Construction Of Photoelectrochemical Sensor Based On Bismuth Sulfide Composite And Its Application In Food Analysis

Photoelectrochemical（PEC）sensing is a detection technology that combines PEC technology with electrochemical sensing.PEC sensor is regarded as a promising detection technology because it has the advantages of high sensitivity,low background signal,fast analysis speed and simple operation.The detection signal of PEC sensing comes from the photoactive materials.Bismuth sulfide（Bi₂S₃）,as a narrow-band gap semiconductor,has strong visible light absorption ability.However,it also has the phenomenon that photogenerated electrons and holes are easy to recombine,which leads to low photoelectric conversion efficiency and limits its application in PEC sensing.It has become a research hotspot in PEC sensing field to improve PEC performance of Bi₂S₃by adopting such strategies as element doping,conductive material modification and heterojunction construction.In this thesis,different morphologies of Bi₂S₃-based composites were prepared by different synthesis methods,and the micromorphology,chemical composition and light absorption capacity of the composites were investigated by various characterization methods.On the basis of Bi₂S₃-based composite material,a series of PEC sensing platforms were constructed by combining different PEC detection strategies for the detection of food contaminants.The main research results are as follows:（1）Molecularly imprinted photoelectrochemical sensor（MIP-PEC sensor）based on Bi₂S₃/Bi₄O₅Br₂composite for the detection of fumonisin B1.Using Bi₂S₃/Bi₄O₅Br₂composite as photosensitive substrate,a MIP-PEC sensing platform is constructed for sensitive detection of fumonisin B1（FB1）.Bi₄O₅Br₂nanoparticles containing oxygen vacancies are prepared by alcohol hydrolysis.The introduction of oxygen vacancies can generate new energy level,adjust the band position,narrow the band gap,and capture electrons or holes to promote the separation of photogenerated charge,so as to obtain a higher photocurrent response.Bi₂S₃/Bi₄O₅Br₂composite is prepared by in-situ growing Bi₂S₃thin sheets on Bi₄O₅Br₂nanoparticles by self-sacrificing method.Bi₂S₃/Bi₄O₅Br₂shows strong PEC activity due to its strong light absorption capacity and effective separation of photogenerated carriers,which provides stable photocurrent signal for MIP-PEC sensor.On this basis,MIP is modified on the surface of Bi₂S₃/Bi₄O₅Br₂by UV polymerization.After elution of template molecule FB1,amount of specific recognition sites are generated in MIP.In the existence of FB1,MIP can recognize and recombine with it.The combination of MIP as a recognition element with PEC sensor greatly improves the selectivity of the prepared sensor.The linear range of FB1 detection is 1.0-1.0×10⁵ng/mL,and the detection limit is 0.028 ng/mL（S/N=3）.The sensing platform has been successfully applied to the detection of FB1 in maize and milk samples,and the recovery is 95.4-108.0%.（2）Molecularly imprinted photoelectrochemical sensor based on Bi₂S₃/Bi₂O₂CO₃composite for the detection of aflatoxin B1.A MIP-PEC sensor based on Bi₂S₃/Bi₂O₂CO₃direct Z-heterojunction is constructed for the detection of aflatoxin B1（AFB1）.Bi₂S₃nanofibers grow on the two-dimensional Bi₂O₂CO₃disks to form Bi₂S₃/Bi₂O₂CO₃heterostructure by adding thiourea.Under light illumination,the Z-scheme charge transfer system in Bi₂S₃/Bi₂O₂CO₃is favorable for the separation of photogenerated carriers,resulting in higher photocurrent response than pure Bi₂O₂CO₃and Bi₂S₃.Due to the limited selectivity of PEC sensor,MIP is introduced to achieve the specific recognition of AFB1.With MIP as the identification element and Bi₂S₃/Bi₂O₂CO₃as the signal conversion element,the linear range of MIP-PEC sensor is 0.01-1000 ng/mL,and the detection limit is as low as 2.95 pg/mL.The MIP-PEC sensor has been applied to detect AFB1 in maize and sesame oil samples.The recovery ranges from 96.8 to 105.0%.