Studies On Electroanalysis And Electrocatalysis Of Several Small Molecules Based On Graphene,noble Metals And Their Composites

Graphene materials,such as graphene oxide?GO?and reduced graphene oxide?RGO?,are important materials to construct nanostructures for various applications.Composite materials of noble metal?NM?-RGO?or GO?are of unique nature and have been widely studied for various applications.In this dissertation,we have briefly reviewed the electrochemistry of NMs,graphene and their composite materials,mainly for catalysis and detection of small molecules,and have prepared several materials of Pt,Au,and their graphene composites for detection of glucose,ascorbic acid?AA?,dopamine?DA?,uric acid?UA?,hydrogen peroxide?H₂O₂?,nitrite?NO₂-?,Pb²⁺ and Cd²⁺ and electrocatalysis of methanol oxidation.The main contents are as follows:1.A composite film of glucose oxidase?GOx?,imidazolium alkoxysilane?ImAS,a silane-ionic liquid?IL?bifunctional reagent?and chitosan?CS?was electrodeposited in an one-pot way on a reduced graphene oxide?RGO?-Pt nanoparticles?PtNPs?modified Au electrode?RGO-PtNPs?for biosensing of glucose.CV electroreduction of coexisting p-benzoquinone was used to lift the electrode-surface pH for the GOx-ImAS-CS deposition,was results of protonation of CS and hydrolyzation/condensation of Im AS at lifted pH.The RGO-PtNPs composite was prepared through mild room-temperature chemical reduction of graphene oxide and H₂PtCl6·6H₂O by formic acid,as characterized by UV-visible/FTIR/Raman spectrophotoscopy,SEM and electrochemical techniques.The GOx-ImAS-CS/RGO-PtNPs/Au electrode was used for glucose biosensing by anodically detecting the enzymatically generated H₂O₂ at 0.55 V vs SCE.Under the optimal conditions,the GOx-Im AS-CS/RGO-PtNPs/Au electrode showed a linear ampeometric response to glucose concentration from 2.0 ?M to 5.5 m M with a sensitivity of 84.4 ?A mM-1 cm-2 and a limit of detection of 0.02 ?M?S/N=3?,which was superior to the GOx-CS/RGO-PtNPs/Au,GOx-?IL-NH₂?-CS/RGO-PtNPs/Au,GOx-?3-aminopropyltriethoxysilane?-CS/RGO-PtNPs/Auand GOx-ImAS-CS/Au electrodes as well as many reported enzyme electrodes.2.A glassy carbon electrode?GCE?was anodically oxidized by CV in 0.1 M sulfuric acid to introduce hydroxyl groups on its surface?GCEox?.Next,an imidazolium alkoxysilane?Im AS?was covalently tethered to the surface of the GCEox via silane chemistry.This electrode was further modified with GO,which dispersed in water,spontaneously assembles on the electrode surface through electrostatic interaction and?-? interaction to give an electrode of type GO/ImAS/GCE.Electroduction of GO and GCEox on the electrode by CV yields electroreduced GO?er GO?and an electrode of the type erGO/ImAS/GCE.This electrode display excellent electrocatalytic activity for the oxidation of ascorbic acid?AA?,dopamine?DA?and uric acid?UA?.Three fully resolved anodic peaks?at-50 mV,150 mV and 280 m V vs Ag/AgCl?were observed during the differential pulse voltammatry?DPV?determination.Under optimized conditions,the linear detection ranges were from 30 to 2000 ?M for AA,from 20 to 490?M for UA,and from 0.1 to 5 ?M and from 5 ?M to 200 ?M?two linear ranges?for DA.The respective detection of limits?S/N=3?are 10 ?M,5 ?M and 0.03 ?M.The GCE modified with er GO and ImAS performs better than a bare GCE or a GCE modified with ImAS only,and also outperforms other reported electrodes for the three analytes.The method was successfully applied to simultaneous analysis of AA,DA and UA in spiked human urine.3.A BSA-RGO composite material was synthesized by hydrothermal reaction in the mixture solution of BSA and GO,cast-coating this material on a GCE surface yielded a BSA-RGO/GCE.Reduction of chloroplatinic acid by formic acid on this electrode yielded a PtNPs/BSA-RGO/GCE.This electrode showed good and selective nonenzymatic oxidation of glucose in neutral solution.PtNPs/BSA-RGO/GCE at 0.5 V in pH 7.4 phosphate buffer showed linear amperometric response to glucose from 2.0?M to 7.5 mM,with a sensitivity of 1.69 ?A m M-1 cm-2 and a limit of detection of2.0 ?M?S/N=3?.The obtained sensitivity was higher than those of reported analogues.Practical applications for serum sample analysis were also satisfactory.4.A RGO-CeO₂ composite material was synthesized by hydrothermal reaction inan aqueous dispersion of GO and Ce?NO₃?