Photochemical Degradation Processes Research Articles

Comparison of the differences in photochemical degradation of dissolved organic matter in rivers, lakes, and ponds by adding nanoparticles TiO2.

This study examines the photolysis of Dissolved Organic Matter (DOM) in urban rivers, lakes, and ponds using photocatalysis experiments. Employing a photochemical reactor and UV spectrophotometer, we investigated the precise effects of TiO2 nanoparticles and illumination duration on the degradation efficiency, rate, and kinetics in water bodies. Simultaneously, an analysis was conducted on the photochemical degradation process of DOM from various sources. The results demonstrate that the photocatalyst TiO2 can effectively improve DOM degradation and light absorption degradation efficiency, with longer illumination durations inversely correlating with DOM content. Both Dissolved Organic Carbon (DOC) and 254 nm absorbance degradation kinetics follow pseudo-first-order degradation kinetics. Notably, the pond exhibited the most significant change in degradation efficiency, reaching 96.7%. Our findings suggest that degradation efficiency in water bodies may be influenced by surrounding vegetation, population density, and rainfall conditions. This study contributes to a deeper understanding of DOM degradation processes by photocatalysts and provides a feasible method to effectively mitigate water pollution.

Role of Lakes, Flood, and Low Flow Events in Modifying Catchment‐Scale DOC:TN:TP Stoichiometry and Export

AbstractThe balance of organic carbon (OC), nitrogen (N) and phosphorus (P) plays a crucial role in determining the processing, retention, and movement of these solutes across the aquatic continuum. Floods and droughts can significantly alter the quantity and ratios of OC:N:P export within inland waters, but how these ratios change, and are coupled within watersheds that integrate rivers and lakes, is not well known. We investigated the stoichiometry and export of dissolved organic carbon (DOC), total N (TN) and total P (TP) in two lake watersheds (10 inflows, 2 outflows) in the southern Boreal Shield over a 37‐year period. Although DOC, TN, and TP concentration behaved similarly, DOC:TN:TP ratios varied seasonally, strongly modulated by stream discharge. DOC:TN, DOC:TP and TN:TP export initially increased rapidly with increasing discharge, peaking at 10%–20% exceedance of the annual discharge for DOC:TP and TN:TP ratios, indicating a rapid depletion of catchment OC sources. Both flood and low flow events resulted in lower DOC:TN and lower DOC:TP export—thereby increasing the relative contributions of stream TN and TP. Consequently, elevated annual discharge coupled with infrequent but high floods and periods of low flow events increased the contributions of TN and TP relative to DOC. Overall, the lakes retained DOC, while increasing TN relative to TP. Nonetheless, the flow regime played a role in modulating nutrient retention in the lakes, likely due to changes in residence time, and the interplay of physical, photochemical, and biological degradation processes.

Dynamic distribution and photochemical-microbial coupling degradation of dissolved organic matter in a large river-Influenced Bay

A large river-influenced offshore area is the junction where land and open sea meet, which is important in the biogeochemical processes of dissolved organic matter (DOM). Because hydrodynamic and biogeochemical processes are complex, processes such as the photochemical and microbial degradation of DOM are poorly understood. In this study, to further understand the degradation mechanisms of DOM from different sources, water was sampled from three cruises during autumn 2018 and spring and summer 2019 in Laizhou Bay (LZB), as this bay is greatly influenced by the Yellow River. Field incubation experiments examining the riverine, mixed, and marine DOM photochemical and microbial degradation processes alone or in combination were conducted onboard. Due to the dual influence of the Yellow River input and phytoplankton autogenous production, dissolved organic carbon (DOC) and chromophoric DOM (CDOM) show relatively conservative mixing behaviour with maximum values in summer, and the S275–295 gradually increases from the river to nearshore. In addition, it is indicated that higher primary productivity from large nutrient inputs in areas with moderate salinity during the summer is often accompanied by higher bioavailability DOM based on field investigation results. Various sources of DOM have different sensitivities to photochemical and microbial degradation due to their components and properties. Riverine DOM is susceptible to photochemical degradation, while marine DOM is more susceptible to microbial degradation. Moreover, the low-molecular-weight organic matter produced by photochemical degradation effectively promotes the microbial degradation of DOM from riverine sources, whereas photodegradation from mixed and marine sources do not significantly increase the biodegradation efficiency due to the low content of aromatic substances. Furthermore, photoammonification and bioammonification of autochthonous and allochthonous DOM may be the potential processes driving ammonia regeneration.

