Publications by authors named "Ambra Fioravanti"

3 Publications

  • Page 1 of 1

Charge Carrier Processes and Optical Properties in TiO and TiO-Based Heterojunction Photocatalysts: A Review.

Materials (Basel) 2021 Mar 27;14(7). Epub 2021 Mar 27.

Department of Physics "E. Pancini", University of Naples "Federico II", Complesso Universitario di Monte S. Angelo, Via Cupa Cintia 21, 80126 Napoli, Italy.

Photocatalysis based technologies have a key role in addressing important challenges of the ecological transition, such as environment remediation and conversion of renewable energies. Photocatalysts can in fact be used in hydrogen (H) production (e.g., via water splitting or photo-reforming of organic substrates), CO reduction, pollution mitigation and water or air remediation via oxidation (photodegradation) of pollutants. Titanium dioxide (TiO) is a "benchmark" photocatalyst, thanks to many favorable characteristics. We here review the basic knowledge on the charge carrier processes that define the optical and photophysical properties of intrinsic TiO. We describe the main characteristics and advantages of TiO as photocatalyst, followed by a summary of historical facts about its application. Next, the dynamics of photogenerated electrons and holes is reviewed, including energy levels and trapping states, charge separation and charge recombination. A section on optical absorption and optical properties follows, including a discussion on TiO photoluminescence and on the effect of molecular oxygen (O) on radiative recombination. We next summarize the elementary photocatalytic processes in aqueous solution, including the photogeneration of reactive oxygen species (ROS) and the hydrogen evolution reaction. We pinpoint the TiO limitations and possible ways to overcome them by discussing some of the "hottest" research trends toward solar hydrogen production, which are classified in two categories: (1) approaches based on the use of engineered TiO without any cocatalysts. Discussed topics are highly-reduced "black TiO", grey and colored TiO, surface-engineered anatase nanocrystals; (2) strategies based on heterojunction photocatalysts, where TiO is electronically coupled with a different material acting as cocatalyst or as sensitizer. Examples discussed include TiO composites or heterostructures with metals (e.g., Pt-TiO, Au-TiO), with other metal oxides (e.g., CuO, NiO, etc.), direct Z-scheme heterojunctions with g-CN (graphitic carbon nitride) and dye-sensitized TiO.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/ma14071645DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8036967PMC
March 2021

Growth Mechanisms of ZnO Micro-Nanomorphologies and Their Role in Enhancing Gas Sensing Properties.

Sensors (Basel) 2021 Feb 13;21(4). Epub 2021 Feb 13.

Istituto di Scienze e Tecnologie per l'Energia e la Mobilità Sostenibili (CNR-STEMS), Via Canal Bianco 28, 44124 Ferrara, Italy.

Zinc oxide (ZnO) is one of the main functional materials used to realize chemiresistive gas sensors. In addition, ZnO can be grown through many different methods obtaining the widest family of unique morphologies. However, the relationship between the ZnO morphologies and their gas sensing properties needs more detailed investigations, also with the aim to improve the sensor performances. In this work, seven nanoforms (such as leaves, bisphenoids, flowers, needles, etc.) were prepared through simple wet chemical synthesis. Morphological and structural characterizations were performed to figure out their growth mechanisms. Then, the obtained powders were deposited through screen-printing technique to realize thick film gas sensors. The gas sensing behavior was tested toward some traditional target gases and some volatile organic compounds (acetone, acetaldehyde, etc.) and compared with ZnO morphologies. Results showed a direct correlation between the sensors responses and the powders features (morphology and size), which depend on the specific synthesis process. The sensors can be divided in two behavioral classes, following the two main morphology kinds: aggregates of nanocrystals (leaves and bisphenoids), exhibiting best performances versus all tested gases and monocrystal based (stars, needle, long needles, flowers, and prisms).
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/s21041331DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7918259PMC
February 2021

(Ti,Sn) Solid Solution Based Gas Sensors for New Monitoring of Hydraulic Oil Degradation.

Materials (Basel) 2021 Jan 28;14(3). Epub 2021 Jan 28.

Istituto di Scienze e Tecnologie per l'Energia e la Mobilità Sostenibili (CNR-STEMS), 44124 Ferrara, Italy.

The proper operation of a fluid power system in terms of efficiency and reliability is directly related to the fluid state; therefore, the monitoring of fluid ageing in real time is fundamental to prevent machine failures. For this aim, an innovative methodology based on fluid vapor analysis through metal oxide (shortened: MOX) gas sensors has been developed. Two apparatuses were designed and realized: (i) A dedicated test bench to fast-age the fluid under controlled conditions; (ii) a laboratory MOX sensor system to test the headspace of the aged fluid samples. To prepare the set of MOX gas sensors suitable to detect the analytes' concentrations in the fluid headspace, different functional materials were synthesized in the form of nanopowders, characterizing them by electron microscopy and X-ray diffraction. The powders were deposited through screen-printing technology, realizing thick-film gas sensors on which dynamical responses in the presence of the fluid headspace were obtained. It resulted that gas sensors based on solid solution TiSnO with x = 0.9 and 0.5 offered the best responses toward the fluid headspace with lower response and recovery times. Furthermore, a decrease in the responses (for all sensors) with fluid ageing was observed.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/ma14030605DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7865283PMC
January 2021
-->