Photolytic Behavior Research Articles

A preliminary study for the photolysis behavior of biodiesel and its blends with petroleum oil in simulated freshwater

With the increasing use of biodiesel and its blends with petroleum fuel, the corresponding environmental issues also occur during its production, application and transportation. The photolysis behavior for biodiesel and the impacts of biodiesel on the photo-oxidation of petroleum hydrocarbons in simulated freshwater was studied by irradiated with ultra violet (UV) and simulated sunlight in the present study. The results indicated that the photolysis rates of fatty acid methyl esters (FAMEs) were mainly depended on their degree of saturation, slightly on water matrices and the initial concentration of biodiesel, regardless of biodiesel sources. Similar results were observed for total organic carbon (TOC) removal rates; however, TOC removal rates were slightly dependent on the initial concentration of biodiesel. The presence of humic acid and pyrogallic acid or lake water matrices slightly inhibited the removal rates of TOC. The photolysis rates of individual petroleum hydrocarbons with and without the presence of biodiesel followed similar rules. In brief, alkanes with light molecular weights were transformed faster than those with heavy molecules, the removal of polycyclic aromatic hydrocarbons (PAHs) were more significantly than alkanes, and the removal of alkylated PAHs (APAHs) increased concurrently with the alkylation level in each family. The presence of biodiesel only inhibited the photolysis of some heavy alkanes and PAHs, not for all other petroleum hydrocarbons. Biodiesel, as a surfactant-like material, could stabilize small oil droplets initially formed by agitation, therefore, these droplets experience longer lifetimes in the water phase before re-aggregating into larger globules and rising to the surface. The apparent solubility of petroleum hydrocarbons, especially for those with heavier molecular weights, has been enhanced in the presence of FAMEs. In this scenario, light needs to penetrate water phase to degrade these targets compared with diesel alone. The direct contacting opportunities between UV light and targets, and radicals produced to attack targets were reduced, which finally resulted in the inhibited photolysis rates of some heavy molecular weight hydrocarbons.

Bimolecular reaction of CH3 + CO in solid p-H2: infrared absorption of acetyl radical (CH3CO) and CH3-CO complex.

We have recorded infrared spectra of acetyl radical (CH3CO) and CH3-CO complex in solid para-hydrogen (p-H2). Upon irradiation at 248 nm of CH3C(O)Cl/p-H2 matrices, CH3CO was identified as the major product; characteristic intense IR absorption features at 2990.3 (ν9), 2989.1 (ν1), 2915.6 (ν2), 1880.5 (ν3), 1419.9 (ν10), 1323.2 (ν5), 836.6 (ν7), and 468.1 (ν8) cm(-1) were observed. When CD3C(O)Cl was used, lines of CD3CO at 2246.2 (ν9), 2244.0 (ν1), 1866.1 (ν3), 1046.7 (ν5), 1029.7 (ν4), 1027.5 (ν10), 889.1 (ν6), and 723.8 (ν7) cm(-1) appeared. Previous studies characterized only three vibrational modes of CH3CO and one mode of CD3CO in solid Ar. In contrast, upon photolysis of a CH3I/CO/p-H2 matrix with light at 248 nm and subsequent annealing at 5.1 K before re-cooling to 3.2 K, the CH3-CO complex was observed with characteristic IR features at 3165.7, 3164.5, 2150.1, 1397.6, 1396.4, and 613.0 cm(-1). The assignments are based on photolytic behavior, observed deuterium isotopic shifts, and a comparison of observed vibrational wavenumbers and relative IR intensities with those predicted with quantum-chemical calculations. This work clearly indicates that CH3CO can be readily produced from photolysis of CH3C(O)Cl because of the diminished cage effect in solid p-H2 but not from the reaction of CH3 + CO because of the reaction barrier. Even though CH3 has nascent kinetic energy greater than 87 kJ mol(-1) and internal energy ∼42 kJ mol(-1) upon photodissociation of CH3I at 248 nm, its energy was rapidly quenched so that it was unable to overcome the barrier height of ∼27 kJ mol(-1) for the formation of CH3CO from the CH3 + CO reaction; a barrierless channel for formation of a CH3-CO complex was observed instead. This rapid quenching poses a limitation in production of free radicals via bimolecular reactions in p-H2.

