Photocatalytic degradation of selected herbicides in aqueous suspensions of doped titania under visible light irradiation.

The aim of this work was to study the efficiency of Fe- and N-doped titania suspensions in the photocatalytic degradation of the herbicides RS-2-(4-chloro-o-tolyloxy)propionic acid (mecoprop, MCPP), (4-chloro-2-methylphenoxy)acetic acid (MCPA), and 3,6-dichloropyridine-2-carboxylic acid (clopyralid, CP) under the visible light (lambda > or = 400 nm) irradiation. The obtained results were compared with those of the corresponding undoped TiO(2) (rutile/anatase) and of the most frequently used TiO(2) Degussa P25. Computational modeling procedures were used to optimize geometry and molecular electrostatic potentials of MCPP, MCPA and CP and discuss the obtained results. The results indicate that the efficiency of photocatalytic degradation is greatly influenced by the molecular structure of the compound. Lowering of the band gap of titanium dioxide by doping is not always favorable for increasing photocatalytic efficiency of degradation.

Direct detection of unamplified DNA from pathogenic mycobacteria using DNA-derivatized gold nanoparticles.

Mycobacterial infections have a high economic, human and animal health impact. Herein, we present the development of a colorimetric method that relies on the use of gold nanoparticles for fast and specific detection of Mycobacterium spp. dispensing with the need for DNA amplification. The result can be recorded by visual and/or spectrophotometric comparison of solutions before and after acid induced AuNP-probe aggregation. The presence of a complementary target prevents aggregation and the solution remains pink, whereas in the opposite event it turns to purple. The application of the proposed method on isolated bacteria produced positive results with the mycobacterial isolates and negative with the controls. The minimum detection limit of the assay was defined at 18.75 ng of mycobacterial DNA diluted in a sample-volume of 10 microl. In order to obtain an indication of the method's performance on clinical samples we applied the optimized assay to the detection of Mycobacterium avium subsp. paratuberculosis DNA in faeces, in comparison with real-time PCR. The concordance of the two methods with connection to real-time PCR positive and negative sample was defined respectively as 87.5% and 100%. The proposed method could be used as a highly specific and sensitive screening tool for the detection of mycobacteria directly from clinical samples in a very simple manner, without the need of high-cost dedicated equipment. The technology described here, may develop into a platform that could accommodate detection of many bacterial species and could be easily adapted for high throughput and expedite screening of samples.

Synthesis and Characterization of Rutile TiO(2) Nanopowders Doped with Iron Ions.

Titanium dioxide nanopowders doped with different amounts of Fe ions were prepared by coprecipitation method. Obtained materials were characterized by structural (XRD), morphological (TEM and SEM), optical (UV/vis reflection and photoluminescence, and Raman), and analytical techniques (XPS and ICP-OES). XRD analysis revealed rutile crystalline phase for doped and undoped titanium dioxide obtained in the same manner. Diameter of the particles was 5-7 nm. The presence of iron ions was confirmed by XPS and ICP-OES. Doping process moved absorption threshold of TiO(2) into visible spectrum range. Photocatalytic activity was also checked. Doped nanopowders showed normal and up-converted photoluminescence.

TiO2 doped with nitrogen: synthesis and characterization.

In this study, nitrogen-doped titanium dioxide (TiO2) powders were synthesized in two ways: by heating of titanium hydroxide with urea and by direct hydrolysis of titanium tetraisopropoxide (TTIP) with ammonium hydroxide. The samples were characterized by structural (XRD), analytical (XPS), optical (UV/Vis absorption/reflection and Raman spectroscopy) and morphological (SEM, TEM) techniques. The characterization suggested that the doped materials have anatase crystalline form without any detectable peaks that correspond to dopants. The absorption threshold of titanium dioxide was moved in the visible range of optical spectrum from 3.2 eV to 2.20 eV. Particle sizes of synthesized powders were obtained from XRD measurements and from TEM data ranging from 6-20 nm. XPS and Raman spectroscopy were used for detection of nitrogen in doped samples.

Photoluminescence of anatase and rutile TiO2 particles.

Nonaqueous reactions between titanium(IV) chloride and alcohols (benzyl alcohol or n-butanol) were used for the synthesis of anatase TiO2 particles, while rutile TiO2 particles were synthesized in aqueous media by acidic hydrolysis of titanium(IV) chloride. The X-ray diffraction measurements proved the exclusive presence of either the anatase or the rutile phase in prepared samples. The photoluminescence of both kinds of particles (anatase and rutile) with several well-resolved peaks extending in the visible spectral region was observed, and the quantum yield at room temperature was found to be 0.25%. Photon energy up-conversion from colloidal anatase and rutile TiO2 particles was observed at low excitation intensities. The energy of up-converted photoluminescence spans the range of emission of normal photoluminescence. The explanation of photon energy up-conversion involves mid-gap energy levels originating from oxygen vacancies.