Walter A. Zeltner

The gas-phase photocatalytic mineralization of benzene on porous titania-based catalysts

Photocatalytic degradation of benzene in oxygen-containing gaseous feed streams was investigated using titania and platinized (0.1 wt.-%) titania photocatalysts. The titania catalyst was synthesized using sol-gel techniques. Results of this study indicate that, when using this particular photocatalyst, benzene was oxidized to carbon dioxide and water without forming any detectable organic reaction products in the reactor effluent, although only some of the benzene reacted. Both the overall conversion of benzene and its mineralization were improved by platinizing the titania. When the titania catalyst was platinized, both photocatalytic and thermocatalytic reactions were promoted. Rates of photocatalytic reactions were significantly enhanced at reaction temperatures between 70 and 90°C, while at temperatures above 90°C the rates of thermocatalytic oxidation reactions were noticeably increased. It proved possible to obtain the continuous and essentially complete mineralization of benzene by using the platinized titania catalyst and optimizing such parameters as the reaction temperature, space time, and the concentrations of oxygen and water vapor in the feed stream.

ZrO2- and Li2ZrO3-stabilized spinel and layered electrodes for lithium batteries

Strategies for countering the solubility of LiMn{sub 2}O{sub 4} (spinel) electrodes at 500 {sup o}C and for suppressing the reactivity of layered LiMO{sub 2} (M = Co, Ni, Mn, Li) electrodes at high potentials are discussed. Surface treatment of LiMn{sub 2}O{sub 4} with colloidal zirconia (ZrO{sub 2}) dramatically improves the cycling stability of the spinel electrode at 50 {sup o}C in Li/LiMn{sub 2}O{sub 4} cells. ZrO{sub 2}-coated LiMn{sub 0.5}Ni{sub 0.5}O{sub 2} electrodes provide a superior capacity and cycling stability to uncoated electrodes when charged to a high potential (4.6 V vs Li{sup 0}). The use of Li{sub 2}ZrO{sub 3}, which is structurally more compatible with spinel and layered electrodes than ZrO{sub 2} and which can act as a Li{sup +}-ion conductor, has been evaluated in composite 0.03Li{sub 2}ZrO{sub 3} - 0.97LiMn{sub 0.5}Ni{sub 0.5}O{sub 2} electrodes; glassy Li{sub x}ZrO{sub 2 + x/2} (0

Effects of reaction temperature and water vapor content on the heterogeneous photocatalytic oxidation of ethylene

The photocatalytic degradation of ethylene in airstreams has been studied over the temperature range 30–110 °C using a packed bed reactor containing sol-gel-derived TiO2 or platinized TiO2 particulates. Results of this study indicate that the reactivity of ethylene is greatly enhanced at increased temperatures and that the fraction of ethylene that reacts is stoichiometrically oxidized to CO2 under all operating conditions. The effect of raising the temperature has been ascribed to decreasing adsorption of water for both types of catalysts, as well as an increase in conventional heterogeneous catalytic reactions occurring on the Pt/TiO2 catalyst. In addition, platinizing the TiO2 photocatalyst and increasing the content of water vapor in the gaseous feed streams both decrease the rate of photocatalytic oxidation of ethylene. The activation energies for the photocatalytic and heterogenous catalytic oxidation of ethylene were determined to be 13.9–16.0 kJ mol−1 and 82.8 kJ mol−1 respectively.

Photocatalytic oxidation of acetone vapor on TiO2/ZrO2 thin films

Abstract The photocatalytic oxidation of acetone vapor on TiO2/ZrO2 thin films is presented in this study. Acetone conversion data collected using a non-circulating tubular reactor are analyzed using a general power law model and a Langmuir–Hinshelwood–Hougen–Watson (LHHW) model; the LHHW model provides a slightly better fit than the 1/2 order power law model. The effects of reaction temperature and relative humidity on the rate of reaction are presented. Using either kinetic model, increasing the reaction temperature from 30 to 77°C (in a dry feed stream) significantly increases the reaction rate constant at a 95% confidence level; however, increasing the temperature from 77 to 113°C does not have a significant effect. The addition of water vapor (50% relative humidity) to the feed stream at 77°C significantly increases the reaction rate constant at a 95% confidence level. Also, at three different temperatures and a single reaction condition, the conversion of acetone is enhanced in the presence of water vapor. No byproducts are detected in the effluent stream of the photocatalytically active reactor.