Properties of ThFx from Infrared Spectra in Solid Argon and Neon with Supporting Electronic Structure and Thermochemical Calculations

Laser-ablated Th atoms react with F2 in condensing noble gases to give ThF4 as the major product. Weaker higher frequency infrared absorptions at 567.2, 564.8 (576.1, 573.8) cm(-1), 575.1 (582.7) cm(-1) and 531.0, (537.4) cm(-1) in solid argon (neon) are assigned to the ThF, ThF2 and ThF3 molecules based on annealing and photolysis behavior and agreement with CCSD(T)/aug-cc-pVTZ vibrational frequency calculations. Bands at 528.4 cm(-1) and 460 cm(-1) with higher fluorine concentrations are assigned to the penta-coordinated species (ThF3)(F2) and ThF5(-). These bands shift to 544.2 and 464 cm(-1) in solid neon. The ThF5 molecule has the (ThF3)(F2) Cs structure and is essentially the unique [ThF3(+)][F2(-)] ion pair based on charge and spin density calculations. Electron capture by (ThF3)(F2) forms the trigonal bipyramidal ThF5(-) anion in a highly exothermic process. Extensive structure and frequency calculations were also done for thorium oxyfluorides and Th2F4,6,8 dimer species. The calculations provide the ionization potentials, electron affinities, fluoride affinities, Th-F bond dissociation energies, and the energies to bind F2 and F2(-) to a cluster as well as dimerization energies.

Kinetics, intermediates and acute toxicity of arsanilic acid photolysis

Arsanilic acid (4-amino phenyl arsenic acid, ASA) is widely used in poultry production as feed additives, while most of ASA in the feed is excreted in the animal manure and released into the environment. However, the environmental behaviors of ASA were not well understood. In the present study, the photolysis behaviors of ASA and the toxicity of its metabolites to luminescent bacterium were studied. The results showed that ASA could be photodegraded and this process was strongly affected by solution pH, humic acid and dissolved oxygen. Upon UV irradiation for 360min, ASA could be completely eliminated, but the reduction of total organic carbon (TOC) was not significant. In addition, NH4+ ions and inorganic arsenic including arsenite and arsenate were identified as the predominant end-products. The conversion of ASA included both direct and indirect photolysis involving radicals, and its possible photolysis pathways were proposed on the basis of the identified intermediates. Unfortunately, higher adverse effects of the conversion products of ASA on bacteria were observed during the photolysis reaction. The results of present study might be helpful for assessing the environmental persistence and risks of ASA.

Infrared absorption of 3-propenonyl (⋅CH2CHCO) radical generated upon photolysis of acryloyl chloride [CH2CHC(O)Cl] in solid para-H2

Irradiation at 193 nm of a p-H2 matrix containing acryloyl chloride CH2CHC(O)Cl at 3.2 K yielded infrared absorption lines at 3143.6 (ν1), 3057.0 (ν2), 3048.0 (ν3), 2103.1 (ν4), 1461.0 (ν5), 1349.8 (ν6), 1223.7 (ν11+ν12 or 2ν12), 1092.8 (ν8), 918.1 (ν9), 691.0 (ν10), 624.3 (ν11), and 597.1 (ν12) cm(-1) that are assigned to the 3-propenonyl (·CH2CHCO) radical. The assignments are based on the photolytic behavior and a comparison of observed vibrational wavenumbers and infrared intensities with those predicted with the B3PW91/aug-cc-pVDZ method. The observation is consistent with a major radical formation channel CH2CHCO + Cl followed by escape of the Cl atom from the original p-H2 cage. The observation of 3-propenonyl (·CH2CHCO) radical but not 3-propenalyl (s-cis- or s-trans-CH2CHĊO) radical indicates that the former is the most stable isomer and that the barrier heights for conversion from s-cis- or s-trans-CH2CHĊO to ·CH2CHCO are small.

