Byung Min Yoo

Selective Gas Transport Through Few-Layered Graphene and Graphene Oxide Membranes

Gas Separations When gas separation membranes are made thinner, they usually allow permeating gases to pass through faster. However, a thinner membrane may be poorer at separating between gas species. Kim et al. (p. 91) examined the permeability and selectivity of layered graphene and graphene oxide membranes. Gas molecules diffuse through defective pores and channels that form between the layers. Controlling these structures tuned the properties of the membranes to allow the extraction of carbon dioxide from other gases. Li et al. (p. 95) describe membranes as thin as 1.8 nanometers made from only two to three layers of graphene oxide. Small defects within the layers allowed hydrogen to pass through, separating it from carbon dioxide and nitrogen. Stacked graphene and graphene oxide membranes prepared with gas flow channels exhibit tunable gas separation performance. Graphene is a distinct two-dimensional material that offers a wide range of opportunities for membrane applications because of ultimate thinness, flexibility, chemical stability, and mechanical strength. We demonstrate that few- and several-layered graphene and graphene oxide (GO) sheets can be engineered to exhibit the desired gas separation characteristics. Selective gas diffusion can be achieved by controlling gas flow channels and pores via different stacking methods. For layered (3- to 10-nanometer) GO membranes, tunable gas transport behavior was strongly dependent on the degree of interlocking within the GO stacking structure. High carbon dioxide/nitrogen selectivity was achieved by well-interlocked GO membranes in high relative humidity, which is most suitable for postcombustion carbon dioxide capture processes, including a humidified feed stream.

Defect-free surface modification methods for solubility-tunable carbon nanotubes

Although carbon nanotubes (CNTs) have outstanding physical properties, there are still challenging issues such as poor dispersibility and miscibility between organic polymers and CNTs for polymer nanocomposites. Chemical modifications (e.g., strong acid based oxidation, carboxylation, etc.) can improve dispersion properties and compatibility, but such surface modification methods often lead to damage to the pristine CNT structure and also deteriorate the mechanical properties of CNTs. Here we demonstrate a simple, defect-free and scalable method for well-dispersed CNTs in common organic solvents, using dopamine and amine-terminated polyethylene glycol derivatives. This method makes it possible to prepare solubility-tunable CNTs without any severe structural deformation. As-modified CNTs were successfully characterized by thermal gravimetric analysis (TGA), Fourier-transformed infrared spectroscope (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscope (TEM). The surface modified-CNTs were well-dispersed in polar and/or non-polar common solvents. The well-dispersed CNTs can be used in a nanofiller in commercial polymers such as thermoplastic polyurethane (TPU) polymer. The CNT/TPU composite showed improved tensile strength without sacrificing elongation at break relative to those of pristine TPU.