In the last year, we have been working to extend the CEINT online catalog. The products include a combination of nanomaterials acquired from commercial sources and nanomaterials synthesized, purified, and characterized by Core A. Currently, there are 31 nanomaterials available. Since the beginning of this year, there have been 26 orders filled, with 60 products ordered, including silver nanoparticles, gold nanoparticles, metal oxide nanomaterials, and carbon nanotubes. In addition, we have been working on varying conditions to make the synthesis of PVP-coated silver nanoparticles more consistent.
We also handle some extended characterization of nanomaterials, such as the collaboration with Keith Houck and Amy Wang of the EPA. This project is part of the NCCT ToxCast program, which correlates physical and chemical characteristics of materials (chemical compounds and nanomaterials) to toxicity in cell and zebrafish high-throughput assays. The Core A contribution to the project includes making the nanomaterial dispersions, as well as characterization of the materials using TEM, SEM, XRD, zeta potential, and DLS of stock dispersions and dilutions in various media. Thus far, 45 of the 60 dispersions have been made. For these materials, TEM, SEM and XRD have been completed, and zeta potential and DLS measurements are underway. We are also in the process of analyzing the XRD data for phase, grain size, and lattice information.
Thirdly, we have studied the formation of composite nanomaterials made from carbon nanotubes and graphene with metal oxides and studied their performances as electrode materials in supercapacitors. The effect of carbon nanotubes and graphene are compared. In our approach, we synthesized the composites of graphene/MnO2 and carbon nanotube/MnO2 through a simple but effective chemical co-precipitation method. Electrochemical measurements using cyclic voltammetry (CV) and galvanostatic charge-discharge techniques show that the efficiency of MnO2 was greatly improved, with the specific capacitance generally higher than 300 F/g (at 10 mV/s) and 55%~65% of the high Csp retained at 500 mV/s across a range of material ratios and mass loading densities. Compared with graphene, carbon nanotubes was able to provide MnO2 better performance as ultra-thin film due to its higher conductivity. However, as the film goes thicker, the electrolyte ion diffusion resistivity across the composite film seems to become the major limitation and these two composites behave very similarly.
Finally, in collaboration with Professor Lee Ferguson, we have studied the light emission from double walled carbon nanotubes (DWNTw). Light emission from carbon nanotubes, including single walled carbon nanotubes (SWNTs) and DWNTs is one of the best method to track nanotubes in the environment. DWNTs have recently been recognized as important members in the carbon nanotube family because they are expected to have certain unique properties. For example, DWNTs are expected to replace SWNTs in biomarker applications and optoelectronics if the observed luminescence from DWNTs can be verified. However, due to unavoidable byproducts, such as SWNTs, optical properties of DWNTs still remains controversial. There is an on-going debate concerning the ability of DWNTs to exhibit photoluminescence (PL). We have clearly resolved this debate through the study of carefully separated DWNTs. DWNTs were successfully separated from SWNTs using density gradient ultra-centrifugation. We clearly show that light is emitted from the inner wall of DWNTs; however, the intensity of the emission is significantly quenched. Interestingly, it was found that a very narrow range of diameters of the inner walls of DWNTs is required for PL to be observable. All other diameters led to complete PL quenching in DWNTs. In short, we have shown that both sides of the debate are correct under certain situations. The real answer to the question is that some DWNTs do emit light but most DWNTs do not.