Fe(III)/Polydopamine-Mediated Capture and Release of Catecholic Compounds

Experimental

Materials. Dopamine hydrochloride (98%, Aldrich), trizma base (99%, Sigma), trizma HCl (99%, Sigma), iron(III) chloride hexahydrate (FeCl3·6H2O, 97%, Sigma-Aldrich), pyrocatechol violet (99%, Sigma-Aldrich), silica gel (99%, Sigma-Aldrich), and absolute ethanol (Merck) were used as received.

pDA Coating on Silica Beads. pDA coating was performed by combining silica gel (200-425 mesh particle size, 10 mg/mL) with a dopamine solution (10 mM, pH 8.5) at room temperature. After 1-hr coating, pDA-coated silica beads were separated from the suspension and washed several times by centrifuging/redispersing in water and ethanol.

Column Preparation and Fe(III) Complexation. 1 g of pDA-coated silica beads were suspended in ethanol and poured into the column. After packing, an ethanolic solution of FeCl3 (10 mM, 10 mL) was added to the column for the complexation reaction. Residual FeCl3 was then washed away with ethanol (50 mL).

Capture and Release of Pyrocatechol Violet (PCV). 8 μmol of PCV was dissolved in ethanol and passed through the column. Non-captured PCV was monitored by UV-Vis spectroscopy. Captured molecules were then released by eluting with an EDTA solution (1 mM, pH 3.5). Typically, the eluent was added onto a column and allowed to flow forced by gravity. The elution of the PCV was analyzed by UV-Vis spectroscopy, and the detection wavelength was 445 nm.

Characterizations. X-ray photoelectron spectra were obtained using a MultiLab 2000 system (Thermo VG Scientific, UK) with a Mg Kα X-ray source and ultrahigh vacuum (~10−10 mbar). UV-Vis spectroscopy was performed on a LAMBDA 35 UV/Vis spectrophotometer (Perkin Elmer).