Adsorption of methylene blue onto silylated silica surfaces, studied using visible attenuated total reflection spectroscopy with a slab optical waveguide.
The behavior of methylene blue (MB) molecules at silica/water and silylated silica/water interfaces was examined using visible attenuated total reflection spectroscopy with a slab optical waveguide (SOWG). An alkyl silane coating changed the adsorbed form of MB on the surface from a dimer (lambda max = 600 nm, bare silica surface) to a monomer (lambda max = 670 nm), and the carbon number of the silylation reagent influenced the amount of adsorption and the orientation of the molecule. Moreover, the addition of an anionic surfactant, dodecylbenzenesulfonate (DBS), caused the deposition of MB/DBS ion pairs, which gave an identical attenuated total reflection (ATR) spectrum to that of the dimer. Linear dichroism measurements revealed that the ion pairs were adsorbed onto the silylated silica surface randomly in terms of the orientation angle of MB, while the MB monomer was strongly oriented, i.e., the direction of the transition moment of MB roughly parallels the surface plane. This difference in the orientation angles of the adsorbed species can be utilized for their selective detection using polarization SOWG measurements.
Tsunoda
Kin-Ichi
K
Department of Chemistry, Gunma University, Kiryu 376-8515, Japan. tsunoda@chem.gunma-u.ac.jp
Umemura
Tomonari
T
Ueno
Hiroko
H
Okuno
Eriko
E
Akaiwa
Hideo
H
D000327:Adsorption; D008751:Methylene Blue / Q000737:chemistry*; D012821:Silanes / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D013053:Spectrophotometry / Q000379:methods*; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry; D014867:Water / Q000737:chemistry
D012821:Silanes; D013501:Surface-Active Agents; D014867:Water; D012822:Silicon Dioxide; D008751:Methylene Blue