Electroreduction of selected aliphatic chlorides at nanostructured metallic electrodes

Rosnące zanieczyszczenie środowiska stało się przyczyną intensywnych badań nad znalezieniem efektywnych metod oczyszczania wód z substancji pochodzenia antropogenicznego. Szczególnym wyzwaniem okazuje się usuwanie halogenków organicznych, związków opornych na degradację, a jednocześnie bardzo toksycznych. Związki te są powszechnie stosowane w przemyśle, głównie jako rozpuszczalniki. W niniejszej pracy wykorzystano niezwykłą katalityczną aktywność Ag i Au w procesie elektroredukcji halogenowych pochodnych węglowodorów alifatycznych. Za pomocą dwóch metod elektrochemicznych zmodyfikowano matrycę z nanoporowatego tlenku glinu. Pierwsza z nich opiera się na stopniowym obniżaniu potencjału po anodyzacji Al w celu zmniejszenia grubości warstwy zaporowej na dnie porów matrycy. Warstwa zaporowa tlenku glinu uniemożliwia elektroosadzanie, gdyż nie przewodzi prądu elektrycznego. Druga metoda, tzw. szoku potencjałowego polega na oddzieleniu tlenku glinu od glinu za pomocą pulsów potencjału o 15 V wyższych od potencjału anodyzacji glinu w mieszaninie kwasu chlorowego(VII) i etanolu (1:1 vol.). Elektrody z nanodrutów metalicznych (Ag, Au i Ag/Au) otrzymano w wyniku elektroosadzania w porach membrany uzyskanej metodą szoku potencjałowego. Następnie określono aktywność elektrokatalityczną tak uzyskanych katod względem redukcji chloroformu w acetonitrylu metodą cyklicznej woltamperometrii.Increasing environmental pollution has caused extensive research on finding effective methods that can be used for purification of water, soil and air from antropogenic substances. A particular challenge is an efficient removal of organic halides, compounds which are highly resistant to degradation, toxic and carcinogenic. These compounds are widely used in industry, mainly as solvents, and their unavoidable accidental leakages can result in dangerous environmental pollution. In this thesis, a remarkable catalytic activity of Ag and Au toward the electroreduction of halogenated derivatives of aliphatic hydrocarbons was studied. Two electrochemical methods were used to modify nanoporous alumina templates in order to remove or reduce the thickness of the barrier layer. The insulating barrier layer prevents the electrodeposition process. The metallic nanowire electrodes (Ag, Au and Ag/Au) were synthesized by electrodeposition of metals into the pores of templates obtained by the detachment method. Next, the electrocatalytic activity of the nanostructured cathode toward the reduction of trichloromethane in acetonitryle was investigated by cyclic voltammetry

Effect of processing parameters on pore opening and mechanism of voltage pulse detachment of nanoporous anodic alumina

The free-standing through-hole porous alumina membranes (PAMs) were fabricated by two-step self-organized anodization of aluminum in oxalic acid followed by the subsequent voltage pulse detachment performed in an environmental-friendly solution based on HClO4 and C2H5OH. The effects of oxalic acid concentration used for anodic oxide synthesis and the chemical composition of the barrier oxide layer on the effective detachment of PAMs were studied. On the other hand, the voltage detachment conditions such as applied voltage, number of pulses, and temperature of electrolyte were tested as parameters which might affect the detachment of PAMs and their bottom side morphology. It was found that the voltage detachment process is affected by applied detachment voltage while the bottom surface morphology of detached PAMs is influenced by oxalic acid concentration used for anodization, the chemical composition of the barrier oxide layer, and the time gap between anodization and detachment (storage period). Furthermore, it was revealed that number of applied pulses and electrolyte temperature maintained during the detachment have a little effect on the morphology of PAM films. The most feasible and detailed mechanism of the voltage pulse detachment, considering the individual stages of the process, was proposed. At the beginning, the mechanism was related to an electric field assisted dissolution of oxide enhanced by its chemical dissolution induced by Joule's heating. These processes occur at the pore bottoms upon application of the voltage pulse and results in pore widening and thinning of the barrier layer. Then, after the electrical breakdown of the barrier layer, the intensive electropolishing of aluminum at the metal/oxide interface takes place