| As a "green" oxidant,hydrogen peroxide(H2O2)is widely used in the areas of pharmaceutics,agriculture,environment,food industry and so on.However,the overuse or abuse of H2O2 can cause damages to human cells,accelerate the ageing process and induce cancerization,largely harming human health.On the other hand,as an important intermediate product during the body metabolism,the detection of the concentration of H2O2 can be applied to monitor the human physiological indicators.Therefore,it is of great importance to develop a simple and cost-effective operation method to accurately detect the concentration of H2O2.Among various detection approaches,the technique based on non-enzymatic electrochemical sensors exhibit great appliance and business value due to its high accuracy,quick response and easy operation,etc.The selection of electrode materials in the sensor is one of the important factors affecting the efficacy of the electrochemical detectionIn this thesis,a series of electrode materials based on nickel oxide,bimetal oxides,or their composites with various structures are prepared.These materials demonstrate high sensitivity and low detection limit for electrochemical detection of H2O2.The structure activity relationship between nickel oxide-based electrode materials and electrochemical detection of H2O2 is investigated.An enhancement mechanism of electrochemical performance based on material specific surface area,oxygen vacancies,concerted catalysis and carrier structure is proposed.It provides important scientific theory for the design of nickel oxide-based electrode material and electrochemical performance evaluation.The main achievements are as follows:1.The controlled preparation of mesoporous nickel oxide nanospheres(NiO-MNS)was achieved by controlling the solvothermal reaction conditions.The role of polyethylene glycol(PEG)in the formation of mesoporous nanospheres was studied,and the formation mechanism of the mesoporous nanospheres was analyzed.The results indicated that a spot of PEG,as the stabilizer and morphology-directing agent,could induce the growth of Ni(OH)2 in the sheet-like directions and improve the size uniformity.The broccoli-like and mesoporous structured NiO blocks with large surface area and a large number of mesopores was obtained after the calcination treatment.The large specific surface area of the prepared material was favorable for increasing the number of active sites,and the developed mesoporous structure was beneficial to the improvement of mass transfer.Thus,the obtained NiO-MNS sensor presented superior electrochemical performance with a high sensitivity(236.7 ?A mM-1 cm-2)and a low detection limit(0.62 ?M),as well as a good selectivity and reliability for the further application of H2O2 detection.2.On the basis of the successful preparation of NiO-MNS,we introduced cobalt salt into the reaction system to synthetize microtubular Ni-Co bimetallic oxide.The effects of solvothermal reaction time on the morphology and structure o were studied,and the growth mechanism of microtubules was analyzed.Then,a series of microtubular Ni-Co double oxides(NixCoy-DO)with different nickel/cobalt metal ratios were prepared by changing the mass ratio of the nickel/cobalt salt.The introduced Co ions in NixCoy-DO could induce the production of surficial oxygen vacancies and further enhance the surface activity of the electrode.In particular,when the mass ratio of nickel/cobalt was 4:3,the obtained NiCo-DO sample showed the richest surficial oxygen vacancies and presented the highest H2O2 detection activity among all of the as-prepared samples,demonstrating an excellent sensitivity of 698.60 ?A mM-1 cm-2(0?0.4 mM)and a low detection limit(0.28 ?M,S/N=3).Its sensitivity was three times higher than that of NiO-MNS.3.Nickel oxide-nickel/graphene composite material(NiO-Ni/GO)was prepared by hydrothermal method with the introduction of highly dispersed graphene.The dispersion of the nickel oxide and the morphology of the composite were tailored by adjusting the mass ratio of nickel salt to graphene oxide.The result showed that,as a dispersant,graphene improved the dispersion and nucleation of intermediates and further promoted the even distribution of NiO-Ni in the form of nano wires on the surface of graphene layer,which could increase the exposure of active sites and enhance the electrochemical detection performance.In particular,when the mass ratio of nickel salt/graphene was 10:1,the as-prepared NiO-Ni/GO composite showed the best electrochemical performance,demonstrating an excellent sensitivity of 549.60 ?A mM-1 cm-2 and a low detection limit of 0.29 ?M(S/N=3).Its electrochemical performance was higher than that of the pure nickel oxide prepared under the same condition.4.To further improve the H2O2 electrochemical detection performance of nickel oxide-based material,nickel oxide nanosheets and Ni-Co double oxide nanosheets were loaded in-situ on a porous nickel foam.The direct contact between oxides and nickel foam constructed the electronic fast transport channel.Meanwhile,oxide nanosheets were interrelated and formed a large number of pores,which worked synergistically with the porous structure of nickel foam to promote the rapid infiltration of the electrolyte.At the same time,the reasonable surface coating thickness and structure of the oxides provided sufficient active sites could increase their electrochemical detection performance.The sensitivity of nickel oxide nanosheets was 1037 ?A mM-1 cm-2,and the detection limit was 0.23 ?M(S/N=3).Its sensitivity was increased nearly 4.3 times and the detection limit was almost half reduced relative to the case of NiO-MNS.The sensitivity of Ni-Co double oxide nanosheets were 1541 ?A mM-1 cm-2 and the detection limit was 0.13 ?M(S/N=3).In order to improve the electrochemical H2O2 detection performance of nickel oxide-based electrode materials,we can start from the following four points:(i)Increasing surface area and constructing a reasonable pore structure can effectively improve the number of active sites and promote the mass transfer.(ii)Introducing Co ions can induce the production of surficial oxygen vacancies,and further enhance the electrode surface intrinsic activity.(iii)In situ loading on carrier(or conductive matrix)can not only effectively improve the deficiency of intrinsic conductivity and the electronic conduction ability of electrochemical detection materials,but also promote the dispersion of the active oxides,increase the number of reaction sites.(iv)Comprehensive use of the above three kinds of methods can not only increase the distribution of active sites and vacancies to improve the intrinsic activity but also enhance the multiple synergistic catalysis,promoting the conductivity and mass transfer capacity.Multiple mechanisms work together to enhance the electrochemical activity of nickel oxide-based electrode materials. |
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