Mirjana I. Čomor

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 TiO2into visible spectrum range. Photocatalytic activity was also checked. Doped nanopowders showed normal and up-converted photoluminescence.

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 methods 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.

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.

Surface modification of anatase nanoparticles with fused ring catecholate type ligands: a combined DFT and experimental study of optical properties

Surface modification of nanocrystalline TiO(2) particles (45 Å) with catecholate-type ligands consisting of an extended aromatic ring system, i.e., 2,3-dihydroxynaphthalene and anthrarobin, was found to alter the optical properties of the nanoparticles in a similar way to modification with catechol. The formation of inner-sphere charge-transfer (CT) complexes results in a red shift of the semiconductor absorption compared to unmodified nanocrystallites and the reduction of the band gap upon the increase of the electron delocalization on the inclusion of additional rings. The binding structures were investigated by FTIR spectroscopy. The investigated ligands have the optimal geometry for binding to surface Ti atoms, resulting in ring coordination complexes of catecholate type (binuclear bidentate binding-bridging) thus restoring the six-coordinated octahedral geometry of surface Ti atoms. From the Benesi-Hildebrand plot, stability constants in methanol/water = 90/10 solutions at pH 2 of the order 10(3) M(-1) have been determined. Quantum chemical calculations on model systems using density functional theory (DFT) were performed to obtain vibrational frequencies of charge transfer complexes, and the calculated values were compared with the experimental data.

Optical, structural and thermal characterization of gold nanoparticles – poly(vinylalcohol) composite films

We report synthesis and characterization of gold NPs/PVA composite films. Gold colloidal NPs were introduced into a PVA matrix by simple solution-casting method to obtain homogenous, transparent, and colored films. NPs and NC films with different contents of inorganic phase (0.7, 1.4, and 2.1 wt %) were characterized by UV/Vis and FTIR spectrophotometry. Dimensions of the colloidal NPs were obtained by TEM (d ∼ 15±3 nm) and compared with results obtained by AFM of NC films. Comparison of thermal properties of the pure PVA and NC films showed that thermal stability is slightly reduced. DSC measurements revealed that Tg and melting temperatures of NCs are higher compared to pure PVA films.

The influence of reaction media on CdIn2S4 and ZnIn2S4 nanocrystallite formation and growth of mesocrystal structures

A hot-injection method for the synthesis of CdIn2S4 in three different compositions of organic media/solvents was studied. Nanosized CdIn2S4 is successfully synthesized in an oleic acid/oleylamine mixture of complexing/capping agents. The obtained mesocrystals of 20–30 nm in diameter are self-organized in marigold-like structures. The estimated band-gap of synthesized semiconductor is in the visible spectral region and has a value of about 2.1 eV. The potential of the band edges is calculated using an empirical equation. The as-prepared material was successfully transferred from organic to aqueous media by using 2-mercaptoethanol in a surface ligand exchange process. Using a similar synthetic procedure, ZnIn2S4 synthesis was performed. The obtained materials were characterized using UV/vis spectroscopy, XRD and TEM. Formation and growth mechanisms of the synthesized materials are proposed.

ROOM-TEMPERATURE LUMINESCENCE OF AGBR QUANTUM DOTS

Abstract A new method for the preparation of 25 A AgBr quantum dots has been developed. The room-temperature emission of size-restricted AgBr crystallites was observed. The emission spectrum of 25 A AgBr quantum dots is characterized by the presence of two bands centered at 340 and 420 nm. A room-temperature luminescence quantum yield of ∼0.4% was determined. Several reasons for the enhancement of the emission of the normally nonemissive indirect band gap of the AgBr material are discussed.

Polystyrene/hematite composites: thermal degradation kinetics

The kinetics of thermal degradation of polystyrene/Fe2O3 composites was studied by dynamic thermogravimetry. The samples were heated in nitrogen atmosphere, applying three different heating rates 5, 20, and 40°C/min. We calculated kinetic parameters using modified KAS isoconversional method. Results showed that polystyrene in all composites has higher thermal degradation activation energies compared to pure polystyrene. Maximal activation energy of thermal degradation is achieved for PS/Fe2O3 composite with about 10% of filler. Vyazovkin model-free method was used to predict thermal degradation parameters.

Photocatalytic decomposition of selected biologically active compounds in environmental waters using TiO2/polyaniline nanocomposites: Kinetics, toxicity and intermediates assessment

A comprehensive study of the removal of selected biologically active compounds (pharmaceuticals and pesticides) from different water types was conducted using bare TiO2 nanoparticles and TiO2/polyaniline (TP-50, TP-100, and TP-150) nanocomposite powders. In order to investigate how molecular structure of the substrate influences the rate of its removal, we compared degradation efficiency of the initial substrates and degree of mineralization for the active components of pharmaceuticals (propranolol, and amitriptyline) and pesticides (sulcotrione, and clomazone) in double distilled (DDW) and environmental waters. The results indicate that the efficiency of photocatalytic degradation of propranolol and amitriptyline was higher in environmental waters: rivers (Danube, Tisa, and Begej) and lakes (Moharač, and Sot) in comparison with DDW. On the contrary, degradation efficacy of sulcotrione and clomazone was lower in environmental waters. Further, of the all catalysts applied, bare TiO2 and TP-100 were found to be most effective in the mineralization of propranolol and amitriptyline, respectively, while TP-150 appeared to be the most efficient in terms of sulcotrione and clomazone mineralization. Also, there was no significant toxicity observed after the irradiation of pharmaceuticals or pesticides solutions using appropriate catalysts on rat hepatoma (H-4-II-E), mouse neuroblastoma (Neuro-2a), human colon adenocarcinoma (HT-29), and human fetal lung (MRC-5) cell lines. Subsequently, detection and identification of the formed intermediates in the case of sulcotrione photocatalytic degradation using bare TiO2 and TP-150 showed slightly different pathways of degradation. Furthermore, tentative pathways of sulcotrione photocatalytic degradation were proposed and discussed.