From Titania to Titanates: Phase and Morphological Transition

Regarding their extraordinary properties, such as biological and chemical sta- bility, photocatalytic activity, cost-effectiveness, the titanium-based nanoma- terials are the subject of an intense research. Although titania is well known as a photocatalyst, the titanates are promising candidates for the wide range of applications including ion exchange, high adsorption capacity toward or- ganic molecules and radioactive toxic metal ions[2], in photovoltaics, H- and Li-storage, gas sensors, etc. The hydrothermal process became a very import- ant way to obtain these materials in nanostructural form since the discovery of anatase-based alkaline hydrothermal treatment reported by Kasuga et al. [1]. In this work, nine products were obtained by modifying the experimental conditions (6, 12 and 18 h at 110, 135 and 160 °C) of hydrothermal treatment of starting nano- anatase in less alkaline medium (5 mol dm–3 NaOH solution) than usual. Specimens are labeled as TT–t, where T is temperature of the treatment and t is duration of the treatment. The step-by-step optimization of this simple and costless procedure was necessary in order to obtain a pure titanate phase and to finally distinguish the ti- tanates from titania in terms of structure and microstructure. The nanocrystalline samples were characterized by HRTEM/SAED, XRPD, EDS, TG, UV-VIS and BET techniques.According to XRPD and HRTEM, the complete conversion of anatase to pure titanate phase was achieved after energetically the most intensive treatment, i.e. 18 h at 160 °C. Among other products, a certain amount of anatase remained, with its decreasing content as the temperature and time of hydrothermal treatment increases. This increment significantly improves the solubility of TiO2 promoting the changes in morphology from the approximately spherical anatase nanoparticles into elongated titanate nanosheets (Fig. 1). Based on EDS and TG, the Na0.4H1.6Ti2O5·H2O formula could be assigned to T160_18. The HRTEM/SAED revealed the shortening of interplanar distances along aaxis because of the dehydratation due to the high vacuum of the TEM chamber and high energy of the electron beam irradiation confirming the layered structure of Na0.4H1.6Ti2O5·H2O (Fig. 2). Because of the poor characterization of titanate nanosheets found in literature, the optical and textural properties of products were also investigated. A blue shift toward lower wavelength is observed with the temperature increasing being the most pronounced for the T160_18 (Fig. 3). This is the consequence of full transformation of TiO2 into Na0.4H1.6Ti2O5·H2O. For the same reason, the values of specific surface areas decreased with the temperature increasing. As shown in this work, the structure, morphology and texture of samples strongly depend of the conditions of hydrothermal treatment. The production of single phase titanate and its detailed microscopic characterization finally allowed the clarification of long-standing confusion between titania and titanates. References: [1] T Kasuga et al, Langmuir 14 (1998), p. 3160. [2] Y Zhang et al, RSC Advances 5 (2015), p. 79479. [3] The authors acknowledge funding from the Ministry of Education, Science and Technological Development of the Republic of Serbia, Grant Numbers III45007 and III45019. The support of the bilateral cooperation with Slovenia is also gratefully acknowledged (Project No. 451-03-3095/2014-09/32)

Electrospun Nickel Manganite (NiMn2O4) Nanocrystalline Fibers for Humidity and Temperature Sensing

Nickel manganite nanocrystalline fibers were obtained by electrospinning and subsequent calcination at 400 degrees C. As-spun fibers were characterized by TG/DTA, Scanning Electron Microscopy and FT-IR spectroscopy analysis. X-ray diffraction and FT-IR spectroscopy analysis confirmed the formation of nickel manganite with a cubic spinel structure, while N-2 physisorption at 77 K enabled determination of the BET specific surface area as 25.3 m(2)/g and (BJH) mesopore volume as 21.5 m(2)/g. The material constant (B) of the nanocrystalline nickel manganite fibers applied by drop-casting on test interdigitated electrodes on alumina substrate, dried at room temperature, was determined as 4379 K in the 20-50 degrees C temperature range and a temperature sensitivity of -4.95%/K at room temperature (25 degrees C). The change of impedance with relative humidity was monitored at 25 and 50 degrees C for a relative humidity (RH) change of 40 to 90% in the 42 Hz pi 1 MHz frequency range. At 100 Hz and 25 degrees C, the sensitivity of 327.36 +/- 80.12 k omega/%RH was determined, showing that nickel manganite obtained by electrospinning has potential as a multifunctional material for combined humidity and temperature sensing

Alginate-derived activated carbon hybridized with NiMn2O4 for use in supercapacitors

