Preparation And Electrochemical Characterization Of Viologen Composite

Viologens,N,N’-disubstituted-4,4’-bipyridinium salts,is an organic functional material formed by conjugated pyridine groups.It has attracted much attention for decades owing to their properties such as unique electrochromic and radical-rich features under redox manipulation,biosensitive properties,ionic and localized conjugation.However,in practical applications,the disadvantages of poor conductivity and long response time still need to be improved.Therefore,the electrochemical properties of viologen compounds can be improved by introducing new functional materials.Viologen composites materials can generally be divided into two categories,one is to utilize the ability of viologen as an excellent electron acceptor and introduce functional materials with unique catalytic properties,such as inorganic semiconductor materials,nano materials,and biological enzyme materials,to improve the overall catalytic performance of composite materials.The other is to enhance the conductivity of composite by introducing materials with high conductivity,such as conductive polymers,graphene,carbon nanotubes,and so on.In this thesis,different novel viologen precursors（FCP,T0）or viologen polymer（PHV）were synthesized and used as substrates to prepare viologen composites by introducing inorganic materials with different electrochemical properties,such as Cadmium Sulfide Nanoparticles（Cd S）,Gold Nanoparticles（Au NPs）or Reduced Graphene Oxide（r GO）.The prepared composites will be analyzed and characterized by means of electrochemistry,spectrochemistry,scanning/transmission electron microscopy and other means,so as to determine the optimal conditions for preparing viologen composites and expand their application scenarios.The specific work is as follows:（1）Preparation and Analysis of PHV/Cd S Hybrid Films with Good Photochemical PropertiesDue to its suitable band gap and light response,Cd S has been widely used as a semi conductive photocatalyst in previous studies for photocatalytic hydrogen production and photodegradation of environmental pollutants.However,the recombination of photogenerated electrons limits the application of Cd S.In order to enhance the photocatalytic efficiency of Cd S,a viologen-based polymer（PHV）was utilized as a substrate to create a PHV/Cd S hybrid film in this work.The electrochemical,spectroscopic,and microscopic methods were used to analyze the hybrid films.It has been proved that the introduction of PHV can better improve the performance of Cd S.The photoelectrochemical activity of the hybrid films were also evaluated through various ratios,and it was found that PHV∶Cd S=2∶1 was the ideal ratio for the hybrid film.The PHV/Cd S hybrid films with redox activity will become a strong candidate for future photocatalytic applications.（2）Electrochemical One-step Synthesis and Characterization of FPV/Au NPs Hybrid FilmsThe Au NPs have attracted a lot of attentions as photocatalysis materials in photochemical applications,since the Au NPs have strong catalytic activity for a variety of processes and can be catalyzed at room temperature.In previous work,we obtained good results by electrochemical one-step preparation of viologen polymers using viologen precursors.Therefore,in this work,viologen polymer（FPV）were prepared using viologen precursor FCP,and FPV/Au NPs hybrid films were synthesized by electrochemical one-step reduction of FCP and HAu Cl₄.The hybrid films were characterized and analyzed using different electrochemical,spectroscopic,and microscopic methods,indicating that they have good redox and photocatalytic properties.By changing the concentration ratio of the initial solution,the size of Au NPs in the mixed film can be adjusted,and the photochemical properties can be adjusted accordingly.Due to the fact that the redox active FPV can act as an electron acceptor to receive photoelectrons from Au NPs,greatly promoting the effective separation and migration of photoelectrons and holes,and inhibiting the recombination of electrons and holes,the photoelectrochemical properties of hybrid films have been significantly improved.The results show that the optical properties of hybrid films can be successfully improved by preparing hybrid films with appropriate proportions.Therefore,FPV/Au NPs hybrid films are a new type of photocatalytic material with potential for photocatalytic applications.（3）Electrochemical One-step synthesis and Characterization of poly T0/r GO Hybrid FilmsGraphene has been widely used in the conduction of different electronic devices due to its excellent physical,chemical,electronic,thermal and mechanical stability.In this work,we first prepared viologen polymer（poly T0）by electrochemical one-step reduction of viologen precursor（T0）,and studied its electrochemical properties.The results showed that viologen polymer has excellent redox properties.The T0 and GO were mixed and electrochemically reduced（polymerized）.After mixing T0 with GO,we synthesized a poly T0/r GO hybrid film by electrochemical one-step reduction polymerization.While polymerizing to form poly T0,GO was reduced to r GO and successfully fixed in the polyviologen film.The process was driven byπ-πstacking and the electrostatic attraction of the negatively charged GO and positively charged viologen.All the characterization indicated that the poly T0/r GO hybrid films have better redox and conductive properties,which makes it has broad application prospects in energy storage devices.