Molecular interaction of natural dye based on Zea Mays and Bixa Orellana to nanocrystalline TiO2 into dye sensitized solar cells.

This work studies the interaction between natural dyes obtained from Peruvian Zea mays and Bixa orellana seeds and nanostructured titanium dioxide in order to evaluate their function as sensitizers into solar cell devices. The effective attachment of dyes to the TiO2 layer is corroborated by the comparison of UV-Visible absorption and FT-IR spectra of the extracted dye solutions and sensitized TiO2 electrodes. The principal compounds from the seed extraction of Zea mays and Bixa orellana are cyanidin-3-glucoside (C3G) and bixin, respectively, which were analyzed in an isolated dye/cluster TiO2 system by molecular dynamic simulation. The results showed that the chemisorption is carried out through a consecutive deprotonation process and Ti-O bond formation by the monodentate OH and COOH anchoring groups, for C3G and bixin, respectively. Finally, we tested the effect of the dye – TiO2 interaction on the charge transfer by the comparison of the current-voltage (I-V) curves and incident photon-to-current conversion efficiency (IPCE) of the cells. We found that dye agglomeration in films with Bixa orellana and the high charge recombination of films with Zea mays are critical points to be solved. For this reason, we propose the pretreatment of the TiO2 film before sensitization with Bixa orellana and analyze the effects of pH in Zea Mays solution, in order to obtain better device efficiencies.

Extraction–Pyrolytic Method for TiO2 Polymorphs Production

The unique properties and numerous applications of nanocrystalline titanium dioxide (TiO2) are stimulating research on improving the existing and developing new titanium dioxide synthesis methods. In this work, we demonstrate for the first time the possibilities of the extraction–pyrolytic method (EPM) for the production of nanocrystalline TiO2 powders. A titanium-containing precursor (extract) was prepared by liquid–liquid extraction using valeric acid C4H9COOH without diluent as an extractant. Simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA–DSC), as well as the Fourier-transform infrared (FTIR) spectroscopy were used to determine the temperature conditions to fabricate TiO2 powders free of organic impurities. The produced materials were also characterized by X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). The results showed the possibility of the fabrication of storage-stable liquid titanium (IV)-containing precursor, which provided nanocrystalline TiO2 powders. It was established that the EPM permits the production of both monophase (anatase polymorph or rutile polymorph) and biphase (mixed anatase–rutile polymorphs), impurity-free nanocrystalline TiO2 powders. For comparison, TiO2 powders were also produced by the precipitation method. The results presented in this study could serve as a solid basis for further developing the EPM for the cheap and simple production of nanocrystalline TiO2-based materials in the form of doped nanocrystalline powders, thin films, and composite materials.

Nanocrystalline TiO2/Carbon/Sulfur Composite Cathodes for Lithium–Sulfur Battery

This paper evaluates the influence of the morphology, surface area, and surface modification of carbonaceous additives on the performance of the corresponding cathode in a lithium–sulfur battery. The structure of sulfur composite cathodes with mesoporous carbon, activated carbon, and electrochemical carbon is studied by X-ray diffraction, nitrogen adsorption measurements, and Raman spectroscopy. The sulfur cathode containing electrochemical carbon with the specific surface area of 1606.6 m2 g−1 exhibits the best electrochemical performance and provides a charge capacity of almost 650 mAh g−1 in cyclic voltammetry at a 0.1 mV s−1 scan rate and up to 1300 mAh g−1 in galvanostatic chronopotentiometry at a 0.1 C rate. This excellent electrochemical behavior is ascribed to the high dispersity of electrochemical carbon, enabling a perfect encapsulation of sulfur. The surface modification of carbonaceous additives by TiO2 has a positive effect on the electrochemical performance of sulfur composites with mesoporous and activated carbons, but it causes a loss of dispersity and a consequent decrease of the charge capacity of the sulfur composite with electrochemical carbon. The composite of sulfur with TiO2-modified activated carbon exhibited the charge capacity of 393 mAh g−1 in cyclic voltammetry and up to 493 mAh g−1 in galvanostatic chronopotentiometry. The presence of an additional Sigracell carbon felt interlayer further improves the electrochemical performance of cells with activated carbon, electrochemical carbon, and nanocrystalline TiO2-modified activated carbon. This positive effect is most pronounced in the case of activated carbon modified by nanocrystalline TiO2. However, it is not boosted by additional coverage by TiO2 or SnO2, which is probably due to the blocking of pores.

Study of Effect TiO2 Thin Film Morphological on Polyaniline/TiO2 Solar Cell Efficiency

In this work study preparation, structural, optical and electrical properties of polyaniline (PANi), nanocrystalline TiO2 and PANi: TiO2 nanocomposites. The TiO2 powder of particle size 50-60 nm was synthesized by sol-gel technique and the polyaniline was synthesized by chemical oxidative polymerization of aniline. The composite films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) and UV-Vis spectroscopy and the results were compared with polyaniline films. The intensity of diffraction peaks for PANi: TiO2 composites are lower than for TiO2. The characteristic FTIR peaks of PANi were found shift to higher wave number in PANi: TiO2 composite. These observed effects have been attributed to interaction of TiO2 particles with PANi molecular chains.

Facet-engineered TiO2 nanomaterials reveal the role of water-oxide interactions in surface protonic conduction

Water adsorption and surface protonic conduction have been investigated at 25 – 400 oC in wet (H2O and D2O) atmospheres on nanocrystalline TiO2 hydrothermally grown to a predominance of different...

The Influence of Calcination Temperature on Photocatalytic Activity of TiO2-Acetylacetone Charge Transfer Complex towards Degradation of NOx under Visible Light

The improvement of photocatalytic activity of TiO2-based nanomaterials is widely investigated due to the tentative of their industrialization as environmental photocatalysts and their inherently low solar spectrum sensitivity and rapid recombination of charge carriers. Coupling of oxygen-based bidentate diketone to nanocrystalline TiO2 represents a potential alternative for improving the holdbacks. Formation of TiO2-acetylacetone charge transfer complex (CTC) by sol-gel route results in a hybrid semiconductor material with photodegradation activity against toxic NOx gas. In this research, the influence of the chelating agent acetylacetone (ACAC) content on the CTC photocatalytic efficiency under visible light was evaluated. A high content of ACAC in the CTC is not a decisive factor for efficiency of photocatalytic reactions. In fact, the highest efficiency for NOx degradation (close to 100%, during 1 h of visible light exposure) was reported for the material calcined in air at 300 °C with the content of strongly bonded acetylacetone not higher than 3 wt.%. Higher calcination temperature (400 °C) left TiO2 almost completely depleted in ACAC, while at the highest applied temperature (550 °C) a portion of anatase was transformed into rutile and the sample is free of ACAC. The analyses pointed out that superoxide anion radical (O2−) plays an active role in photo-oxidation of NOx. Our findings indicate that this CTC has both high visible light spectral sensitivity and photocatalytic efficiency.