The Electrochemical Stability of Spinel Electrodes Coated with ZrO2 , Al2 O 3 , and SiO2 from Colloidal Suspensions

Stoichiometric LiMn 2 O 4 and substituted Li 1.05 M 0.05 Mn 1.9 O 4 (M = Al,Ni) spinel electrodes, coated with ZrO 2 , Al 2 O 3 , and SiO 2 from colloidal suspensions, have been evaluated in lithium cells. ZrO 2 -coated Li 1.05 Ni 0.05 Mn 1.9 O 4 electrodes provide the best cycling stability at 50°C. The excellent cycling stability is attributed to a porous network of amphoteric ZrO 2 particles, less than 4 nm in dimension, that protect the spinel surface from acid attack by scavenging HF and H 2 O from the electrolyte, while still allowing access of the electrolyte to the active electrode.

Applications in photocatalytic purification of air

Publisher Summary Semiconductor-mediated photocatalytic oxidation has received wide interest as a promising technique for remediating environmental pollution. The semiconductor mediated gas-solid heterogeneous photocatalytic oxidation technique provides a promising approach for the purification of air and, in conjunction with air stripping, purification of soils and water that are contaminated with volatile organic compounds (VOCs). Compared to liquid–solid photocatalytic reactions, the gas-phase photocatalytic degradation of organic compounds has much higher reaction rates and photoefficiencies. Most efforts to apply the photocatalytic oxidation process for the destruction of environmental contaminants have focused on purification of water. The effect of water vapor on the rates of oxidation in these systems appears to be system specific. However, if a given VOC requires water for its complete oxidation, water vapor must be present in the feed stream or else the reaction rate will eventually decrease to near zero. In general, increasing the reaction temperature increases the rate of oxidation, although some exceptions have been noted.

Stabilization of iron(VI) ferrate cathode materials using nanoporous silica coatings

Ferrate salts containing Fe(VI) have received attention as cathode materials in recent years due to their theoretical ability to accept three electrons while being reduced to Fe(III). Unfortunately, ferrate salts are also somewhat unstable, particularly when stored at elevated temperatures or in the presence of an alkaline electrolyte. In this paper, we document the stability of solid barium and potassium ferrate salts under various environmental conditions and report on the use of SiO 2 thin-film coatings to stabilize cathodes composed of solid barium ferrate. The nanoporous coatings are deposited from colloidal silica suspensions using sol-gel techniques. The enhanced stability of coated ferrates is demonstrated, and their discharge performance is characterized relative to uncoated materials. The coating technique employed may be applicable to other nanoparticulate metal oxide chemistries, thus presenting a possible method to modify ferrates and perhaps overcome their stability limitations.

TiO2-Mediated Photoelectrocatalytic Purification of Water

Abstract Sol-gel processing methods were employed to coat thin, porous films of titania on metal plates, specifically on aluminum, 304 stainless steel, and titanium. After coating and firing, all of these materials displayed photocatalytic activity when tested with a solution of formic acid that contained dissolved sodium chloride. However, only the titanium-supported photoelectrodes were stable with repeated use. Activities of these titaniumsupported photoelectrodes increased, often by factors of two to three, when positive potentials were applied across the titania coatings. Electrode activities increased when multiple coatings of titania were applied to the electrodes, although electrode stability was problematic when multiple coatings were deposited. Photoelectrocatalytic activities were not inhibited significantly by the presence of sodium chloride in the test solutions, while copper could be deposited on platinum cathodes when the test solutions contained dissolved copper in addition to sodium chloride and formic acid.

Effect of Fluorescent Illumination on Bacteria Supported on Glass Slides

Abstract The photocidal effect of exposing S. aureus BC12041 to UVA-rich fluorescent light is demonstrated. In UVA-exposure studies with appropriate controls, CFUs of S. aureus BC 12041 are reduced by approximately two logarithms in a high humidity environment 85% RH) and by one logarithm in moderate humidity (~ 50% RH) over a 30-min treatment period. In similar studies at the high humidity, no differential effect was observed between test and control studies with B. subtilis ATCC 6633. Thus, it appears that UVA-rich fluorescent lighting may be a useful side effect obtained when employing an UVA-activated photocatalyst for the degradation of volatile organic compounds (VOCs) in indoor air.