The photocatalytic decomposition of phenol in oxygenated aqueous suspensions of lightly-reduced anatase TiO2, being the most satisfactory among the semiconductors investigated from the standpoint of the photocatalytic activity and stability, has been investigated at the optimum pH 3.5. The products at the initial stage of the reaction were hydroquinone, pyrocatechol, 1,2,4-benzenetriol, pyrogallol, and 2-hydroxy-1,4-benzoquinone. These intermediates underwent further photocatalytic oxidation via acids and/or aldehydes finally into CO2 and H2O. A reaction scheme involving hydroxyl radicals as real reactive species has been proposed. Although H2O2 was formed via O2\ewdot produced by electron trapping of adsorbed oxygen, its concentration remained constant at a low value during the reaction. About 0.7 mole of O2 was consumed for the consumption of one mole of phenol at the initial stage of the reaction. These results indicated that hydroxyl radicals were formed not only via holes but also via H2O2 from O2\ew...

Heterogeneous Photocatalytic Decomposition of Phenol over TiO2 Powder

Scrapie is a slowly developing disease of the nervous system. Experiments on the effects of ultra-violet irradiation of suspensions of infected mouse brain extracts confirm that the agent responsible for it does not depend on a nucleic acid for its ability to replicate. No evidence is obtained, however, to indicate whether the agent is associated with a protein.

Does the Agent of Scrapie Replicate without Nucleic Acid

The total radiant flux from a solution containing a radioactive compound, hexadecane-1-C14, plus an appropriate scintillator has been determined. The procedure used involves comparison of its luminescent emission with the light scattered by glycogen illuminated with a monochromatic homogeneous light beam of known photon flux. From the result obtained the scintillation quantum yield of β− disintegration from carbon 14 has been determined to be 793 photons; thus 5.25% of the energy appears as light.

Total Quantum Flux of Isotropic Sources

Fluorochemicals (FCs) are oxidatively recalcitrant, environmentally persistent, and resistant to most conventional treatment technologies. FCs have unique physiochemical properties derived from fluorine which is the most electronegative element. Perfluorooctanesulfonate (PFOS), and perfluorooctanoate (PFOA) have been detected globally in the hydrosphere, atmosphere and biosphere. Reducing treatment technologies such as reverses osmosis, nano-filtration and activated carbon can remove FCs from water. However, incineration of the concentrated waste is required for complete FC destruction. Recently, a number of alternative technologies for FC decomposition have been reported. The FC degradation technologies span a wide range of chemical processes including direct photolysis, photocatalytic oxidation, photochemical oxidation, photochemical reduction, thermally-induced reduction, and sonochemical pyrolysis. This paper reviews these FC degradation technologies in terms of kinetics, mechanism, energetic cost, and applicability. The optimal PFOS/PFOA treatment method is strongly dependent upon the FC concentration, background organic and metal concentration, and available degradation time.

Treatment technologies for aqueous perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA)

— A solution of 0.6 M iodide and 0.1 M iodate in 0.01 M borate buffer (pH 9.25) can be used as a chemical actinometer to measure the incident fluence from a low-pressure mercury lamp that puts out more than 85% of its energy at 254 nm. The actinometric solution is optically opaque to light below 290 nm and is optically transparent to wavelengths greater than 330 nm. Hence, the solution absorbs all of the germicidal wavelengths but little if any of the ambient light normally present in the laboratory. Iodate acts as an electron scavenger and prevents the back reaction of the free electron with the iodine atom following UV excitation of KI. Irradiation results in the linear formation of triiodide, which is quantitated by measuring its absorbance at 352 nm. The quantum yield for this system is approximately 0.75 0.03 at 20.7AoC or approximately three times greater than that obtained previously using nitrous oxide as an electron scavenger. A model is proposed to account for this difference. A precise expression to account for the concentration and temperature dependence of the quantum yield is given by pH = 0.75(1 + 0.23[C - 0.577])(1 + 0.02[T - 20.7]) where C is the concentration of iodide and T is the temperature. The concentration of iodide can be obtained from the absorbance at 300 nm prior to irradiation using 1.061 MJ cm−1 as the molar extinction coefficient. This actinometric system meets the quality criteria established by the International Union of Pure and Applied Chemistry with the caveat that it is designed to measure only germicidal radiation (i.e. wavelengths less than 290 nm).

Potassium Iodide as a Chemical Actinometer for 254 nm Radiation: Use of Iodate as an Electron Scavenger

A chemical actinometer has been devised whose high sensitivity and precision depends upon the spectrophotometric determination of the photolysis products of potassium ferrioxalate with 1:10 phenanthroline. The sensitivity is some hundreds of times greater than that of the uranyl oxalate actinometer. The behaviour of the actinometer has been investigated in detail at 3650 to 3663 A, and tests also show that it is suitable for use over a wide range of wavelengths. The approximate quantum efficiency has been determined at twelve wave-lengths between 4900 and 2537 A. The advantages and possible applications of the actinometer in the measurement of small doses of radiation are discussed.

C. A. Parker

Papers

A New Sensitive Chemical Actinometer. I. Some Trials with Potassium Ferrioxalate