Resumen de Surface-Enhanced Resonance Raman Scattering and Visible Extinction Spectroscopy of Copper Chlorophyllin:: An Upper Level Chemistry Experiment
Cheryl S. Schnitzer, Candace Lawson Reim, John J. Sirois, Paul G. House
Advanced chemistry students are introduced to surface-enhanced resonance Raman scattering (SERRS) by studying how sodium copper chlorophyllin (CuChl) adsorbs onto silver colloids (CuChl/Ag) as a function of pH. Using both SERRS and visible extinction spectroscopy, the extent of CuChl adsorption and colloidal aggregation are monitored. Initially at pH ∼10, the colloids possess an overall negative surface charge, preventing attraction. Surface-enhanced Raman scattering (SERS) is not detected at that pH because the relatively small colloids do not possess a surface plasmon in resonance with the laser excitation frequency (633 nm). Once the solution pH decreases slightly, colloidal clusters form and SERRS is detected. As the pH is lowered to a value of 4 or 3, protonation of CuChl results in colloidal aggregation and precipitation. If adsorption and aggregation are halted by adding H2SO4(aq) and then NaOH(aq), an intense SERRS signal is steadily detected from acidic pH (about 4), back to the initial basic pH (about 10).
