Analytical Sciences

Abstract − Analytical Sciences, 22(3), 357 (2006).

Adsorption Characteristics of a Nanodiamond for Oxoacid Anions and Their Application to the Selective Preconcentration of Tungstate in Water Samples
Hiroki SAKURAI,* Noboru EBIHARA,** Eiji OSAWA,*** Makoto TAKAHASHI,*** Masanori FUJINAMI,* and Koichi OGUMA*
*Department of Applied Chemistry and Biotechnology, Faculty of Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
**Chiba Industrial Technology Research Institute, 889 Kasori-cho, Wakaba-ku, Chiba 264-0017, Japan
***NanoCarbon Research Institute, Rm 301, Toudai Kashiwa Venture Plaza, 5-4-19 Kashiwa-no-ha, Kashiwa, Chiba 277-0882, Japan
A nanodiamond with a mean particle size of 4 nm, which was prepared by the detonation of a nanodiamond, has been characterized and used as a collector for tungstate in water samples. An aqueous solution of nanodiamond was found to be stable over the pH range from 3 to 10. Coagulation of the nanodiamond could be brought about by adding an electrolyte solution. The adsorption characteristics of nanodiamond have been elucidated to be attributable to amino groups on its surface by the elemental-analysis data and the zeta potential measured in weak acid media. The unique adsorption properties of the nanodiamond for oxoacid anions were applied to a selective preconcentration method for tungstate in water samples. An appropriate amount of nanodiamond was added to a sample solution at pH 5 and a calcium chloride solution was added to aggregate nanodiamond. The sample solution was then allowed to stand for 2 h and centrifuged. The nanodiamond was transferred onto a membrane filter, washed with a diluted calcium chloride solution and treated in advance of an ICP-AES measurement by either of the following procedures: (a) redispersion of the nanodiamond into dilute nitric acid with an ultrasonic washer and (b) ashing of the membrane filter and the coagulated nanodiamond at 700°C, followed by a treatment of the ash with hydrochloric and tartaric acids. The average recovery of tungstate from 100-ml artificial river-water was found to be 99% at the 0.25 ppm level with an RSD of 2.2% (n = 3). The concentration factor at present is 10.