Research On The Preparation Of Nano-structured Metal Complex Oxides And Their Application In Electrochemical Sensors

Nanomaterials are widely used in many fields due to their good properties resulted from their special structures. A series of novel nano-structrued materials such as layered double hydroxides, perovskite and semicondcutive complex oxides composed of copper and nickel elements have been synthesized by coprecipitation, sol-gel and electrospinning technics, respectively. New-type amperometric electrochemical sensors based on these nanomaterrials are fabricated with glassy carbon eletrode (GCE) or carbon paste electrode (CPE) by different processes. Many techniques such as XRD, IR, XRF, TG-DTA, TEM, SEM, EIS, UV-Vis and BET are used to characterize the structures and properties of the materials and/or electrochemical sensors. The properties of as-fabricated electrochemical sensors are investigated and their experimental conditions are all optimized. The rusults show that the novel sensors based on these nanomaterials exhibit good electrochemical properties.1) A layered double hydroxide Ni²⁺/MgFe-LDH (NLDH) and the precursors of Mg(Ni)FeO, Mg(Ni)Fe₂O₄ and NiFe₂O₄ have been synthesized by coprecipitation method. A series of simple and cheap biosensors GOD-NLDH-CHT/GCE, GOD-Mg(Ni)FeO-CHT/GCE, GOD-Mg(Ni)Fe₂O₄-CHT/GCE and GOD-NiFe₂O₄- CHT/GCE are proposed based on these nano-structured materials immobilizing glucose oxidase (GOD). The optimization of experimental parameters has been investigated with regard to the amount of modifier, pH and applied potential. The optimized biosensor show good properties. For example, GOD-NLDH-CHT/GCE has a low detection limit of 0.12 mM (S/N = 3), a fast response and a sensitivity of 1.995μA mM^-1; The biosensors based on these derivatives exhibit better properties. For example, GOD-Mg(Ni)Fe₂O₄-CHT/GCE exhibits good properties at 0.50 V: a high sensitivity and good selectivity, a low detection limit of 0.05 mM (S/N = 3). A H₂O₂ sensor with good properties has been successfully fabricated based on NiFe₂O₄ immobilizing horseradish peroxidase (HRP). These works provide interesting materials of LDHs and their derivatives with low cost and biocompatibility, and different possible techniques and methods for further investigation of biosensors.A electrochemical sensor Mg(Ni)FeO/CPE (NMCPE) is proposed for p-nitrophenol (PNP) determination. NMCPE exhibits an obvious electrochemical oxidation for PNP under the optimum conditions (Mg(Ni)FeO/graphite = 10%, pH 5.0, 120s quiescence). I_p of PNP on NMCPE is found to be linear with its concentration from 2.0μM to 0.2 mM with a low detection limit of 0.2μΜ, high sensitivity of 811μA mM^-1 cm^-2, good reproducibility, stability and selectivity. It is a promissing sensor for PNP detection in environmental, chemical and medical fields.2) A series of nano-structured perovskite-type oxides LaNiTiO₃ (L600 and L800 calcined at 600℃and 800℃, respectively), LaNiTiO₃-CoFe₂O₄ (L600-CFO) and LaNiTiO₃-NiFe₂O₄ (L800-NFO) are synthesized for the first time by sol-gel method. The electrochemical hydrogen peroxide (H₂O₂) sensors (L600/GCE, L600-CFO/GCE) and glucose sensors (L800/CPE, L800-NFO/CPE) are developed based on these nanomaterials. The sensors all exhibit high electrochemical properties, good reproducibility, stability and selectivity in NaOH (0.1 M) under optimum conditions: L600/GCE gives high activity for H₂O₂ oxidation with a fast response ( 2s), a wide linearity from 0.05μM to10 mÎœand a low detection limit of 0.01μM; L600-CFO/GCE shows higher sensitivity for H₂O₂ oxidation; L800/CPE shows high activity for glucose oxidation with a wide linear range of 0.2 - 20μM and 20μM - 1 mM and a low detection limit of 0.07μM; The sensor based on CPE modified with L800-NFO immobilizing GOD also shows good properties for glucose oxidation. These researches exploit the application of perovskite-type oxides as nonenzyme and enzyme sensors in the electrochemical field and propose possible methods for detection H₂O₂ or glucose in industries and medical fields.3) The semicondcutive complex oxides CuO-NiO are prepared after calcining the electrospun one-dimensional nanofiber at 450℃and 600℃, respectively. The electrochemical sensors based on these two materials are developed and the properties of the nonenzyme sensors for direct glucose oxidation have been investigated. The results show that the two electrochemical sensors exhibit good catalytic properties for glucose at 0.55 V. Especially, the sensor CuO-NiO/GCE based on the sample calcined at 450℃gives a high sensitivity (284.14μA mM^-1), a fast response ( 1s), a wide lieaner range of 0.2μM - 1 mM, a low detection limit of 0.08μM, good selectivity, stability and reproducibility. The research provides novel nonenzyme glucose sensors based on CuO-NiO nanomaterials which exhibit good electrochemical properties and a general synthetic technique for the prepareation of other functional complex-oxides with multiple compnents. The complex oxides have good prospects for development in electrochemical sensor field.