₃·6H₂O.After ultrasomic dispersion of RGO-CeO₂ in 0.5% Nafion for cast-coating a GCE,followed by modification of PtNPssynthesized by formic acid reductant,a PtNPs/RGO-CeO₂/GCE was obtained.XRD and FTIR were used to characterize the composition of the hybrid nanomaterials.EIS and SEM were employed to study the interfacial properties and morphologies of different electrodes.The electrochemical properties of electrochemical sensor were investigated by CV and i-t methods.After all experimental parameters were optimized,the Pt NPs/RGO-CeO₂/GCE showed a good performance towards the electrocatalytic reduction of H₂O₂.A linear detection range?LDR?from 4.0 ?M to 4.0 mM?R2=0.9993?and a limit of detection?LOD?of 0.40×10-3 mM?S/N=3?were obtained.It was applied to the determination of H₂O₂ incontact lens care solutions with good accuracy and recovery.5.CV reduction of GO led to erGO modified GCE.PtNPs modified erGO/GCE were fabricated via Pt-Cu co-electrodeposition followed by electrochemical stripping of Cu,and the electrocatalytic reduction of NO₂-was examined on the PtCS/erGO/GCE.Under optimum conditions,the CV current peak was linear with NO₂-concentration from 0.01 to 0.2 mM,with a limit of detection?LOD?of 0.8 m M?S/N=3?.The sensitivity was ca.1.5-fold of that via conventional Pt-electrodeposition protocol.6.An electrochemical sensor based on AuNPs/RGO-Nafion nanocomposite film modified screen-printed carbon electrode?SPCE?was fabricated?AuNPs/RGO-Nafion/SPCE?for simultaneous determination of trace lead ions(Pb²⁺)and cadmium ions(Cd²⁺)in water by differential pulse anodic stripping voltammetry?DPASV?.FTIR,XRD and SEM were employed to characterize the RGO,AuNPs preparation and the construction processes of AuNPs/RGO-Nafion/SPCE.DPASV was used to study the electrochemical determination of Pb²⁺ and Cd²⁺.Under optimum experimental conditions,the stripping peak current showed good linear relationship with Pb²⁺ and Cd²⁺ in the range of 5.0×10-10⁶.0×10-8 and 8.0×10-10⁵.0×10-8 g mL-1,respectively.The detection limit were estimated to be around 2.3×10-10 g mL-1 for Pb²⁺and 3.5×10-10 g mL-1 for Cd²⁺?S/N=3?.The recovery was 94%¹06% in real water samples.The analytical results were comparable well with graphite furnace atomic absorption spectrometry?GFAAS?method.The method was successfully applied to simultaneous analysis of Pb²⁺ and Cd²⁺ in river and ponder water samples.7.A rough Pt film(Pt_meth)was electrodeposited on a GCE in a methanol-containing aqueous bath for electrocatalytic oxidation of methanol.SEM,energy dispersive spectrometry?EDS?,XRD and electrochemistry techniques were used to characterize the electrodeposited Pt films.Comparing to the conventional Pt film electrodeposited in a methanol-free aqueous bath?Ptcon/GCE?,the Pt_meth/GCE exhibits an improved catalytic activity and poisoning-tolerance towards electrooxidation of CH₃ OH.Compared with the electrodeposited Pt films in the presence of CH₃CH₂ OH or CH₃CH₃CH₂ OH,the Pt_meth showed improved electrocatalysis for oxidation of CH₃ OH.In addition,similarly prepared Pt_meth-Au/erGO/GCE showed better electrocatalysis for oxidation of CH₃ OH than Au/erGO/GCE,Pt_meth/erGO/GCE,Pt_meth-Au/GCE or Pt_meth-Au/erGO/GCE.Introduction of Au and erGO can improve not only the catalytic activity but also the poisoning-tolerance towards electrooxidation of CH₃OH.