Herein, we report the effect of the laser illumination during the diffuse-reflectance laser-flash-photolysis measurements on the morphological and optical properties of TiO2 powders. A grey-blue coloration of the TiO2 nanoparticles has been observed after intense laser illumination. This is explained by the formation of nonreactive trapped electrons accompanied by the release of oxygen atoms from the TiO2 matrix as detected by means of UV-vis and EPR spectroscopy. Moreover, in the case of the pure anatase sample a phase transition of some TiO2 nanoparticles located in the inner region from anatase to rutile occurred. It is suggested that these structural changes in TiO2 are caused by an energy and charge transfer to the TiO2 lattice. ; BMBF/13N13350 ; Government of the Russian Federation ; Global Research Laboratory (GRL)/NRF-2014K1A1A2041044
The adsorption of water and deuterium oxide on TiO2 surfaces was investigated in the dark as well as under UV(A) irradiation using in situ ATR-FTIR spectroscopy under oxygen and oxygen free conditions. Adsorption of H2O–D2O mixtures revealed an isotopic exchange reaction occurring onto the surface of TiO2 in the dark. Under UV(A) irradiation, the amount of both OH and OD groups was found to be increased by the presence of molecular oxygen. Furthermore, the photocatalytic formation of hydroperoxide under oxygenated condition has been recorded utilizing Attenuated Total Reflection Fourier Transformed Infrared (ATR-FTIR) spectroscopy which appeared as new band at 3483 cm−1. Different possible mechanisms are discussed in terms of the source of hydroxyl groups formed and/or hydration water on the TiO2 surface for the photocatalytic reaction and photoinduced hydrophilicity. ; Mega-grant of the Government of the Russian Federation/Establishment of the Laboratory 'Photoactive Nanocomposite Materials'/No. 14.Z50.31.0016
The degradation of organic pollutants in the aqueous medium using semiconductor photocatalysts has become an attractive method for detoxification of water. ZnO is an efficient photocatalyst with few disadvantages such as: (i) the wide band gap (3.37 eV); and (ii) the fast recombination rate of photogenerated electron–hole pairs which limit the photodegradation efficiency of bare ZnO photocatalyst. Herein, we report a strategy for the suppression of electron–hole pair recombination rate, extention the absorption edge in the visible region and enhancement of photocatalytic efficiency by introducing rare earth metal as a dopant. We present the fabrication of pure and Er/Nd doped ZnO semiconductor photocatalysts with hexagonal wurtzite structure using sol gel method. The prepared photocatalysts were characterized by standard analytical techniques, such as XRD, SEM-EDS, TEM, FTIR, XPS, BET, TGA, DTA, DSC, PL, DRS and UV-vis spectroscopy. The photocatalytic activity of pure and doped ZnO nanoparticles (NPs) was investigated by studying the degradation of two different organic dyes as a function of irradiation time. The results indicate that the photocatalytic activity of doped ZnO was found to be higher than bare ZnO for degradation of dyes. This may be attributed predominantly due to decrease in the recombination rate by the efficient charge separation of photoinduced electron–hole pair as inferred from PL studies. The results also indicate that parameters such as amount of photocatalyst dose, initial pH and different quenchers play a significant role for degradation of model dyes. The synthesized photocatalyst was recycled four times for degradation of dye with very little decrease in efficiency. Interestingly, comparative in vitro antibacterial and anticancer potential of the pure and Er/Nd doped ZnO NPs were also investigated against human pathogenic bacterial strains and various human cancer cell lines. The result of our study clearly revealed that Nd doped ZnO NPs showed better antibacterial as well as anticancer efficacy as compared to pure and Er doped ZnO NPs. ; Ministry of Mines, Government of India ; Alexander von Humboldt foundation
A series of carbazole based sensitizers with either phenyl based donors (TBC, TMC, OMC, PC, TBR, TMR, OMR and PR) or aryl amine based donors (OMNC, CNC and HNC) as well as one without a donor group (CC) have been synthesized to understand the influence of the strength of the donor moiety on the optical, electrochemical and photovoltaic properties. Two different acceptor moieties such as cyano acrylic acid and rhodanine acetic acid were introduced and evaluated. Different substituents on the phenyl group have a significant impact on the light harvesting ability of the sensitizers. Among phenyl based donors, anisole based carbazole (OMC) shows the highest short circuit current (JSC) of 4.96 mA cm−2 with overall power conversion efficiency (PCE) of 2.69%. In the case of the sensitizers with aryl amine based donors, the increasing bulkiness of the donor group lead to increasing open circuit potential. Transient photocurrent and photovoltage measurements signify the importance of a bulky donor fragment in determining the open circuit potential of the dyes. Sensitizers with hexyloxy substituted phenyl amine as the donor group shows a JSC of 6.84 mA cm−2 with PCE of 3.33%. The overall investigation provides vital information about the influence of donor groups on the optoelectronic properties of the sensitizers for its photovoltaic applications. ; EU/FP7/2007-2013/604032 ; Government of the Russian Federation
