Tomoki Tsumura

Carbon coating of anatase-type TiO2 and photoactivity

Carbon coating of photocatalytic anatase-type TiO2 powders was successfully carried out by heating a powder mixture of poly(vinyl alcohol) and TiO2 under N2 gas flow at temperatures above 700 °C. All particles of TiO2 were covered by a carbon layer and looked black. For methylene blue (MB) in aqueous solution, carbon-coated anatase powders thus prepared showed marked adsorption and decomposition under UV irradiation and were confirmed to keep almost the same photoactivity as that without any carbon coating. Carbon coating of anatase-type TiO2 was found to give different merits for photoactive performance; suppression of phase transformation from anatase to rutile at high temperatures, quick adsorption of MB into the carbon layer, decomposition of adsorbed MB by TiO2 and prevention of the interaction of TiO2 with binder resin. Repeated cycles of adsorption and decomposition of methylene blue in aqueous solution were experimentally confirmed.

Structure and photoactivity of titania derived from nanotubes and nanofibers

Photoactivity under UV irradiation for the decomposition of methylene blue in water and for the oxidation of NO gas was studied on titania powders derived from titanate nanotube (TNT) and nanofiber (TNF) by annealing at high temperatures, comparing with granular titania (ST-01). Rate constant for methylene blue decomposition k(MB) increased with increasing annealing temperature above 300 degrees C after the conversion from titanate to tinania. It tended to decrease above 700 degrees C, mainly due to the phase transformation from anatase to rutile. The dependences of k(MB) on full width at half maximum intensity (FWHM) were common for three samples, a sharp maximum at around 0.4 degrees in FWHM, but TNF-derived sample gave much higher maximum than ST-01. Change in fraction of oxidized NO with annealing temperature showed a plateau at around 50% and then decreased abruptly by high temperature annealing. Starting from TNT and TNF has an advantage to form fine particles by annealing above 300 degrees C, giving high photoactivity due to high crystallinity and high adsorptivity particularly for methylene blue.

Synthesis of LiMn2O4 spinel via tartrates

A fine powder of LiMn2O4 spinel was prepared by thermal decomposition of a finely mixed powder of lithium and manganese tartrates above 250 °C. By using ethylene glycol as the dispersion medium, a thin layer consisting of fine particles of an LiMn2O4 spinel was prepared on a platinum substrate.

Carbon modified TiO2 photocatalysts for water purification

Carbon modified TiO2 photocatalysts for water purification Carbon can form different structures with TiO2: carbon-doped TiO2, carbon coated TiO2 and composites of TiO2 and carbon. The presence of carbon layer on the surface of TiO2 as well as the presence of porous carbon in the composites with TiO2 can increase the concentration of organic pollutants on the surface of TiO2, facilitating the contact of the reactive species with the organic molecules. Carbon-doped TiO2 can extend the absorption of the light to the visible region by the narrowing of the band gap and makes the photocatalysts active under visible light irradiation. TiO2 loaded carbon can also work as a photocatalyst, on which the molecules are adsorbed in the pores of carbon and then they undergo the photocatalytic decomposition with UV irradiation. Enhanced photocatalytic activity for the destruction of some organic compounds in water was noticed on the carbon coated TiO2 and TiO2 loaded activated carbon, mostly because of the adsorptive role of carbon. However, in carbon-doped TiO2, the role of carbon is somewhat different, the replacement of carbon atom with Ti or oxygen and formation of oxygen vacancies are responsible for extending its photocatalytic activity towards the visible range.

Formation and Annealing of BaTiO3 and SrTiO3 Nanoparticles in KOH Solution

Barium titanate (BaTiO 3 ) and strontium titanate (SrTiO 3 ) nanoparticles were synthesized separately through hydrothermal reaction of crystalline TiO 2 particles and corresponding alkaline earth hydroxides, Ba(OH) 2 and Sr(OH) 2 respectively, in 50 mol·dm −3 KOH solution at 150°C. Each structural evolution of BaTiO 3 and SrTiO 3 during the hydrothermal treatment was investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), field emission transmission electron microscopy (FE-TEM) and thermogravimetry-differential analysis (TG-DTA). In the BaTiO 3 system, round particles with cubic perovskite-type structure were obtained within 1 h. However, these particles were gradually dissolved and then were re-precipitated in the form of cube-shape BaTiO 3 particles with a smaller lattice constant a c than that of the former phase. After the BaTiO 3 particles formed firstly have disappeared completely, or the two phases coexistence stage with different lattice constant a c passed, lattice constant a c of BaTiO 3 phase re-precipitated continuously decreased with annealing time. In contrast, once SrTiO 3 particles are formed, the lattice constant a c decreased continuously throughout the reaction. The result indicates that SrTiO 3 particles were annealed without dissolution and precipitation process under the present condition.

Control of crystalline structure of porous carbons

Control of the crystalline structure in porous carbons by high temperature treatment and catalytic carbonization is reviewed, after a brief review of the control of pore structure. The development of crystallinity and the preservation of the porous structure in porous carbons by high temperature treatment depend predominantly on carbon precursors. The published experimental results are summarized, which suggest the necessity of more detailed and systematic investigations.