Aquatic photochemistry of the sulfonamide antibiotic sulfapyridine

Abstract The photolytic behavior of the sulfonamide antibiotic sulfapyridine in water was investigated using a laboratory photoreactor approximating full-spectrum sunlight. Direct photolysis of sulfapyridine was rapid, with a half-life of 2.6 h and 31 min, and an observed quantum yield of 0.0013 ± 0.0002 and 0.013 ± 0.001, for the neutral species and fully deprotonated species, respectively. Direct photolysis rates increased dramatically with degree of deprotonation, with measured p K a 1 and p K a 2 values of 2.22 ± 0.03 and 8.58 ± 0.02, respectively. Indirect photolysis was assessed using water from constructed wetland mesocosms. A four-fold increase in the dissipation rate of sulfapyridine was observed due to the influence of high levels of dissolved organic carbon, after accounting for light screening by such materials. Nitrates had no observable effect on indirect photolysis rates. Major photoproducts identified were SO 2 extrusion and OH addition products. These results show that photolytic processes are a major removal mechanism of sulfonamide drugs in aquatic systems.

Photocatalytic degradation of humic acid in the presence of montmorillonite

Humic acids (HA) representing the major fraction of the naturally occurring humic substances (HS) are composed of highly functionalized carbon rich polydisperse organic fractions. Clay minerals which are responsible for the transport of inorganic and organic contaminants constitute the main component of the dispersed inorganic material in natural waters. The understanding of interactions between humic substances and clay minerals is an important task for the achievement of an effective water treatment performance. The aim of this research was to investigate the influence of montmorillonite as a representative clay mineral on the TiO2 photocatalytic removal of humic acids as the model compound of natural organic matter. The interactions prevailing between humic acid, montmorillonite and TiO2 surface were assessed prior to the application of photocatalysis in order to address the adsorptive and photolytic behavior of humic acids. The changes attained in humic acid were described by UV–vis spectroscopic i.e. color forming moieties (Color436) and UV absorbing centers (UV365 and UV254), and dissolved organic carbon (DOC) contents. Application of the pseudo first order kinetic model revealed both an enhancement and retardation with respect to the applied montmorillonite dose. The overall effect of montmorillonite on the photocatalytic degradation of humic acid was also evaluated in terms of molecular size distribution profiles (0.45μm filtered fraction, 100kDa fraction, 30kDa fraction and 3kDa fraction) described by the specified and DOC normalized specific UV–vis parameters.

Photolysis of tembotrione and its main by-products under extreme artificial conditions:: Comparison with another β-triketone herbicide

The photolytic behaviour of tembotrione, a new chemical herbicide intended for foliar application in corn, was investigated under unnatural and extreme photochemical exposure in aqueous solutions in the laboratory. It appeared that degradation was dependent on pH and occurred more rapidly under acidic and neutral conditions, leading predominantly to the formation of a xanthenedione type compound by intramolecular cyclisation with loss of HCl. Trace amounts of benzoic acid by-products appeared also during UV-C irradiation (λ=254nm) of the parent compound. Results were comparable to those obtained with sulcotrione, another β-triketone herbicide. These extreme irradiation conditions clearly accelerated the phototransformation of sulcotrione vs. simulated sunlight irradiation. Furthermore, the photolysis of the degradation by-products, resulting from either photolysis, hydrolysis or biotic pathways of the two active ingredients, was also carried out. The benzoic acid by-products appeared more stable to photolysis than their parent molecules. Xanthenedione derivatives were degraded more rapidly with several differences depending on the pH value.

