Zoran Šaponjić

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.

Sonophotocatalytic degradation of dye C.I. Acid Orange 7 by TiO2 and Ag nanoparticles immobilized on corona pretreated polypropylene non-woven fabric.

This study discusses the possibility of using corona pre-treated polypropylene (PP) non-woven fabric as a support for immobilization of colloidal TiO2 and Ag nanoparticles in order to remove dye C.I. Acid Orange 7 from aqueous solution. Dye removal efficiency by sonocatalysis, photocatalysis and sonophotocatalysis was evaluated on corona pre-treated fabric loaded with TiO2 nanoparticles, corona pre-treated fabric double loaded with TiO2 nanoparticles and corona pre-treated fabrics loaded with TiO2 nanoparticles before and after deposition of Ag nanoparticles. In addition, the stability of PP non-woven fabric during these processes was investigated. The substrates were characterized by SEM, EDX and AAS analyses. The change of the dye concentration was evaluated by UV-VIS spectrophotometry. Unlike sonocatalysis and photocatalysis, complete dye removal from both solution and non-woven fabric was obtained already after 240-270 min of sonophotocatalysis. Corona pre-treated PP non-woven fabric loaded with Ag nanoparticles prior to deposition of TiO2 nanoparticles provided excellent degradation efficiency and superior reusability. Sonophotocatalytic degradation of dye in the presence of all investigated samples was the most prominent in acidic conditions. Although this nanocomposite system ensured fast discoloration of dye solution, TOC values of water measured after sonophotocatalysis were not satisfactory because of PP degradation. Therefore, it is suggested to include TOC evaluation in each case study where different supports for TiO2 nanoparticles are used since these nanoparticles may guarantee the dye removal from solution but the stability of support could be problematic causing even more serious environmental impact.

In situ photoreduction of Ag+-ions by TiO2 nanoparticles deposited on cotton and cotton/PET fabrics

The possibility of in situ photoreduction of Ag+-ions using TiO2 nanoparticles deposited on cotton and cotton/PET fabrics in the presence of amino acid alanine and methyl alcohol has been discussed. The possible interaction between TiO2, alanine and Ag+-ions was evaluated by FTIR analysis. The fabrication of TiO2/Ag nanoparticles on both fabrics was confirmed by SEM, EDX, XRD, XPS and AAS analyses. Cotton and cotton/PET fabrics impregnated with TiO2/Ag nanoparticles provided maximum reduction of Gram-negative bacteria Escherichiacoli and Gram-positive bacteria Staphylococcusaureus. Although excellent antibacterial activity was preserved after ten washing cycles, a significant amount of silver leached out from the fabrics into the washing bath. The perspiration fastness assessment revealed that smaller amounts of silver were also released from the fabrics into artificial sweat at pH 5.50 and 8.00. In addition, deposited TiO2/Ag nanoparticles imparted maximum UV protection to fabrics.

Colloidal TiO2 nanoparticles as substrates for M(S)ALDI mass spectrometry of transition metal complexes

RATIONALEnNanoparticles as substrates for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) have advantages over organic matrices, since they enable acquisition of spectra in the low-mass range. It has been previously shown that TiO(2) nanoparticles can be used as substrate for MALDI-TOF MS analysis of phospholipids and for other types of molecules, but none of them was applied to the analysis of transition metal complexes.nnnMETHODSnThe MALDI-TOF mass spectra of potential anti-tumor drugs [AuCl(2)(bipy)]Cl, [PtCl(4)(bipy)], and [RuCl(2)(bipy)(2) ]Cl acquired with organic matrices have been compared with spectra acquired with colloidal titanium dioxide nanoparticles. Colloidal TiO(2) nanoparticles (NPs) with average diameter of 5 nm were synthesized and characterized by microscopy. For some experiments, the TiO(2) NPs were treated at 60 °C. Suspensions of matrix and the analyte were premixed, applied to the MALDI target and left at room temperature. Mass spectra were acquired with a 50-Hz pulsed nitrogen laser emitting at a wavelength of 337 nm.nnnRESULTSnThe MALDI spectra of transition metal complexes acquired with TiO(2) NPs exhibited somewhat lower sensitivity than those with organic matrices; on the other hand, they are characterized by significantly lower number of signals arising from the tested complexes than the organic matrices. Whereas adducts between organic matrices and the analytes were detectable in the spectra, this was not the case for the TiO(2)-assisted mass spectra.nnnCONCLUSIONSnWe have shown that colloidal TiO(2) NPs can be used as substrates for MALDI-TOF MS of transition metal complexes. Although the sensitivity of this approach in comparison with the use of organic matrices might still be a problem, the potential of the applications of NPs for the mass spectrometric characterization of transition metal complexes is clearly demonstrated.

