ABSTRACT
The photocatalytic decomposition of ethylene was performed under UV-LED irradiation in the presence of nanocrystalline TiO2 (anatase, 15 nm) supported on porous nickel foam. The process was conducted in a high-temperature chamber with regulated temperature from ambient to 125 °C, under a flow of reacted gas (ethylene in synthetic air, 50 ppm, flow rate of 20 mL/min), with simultaneous FTIR measurements of the sample surface. Ethylene was decomposed with a higher efficiency at elevated temperatures, with a maximum of 28% at 100-125 °C. The nickel foam used as support for TiO2 enhanced ethylene decomposition at a temperature of 50 °C. However, at 50 °C, the stability of ethylene decomposition was not maintained in the following reaction run, but it was at 100 °C. Photocatalytic measurements conducted in the presence of certain radical scavengers indicated that a higher efficiency of ethylene decomposition was obtained due to the improved separation of charge carriers and the increased formation of superoxide anionic radicals, which were formed at the interface of the thermally activated nickel foam and TiO2.
ABSTRACT
Acetaldehyde decomposition was performed under heating at a temperature range of 25-125 °C and UV irradiation on TiO2 doped by metallic Ni powder and TiO2 supported on nickel foam. The process was carried out in a high-temperature reaction chamber, "The Praying MantisTM", with simultaneous in situ FTIR measurements and UV irradiation. Ni powder was added to TiO2 in the quantity of 0.5 to 5.0 wt%. The photothermal measurements of acetaldehyde decomposition indicated that the highest yield of acetaldehyde conversion on TiO2 and UV irradiation was obtained at 75 °C. The doping of nickel to TiO2 did not increase its photocatalytic activity. Contrary to that, the application of nickel foam as a support for TiO2 appeared to be highly advantageous because it increased the decomposition of acetaldehyde from 31 to 52% at 25 °C, and then to 85% at 100 °C in comparison with TiO2 itself. At the same time, the mineralization of acetaldehyde to CO2 doubled in the presence of nickel foam. However, oxidized nickel foam used as support for TiO2 was detrimental. Most likely, different mechanisms of electron transfer between Ni-TiO2 and NiO-TiO2 occurred. The application of nickel foam greatly enhanced the separation of free carriers in TiO2. As a consequence, high yields from the photocatalytic reactions were obtained.
ABSTRACT
The Cracked Chevron Notched Brazilian Disc (CCNBD) method was selected for Mode I fracture toughness tests on Poorman schist, Yates amphibolite, and rhyolite dikes from the EGS Collab site at the SURF in Lead, South Dakota. The effects of lithology, anisotropy, and loading rate were investigated. Fracture toughness was greatest in amphibolite, with schist and rhyolite having similar toughness values ([Formula: see text] > [Formula: see text] ≈ [Formula: see text]). The effects of anisotropy on fracture toughness were investigated in the foliated schist samples. Schist samples were prepared in three geometries (divider, arrester, and short transverse) which controlled how the fracture would propagate relative to foliations. The divider geometry was strongest and short transverse geometry was the weakest ([Formula: see text] > [Formula: see text] > [Formula: see text]). Fracture toughness was observed to decrease with decreasing loading rate. Optical and SEM microscopy revealed that for the short transverse geometry, fractures tended to propagate along grain boundaries, whereas in arrester and divider geometries fractures tended to propagate through grains. In foliated samples, the tortuosity of the fracture observed in thin section was greater in arrester and divider geometries than in short transverse geometries.
ABSTRACT
The nature and kinetics of fluoride uptake by hydroxyapatite under various conditions remain the object of interest. This problem was now investigated with an experimental model reproducing as closely as possible the conditions in vivo. The aim of this work was: (1) to study the kinetics of fluoride uptake by natural and artificial hydroxyapatite depending on experimental conditions and to determine the reaction rate constants; (2) to describe the equilibrium of fluoride uptake with adsorption isotherms and develop a best fit mathematical model for the process taking place under various experimental conditions; (3) to determine and compare the capacity for fluoride uptake by natural and artificial hydroxyapatite depending on experimental conditions. Attention has focused on the equilibrium and kinetics of the process of fluoride uptake under conditions as similar to those in a living organism as it is possible to reproduce in vitro. Those conditions represented just one of sixteen various experimental setups differing as to process parameters of the experimental system. The equilibria and kinetics of the experimental system were determined basing on measurements of selected parameters. Adsorption isotherms were obtained experimentally and a best fit mathematical model was developed to describe the process. Additionally, maximal capacity for fluoride uptake was calculated, as well as equilibrium constants, adsorption and desorption rate constants for both hydroxyapatite types. The following conclusions were drawn: 1. Fluoride uptake by artificial and natural hydroxyapatite is a biphasic process essentially independent of conditions in the reaction environment adopted in the present work. The first phase is rapid and does not exceed some 15 minutes. The second phase is much slower and takes place over a period of several dozen hours. 2. Fluoride sorption by both hydroxyapatites is essentially a physico-chemical process which can mathematically be best described with Langmuir and Langmuir-Freundlich adsorption isotherms. Under conditions of equilibrium, the adsorbed substance forms a monolayer on the surface of the sorbent. 3. The binding of fluoride by natural hydroxyapatite is stronger than by its artificial counterpart. 4. The stability of fluoroapatite formed during fluoride uptake by natural hydroxyapatite is greater than that of its artificial counterpart. 5. Natural hydroxyapatite has a relatively large capacity for fluoride ions under experimental conditions adopted in the present work. This capacity exceeds that of artificial hydroxyapatite in spite of smaller specific surface of the natural substance.