Extracellular biosynthesis of Cu_2-xSe nanocrystallites with photocatalytic activity

Semiconductor Cu_2-xSe nanospheres were successfully biosynthesized based on bioreduction of SeO₃ ²⁻ into Se^2- by the selenite-reducing bacterium, Pantoea agglomerans. The Cu_2-xSe nanospheres had excellent crystallinity with a face-centered cubic structure and an average diameter of 80 nm. Composition and oxidation states analysis using X-ray photoelectron spectroscopy and X-ray energy dispersive spectroscopy followed by optical characterization using ultraviolet-visible and Fourier transform infra-red spectroscopy confirmed that the biosynthesized Cu_2-xSe nanospheres were capped by proteins. The extracellular proteins which mediated biosynthesis were visualized by excitation–emission matrix fluorescence spectroscopy. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis revealed that the molecular masses of proteins were about 110, 50, 38, 35 and 25 kDa. The biosynthesized Cu_2−xSe nanospheres showed an excellent and stable photocatalytical activity under sunlight irradiation in the degradation of methylene blue for four cycles. This study put forward a green and toilless way to manufacture copper selenide nanoparticles using a biological process.