Ornthida Sae-Khow

Water desalination using carbon-nanotube-enhanced membrane distillation.

Carbon nanotube (CNT) enhanced membrane distillation is presented for water desalination. It is demonstrated that the immobilization of the CNTs in the pores of a hydrophobic membrane favorably alters the water-membrane interactions to promote vapor permeability while preventing liquid penetration into the membrane pores. For a salt concentration of 34 000 mg L(-1) and at 80 °C, the nanotube incorporation led to 1.85 and 15 times increase in flux and salt reduction, respectively.

Carbon nanotubes as the sorbent for integrating μ-solid phase extraction within the needle of a syringe

In this research we report the implementation of micro-solid-phase extraction (mu-SPE) in the needle of a syringe for integrating sampling, analyte enrichment and sample introduction into a single device. Both single- and multi-walled carbon nanotubes (CNTs) were explored as high performance sorbents for mu-SPE in packed and self assembled formats. The need for such a sorbent was critical because the needle probe could hold only a small amount of material (around 300 microg). Conventional C-18 and self-assembled CNTs were found to be ineffective with enrichment factors less than one. However, packed beds of CNTs were found to be excellent sorbent phases, where high extraction efficiencies (as high as 27%) as well as enrichment factors (close to 7) could be achieved. The overall method showed excellent linearity, reproducibility, and low method detection limit (0.1-3 ng/mL for MWNTs). The sorption on CNTs followed Freundlich isotherms, and the functionalized CNTs were more effective for enriching the polar compounds.

Effects of Polymer Wrapping and Covalent Functionalization on the Stability of MWCNT in Aqueous Dispersions

The colloidal behavior of aqueous dispersions of functionalized multiwall carbon nanotubes (F-CNTS) formed via carboxylation and polymer wrapping with polyvinyl pyrrolidone (PVP) is presented. The presence of polymer on the nanotube surface provided steric stabilization, and the aggregation behavior of the colloidal system was quite different from its covalently functionalized analog. Based on hydrophobicity index, particle size distribution, zeta potential as well as the aggregation kinetics studied using time-resolved dynamic light scattering, the PVP wrapped CNT was somewhat less prone to agglomeration. However, its long-term stability was lower, and this was attributed to the partial unwrapping of the polyvinyl pyrrolidone layer on the CNT surface.

Pervaporation in chemical analysis.

Unlike thermal processes such as distillation, pervaporation relies on the relative rates of solute permeation through a membrane and is a combination of evaporation and gas diffusion. The analytical pervaporation systems consist of a membrane module suitable for liquid sample introduction and a vacuum (or a sweeping gas) on the permeate side. It has been used in a wide range of applications including the analysis of various organic and inorganic compounds, and sample concentration. It has been directly interfaced with gas chromatography, spectrophotometry, capillary electrophoresis, electrochemical detectors, liquid chromatography, and mass spectrometry. A wide range of liquids, slurries, and solids samples has been analyzed using these techniques. This review highlights the basic principles of the pervaporation and the state of its current development as applied to analytical chemistry.

Simultaneous extraction and concentration in carbon nanotube immobilized hollow fiber membranes.

Analytical enrichment during continuous hollow fiber membrane extraction involves the movement of analytes from the sample to the extractant. At the same time, a second preconcentration mechanism is provided by out-diffusion of the extracting solvent. These effectively combine extraction and concentration into one step. In this paper, we demonstrate for the first time that the presence of carbon nanotubes (CNTs) can enhance both these phenomenon leading to superior performance in terms of higher enrichment factors and extraction efficiency. The CNTs were immobilized in the pores of a polypropylene hollow fiber and led to nearly 250% enrichment enhancement over the unmodified parent membranes. The detections limits for polycyclic aromatic compounds were between 0.042 and 0.25 microg/L.

Fabrication and characterization of carbon nanotubes immobilized in porous polymeric membranes

We demonstrate that the incorporation of carbon nanotubes (CNTs) in the pores of a membrane can offer several advantages. A dispersion of CNTs in polyvinylidene fluoride was injected through a porous membrane, which immobilized the nanotubes in the pore structure. The CNTs served as a sorbent facilitating solute exchange between the two phases leading to enhancement of the enrichment factor by as much as 93%. The presence of CNTs also developed a diffusion barrier by sorbing solvent on its surface, which led to higher retention of the extractant within the membrane.