ABSTRACT
To evaluate the potential role of in situ formed Sr-Ti-O species as a ferroelectric component able to enhance the photocatalytic properties of an adjacent TiO2 semiconductor, Cu-doped/graphene oxide (GO)/TiO2 nanotubes (TiNTs) composites (with 0.5 wt % Cu and 1.0 wt % GO) have been synthesized while progressive amounts of strontium (up to 1.0 wt %) were incorporated at the surface of the composite through incipient wetness impregnation followed by post-thermal treatment at 400 °C. The different resulting photocatalytic systems were then first deeply characterized by means of N2 adsorption-desorption measurements, X-ray diffraction (XRD), UV-vis diffuse reflectance (UV-vis DR), Raman and photoluminescence (PL) spectroscopies, and scanning electron microscopy (SEM) (with energy-dispersive X-ray (EDX) spectroscopy and Z-mapping). In a second step, optimization of the kinetic response of the Sr-containing composites was performed for the formic acid photodegradation under UV irradiation. The Sr-containing Cu/GO/TiNT composites were then fully characterized by electrochemical impedance spectroscopy (EIS) for their dielectric properties showing clearly the implication of polarization induced by the Sr addition onto the stabilization of photogenerated charges. Finally, a perfect correlation between the photocatalytic kinetic evaluation and dielectric properties undoubtedly emphasizes the role of ferroelectric polarization as a very valuable approach to enhance the photocatalytic properties in an adjacent semiconductor.
ABSTRACT
The ground (S0) and excited triplet (T1) electronic states and corresponding optical spectra of a series of cationic complexes [RuH(CO)L(PPh3)2]+ (L=2,2´-bipyridyl) (Rubpy), 4,4´-dicarboxylic-2,2´-bipyridyl (Rudcbpy), bis-4,4'-(N-methylamide)-2,2´-bipyridyl (Rudamidebpy), bis-4,4'-(methyl)-2,2´-bipyridyl (RudMebpy), [Ru(CO)2dcbpy(PPh3)2]2+ (Ru(2CO)dcbpy), and [Ru(H)2dcbpy(PPh3)2] (Ru(2H)dcbpy) have been studied by combined Density Functional/Time-Dependent Density Functional (DFT/TDDFT) techniques using different combinations of DFT exchange-correlation functionals and basis sets. PBE0/LANL2DZ provided more accurate geometries to describe S0 whereas B3LYP/LANL2DZ predicted spectral energies that correlated better with the available experiment data. The Ru (II) complexes with different substituents emit photons ranging from 560-610 nm in the series RudMebpy, Rubpy, Rudamidebpy, Rudcbpy. The calculations predicted a maximum emission at about 540 nm for the complex constructed from two carbonyl π-acceptors ligands trans to the dcbpy, while an emission in the far infrared region is calculated when two H σ-donor ligands trans to the dcbpy. Our calculation results show correlations between HOMO-LUMO energy gap, Stokes shift, and T1 distortion, which reflect the different effects of electron-withdrawing and donating groups. We proposed that these correlations can be used to predict the photophysical properties for new complexes.