Evaluation of layered graphene prepared via hydroxylation of potassium-graphite intercalation compounds

Layered graphene was prepared via the hydroxylation of potassium-graphite intercalation compound (KC8) produced from exfoliated graphite flake powder. When a small amount of water was dropped onto the KC8 in an oxygen-free atmosphere, the stage structure of the intercalation compounds was broken, and agglomerated graphene was obtained. Sonication of this agglomerated graphene in buffered water containing sodium dodecyl sulfate followed by rinsing with hot water yielded gray samples. Using scanning electron microscopy, X-ray diffraction analysis, and Raman spectroscopy, the gray samples were determined to be composed of a few layers of graphene with an area of 20-100 µm2 and thickness of 1.7 nm. They were thinner than those obtained when starting with natural graphite.

Degradation of Ibuprofen Sodium Salt in a Hybrid Photolysis – Membrane Distillation System Utilizing Germicidal UVC Lamp

Abstract The present paper describes photodegradation of non-steroidal anti-inflammatory drug ibuprofen sodium salt (C13H17O2Na) in a new hybrid system coupling photolysis and direct contact membrane distillation (DCMD). Photodegradation was conducted using UV254 germicidal lamp. The initial concentration of C13H17O2Na was c0= 0.05, 0.1, 0.2 or 0.4 mmol/dm3. After 5 h of the process the mass of C13H17O2Na in the feed decreased for 99.8-96.7% for c0 of 0.05-0.4 mmol/dm3, respectively. The amount of total organic carbon (TOC) in the feed was lowered by ca. 75%, regardless of initial C13H17O2Na concentration. Among the volatile compounds which passed through the membrane low amounts of C13H18O2 (0.04-0.16 μmol) and some other organic compounds measured as TOC (1.2-3.7 mg) were present. The conductivity of distillate did not exceed the value of 2.6 μS/cm and pH was about 5.7. The total effectiveness of organics removal was 99.97-99.99% for C13H18O2 and 94.8- 98.0% for TOC, dependent on initial concentration of ibuprofen sodium salt.

Carbon-Coated TiO2 - Hybridization between Photoactivity and Adsorptivity

Carbon-coated TiO2 photocatalysts were prepared by a simple heat treatment of the powder mixtures of anatase-type TiO2 with PVA at a temperature of 700 and 900 oC in a N2 atomosphere. Diffuse optical reflectance spectra for carbon-coated TiO2 showed the absorption edge for anatase structure clearly, overlapping with absorption due to coated carbon over whole range of wavelegth. These carbon-coated TiO2 photocatalysts had relatively high apparent BET surface area, from 50 to 170 m2/g, which suggested the formation of porous carbon layers, and showed relatively high adsorption of various pollutants, methylene blue (MB), reactive black (RB-5), phenol (Ph) and iminoctadine triacetate (IT), in water. Photocatalytic activity of carbon-coated TiO2 thus prepared was evaluated through the determination of the rate constant for the decomposition of different pollutants in water. Rate constant values were strongly depend on the pollutants, but their dependence on the crystallinity of TiO2 phase. The relations between adsorptivity and rate constant for four pollutants looked similar with each other, and the pollutants adsorbed in the larger amount was decomposed with the higher rate. Adsorptivity of carbon-coated TiO2 photocatlysts was determined and discussed on the relations to BET surface area, amount of carbon coated and also rate constant k for the decomposition of MB, RB5, Ph and IT. Adsorptivity of carbon-coated catalysts depends strongly on the adsorbate (pollutant) but also on the surface nature of carbon layer on TiO2 particles. The relations between adsorptivity and rate constant k for four pollutants looked similar, suggesting that the pollutant adsorbed in the larger amount being decomposed with the higher rate.

Activity of TiO2 Photocatalyst Modified with H2WO4 for Degradation of Organic Compounds in Water

Abstract TiO2 of anatase structure was modified with H2WO4 by wet impregnation method in a vaccuum evaporator and in autoclave under established temperature and pressure. After impregnation the samples were dried and submitted to calcination at 400 and 600 °C. The characteristics of obtained photocatalysts was investigated by XRD, UVVis/ DR, BET surface area, zeta potential, photoluminescence and OH radicals measurements. These photocatalysts were tested for photocatalytic decomposition of Acid Red, Methylene Blue, phenol and humic acids in water. The results showed that the presence of tungsten oxides compounds on the surface of TiO2 is beneficial because improves separation of free carriers what results in increasing the OH radicals formation on the photocatalyst surface. Calcination of the photocatalysts causes growing of the anatase crystals and results in reduction of their BET surface area. This is beneficial for OH radicals formation on the surface of anatase crystals, however adsorption abilities of such prepared photocatalysts are lower. In that case some organic compounds like phenol, which undergoes decomposition mainly by OH radicals attack, can be efficiently decomposed with using these photocatalysts. In case of uncalcined samples, they have high BET surface area and they can quantatively adsorb some organic compounds such as Acid Red and humic acids. By combination of adsorption with photocatalytic activity of uncalcined samples fast decomposition of organic compounds was achieved due to their fast oxidation by the formed reactive species under both, UV and artificial solar light irradiations, however this activity was much more higher under UV light.