All solution preparations and syntheses were carried out under a fume hood. Catechol is harmful upon contact with tissue or if ingested. Acetonitrile is toxic or fatal by inhalation, ingestion or skin absorption. Tetrabuytlammonium tetrafloroborate is an irritant to eyes, the respiratory system and the skin. The compound 3-methylthiophene is highly flammable, and harmful through inhalation.
Upon mixing concentrated sulfuric acid with water (Corning Mega Pure system) and hydrochloric acid, heat evolves so precaution was taken in this mixing step. All waste was disposed of in the proper waste container with labels. Protective garment and gloves were worn at all times. For preparation of the modified sonogel-carbon titanium oxide electrode, all steps were carried out under a hood and care was taken not to inhale the methyltrimethoxysilane (MTMOS) or graphite powder. All MSDS information can be found at www.sigmaaldrich.com for all products.
Construction of the modified electrodes
The sonogel-carbon electrode was prepared by first creating a carbon mixture to be packed in a small glass capillary tube. The carbon material was manually packed into the glass tube by pushing the glass tube into the thick carbon layer. The methyltrimethoxysilane (MTMOS, Fluka) and 0.2 M HCl (A.C.S. Reagent by Fisher) were combined in a vial, and the mixture was ultrasonicated (2510R-DH, Bransonic) in a 40 mL borosilicate glass vial with cap for 15 seconds. Graphite powder (Alfa Aesar 99.9%, 2-15 micrometer) was added and homogenously dispersed. Prior to placing the mixture of 500 μL MTMOS, 100 μL 0.2 M HCl and graphite, into a capillary tube (Sutter Instrument, 0.69 mm I.D., 1.2 mm O.D., 10 cm length, borosilicate glass both ends open), a 0.25 mm copper wire was inserted to serve as an electrical contact, the copper wire (Alfa Aesar) was coated with thin insulator, but removal is not necessary since the insulator layer was removed during the 500οC heating process in air. The titania precursor titanium tetraisopropyloxide (TTIP, Aldrich) material was prepared as follows: Tween 80 (Aldrich) 2.62 grams was dissolved in isopropanol (99%, Fisher), followed by the addition 0.68 mL of concentrated acetic acid (Aldrich) and 0.61 mL of titanium tetraisopropyloxide under vigorous stirring. The capillary tube containing the carbon material was dip coated with the titanium oxide (Aldrich) material. After coating, the capillary tubes were heated to 500οC for 20 minutes , and cooled naturally.
Electropolymerization was carried out in a one compartment cell, illustrated in Figure 1, that contained 0.05 M 3-methylthiophene (P3MT, Aldrich), 0.1 M tetrabutylammonium tetrafluoroborate (Fisher Scientific), and acetonitrile (HPLC grade, Aldrich). The P3MT was grown on a sonogel-carbon electrode at a potential range of -0.2 V to+1.7 V for 5 cycles. All cyclic voltammograms were carried out in 10 mM sulfuric acid (A.C.S. Reagent by Fisher Scientific).
All electrochemical measurements were carried out on a Bioanalytical Systems Epsilon, in a single compartment cell as displayed in Figure 1, at room temperature. The auxiliary electrode was a platinum wire, and an Ag/AgCl/3 M NaCl electrode was used as the reference electrode, and the composited filled capillary tubes dipped in TiO2 sol-gel and electrodeposited with P3MT were used as the working electrodes. The Catechol (99% HPLC grade) and ascorbic acid (99% HPLC grade) were all purchased from Aldrich. All solutions such as catechol and ascorbic acid were prepared with Corning Mega Pure Water. Cyclic voltammetry at a scan rate of 100 mV/s was the electrochemical technique applied to study the behavior of the modified electrodes.
Figure 1. Schematic diagram of three-electrode compartment single compartment cell.