Phototransformation of Cephalosporin Antibiotics in an Aqueous Environment Results in Higher Toxicity

Photodegradation may be the most important elimination process for cephalosporin antibiotics in surface water. Cefazolin (CFZ) and cephapirin (CFP) underwent mainly direct photolysis (t(1/2) = 0.7, 3.9 h), while cephalexin (CFX) and cephradine (CFD) were mainly transformed by indirect photolysis, which during the process a bicarbonate-enhanced nitrate system contributed most to the loss rate of CFX, CFD, and cefotaxime (CTX) (t(1/2) = 4.5, 5.3, and 1.3 h, respectively). Laboratory data suggested that bicarbonate enhanced the phototransformation of CFD and CFX in natural water environments. When used together, NO(3)(-), HCO(3)(-), and DOM closely simulated the photolysis behavior in the Jingmei River and were the strongest determinants in the fate of cephalosporins. TOC and byproducts were investigated and identified. Direct photolysis led to decarboxylation of CFD, CFX, and CFP. Transformation only (no mineralization) of all cephalosporins was observed through direct photolysis; byproducts were found to be even less photolabile and more toxic (via the Microtox test). CFZ exhibited the strongest acute toxicity after just a few hours, which may be largely attributed to its 5-methyl-1,3,4-thiadiazole-2-thiol moiety. Many pharmaceuticals were previously known to undergo direct sunlight photolysis and transformation in surface waters; however, the synergistic increase in toxicity caused by this cocktail (via pharmaceutical photobyproducts) cannot be ignored and warrants future research attention.

Ultrafast formation of the benzoic acid triplet upon ultraviolet photolysis and its sequential photodissociation in solution

Time-resolved infrared (TR-IR) absorption spectroscopy in both the femtosecond and nanosecond time domain has been applied to examine the photolysis of benzoic acid in acetonitrile solution following either 267 nm or 193 nm excitation. By combining the ultrafast and nanosecond TR-IR measurements, both the excited states and the photofragments have been detected and key mechanistic insights were obtained. We show that the solvent interaction modifies the excited state relaxation pathways and thus the population dynamics, leading to different photolysis behavior in solution from that observed in the gas phase. Vibrational energy transfer to solvents dissipates excitation energy efficiently, suppressing the photodissociation and depopulating the excited S(2) or S(3) state molecules to the lowest T(1) state with a rate of ∼2.5 ps after a delayed onset of ∼3.7 ps. Photolysis of benzoic acid using 267 nm excitation is dominated by the formation of the T(1) excited state and no photofragments could be detected. The results from TR-IR experiments using higher energy of 193 nm indicate that photodissociation proceeds more rapidly than the vibrational energy transfer to solvents and C-C bond fission becomes the dominant relaxation pathway in these experiments as featured by the prominent observation of the COOH photofragments and negligible yield of the T(1) excited state. The measured ultrafast formation of T(1) excited state supports the existence of the surface intersections of S(2)/S(1), S(2)/T(2), and S(1)/T(1)/T(2), and the large T(1) quantum yield of ∼0.65 indicates the importance of the excited state depopulation to triplet manifold as the key factor affecting the photophysical and photochemical behavior of the monomeric benzoic acid.

Nitrate-induced photodegradation of atenolol in aqueous solution: Kinetics, toxicity and degradation pathways

The extensive utilization of β-blockers worldwide led to frequent detection in natural water. In this study the photolysis behavior of atenolol (ATL) and toxicity of its photodegradation products were investigated in the presence of nitrate ions. The results showed that ATL photodegradation followed pseudo-first-order kinetics upon simulated solar irradiation. The photodegradation was found to be dependent on nitrate concentration and increasing the nitrate from 0.5mML−1 to 10mML−1 led to the enhancement of rate constant from 0.00101min−1 to 0.00716min−1. Hydroxyl radical was determined to play a key role in the photolysis process by using isopropanol as molecular probe. Increasing the solution pH from 4.8 to 10.4, the photodegradation rate slightly decreased from 0.00246min−1 to 0.00195min−1, probably due to pH-dependent effect of nitrate-induced OH formation. Bicarbonate decreased the photodegradation of ATL in the presence of nitrate ions mainly through pH effect, while humic substance inhibited the photodegradation via both attenuating light and competing radicals. Upon irradiation for 240min, only 10% reduction of total organic carbon (TOC) can be achieved in spite of 72% transformation rate of ATL, implying a majority of ATL transformed into intermediate products rather than complete mineralization. The main photoproducts of ATL were identified by using solid phase extraction–liquid chromatography–mass spectrometry (SPE–LC–MS) techniques and possible nitrate-induced photodegradation pathways were proposed. The toxicity of the phototransformation products was evaluated using aquatic species Daphnia magna, and the results revealed that photodegradation was an effective mechanism for ATL toxicity reduction in natural waters.

Infrared absorption of CH3OSO and CD3OSO radicals produced upon photolysis of CH3OS(O)Cl and CD3OS(O)Cl in p-H2 matrices

Irradiation at 239 ± 20 nm of a p-H(2) matrix containing methoxysulfinyl chloride, CH(3)OS(O)Cl, at 3.2 K with filtered light from a medium-pressure mercury lamp produced infrared (IR) absorption lines at 3028.4 (attributable to ν(1), CH(2) antisymmetric stretching), 2999.5 (ν(2), CH(3) antisymmetric stretching), 2950.4 (ν(3), CH(3) symmetric stretching), 1465.2 (ν(4), CH(2) scissoring), 1452.0 (ν(5), CH(3) deformation), 1417.8 (ν(6), CH(3) umbrella), 1165.2 (ν(7), CH(3) wagging), 1152.1 (ν(8), S=O stretching mixed with CH(3) rocking), 1147.8 (ν(9), S=O stretching mixed with CH(3) wagging), 989.7 (ν(10), C-O stretching), and 714.5 cm(-1) (ν(11), S-O stretching) modes of syn-CH(3)OSO. When CD(3)OS(O)Cl in a p-H(2) matrix was used, lines at 2275.9 (ν(1)), 2251.9 (ν(2)), 2083.3 (ν(3)), 1070.3 (ν(4)), 1056.0 (ν(5)), 1085.5 (ν(6)), 1159.7 (ν(7)), 920.1 (ν(8)), 889.0 (ν(9)), 976.9 (ν(10)), and 688.9 (ν(11)) cm(-1) appeared and are assigned to syn-CD(3)OSO; the mode numbers correspond to those used for syn-CH(3)OSO. The assignments are based on the photolytic behavior and a comparison of observed vibrational wavenumbers, infrared intensities, and deuterium isotopic shifts with those predicted with the B3P86∕aug-cc-pVTZ method. Our results extend the previously reported four transient IR absorption bands of gaseous syn-CH(3)OSO near 2991, 2956, 1152, and 994 cm(-1) to 11 lines, including those associated with C-O, O-S, and S=O stretching modes. Vibrational wavenumbers of syn-CD(3)OSO are new. These results demonstrate the advantage of a diminished cage effect of solid p-H(2) such that the Cl atom, produced via UV photodissociation of CH(3)OS(O)Cl in situ, might escape from the original cage to yield isolated CH(3)OSO radicals.

A Study on the Photolysis Behavior of Photoacid Generators

A method for evaluating the photolysis behavior of photoacid generator in solvent and high polymer film has been established through spectrophotometry and fluorospectrophotometry by using the acid-sensitive Rhodamine B as tracer. Results showed that this method is feasible and practicable for evaluating the acid generating efficiency of photoacid generator in organic solvents or polymer film, yielding quantitatively precise data of the photochemical reaction and acid generating behavior, thus is very useful for evaluating the quality of different types of photacid generators e.g. triazines, sulfonium salts etc.

Photolysis, Biodegradation, and Sorption Behavior of Three Selected Phenolic Compounds on the Surface and Sediment of Rivers

In this study, laboratory experiments were carried out to investigate the environmental behavior of three selected phenolic compounds [2, 4-Dichlorophenol (DCP), 2, 4-Dinitrophenol (DNP) and 2, 4-Dimethylphenol (DMP)] in the aquatic environment. The results of batch sunlight photolysis experiments showed that the three phenolic compounds were photodegraded relatively easily (i.e., half-life <151 h) in June, whereas these compounds were relatively stable against sunlight in September (i.e., half-life <330 h). The results of batch biodegradation experiments using river water suggested relatively slow biodegradation (i.e., half-life <2,310 h in June, half-life <1,155 h in September, and half-life <3,466 h in January) of three phenolic compounds, and the rate constant was dependent on sampling time. Freundlich model and the pseudo second-order model can describe the sorption behaviors of phenolic compounds on sediments very well. The intraparticle diffusion model for adsorption was also investigated and compared with the pseudomodel to identify sorption mechanism.

