Haslet Ekşi

Effect of Au and Au@Ag core–shell nanoparticles on the SERS of bridging organic molecules

Gold nanoparticles (AuNPs) with about 6 nm size were produced and stabilized with mercaptopropionic acid (MPA) film to produce a monolayer protected cluster (MPC) of AuS(CH(2))(2)COOH. 4-Aminothiophenol (ATP) molecules were introduced to the activated carboxylic acid ends of the film surrounding the AuNPs to produce AuS(CH(2))(2)CONHPhSH MPC. These modified AuNPs were again self-assembled with Au@Ag core-shell bimetallic nanoparticles via the -SH groups to produce an organic bridge between Au and Au@Ag metallic nanoparticles. An unusually strong enhancement of the Raman signals was observed and assigned to the plasmon coupling between the AuNPs and Au@Ag NPs bridged assembly. Formation of AuS(CH(2))(2)COOH and AuS(CH(2))(2)CONHPhSH clusters and AuS(CH(2))(2)CONHPhS(Au@Ag) assembly is confirmed by UV-Vis, reflection-absorption IR spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS), as well as by TEM analysis. The SERS activity of the AuNPs and Au@Ag NPs was tested using the HS(CH(2))(2)CONHPhSH molecule as a probe to compare the effectiveness of monometallic and bimetallic systems. SERS spectra show that Au@Ag bimetallic nanoparticles are very effective SERS-active substrates.

Syntheses and modifications of bisdiazonium salts of 3,8-benzo[c]cinnoline and 3,8-benzo[c]cinnoline 5-oxide onto glassy carbon electrode and the characterization of the modified surfaces

The goal of this study was to prepare novel glassy carbon electrode surfaces using two similar bis-diazonium salts, 3,8-benzo[c]cinnoline (3,8-BCC-BDAS) and 3,8-benzo[c]cinnoline 5-oxide (3,8-BCCNO-BDAS) at the glassy carbon (GC) surface. These diazonium salts were reduced electrochemically and covalently electrografted onto the glassy carbon electrode surface to form modified electrodes. Electrochemical reduction of 3,8-BCC-BDAS and 3,8-BCCNO-BDAS salts on the electrode surface yielded a compact and stable film. The existence of BCC moieties on the GC surface was characterized by X-ray photoelectron spectroscopy, reflectance-adsorption infrared spectroscopy, cyclic voltammetry, ellipsometry, and electrochemical impedance spectroscopy. The stability and working potential range of the novel modified electrodes were also studied. The possibility of analytical application of these novel surfaces for inorganic cations and especially selectivity to copper ions was investigated. 3,8-diaminobenzo[c]cinnoline (3,8-DABCC) and its 5-oxide derivative (3,8-DABCCNO) were synthesized from the reductive cyclization of 2,2′-dinitrobenzidine and prepared their bisdiazonium salts via the tetrazotization reactions of the diamines with NaNO2. The structures of 3,8-DABCC and 3,8-DABCCNO and their corresponding bisdiazonium salts are confirmed by spectral analysis.

Spectroscopic and Electrochemical Characterization of Benzoylglycine-Modified Glassy Carbon Electrode: Electrocatalytic Effect Towards Dioxygen Reduction in Aqueous Media

ABSTRACT Present work aims to create a benzoylglycine (BG)-modified glassy carbon (GC) substrate exploiting the electroreduction of diazonium salts. Dopamine was used to confirm the attachment of benzoylglycine molecules onto the glassy carbon surface by observing the blockage of the electron transfer using cyclic voltammetry (CV). BG-modified GC surface (BG-GC) was also characterized by Raman spectroscopy and electrochemical impedance spectroscopy (EIS) techniques. The ellipsometric thickness of the BG film was measured as approximately 14 nm for seven CV cycles. The electrocatalytic effect of BG-GC electrode surface against dioxygen reduction was investigated. The catalytic effect for dioxygen reduction of the BG-GC surface was compared with that of 2-benzo[c]cinnoline, 2-benzo[c]cinnoline 6-oxide- and diethylene glycol bis(2-aminophenyl)ether-modified GC surfaces to clarify the mechanism of catalysis of the surfaces in terms of molecular structure.