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The photocatalytic degradation in the aqueous phase of CCl4, CHCl3 and CH2Cl2 over irradiated TiO2 has been investigated in the presence of electron and hole scavengers, including atmospheric oxygen. Chloromethanes degrade through combined reductive and oxidative processes, the importance of which varies on going from CCl4, to CHCl3 and CH2Cl2.Under aerated conditions at pH 5, almost complete conversion into CO2 and HCl has been observed. Although chloride ions were evolved stoichiometrically, at pH 11 persistent formation of formaldehyde and formic acid was observed. Stable intermediates, either chlorinated or dechlorinated (formic acid, formaldehyde and methanol) have been quantified. An initial reductive dominance was observed for CCl4 even in the presence of oxygen. CH2Cl2 degradation was largely oxidative, even from the early stages of degradation, whereas the roles of the oxidative and reductive pathways were comparable for CHCl3.The effect of hole and electron scavengers highlights the importance of reductive and oxidative pathways. Reductants suchas alcohols (methanol, propan-2-ol, tert-butanol) enhance CCl4 degradation remarkably, have a limited effect on CHCl3 andstrongly decrease the degradation rate of CH2Cl2. Electron scavengers like periodate and peroxydisulfate decrease the degradation rate of CCl4 and have limited effects on CHCl3. Halides (chloride and bromide) show a peculiar behaviour. Acting as hole scavengers, they produce active species (ClNsbd and BrNsbd) that participate in reactions with transient intermediates. During degradation of CHCl3 in the presence of chloride, formation of CCl4 was reported. Interestingly, for CCl4 the degradation rate decreases and in the presence of bromide CBrCl3 is detected at trace level.

A procedure for the determination of nitro-substiruted polynuclear aromatic hydrocarbons (nitro-PAH) on crude air-particulate and soil extracts is introduced. Elimination of purification and fractionation procedures was made possible by the use of both a selective ionization method, such as electron-capture chemical ionization, and a specific fragmentation process, in an experiment of tandem mass spectrometry (gas chromatography-electron capture tandem mass spectrometry). Different mass spectrometric procedures were compared. The best performance was observed when the nitro-PAH molecular ions [M](-) were mass-selected by the first analyzer under multiple reaction monitoring conditions and then fragmented to NO 2 (-) (m/z 46). Detection limits were on the order of hundreds of femtograms, as determined in extracts of real environmental samples. This corresponds approximately to 5-15 pg of nitro-PAH per cubic meter of air sampled. Calibration curves were linear over 3 orders of magnitude. Applications to contamination from motor vehicle combustion and the iron industry are briefly discussed.

The photocatalytic degradation of atrazine has been examined under simulated solar light irradiation of various semiconductors powders (TiO2, ZnO, WO3, SnO2, and Fe2O3) and different titania specimens (nanometersize colloids, micrometer particles and millimeter spherical beads). Three major different degradation pathways operate in the photocatalyzed process: (a) dehalogenation, (b) dealkylation, and (c) deamination; the final product is cyanuric acid. Comparison of the results suggests that, amongst the different semiconductors, TiO2 is the most efficient. Titania, ZnO and WO3 degrade atrazine through the generation of active species which mainly promote the alkyl chain oxidation. Fe2O3 and SnO2 behave similarly to Al2O3 (an insulator) through a slow surface-assisted hydrolysis at the chlorine substituent position. The activity and selectivity of titania definitely depends on the differently preparative modes used to make the titania specimens. The temporal distribution of intermediates changes significantly as a consequence of the manner by which the organic probe and the catalyst interact.

The study of host-guest interactions has recently expanded from solution chemistry to the gas phase, where solvent effects are not present, allowing better understanding of the intrinsic phenomena responsible for molecular recognition. Important aspects under investigation include the mechanism of interaction, the identification of binding groups, as well as the discovery of structural requirements for the host to undergo inclusion complexation. The information gained from these gas phase studies can be exploited to design new practical applications of host-guest chemistry, particularly when gas-solid interactions are involved. Analytical devices such as gas sensors and chromatographic adsorbing cartridges take advantage of the structural recognition capability of the host to achieve high levels of selectivity.

