Preparation Of Bi₂WO₆/Graphene-based Functional Nanocomposites And Their Applications In Photoelectrochemical Sensing

Recently,various photoelectrochemical（PEC）sensors have been fabricated in the field of bioanalysis and environmental monitoring.Meanwhile,searching and engineering for innovative and advanced nanomaterials with excellent photoelectrochemical properties are still needed to develop long-term stable,sensitive,and selective PEC sensing system.In this thesis,two graphene-based nanocomposites（NCs）,Bi₂WO₆-reduced graphene oxide（Bi₂WO₆/rGO）and Bi₂WO₆-nitrogen doped graphene quantum dots（Bi₂WO₆/NGQDs）were synthesized by one-pot hydrothermal process successfully.Based on the outstanding photoelectrochemistry（PEC）property,they were employed as sensing interface and further applied for the construction of PEC sensor platform for pentachlorophenol（PCP）and lead ion(Pb²⁺)determination respectively.In addition,on the basis of Ag-TiO₂/3D nitrogen doped graphene hydrogel（3DNGH）and aptamer sensor thechnology,a facile PEC sensor has been constructed for the determination of thrombin.The major details were as follows:1.The Bi₂WO₆/rGO NCs were prepared by a one-pot solvothermal method using ethylene glycol as reducing agent.Furthermore,the photoelectrochemical performances of Bi₂WO₆/rGO with different starting mass ratios of rGO to Bi（NO₃）3 were also discussed.When the starting mass ratio of rGO to Bi（NO₃）3 was 2.94 %,the Bi₂WO₆/rGO had the optimum PEC response and the photocurrent intensity of Bi₂WO₆/rGO with the optimal doping ratio was 2.7 times higher than Bi₂WO₆.Based on the coupling of Pb²⁺-induced allosteric transition of G-quadruplex DNAzyme and the enzymatic biocatalytic precipitation（BCP）,Bi₂WO₆/rGO₂.94% NCs was applied in the construction of a novelPEC sensor for the determination of Pb²⁺.The as-prepared PEC sensor exhibited good anti-interference ability and a favourable linear relationship was received between the photocurrent intensity and the logarithm of the Pb²⁺ concentration over a concentration range from 0.01 to 50 μM and with a detection limit of 3.3 nM（S/N=3）,indicating that Bi₂WO₆/rGO NCs would be a promising material for PEC sensing.2.NGQDs precursor was prepared with using ammonium citrate as raw material under atmospheric pressure.Furthermore,a variety of Bi₂WO₆/NGQDs nanocomposites with different NGQDs content were prepared through a one-pot solvothermal method.In addition,the photoelectrochemical（PEC）performance of Bi₂WO₆/NGQDs with different starting mass ratios of NGQDs to Bi₂WO₆ was also investigated.The results demonstrated that all of the as-prapared Bi₂WO₆/NGQDs produced excellent PEC response than pure Bi₂WO₆.Moreover,when the starting mass ratio of NGQDs to Bi（NO₃）3 was 0.239,the Bi₂WO₆/NGQDs had the optimum PEC response and the photocurrent intensity of Bi₂WO₆/NGQDs with the optimal doping ratio was 6 times higher than Bi₂WO₆.Based on this,a brief sensitive PEC sensor for the determination of PCP was developed.The PEC sensor showed an acceptable linear range from 0.2 pM to 1 nM with a limit of detection of0.06 pM（S/N=3）.Meanwhile,this sensor could be used for PCP determination sensitively and selectivity.3.Ag-TiO₂/3D nitrogen doped graphene hydrogel（3DNGH）was prepared via a one-pot hydrothermal process for the first time and the photocurrent intensity enhanced around 59.5 times than that of bare TiO₂ due to the rational design of the nanocomposite.The introduction of nitrogen doped graphene was capable to facilitate the separation efficiency and transfer rate of the photoinduced electron-hole pairs.Then the PEC performance was further improved because of the localizedsurface plasmon resonance of Ag nanoparticles.On the basis of excellent PEC properties of Ag-TiO₂/3DNGH,a facile PEC sensor has been developed for the determination of thrombin successfully.This proposed Ag-TiO₂/3DNGH PEC bisosensor exhibited good PEC performances with a wide linear range from 0.01 pM to 10 pM and a relative low detection limit of 3 fM（S/N=3）,indicating that Ag-TiO₂/3DNGH would serve as a potential photoactive material for PEC sensing.