A Novel MOF/Graphite Oxide Composite And Its Adsorption Performance Toward Oil Vapor

This work is mainly involved with preparation of a novel MOF/graphite oxide composite and study of its adsorption performance toward oil vapor. Recovery of oil vapor emitted from gas stations and fuel transportation has become very urgent task due to strict environmental regulations. Metal-organic frameworks(MOFs) show great promises in a variety of applications including oil vapor adsorption and recovery. However, although MOFs have ultrahigh specific area, they show low heat conductivity. In addition, their low density of atoms in structure cannot provide strong enough dispersive forces to bind small molecules. Therefore, there are spaces to improve further adsorption performance of MOFs. To resolve these issues, novel MOF/GO composites were synthesized and characterized. Then their adsorption performance toward oil vapor were also examined. Furthermore, a solvent-assisted mechanochemical method was developed for the reconstruction of moisture-degraded MOF. This work has great scientific research value and practical significance.Adsorption equilibrium and kinetics of n-hexane on MIL-101(Cr) were systematically investigated. The n-hexane adsorption isotherms and kinetic curves were determined by gravimetric method. Then the diffusion coefficients, the isosteric heat of adsorption and the adsorption activation energies of n-hexane on MIL-101 were estimated. Results showed that the n-hexane uptake of MIL-101(Cr) was up to 5.62 mmol/g, much higher than that of some conventional adsorbents and some MOFs. The isosteric adsorption heat of n-hexane on the MIL-101 was in the range of 40.93-42.28 k J/mol, which increased slightlywith the increase of n-hexane uptake. And the diffusion coefficients of n-hexane were in the range of 1.35× 10-10 to 2.35× 10-10 cm2/s.Novel MIL-101(Cr)/graphite oxide(GO) composites(MIL-101@GO) were synthesized by a solvothermal synthesis method. The as-synthesized MIL-101@GO-5 showed high BET surface area of 3502.2 m2/g, which increased by 21% as compared to the original MIL-101. The heat conduction properties of these composites were improved with the increase of GO content. The heat conductivities of the composites MIL-101@GO-5 and MIL-101@GO-10 were separatly 0.369 W/m?K and 0.463 W/m?K, which were 1.6-2 times that of the original MIL-101 and much higher than that of MOF-5 and ZIF-8 reported by some other investigators.The adsorption performances of the MIL-101@GO composite for a series of n-alkanes and aromatics were investigated. The adsorption mechanisms of these VOCs on MIL-101 and MIL-101@GO were discussed. Results showed that at region of low pressure, the adsorption capacities of VOCs were mainly dependent on the interaction between VOCs and MIL-101@GO. Thus, adsorption capacities of n-alkanes on MIL-101@GO increased with the hydrocarbon chain length, and the adsorption capacity of aromatics on MIL-101@GO followed the order: Ethylbenzene >Toluene > Benzene. However, at regions of high pressure, the trend was reversed. The adsorption capacities of VOCs decreased linearly with their molecular cross-sectional areas. Overall, the VOCs capacities of MIL-101@GO increased by 13%-29% in comparison with that of MIL-101, much higher than those of some conventional adsorbents.A solvent-assisted mechanochemical method was successfully developed for the reconstruction of moisture-degraded HKUST-1. The effects of the amount of solvent and grinding time on the crystalline, surface morphology, textural structure and adsorption performance of the reconstructed samples were examined. Results showed that BET surface area of the moisture-degraded HKUST-1 was only 66.2 m2/g, much lower than that of the fresh HKUST-1(SBET=1215.1 m2/g). The application of mechanochemical method can reconstruct the degraded HKUST-1. The moisture-degraded HKUST-1 can be restored within 30 minutes. The reconstructed samples were confirmed to have 95% surface area and 92% benzene capacity of the fresh HKUST-1. In contrast to that, the reconstructed samples prepared by conventional liquid immersion method showed 51% surface area and 56% benzene adsorption capacity of the fresh HKUST-1. The mechanochemical approach demonstrated in this work may provide an effective strategy for the reconstruction of some moisture-degraded MOFs for industrial applications.