Heterogeneous photocatalysis of many organic compounds, in oxic aqueous suspensions of semiconductor particles (e.g., Ti02) leads in almost all cases to quantitative formation of carbon dioxide and, eventually, inorganic anions. The fundamentals of heterogeneous photocatalysis and the possible application in the treatment of both waste waters and drinking water are presented.

The study of the photocatalytic activity of TiO(2) inverse opals showed that these structures behave as metamaterials: their properties arise principally from the 3D periodic structure of the material and marginally from porosity, reflectivity and scattering.

Heterogeneous photocatalysis with TiO2 particulate has rapidly progressed with increasing interest in the photo-oxidative degradation of various organic contaminants. The present review will briefly present some debated mechanistic details of this photo-oxidative process: the primary events and the reactive species; the role of the surface properties of the catalyst and the location of the reaction.

The photocatalytic degradation of six dichlorophenols (DCPs) and three trichlorophenols (TCPs) in TiO2 aqueous suspensions was studied. The apparent first-order rate constants kapp of disappearance of these CPs and monochlorophenols (MCPs) were found to correlate with their Hammett constants λ and their 1-octanol-water partition coefficients Kow: kaw (h−1)= −10σ+5.2 log Kow−7.5 under the conditions used (correlation coefficient, 0.987, if 2,4,6-TCP was omitted). The aromatic intermediates identified by their UV spectra (high performance liquid chromatography (HPLC) separation) and mass spectra (gas chromatography (GC) separation) corresponded to the hydroxylation of the aromatic nucleus with the following order of reactivity para> ortho>meta. Para-benzoquinones with 0–2 Cl atoms and 0 or 1 OH group and intermediates with two aromatic or quinone rings were also detected. The temporal variations of some intermediates were determined. All of these compounds, in which the C6 ring subsisted, were very unstable, so that their maximum concentration was very low compared with the initial CP concentration. The release of chloride and the evolution of CO2 also followed apparent first- order kinetics within the first part of the degradation. The effects of the number and position of Cl atoms on these fkinetics are discussed.

The paper reviews the theoretical models and equations used for the interpretation of weak acid dissociation equilibria in the presence of micellar systems. The models and the equations of the literature can be rewritten and reinterpreted in terms of the generalized pseudophase model, for which the basic equations are reported. Some new relationships for the titration of weak acids in micellar systems are presented.

The transformation of atrazine under simulated solar light in the presence of particulates of titanium dioxide has been shown to occur through different routes: (i) hydrolysis of the 2-chloro substituent; (ii) alkyl chain oxidation; (iii) dealkylation of the side chain and final displacement of the amino with hydroxy groups. A series of degradation intermediates have been identified by means of chromatographic and mass spectrometric techniques. Cyanuric acid (e.g. 2,4,6-trihydroxy-1,3,5-triazine) is found not to be susceptible of further fast decomposition and can be considered as the final product of photodegradation. Comparison with other photolytic processes (e.g. direct, sensitized, in the adsorbed phase on alumina, in the presence of humic materials) is presented.

Photooxidationof many organic compounds (e.g., haloorganics, surfactants, pesticides, etc.) dissolved in aqueous systems over illuminated semiconductor materials (e.g., TiO2) leads in almost all cases to quantitative formation of carbon dioxide and, eventually, of inorganic acids (e.g., HC1 from chlorinated compounds). The possible application in the treatment of both waste waters and drinking water is illustrated.

