Annalisa Vacca, graduate in Chemical Engineering and PhD in Industrial Engineering, got the associate professor position in the field of “Fundamentals of chemical technology” (SSD CHIM/07). She carries out didactic and scientific activity at the Department of Mechanical, Chemical and Materials Engineering (University of Cagliari). From 2006, she is teacher of the course of General Chemistry at the first level degree for the Faculty of Engineering.
The research activities are focused in the field of electrochemical engineering applied to the study of processes for environmental remediation and energy conversion. In particular, the study covers both key aspects such as the catalytic activity of electrode materials and the identification of reaction mechanisms, both practical aspects such as design and characterization of electrochemical reactors.
With regard to the environmental remediation, processes for removal of toxic organic pollutants from industrial wastewater and from natural waters have been studied. Different electrodic materials have been tested in order to identify the reaction mechanisms involved in the removal process, depending on the chemistry of pollutant and on the nature of the selected anodic material.
Techniques such as voltammetry and electrochemical impedance spectroscopy have been used to analyze the phenomena that occur at the interphase electrode / solution.
Different electrode materials have been tested for the pollutants removal: commercial Ti/RuO2-IrO2 anodes, usually adopted in chlor-alkali process, have been tested for oxidation of phenol and chlorophenol compounds, which were selected as a model of toxic and biorefractory compounds.
The removal of phenolic compounds has been tested also in presence of biodegradable organic substrate such as glucose and aspartic acid. The study was extended to olive oil mill wastewaters which present an high fenolic fraction together with a very high organic load. These studies have shown that the electrochemical treatment reduce the toxicity of the wastewater and it could be used as pretreatment in a combined electrochemical-biological process. Similarly, also boron doped diamond electrodes have been tested: these anodes allow to a fast oxidation of organics pollutants, thanks to the formation of weakly adsorbed OH radicals form water oxidation. Several compounds have been removed with BDD anode form aqueous solutions up to their mineralization; among the others phenols and pesticides. Also waters polluted by MTBE and BTEX at very low concentrations have been successfully treated: in this case a suitable design of the electrochemical reactor and its hydrodynamic characterization have been studied. The development of mathematical models of the electrochemical reactors had allowed to optimize the process for the removal of pollutant in traces.
Using different electrochemical reactors such as flow-by and flow-through configuration bacteria and microalgae have been removed from natural and sea waters.
In view of the application of these processes on the real-scale, studies on the stability and lifetime of electrode materials have been also carried out; these studies allowed to determine in what extent and how the structural changes induced by high lifetime affect the catalytic activity of the material.
The second topic on environmental applications of her research concerns the heavy metal pollutions of soils: in particular the interactions between the pollutants (Pb+2, Zn+2 e Cd+2 ) and the solid matrix of the soils has been studied and a mathematical model of the process has been proposed in order to predict the diffusion of the heavy metal ions in the environment and to better understand which remediation process is more suitable. Tests of electrokinetic remediation of clayey soil has been also performed and a model of the overall process, which take into account for the effect of the electric field on pH gradient and heavy metal concentrations across the soil specimen, has been elaborated. Electrokinetic remediation of soils has been also applied to organic pollutants.
The research on energy conversion have focused mainly on the study of electrocatalysts both effective for the hydrogen production by water electrolysis, both for the use of hydrogen for energy production in cells fuel. Since the redox reaction of oxygen represents the limiting step for both processes, different catalytic materials towards this reaction have been studied: electrodes based on mixed oxides of iridium, tin and titanium were tested for electrolysis in acidic medium whereas spinels containing cobalt oxide and ferrites were studied in alkaline solutions.
In the field of applications to fuel cells, the study has been directed to the preparation of catalysts which are tolerant to CO by using Ru, Sn, Co and Fe combined with Pt.
Attention was then turned to the photo-electro water splitting: this technique combines the process of electrolysis with the photocatalysis in order to obtain hydrogen exploiting the solar radiation. The research involves the preparation and characterization of electrodes based on titanium dioxide both in nanopowder and in nanotubes forms, which present very high surface and high photo-electrochemical capability. Currently, modification of the nanotubular surface with organic sensitizer are under investigation, with the aim to improve the harvest of the visible light. The grafting of organic on titania nanotubes have been performed by the electroreduction of diazonium salts, which allows to a covalent and very stable link. With this technique, TiO2 has been functionalized by cumarin-343 and polyaniline obtaining improvements of the electrode performances. Analogously, hybrid electrodes have been obtained for sensing application modifying gold and porous silicon with oligonucleotides chains and conducting polymers respectively.
Another research interest is the electrodeposition of refractory metals such as niobium, tantalum and zirconium using ionic liquids as solvents: multilayer of these metals can be used for the control of the radiations in nuclear reactors. In particular Nb/Cu and Ta/Cu have been prepared and characterized.
The research activities are documented by 66 papers published in international peer-reviewed scientific journals and by more than 100 contribution at national and international congresses. Bibliometrics (SCOPUS 2002-Genuary 2020):
Scientific papers: 70;
Total citations: 1620;