The Preparation Of Metal Oxide/CdS Heterojuntions And Their Applications For Photoelectrochemical Assay

Due to the advantages of high natural abundance,low cost,simple preparation,controllable morphology and good stability,metal oxide semiconductor materials are commonly used in the preparation of photoelectrode materials,and have shown infinite potential in the fields of photocatalysis and photoelectrochemical?PEC?sensing.However,due to the inherent limitations of metal oxides,they have the problems of narrow light absorption range and low PEC conversion efficiency.The PEC conversion efficiency is closely related to the morphology,composition and energy level structure of the semiconductor.Therefore,it is of great significance to design and prepare reasonable semiconductor materials with high optical conversion efficiency.In this paper,by adjusting the morphology of metal oxides and combining with quantum dot sensitization to form heterogeneous structures,two kinds of PEC sensors for environmental pollutant detections are constructed.The main contents are as followsIn the first chapter,based on the space-limiting effect of TiO₂ nanotubes and CdS heterojunction,the molecularly imprinted polymer?MIP?was prepared by electrochemical polymerization with chlorpyrifos as the template and o-phenylenediamine as the functional monomer,and a PEC sensor with high selectivity and sensitivity was developed.Firstly,Ti sheet was etched by anodic oxidation and calcined at high temperature to form TiO₂ nanotubes.Mn²⁺doped CdS?CdS:Mn?was modified in TiO₂ nanotubes by successive ionic layer adsorption and reaction?SILAR?to further increase the specific surface area of the interface and improve the PEC conversion efficiency.The resulting CdS:Mn/TiO₂ nanotubes were used as the electrode base of the sensor.Then the electrochemical polymerization was carried out in the presence of template molecules and functional monomers,and the MIP film was obtained by further elution of template molecules.The photoelectrode of the sensor has been prepared.In the detection of chlorpyrifos?CPF?,different concentrations of CPF were bound to the photoelectrode by the recognition reaction of molecular imprinting sites,and the quantitative analysis of chlorpyrifos could be realized according to the reduction degree of photocurrent.In the concentration range of 0.01 pg/mL to 100 ng/mL,the decrease of the photocurrent was linearly related to the logarithmic value of CPF concentration,and the limit of detection was0.01 pg/mL.In the second chapter,the photoelectric response of the CdS/Bi₂O_2.33 direct Z-scheme heterojunction,synthesized by in situ deposition of CdS nanocrystals on the defect engineered Bi₂O_2.33,can be modulated by oxygen defect concentration.The appropriate oxygen defects not only increase the visible light absorption,provide active reaction sites to enhance PEC activity,but also promote the separation of carriers.The formation of CdS/Bi₂O_2.33 direct Z-scheme heterojunction further improves these properties by extending the visible light absorption and promoting separation and transport of carriers,but avoids the usage of noble metal nanoparticles as electron transfer mediators,thus has a low cost and easy fabrication technology.The CdS/Bi₂O_2.33 direct Z-scheme junction shows significantly improved photocurrent response as compared with those containing less oxygen defects,and is applied as a photoelectrochemical assay platform for Hg²⁺.The specific interaction between Hg²⁺and the S^2-in CdS significantly quenches the photocurrent response of the CdS/Bi₂O_2.33.33 due to the formation of HgS.The photocurrent decrease is linear to the concentration of Hg²⁺in the range from 10^-11 to 10^-6 g/mL,with the limit of detection of 3.2 pg/mL.High accuracy and good reproducibility are realized in the real sample analysis of urine,river water,and sea water.The integration of oxygen defect engineering and direct Z-scheme electron transport principle provides a new avenue for fabricating high performance photoelectrochemical materials,which can be further combined with bio-recognition strategy for the ultrasensitive detection of biological molecules.