The sonochemical oxidation of phenol has been examined in airequilibrated aqueous media at various pH’s and at various insonation powers. Its disappearance follows zero-order kinetics at [phenol]initial ~ 30 to 70 μM Three principal intermediate species formed at pH 3: catechol (CC), hydroquinone (HQ), and p-benzoquinone (BQ); at natural pH (5.4–5.7) only catechol and hydroquinone formed. No intermediate species were detected at pH 12 under the conditions used. The sonochemical fate of CC, HQ, and BQ was also examined at pH 3 and at natural pH’s. At pH 3, BQ is the major species formed during insonation of HQ, while HQ is produced during insonation of BQ. In both cases, an additional intermediate formed in trace quantities that is identified as hydroxy-p-benzoquinone. These same intermediate species have been identified in the heterogeneous photocatalyzed oxidation of phenol in irradiated titania suspensions. The present results confirm the important role of ’OH radicals in degradation processes. Although CO2 is the ultimate product in heterogenous photocatalysis, irradiation of a phenolic aqueous solution by ultrasounds showed no loss of total organic carbon (TOC) after several hours, even though the aromatic substrate and the intermediates had degraded. A simple kinetic model/scheme is described to account for the events in the conversion of the substrates to products. It is concluded that the hydrophobic benzoquinone reacts with ¹OH and H¹ radicals at the hydrophobic gas bubble/liquid interface, while the hydrophilic species (phenol, CC, and HQ) react, to a large extent, with the ¹ OH radicals in the solution bulk.

Industrial activities release many toxic agents into the environment. Society faces two major hurdles: (i) the removal of undesirable substances from chemical and nuclear process effluents and (ii) the need to obtain and/or recover some substances from progressively leaner initial sources. Hydrogen sulfide is a major constituent of natural gas and is the principal product in the hydrodesulfurization of petroleum and coal. Although it is a toxic pollutant, it is an important energy vector. Cyanide is a very toxic substance frequently found above safe threshold levels in aquatic ecosystems. Unlike H2S and CN-, metals are not biodegradable. They possess infinite lifetimes and cannot be detoxified by chemical means. In recent years, alternative biological and photochemical methods have surfaced as potential new technologies for treating water effluents to transform H 2 S and CN - into less harmful substances, and to recover Pt, Pd, Au, Ag, Rh, Cr, Cu, Pb, and Hg. This paper focusses on photocatalysis, which uses semiconductor particulates as light harvesters and photocatalysts to transform/recover undesirable inorganic substances from the environment. Actual industrial effluents can be detoxified by this heterogeneous photocatalytic technique. A few examples are given.

Photooxidation of many organic compounds (e.g., haloorganics, surfactants, pesticides, etc.) dissolved in aqueous systems over illuminated semiconductor materials (e.g., TiO2) leads in almost all cases to quantitative formation of carbon dioxide and, eventually, of inorganic acids (e.g., HCl from chlorinated compounds). The possible application in the treatment of both waste waters and drinking water is illustrated.

The use and application of surfactants and their organized assemblies in separation science is surveyed. The unique properties of the amphiphilic aggregates have been utilized to improve existing methods or to overcome problems associated with the development of new procedures. Specific areas include chromatography, membrane based separations, extractions, foam based separations and other fields for possible future development.

Concentrated dispersions of Al(OH)3 in caustic solutions are examined in the presence and in the absence of additives. Sedimentation kinetics are influenced by the increase in viscosity of the solution due to the addition of the additives. Rheological data confirm the stabilization of the particles. Microscopy and light diffraction data show the effect of additives on the size and shape of the particles. Evidence of the influence of the additives on the nucleation and growth processes are given.

The photocatalysed mineralization of methylhydroquinone (MHQ) and 4-methylcatechol (4-MCC) was examined in air-equilibrated, irradiated (UV—visible light) aqueous suspensions of TiO2 (Degussa P 25) at pH 3. The temporal course of the degradation was followed by high performance liquid chromatography and gas chromatography (for CO2 evolution), and also by diffuse reflectance spectroscopy for 4-MCC. Total disappearance of MHQ occurs in approximately 1 h via apparent first-order kinetics (kapp ≈ 0.041±0.003 min−1; t 1 2 = 17 min), followed by the concomitant stoichiometric evolution of CO2 which is complete after approximately 1 h of irradiation. 4-MCC is strongly adsorbed (approximately 53%) to the catalyst's surface, and its disappearance is complete within approximately 20 min of irradiation (confirmed by the diffuse reflectance spectra of the catalyst powder). Evolution of CO2 for 4-MCC occurs via first-order kinetics (kapp ≈ 0.025 ± 0.005 min−1; t 1 2 = 28 min) and is complete after approximately 1.5 h of irradiation.