Surface modification of submicronic TiO 2 particles prepared by ultrasonic spray pyrolysis for visible light absorption

Spherical, submicronic TiO2 assemblage with high specific surface area and controllable phase composition was prepared in the process of ultrasonic spray drying/pyrolysis in a wide temperature range (150–800xa0°C) by using as a precursor aqueous colloidal solution consisting of TiO2 nanoparticles (4.5xa0nm). Submicronic, soft and grained spherical TiO2 particles (dxa0=xa0370–500xa0nm) comprising clustered nanocrystals (<10xa0nm) were obtained at low processing temperature, while particle densification, intensive growth of the clustered primary units and anatase-to-rutile transformation (~30xa0wt%) were observed at the higher temperatures. Detailed structural and morphological characterisation were performed by X-ray powder diffraction, scanning and field emission electron microscopy, transmission electron microscopy, and laser particle size analysis. Moreover, the surface modification of TiO2 particles through the formation of charge-transfer (CT) complex was achieved with different ligands: ascorbic acid, dopamine, catechol, 2,3-dihydroxynaphthalene, and anthrarobin. Optical properties of the surface-modified TiO2 particles were studied by using diffuse reflection spectroscopy. The binding structure between the surface titanium atoms and different ligands was determined by using Fourier transform infrared spectroscopy. The formation of CT complexes induced significant red shift of optical absorption in comparison to unmodified TiO2 particles.

In situ generation of Ag nanoparticles on polyester fabrics by photoreduction using TiO 2 nanoparticles

This study discusses the possibility of in situ generation of Ag nanoparticles on polyester fabric by photoreduction of Ag+ ions with deposited TiO2 nanoparticles in the presence of amino acid alanine and methyl alcohol. The presence of TiO2/Ag nanoparticles on the polyester fiber surface was confirmed by XRD, XPS, and SEM analyses. Such nanocomposite textile material provides excellent antimicrobial activity against Gram-negative bacterium E. coli, Gram-positive bacterium S. aureus, and fungus C. albicans. Maximum microbial reduction was preserved even after ten washing cycles. In spite of satisfactory laundering durability, the release of silver occurred during washing. The leaching of silver was also present when the fabrics were exposed to artificial sweat at pH 5.5 and pH 8.0 for 24xa0h. In addition to excellent antimicrobial properties, TiO2/Ag nanoparticles imparted maximum UV protection to polyester fabrics.

Negative influence of Ag and TiO2 nanoparticles on biodegradation of cotton fabrics

AbstractnRecently, many efforts have been made to efficiently impregnate different textile materials with metal and metal oxide nanoparticles in order to provide antimicrobial, UV protective or self-cleaning properties. Evidence of their environmental risks is limited at this point. The aim of this study was to explore the influence of Ag and TiO2 nanoparticles on biodegradation of cotton fabrics. Biodegradation behavior of cotton fabrics impregnated with Ag and TiO2 NPs from colloidal solutions of different concentrations was assessed according to standard test method ASTM 5988-03 and soil burial test. Degradation of cotton fabrics was also evaluated by enzymatic hydrolysis with cellulase. The morphology of fibers affected by biodegradation was analyzed by scanning electron microscopy (SEM). In order to get better insight into biodegradation process, dehydrogenase activity of soil has been determined. Ag and particularly TiO2 nanoparticles suppressed the biodegradation of cotton fabrics. The dehydrogenase activity of soil with cotton fabrics impregnated with TiO2 nanoparticles was the weakest. Severe damage of cotton fibers during the biodegradation process was confirmed by SEM.Graphical Abstract

Structural and magnetic properties of nanocomposites based on nanostructured polyaniline and titania nanotubes

