4. Experimental sections
Sodium molybdate dihydrate (Na2MoO4∙2H2O, 99.5% purity; Sigma aldrich), selenium powder (Se, 99.5% purity, Sigma aldrich), sodium borohydride (NaBH4, 97% purtiy; Daejung), and ethanol (C2H5OH, 99.5% purity; Daejung) were used without purification. Deionized (DI) water of 18.2 MΩ cm−1 was obtained using a water purification system (V-RO up 15-S, A.F ENG, Korea).