Aquatic components which can be active in the photochemically induced transformation of organic compounds include colloidal and sedimentary oxides and Sulfides, and organic colloids, either xenobiotic or naturally occurring. Particular attention is devoted to the degradation processes taking place at the semiconductor/water interface. The possible application of these photocatalytic degradation processes to water purification is outlined.

With the aim to ascertain the possibility of diffusion of fenoxycarb in the agro-ecosystem, investigations were done in a greenhouse of about 40 m3 in which two-year-old mulberry plants were growing. A water solution of the commercial product Insegar (2.0 gl−1) was poured in Petri dishes for a total area of 6,104 cm2. The air inside the greenhouse was collected by a suction pump when 1/3 of the solution evaporated. It contained 3.56μg m−3 of fenoxycarb. As soon as the solution evaporated completely, the mulberry leaves were collected and washed with water. This water contained 390μg of fenoxycarb kg−1 of leaves. The leaves, dried in the shade and analyzed 15 months after collection, contained 13μg kg−1 of fenoxycarb.

The results of a study of photocatalytic degradation of phenol using aqueous oxygenated TiO2 (anatase) suspensions in a batch Pyrex photoreactor are reported. The influence on the photodegradation rate of various parameters as pH, phenol and TiO2 content, oxygen partial pressure, anions present in the dispersions was investigated. A complete oxidation of phenol was observed. Intermediate compounds, catechol and quinone, were detected. It was observed that the photodegradation also proceeded with sunlight radiation. A mechanistic and kinetic model, which accounts for the results obtained, is given. Likely reasons for inactivity of the rutile modification for this reaction are also given.

The kinetics of reduction of aqueous solutions of CeIV and Ru(bpy)33+ in the presence of catalytic amounts of RuO2 colloids stabilized with polybrene and colloidal TiO2 particles loaded with RuO2 have been investigated by means of stopped-flow spectrophotometric techniques. The effect of pH, catalyst preparation and loading concentration have been considered. The TiO2/RuO2 colloidal particles (45 nm radius) are extremely active catalysts.

Modelisation de la cinetique du transfert de charge entre les especes IrCl 6 2− et Fe 2+ en tenant compte de l'agent de surface et de l'effet de sel. Cette approche permet une bonne estimation des constantes cinetiques en fonction de la concentration de l'agent tensio-actif et de la force ionique

The complete photocatalytic degradation of two polychlorinated dibenzo-p-dioxins and one polychlorinated biphenyl to CO 2 and HC1 has been investigated in aerated aqueous suspensions of several semiconductors (TiO 2 , ZnO, CdS, TiO 2 Pt 5% by weight, and Fe 2 O 3 ) irradiated by simulated solar light. The particular compounds were the 2-chlorodibenzo-p-dioxin (CDD), the 2,7-dichlorodibenzo-p-dioxin (DCDD), and the 3,3′-dichlorobiphenyl (DCB). TiO 2 shows the highest photo-activity for the degradation process studied; platinization seems to have little effect. The presence of conduction band electron scavengers such as Ag + and Fe 3+ ions increase the activity of TiO 2 .

