Cristina Navio

Synthesis and Characterization of Boron Azadipyrromethene Single-Wall Carbon Nanotube Electron Donor-Acceptor Conjugates

The preparation of a novel donor-acceptor material, consisting of a red/near-infrared (NIR) absorbing boron azadipyrromethene donor covalently attached to a highly functionalized single-wall carbon nanotube (SWNT) acceptor, which bears great potential in the field of organic photovoltaics, has been demonstrated. Both purification and covalent functionalization of SWNTs have been demonstrated using a number of complementary characterization techniques, including atomic force microscopy, Raman, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared, and NIR-photoluminescence spectroscopy, and a functionalization density of approximately 1 donor molecule per 100 SWNT atoms has been estimated by XPS. The redox behavior of the fluorophore has been investigated by electrochemistry and spectroelectrochemistry as well as by pulse radiolysis. The donor-acceptor properties of the material have been characterized by means of various spectroscopic techniques, such as UV-vis NIR absorption spectroscopy, steady-state and time-resolved fluorescence spectroscopy, and time-resolved transient absorption spectroscopy. Charge transfer from the photoexcited donor to the SWNT acceptor has been confirmed with a radical ion pair state lifetime of about 1.2 ns.

Controlled carboxylic acid introduction: a route to highly purified oxidised single-walled carbon nanotubes

A chemical treatment for preparing high purity selectively oxidised SWNTs while preserving optical/electronic properties of the material has been developed. Efficient removal of both metal and carbonaceous impurities has been demonstrated by AFM, TEM, Raman and absorption spectroscopy, while XPS confirmed quantitative conversion of oxidised defects to functionalisable carboxylic acid groups. Furthermore persistence of the characteristic optical properties was confirmed using absorption and NIR photoluminescence spectroscopy, thus indicating preservation of the electronic structure. This chemical treatment thus paves the way for the preparation of high purity, covalently functionalised SWNTs enhancing their potential for use in high-performance optical/electronic applications. A comparison with commonly used purification protocols that utilize nitric acid and sodium hydroxide followed by piranha solution treatments or simple solvent washing is made, highlighting the advantages of the reported method for the production of SWNT starting materials ideal for efficient chemical modifications.

Synthesis and Characterization of Sodium Titanate and TiO2 Nanostructures Loaded with Silver Nanoparticles

Sodium titanate nanostructures loaded with Ag0 nanoparticles were synthesized from anatase TiO2 doped with Ag+ and NaOH(aq) under hydrothermal conditions. Presence of Ag+ ions in reaction mixture prevented the growth of sodium titanate nanotubes. Instead of nanotubes half rolled sodium titanate slabs were formed. HAADF‐STEM characterization revealed that Ag0 nanoparticles are homogenously distributed on titanate matrix. By an ion exchange process sodium ions were exchanged with H3O+ in a solution of acetic acid. Further thermal treatment at 400 °C in a reductive atmosphere transformed protonated titanate slabs into TiO2 slabs loaded with Ag0 nanoparticles. The ion exchange process slightly reduced the average diameter of Ag0 nanoparticles when compared to the diameter of Ag0 nanoparticles in the as synthesized sample. The samples were characterized by high angle annular dark field scanning transmission electron microscopy (HAADF‐STEM), X‐ray photoelectron spectroscopy (XPS) and X‐ray diffraction (XRD).

Improvement in selectivity of NO 2 sensors based on WO 3 thin films with MnO 2 filters deposited by radio frequency sputtering

Thin-film WO<inf>3</inf> sensor with a MnO<inf>2</inf> filter was prepared to reduce interference of O<inf>3</inf> for NO<inf>2</inf> detection. The multi-films (WO<inf>3</inf> film, MnO<inf>2</inf> filter and WO<inf>3</inf>+MnO<inf>2</inf> insulting layer) were deposited by radio frequency sputtering. The microstructure and crystalline phase of the films were characterized with SEM and XRD. The sensors were tested for 25–200 ppb O<inf>3</inf> and 50–400 ppb NO<inf>2</inf> in moist air at temperatures ranging from 150°C to 250°C. The results show that the sensors with thin filters are capable to reduce the interference from O<inf>3</inf>.