β-Cyclodextrin Covalently Functionalized Carbon Nanotubes And Its Application In Electrochemical Analysis

Chemically modified electrodes (CMEs) have been a research interest inelectrochemical field since1979. CMEs are different from some other kinds ofelectrodes as they have a molecular monolayer or micrometers-thick layers of filmmade from a certain chemical (depending on the function of the electrode). Thecharacteristics endow CMEs with special new chemical properties in terms ofphysical, chemical, electrochemical, optical, electrical, transport, and other usefulproperties.Carbon nanotubes (CNTs) have been widely used to construct novel nanostructuredelectrochemical sensors and biosensors with enhanced analytical performance due toits excellent electrical and mechanical properties. Many studies demonstrated thatCNTs can enhance the electrochemical reactivity of many kinds of molecules andpromote their electron-transfer reactions at the electrode. Therefore, CNTs-modifiedelectrodes have brought forth many important electroanalytical applications in thepast years. However, the intrinsic van der Waals interactions between pristine tubesresult in the formation of large nanotube bundles, which makes CNTs insoluble incommon solvents and injures the electrical properties. Therefore, functionalization ofCNTs is necessary and important prior to being used to modify electrode. And manystrategies have been applied to the modification of CNTs.β-Cyclodextrin (β-CD) present a conical structure with a hydrophobic inner cavityand a hydrophilic outer side. The most characteristic property of CDs is theirremarkable ability to form inclusion complexes with a wide variety of guestmolecules with appropriate geometry. This property enables CDs to be used in manyfields, including food, drug, cosmetics as well as electronic chemistry.In the present study, we constructed a modified electrode, which combined theexcellent electronic catalytic properties of single-wall carbon nanotubes (SWCNTs)with reorganization ability of β-CD. The modified electrode demonstrated enhancedelectronic properties when applied to detect the detrimental compounds, includingbisphenol A (BPA) and Sudan I. The specific research content is summarized asfollows:(1) Covalent functionalization of SWCNTs with β-CD. β-CD was grafted on the surface of SWCNTs by two successive chemical reactions. This process resulted inthe exfoliation of aggregated SWCNTs bundles as well as the improvement of watersolubility of SWCNTs. The content of β-CD on the surface of SWCNTs was8wt%according to TGA analysis. TEM images revealed that the β-CD components weregrafted on the sidewalls and the tips of SWCNT.(2) The construction of modified electrode. β-CD covalent functionalized SWCNTs(SWCNT–CD) was applied to modify the bare glass electrode. The modified GCEwas then used as a sensor for the determination of bisphenol A (BPA) in aqueoussolution by cyclic voltammetric. The electron transfer properties of the modifiedelectrode were also characterized by electrochemical impedance spectroscopy (EIS).It exhibited a highly sensitive response to BPA, and the enhanced performance can beattributed to the combination of the excellent electrocatalytic properties of SWCNTsand the molecular recognition ability of β-CD as well as the topology of SWCNT–CDconjunct.(3) The electronic chemistry behavior of food additive, Sudan I, was studied on themodified electrode. Some influencing factors, including the supporting electrolyte, thepH of solution, scan rate, accumulation time etc were investigated. And a sensitivedetermination of Sudan I based on electronic chemistry was thus set up.