value of-33.6 dB was observed at 15.28 GHz with a thickness of 1.6 mm.Another kind of graphene/BN “sandwich”-like alternative B-C-N hybrid material was obtained from GO using ammonia boron as the organizing reagent. The content of h-BN can be increased with increasing the weight fraction of ammonia boron. At the same time, the band gap was widened, the dielectric constant was decreased and the impedance was increased. When the ratio of GO:AB is 1:1, the absorbing ability of the product is preferable for microwave in the range of 6-18 GHz. A minimum value of-40.5 d B was observed at 15.28 GHz with a thickness of 1.6 mm.A kind of B-C-N-O photoluminescence material was prepared by one-step high temperature annealing method in air using a mixture of GO, boric acid and urea. In a certain range, the lower the temperature or the higher the GO content, the wider the band gap of the hybrid materials. The obtained material has a well-performed full color emission photoluminescence with peak emission adjustable in full chromatography. The one-step synthesis of white-lighting B-C-N-O phosphor was reported for the first time. The backbone of graphene acts as the network platform for the electron delivering. Boron and nitride was doped into the graphene layer acting as the electron/hole doping agent. In this way, a series of carbon-related defect energy levels were introduced in the crystal structure of h-BN. The electron transition from higher energy level to the series of lower energy levels will emit series of visible light, to the extent generating white light.Consequently, no matter the doping was made in-plane or in a hybridization way through layer-by-layer assembly, the band gap of the obtained B-C-N hybrid material can be both regulated. This gives us a way to further tune its microwave absorbing and photoluminescence properties, greatly broadening the applications of graphene. |
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