Preparation And Modification Of Ni?OH?₂ Grown On Ni Foam For Glucose Sensing

Glucose concentration is a key parameter of many diseases such as diabetes,endocrine and metabolic disorders.Accurate determination for glucose concentration is an important link in the diagnosis and control of relative diseases.Furthermore,glucose has been also widely applied in many fields such as food industry,pharmaceutical manufacturing,environmental monitoring and biological process monitoring.Therefore,in recent years,the low cost glucose sensor with high sensitivity and fast response has become a hot spot in biosensor.The nonenzymatic glucose sensors based on transition metal have been extensively studied owe to the advantages of low cost,simple preparation process and good stability,and so on.Nickel or nickel oxide/hydroxide as a non-enzymatic glucose sensor sensitive material has good characteristics for glucose.The possible mechanism is that Ni?OH?₂/Ni OOH is formed in alkaline solution.While Ni³⁺ oxidizes glucose the current is changed.Therefore,compared with Ni or Ni O,using Ni?OH?₂ directly as a sensitive material will effectively improve the utilization efficiency of the sensing material,which is benefical for realizing the rapid detection and improving the sensitivity to glucose.Nickel foam,a three-dimensional network structure,shows a high conductivity and permeability structure,a small diffusion resistance between the electrolytes,as well as a fast charge-discharge reaction and high proton transport capacity,is a good electrode material.In view of the above mentioned,in this work nickel foam was used as the electrode substrate,on which the nickel hydroxide was prepared directly and modified by doping in order to improve the sensing properties for glucose.The main research work was shown as follow.Firstly,Ni?OH?₂ nanosheets are successfully prepared on a nickel foam substrate by precipitation using the pure ammonia solution as the precipitant at 30 °C.The deposition temperature and time have an important effect on the formation of Ni?OH?₂ nanosheets.It is found that the evenly Ni?OH?₂ nanosheet structure can be obtained on the nickel foam substrate for 10 hours at 30?.The Ni?OH?₂ nanosheet structure is both ?-Ni?OH?₂ and ?-Ni?OH?₂.The glucose sensing test is carried out by using the prepared Ni?OH?₂ nanosheets / nickel foam as the working electrode of the nonenzymatic glucose sensor.The sensitivity in the glucose reaches 1130 ?A m M^-1 cm^-2 when the concentration range is from 2 ?M to 40 ?M and the sensitivity to glucose reaches 1097 ?A m M^-1 cm^-2 in the range of concentration 0.1 m M to 2.5 m M.The pure ammonia has strong volatility and irritation,which increases the difficulty of material preparation.In the follow-up experiment,the hydrothermal method was used,and the electrode was modified by doping method to improve the glucose sensing properties.In chapter 3,noble metal was used to improve the response to glucose.When the Au or Pd was doped respectively,the electrode performance can be improved,but it is not easy to adjust.When Au and Pd are co-doped as doping,it is easier to improve the sensitivity of the electrode to glucose.The electrode formed by co-doping of noble metal Au and Pd has a porous spherical morphology.The structure of the electrode material is Ni?OH?₂.Au and Pd co-doped can improve the detection of glucose on the performance due to the favorable effect of mass transfer and the synergistic effect of bimetallic catalyst.When the molar ratio of Au and Pd is 2: 3,the prepared electrode has a good sensitivity to glucose,which reaches 15.20 m A m M^-1 cm^-2 in a linear range of 1 ?M to 2 m M?R2 = 0.998?cm^-2.The sensitivity to glucose is still 4.88 m A m M^-1 cm^-2 in the range of 3 m M to 12 m M?R2 = 0.963?.The increase in the sensitivity for glucose detection is attributed to porous morphology and the synergistic effect of bimetallic catalyst.In the fourth chapter,the variable valence iron was used as dopant instead of noble metal.Fe-doped electrode was prepared by hydrothermal method.The Fe doping makes the morphology of Ni?OH?₂ shifting from nanoparticles to nanosheets and nanospheres.The product of Fe is Fe₃O₄.The Fe doping reduces the potential distance of the redox peak and accelerates the catalytic reaction between the electrode and glucose.When the molar ratio of Fe and Ni is 3: 7,the detection limit of the prepared electrode is 1?M.The sensitivity to glucose reaches 40.65 m A m M^-1cm^-2 while the glucose concentration is from 1 ?M to 50 ?M.The sensitivity reaches 5.26 m A m M^-1cm^-2 while the glucose concentration is from 50 ?M to 10 m M.Finally,the effects of Co doping on electrode morphology and glucose sensing properties are studied.Co-doped Ni?OH?₂ was directly grown on the nickel foam substrate by hydrothermal method.The addition of Co contributes to the formation of Ni?OH?₂ nanosheets.Co O is the product of Co,and will produce Co?OH?₂ in alkaline solution.Co²⁺/Co³⁺ redox in alkaline solution has enhanced the catalytic reaction of Ni²⁺/Ni³⁺ to glucose.Co doping enhances the ability of the electrode to detect glucose,which was possibly ascribed to the formation of a porous uniform electrode surface and synergistic effect of Co²⁺/Co³⁺ with Ni²⁺/Ni³⁺.The low detection limit for glucose is 5 ?M.The sensitivity is high even while the glucose concentration is up to 14 m M.The sensitivity reaches 85.889 m A m M^-1cm^-2 when the glucose concentration the linear is in the range of 10 ?M to 4.0 m M.The sensitivity still reaches 32.41 m A m M^-1 cm^-2 when the glucose concentration the linear is in the range of 4.0 m M to 14 m M.