The direct reaction between phenol and oxygen in water becomes rapid above 150°C, but the thermochemistry is very unfavorable for a process involving H-atom transfer to oxygen from phenol; rate constants for this process are one thousand to one billion times slower than measured rates. An electron transfer model appears to fit the measured data much better. The Arrhenius plot of oxidation rate constants over the range 100° - 420°C is reasonably linear, suggesting that the oxidation process follows similar reaction paths over this range. However, analyses indicate significant differences among products reported at 200° and 380°- 420°C. Clearer understanding of this relatively simple process is needed to optimize hydrothermal oxidations of the complex waste streams the processes are intended to treat.

This article focuses on the routes of transport and abiotic processes involved in the environmental transformation of synthetic organic chemicals and how molecular structure controls the products and lifetimes of several important classes of organic chemicals. The chapter also discusses the current methods to reliably determine the rates and products of degradation of new chemicals based on combinations of chemical structure and environmental processes as well as use of laboratory and field measurements. Methods are also discussed for use of structure activity relations for this purpose.

Photocatalytic oxidation of ibuprofen, clofibric acid, diclofenac and naproxen were studied in near-UV illuminated (> 300nm) aqueous TiO2 suspensions with emphasis on reaction rates, intermediates and oxidation pathways. First order rate constants for 0.1 mM compounds are in the order NP > IBN > CFA >DC over the range of 0.091 to 0.026 min(-1). The kinetics constants derived from the Langmuir-Hinshelwood preequilibrium absorption model have the same reactivity order. Two oxidation pathways were identified for these compounds: (1) low pH electron transfer from carboxyl group to the TiO2 valence band hole giving ketone and alcohol from ibuprofen and naproxen and chlorophenol from clofibric acid; (2) HO center dot radical aromatic ring oxidation dominant at pH 5 and above for all compounds giving Cl ion from clofibric acid and diclofenac. Diclofenac oxidized only through HO center dot radical ring oxidation to form a phenol and quinone on one ring and Cl ion from the other ring.

Analytical methods for determining formic, acetic and oxalic acids, formaldehyde, and methanol have been evaluated and/or optimized for measuring products from photoreduction of CO{sub 2} in illuminated, aqueous suspensions of photocatalysts. An electrophoresis anion separation method (CIA) can detect aqueous formate and oxalate ions at 22 and 17 {micro}M (1 ppm), respectively. Recalibration of the Nash formaldehyde determination shows that as little as 10 {micro}M (0.3 ppm) can be detected spectrally. Several experiments using suspensions of Pt/TiO{sub 2}, SrTiO{sub 3}, and SrTiO{sub 3} with Cr and Sb were illuminated in CO{sub 2} saturated solutions. No acids were detected in most experiments using CIA; however, ion chromatography (IC) was able to detect formate and acetate at low {micro}M (sub ppm) concentrations in several experiments using Pt/TiO{sub 2} and SrTiO{sub 3} in sunlight and with xenon uv light. Analysis for methanol by gas chromatography showed that not more than 2 ppm methanol could have formed and probably less. Adding 0.6 mM 2-propanol to an irradiated CO{sub 2}/TiO{sub 2} suspension led to formation of 550 {micro}M formate, but no formaldehyde, probably because re-oxidation of formate by semiconductor holes was competitively blocked. Loss of C{sub 1} products at higher concentrations by re-oxidation may be an important process, limiting the accumulation of products. Preliminary estimates were made of the physical size of a solar CO{sub 2} photoreduction unit large enough to reduce the CO{sub 2} produced from a 1000 MW coal-fired electricity plant. A perfectly efficient system could be as small as 2 to 3 km{sup 2}.

This report summarizes the activities of a project initiated in September 2001 for the development of tools for the combinatorial analysis of materials with respect to the photocatalytic water splitting to generate hydrogen. As this project is just beginning the majority of the initial effort has been in developing prototype analysis modules and assembling the necessary optical, electrochemistry, sampling and analysis equipment. The prototypes for the photoelectrochemical analysis of materials, has been divided into a module for the analysis of nano-particulate suspensions and for monoliths. In the case of the powder suspensions each photolysis cell contains a micropressure transducer and a sampling port for collection of headspace gas for GC analysis. The signal from the micropressure transducer will initiate the autosampling of the headspace gas by an in house modified Gilsen sample handler. In the case of the monolith samples a design that incorporates the ability to make an ohmic contact and hence monitor electrochemical response of the sample has been developed. These tools will then be used to screen materials generated by our partner, NanoGram Corporation, using their proprietary nanoparticulate synthesis.

This report summarizes the activities of a project initiated in September 2001 for the development of tools for the combinatorial analysis of materials with respect to the photocatalytic water splitting to generate hydrogen. As this project is just beginning the majority of the initial effort has been in developing prototype analysis modules and assembling the necessary optical, electrochemistry, sampling and analysis equipment. The prototypes for the photoelectrochemical analysis of materials, has been divided into a module for the analysis of nano-particulate suspensions and for monoliths. In the case of the powder suspensions each photolysis cell contains a micropressure transducer and a sampling port for collection of headspace gas for GC analysis. The signal from the micropressure transducer will initiate the autosampling of the headspace gas by an in house modified Gilsen sample handler. In the case of the monolith samples a design that incorporates the ability to make an ohmic contact and hence monitor electrochemical response of the sample has been developed. These tools will then be used to screen materials generated by our partner, NanoGram Corporation, using their proprietary nanoparticulate synthesis.

