Preparation And Electrochemical Detection Performance Of Cobalt-Based Heterojunction Composites

Biological small molecules such as glucose and heavy metal ions are closely related to human life activities,and it is especially important to achieve quantitative detection of common small molecules in daily life.With the emergence of nanomaterials and the rapid development of modified electrode strategies,electrochemical detection techniques have been widely used for the detection of small biological molecules due to their short time consumption,high sensitivity and convenience.Transition group metal oxides are often used as modified electrode materials because of their high natural abundance,low cost and easy modification.Among them,cobalt（Co）-based oxides such as Co₃O₄ are widely used in electrochemical detection because of their advantages of Co²⁺/Co³⁺cycling and strong adsorption ability.However,the disadvantages of poor conductivity,few active sites and small specific surface area limit its further development.Based on this,this thesis modulates the electronic structure of cobalt-based heterojunctions by various means such as multivalent interactions,defect engineering and morphology modulation to achieve highly sensitive and selective detection of heavy metal ions and glucose,and analyzes the sensing mechanism from the process of electronic structure and electron transfer,including:（1）Co/CoO/Co₃O₄ heterojunctions are successfully synthesized by a hydrothermal-assisted microwave carbon bath method,which is applied to the detection of heavy metal ions.The effect of different embedding depths on the generation of heterojunctions in the microwave carbon bath process is investigated.Compared with Comonomer and Co/CoO generated by complete embedding,Co/CoO/Co₃O₄ has excellent detection performance for Cd（II）,Cu（II）and Hg（II）,and the individual detection sensitivity are 4.58,22.34 and 9.72μAμM^-1 for Cd（II）,Cu（II）and Hg（II）in the detection range of 0.5-5.0μM,respectively The Co/CoO/Co₃O₄shows good reproducibility,stability and interference resistance for the detection of Cd（II）,Cu（II）and Hg（II）,and also shows good detection performance in real water environment.Combining experimental analysis and DFT calculations,the excellent electrochemical performance of Co/CoO/Co₃O₄ heterojunction is attributed to the synergistic effects of the heterogeneous interface,Co⁰/Co²⁺/Co³⁺cycle and oxygen vacancies.The individual and simultaneous detection mechanism based on the Co⁰/Co²⁺/Co³⁺cycle is proposed to elucidate the electron transfer process of Co/CoO/Co₃O₄ for the detection of heavy metal ions,which provides a feasible strategy for the design application of heterojunctions in the sensing field.（2）The Cu/Cu₂₊₁O/Co₃O₄ Z-type heterojunctions with Cu,Coand O defects are synthesized.Cu/Cu₂₊₁O/Co₃O₄ is applied to the sensitive detection of glucose,exhibiting a high sensitivity of 12.567 m A m M^-1 cm^-2 and a response time of 1.8 s.Also,Cu/Cu₂₊₁O/Co₃O₄ shows excellent sensitivity and photoelectric response in the photoelectrochemical detection of glucose,with an improved sensitivity of 0.863 m A m M^-1cm^-2 compared with the no-light condition.Moreover,Cu/Cu₂₊₁O/Co₃O₄ exhibits anti-interference properties and can be applied to the detection of blood glucose in serum.Combining XANES,EXAFS,experimental analysis and DFT calculations,it can be found that the excellent electrochemical performance of Cu/Cu₂₊₁O/Co₃O₄ is mainly attributed to its heterogeneous interface and the modulation of metal and oxygen defects.The possible mechanism of Cu/Cu₂₊₁O/Co₃O₄ Z-type heterojunction photoelectrochemical detection of glucose is presented.（3）The Cu/Co₃O₄/MXene heterojunctions with hollow and two-dimensional lamellar structures have been designed,and electrochemical sensors based on this nanomaterial are used for highly sensitive and selective detection of glucose.Meanwhile,the Cu/Co₃O₄/MXene heterojunction has significantly enhanced performance for glucose detection under light conditions,and the sensitivity can reach 57.804 m A m M^-1 cm^-2 with a significant photocurrent response.The hollow structure increases the absorption of light and the formation of Z-type structure greatly improves the separation efficiency of photogenerated carriers,which results in better photoelectric activity and higher photocurrent response and greatly enhances the sensitivity of detection.In addition,Cu/Co₃O₄/MXene has excellent anti-interference performance.