New strategies for the synthesis of t-selenium nanorods and nanowires

Selenium exhibits several useful properties such as high photoconductivity and catalytic activity and has commercial use in photocopiers and rectifiers. It also undergoes an interesting amorphous to t-phase transition. Nanorods of selenium of different diameters from 20 nm to several hundred nanometers have been prepared by laser ablation of selenium powder. Se nanowires have been prepared by refluxing selenous acid with N2H4. 2 Se nanorods are also prepared by the reduction of sodium selenate using cytochrome c3. The solution methods generally yield amorphous selenium as the initial product which then transforms to t-selenium. Xie et al. have recently reported the spontaneous transformation of monoclinic Se microballs to trigonal nanorods in ethanol solution. In this communication, we describe a simple and novel solution based synthesis wherein selenium powder is first reacted with NaBH4 to yield NaHSe 6 in solution which then transforms to amorphous selenium. In a typical room temperature reaction, 0.025 g (0.32 mmol) of selenium was mixed with 20 ml of deionized water in a three necked round bottom flask. 0.030 g (0.81 mmol) of NaBH4 was added to this mixture and the flask was immediately purged with nitrogen gas in order to create an inert atmosphere. The entire selenium dissolves in water within 60 minutes giving rise to a clear colourless solution. The colour of the solution starts turning red thereafter. We propose the following reaction scheme for the formation of Se: