Degradation of estrone in aqueous solution by photo-Fenton system

Photodegradation of estrone (E1) in aqueous solutions by UV-VIS/Fe(III)/H2O2 system (photo-Fenton system) was preliminarily investigated under a 250-W metal halide lamp (lambda > or = 313 nm). The influences such as initial pH value, initial concentration of Fe(III), H2O2 and E1 on degradation efficiency of E1 were discussed in detail. The results indicated that E1 could be decomposed efficiently in UV-VIS/Fe(III)/H2O2 system. After 160-min irradiation, the photodegradation efficiency of 18.5 micromol L(-1) E1 reached 98.4% in the solution containing 20.8 micromol L(-1) Fe(III), and 1664 micromol L(-1) H2O2 at initial pH value 3.0. The degradation efficiencies of E1 were dependent on initial pH value, Fe (III) concentration and H2O2 concentration. The degradation of four estrogens estrone (E1), estradiol (E2), 17alpha-ethynylestradiol (EE2) and diethylstibestrol (DES) in UV-VIS/Fe(III)/H2O2 system were also conducted. Under the conditions of pH 3.0, the E1 apparent kinetics equation -dC(E1)/dt=0.00093[H2O2]0.47[Fe(III)]0.63[E1]0.24 (r=0.9935, n=11) was obtained. The E1 mineralization efficiency was lower than degradation efficiency under the same conditions, which implied the mineralization occurred probably only at aromatic ring. There are several intermediate products produced during the course of E1 degradation. The comparison of the degradation efficiencies of E1, E2, EE2 and DES degradation in UV-VIS/Fe(III)/H2O2 system were also conducted, and the relative degradability among different estrogens were followed the sequence: DES>E2>EE2>E1.     

Chlorine photolysis and subsequent OH radical production during UV treatment of chlorinated water

The photodegradation of chlorine-based disinfectants NH(2)Cl, HOCl, and OCl(-) under UV irradiation from low- (LP) and medium-pressure (MP) Hg lamps was studied. The quantum yields of aqueous chlorine and chloramine under 254nm (LP UV) irradiation were greater than 1.2molEs(-1) for free chlorine in the pH range of 4-10 and 0.4molEs(-1) for monochloramine at pH 9. Quantum yields for MP (200-350nm) ranged from 1.2 to 1.7molEs(-1) at neutral and basic pH to 3.7molEs(-1) at pH 4 for free chlorine, and 0.8molEs(-1) for monochloramine. Degradation of free chlorine was enhanced under acidic water conditions, but water quality negatively impacted the MP Hg lamp degradation of free chlorine, compared to the LP UV source. The production of hydroxyl radical via chlorine photolysis was assessed along with the rate of reaction between ()OH and HOCl using radical scavengers (parachlorobenzoic acid and nitrobenzene) in chlorinated solutions at pH 4. The quantum yield of OH radical production from HOCl at 254nm was found to be 1.4molEs(-1), while the reaction of HOCl with OH radical was measured as 8.5x10(4)M(-1)s(-1). NH(2)Cl was relatively stable in all irradiated solutions, with <0.3mgL(-1) increase in nitrate following a UV dose of 1000mJcm(-2). For water treatment plants, no significant changes in chlorine concentration would be expected under typical pH levels and UV doses; however, the formation of ()OH could have implications for chlorinated byproducts or decay of unwanted chemical contaminants.     

