Kunsil Lee

MOF-derived ZnO and ZnO@C composites with high photocatalytic activity and adsorption capacity

Nanostructured ZnO materials have unique and highly attractive properties and have inspired interest in their research and development. This paper presents a facile method for the preparation of novel ZnO-based nanostructured architectures using a metal organic framework (MOF) as a precursor. In this approach, ZnO nanoparticles and ZnO@C hybrid composites were produced under several heating and atmospheric (air or nitrogen) conditions. The resultant ZnO nanoparticles formed hierarchical aggregates with a three-dimensional cubic morphology, whereas ZnO@C hybrid composites consisted of faceted ZnO crystals embedded within a highly porous carbonaceous species, as determined by several characterization methods. The newly synthesized nanomaterials showed relatively high photocatalytic decomposition activity and significantly enhanced adsorption capacities for organic pollutants.

Easy Preparation of Self-Assembled High-Density Buckypaper with Enhanced Mechanical Properties

A controlled assembly and alignment of carbon nanotubes (CNTs) in a high-packing density with a scalable way remains challenging. This paper focuses on the preparation of self-assembled and well-aligned CNTs with a densely packed nanostructure in the form of buckypaper via a simple filtration method. The CNT suspension concentration is strongly reflected in the alignment and assembly behavior of CNT buckypaper. We further demonstrated that the horizontally aligned CNT domain gradually increases in size when increasing the deposited CNT quantity. The resultant aligned buckypaper exhibited notably enhanced packing density, strength, modulus, and hardness compared to previously reported buckypapers.

Determination of solubility parameters of single-walled and double-walled carbon nanotubes using a finite-length model

Carbon nanotube (CNT) dispersions have been prepared using a variety of surface modification methods; however, these methods frequently have a negative effect on the intrinsic properties of CNTs or need to remove the surface modifiers. The Flory-Huggins theory suggests that such problems can be alleviated or eliminated, if ideally, when the solubility parameters of CNTs and a given medium are very similar or equal to each other. Since the earlier reported solubility parameters of CNTs were determined by indirect methods and varied in wide ranges, we suggested herein a possible way of directly determining the solubility parameter of various types of CNTs by using a finite-length model, and reported the determined solubility parameters of pristine single-walled carbon nanotubes (SWCNTs) and pristine double-walled carbon nanotubes (DWCNTs). Through the validity test of the suggested model it was found that a 2 nm finite-length of CNTs can represent the longer CNTs for the study of the solubility parameters. In addition, the pristine DWCNTs were found to have higher solubility parameters than the pristine SWCNTs, and within the given type of CNTs, the solubility parameters varied inversely with the diameter of the CNTs. Based on the obtained results, it was expected that the solubility parameters for pristine multi-walled carbon nanotubes (MWCNTs) should be similar to or slightly higher than the values for DWCNTs.

Effects of chirality and diameter of single-walled carbon nanotubes on their structural stability and solubility parameters

The chirality and diameter are found to simultaneously affect the solubility of SWCNTs. The solubility parameter of armchair SWCNTs is greater than that of zigzag SWCNTs, for a given diameter and length, except for very small diameters. The lower structural stability of the armchair SWCNTs leads to smaller molar volumes. Thus, the chirality of SWCNTs alters the structural stability and consequently the solubility parameter of the SWCNTs.