Antti Viinikanoja

Electrochemical reduction of graphene oxide and its in situ spectroelectrochemical characterization

The electrochemical properties of self-assembled films of graphene oxide (GO) on mercaptoethylamine (MEA) modified rough Au-surfaces were studied. The film deposition process on MEA primed gold was followed by surface plasmon resonance measurements and the film morphology on 3-aminopropyltriethoxysilane primed Si(100)-surface was studied by atomic force microscopy. The deposited few layer thick GO films on gold were electrochemically reduced by cyclic voltammetry simultaneously as the structural changes in the film were recorded by in situ vibrational spectroscopies. In situ surface enhanced infrared spectroscopy results indicate that the effect of the applied potential on the GO structure could be divided into two parts where the changes occurring at moderate negative potentials are mainly related to changes in the double layer at the film-electrolyte interface and to hydrogen bonding of intercalated water between the GO sheets. At potentials more negative than -0.8 V vs. Ag/AgCl the reduction of GO starts to take place with concomitant conversion of the different functional groups of the film.

Graphene-modified electrode. Determination of hydrogen peroxide at high concentrations

A gold electrode partially coated by graphene multilayer is developed and tested with respect to high concentrations of hydrogen peroxide. The effective use of conventional electrode materials for the determination of such an analyte by anodic oxidation or cathodic reduction is prevented by the occurrence of adsorptions fouling the electrode surface. This prevents reliable and repeatable voltammetric curves for being recorded and serious problems arise in quantitative analysis via amperometry. The gold–graphene electrode is shown to be effective in quantitative evaluation, by cathodic reduction, of hydrogen peroxide at concentration levels that are of interest in an industrial. Acid, neutral, and basic pH values have been tested through correct adjustment of a Britton Robinson buffer. The experiments have been performed both by cyclic voltammetry and with amperometry at constant potential in unstirred solution. The latter technique has been employed in drawing a calibration linear plot. In particular, the performances of the developed electrode system have been compared with those of both pure gold and pure graphene electrode materials. The bi-component electrode was more sensitive; co-catalytic action by the combination of the two components is hypothesised. The system is stable over many potential cycles, as checked by surface-enhanced Raman spectra recorded over time.

Mechanisms of Tenebrescence and Persistent Luminescence in Synthetic Hackmanite Na8Al6Si6O24(Cl,S)(2)

Synthetic hackmanites, Na8Al6Si6O24(Cl,S)2, showing efficient purple tenebrescence and blue/white persistent luminescence were studied using different spectroscopic techniques to obtain a quantified view on the storage and release of optical energy in these materials. The persistent luminescence emitter was identified as impurity Ti(3+) originating from the precursor materials used in the synthesis, and the energy storage for persistent luminescence was postulated to take place in oxygen vacancies within the aluminosilicate framework. Tenebrescence, on the other hand, was observed to function within the Na4(Cl,S) entities located in the cavities of the aluminosilicate framework. The mechanism of persistent luminescence and tenebrescence in hackmanite is presented for the first time.

One-pot synthesis of an Au/Au2S viologen hybrid nanocomposite for efficient catalytic applications

We report a facile one-pot synthesis of Au/Au2S multicomponent nanoparticles supported on viologen (V) as a hybrid nanocomposite. Sodium dithionite was used as the reducing agent for both Au and V precursors and SDS as the stabilizing agent for Au nanoparticles in aqueous reaction medium. Spectroscopy, microscopy and electrochemical measurements confirm the successful composite formation. The as-prepared flower-like composite showed excellent catalytic properties towards the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The catalytic activity factor of the Au/Au2S–V hybrid was highest in comparison to those reported for polymer supported Au nanoparticle catalysts. The enhanced catalytic performance can be attributed to the strong adsorption of 4-NP molecules onto the cationic V matrix and Au2S nanoparticle surface along with effective donor–acceptor interactions between Au–Au2S nanoparticles and V facilitating the electron transfer at the hybrid interface.

Conformational changes of a self-assembled polyalkoxythiophene during electrochemical doping: an in situ SERRS study

Abstract The changes in charge carrier generation, structure, and conjugation length during the oxidative doping of a self-assembled poly-3-(3′-thienyloxy)-1-propanesulfonate (P3TOPS) monolayer on a gold surface modified by 2-mercaptoethylamine (MEA) were studied by electrochemical in situ Surface Enhanced Resonance Raman spectroscopy (SERRS) using laser excitation at 1064 nm. The oxidative doping of P3TOPS has been carried out in the potential range from −0.3 to +0.7 V vs Ag/AgCl. The potential dependence of the integrated normalized SERRS intensities of the inter-ring vibrations exhibits a bell-shaped curve with a maximum at 0 V. The highest effective conjugation was observed between −0.1 to +0.1 V. During the oxidation polaronic charge carriers appear first, followed by the generation of bipolarons at higher oxidation levels. Our results imply that the highest expected p -conductivity of P3TOPS might be a result of joint action of polarons and bipolarons. The alkoxy side chain experiences trans – gauche conformational changes at potentials above 0 V, resulting in the orientation more normal to the surface. Distortions in the CSC bonds with further deplanarization of the thiophene rings were observed at potentials positive of +0.3 V.

Oxidation induced variation in polyelectrolyte multilayers prepared from sulfonated self-dopable poly(alkoxythiophene)

Polyelectrolyte multilayers have been prepared using both the nneutral and oxidised forms of a poly(alkoxythiophene) derivative with npendant sulfonate groups and it is shown that the oxidation state of the npolymer affects multilayer formation.