Photodegradation of estrone and 17beta-estradiol in water

The TiO(2)-assisted photodegradation of two natural female hormones, estrone (E1) and 17beta-estradiol (E2), was investigated in two UV-photo-reactors, followed by solid-phase extraction and analysis by gas chromatography-mass spectrometry (GC-MS). The degradation of E1 and E2 in both reactors followed the pseudo-first-order kinetics. In reactor 1 (150W), 97% of compounds were degraded within 4h of irradiation. Even more rapid degradation was observed in reactor 2 (15W) where 98% of both compounds disappeared within 1h, due to the shorter wavelength of UV-light in reactor 2 (fixed at 253nm) than reactor 1 (238-579nm). The influences of different initial chemical concentrations, pH value, the presence of dissolved organic matter and hydrogen dioxide, and the catalyst concentration on the degradation rate of E1 and E2 in aqueous solutions were investigated. The results show that the extent of photo-induced degradation of E1 and E2 strongly depends on the water constituents in solution. The degradation rate was increased when pH value was increased from 2 to 7.6, beyond which the degradation rate started to decrease. The presence of humic acid enhanced the degradation of E1 and E2 in both reactors as a result of photosensitisation effect of humic acid chromophore. The degradation rate increased with an increase in H(2)O(2) concentration. The degradation rate was also enhanced by increasing catalyst concentration up to 2g/l. The findings therefore suggest that photocatalysis can be a very effective method of rapidly removing certain EDCs from water.     

Photodegradation of sulcotrione in various aquatic environments and toxicity of its photoproducts for some marine micro-organisms

Photochemical behaviour of sulcotrione, a triketone herbicide, was studied in a variety of aqueous solutions including natural waters (sea and river) under laboratory conditions. Photodegradation experiments were carried out under two irradiation systems (UV-B and simulated solar radiation) in order to evaluate kinetics of active ingredient. The degradation kinetics, more rapid under UV-B radiation than solar simulator, followed a first-order reaction (photolysis half-lives ranged between 3 and 50 h) and appeared strongly dependent on water origin, pH value and molecular structure of the herbicide. Dissolved organic matter showed a retarding effect while low concentrations of nitrate ions had no effect on photolysis rate. Identification of photoproducts indicated that hydrolysis, a pH-dependent process (no degradation at pH >6 but at pH=3, k=0.0344 h(-1)), could be photoassisted. These results were compared to those of mesotrione, another triketone herbicide, which appeared more stable under UV-B irradiation. Toxicological studies on two marine heterotrophic bacteria and one cyanobacterium showed absence of effects up to 100 microgL(-1) for both sulcotrione and its photoproducts.     

Photochemical oxidation of As(III) by vacuum-UV lamp irradiation

In this study, vacuum-UV (VUV) lamp irradiation emitting both 185 and 254 nm lights has been investigated as a new oxidation method for As(III). Laboratory scale experiments were conducted with a batch reactor and a commercial VUV lamp. Under the experimental conditions of this study, the employed VUV lamp showed a higher performance for As(III) oxidation compared to other photochemical oxidation methods (UV-C/H(2)O(2), UV-A/Fe(III)/H(2)O(2), and UV-A/TiO2). The VUV lamp oxidized 100 microM As(III) almost completely in 10 min, and the reaction occurred mainly due to OH radicals which were produced by photo-splitting of water (H(2)O+hv (lambda=185 nm)-->OH.+H.). There was a little possibility that photo-generated H(2)O(2) acted as a minor oxidant of As(III) at alkaline pHs. The effects of Fe(III), H(2)O(2), and humic acid (HA) on the As(III) oxidation by VUV lamp irradiation were investigated. While Fe(III) and H(2)O(2) increased the As(III) oxidation efficiency, HA did not cause a significant effect. The employed VUV lamp was effective for oxidizing As(III) not only in a Milli-Q water but also in a real natural water, without significant decrease in the oxidation efficiency. Since the formed As(V) should be removed from water, activated alumina (AA) was added as an adsorbent during the As(III) oxidation by VUV lamp irradiation. The combined use of VUV lamp irradiation and AA was much more effective for the removal of total arsenic (As(tot)=As(III)+As(V)) than the single use of AA. The As(tot) removal seemed to occur as a result of the pre-oxidation of As(III) and the subsequent adsorption of As(V) on AA. Alternatively, the combination of VUV lamp irradiation and coagulation/precipitation with FeCl(3) was also an effective removal strategy for As(tot). This study shows that vacuum-UV (VUV) lamp irradiation emitting both 185 and 254 nm lights is a powerful and environmentally friendly method for As(III) oxidation which does not require additional oxidants or catalysts. The As(III) oxidation by VUV lamp irradiation was tested not only in a batch reactor but also in a flow-through quartz reactor. The As(III) oxidation rate became much faster in the latter reactor.     

Photooxidation of bisphenol A (BPA) in water in the presence of ferric and carboxylate salts

In this work, the photooxidation of bisphenol A (BPA), a suspected endocrine disruptor (ED), in water in the presence of ferric and oxalate ions was investigated in a concentric reactor under a 125 W high-pressure mercury lamp (lambda> or = 365 nm). The photooxidation efficiencies were dependent on the pH values and ferric/oxalate concentration ratios (Fe(III)/Ox) in the water, with higher efficiency at pH 3.50+/-0.05 and Fe(III)/Ox 10.0/120.0 micromol l(-1). The initial rate of photooxidation increases with increasing the initial concentration of BPA from 2.0 to 5.0 mg l(-1) while do not change at 5.0 and 10.0 mg l(-1). However, higher removal efficiency of BPA is archived at lower BPA initial concentration over range of 2.0 to 10.0 mg l(-1). For 2.0 mg l(-1) BPA, the initial rate of photooxidation is 0.06 mg l(-1)min(-1). By using UV-Vis spectrum and LC-MS techniques, the predominant photooxidation product BPA-o-catechol was identified and the mechanisms for the oxidative degradation were proposed. When BPA reacted with OH radicals, C atoms in 3-position were added with OH radicals followed by O2 peroxidation and HO2 radical escape. Then catechol derivatives were produced. After that, the two H atoms on the hydroxy group were extracted in two individual steps to form intermediates semiquinone radical and o-quinone. The intermediates underwent further oxidation, benzene ring cleavage and decarboxylation, up to mineralization ultimately.     

Degradation of monomethylmercury chloride by hydroxyl radicals in simulated natural waters

The degradation of methylmercury chloride by hydroxyl radicals (*OH) has been investigated using nitrate photolysis from 285 to 800 nm with a 450 W Xenon lamp as the (*OH source. The identified products are Hg(2+), Hg(0), CHCl(3) and formaldehyde. The second-order rate constant at pH of 5 at room temperature was determined to be 9.83(+-0.66)x10(9) M(-1) x s(-1)using benzoic acid as the *OH scavenger. The effects of chloride concentration and methylmercury speciation have also been investigated. A mechanism of the CH(3)HgCl-*OH reaction has been proposed. The calculated methylmercury degradation rates in natural waters using the above rate constant were comparable to the in situ photodegradation rates reported previously, indicating that degradation by (*)OH may be one of the important pathways of methylmercury degradation in sunlit surface waters.     

Evidence from surface tension and fluorescence data of a pyrene-assisted micelle-like assemblage of humic substances

Surface activity and fluorescence of humic substances (HS) and HS/pyrene solutions were monitored under various pH conditions. For HS alone the surface tension of the solutions decreased with increasing acidity, with a minimum at around pH 4. This effect, which is a consequence of an increase in the amphiphilic character of structures, is much more pronounced in humic (HA) than in fulvic acids (FA). The addition of pyrene (0.1 micromolL(-1)) results, for HA, in a marked reduction in the migration of amphiphilic species to the solution surface. FA profiles are not modified in presence of pyrene at that concentration. A decrease in the pyrene I1/I3 ratio in HS solutions shows that below pH 9 pyrene molecules react progressively to the change to a more hydrophobic environment, the greatest effect being observed at around pH 6 to 7. These signals are followed by a significant increase in the pyrene excimer fluorescence (lambda(exc)/lambda(em)=334 nm/450 nm), which is a consequence of the proximity of pyrene molecules. For FA, the I1/I3 decrease is less significant and no excimers develop. This set of effects is explained in view of conformational adjustments of HS, mainly HA, which become arranged in micelle-like domains in aqueous solution, the aromatic moieties being assembled around the pyrene molecules.     

