Design Of ZnO-Based Composite Nanostructure Photoanodes And Studies On Photoelectrochemical Biosensors

ZnO is a kind of n-type, direct, wide-band-gap, ?-? metal oxide semiconducting materials, which possess a variety of outstanding physical and chemical properties. 1D ZnO nanostructures have significantly improved their photo-electric and electric transport properties, thus being widely applied in the solar cells, photoelectrochemical (PEC) cells and other energy conversion devices, as well as UV detectors, biosensors and other information sensing devices. In this thesis, the normal hydrothermal method was adopted to produce high crystal quality ZnO nanorods (NRs) array with low temperature, high yield, and without any catalyst. Based on such materials,2D graphene materials, network 3D graphene foam (3DGF), plasmonic gold nanoparticles and narrow band gap Cu2O p-type semiconducting materials were sequentially taken into combination to form ZnO based composite nanostructures, in which each component worked synergistically to compensate each other. Then the enhancement effect of PEC performance and strengthening mechanism were systematically studied. Such composite nanostructures were further applied in the construction of self-powered PEC biosensor.ZnO NRs array was directly in-situ synthesized on the surface of reduced graphene oxide (rGO) layer. Under UV illumination, the electron transport within photoanode was improved due to the electron extraction property of rGO layer. Therefore, the PEC performance of ZnO/rGO was obviously elevated compared with pristine ZnO. Under 0 V (vs. Ag/AgCl) bias, the so-fabricated ZnO/rGO based PEC biosensor acquired detection limit of 2.17 ?M (n=3) and linear range of 10?200 ?M(R2=0.997).ZnO NRs array was also directly in-situ synthesized on the surface of network 3DGF. Under illumination, the ZnO/3DGF exhibited superior PEC performance compared with ZnO/rGO or pristine ZnO due to the large surface area and high electron transfer efficiency of 3DGF. Under 0 V (vs. Ag/AgCl) bias, the so-fabricated ZnO/3DGF based PEC biosensor acquired detection limit of 1.79 ?M (n=3) and linear range of 10?300 ?M (R2=0.997).Au nanoparticles (NPs) were modified on the surface of ZnO NRs array through UV reduction approach. Under solar light illumination, the light absorption in visible light region was strengthened with localized surface plasmon resonance (LSPR) effect. The excited hot electrons at Au surface were subsequently injected into the conduction band of ZnO, which finally enhanced the PEC performance. Under 0 V (vs. Ag/AgCl) bias, the so-fabricated Au@ZnO based PEC biosensor acquired detection limit of 3.29 ?M (n=3) and linear range of 20?1000 ?M (R-=0.996).ZnO/Cu2O all-oxide p-n heterostructures were assembled through directly electrodepositing Cu2O film onto ZnO NRs array. The thickness of Cu2O film and the electronic structure at the ZnO/Cu2O heterostructure interface were adjusted by changing the electrodepositing time and the carrier concentration in Cu2O, respectively. The sample with optimal light harvesting ability and maximum built-in electric field intensity exhibited elevated PEC performance, which was originated from superiorities in both light absorption and photoinduced charge carrier separation aspects. Under 0 V (vs. Ag/AgCl) bias and solar light illumination, the so-fabricated ZnO/Cu2O based PEC biosensor acquired detection limit of 0.42 ?M (n=3) and linear range of 10?1000 ?M (R2=0.991).In addition, through comparing the PEC biosensing performance of each fabricated ZnO composite nanostructure based photoanodes, it is revealed that the PEC sensing parameters were optimized following the improvement of PEC performance.In this thesis, towards fabricating functional devices, self-powered PEC biosensor with high performance was realized, simultaneously, the PEC property of ZnO based composite nanostructures as well as their corresponding enhancement mechanism were in-depth studied. Based on these works, a further understanding of ZnO based composite nanomaterials'properties is highly expected, which is believed to be necessary for accelerating the development of such materials in PEC or other related solar photovoltaic research fields.