The partition equilibria of a series of thirty substituted phenols bearing different chemical groups between aqueous solutions and sodium dodecylsulfate micelles was investigated by using micellar high-performance liquid chromatography and by studying the variation of the acidity constant. The contribution of each substituent to the free energy of transfer from water to micelles was estimated. The group contribution approach is shown to be valid for polysubstituted compounds under well defined conditions. A comparison with partition coefficients obtained in classical two-phase system (1-octanol/water), frequently used as biochemical model systems, is discussed

The kinetics and equilibria of electron transfer between N-methylphenolthiozine and aquoiron(III) or octacyanomolybdate(V) in the presence of various micellar-forming surfactants (CTAN, Triton, SDS) were investigated by using several spectrophotometric techniques. The presence of micelles strongly influences the equilibria and the kinetics of the reactions. Binding constants are determined and electrostatic and hydrophobic effects in the various micellar systems are analyzed. 8 figures, 5 tables.

The formation of the ground state charge transfer complex between durene and chloranil has been investigated in CH 2 Cl 2 and in microemulsions. The CH 2 Cl 2 or CH 2 Cl 2 /hexadecane microemulsion systems in water are stabilized by a cationic (hexadecyltrimethylammonium bromide) surfactant and 1-butanol as cosurfactant; the droplets have an average radius of 3.5 ± 0.5 nm. If the effective concentration in the oil phase (CH 2 Cl 2 or CH 2 Cl 2 /hexadecane) is accounted for, the equilibrium constant is not significantly changed with respect to the homogeneous CH 2 Cl 2 solution. The equilibrium of formation or dissociation of the complex is reached in less than 1 × 10 −3 s.

The degradation of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) by simulated sunlight ( > 340 nm) has been investigated in the presence of aqueous suspensions of semiconductor particulates (TiO2, ZnO, CdS, WO3, α-Fe2O3 and TiO2/5 wt.% Pt). Titanium dioxide appears to be the most effective catalyst; the half-life for the processes is −40 min (at initial DDT concentration 1 mg L−1 and 2 g L−1 TiO2, photon flux 3 × 10−5 einstein/min, over a cell cross-section of 4 cm2). The near quantitative recovery of chloride ions after long irradiation periods suggests that the end products of the degradative process are CO2 and HCl. To the extent that neither DDE (1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene) nor DDD (1,1-dichloro-2,2-bis(p-chlorophenyl)ethane) were observed by gas chromatographic techniques, the reaction proceeds through hydroxyl radical attack on the aromatic moieties with subsequent ring opening.

Highly hydrophilic compounds, with multiple carboxylic, hydroxylic, or aminic groups, have been determined at ultratrace level (3–30 fmol injected) in aqueous solution by direct derivatization with 2,2,3,3,4,4,5,5-octafluoropentyl chloroformate, followed by n-hexane extraction and analysis by gas chromatography-electron capture negative ion mass spectrometry (GC-ECNI-MS). The products have high molecular weights, but also high volatility, making their elution from the GC column efficient. The derivatizing agent was synthesized from the corresponding alcohol and phosgene. The derivatization reaction is catalyzed by a pyridine solution of N,N-dicyclohexylcarbodiimide. At 200 °C ion-source temperature, most negative ion mass spectra showed only a weak or no molecular ion, but a controlled and interpretable fragmentation, allowing the derivatives to be easily monitored by high-mass ion chromatograms. Typical distinctive fragments are located in the m/z 500–800 mass range. Optimization of the operating conditions for the derivatization was performed. This was done in order to minimize number and intensity of peaks due to the hydrolysis of chloroformate in the total ion chromatogram. Calibration curves proved linear over two orders of magnitude concentration.

The elution behaviour of 11 inorganic anions is investigated by unsuppressed ion chromatography with PRP-X100 a macroporous poly(styrene-divinylbenzene) strong-base anion-exchanger. Weak acids (cyanide and sulfide) can be separated and detected at pH 9 with sodium p-hydroxybenzoate as the eluent.

