Lórant Szatmáry

Transformation of brookite-type TiO2 nanocrystals to rutile: correlation between microstructure and photoactivity

Nanometric particles of pure brookite TiO2 were synthesized by modified thermolysis of reactant solutions containing titania powder, HCl, urea and PEG 10000. Unique flower-like brookite agglomerates with an average diameter of ∼400–450 nm composed of single brookite nanocrystals of ∼4–5 nm were obtained at 105 °C. The brookite → rutile transformation has been studied and TiO2 mixtures with variable amount of anatase, brookite and rutile polymorphs at different temperatures (from 200 to 800 °C) were obtained. High resolution transmission electron microscopy (HRTEM), electron diffraction pattern and BET/BJH analyses were used to characterize the phase assemblages, crystallite size and pore volume of the pure-phase brookite and TiO2 mixtures. In order to understand the metastable–stable TiO2 phase transformation X-ray powder diffraction (XRD) was performed. The photoactivity of pure brookite and TiO2 powders with different compositions of the brookite–anatase–rutile and anatase–rutile polymorphs obtained during the transitions was examined by photocatalyzed degradation of 4-chlorophenols in aqueous solution. The titania sample having the highest catalytic activity was obtained at 500 °C, contained 3.2% brookite, 42.9% anatase and 53.9% rutile and is referred to as TiO[B])/500 .

Antibacterial nanofiber materials activated by light

Electrospun polymeric nanofiber materials doped with 5,10,15,20-tetraphenylporphyrin (TPP) photosensitizer were prepared from four different polymers and were characterized with microscopic methods, steady-state, and time-resolved fluorescence and absorption spectroscopy. The polymers used included polyurethane Larithane™ (PUR), polystyrene (PS), polycaprolactone (PCL), and polyamide 6 (PA6). The antibacterial activity of all nanofiber materials against E. coli was activated by visible light and it was dependent on oxygen permeability/diffusion coefficients and the diameter of the polymeric nanofibers. This activity is based on oxidation ability of singlet oxygen O₂(¹Δ(g)) that is generated upon irradiation. All tested nanofiber materials exhibited prolonged antibacterial properties, even in the dark after long-duration irradiation. The post-irradiation effect was explained by the photogeneration of H₂O₂, which provided the material with long-lasting antibacterial properties.

Mechanochemical Synthesis of Visible Light Sensitive Titanium Dioxide Photocatalyst

Phase transition of anatase nanoparticles into the phases TiO2-II and rutile under grinding was studied. The addition of ammonium carbamate to the reaction mixture inhibits the phase conversion and the cold welding of particles. The UV-visible absorption spectrum showed narrowing the band gap width after grinding with an ammonium carbamate additive resulting in shift of the light absorption of the ground sample towards the visible region. By EPR, intensive formation of OH• radical at irradiation of the sample with both UV (λ > 300 nm) and visible (λ > 435 nm) light was observed. High photocatalytic activity of the ground sample in visible light region was demonstrated also by measurement of kinetics of the photocatalytic decomposition of 4-chlorophenol.

Polysaccharide biopolymers modified with titanium or nickel nanoparticles for removal of radionuclides from aqueous solutions

New composite nanomaterials of cellulose, chitin, and chitosan modified with titanium or nickel nanoparticles were developed and tested for removal of 137Cs, 85Sr, 60Co, and 152+154Eu from aqueous solutions. The composite nanomaterials were characterized by X-ray diffraction, high-resolution scanning electron microscopy, infrared spectroscopy, and nitrogen adsorption–desorption isotherms. The influencing factors of metal adsorption were investigated, including contact time, pH, and metal ions concentration. Freundlich and Langmuir models were applied to fit the Sr(II) equilibrium adsorption data. All Ti modified biopolymers are promising adsorbents for 85Sr, 60Co, and 152+154Eu removal from radioactive wastewater.