Detection of aromatics in aqueous solution by surface-enhanced Raman scattering by substrates chemically modified with p-tert-butylcalix[4]arenetetrathiol

Abstract

Chemical modification of rough silver surfaces by p-tert-butylcalix[4]arenetetrathiol (BCAT) has been demonstrated to produce substrates for surface-enhanced Raman scattering (SERS) that form reversibly complexes with aromatics from aqueous solutions. Due to this complexation, the detection limits for aromatics without groups that attach to silver are clearly decreased in comparison to mere adsorption at the bare metal surface and were found to be 100 μM for benzene, 50 μM for chlorobenzene, and 5 μM for 1,2-dichlorobenzene in water. The SERS bands of the surface-bound BCAT have been used as an internal standard for the surface concentration of aromatics. The intensity ratio of bands of adsorbed aromatics and surface-bound BCAT has given a measure for the solution concentration of the aromatics with a dynamic range of about 2 orders of magnitude. Characteristic shifts of aromatics bands due to substitution have permitted the identification of benzene derivatives as well as mixture analyses. An adsorption enthalpy of -6.7 kJ/mol has been determined for the adsorption of chlorobenzene by measuring its temperature dependence.