Resultats d'etudes par diffusion de lumiere de laser, par tensiometrie et par conductimetrie. Estimation des concentrations critiques micellaires, du nombre d'agregation, du rayon hydrodynamique et de l'hydratation micellaire en fonction du nombre d'unites d'oxyethylene et de la concentration du sel

Solutions of the nonionic amphiphile n‐dodecyl octaoxyethylene glycol monoether (C12E8) in D2O and in salty H2O have been investigated by static and dynamic light scattering. It is found that the micellar properties are little influenced by the choice of the solvent, whereas the critical properties (in particular, the critical exponents γ and ν) show a marked solvent effect. The interpretation of the observed critical behavior in terms of first‐order correction‐to‐scaling contributions is discussed.

Resultats d'etudes par diffusion de lumiere de laser, par tensiometrie et par conductimetrie. Estimation des concentrations critiques micellaires, du nombre d'agregation, du rayon hydrodynamique et de l'hydratation micellaire en fonction du nombre d'unites d'oxyethylene et de la concentration du sel

We describe in this paper light-scattering measurements performed on micellar solutions. The emphasis is put here on the experimental problems whereas a detailed account of the physico-chemical information which can be extracted from the data is presented elsewhere. In particular, we discuss a simple and accurate absolute calibration method of the light-scattering apparatus. Such a method is based upon turbidity measurements near the critical consolution point of a nonionic amphiphile solution.

This paper emphasizes the practical aspects of photocatalysis as applied to practical problems of some concern and employs semiconductor dispersions of CdS and TiO2. It presents our recent contributions to (i) the photocleavage of hydrogen sulfide, (ii) the treatment of wastes, and (iii) the photoreduction of and recovery of metals on TiO2. It further stresses the point that our present knowledge of photocatalysis and photocatalytic processes can be and must be applied to resolving environmental problems caused by discharge of toxic materials into the aquatic and atmospheric ecosystems. The problems are many; they must be addressed.

A turbidimetric apparatus has been developed for the determination of the consolution curve of binary mixtures. Measurements are fast and fairly accurate. The apparatus has been used to carry out a systematic study of the effect of various added salts on the consolution curve of alkyl poly(ethylene oxide) (C m E n ) micellar solutions. Measurements of the aging effect on the critical consolution temperature of C 12 E 8 are also presented.

Aqueous solutions of the nonionic amphiphile n-dodecyl octaoxyethylene glycol monoether (C12E8 ) with the addition of various electrolytes (CsCl,CsI or (CH3)4 NCl) or hydrocarbons (octane or dodecane) are investigated by static and dynamic light scattering and by other complementary techniques. It is found that the miceliar properties are little influenced by the additives, whereas the critical temperature shows a marked effect. The apparent critical exponents γ and V are strongly influenced by the addition of electrolyte, but are not sensitive to the addition of hydrocarbons.

Irradiation of aqueous TiO/sub 2/ dispersions containing palladium(II) or rhodium(III) chloride salts with AM1 simulated sunlight leads to the photoreduction of these metals, which are deposited on the semiconductor particle surface. Oxygen is detrimental to the photoreduction of rhodium(III) but not the photoreduction of palladium(II). However, in both cases the reduction process is most efficient if the solution contains CH/sub 3/OH, which acts to scavenge valence band holes of the illuminated TiO/sub 2/ semiconductor. The selective photoreduction and recovery of precious metals from a dilute solution (as might be found in industrial wastes) have been investigated for a mixture of gold(III), platinum(IV), and rhodium(III) chloride salts as a function of various parameters (pH, presence or absence of O/sub 2/, presence or absence of a hole scavenger, and the concentration of the semiconductor). At pH 0, gold is easily separated from platinum and rhodium. The rate of photoreduction of gold(III) on TiO/sub 2/ is nearly independent of the concentration of the semiconductor, under the experimental conditions employed; the limiting rate is 2.7 x 10/sup -7/ M s/sup -1/. The potential utility of this selective photochemical technique is discussed.

