No abstract

The synthetic procedures for preparation of free-standing and attached to polymer support surface-modified TiO2 nanoparticles (NPs) with absorption extended into the visible spectral region due to charge transfer complex formation were developed. The one-step synthesis of colloids consisting of surface-modified TiO2 NPs is based on the reaction between titanium­(IV) isopropoxide (TTIP) and lauryl galatte in nonprotic organic solvents (tetrahydrofuran, xylol, chloroform). The poly­(GMA-co-EGDMA) copolymer decorated with surface-modified TiO2 NPs was obtained in two steps. First, copolymer was functionalized with dopamine and then treated with TTIP in organic solvent at slightly elevated temperature. Thorough microstructural and optical characterization of free-standing and attached to polymer support surface-modified TiO2 NPs was performed involving transmission electron microscopy as well as absorption and reflection spectroscopy. Infrared spectroscopy was used to understand coordination of ligands to surface Ti atoms. Photoredox chemistry of surface-modified TiO2 NPs attached to the polymer support was tested. Enhanced photooxidative ability of composite was demonstrated by degradation of organic dye crystal violet under visible light illumination, i.e., using photons with energy smaller than 2.75 eV. On the other hand, photocatalytic hydrogen production was used to demonstrate photoreduction ability of surface-modified TiO2 NPs attached to the polymer support.

The mechanical properties of nanocomposites obtained by incorporation of fairly uniform hematite nanorods (α-Fe 2 O 3 NRs) into epoxy resin were studied as a function of the content of the inorganic phase. A thorough microstructural characterization of the α-Fe 2 O 3 NRs and the nanocomposites was performed using transmission electron microscopy (TEM) and atomic force microscopy (AFM). The TEM measurements revealed rod-like morphology of the nanofiller with a uniform size distribution (8.5 nm×170 nm, dia-meter×length). High-magnification TEM and AFM measurements indicated agglomeration of α-Fe 2 O 3 NRs embedded in the epoxy resin. Stress at break, strain at break, elastic modulus and tensile toughness of the nanocomposites were compared with the data obtained for pure epoxy resin. Significant influence of nanofiller on the mechanical properties of epoxy resin, as well as on the glass transition temperature, could be noticed for samples with low contents of the inorganic phase (up to 1 wt. %).

Surface modification of titanium dioxide nanoparticles (TiO 2 NPs) with the biologically active molecule pyridoxine hydrochloride (vitamin B 6) was found to alter the optical properties. Microstructural characterization involving transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis revealed that the anatase TiO 2 NPs had a narrow size distribution with an average diameter of 45 Å. The absorption onset of the surface-modified TiO 2 samples was red-shifted by about 0.4 eV compared to the unmodified particles. The mode of binding between vitamin B 6 and the surface Ti atoms was investigated by Fourier transform infrared spectroscopy (FTIR). From the Benesi-Hildebrand plot, the stability constant of the surface complex was found to be of the order 10 2 M-1. The experimental findings were supported by detailed quantum chemical calculations based on the density functional theory (DFT). Agreement was found between the experimentally measured absorption spectra of the TiO 2 NPs surface-modified with vitamin B 6 and the theoretically calculated electronic excitation spectra of the corresponding model system.

The surface of anatase TiO 2 nanoparticles was modified with in situ synthesized imine, based on 3,4-dihydroxybenzaldehyde and octadecylamine. The modified TiO 2 nanoparticles were investigated using FTIR and UV-Vis spectroscopy, which confirmed the formation of the charge transfer complex between imine and surface of TiO 2 nanoparticles by the reaction of surface Ti atoms with hydroxyl groups of a modifying agent. TiO 2 nanoparticles modified with imine were further applied as a filler for the preparation of epoxy based nanocomposites. Thermal and mechanical properties of the prepared nanocomposites were examined using the dynamic mechanical analysis, differential scanning calorimetry, thermogravimetric analysis and hardness measurements. The obtained results have shown that modified TiO 2 nanoparticles have no significant influence on the glass transition temperature and that they slow down thermo-oxidative degradation of epoxy resin in the first stage and increase hardness of the crosslinked epoxy resin.