Facile synthesis of nanocellulose-based Cu 2 O/Ag heterostructure as a surface-enhanced Raman scattering substrate for trace dye detection.

Semiconductor metal-oxide/metal heterostructures with synergetic properties have potential applications in photocatalysis and optical sensors. Here, Cu ₂ O sub-micro cubes were synthesized under environmentally benign conditions using 2, 2, 6, 6-tetramethylpyperdine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils as a reducing and stabilizing agent. Then the surface of the Cu ₂ O cubes was decorated with silver nanoparticles (AgNPs) by a substitution reaction. The Cu ₂ O/Ag heterostructures within the cellulose nanofibrils (CNFs) network were employed as a promising surface-enhanced Raman scattering (SERS) assay for efficient sensing of methylene blue (MB), reaching a maximum enhancement factor (EF) of 4.0 × 10 ⁴ . Their SERS intensities depended on the coverage density of AgNPs and the wavelength of the excitation laser. The excellent SERS performance may result from the charge transfer between Ag and Cu ₂ O molecules and the strong electromagnetic field at the interface. The CNF-Cu ₂ O/Ag substrates were capable of detecting MB dye down to 10 ^-8  M level with a relative standard deviation of 10-15%, demonstrating great sensitivity and reproducibility.
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