Irradiation of aqueous TiO/sub 2/ dispersions containing palladium(II) or rhodium(III) chloride salts with AM1 simulated sunlight leads to the photoreduction of these metals, which are deposited on the semiconductor particle surface. Oxygen is detrimental to the photoreduction of rhodium(III) but not the photoreduction of palladium(II). However, in both cases the reduction process is most efficient if the solution contains CH/sub 3/OH, which acts to scavenge valence band holes of the illuminated TiO/sub 2/ semiconductor. The selective photoreduction and recovery of precious metals from a dilute solution (as might be found in industrial wastes) have been investigated for a mixture of gold(III), platinum(IV), and rhodium(III) chloride salts as a function of various parameters (pH, presence or absence of O/sub 2/, presence or absence of a hole scavenger, and the concentration of the semiconductor). At pH 0, gold is easily separated from platinum and rhodium. The rate of photoreduction of gold(III) on TiO/sub 2/ is nearly independent of the concentration of the semiconductor, under the experimental conditions employed; the limiting rate is 2.7 x 10/sup -7/ M s/sup -1/. The potential utility of this selective photochemical technique is discussed.

As a part of a systematic study of the micellar properties and of the cloud-point transition in nonionic micellar solutions, measurements of a coexistence curve by a turbidimetric technique and of osmotic compressibility by light scattering have been performed on C 12 E 8 solutions to which n -octane or n -dodecane has been added. Some preliminary results of electric birefringence measurements performed on C 12 E 6 and C 12 E 8 solutions are also presented.

The degradation of 3-isopropy1–2,1,3-benzothiadiazin-4-one-2,2-dioxide, the herbicide bentazon, by AMI simulated sunlight has been investigated in the presence of aqueous suspensions of TiO2. The half-life of the degradation process is ca. 30 minutes at pH=2 and ca. 4 minutes at pH=7 in the presence of 0.5 g L−1 of TiO2. The near quantitative recovery of sulfate ions and CO2 as well as the variation with time of dissolved and adsorbed organic carbon suggest that the process leads to complete mineralization of the herbicide. The process is extremely efficient even at very low concentration: in fact irradiation of 20 ppb of bentazon in the presence of 50 ppm TiO2 allows to recover < 0.1 ppb after 10 minutes.

Etude des solutions micellaires aqueuses de composes amphiphiles non ioniques C 6 E 3 , C 8 E 4 , C 12 E 8 et C 14 E 7 , en fonction de la temperature et de la concentration, par diffusion dynamique et statique de la lumiere, par turbidimetrie et viscosimetrie. Les mesures de diffusion de lumiere a la concentration critique de separation des phases montre que la compressibilite osmotique et la serie de correlation de fluctuations de concentration diverge pres du point critique des systemes etudies

Photochemical reactions in aquatic systems are gaining increasing interest in the last years. Marine and fresh waters are a quite complex mixture of dissolved inorganic and organic compounds, biological species and colloidal aggregates. The exposure of such mixture to light can give rise to a series of reactions (1–3). The sun is the light source and the energy supply for environmental photoreactions. Since the sunlight penetrates in the fresh or marine water, it is adsorbed by naturally dissolved species or particulate matter.

Aqueous solutions of Fenton's reagent (Fe2+ + H2O2) have been used to effect the total decomposition of the chlorophenols: 2-chlorophenol, 3-chlorophenol, 4-chlorophenol, 3,4-dichlorophenol and 2,4,5-trichlorophenol. The mineralization of these chlorinated aromatic substrates to CO2 and free Cl− has been studied as a function of [Fe2+] and [HClO4]. Increasing the concentration of Fe2+ enhances the decomposition process, while an increase in the concentration of HClO4, inhibits the reaction. The presence of Fe3+ alone (without any Fe2+) with H2O2 has no effect on the degradation of the chlorophenols. In all cases, the stoichiometric quantity of free Cl− was obtained at the completion of the decomposition reaction; but the rates of disappaearance of the chlorophenol and of the formation of the Cl− are not similar. This suggests that some chlorinated aliphatic species may be formed as possible intemediates.