Synthesis And Microwave Absorbing Properties Of Graphene And G-C₃N₄

Microwave absorbing material not only has its special importance in the defense field, but also find more and more wide applications in the civilian field. Graphene is a new type of two-dimensional carbon material, which has excellent photoelectrical properties and is a very promising microwave absorbing material based on the easy regulation of properties. Graphic carbon nitride(g-C3N4) is another graphene-like two-dimensional non-metallic semiconductor material. Its band gaps can be tuned based on its unique structures and has great potential applications in multiple areas. In this paper, we tried to tune the wave absorption performance of graphene and g- C3N4 through regulating their microstructures.The main research contents and results are as follows:(1) Monolayer graphene oxide(GO) was prepared using the improved Hummers method. Thermal reduction of GO was carried out and various of reduced GO(rGO) was obtained with different degree of reduction. Their microwave absorption performance were studied. The results showed that different degree of reduction led to different absorbing properties, of which 400℃-reduced sample, rGO- 400, has the best performance. When the thickness is 3 mm, the total frequency width is 5.4 GHz(9.5 to 14.9 GHz) on RL value below- 10 d B. The lowest reflection value of rGO- 400 is-39.7 dB at 12 GHz.(2) Two different types of graphene quantum dots, BCN-GQDs and CN-GQDs, were prepared from the mixture of citric acid(C6H8O7?H2O, C source), boric acid(H3BO3, B doped source) and urine(H2NCONH2, N doped source). The results indicated that graphite structure was successfully obtained from citric acid. Both BCNGQDs and CN-GQDs have good fluorescence properties. The microwave absorbing performance of CN- GQDs is better than BCN-GQDs. The lowest reflection value is-20.6 dB at 14.5 GHz with a thickness of 4 mm.(3) g-C3N4 was chemically exfoliated using KOH and different solvents. Different shaped microstructures of g-C3N4-T1 was obtained due to the self-assembly effect. g-C3N4-T1 is rich of C, O and a small amount of N, very similar to destructive GO. Moreover, a number of oxygen-containing groups were introduced to g-C3N4-T2 with the joint effect of KOH and alkyl alcohol, which has good fluorescence property and good dispersion in water. The lowest reflection value is-21.2 dB at 11.3 GHz with a thickness of 4mm.