It was established that the silver nanoparticles (AgNPs) in an equimolar ratio have the highest electrochemical activity on a graphite electrode (GE) surface in an alkaline medium. The electrocatalytic oxidation mechanism of hydrogen peroxide on the GE surface was proposed. We detected an additional maximum at E = 0.3 V on the cathodic branch of the cyclic curve in the potential range from +2.0 to -1.0 V. The appearance of this maximum indicates the reduction of hydrogen peroxide generated during AgNPs electrooxidation in the potential range from -1.0 to +2.0 V.
The “inverse” cathodic peak of gold nanoparticles is observed in the reaction mixture used to obtain gold nanoparticles HAuCl4:Na3C6H5O7:NaBH4=125:8:1 and accumulation time is 90 s. The conditions in which methionine has the greatest electrochemical activity were determined. They are as follows: the molar ratio of reagents HAuCl4:Na3C6H5O7:NaBH4=125:8:1 and accumulation time is 90 s, 0.1 M NaOH. The mechanism of methionine oxidation is proposed to be on the surface of the graphite electrode modified with gold nanoparticles in 0.1 M NaOH. The determination limit of methionine is 0.7 •10-14 M. The proposed method is simple, sensitive, and does not need toxic substances.
Influence of stabilizing agent and synthesis temperature on the optical properties of silver nanoparticles as active materials in surface plasmon resonance (SPR) vbimatov@mail.ru Abstract. The shape, size, optical properties and electrochemical activity of silver nanoparticles (AgNPs) obtained by chemical reduction methods depending on the preparation conditions were investigated. Silver sols consist of AgNPs of different shapes. They are as follows spherical -30 nm, polyhedral -35 nm, 50 nm nanorods. It was shown that the position of the absorption spectrum peak in AgNPs depend on the molar ratio of mixture AgNO 3 :Na 3 C 6 H 5 O 7 . The maximum of the absorption spectrum peak of AgNPs is shifted by 10 nm to longer wavelengths area in presence excess of a reducing agent or the increasing of boiling time. After storage for one week the spectrum intensity of AgNPs obtained in the mixture AgNO 3 :Na 3 C 6 H 5 O 7 = 1:1 is increased in comparison with freshly prepared AgNPs, which is caused by the increase of AgNPs quantity of a given size. The AgNPS obtained in the mixture AgNO 3 :Na 3 C 6 H 5 O 7 = 1:3 have the most electrochemical activity. The conditions that the AgNPs have the most electrochemical activity were found.
The shape, size, optical properties and electrochemical activity of the silver nanoparticles (AgNPs) were studied, as well as their dependence on the amount of the reducing agent, the method of initiation of the formation of nanoparticles and the introduction order of reagents in the reaction mixture. It was determined that in the sols obtained without polyethylene glycol (PEG) AgNPs are predominant with the average size of 40 nm. With PEG the triangular AgNps predominate with the average size of 20 nm due to the silver ions reduction on the surface of the nuclei. It was determined that AgNPs are most active when obtained with PEG and the molar ratio [Ag]:[C 6 H 5 O73-] = 1:5. On the anodic branch of the cyclic AgNPs curve the splitting of anodic maximum into two due to AgNPs oxidation was observed. AgNPs obtained in the presence of PEG by light have the most electrochemical activity. The processes of AgNPs oxidation become easier when PEG is present which is caused by the formation of the most stable silver oxides.
The work considers the influence of the morphological characteristics of the AgNPs (form, sizes of silver nanoparticles (AgNPs), the average size of the area) from the composition of the reducing agent and their influence on the optical characteristics and electrochemical activity of the sensor based on the AgNPs to H2O2. The intensity of the optical spectra of absorption AgNPs and the electrochemical activity of the sensors based on them correlate with the size and shape of the particles. It is shown that the greatest electrochemical activity of H2O2 is possessed by AgNPs-based sensors obtained by using sodium citrate. The reason for increasing the electrochemical activity of the sensor based on the AgNPs obtained in the presence of the soft restorer of sodium citrate is an increase in the area of their active surface 1.3–2.7–3.3 μm2 due to the non-spherical form of particles (triangular, prismatic, pyramidal form), compared with spherical particles obtained using borhydridicitrate and borohydride-based reducing agents.
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