Transition metal oxides (TMOs) are promising materials because of their specific properties enabling their application in energy solutions, such as their pseudocapacitive behavior enabling utilization as electrode materials in supercapacitors. Activated carbon is a material well known as an electric double layer capacitor (EDLC). Bringing together the two different capacitor materials- TMOs as pseudocapacitors and carbon materials as EDL capacitors is the goal for generating future generation supercapacitors. Nickel manganite is a material of interest because of various oxidation states of manganese which provide its reactivity in oxidoreduction reactions, enhancing the pseudocapacitive behavior. Herein, we synthesized nano-sized nickel manganite by a sol-gel combustion synthesis process using glycine as fuel and subsequent calcination process. The structure and morphology of synthesized material was investigated via XRD, FESEM, and FTIR spectroscopy. Specific surface area and was determined from measured nitrogen desorption/desorption isotherms. Activated carbon was obtained by pyrolytic carbonization of alginate hydrogel in nitrogen atmosphere and activation with KOH. The material was combined with synthesized NiMn2O4 nanopowder and tested as supercapacitor electrode. The second alternative was incorporating NiMn2O4 powder into alginate hydrogel, followed by pyrolysis in nitrogen atmosphere to obtain a NiMn2O4 -activated carbon composite. The obtained materials were electrochemically characterized with cyclic voltammetry (LV) and galvanostatic chronopotentiometry to get galvanostatic charge-discharge curves. We calculated high specific capacitance values ranging to several hundred F/g, showing our hybrid material is a promising electrode in a supercapacitor system

Microwave-hydrothermal synthesis of TiO2 and zirconium doped TiO2 adsorbents for removal of As(III) and As(V)

Microwave-hydrothermal method was used for the synthesis of TiO2 and TiO2 doped with zirconium. The method was fast and simple and adsorbents were used for removal of As(III) and As(V) from aqueous solutions. The adsorbents were characterized by BET surface area measurements and powder XRD. Experiments showed that TiO2 doped with 10% of Zr using the microwave-hydrothermal method have greater specific surface area and total pore volume in comparison with TiO2 synthesized using the same method. Better removal with doped adsorbent was obtained for both, As(III) and As(V). Further experiments were carried out with Zr doped TiO2 sorbent in order to examine kinetic of adsorption, influence of pH and effect of common anions present in natural waters. (C) 2014 King Saud University. Production and hosting by Elsevier B.V. All rights reserved

Fenton-like oxidation of an azo dye using mesoporous Fe/TiO2 catalysts prepared by a microwave-assisted hydrothermal process

Fe-doped TiO2 photocatalysts with different contents of Fe (0.5, 1.6, 3.4 and 6.4 %) were synthesized by a microwave-hydrothermal method and characterized by X-ray diffraction analysis, N-2 physisorption at 77 K and UV-Vis spectrometry. The characterization showed that the Fe ions were highly dispersed in the TiO2 lattice. It was found that all the synthesized catalysts had a mesoporous structure and that Fe-doping increased the BET surface area. The UV-Vis study showed that the absorption spectra were shifted to longer wavelengths (red shift) with increasing dopant concentration. The photocatalytic activity of the samples was evaluated by the decolorization of the textile dye Reactive Blue 52 (RB) in aqueous solutions under sun-like radiation in the presence of H2O2 (a heterogeneous photo-Fenton process). The photocatalyst with 3.4 % Fe was found to be the most efficient in the presence of H2O2. The effect of the initial pH of the dye solution was assessed and dissolution of iron ions was studied as a function of pH value. It was concluded that decolorization was more favorable in acidic pH, and that at pH values gt 4, the release of Fe ions into the solution was negligible. Photocatalytic degradation of 4-chlorophenol (4-CP) was investigated under the optimal conditions and it was shown that the catalyst was capable of degrading colorless pollutants

Fe Doped TiO2 Prepared by Microwave-Assisted Hydrothermal Process for Removal of As(III) and As(V) from Water

Elevated concentrations of arsenic in groundwater, which is used as a source for drinking water, is a worldwide problem. Use of TiO2 and iron doped TiO2 synthesized by a microwave-assisted hydrothermal method for As(III) and As(V) removal were examined. Synthesized sorbents were characterized with XRD and nitrogen physisorption. Synthesized sorbents have predominantly anatase structure, and no peaks for iron could be observed. Doping of iron increases the surface area of synthesized sorbents. Sorption experiments show that increase of iron in sorbents increases the sorption capacity for As(III) and As(V). Increase of pH from 3 to 11 has no influence on As(III) sorption but decreases the sorption of As(V). Batch isotherm studies were performed to determine the binding capacities of As(III) and As(V). As(III) followed the Freundlich isotherm model, while for As(V) a better fit was with the Langmuir isotherm. The results of competition of SO42- and PO43- anions on adsorption of As(III) indicated that both anions reduced substantially the efficiency of adsorption on both adsorbents while for As(V) only the presence of PO43- anion interfered with adsorption. Testing 10Fe/TiO2 sorbent with arsenic contaminated natural water showed that this material could be used for removal of arsenic to the level recommended by WHO without pretreatment

Preparation, characterization and photocatalytic activity of lanthanum and vanadium co-doped mesoporous TiO2 for azo-dye degradation