Nanocomposites consisting of self-assembled polyaniline (PANI) nanostructures and titania nanotubes (TiO2-NT) were synthesized by the oxidative polymerization of aniline with ammonium peroxydisulfate in an aqueous dispersion of TiO2-NT (outer diameter ~10xa0nm), without added acid. The influence of initial mole ratio of aniline to TiO2 (80, 20, and 5) on the morphology, electrical conductivity, molecular structure, crystallinity, and magnetic properties of synthesized PANI/TiO2 nanocomposites was studied. Transmission electron microscopy, Raman spectroscopy, and X-ray powder diffraction proved that the shape and structure of TiO2-NT in the final nanocomposites were preserved. The shape of PANI nanostructures formed in the nanocomposites was influenced by the initial aniline/TiO2-NT mole ratio. Nanotubes and nanorods are predominant PANI nanostructures in the nanocomposite prepared with the highest aniline/TiO2xa0mol ratio of 80. The decrease of aniline/TiO2 molar ratio induced more pronounced formation of nanorod network. The electrical conductivity of PANI/TiO2 nanocomposites was in the range (1.3–2.4)xa0×xa010−3xa0Sxa0cm−1. The nanocomposites exhibit weak ferromagnetic behavior. Approximately order of magnitude lower values of coercive field and remanent magnetization were obtained for nanocomposite samples in comparison to pure PANI.

Biodegradation of cotton and cotton/polyester fabrics impregnated with Ag/TiO2 nanoparticles in soil

This study discusses the biodegradation behavior of cotton and cotton/PET fabrics impregnated with Ag/TiO2 nanoparticles in soil. Biodegradation behavior was evaluated by standard test method ASTM 5988-03 based on determination of percentage conversions of carbon content to CO2 as well as by soil burial test and enzymatic hydrolysis with cellulase where the extent of biodegradation was estimated by the calculation of fabric weight loss. The morphological and chemical changes of fibers during biodegradation process were analyzed by SEM and FTIR spectroscopy, respectively. The results obtained by all applied methods suggested that Ag/TiO2 nanoparticles hindered the biodegradation of investigated cotton and cotton/PET fabrics. Soil burial test indicated faster biodegradation of the impregnated blend compared to impregnated cotton fabric which is attributed to smaller amount of fabricated Ag nanoparticles on the blend proved by AAS measurement. Similar trend was established by enzymatic hydrolysis of cotton fibers. Severe damage of cotton fibers in both fabrics due to biodegradation process was confirmed by SEM. However, the cotton fiber damage occurred to a lesser extent in the samples that were impregnated with Ag/TiO2 nanoparticles. PET fibers remained intact which was also indicated by FTIR analysis.

SALDI-TOF-MS analyses of small molecules (citric acid, dexasone, vitamins E and A) using TiO2 nanocrystals as substrates.

Surface-assisted laser desorption/ionisation time-of-flight mass spectrometry (SALDI-TOF-MS) might be the method of choice for the analysis of low mass molecules (less than m/z 500). Titanium dioxide (TiO2) nanocrystals as a substrate for SALDI-TOF-MS improve the reproducibility of the signal intensities and prevent the fragmentation of some molecules upon laser irradiation, as we have previously shown. In addition, variously shaped and sized TiO2 nanocrystals/substrates for SALDI-MS could be used for quantification of small molecules, which are otherwise difficult to detect with the assistance of organic matrices. TiO2-assisted LDI-MS spectra could be acquired with excellent reproducibility and repeatability and with low detection limit. In the current study, we analysed the spectra of dexasone, citric acid, vitamin E and vitamin A acquired with TiO2 nanocrystals of various shapes and dimensions, i.e. the colloidal TiO2 nanoparticles (TiO2 NPs), TiO2 prolate nanospheroids (TiO2 PNSs) and TiO2 nanotubes (TiO2 NTs). Various shapes and dimensions of substrates were used since these factors determine desorption and ionisation processes. The homogeneity on the target plate was compared based on signal-to-noise values of peaks of interest of analysed molecules as well as the within-day and day-to-day repeatability. In summary, the obtained results show that the applicability of individual TiO2 nanocrystals depends on the analyte. Signals which are acquired with the assistance of TiO2 PNSs have the highest sensitivity and reproducibility (the smallest standard deviation), even compared with those in the LDI mode. This implies that TiO2 PNSs could also be suitable for quantitative analyses of small molecules.