Graphene oxide (GO) has shown a high potential to adsorb and store water molecules due to the oxygen-containing functional groups on its hydrophilic surface. In this study, we characterized the water absorbing properties of graphene oxide in the form of papers. We fabricated three kinds of graphene oxide papers, two with rich oxygen functional groups and one with partial chemical reduction, to vary the oxygen/carbon ratio and found that the paper with high oxygen content has higher moisture adsorption capability. For the GO paper with reduction, the overall moisture absorbance was reduced. However, the absorbance at high humidity was significantly improved due to direct formation of multilayer water vapor in the system, which derived from the weak interaction between the adsorbent and the adsorbate. To demonstrate one application of GO papers as a desiccant, we tested grape fruits with and without GO paper. The fruits with a GO paper exhibited longer-term preservation with delayed mold gathering because of desiccation effect from the paper. Our results suggest that GO will find numerous practical applications as a desiccant and is a promising material for moisture desiccation and food preservation.
wileyonlinelibrary.commolecules, so GO is hydrophilic and can easily be dispersed in water. [ 2 ] The freestanding laminated GO membranes that are prepared from GO solutions can play an important role in many technological applications, including surface coatings, [ 3 ] ionic and molecular sieving, [4][5][6] hydrogen storage, [ 7,8 ] transparent and fl exible electronics, [9][10][11][12] composites, [ 13,14 ] micro-and nanoscale devices, [ 15 ] and biology and medicine. [ 16,17 ] GO papers require certain mechanical properties to provide adequate resistance to the mechanical loads and harsh environments that arise in commercial applications and must retain structural integrity over their lifetimes.Dikin et al. investigated the mechanical properties of GO papers with thicknesses varying from 2.5 to 25 µm with tensile testing. [ 2 ] Kang et al. used nano-indentation on a dynamic contact module system to measure the mechanical properties of 50-and 60-nm-thick GO fi lms. [ 18 ] Park et al. characterized the mechanical properties of one, two, and three overlapped layers of GO platelets using atomic force microscopy (AFM). [ 19 ] The Young's moduli measured with nanoresonators consisting of thin, stacked GO fi lms were found to surpass values obtained in previous measurements. [ 20 ] These results suggest that the mechanical properties of GO fi lms or papers, such as stiffness and fracture strength, might vary with thickness; however, no systematic study of this issue has been carried out to date.Graphene oxide (GO) papers are candidates for structural materials in modern technology due to their high specifi c strength and stiffness. The relationship between their mechanical properties and structure needs to be systematically investigated before they can be applied to the broad range fi elds where they have potential. Herein, the mechanical properties of GO papers with various thicknesses (0.5-100 µm) are investigated using bulge and tensile test methods; this includes the Young's modulus, fracture strength, fracture strain, and toughness. The Young's modulus, fracture strength, and toughness are found to decrease with increasing thickness, with the fi rst two exhibiting differences by a factor of four. In contrast, the fracture strain slightly increases with thickness. Transmission electron, scanning electron, and atomic force microscopy indicate that the mechanical properties vary with thickness due to variations in the inner structure and surface morphology, such as crack formation and surface roughness. Thicker GO papers are weaker because they contain more voids that are produced during the fabrication process. Surface wrinkles and residual stress are found to result in increased fracture strain. Determination of this structure-property relationship provide improved guidelines for the use of GO-based thin-fi lm materials in mechanical structures.
Density-functional theory is used to evaluate the mechanism of copper surface oxidation. Reaction pathways of O2 dissociation on the surface and oxidation of the sub-surface are found on the Cu(100), Cu(110), and Cu(111) facets. At low oxygen coverage, all three surfaces dissociate O2 spontaneously. As oxygen accumulates on the surfaces, O2 dissociation becomes more difficult. A bottleneck to further oxidation occurs when the surfaces are saturated with oxygen. The barriers for O2 dissociation on the O-saturated Cu(100)-c(2×2)-0.5 monolayer (ML) and Cu(100) missing-row structures are 0.97 eV and 0.75 eV, respectively; significantly lower than those have been reported previously. Oxidation of Cu(110)-c(6×2), the most stable (110) surface oxide, has a barrier of 0.72 eV. As the reconstructions grow from step edges, clean Cu(110) surfaces can dissociatively adsorb oxygen until the surface Cu atoms are saturated. After slight rearrangements, these surface areas form a "1 ML" oxide structure which has not been reported in the literature. The barrier for further oxidation of this "1 ML" phase is only 0.31 eV. Finally the oxidized Cu(111) surface has a relatively low reaction energy barrier for O2 dissociation, even at high oxygen coverage, and allows for facile oxidation of the subsurface by fast O diffusion through the surface oxide. The kinetic mechanisms found provide a qualitative explanation of the observed oxidation of the low-index Cu surfaces.
An ultraclean method to directly transfer a large-area MoS film from the original growth substrate to a flexible substrate by using epoxy glue is developed. The transferred film is observed to be free of wrinkles and cracks and to be as smooth as the film synthesized on the original substrate.
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