Photochemical synthesis of ZnO@Au nanorods as an advanced reusable SERS substrate for ultrasensitive detection of light-resistant organic pollutant in wastewater.

The prospect of wielding surface-enhanced Raman spectroscopy (SERS) as a powerful technique for ultrasensitive detection of organic molecules in wastewater has received extensive attention in environmental surveillance. Based on ultraviolet (UV, 405 nm) laser irradiation of ZnO nanorods in HAuCl4 solution, ZnO@Au nanorods with controllable Au nanoparticles were successfully fabricated and established as an advanced SERS-based substrate. The reduction of Au ions was driven by the generation of electron-hole pairs via UV laser excitation of semiconductor-based nanomaterials, resulting in the moderate overgrowth of Au nanoparticles on the ZnO nanorods. The Au composition-dependent SERS analysis of crystal violet (CV) molecules revealed that the ZnO@Au nanorods with 16.21% Au contents exhibited optimized SERS activity in comparison with other nano-substrates in this paper. Furthermore, the detection limit of light-resistant methyl blue (MB) dye molecules was achieved at nanomole (nM) level of 10-9 M (0.8 μg/L), providing ultrasensitive detection of organic pollution in wastewater. Even after twenty recycles, the excellent reusability of this novel substrate with 65% original SERS intensity was achieved by subsequently eliminating the residual MB molecules via photocatalytic degradation. Therefore, the as-prepared ZnO@Au nanorods can serve as a cost-effective, clean, reusable and active SERS substrate for ultrasensitive monitoring of light-resistant organic pollutant in natural ecosystems.