UV-Vis absorption spectral changes of the DDTC-metal complexes before and after applying to the AuNP colloidal solution were obtained with a 3220 PC spectrophotometer (Mecasys, Daejeon, Korea). Atomic percentages in wastewater was obtained using a NEXION 350 D ICP-MS spectrometer (Perkin-Elmer, Boston, MA, USA). DFT calculations [30 (link)] and potential energy distribution were performed using the previous literatures [31 (link)]. The Au6 cluster is one of the simplest models of gold atoms. It includes calculations to predict the energetic stabilities and intramolecular interactions of the adsorbates on Au surfaces. This model includes six gold atoms that can connect with each other to generate the triangular geometry needed to form gold clusters.
All Raman data were obtained by using a Raman microscope system RM 1000 spectrometer (Renishaw, Gloucestershire, UK) with a 632.8 nm HeNe excitation laser and a CCD camera. The SERS spectra were recorded by using spectroscopic glass tubes after the preparation of the Cu2+ detection samples. The integration time for SERS measurement was set up at 10 s per spectrum with a range of 200–3200 cm−1. Prior to performing SERS, the spectral positions were calibrated based on Si peak at 520 cm−1.
All Raman data were obtained by using a Raman microscope system RM 1000 spectrometer (Renishaw, Gloucestershire, UK) with a 632.8 nm HeNe excitation laser and a CCD camera. The SERS spectra were recorded by using spectroscopic glass tubes after the preparation of the Cu2+ detection samples. The integration time for SERS measurement was set up at 10 s per spectrum with a range of 200–3200 cm−1. Prior to performing SERS, the spectral positions were calibrated based on Si peak at 520 cm−1.