Molecular Recognition of Caffeine by Shell Molecular Imprinted Core–Shell Polymer Particles in Aqueous Media
✍ Scribed by S.R. Carter; S. Rimmer
- Publisher
- John Wiley and Sons
- Year
- 2002
- Tongue
- English
- Weight
- 101 KB
- Volume
- 14
- Category
- Article
- ISSN
- 0935-9648
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✦ Synopsis
ter, nearly perfectly cylindrical, well-ordered pores with a very low density of defects. It may also be possible to increase pore filling by improving mass transport in the deposition environment with ultrasonication during deposition and careful control over the bath temperature. [25] In summary, by employing DC electrochemical deposition into porous anodic alumina templates, we have demonstrated a method to reproducibly fabricate high-density, high aspect ratio, narrow Bi 2 Te 3 nanowire arrays. SEM studies indicate that the individual wires are dense and parallel, with approximately 70 % of the pores of the anodic alumina templates completely filled, giving a wire density of ~510 9 cm ±2 . The final composite thickness is ~55±70 lm, and the average wire diameter is ~45 nm, giving wire aspect ratios of greater than 1000. The composition of the arrays has been determined to be Bi 2 Te 3 by EDS and XRD. Because the array-template composites have a high wire density over a large area (>1 mm 2 ) and are relatively thick, they can be easily handled, and the properties of the nanowires can be readily assessed using standard bulk and thin film assessment techniques. Moreover these composites are suitable for direct incorporation into existing device structures for potential thermoelectric or other applications.
Experimental
Nanochannel templates were produced from pieces of Al foil (99.9995 %, AlfaAesar). Coarse mechanical polishing (of the Al foil and the nanocomposite arrays) was performed with 1 lm diamond polishing paste, and the composite arrays were finely polished prior to SEM imaging using a suspension of colloidal SiO 2 . Before anodization, the Al was electrochemically polished in a solution of 95 vol.-% H 3 PO 4 , 5 vol.-% H 2 SO 4 , 20 g L ±1 CrO 3 at ~85 C with Pt gauze as the counter electrode at ~10±20 V for ~10±30 s. Immediately prior to electrode deposition and anodization, the Al working piece was immersed in a solution of 3.5 vol.-% H 3 PO 4 , 45 g L ±1 CrO 3 at ~90 C for at least two minutes to remove any oxide from the surface. Typical anodization conditions were 30 V in 4 % oxalic acid at ~2±5 C. After anodization, the template was rinsed with Millipore H 2 O and transferred without drying to the electrochemical deposition solution. Bismuth telluride was deposited at ±0.46 V vs. Hg/Hg 2 SO 4 (in saturated K 2 SO 4 ) in an ice bath using concentrations of 0.075 M Bi and 0.1 M Te in 1 M HNO 3 in a three-electrode configuration consisting of the reference electrode, a Ag-sputtered alumina template as the working electrode assembly, and Pt gauze as the counter electrode. The reference electrode was immersed in a separate beaker of 1 M KNO 3 and connected to the beaker containing the deposition solution by a KNO 3 /agar salt bridge.
The array structure was studied using a JEOL 6340F SEM, under typical working conditions of 5 kV. The arrays were coated with a thin carbon layer prior to imaging. EDS was conducted in a JEOL 35CF SEM. A Siemens D5000 diffractometer was employed for XRD.