Study On Glucose Sensor Based On Transition Metal Materials With Hierarchical Hollow Nanostructures

With the improvement of people’s living standard,the number of diabetes patients in the world is sharply increasing,becoming a public problem that seriously endangers human health.It is urgent to develop a glucose electrochemical sensor with merits of simple operation,great accuracy,and low price.Hereinto,the composition selection and structure design of electrode materials are the key to realize highly sensitive glucose sensing.Benefiting from the advantages of nanostructures such as surface effect and small size effect,transition metal-based nanostructure engineering has been developed vigorously in the field of glucose sensing.The common problem is that the electrocatalytic kinetics of the developed nanostructures is still not ideal.Designing three-dimensional（3D）hollow nanostructures is proposed to circumvent this problem,the advantages of which are reflected in the structural characteristics of abundant porosity,high specific surface area,good dispersion,and the limited electron transfer path.At present,most of the relevant researches have focused on single-layered hollow nanostructures.However,hollow nanomaterials with simple composition and structure have non-negligible shortcomings during the electrocatalysis:（i）The single component limits the type of electrocatalytically active site,leading to unsatisfying sensitivity and detection limit.（ii）The single-shelled hollow nanostructures have poor structural stability in electrochemical reaction associated with short glucose monitoring life.In this thesis,cubic Cu₂O templates combined with some advanced fabrication methods were used to synthesize four transition metal-based hollow hierarchical nano-electrocatalysts,aiming at upgrading 3D hollow nano-structured materials and optimizing their comprehensive analysis ability during glucose detection.Simultaneously,the composition and morphology of nanostructured units were systematically regulated to probe deeply into the structure-activity relationship,and hence to clarify the catalytic mechanism with the assistant of DFT calculations.The main research contents are as follows:（1）CuS nanocages（NCs）were modified into the interior of Ni（OH）₂ NCs by CEP and sulfidation methods to form CuS@Ni（OH）₂ double-shelled nanocages（DSNCs）,in which the gap existed between CuS layer and Ni（OH）₂ layer.CuS NCs can not only significantly enhanced the conductivity,but also provided many Cu²⁺/Cu³⁺redox couples.At the same time,the structure design of DSNCs can improve the volume occupying rate in ensuring sufficient active sites of the integrated electrocatalyst.These advantages made the electrocatalyst highly sensitive to glucose molecules.Significantly,CuS@Ni（OH）₂ DSNCs modified electrode reached a stable glucose catalytic current within 1.25 s combined with linear range of 0.002-5.3 m M,sensitivity of 1106.9μM m M^-1 cm^-2,and detection limit of 0.28μM.The electrocatalytic performance of CuS@Ni（OH）₂ DSNCs was better than that of CuS NCs and Ni（OH）₂ NCs.The results indicate that the design of hollow hierarchical nanostructures is promising to improve the catalytic performance of electrocatalysts towards glucose,which is worthy of intensive research.（2）On the basis of the first work,the research continued to optimize the structure and composition of CuS@Ni（OH）₂ DSNCs.The sulfidation and CEP methods were successively used to realize the deposition of Ni Co double hydroxide（LDHs）nano-sheets on the CuS NCs surface,thus successfully preparing CuS NCs@Ni Co LDHs hollow core-shell nanostructure.The effect of different Ni/Co ratios on the 2D structure of LDHs NSs was investigated,and the optimum CuS NCs@Ni Co LDHs were obtained.Bader charge calculations indicated that Co had more positive charge than Ni in Ni Co LDHs,proving that the introduction of Co phase improved the ability of the electrocatalyst in capturing electron.The coupling between CuS NCs and Ni Co LDHs not only expanded the contact area between electrocatalyst and electrolyte along with the improved electrocatalytic activity,but also increased the glucose adsorption energy（-0.6 e V）.Compared with the cage-in-cage nanostructures for the first work,the hollow core-shell nanostructures possessed better stability during the electrochemical reaction.The glucose oxidation current of CuS NCs@Ni Co LDHs remained 90%of the initial value after continuous glucose detection for one month.Moreover,CuS NCs@Ni Co LDHs had a sensitivity as high as 2236.4μM m M^-1 cm^-2 with detection limit of 0.18μM,linear range of 0.001-4.6 m M,and current response time of 1 s.（3）Next,this thesis further comprehended the effect of the hollow core-shell nanostructure on electrocatalytic performance.Combinating CEP and ion exchange methods enabled Ni（OH）₂ NCs to be completely coated by Cu₂Se nanosheets（NSs）,forming hollow core-shell nanostructured Ni（OH）₂ NCs@Cu₂Se NSs.Cu₂Se had metal-like conductivity and high activity.Hence,electrocatalytic kinetics for the designed electrocatalyst can be significantly improved when coupling Cu₂Se NSs with Ni（OH）₂ NCs.The DFT calculation revealed that the glucose adsorption energy of Cu₂Se was-1.84 e V,much higher than that of Ni（OH）₂（-0.18 e V）,suggesting that designing Cu₂Se with 2D nanostructures on the outer surface of Ni（OH）₂ NCs favored the smooth diffusion of a large amount of glucose to electrode surface followed by the completion of rapid electrooxidation.Moreover,Cu₂Se layer greatly increased the overall shell thickness of Ni（OH）₂ NCs@Cu₂Se NSs（about 100 nm）,which endowed the hollow electrocatalyst with desirable strain resistance during the electrochemical reaction along with the prolonged glucose detection life.The oxidation current of Ni（OH）₂ NCs@Cu₂Se NSs remained 94.3%of the initial value after continuous glucose detection for three weeks.Remarkably,Ni（OH）₂ NCs@Cu₂Se NSs delivered excellent glucose sensing behavior,achieving a sensitivity as high as 2420.4μM m M^-1 cm^-2combined with linear range of 0.001-7 m M,detection limit of 0.15μM,and response time less than 2 s.The study further proves that the hollow core-shell nanostructured electrocatalyst can achieve highly sensitive glucose detection.（4）Finally,this thesis upgraded the hollow core-shell nanostructure.Different structural CuS was modified to the interior and exterior surfaces of Ni（OH）₂NCs by CEP,sulfidation and ion reuse methods,forming a triple-shelled hollow nanostructured CuS@Ni（OH）₂@CuS.The inner CuS layer was composed of nanoparticles and provided a good supporting effect to ensure structural stability when cooperated with Ni（OH）₂ layer.The outer CuS layer was assembled with 2D NSs,which facilitated electron transfer and glucose adsorption（-0.95 e V）associated with short glucose response time of 0.75 s and low detection limit of 0.08μM.The 2D structure of the outer CuS was systematically regulated,and the optimal hierarchical hollow architecture（HHA）enabled CuS@Ni（OH）₂@CuS to have higher catalytic activity(3128.1μM m M^-1 cm^-2).The inner/outer CuS layers created a synergistic protective effect on the intermediate Ni（OH）₂ layer in CuS@Ni（OH）₂@CuS HHA to increase the thickness and diversity of functional nano-shell.The elevated volume occupying rate made the electrocatalyst to guarantee sufficient Cu³⁺/Ni³⁺,and hence to cope with the increased glucose concentration during the catalytic process,obtaining a wide linear range of 0.001-7.6 m M.The robust nanostructure also allowed the sensor to detect glucose for up to 60 days.These electrocatalytic properties validate the development and utilization potential of hollow hierarchical nano-materials in the field of enzyme-free sensing.