(Photo)Electrochemistry Studies Based On TiO₂,Au,and/or Graphene Nanomaterials

Photoelectrochemical study is helpful to the process of photo-to-electric/chemical energy conversion,which has received great attention in the fields such as solar cells,water decomposition,catalytic reduction of CO2 and analytical sensing.On the other hand,nanomaterials and nanotechnology have become one of the engines of contemporary scientific and technological progress.In this dissertation,after reviewing some literatures in relevant fields,the development of functional materials and the performance of electrochemical devices have been studied on the basis of TiO₂,gold,and/or graphene nanomaterials(or their composites).The main contents are as follows.1.A new ternary plasmonic photocatalyst based on multilayered gold nanoparticles decorated graphene(GR)-TiO₂ heteronanostructure((Au NPs)x/GR-TiO₂)is fabricated via a simple poly(diallyldimethylammonium chloride)(PDDA)assisted calcination process in combination with the layer-by-layer assembly(LBL)technique.A remarkably enhanced charge separation efficiency of the as-prepared(Au NPs)x/GR-TiO₂ is obtained by the plasmonic Au NPs and high electron-conducting GR sheets.Compared with TiO₂ and GR-TiO₂,(Au NPs)2/GR-TiO₂ modified indium tin oxide(ITO)electrode shows significantly enhanced photocurrent intensity(6-fold of TiO₂/ITO and 3-fold of GR-TiO₂/ITO).A sandwich thrombin photoelectrochemical aptasensor is fabricated by using(Au NPs)2/GR-TiO₂/ITO immobilized aptamer 1 as the capture probe.The detection probe is graphene oxide(GO),horseradish peroxidase(HRP),and Au NPs triple-labeled aptamer 2(GO-HRP-Au NPs-apt2). On the basis of HRP catalyzed H2O2 oxidation of 4-chloro-1-naphthol to yield an insulating product on the transducer surface that obstructs the electron transfer of the electron donor(ascorbic acid,AA)to the electrode surface,the sensitive detection of thrombin can be carried out by the decrement of photocurrent intensity.The covalent immobilization of HRP on GO can effectively improve the HRP enzyme loading and thus the sensitivity of the sensor.Under the optimum conditions,a linear response is obtained over the range of 0.05–110 p M,with a limit of detection of 0.02 p M.2.The photoelectrochemistry performance of TiO₂ is somewhat limited by its wide band gap and low quantum efficiency,and the innovation of its composite materials provides a promising solution for an improved performance.Herein,a composite of melanin-like L-3,4-dihydroxyphenylalanin(L-DOPA)polymer(PD)modified Au nanorod@TiO₂ core-shell nanostructure(AuNR@TiO₂)is designed and prepared by chemical oxidation polymerization and electrochemical oxidation polymerization.The AuNR core and the outer-layer PD polymer tethered by the TiO₂-hydroxyl complexation can intensify the long-wavelength light harvesting,and the AuNR core can enhance the hot-electron transfer and the electron-conductance.The photocurrent of the PD/AuNR@TiO₂ is 8.4-fold improved versus that of commercial TiO₂,and the maximum incident photon-to-electron conversion efficiency(IPCE)reaches 65% in the UV-visible-near-infrared region.Glucose oxidase(GOx),horseradish peroxidase(HRP),Au nanoparticles,PD nanocomposite(HRP-GOx-Au-PD)and chitosan(CS)is modified on the calcined AuNR@TiO₂/fluorine-doped tin oxide(FTO)successively to obtain the CS/HRP-GOx-Au-PD/AuNR@TiO₂/FTO enzymatic electrode.In phosphate buffer containing glucose and 4-chloro-1-naphthol,the GOx-catalyzed oxidation of glucose by O2 generates H2O2,and HRP catalyzes H2O2 to oxidize 4-chloro-1-naphthol to form a precipitate on the electrode,resulting in photocurrent decrement.The decrement of photocurrent intensity is proportional to the common logarithm of glucose concentration.The linear detection range is from 0.05 ?M to 10.0 m M glucose,with a limit of detection of 0.01 ?M(S/N=3).The application potential of human serum sample analysis is examined with satisfactory results.3.Enzyme-induced biocatalytic deposition(BCP)strategy has been widely used in developing photoelectrochemical immunosensors.Herein,an AuNR@CeO₂-HRP nanocomposite is prepared,which can catalyze the oxidation reaction of 4-chloro-1-naphthol by H2O2 to form a precipitate.A graphite carbon nitride(g-C3N4)-TiO₂ modified ITO electrode(g-C3N4-TiO₂/ITO)is used to immobilize the primary antibody(Ab1)of human IgG by CS-glutaraldehyde cross-linking method.A sandwich photoelectrochemical immunosensor is fabricated by using an AuNR@CeO₂-HRP nanocomposite adsorbed secondary antibody(Ab2)as the signal unit.The g-C3N4-TiO₂ composite possesses high photoelectric activity due to the good energy-level match between TiO₂ and g-C3N4.The excellent biocatalytic property of AuNR@CeO₂-HRP nanocomposite leads to high analytical performance.Under the optimum conditions,the linear detection range is 0.7-100 ng m L-1,with a limit of detection of 0.2 ng m L-1.4.A gold nanoparticles-graphene complex(Au NPs-GR)is deposited by cyclic voltammetry on the surface of a glassy carbon electrode(GCE)in the mixed solution of GO and HAu Cl4.After assembling HS-thrombin aptamer on Au NPs-GR/GCE,and adsorbing methylene blue(MB)after bovine serum albumin(BSA)blocking treatment,the simple,rapid,sensitive and specific detection of thrombin is achieved by detecting the change of voltammetry signal of MB.The Au NPs-GR can effectively increase the surface adsorption capacity and thus the voltammetric signal of MB.Under the optimized conditions,the linear detection range for thrombin detection is 0.02–100 n M,and the limit of detection is 8 p M.5.A porous graphene-Au(p GR-Au)composite is deposited on gold electrode by potentiostatic reduction method in a mixed solution of NH4 Cl,HAu Cl4 and GO.The supercapacitor and electrocatalytic properties of p GR-Au/Au electrode are investigated.The p GR-Au/Au electrode shows a specific capacitance of 10.5 m F cm-2 at the current density of 0.3 m A cm-2 and possesses good catalytic performance for oxygen reduction.