Conformational Behavior and Tautomer Selective Photochemistry in Low Temperature Matrices: The Case of 5-(1H-Tetrazol-1-yl)-1,2,4-triazole

The conformational properties and the photolysis behavior of one of the simplest N-C bonded bicyclic azoles, 5-(1H-tetrazol-1-yl)-1,2,4-triazole (T), were studied in argon and xenon matrices by infrared spectroscopy. Analysis of the experimental results was supported by extensive theoretical calculations carried out at the B3LYP/6-311++G(2d,2p) level of approximation. Out of the eight T minima located on the potential energy surface, the three most stable species were detected in low temperature matrices, namely, 5-(1H-tetrazol-1-yl)-1H-1,2,4-triazole (T1) and two conformers of 5-(1H-tetrazol-1-yl)-2H-1,2,4-triazole (T2a and T2b). With increase of the substrate temperature either during deposition of the matrices or during annealing the T2b → T2a conversion took place, in agreement with the predicted low energy barrier for this transformation (5.38 kJ mol(-1)). Both broad band and narrow band laser UV irradiations of T isolated in Xe and Ar matrices induce unimolecular decomposition involving cleavage of the tetrazole ring of T1 and T2a (T2b) that leads to the production of 1H-1,2,4-triazol-5-yl carbodiimide (P1) and 1H-1,2,4-triazol-3-yl carbodiimide (P2), respectively. When the laser is used, in addition to the main P1 and P2 photoproducts, several minor products could be successfully identified in the matrices: N-cyanocarbodiimide HNCNCN (detected for the first time) associated with nitrilimine HNNCH and HCN. An interesting phenomenon of tautomer-selective photochemistry was observed for the matrix-isolated compound. It could be explained by the different LUMO-HOMO energy gaps estimated for T1, T2a, and T2b, connected with different threshold energies necessary to start the photolysis of T1 and T2a (T2b).

Manganese-Schiff base complexes as catalysts for water photolysis

Four manganese(III)-Schiff base complexes (1-4) of formula [MnL(n)(H(2)O)(2)](2)(ClO(4))(2)·mH(2)O (n = 1-4; m = 0, 1) have been prepared. The multidentate H(2)L(n) Schiff base ligands consist of 3R,5R-substituted N,N'-bis(salicylidene)-1,2-diimino-2,2-dimethylethane, where R = OEt, OMe, Br or Cl. The complexes have been thoroughly characterized by elemental analysis, mass spectrometry, magnetic susceptibility measurements, IR, UV, paramagnetic (1)H NMR and EPR spectroscopies. Other properties, including redox studies and molar conductivity measurements, have also been assessed. The crystal structure of 1 was solved by X-ray diffraction, which revealed the dimeric nature of the compound through μ-aqua bridges. The ability of these complexes to split water has been studied by water photolysis experiments, with the oxygen evolution measured in aqueous media in the presence of a hydrogen acceptor (p-benzoquinone), the reduction of which was followed by UV-spectroscopy. The discussion of the photolytic behaviour includes advances in the knowledge of the structural motifs and the chemical activity of this type of complex, as revealed by the development of several characterization techniques in the last decade. Parallel-mode Mn(III) EPR shows that complexes 1-4 not only mimic reactivity but also share some structural characteristics from partially assembled natural OEC clusters.

