Synthesis And Properties Of Graphene And MOF Composites

Various MOFs with tailored nanoporosities, ultrahigh porosity and enormous internal surface areas have recently been developed as potential storage media for gases. Graphene which has OH (hydroxyl group), C-O-C (epoxy group) on its surface and -COOH (carboxylic groups) found at the edges can be decorated with functional groups on either side of its basal plane, giving rise to a bifunctional nanoscale building block that can undergo face-to-face assembly with MOFs. Here, we reveal some composites made from the assembly of diazonium salt-functionalized graphene (BFG) with HKUST-1 and graphene with NENU-5 and graphene quantum dots with HKUST-1. Those nanocomposites with various ratios in the two components show good performance in separation and storage systems for specific gas molecules and the hydrogen evolution reaction (HER). The work was summarized as follows:(1)We performed chemical reduction to remove epoxy and hydroxyl groups from the surface of GO. Then, the chemically reduced GO (rGO) is functionalized with 5-((4-aminophenyl)diazenyl)isophthalic acid (abbreviated as BFG). Finally, by mixing BFG with the precursors used for synthesizing HKUST-1, we get the BFG/HKUST-1=1:3、1:4、1:5 composites. To evaluate the porosity of the materials, nitrogen adsorption measurements were carried out at 77 K under 1 atm. HKUST-1 and the composites exhibit a type Ⅰ isotherm which indicates that the composites were microporous. The isotherms for CO2 at 273 K and 1 atm on HKUST-1, BFG/HKUST-1 are given. The CO2 storage capacities of BFG/HKUST-1=1:5 (8.84 mmol/g) is enhanced 31%, higher than that of HKUST-1. On the other hand, too much BFG in HKUST-1 resulted in a lower CO2 capacity than that of HKUST-1. The composites BFG/HKUST-1=1:3 exhibits highest current density, lowest onset potential and lowest Tafel slope which suggests smaller activation energy for HER in the presence of BFG.(2)We used different methods that solution method and mechanochemical method to synthetic a class of GO/NENU-5=4%、6%、15% composite materials. To evaluate the porosity of the materials, nitrogen adsorption measurements were carried out at 77 K under 1 atm. The composites GO/NENU-5=4%、6%、15% exhibit a type Ⅰ isotherm which indicates that the composites were microporous. The isotherms for CO2 and CH4 at 273 K and 1 atm on GO/NENU-5=4%、6%、15% are given. To our disappointment, the GO in composites resulted in a lower CO2 and CH4 capacity than that of NENU-5. When GO/NENU-5=6%, its exhibits highest current density, lowest onset potential and lowest Tafel slope which suggests smaller activation energy for HER in the presence of GO. On the other hand, we used solution method to synthetic a various of rGO/NENU-5=4%、6%、15% composite materials. Nitrogen adsorption measurements were carried out at 77 K under 1 atm indicated that the composites were microporous. However, the rGO in composites resulted in a lower CO2 and CH4 at 273 K under 1 atm capacity than that of NENU-5. The HER test indicated that rGO/NENU-5=15% exhibits highest current density, lowest onset potential and lowest Tafel slope.(3)We used an easy method for the preparation of graphene quantum dots(GQDs). Then, by mixing GQDs with the precursors used for synthesizing HKUST-1, we get the GQDs/HKUST-1=3:1、1:5、2:5 composites. Nitrogen adsorption measurements were carried out at 77 K under 1 atm which indicated that the composites were microporous. But, the GQDs in the composites resulted in a lower CH4 adsorption under 273 K,1 atm. Its amazing that the GQDs in the composites enhanced the CO2 adsorpotion under 273 K and 1 atm. Thus, GQDs/HKUST-1=2:5 composite is a good CO2 adsorpotion medium.