Construction Of Photoelectric Chemical Sensing Platform Based On Metal Sulfide Heterojunction

Photoelectric chemical（PEC）sensor has been proposed as an considerable detection method developed by combining photoelectric technology,which has the advantages of fast response,simple operation,high sensitivity and low cost.It combines the traditional electrochemical sensor with the photoelectric technology,using the visible light to excite the materials to generate excited electrons and charge transfer,realize the conversion process of light energy to electric energy,and the electrical signals are regarded as identification signals.As the core parts of PEC sensors,photosensitive materials play an important role in signal generation and light capturing.Therefore,it is very important to synthesize materials with high activity,good stability,low cost and non-toxic properties.Among them,metal sulfides have attracted extensive attention due to their wide light absorption bands,abundant exposed active sites and strong carrier migration ability.However,these materials exhibit relatively low chemical stability due to photocorrosion,which severely hinders their photoelectric properties.In order to enhance the optical activities,doping,polymer modification,heterojunction construction and other strategies are widely used to expand the optical absorption range,improve the carrier migration efficiency and the photoelectric activity of the catalyst.Therefore,the PEC sensors based on metal sulfide composites were constructed in this paper to detect toxic pollutants and small molecules.The main content of this paper includes the following aspects:（1）Preparation of ZnO/SnIn₄S₈heterojunction and its application in Cr（Ⅵ）detectionIn this study,ZnO/SnIn₄S₈was synthesized by solvothermal method to detect hexavalent chromium（Cr（Ⅵ））.The composition,surface structure,valence state and photoelectric properties of ZnO/SnIn₄S₈were investigated by X-ray diffraction,scanning electron microscopy,transmission electron microscopy,X-ray photoelectron spectroscopy,UV-vis diffuse reflectance spectroscopy and photoluminescence spectra.The results found ZnO/SnIn₄S₈composites show better photocatalytic activities than these of ZnO and SnIn₄S₈.Meanwhile,the mass ratio of ZnO/SnIn₄S₈could also affect its photoelectric performance.The sensor testing results show when the mass ratio of ZnO/SnIn₄S₈is 1:4（ZnO:SnIn₄S₈=1:4）,it has the best performances among all the composites.The linear range and detection limit of Cr（Ⅵ）based on ZnO/SnIn₄S₈-4 sensor are 0.5-300μM and 0.039μM.Moreover,density function theory（DFT）calculation confirm the enhanced photoelectric properties are attributable to the form of a Z-scheme heterojunction between ZnO and SnIn₄S₈,which facilitates charge separation through the action of an internal electric field,and retains strong redox ability of electrons（e^-）or holes（h⁺）.Thus,Z-scheme ZnO/SnIn₄S₈heterojunction will provide new insights and potential application in Cr（Ⅵ）detection.（2）Preparation of PDA/CeO₂/In₂S₃heterojunction and its application in Cr（Ⅵ）and glucose detectionIn this paper,PDA_n/CeO₂/In₂S₃-X（X=m（CeO₂）/m（CeO₂+In₂S₃）,n=m（PDA）/m（catalyst））heterojunction was successfully fabricated by three steps to detect glucose and hexavalent chromium（Cr（Ⅵ））.CeO₂was initially synthesized,followed by a hydrothermal method to make In₂S₃compounded with CeO₂.Specifically,by optimizing the ratio of CeO₂and In₂S₃,CeO₂/In₂S₃-15%showed the best photoelectric responses and sensing performances.In order to further improve the performance of CeO₂/In₂S₃-15%,polydopamine（PDA）was modified on the surface of CeO₂/In₂S₃-15%（PDA_n/CeO₂/In₂S₃-15%）.Besides,the results from optical characterizations and performance testings show PDA_0.1/CeO₂/In₂S₃-15%exhibits the best absorption capacity and photocurrent responses.Interestingly,PDA_0.1/CeO₂/In₂S₃-15%was applied to detect Cr（Ⅵ）and glucose in an effective fashion.The glucose sensor based on PDA_0.1/CeO₂/In₂S₃-15%showed an acceptable detection range between 0.5μM and 27 m M with good sensitivity(575.20μA·m M^-1·cm^-2)and low detection limit（0.076μM）.Meanwhile,for Cr（Ⅵ）sensing,it has a wide linear range of 0.5-240μM with a high sensitivity of1053.60μA·m M^-1·cm^-2,and the low detection limit is 0.098μM.Furthermore,it could be also employed in real samples（human blood serum or sewage）.Thus,the PEC sensor based on PDA/CeO₂/In₂S₃has potential applications in glucose and Cr（Ⅵ）detection.（3）Preparation of MoO₃/Zn_xCd_1-xS heterojunction and its application in Cr（Ⅵ）and4-NP detectionIn this study,the MoO₃/Zn_xCd_1-xS was successfully prepared.Firstly,Zn_xCd_1-xS（x=0.3,0.5,0.7）was synthesized.The results show that the photocurrent response of Zn_0.3Cd_0.7S was better than that of the other two proportional materials.In order to further improve the photoelectric properties of Zn_0.3Cd_0.7S,MoO₃/Zn_0.3Cd_0.7-X was synthesized by hydrothermal method.The composition,surface structure,valence state and optical properties of MoO₃/Zn_0.3Cd_0.7S-X were studied by a series of characterizations.The results show the photoelectric performances of the MoO₃/Zn_0.3Cd_0.7S-X are significantly improved compared with MoO₃and Zn_0.3Cd_0.7S.The optical characterization and performance test results show MoO₃/Zn_0.3Cd_0.7S-0.3 has the best absorption capacity and photocurrent response.In addition,MoO₃/Zn_0.3Cd_0.7S-0.3 could effectively detect Cr（Ⅵ）and 4-nitrophenol（4-NP）.The detection range of Cr（Ⅵ）sensor based on MoO₃/Zn_0.3Cd_0.7S-0.3 is 0.1～240μM,and the detection limit is 0.019μM.The sensor could also detect 4-NP.The concentration detection range of 4-NP sensor is 50 n M～100μM,and the detection limit is 0.028μM.In addition,the designed PEC sensor also has good selectivity,reproducibility and stability,and could be used for the detection of actual samples（sewage）.