Accelerated mineralization of the drug Diclofenac via Fenton reactions in a concentric photo-reactor

The complete mineralization of concentrated solutions of Diclofenac (2-[(2,6-dichlorophenyl) amino] benzene-acetic acid) sodium salt C14H10C12NO2Na was carried out in a concentric cylindrical immersion photoreactor in batch mode operation. Irradiation with a lamp emitting light at 254 nm (400 W) achieved total mineralization of Diclofenac solutions (0.062 mM or TOC 20 mg C l(-1)) in times under an hour. The mineralization was carried out via Fenton photo-assisted treatment. A determination of the solution parameters was carried out to optimize the time of the Diclofenac pretreatment, the type and intensity of the light source, the effect of the concentrations of Fe-ions and the oxidant added in solution and the reactor recirculation rate. Diclofenac disappearance was monitored by high liquid pressure chromatography (HPLC). Concomitantly, the aromatic and aliphatic intermediates were also monitored under low-energy (36 W) light irradiation at 366 nm in order to be able to detect the intermediates by HPLC in the minute time scale. The decrease of the chemical oxygen demand was followed during Diclofenac degradation. The activation energy for the mineralization of Diclofenac was determined to be 4.02 Kcal mol(-1).     

Photodegradation of phenol red in the presence of oxyhydroxide of Fe(III) (Goethite) under artificial and a natural light

The (α‐FeOOH) Goethite composite is a stable and an efficient catalyst in aqueous suspension under irradiation at 365 nm and by solar light. The photocatalytic activities of this composite were evaluated using Phenol Red (PR) dye (phenolsulfonphthalein class). In the dark, controlling factors, such as the pH and the adsorption of PR on Goethite surface were evaluated (before starting the photochemical experiments). It was found that the system PR‐Goethite present a small decrease in the main band of the dye (435 nm) which was explained by the low rate of adsorption of this dye on the Goethite. Also, we note that 40% of PR decolourisation was obtained after 200 min by the system PR‐Goethite‐hydrogen peroxide (H₂O₂) in dark due to the formation of ^?OH by thermal decomposition of H₂O₂ on the surface of Goethite. The effects of various experimental parameters, such as initial dye concentration, pH, photocatalyst amount, tert‐Butyl alcohol effect and H₂O₂ addition were investigated in the study of photodegradation of the dye. The results showed that the photodegradation of PR under UV‐A (365 nm) irradiation could be enhanced greatly in the presence of H₂O₂. Natural radiation tests (under sunlight) showed that degradation was faster comparing with that obtained using the artificial one at 365 nm. Studies of the mineralization using total organic carbon method under naturel light certify that this method, compatible with the environment, may be considered in the treatment of wastewater and generally in the process of removal of this kind of pollutant.     

Photocatalytic oxidative degradation of acridine orange in aqueous solution with polymeric metalloporphyrins

In the presence of polymeric M [meso-tetra (4,4'-biphenybisulfony) phenylporphyrin] (PMTBPBSOPP, M = Co, Mn, Cu, Zn, Fe), the photocatalytic oxidative degradation of acridine orange (AO) was investigated under conditions of irradiation with high-pressure mercury lamp (HPML), iodine tungsten lamp (ITL) and natural sunlight (NSL), respectively. The results indicated that PCoTBPBSOPP had remarkable effects on photodegradation of AO under NSL irradiation. The experiments also proved that the photocatalytic degradation of AO in aqueous solutions could be enhanced when hydrogen peroxide 0.4 g/L was added. When the initial concentration of AO was 43.8 mg/L, the degradation and the decolorization rates of AO under HPML irradiation were up to 98% and 97%, respectively. A number of factors affecting photocatalytic degradation effects, such as the initial concentration of AO, light sources, pH etc., were studied in detail. The experimental results confirmed that polymeric metalloporphyrins could fully decompose AO by using artificial light source such as HPML and ITL, moreover could degrade AO rapidly under NSL in 3 h. Definitely, polymer of metalloporphyrins in the heterogeneous photocatalysis phase had a potential application     

Comparison of natural estrogen removal efficiency in the conventional activated sludge process and the oxidation ditch process

The presence of natural estrogens, 17beta-estradiol (E2), estrone (E1) and estriol (E3), as well as estrogenic activity in wastewater influents and secondary effluents were investigated in 20 full-scale wastewater treatment plants in Japan. In all of the influent samples, natural estrogens were detected at concentrations above the minimum limits of detection (0.5ng/L). The concentrations of natural estrogens detected in the effluent of oxidation ditch plants were generally lower than previously reported values. On the other hand, in the conventional activated sludge plants, increments of E1 during biological treatment were frequently observed although E2 and E3 were removed effectively in the process. The removal rates of natural estrogens or estrogenic activity show no observed statistical relationship with the solids retention time (SRT) and the hydraulic retention time (HRT). However, the plants with high SRT or HRT generally showed high and stable removal of both natural estrogens and estrogenic activity.     

Photochemical induced changes of in vitro estrogenic activity of steroid hormones

Steroid estrogens are endocrine disrupting contaminants frequently detected in natural waters. Because these estrogens can elicit significant biological responses in aquatic organisms, it is important to study their rates and pathways of degradation in natural waters and to identify whether the transformation products retain biological activity. Photochemical kinetics experiments were conducted under simulated solar light for the hormones 17β-estradiol (E2), 17α-ethinylestradiol (EE2), estrone (E1), equilin (EQ), and equilenin (EQN) under direct and indirect photolysis conditions. All of these hormones were susceptible to direct photodegradation, with half-lives ranging from 40 min for E1 to about 8 h for E2 and EE2. Indirect photolysis experiments with added Suwannee River fulvic acid (SRFA) lead to faster degradation rates for E2, EE2, and EQ. Added SRFA caused slower photodegradation rates for E1 and EQN, indicating that it acts primarily as an inner filter for these analytes. The well-established yeast estrogen screen (YES) was used to measure the estrogenicity of the analytes and their photoproducts. Results of YES assay experiments show that only the direct photolysis of E1 gave estrogenic products. Lumiestrone, the major E1 direct photolysis product, was isolated and characterized. It formed in 53% yield and exhibited moderate estrogenic activity. When photolysed in the presence of perinaphthenone, a potent synthetic sensitizer, E1 degraded via an indirect photolysis pathway and did not produce lumiestrone or any other active products. These results suggest that under typical natural water conditions photochemical reactions of E2, EE2, EQ, and EQN are expected to produce inactive products while E1 will give the estrogenic product lumiestrone in moderate yield.     

Anatoxin-a degradation by Advanced Oxidation Processes: Vacuum-UV at 172 nm, photolysis using medium pressure UV and UV/H2O2

Two Advanced Oxidation Processes, namely vacuum-ultraviolet (VUV) photolysis at 172 nm and ultraviolet/hydrogen peroxide (UV/H₂O₂) were investigated for the degradation of anatoxin-a in aqueous solutions. Solutions of anatoxin-a-fumarate were treated with VUV light at 172 nm with a UV dose of 200 mJ/cm², where fumaric acid served as a reference compound for a competition kinetics analysis. The second-order rate constant for the reaction between anatoxin-a and the hydroxyl radical was found to be (5.2 ± 0.3) × 10⁹ M⁻¹ s⁻¹ and was independent of pH, temperature, and initial concentration of anatoxin-a. The direct photolysis of anatoxin-a using a medium pressure (MP) UV lamp was also investigated, in which case a UV dose of 1285 mJ/cm² was required to degrade anatoxin-a by 88% and 50% at concentrations of 0.6 mg/L and 1.8 mg/L of toxin, respectively. Treatment of anatoxin-a with a low pressure (LP) UV lamp in the presence of 30 mg/L of H₂O₂ was examined, where it was found that more than 70% of toxin could be degraded at a UV dose of 200 mJ/cm². The degradation arises from the oxidation of the toxin by hydroxyl radicals. The addition of H₂O₂ clearly enhanced the degradation of anatoxin-a, up to a concentration of 40 mg/L, after which addition of more H₂O₂ had little effect on the degradation kinetics of anatoxin-a. The effect of background constituents in the water on the degradation of anatoxin-a was also investigated using natural and synthetically produced model waters.     

