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Digital archive of theses discussed at the University of Pisa


Thesis etd-03092017-133330

Thesis type
Tesi di dottorato di ricerca
Thesis title
Carbon nanomaterials for sensing of volatile amines
Academic discipline
Course of study
tutor Dott. Di Francesco, Fabio
  • amines
  • sensor
Graduation session start date
Carbon nanomaterials (CNMs) possess outstanding mechanical and electrical properties. In this thesis, pristine and functionalized carbon nanotubes (CNTs), graphene (G) and reduced graphene oxide (rGO) were exploited to realize resistive chemical sensors for the detection of gaseous ammonia (NH3) and trimethylamine (TMA).
Pristine CNTs, G and rGO (p-CNTs, p-G and p-rGO, respectively) and functionalized CNTs, G and rGO (f-CNTs, f-G and f-rGO, respectively) were characterized by using different analytical techniques as Raman, TGA, XPS, UV-Vis-NIR, FT-IR, Fluorescence and SEM. The performance of pristine and functionalized CNMs toward ammonia and trimethylamine detection were evaluated by drop-casting aliquots of CNMs dispersions on glass or FR4 substrates equipped with gold electrodes and then measuring the electrical changes upon exposure of different concentrations of NH3 or TMA. The changes in resistance of the sensitive materials were quantified and compared with each other. The necessity to develop a resistive sensor for the detection of ammonia and trimethylamine originates from the exponential growth of the fish trading as a consequence of the impressive consumption of fish and fishery products all over the world in the last few years. In addition to the contribution to the economic activity, the worldwide commercialization of fish in fact considerably improved the request of quality seafood products. In the European Union (EU), a standard method to assess the freshness of fish was established in 1995 (95/149/EC). After the approval of a regulation for food traceability, which implies the need to assess quality and identify the responsibility of the correct storage along the whole food chain, fisheries industries looked for rapid methods to evaluate real-time freshness of fish and seafood products. In this framework, we aimed to develop a system to monitor the freshness of fish and seafood products basing the research on the development of chemiresistive portable sensors. Fish is among the most perishable flesh food and the odor is a first indication for freshness, since fish flesh releases increasing amounts of characteristic volatile compounds during degradation, such as ammonia (NH3) and trimethylamine (TMA). In particular, TMA can be considered a marker for the determination of fish freshness. In fact, when fresh, the nitrogenous compound is present in the fish flesh in the form of trimethylamine N-oxide (TMAO); when the bacterial and enzimatic activity takes place, TMAO is degraded to TMA, dimethylamine (DMA) and formaldehyde (FA) [1]. A general approach to evaluate the freshness of fish is the quantification of the total volatile basic nitrogen compounds (TVB-N) using different methods. The standard method approved by the European Union for the assessment of the freshness of fish is based on the determination of TVB-N levels in fish tissue samples by extracting the volatiles bases by a perchloric acid solution; then the extract is steam distilled, collected in boric acid and titrated against standard HCl. Although this method is reliable and efficient, it is destructive, time-consuming and requires appropriate instrumentation and highly qualified personnel to be performed. Due to the large variability in the spoilage attitude among different species, harvests and fishes of a same catch, the fishing industry and agencies for the food safety have always shown interest in methods for the fast evaluation of fish freshness. Accurate portable devices are needed to measure NH3 and TMA in the field, as they would help to prevent the degradation of products and allow quality controls at each transfer of product between different actors of the distribution chain. Although ammonia is present even in fresh fish, the TVB-N content produced during the spoilage is very close to that of TMA [2]. When fresh, fish releases up to 10 ppm of TMA, whereas concentrations between 10 and 50 ppm indicate a preliminary rot and concentrations over 60 ppm a rotten product [3,4]. The efforts carried out for the realization of resistive chemical sensors able to detect gaseous amines in real-time led to win a project (MIT-UNIPI Project) titled “Functional Nanomaterials for the Detection of Volatile Amines (FUNDUS)” which was a collaboration between the University of Pisa and the Massachusetts Institute of Technology (Cambridge, MA, USA). Therefore, in this thesis and in the MIT-UNIPI Project, single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), G and rGO were covalently functionalized in order to obtain different materials sensitive to the detection of different concentrations of volatile amines as NH3 and TMA. Very interesting was the comparison of the performance of the different carbon-based nanomaterials toward two different kind of covalent functionalization carried out exploiting the nitrene and diazonium chemistry and the following submission to gas sensing tests. SWCNTs were also functionalized by non-covalent functionalization and their sensing performance were evaluated.