Metasphere-loaded membrane with enhanced dye-filtering efficiency and detection of trace dyes in wastewater at multiple incident wavelengths

Abstract

To ensure aquatic ecosystems and sustainable water supplies, pollutants dissolved or suspended in aqueous systems must be removed and the traces of pollutants must be monitored. Although methods for efficiently removing pollutants and measuring pollutant concentrations with high sensitivity in aqueous systems have been studied and developed separately, an in situ system that simultaneously increases pollutant removal efficiency and detects trace amounts of pollutants is required for effective wastewater management. Here, we developed a metasphere-loaded filter membrane that filters up to 7.4 times more of the target pollutant, the crystal violet (CV) dye, than the unmodified filter membrane and concurrently detects CV down to a minimum concentration of 10-11 M in water. The metaspheres attached to the membrane surface increased the membrane surface area, thereby enhancing filtering efficiency. In addition, because gold colloids are closely associated within the metaspheres, the metaspheres can strengthen the electric fields for broad ranges of incident visible light. For this reason, the metasphere-loaded filter membrane can not only increase the surface-enhanced Raman spectroscopy (SERS) signals but also detect CV under incident excitation at 532 and 785 nm, thereby enabling SERS detection at multiple wavelengths. Moreover, CV could also be identified in an aqueous dye mixture containing CV and methylene blue. The results demonstrate the suitability of this membrane for simultaneously performing multiple important functions in sustaining clean water.