Titanium dioxide photocatalysts co-doped with lanthanum and vanadium were prepared by a facile microwave-assisted hydrothermal method and characterized by XRD, SEM, N-2 physisorption at 77 K and DRS. The characterization showed that co-doped TiO2 samples have a high degree of crystallinity and existence of fully anatase phase. It was found that all the synthesized catalysts have the mesoporous structure. The co-doped TiO2 samples have larger BET surface areas and the mesopores volume than pure TiO2 and La doped samples. The vanadium co-doping contributes to the extension of absorption into the visible region. The photocatalytic activity of the samples was evaluated by the decolorization of textile dye Reactive Blue 52 in aqueous solutions under sun-like radiation. Compared with La singly doped TiO2, the co-doped catalysts showed an important improvement of photoactivity. The photocatalyst with 2% (w/w) La and 0.02% (w/w) V appeared to be the most photoactive. Optimal catalyst loading and the kinetics of degradation were also studied. Demonstrating higher photodegradation efficiency for RB than commercially available TiO2 Evonik P25, easy separation from suspension by spontaneous sedimentation and reusability of the catalyst, make this photocatalyst suitable for wastewater treatment.Peer-reviewed manuscript: [http://cherry.chem.bg.ac.rs/handle/123456789/3514

Synthesis and antibacterial activity of iron manganite (FeMnO 3 ) particles against the environmental bacterium Bacillus subtilis †

Nanocrystalline iron manganite powder was synthesized using the sol-gel combustion process, with glycine as fuel. It was further calcined at 900 C for 8 h, resulting in the formation of a loose cubic FeMnO 3 powder with a small specific surface area, net-like structure and plate-like particles as confirmed by XRD, N 2 physisorption, FESEM and TEM analyses. The metal ion release was studied by ICP-OES and showed that less than 10 ppb of Fe or Mn ions were released by leaching in water, but 0.36 ppm Fe and 3.69 ppm Mn was found in LB (Luria-Bertani) bacterial medium. The generation of reactive oxygen species (ROS) was monitored in distilled water and bacterial medium and showed that FeMnO 3 particles do not generate O 2 c À ions with or without UV irradiation, but synthesize H 2 O 2 and show an antioxidative effect. Besides the higher stability of FeMnO 3 particles in aqueous solution they showed an inhibitory effect on Bacillus subtilis growth in LB medium even at low concentrations (0.01 mg ml À1), but not in BHI medium even at 1 mg ml À1. This study points out that the mechanism of antibacterial action of engineered metal oxides needs continued investigation and specific experimental controls

Fe Doped TiO₂ Prepared by Microwave-Assisted Hydrothermal Process for Removal of As(III) and As(V) from Water

Elevated concentrations of arsenic in groundwater, which is used as a source for drinking water, is a worldwide problem. Use of TiO₂ and iron doped TiO₂ synthesized by a microwave-assisted hydrothermal method for As­(III) and As­(V) removal were examined. Synthesized sorbents were characterized with XRD and nitrogen physisorption. Synthesized sorbents have predominantly anatase structure, and no peaks for iron could be observed. Doping of iron increases the surface area of synthesized sorbents. Sorption experiments show that increase of iron in sorbents increases the sorption capacity for As­(III) and As­(V). Increase of pH from 3 to 11 has no influence on As­(III) sorption but decreases the sorption of As­(V). Batch isotherm studies were performed to determine the binding capacities of As­(III) and As­(V). As­(III) followed the Freundlich isotherm model, while for As­(V) a better fit was with the Langmuir isotherm. The results of competition of SO₄^2– and PO₄^3– anions on adsorption of As­(III) indicated that both anions reduced substantially the efficiency of adsorption on both adsorbents while for As­(V) only the presence of PO₄^3– anion interfered with adsorption. Testing 10Fe/TiO₂ sorbent with arsenic contaminated natural water showed that this material could be used for removal of arsenic to the level recommended by WHO without pretreatment

Transesterification of used cooking sunflower oil catalyzed by hazelnut shell ash

Hazelnut shell ash was investigated as a new base catalyst for the transesterification of used cooking sunflower oil to biodiesel. To understand its catalytic properties, the prepared ash was characterized by EDX, XRD, TGA/DTA, Hg porosimetry, N-2 physisorption, FE-SEM, and basic strength measurements. The effects of the catalyst loading in the range of 1-5% of the oil weight and the methanol-to-oil molar ratio of 6:1-18:1 on the kinetics of the fatty acid methyl esters synthesis were established. Moreover, the leaching and reusability of the catalyst were assessed. The obtained results revealed that hazelnut shell ash was mostly composed of K, Ca, and Mg. The highest ester content (98%) was achieved at the catalyst loading of 5%, the methanol-to-oil molar ratio of 12:1, and the reaction time of 10 min. The contribution of homogeneous catalysis because of the catalyst leaching was confirmed but did not determine the overall reaction rate. The catalyst can be reused after the recalcination at 800 degrees C for 2 h achieving the high methyl esters content (>96%) in 30 min after three subsequent runs. The overall reaction followed the pseudo-first-order kinetics with respect to triacylglycerols. A linear relationship between the apparent reaction rate constant and the catalyst loading and the methanol-to-oil molar ratio was determined. The determined value of the reaction rate constant was 0.0576 dm(6)/(min.mol(2))