Wettability and Surface Free Energy Analyses of Monolayer Graphene

Recently Rafiee et al. experimentally demonstrated the wetting transparency of graphene, but there is still no comprehensive theoretical explanation of this physical phenomenon. Since surface free energy is one of the most important parameters characterizing material surfaces and is closely related to the wetting behavior, the surface free energy of suspended monolayer graphene is analyzed based on its microscopic formation mechanism. The surface free energy of suspended monolayer graphene is shown to be zero, which suggests its super-hydrophobicity. Neumann's equation of state is applied to further illustrate the contact angle, θ, of any liquid droplet on a suspended monolayer graphene is 180 o. This indicates that the van der Waals(vd W) interactions between the monolayer graphene and any liquid droplet are negligible; thus the monolayer graphene coatings exhibit wetting transparency to the underlying substrate. Moreover, molecular dynamics(MD) simulations are employed to further confirm the wetting transparency of graphene in comparison with experimental results of Rafiee et al. These findings provide a fundamental picture of wetting on ideal single atomic layer materials, including monolayer graphene. Thus, these results provide a useful guide for the design and manufacture of biomaterials, medical instruments, and renewable energy devices with monolayer graphene layers.

High and selective capture of low-concentration CO2 with an anion-functionalized ultramicroporous metal-organic framework

CO2 capture,especially under low-pressure range,is of significance to maintain long-duration human operation in confined spaces and decrease the CO2 corrosion and freezing effect for the liquefaction of natural gas.Herein,we for the first time report a novel anion-functionalized ZU-16-Co(TIFSIX-3-Co,TIFSIX=hexafluorotitanate(TiF62−),3=pyrazine),which exhibits one-dimensional pore channels decorated by abundant F atoms,for efficient CO2 capture at a concentration around 400–10,000 ppm.Among its isostructural MFSIX-3(M=Si,Ti,Ge)family materials,ZU-16-Co with fine-tuned pore size of 3.62Åexhibits the highest CO2 uptake at 0.01 bar(10,000 ppm)and 1 bar(2.63 and 2.87 mmol g−,respectively).The high CO2 capture ability of ZU-16-Co originates from the fine-tuned pore dimensions with strong F⋯C=O host-guest interactions and relatively large pore volumes coming from its longer coordinated Ti-F-Co distance(3.9Å)in c direction.The excellent carbon trapping performance was further verified by dynamic breakthrough tests for CO2/N2(1/99 and 15/85)and CO2/CH4(50/50)mixtures.The adsorption and separation performances,resulting from the fine-tuned pore system with periodic arrays of exposed functionalities,demonstrate that ultramicroporous ZU-16-Co can be a promising adsorbent for low-concentration carbon capture.