The United States currently meets 80% of its energy needs by burning fossil fuels to form CO2. The combustion-based production of CO2 has evolved into a major environmental challenge that extends beyond national borders and the issue has become as politically charged as it is technologically demanding. Whereas CO2 levels in the atmosphere had remained stable over the 10,000 years preceeding the industrial revolution, that event initiated rapid growth in CO2 levels over the past 150 years (Stevens, 2000). The resulting accelerating accumulation of CO2 in the troposphere is increasingly linked to global climate-warming, with projections of continued warming in the absence of resolute changes in CO2 management (Revkin, 2000). The worldwide effects of warming on forestry, fresh water supplies, farming, coastal stability, and human health could be enormous. In response to these threats, the 1997 Kyoto Treaty on Global Warming was initiated in a major world-wide effort to curtail CO2 emissions. A major feature of this activity involves separation, collection and storage of a significant fraction of the 6-billion tons of CO2 currently produced worldwide each year. The annual U.S. production is about a third of that value, and sites considered for storing U.S. produced CO2 include depleted gas reservoirs, deep saline aquifers, depleted oil reservoirs, coal beds, and the deep ocean (Noserale, 1999).

We directly measured the absolute reactivity of 17-beta-estradiol (E2) and several phenolic model compounds for E2 toward t-butoxy radical (t-BuO*) by nanosecond time-resolved optical spectroscopy. Compared to other phenols, E2 is a moderate, but not strong deactivator of oxyradicals. The absolute bimolecular rate constant for H-atom transfer from E2 to t-BuO* is 1.3 +/- 0.3 x 10(9) M(-1) x s(-1) (23 degrees C, benzene). We estimate the O-H bond strength of 17-beta-estradiol to be approximately 85 +/- 2 kcal/mol and calculate the reaction rate constant of E2 toward peroxy radical to be 10(5) M(-1) x s(-1) at 37 degrees C. The conjugate phenoxy radical of 17-beta-estradiol, E2O*, is unusually reactive toward alpha-tocopherol and ascorbate by H-atom transfer in homogeneous solution (10(8)-10(9) M(-1) x s(-1)). Our findings suggest that E2 functions in vivo as a highly localized, synergistic biological antioxidant. This may partly explain the clinical effectiveness of ovarian steroids in delaying the manifestations of Alzheimer's Disease as well as in protecting against cardiovascular pathologies. In the absence of complementary antioxidant synergists, E2O* is expected to be a pro-oxidant.

An investigation of the products from the reaction of ozone with aminodinitrotoluenes (ADNTs) provides information about the oxidation pathway. Studies conducted at low conversions of 2- and 4-ADNT show 2:1 ozone/ADNT stoichiometries, prompt formation of glyoxylic and pyruvic acids, and NO2- and NO3- (NO,) ions. Reaction schemes to account for these results involve a 1,3-dipolar cycloaddition of ozone to selected double bonds of the aromatic ring, leading to ring cleavage. N-15-Labeling experiments indicate that the amino function is not involved in the initial ozone oxidation acid eventually is incorporated into pyruvamide (2-ADNT) and oxamic acid (4-ADNT) before being oxidized to nitrate.

Aminodinitrotoluenes [2-amino-4,6-dinitrotoluene (2-ADNT) and 4-amino-2,6-dinitrotoluene (4-ADNT)] are serious groundwater contaminants commonly found in soils and groundwaters near TNT production facilities. To evaluate the kinetics and pathways for their oxidation in peroxone (ozone and hydrogen peroxide) oxidizing systems where both hydroxyl (HO) radical and ozone are important oxidants, competition kinetics and modeling experiments were done. ADNTs react rapidly with both ozone and HO radical. From competition kinetics with resorcinol as a reference, ozone rate constants of 1.45 x 10(5) and 1.8 x 10(5) M-1 s(-1) were determined for 2- and 4-ADNT, respectively. HO radical rate constants, determined using p-nitroacetophenone (PNAP) as a reference compound, are 1.6 x 10(9) and 1.9 x 10(9) M-1 s(-1) for 2- and 4-ADNT, respectively. Although rate constants for HO radical oxidations are 4 orders of magnitude larger than those for ozone, modeling shows that ozone is the dominant oxidant for ADNTs in peroxone mixtures, except at ADNTs concentrations below 1 mu M (200 ppb).

Predicting the rates of photolysis of organic compounds in natural waters is limited by several factors. For direct photolysis of dilute solutions of organic compounds in surface waters, the product of the quantum yield (efficiency) and light absorption rate are needed, but can rarely be calculated from structure activity relations (SARs); direct kinetic constants can be estimated reliably using measured quantum yields and solar models or simple spread sheet data bases to calculate rates as a function of latitude and season. Indirect photoreaction constants can be calculated from measured or estimated rate constants and the average transient photooxidant concentration. SARs for photooxidant rate constants are available for some classes of compounds. The overall indirect photolysis rate for a specific compound is the sum of all significant oxidation reactions for the compound. Quantitation of the rate process requires that a reaction profile be developed for each compound.

: The reaction between peroxone and two isomers of aminodinitrotoluene (ADNT) was studied with respect to kinetics of reaction and the products formed. The ADNTs react rapidly with ozone and hydroxyl radical, the principal components of peroxone. At fairly high ADNT concentrations (ppm), the reaction of ADNT is primarily with ozone. At lower ADNT concentrations (ppb), hydroxyl radical competes with ozone in pure water systems. Reactions of both the 2- and 4-ADNT isomers result in the formation of pyruvic acid, nitrate ion, and nitrite ion. A reaction mechanism consistent with these products is proposed.