Important role of reaction field in photodegradation of deca-bromodiphenyl ether: Theoretical and experimental investigations of solvent effects

Photolysis of deca-bromodiphenyl ether (BDE-209) was investigated in tetrahydrofuran, dichloromethane, isopropanol, acetone, ethanol, methanol, acetonitrile and dimethylsulfoxide. Noticeable differences of the photolytic rates and quantum yields were found in the diverse solvents. Different to the previous deductions, hydrogen donating efficiency and electron donating efficiency of solvents were not the decisive factors for the photolytic rate in this study, which was proved by the fast photolysis of BDE-209 in CCl 4, a solvent without hydrogen and difficult to donate electrons. Besides hydrogen addition process, intermolecular polymerization might occur during the photolysis. Density functional theory (DFT) calculation was performed to understand the molecular properties of BDE-209 in different solvents. The lowest singlet vertical excitation energy ( E ex) and the average formal charge on Br ( q Br + ) of BDE-209, reflecting the difficulty for the excitation of BDE-209 and for the departing of Br atom, respectively, were changed by the reaction fields formed by the different solvents. E ex and q Br + linearly correlated with the photolytic activity (log k). This study is helpful to better understand the photolytic behavior of BDE-209 in different media.

Interpretation and modelling of environmental behaviour of diverse pesticides by revealing photodecomposition mechanisms

Pesticides are commonly applied agrochemicals, however their long-term chemical behaviour and environmental fate involving degradation processes have not been studied thoroughly and extensively yet. As photolytic decomposition might be regarded as one of the key factor in determining environmental behaviour of pesticides, it is of high relevance to have comprehensive knowledge on characteristics of pesticide degradates having potential harmful biological effects. Toxicity of the examined pesticides is well known, however scarce information is available on their natural degradation processes, as well as the quality, structure and biological impact of the decomposition products. Our study is focused on revealing specific details of photolytic degradation behaviour of 3 frequently applied pesticides and mapping the entire decomposition mechanisms. Special, immerseable, low pressure mercury-vapour lamp was applied to induce photolytic transformation, which was followed by TLC and GC. The pesticides and the obtained products were identified by using GC-MS technique. The structure identifications were based on the interpretation of the fragmentation pathways. All the pesticide studied proved to be photosensitive and major stages of the UV-degradation pathway were found to be the loss of alky-groups, cleavage of the chloro-group and the hydroxylation, scission of N-alkyl groups and decarbonylation. In contrast to previous studies, different and specific degradates and end-products have been established, and the existence of alternative conversion pathways was revealed.

Effects of surfactants on the kinetics of acetamiprid photolysis

Photolysis behavior of acetamiprid in different kinds of surfactant solutions were investigated. The results showed that acetamiprid was prone to photolysis when exposed to the irradiation of a mercury lamp, and the photolysis kinetics fit in well with the first-order kinetic equation. Surfactants did not participate in the acetamiprid’s photolysis process directly, whereas they all had obvious inhibiting effects on it.

Aqueous photolysis of tetracycline and toxicity of photolytic products to luminescent bacteria

The extensive utilization of antibiotics in the pharmaceutical therapies and agricultural husbandry has led to the worldwide pollution in environments. In this study the photolysis behaviors of tetracycline (TC) and toxicity of its degradation products were investigated. The results showed that TC photolysis followed first-order kinetics. The photolysis rate was found to be dependent on the initial TC concentration and increasing TC concentration from 10 to 40 mg l −1 led to the decrease of the photolysis rate constant from 0.0045 min −1 to 0.0014 min −1. TC photolysis was highly pH-dependent and strongly enhanced at high pH value. Markedly elevated TC photolysis was also observed in the presence of nitrate and dissolved organic matter. Upon irradiation for 300 min, only 15% reduction of total organic carbon (TOC) occurred in spite of quick conversion of 73% of TC, suggesting that a majority of TC transformed into intermediate products without complete mineralization. The intermediate products from TC photolysis were analyzed using high-performance liquid chromatography–electrospray ionisation-mass spectrometry (HPLC–ESI-MS) and the main photolysis products of TC were proposed. The toxicity of the photolysis compounds was evaluated using luminescent bacterium, and the results revealed that the toxicity increased with irradiation, indicative of a higher adversity risk of the degradation products of TC on bacteria upon photolysis.