UV/H_2O_2降解水中痕量NDMA的效能研究

采用UV/H2O2降解水中的痕量NDMA,考察了水中NDMA初始浓度、H2O2投量、pH、天然有机物及常见阴离子等因素的影响,并分析了NDMA的降解产物。结果表明,在UV辐照度为1 000μW/cm2、NDMA初始浓度为0.1 mmol/L、H2O2投量为20 mg/L、pH值为4的条件下,UV/H2O2对NDMA的降解效果较好(反应5 min后对NDMA的去除率接近100%);水中的天然有机物和Cl-、SO42-、NO3-、HCO3-等阴离子对NDMA的降解均有抑制作用,腐殖酸浓度越大其抑制作用越强,阴离子的抑制作用由大到小依次为HCO3-、NO3-、SO24-、Cl-;NDMA的主要降解产物为二甲胺和硝酸盐,此外还有少量亚硝酸盐、甲酸盐和甲胺生成。     

二氧化钛膜光催化氧化苯酚的动力学规律

采用主波长为２５３７ｎｍ的紫外光杀菌灯或主波长为３６５ｎｍ的黑光灯作为光源,研究了二氧化钛（ＴｉＯ２）膜光催化氧化苯酚水溶液的动力学规律。结果表明：ＴｉＯ２膜光催化氧化苯酚水溶液的动力学可以用ＬａｎｇｍｕｉｒＨｉｎｓｈｅｌｗｏｏｄ（Ｌ－Ｈ）动力学方程描述,但Ｌ－Ｈ方程只是表面反应的必要条件,并不充分;苯酚水溶液在黑光灯／ＴｉＯ２膜处理方式下的降解规律与Ｌ－Ｈ方程揭示的动力学变化过程相吻合;在起始浓度范围相同（２４～１６９０ｍｇ／Ｌ）的情况下,杀菌灯光催化氧化苯酚水溶液表现为一级反应动力学规律;不管哪种光源,ＴｉＯ２膜光催化矿化起始浓度７４０ｍｇ／Ｌ苯酚水溶液的过程均服从一级反应动力学。     

Surface modification of TiO2 by a ruthenium(II) polypyridyl complex via silyl-linkage for the sensitized photocatalytic degradation of carbon tetrachloride by visible irradiation

A new ruthenium(II) photosensitizer, [Ru(II)(py-pzH)(3)](2+) (where py-pzH=3-(2'-pyridyl)pyrazole), has been synthesized. The complex displayed outstanding excited state redox properties (estimated Ru(III)/Ru(II)* approximately -1.24 V vs. NHE) and was expected to sensitize the injection of electrons into the conduction band of anatase TiO(2) upon visible irradiation. The photosensitizer was anchored onto the surface of anatase TiO(2) particles via in situ silylation. The silyl-linkage displayed excellent stability in both aqueous media, over a wide pH range, and in common organic solvents. The resultant material, TiO(2)-[Ru(II)(py-pz-Si identical with )(3)], was found to be able to mediate degradation of CCl(4) in neutral aqueous medium under broad band visible irradiation (lambda>450 nm). The relation between the rate of degradation and concentration of substrate was explored and the mechanism of the photodegradation of the perhalogenated organic was discussed.     

