All chemicals used in this work were of analytic purity and
used without further purification. In a typical procedure, 1.645 g
Na2MoO4·2H2O, 1.5492 g Se and 0.2595 g NaBH4 were dissolved
in 50 mL mixture of distilled water and absolute ethanol (volume
ratio 1:1) under violent stirring. The resulted solution was transferred
into a 100 mL Teflon-lined stainless autoclave. The autoclave
was sealed and maintained at 200 ◦C for 48 h, and then cooled
to room temperature naturally. A black precipitate was collected.
After being washed with absolute ethanol and distilled water, the
final product was dried in a vacuum box at 60 ◦C for 8 h.