Preparation And Nonenzymatic Glucose Sensing Performance Of Ni-based Nanomaterials

Glucose sensing is of great importance in the research fields of biotechnology, clinical diagnostics and food industry. Enzymatic glucose biosensors possess good selectivity and high sensitivity. However, the easy inactivation of enzyme and the difficulty of enzyme immobilization on electrode surface result in the complex preparation process, high cost and short life of enzymatic glucose sensor. Thus, nonenzymatic glucose sensors have attracted more attention. Previous reports demonstrated that Ni-based nanomaterials have been used to perform the nonenzymatic detection of glucose and exhibit good performance in terms of glucose sensing. However, the synthesis of sensing material and its immobilization on electrode surface are performed in two steps in the classical electrode modification. This preparation method was not simple and was not suitable for the direct formation of ordered nanostructure on electrodes surface. This drawback was not convenient for the applications of Ni-based nanomaterials in the nonenzymatic glucose sensing. Therefore, the direct fabrication of nanostructured Ni-based materials on conductive substrates is of great value.This thesis discusses the hydrothermal preparation of Ni-based nanomaterial films with different structures and morphologies on various substrates and investigates their nonenzymatic glucose sensing ability. Nickel oxide and partially graphitized carbon composite nanosheet is prepared by the carbonization of glucose in the hydrothermal reaction. The effects of partially graphitized carbon on the electrochemical performance of glucose sensor are also discussed. In addition, metallic nickel nanoparticle film is synthesized using polyvinyl pyrrolidone as reduction agent. The nonenzymatic glucose sensing ability of the prepared metallic nickel nanoparticle film is also investigated. The details are as follows:1. Powder samples and films of Ni-based LDH nanomaterials are prepared by varying the kind of precipitation agents and the molar ratio of raw materials. The mechanism of the direct formation of LDHs nanosheet film on substrates is discussed.(1) Three kinds of precipitation agents, including ammonia, sodium hydroxide and sodium carbonate, and urea, has been used to synthesize Ni-based LDHs under the same hydrothermal treatment. The morphologies of the prepared powder samples are different from each other using different precipitation agents.(2) The direct fabrication of Ni/Al-LDH nanosheet film on titanium foil, Fe-Co-Ni alloy substrate, ceramic wafer, and mica substrate has been performed through the hydrothermal reaction of the mixing solution containing nickel nitrate, aluminum nitrate, and urea. The direct formation of Ni/Al-LDH film on substrates can be attributed to the hydrolysis of urea and the roughness of substrates. Using urea as precipitation agent, the coprecipitation reaction is mild enough for the Ni/Al-LDH seeds to adhere on substrates. Roughness of substrates surface helps to reduce the binding energy between seeds and substrates.(3) Films with different morphologies are obtained on Ti foil and ceramic wafer substrates by varying the molar ratio of Ni2+ to Al3+ cation.2. The Ni/Al-LDH nanosheet film formed on Ti foil has been used to perform the nonenzymatic detection of glucose. Ti substrate exhibits good stability in the electrochemical measurements and will not be involved in the electrocatalytic oxidation of glucose. Compared to the Ni/Al-LDH powder modified electrode prepared by classical spin coating method, Ni/Al-LDH nanosheet film formed directly on Ti foil exhibits higher sensitivity, lower detection limit and better stability towards the nonenzymatic detection of glucose. These improvements are attributed to the direct formation of LDH nanosheet film on metal substrate.3. NiO nanowire film, NiO nanosheet film, and NiO and partially graphitized carbon composite nanosheet film are prepared on substrates. NiO nanosheet film and NiO/carbon composite nanosheet film modified Ti foil have been used to perform the nonenzymatic detection of glucose.(1) NiO nanowire film on various substrates is prepared by calcining the precursor, which is synthesized through the hydrothermal reaction of nickel nitrate and urea. NiO nanosheet film is prepared by calcining the precursor, which is synthesized through the hydrothermal reaction of nickel nitrate, urea and NH4F. The formation mechanism of nanosheet is discussed. The effect of the amount of NH4F on the film morphology is investigated in the contrast experiments.(2) NiO and partially graphitized carbon composite nanosheet film is prepared on Ti substrate by calcining the precursor in N2 gas, which is synthesized through the hydrothermal reaction of nickel nitrate, urea, NH4F and glucose. The effect of the amount of glucose on the film morphology is investigated in the contrast experiments.(3) NiO nanosheet film and NiO/carbon composite nanosheet film modified Ti foil have been used to perform the nonenzymatic detection of glucose. Compared to pure NiO nanosheet, nickel oxide and partially graphitized carbon composite nanosheet exhibits faster response speed, lower detection limit and higher sensitivity towards the detection of glucose.4. Metallic nickel nanoparticle film on Ti substrate is prepared by calcining the precursor in N2 gas, which is synthesized through the hydrothermal reaction of nickel nitrate, urea and polyvinyl pyrrolidone. The formation mechanism of metallic nickel is discussed and the nonenzymatic glucose sensing ability of the prepared metallic nickel nanoparticle film is also investigated. Compared to sensors based on Ni/Al-LDH and NiO, glucose sensor based on metallic nickel nanoparticles exhibits faster response speed, lower detection limit and higher sensitivity. However, its stability remains to be further improved.