The influence of pH and cadmium sulfide on the photocatalytic degradation of 2-chlorophenol in titanium dioxide suspensions

The influence of pH and cadmium sulfide on the photocatalytic degradation of 2-chlorophenol (2-CP) in titanium dioxide suspensions was investigated to evaluate the feasibility of mixed semiconductors on the photodegradation of chlorinated organics in aqueous solution. Apparent first-order rate constants (k(obs)) and initial rate constants were used to evaluate the degradation efficiency of 2-CP. Higher degradation efficiency of 2-CP was observed at higher pH values. The apparent pseudo-first-order rate constant was 0.036 min(-1) at pH 12.5 in TiO2/UV system, while a 2- to 9-fold decrease in k(obs) was observed over the pH range of 2.5-9.5. The addition of phosphate buffer solutions at different pH values have different effects on the degradation of 2-CP. H2PO4- has little effect on the photodegradation of 2-CP, while HPO4(2-) could inhibit the photodegradation efficiency of 2-CP. Chlorocatechol, hydroquinone, benzoquinone and phenol were identified as the predominant aromatic intermediates for the photocatalytic degradation of 2-CP. Moreover, less aromatic intermediates at higher pH were observed. Direct oxidation contributed significantly to the photodegradation of 2-CP. An addition of a semiconductor decreased the initial and apparent first-order rate constants of 2-CP. The cutoff of wavelength of 320nm could diminish the contribution of direct photolysis of 2-CP. The combination of cadmium sulfide and titanium dioxide can lead to an enhanced rate of disappearance of 2-CP compared to those in single semiconductor system. A 1.2 to 2.5-fold increase in rate constant in coupled semiconductor system relative to the single semiconductor system was obtained.     

Photocatalytic degradation of reactive black 5 in aqueous solutions: Effect of operating conditions and coupling with ultrasound irradiation

The degradation of reactive black 5 (RB 5), a representative diazo dye found in textile effluents, by means of ultraviolet irradiation (9W UVA) over TiO(2) suspensions, ultrasound irradiation (80kHz, 135W) and their combined application was investigated. Several commercial TiO(2) catalysts were screened and an anatase Hombicat UV 100 sample exhibited considerable activity in terms of solution decoloration, COD and ecotoxicity reduction. Photocatalytic degradation increased with increasing TiO(2) loading (in the range 0.05-1g/L) and decreasing dye concentration (in the range 120-20mg/L) and solution pH (in the range 9-2.6). At the typical conditions employed in this study (60mg/L dye, 0.25mg/L catalyst, ambient pH=5.8, oxygen sparging), complete decoloration was achieved after 60min of reaction. Addition of H(2)O(2) up to 0.01M hindered degradation, scavenging the photogenerated holes and hydroxyl radicals. Ultrasound irradiation resulted in low decoloration, e.g. less than 10% after 60min at 60mg/L dye and oxygen sparging and slightly improved under an argon atmosphere. The simultaneous application of ultraviolet and ultrasound irradiation resulted in increased decoloration compared to that achieved by photocatalysis and sonolysis operating separately; moreover, the overall sonophotocatalytic effect was greater than the additive effect of the two processes, implying possible synergy.     

Photolytic removal and mineralisation of 2-halogenated pyridines

The photolytic destruction and mineralisation of 2-halogenated pyridines (2-HalPYs) was studied in a range of conditions by means of ultraviolet irradiation at 254 nm. In all cases pseudo-first order kinetics satisfactorily describe the degradation process. Key decomposition products were identified and primary reaction pathways are proposed. 2-HalPYs were rapidly dehalogenated with a subsequent sharp pH drop. Complete Total Organic Carbon (TOC) removal was achieved. Their photolytic removal rate is not affected by pH or aeration. The fastest TOC removal was observed in 2-fluoropyridine (2-FPY) photolysis. 2-Hydroxypyridine (2-HPY) was identified as the primary intermediate formed by destruction of 2-chloropyridine (2-CPY), 2-bromopyridine (2-BPY) and 2-iodopyridine (2-IPY). 2-HPY is further destructed to form Dewar pyridinone. 2-FPY only marginally reacted to form 2-HPY. Instead, its major intermediate product is Dewar pyridinone. 2-IPY results in a, most likely aliphatic, photostable product, the production of which appears to increase at low pH and high 2-HPY concentration.