Electrochemical Sensor Of Phenolic Compounds Based On Ionic Liquids And Carbon Nanomaterials

3-decyl-l-(3’-pyrrole-propyl) imidazolium tetrafluorob orate (DPPIT) ionic liquid,3-butyl-1-[3’-(N-pyrrolyl)propyl] imidazolium bromide salt (PPBIB) ionic liquid and1-methyl-4-hydroxy-1’-(3-pyrrole-propyl) piperidine bromine salt(HMPPPB) ionic liquid were successfully synthesized. Then, on the basis of the ehanced effects of theseionic liquids and carbon nanomaterials, a series of sensing interfaces were constructed for the electrochemical investigation of phenolic compounds and their determination with high sensitivity.The main research works were presented as following:(1) The3-decyl-l-(3’-pyrrole-propyl) imidazolium bromine ionic liquid was synthesized using1-(3-bromopropyl)pyrrole and1-bromodecane as raw materials. Then, the obtained product was thoroughly mixed with sodium tetrafluorob orate saturated solution to produce3-decyl-1-(3’-pyrrole-propyl) imidazolium tetrafluorob orate (DPPIT) ionic liquid. The ionic liquid not only possesses pyrrole group which can be electrochemically polymerized onto glassy carbon electrode surface using the muti-potential step method, but also contains long carbon chain leading to improve the stability of polymerized ionic film in the aqueous solution. As result, the practical applications of the polymerized ionic liquid film electrode can be improved signifcantly. Voltammetry was emploted to investigate the electrochemical behavior of an environmental estrogen, hexestrol, at the polymerized ionic liquid film electrode. The results show that the hexestrol on the modified electrode has an irreversible oxidation peak. Compared with bare glassy carbon electrode, the oxidation peak of hexestrol increased significantly on the modified electrodes. The oxidation peak current was found linearly related to hexestrol concentration in the range of5.0×10-9～1.0×10-5molL-1. The detection limit was calculated to be1.25×10-9molL-1(S/N=3).(2) Using carboxylic acid-functionalized single walled carbon nanotubes (SWCNTs-COO-) as an anion and3-butyl-1-[3’-(N-pyrrolyl)propyl]imidazolium as a cation, a novel SWCNTs-COO-ionic liquid (SWCNTs-COO-IL) nanocomposite was fabricated successfully. The as-prepared SWCNTs-COO-IL nanocomposite was confirmed with transmission electron microscopy, X-ray photoelectron spectroscopy, UV-vis, FTIR and Raman spectroscopy. The SWCNTs-COO-IL nanocomposite was coated onto a glassy carbon electrode (GCE) surface followed by cyclic voltammetric scanning to fabricate a SWCNTs-COO-/poly{3-butyl-1-[3’-(N-pyrrolyl)propyl] imidazolium ionic liquid} composite film modified electrode (SWCNTs-COO-Poly-IL/GCE).Scanning electron microscope and electrochemical impedance spectroscopy were used to characterize SWCNTs-COO-Poly-IL/GCE. Electrochemical behaviors of bisphenol A (BPA) at the SWCNTs-COO-Poly-IL/GCE were investigated thoroughly. It was found that an obvious oxidation peak appeared without reduction peak in the reverse scanning, indicating an irreversible electrochemical process. The oxidation peak currents of BPA were linearly related to scan rate in the range of20-300mVs-1, suggesting an adsorption controlled process rather than a diffusion controlled process. Differential pulse voltammetry was employed for the voltammetric sensing of BPA. Experimental conditions such as film thickness, pH value, accumulation potential and time that influence the analytical performance of the SWCNTs-COO-Poly-IL/GCEwere optimized. Under optimal conditions, the oxidation peak current was linearly related to BPA concentration in the range of5.0×10-9to3.0×10-5molL-1with a detection limit of1.0×10-9molL-1(S/N=3).(3)1-Methyl-4-hydroxy-1’-(3-pyrrole-propyl)piperidine bromine (HMPPPB) ionic liquid was successfully synthesized, and was characterized with1HNMR, HPLC-MSetc. The ionic liquid was interacted with graphene oxide which has been functionalized with carboxyl though electrostatic attraction to produce a nanocomposite material. The nanocomposite material was characterized by FTIR, UV-Vis, TEM and XPS. Then, the nanocomposite was dispersed with utralpure water and coated onto GCE surface to prepare a modified electrode, then through cyclic voltammetric scanning, a graphene oxide-polymerized ionic liquid film modified electrode was obtained. Elecctrochemical impedance spectroscopy was used to study the interfacial properties of the modified electrode. Electrochemical behaviors of honokiol and magnolol on the modified electrode were investigated with voltammetry. Results indicate that the modified electrode shows better sensitivity towards honokiol than magnolol for the simultaneous determinationA pair of reversible redox peaks was observed for honokiol on the modified electrode, while only a irreversible oxidation peak was found for magnolol. Compared with the unmodified glassy carbon electrode, the redox peak currents of honokiol were significantly enhanced, and in the presence of magnolol, the oxidation peak current was linearly related to honokiol concentration in the range of1.0×10-8～1.0×10-5mol L-1with a detection limit of4.22×10-9mol L-1(S/N=3). Meantime, in the presence of honokiol, the oxidation peak current of was linearly related to magnolol concentration in the range of7.0×10-8～1.0×10-5mol L-1with a detection limit of8.27×10-9molL-1(S/N=3). The as-prepared modified electrode was successfully used to determine honokiol and magnolol in the traditional Chinese medicine.