One-step Fabrication Of Nanoporous Gold Based Integrated Composite Electrodes By Anodization-Disproportionation Method And Their Applications In Electrochemical Sensing

Electrochemical sensors consist of sensitive electroactive materials based identification elements and electrode-based electrochemical transducer,whose performance are closely related to the electrochemical sensing interface.How to improve the controllability and repeatability of electrochemical sensing interface is one of the key issues in the field of electrochemical sensing.Nanoporous gold?NPG?,which has a unique three-dimensional network structure with large specific surface area,high conductivity,stable chemical properties and good biocompatibility,is preferred to be an identification element in the construction of electrochemical sensors.In this dissertation,based on our original electrochemical anodization-disproportionation method,three integrated composite electrodes,Co₃O₄/NPG/Au,SnO₂/HNPG/AuSn and CNP/AuSi,have been successfully one-step fabricated by using different chloride electrolytes and different electrode substrates.The strategy of one-step construction of integrated electrode could reduce the experimental error of artificial operation in the multi-step process of traditional chemically modified electrodes and improve the controllability and repeatability in sensing interface construction.Furthermore,an integrated Pt-modified SnO₂/HNPG/AuSn composite electrode?Pt/HNPG/AuSn?has been constructed by facile potentiostatic deposition.Based on these integrated composite electrodes mentioned above,several electrochemical sensors for the detection of small molecules such as glucose,hydrogen peroxide?H₂O₂?,hydrazine hydrate?N₂H₄?and ascorbic acid?AA?have been developed.Compared with pure NPG,NPG-based integrated composite electrodes have more outstanding advantages in long-term stability,sensitivity,response time,linear range and other sensing performance indicators.The main contents of this dissertation include:?1?A self-supporting Co₃O₄/NPG/Au integrated composite electrode was one-step fabricated from smooth Au electrodes in CoCl₂ electrolyte by electrochemical anodization-disproportionation method.The fabrication time is only 100 s.Under the applied anode potential,two processes occur simultaneously:?1?forming nanoporous structure by“electrochemical dissolution,disproportionation and deposition?EDD?”process;?2?production of Co₃O₄ nanoparticles by chemical reaction between Co²⁺ions from the supporting electrolyte and the OH^-ions generated by the cathode.During 100 s of potentiostatic anodization,a nanoporous film was well developed accompanying with the simultaneous anodic deposition of Co₃O₄ on the electrode surface.Co₃O₄nanoparticles can be dissolved in an acidic solution.The effects of anodic potential,anodic time and electrolyte concentration on the electrochemical active area of the prepared composite electrode were detailedly investigated.The electrochemical behaviors of Co₃O₄/NPG/Au composite electrode on glucose and H₂O₂ in alkaline solution were also investigated.A dual-function enzyme-free electrochemical sensor for the detection of glucose and H₂O₂ was constructed.For glucose detection,there was a good linear relationship between 2?M².11 mM?R²=0.9927?,a low detection limit of 0.085?M?S/N=3?,a ultrahigh sensitivity of 4470.4?A mM^-1cm^-2,and a rapid response time less than 2s;for H₂O₂ detection,there was an excellent linear relationship?R²=0.9992?in the range of 20?M to 19.1 mM,a high sensitivity of1338.7?A mM^-1cm^-2,and a low detection limit of 6.4?M?S/N=3?.The durability of the bifunctional enzyme-free electrochemical sensor can reach 21 days,and the detection of glucose in human serum samples has been successfully realized.?2?A SnO₂/HNPG/AuSn integrated composite electrode with a highly rough surface was rapidly prepared in HCl electrolyte from smooth Au₈₀Sn₂₀?wt.%?alloy electrode by electrochemical anodization-disproportionation mthod.The preparation time is as short as80 s.There are fourelectrochemical/chemical processes in the process of anodization:?i?Sn component in AuSn alloy anodically dissolved to form nanoporous structure by electrochemical dealloying;?ii?formation of nanoporous structure of Au component by“electrochemical dissolution,disproportionationanddeposition?EDD?”process;?iii?oxidation-reduction reaction between Sn²⁺and AuCl₄^–anodically dissolved to form Au nanoparticles(Au_nano);?iv?Sn⁴⁺is saturated near the electrode surface and following hydrolyzed to produce SnO₂nanoparticles due to the migration of H⁺ions to cathode resulting in the decrease of acidity on the surface.The combination of these processes resulted in a unique nanoporous structure with a highly rough surface.The effects of anodic potential,anodic time and electrolyte concentration on the electrochemical active area of SnO₂/HNPG/AuSn were discussed in detail.The electrocatalytic behaviors of NPG/Au and SnO₂/HNPG/AuSn on glucose in NaOH solution were compared by CV method.An efficient electrochemical non-enzymatic glucose sensor based on SnO₂/HNPG/AuSn was developed with an ultrahigh sensitivity(4374.6?A cm^–2 mM^–1),a fast response?4 s?,a wide linear range?2?M⁸.11 mM?,and a high long-term stability?6 weeks?.It also has been successfully applied to the determination of glucose in human serum samples.?3?Based on SnO₂/HNPG/AuSn composite electrode as described in section?2?,a Pt modified SnO₂/HNPG/AuSn composite electrode?Pt/HNPG/AuSn?integrated composite electrode was fabricated by potentiostatic deposition method.The effects of Pt loadings,scan rate and pH on the electrooxidation behavior of N₂H₄ on Pt/HNPG/AuSn electrode were investigated in detail.In PBS?pH=7?solution,it achieves a rapid detection of high concentration N₂H₄ with advantages of a low detection potential?-0.1 V?,an ultrahigh sensitivity(3449.68?A mM^–1cm^–2)and a wide detection range?5?M⁶.105 mM?.The constructed N₂H₄ electrochemical sensor has been successfully used in the detection of N₂H₄ in river and lake water samples,and its long-term stability can be up to 21 days.?4?A unique surface-crater and nanoporous CNP/AuSi integrated composite electrode was fabricated in HCl electrolyte from Au₇₉Si₂₁?wt.%?alloy electrode by electrochemical anodization-disproportionation method.The effects of anodic potential and anodizing time on the the electrochemical active area of CNP/AuSi composite electrode were investigated.An enzyme-free electrochemical sensor for ascorbic acid?AA?detection based on CNP/AuSi was developed under alkaline conditions.Its sensitivity is 1239.8?A cm^–2 mM^–1,linear range is 2?M⁸.11 mM,response time is 3 s,and its stability can be as long as 22weeks.