Identification of Al₁₃ on the Colloid Surface Using Surface-Enhanced Raman Spectroscopy

Abstract

Al is the most active polymeric Al species responsible for coagulation at the solid-liquid interface, whereas the detection techniques for Al at the interface are currently limited. In this study, for the first time, the identification of Al on the silicon dioxide-based colloid surface was realized by using surface-enhanced Raman scattering (SERS), which is an ideal surface method sensitive for single-molecule detection. The high purity Al salts were prepared by an electrolysis procedure followed by precipitation or metathesis. Al-Cl was determined to be feasible for the Raman detection as it exhibited more noticeable signals in comparison to Al-(SO) and Al-(NO). The peak of Al-Cl at 635 cm could be the major characteristic peak of Al, and the other two peaks at 300 and 987 cm could be accessorial evidence for the identification. Further, the identification of Al adsorbed on the surface of Ag and gold-core/silica-shell colloids was confirmed by the SERS response at the above three wavenumbers with a higher signal-to-noise ratio than the normal Raman scattering. According to the least-squares fitting computed Raman spectra, each of the characteristic peaks was associated with specific vibrational modes.

Enhanced Production of in Situ Keggin Al137+ Polymer by a Combined Fe-Al Coagulation Process for the Treatment of High Alkalinity Water

“…The Raman spectrum of the purified Keggin Al 13 -Cl n compared with the bare silicon wafer and the spectrum of Al­(OH) 3 are illustrated in Figure S5. As reported in the previous study, the stretch-mode frequency at 635 cm –1 was the primary characteristic peak of Keggin Al 13 7+ , while the other two signals of 300 and 987 cm –1 were auxiliary proofs for Keggin Al 13 7+ identification . Compared with the blank Au/SiO 2 , the SERS spectrum of the Au/SiO 2 surface after the combined Fe-Al process clearly shows three bands at 300, 635, and 987 cm –1 , corresponding to the unique vibrational characteristics of a Keggin Al 13 7+ molecule (Figure ).…”

“…The quantification of the in situ Keggin Al 13 7+ polymer formed in the water containing kaolin clay is currently limited due to that kaolin particles would interfere with the test of Al species . To clarify the effect of Fe addition on the Al species during coagulation, the Al-Ferron test was used as a compromise method to quantify the in situ Al species formed in the solution. , The distribution of the in situ formed hydrolyzed Al species at different R Fe:Al is presented in Figure a.…”

“…Kaolin clay (Sinopharm Chemical Reagent Co., Shanghai, China) was in chemical grade and used as a model suspension in the tests. A stock suspension of kaolin of 10 g/L was prepared using the similar method as reported by Yu et al , The purified Keggin Al 13 -Cl n for Raman detection was obtained using the ethanol-acetone precipitation method . The treatment of algae containing RW by the combined Fe-Al coagulation was performed using the source water taken from Qingcaosha reservoir in Shanghai, China, to check its applicability in a realistic water matrix.…”

“…A gold-core/silica-shell (Au/SiO 2 ) suspension was prepared according to the method reported in the previous study and used instead of the kaolin clay during a standard jar test. The aggregation was filtered through the ultrafiltration membrane after a 1 min rapid period to avoid the further transformation of Al species. , Then the dried Au/SiO 2 particles were transferred to the silicon wafer for the Raman analysis.…”

“…As reported in the previous study, the stretch-mode frequency at 635 cm −1 was the primary characteristic peak of Keggin Al 13 7+ , while the other two signals of 300 and 987 cm −1 were auxiliary proofs for Keggin Al 13 7+ identification. 26 Compared with the blank Au/SiO 2 , the SERS spectrum of the Au/SiO 2 surface after the combined Fe-Al process clearly shows three bands at 300, 635, and 987 cm −1 , corresponding to the unique vibrational characteristics of a Keggin Al 13 7+ molecule (Figure 4). This result demonstrates the existence of the Keggin Al 13 7+ polymer at the colloids interface during the combined Fe-Al process.…”