（3）Molecularly imprinted photoelectrochemical sensor based on Bi₂S₃/Bi OCl composite for the detection of oxytetracycline.Bi₂S₃/Bi OCl composite is synthesized by a simple one-pot hydrothermal method.Bi₂S₃/Bi OCl shows a higher photocurrent signal than pure Bi₂S₃and Bi OCl.Using o-phenylenediamine as functional monomer and oxytetracycline（OTC）as template molecule,MIP membrane is modified on the surface of Bi₂S₃/Bi OCl by electropolymerization.When OTC molecules are eluted,a number of specific recognition sites are formed within MIP.Through these recognition sites,OTC can be recombined with MIP,and the detection of the OTC can be achieved through changes in the photocurrent before and after binding.The results show that OTC concentration has a good linear relationship with photocurrent in the range of 1.0-1.0×10⁵nmol/L,and the detection limit is0.035 nmol/L（S/N=3）,and the MIP-PEC sensor has good selectivity for OTC.In addition,the actual detection performance of the prepared MIP-PEC sensor in tap water and milk samples is investigated,and the recovery is 92.9-107.1%.（4）Photoelectrochemical aptamer sensor based on ZIF-8/Bi₂S₃composite for the detection of kanamycin.ZIF-8 is a kind of MOF material with zeolite structure,which is grown in situ on sea urchin Bi₂S₃to synthesize ZIF-8/Bi₂S₃composite.Under visible light irradiation,ZIF-8/Bi₂S₃exhibits a higher photocurrent signal than pure ZIF-8 and Bi₂S₃,because the charge transfer system of ZIF-8/Bi₂S₃composite promotes the separation of photogenerated electrons and holes.In the presence of KAN,the chain replacement reaction is triggered to generate single-stranded messenger DNA.The capture DNA on the surface of ZIF-8/Bi₂S₃can hybridize with messenger DNA to form double-stranded DNA,which is used to load the simulated enzyme manganese porphyrin（MnPP）.MnPP can catalyze 4-chloro-1-naphthol to produce benzo-4-chlorohexadienone（4-CD）on the surface of the modified electrode in the presence of H₂O₂.The 4-CD precipitate impedes the charge transfer on the electrode surface and thus weakens the photocurrent.With the increase of KAN concentration,the photocurrent decreases gradually.The linear range is10-1.0×10⁶nmol/L,and the detection limit is 0.1 nmol/L（S/N=3）.The designed sensor platform can be used for the detection of KAN in milk samples,and the recovery is 94.2-109.0%.（5）Photoelectrochemical sensor based on Bi₂S₃/TiO₂composite for the detection of chlorpyrifos.TiO₂nanotube arrays（TNTAs）were prepared by a two-step anodic oxidation process and calcined in an argon atmosphere to intoduce oxygen vacancies（V_o-TNTAs）into it.Oxygen vacancy has the effect of narrowing band gap and trapping photogenerated carrier,which can promote the separation of electrons and holes,so V_o-TNTAs exhibits higher photocurrent response than pure TNTAs.Based on V_o-TNTAs,Bi₂S₃particles are loaded on V_o-TNTAs by successive ionic layer adsorption and reaction method to prepare Bi₂S₃/V_o-TNTAs composite.Due to the efficient charge transfer system of Bi₂S₃/V_o-TNTAs,the photogenerated carrier recombination is inhibited and the photocurrent is further improved.Chlorpyrifos（CPF）will form a Bi-CPF complex with Bi³⁺in Bi₂S₃/V_o-TNTAs,blocking the electron transfer process between the electron donor ascorbic acid and Bi₂S₃/V_o-TNTAs,resulting in weakened photocurrent.Under optimal conditions,the linear range of CPF detected by PEC sensor is 0.07-3.0μmol/L,and the detection limit is 6.0nmol/L.The PEC sensor can be successfully applied to the detection of CPF in lettuce and cucumber samples,and the recovery is 95.7-110.0%.