The Synthesis And Modification Of Bismuth-based Semiconductor Materials And Construction Of Photoelectrochemical Sensor For Hexavalent Chromium

The measurement principle of a photoelectrochemical sensor is based on the change in photocurrent or photovoltage caused by electron transfer between a photoelectrochemical material and an analyte.The photoelectrochemical sensor has the advantages of low detection cost,high detection efficiency,and good selectivity,which is of great significance for solving the problem of Cr（VI）in water environment pollutants.The detection performance of the sensor is mainly related to the photoelectric conversion efficiency of the semiconductor materials,so it is very important to choose a suitable semiconductor material.Bismuth-based semiconductor materials have attracted wide attention due to their wide distribution,low toxicity,and low cost,as well as excellent optical and electrical properties.However,a single bismuth-based semiconductor material has a low utilization of visible light and an electron-hole recombination rate high,low energy conversion efficiency and other limitations.Therefore,this paper explored a series of bismuth-based semiconductor composites and constructed them as photoelectrochemical sensors for the detection of hexavalent chromium.（1）Controllable preparation of Bi/Bi OI materials and their applicationsComposites were prepared from Bi OI and Bi/Bi OI-X（where X can be 1,2,3,or 4） were synthesized through one-step solvothermal way and used to fabricate photoelectrochemical（PEC）method for hexavalent chromium（VI）.The chemical composition and morphology of the materials were characterized by X-ray diffraction,X-ray photoelectron spectroscopy,scanning electron microscopy,and transmission electron microscopy.The results of UV–vis DRS（Diffuse reflection spectra）and photoluminescence show the composites to have higher visible light absorption and a lower electron recombination rate compared to Bi OI alone.Furthermore,the electrochemical performances of the materials were tested by chronoamperometry and electrochemical impedance spectroscopy.And the results show that Bi/Bi OI-3displays the best PEC performance.The PEC sensors based Bi/Bi OI-3 has a wide linear range（1 to 230μM）and a low detection limit of 0.3μM（at S/N=3）for detecting Cr（VI）in 0.1 m M HNO₃.It is also displayed stability,selectivity and reproducibility.（2）Controllable preparation of Bi-Bi PO₄/Bi OI materials and their applicationsIn this work,Bi surface plasmon resonance（SPR）-promoted Bi PO4/Bi OI heterostructures（Bi-BPI）are synthesized through a one-step hydrothermal method.The structure and morphology have been measured by a series of physical characterizations.Furthermore,the photoelectrochemical（PEC）experiments show that the PEC properties of Bi PO₄/Bi OI are higher than those of pure Bi PO₄ and Bi OI,when the mass fraction of Bi PO₄ is 6%（Bi PO₄/Bi OI-6%）,it has the best PEC performance.At the same time,it is found that Bi metal could improve the PEC properties of Bi PO₄/Bi OI-6%,and when the reducing agent glucose content is 0.05 g（0.05-Bi-Bi PO₄/Bi OI-6%）,it has the highest performance among all materials.Ultraviolet-visible diffuse reflection spectra（DRS）and photoluminescence（PL）also prove that 0.05-Bi-Bi PO₄/Bi OI-6%features excellent visible light absorption and a lower electron recombination rate than the other composites.Therefore,PEC sensors based on 0.05-Bi-Bi PO4/Bi OI-6%have been fabricated for the detection of hexavalent chromium（Cr（VI））.They exhibit a wide linear range from 0.5 to 180μM with high stability for sensing Cr（VI）.Thus,the PEC sensor has a great potential application in Cr（VI）detection.（3）Controllable preparation of Cu S/Bi₂XO₆（X=W,Mo）materials and their applicationsFirstly,Bi₂XO₆（X=W,Mo）was synthesized at different temperatures.Through a series of tests,the optimal temperatures of Bi₂WO₆ and Bi₂Mo O₆ were 180°C and160°C（BW-180,BM-160）.Then,the optimal temperature of BW-180 and BM-160was further compounded with different contents of Cu S.The results of photoelectrochemical tests showed that Cu S can improve the PEC performance of semiconductor materials,and it has the best performance when Cu S mass fraction is5%.Therefore,the two are respectively constructed as Cr（VI）PEC sensors.When the PEC sensor based on 5%-Cu S/BW-180 detects Cr（VI）,it has a linear relationship in the linear range of 1μM-80μM,and its detection limit is 0.95μM.The PEC sensor based on 5%-Cu S/BM-160 detects Cr（VI）with a linear range of 0.5-230μM and a detection limit of 0.12μM.The photoelectron potential generated by Cu S/Bi₂XO₆（X=Mo,W）heterojunction reduces the combination of photogenerated electrons and holes,therefore,5%-Cu S/Bi₂XO₆ has better photocatalytic performance.