Peatlands Versus Permafrost: Landscape Features as Drivers of Dissolved Organic Matter Composition in West Siberian Rivers

AbstractWest Siberia contains some of the largest soil carbon stores on Earth owing to vast areas of peatlands and permafrost, with the region warming far faster than the global average. Organic matter transported in fluvial systems is likely to undergo distinct compositional changes as peatlands and permafrost warm. However, the influence of peatlands and permafrost on future dissolved organic matter (DOM) composition is not well characterized. To better understand how these environmental drivers may impact DOM composition in warming Arctic rivers, we used ultrahigh resolution Fourier‐transform ion cyclotron resonance mass spectrometry to analyze riverine DOM composition across a latitudinal gradient of West Siberia spanning both permafrost‐influenced and permafrost‐free watersheds and varying proportions of peatland cover. We find that peatland cover explains much of the variance in DOM composition in permafrost‐free watersheds in West Siberia, but this effect is suppressed in permafrost‐influenced watersheds. DOM from warm permafrost‐free watersheds was more heterogenous, higher molecular weight, and relatively nitrogen enriched in comparison to DOM from cold permafrost‐influenced watersheds, which were relatively enriched in energy‐rich peptide‐like and aliphatic compounds. Therefore, we predict that as these watersheds warm, West Siberian rivers will export more heterogeneous DOM with higher average molecular weight than at present. Such compositional shifts have been linked to different fates of DOM in downstream ecosystems. For example, a shift toward higher molecular weight, less energy‐rich DOM may lead to a change in the fate of this material, making it more susceptible to photochemical degradation processes, particularly in the receiving Arctic Ocean.

Understanding photochemical degradation mechanisms in photoactive layer materials for organic solar cells.

Over the past decades, the field of organic solar cells (OSCs) has witnessed a significant evolution in materials chemistry, which has resulted in a remarkable enhancement of device performance, achieving efficiencies of over 19%. The photoactive layer materials in OSCs play a crucial role in light absorption, charge generation, transport and stability. To facilitate the scale-up of OSCs, it is imperative to address the photostability of these electron acceptor and donor materials, as their photochemical degradation process remains a challenge during the photo-to-electric conversion. In this review, we present an overview of the development of electron acceptor and donor materials, emphasizing the crucial aspects of their chemical stability behavior that are linked to the photostability of OSCs. Throughout each section, we highlight the photochemical degradation pathways for electron acceptor and donor materials, and their link to device degradation. We also discuss the existing interdisciplinary challenges and obstacles that impede the development of photostable materials. Finally, we offer insights into strategies aimed at enhancing photochemical stability and discuss future directions for developing photostable photo-active layers, facilitating the commercialization of OSCs.

Spatio-temporal distribution, photoreactivity and environmental control of dissolved organic matter in the sea-surface microlayer of the eastern marginal seas of China

Abstract. As the boundary interface between the atmosphere and ocean, the sea-surface microlayer (SML) plays a significant role in the biogeochemical cycles of dissolved organic matter (DOM) and macronutrients in marine environments. In our study, the optical properties of DOM were compared between the sub-surface water (SSW) and the SML during spring, summer and winter in the East China Sea (ECS) and the Yellow Sea (YS). In addition, photoexposure experiments were designed to compare photochemical degradation processes of DOM between the SML and the SSW. Chromophoric DOM (CDOM), fluorescent DOM, dissolved organic carbon, chlorophyll a (Chl a), picoplankton, nutrients and bacteria were frequently enriched in the SML. The enrichment factors (EFs) of tryptophan-like component 4 were significantly higher than other fluorescence components; the longer wavelength absorption values of CDOM showed higher EFs in the SML, and a more significant relationship between CDOM and Chl a in the SML, indicating that autochthonous DOM was more strongly enriched in the SML than the terrestrial DOM. Higher EFs were generally observed in the SML in the off-shore regions than in the coastal regions, and CDOM in the SML was photobleached more after relatively strong irradiation, as also indicated by the lower percentages of humic-like DOM and lower specific UV absorbance values (SUVA254) in the SML than the SSW. Compared to the SSW, the elevated nutrients may stimulate phytoplankton growth, biological activity and then production of abundant fresh autochthonous DOM in the SML. Our results revealed a new enrichment model for exploring the air–sea interface environment, which can explain the more autochthonous properties of DOM in the SML than the SSW.

Accumulation of recalcitrant dissolved organic matter in aerobic aquatic systems

AbstractAn oxygenated atmosphere changed life on Earth but it also provided a negative feedback to organic matter accumulation by increasing decomposition rates. Nonetheless, dissolved organic carbon (DOC) is a huge carbon pool (> 750 Pg) and it can accumulate to high concentrations (20–100 mg C L−1) in some freshwater aquatic systems, yet it is not clear why. Here, we examine DOC in several Greenland lakes with varying DOC concentrations and identify processes that could alter its composition to make it increasingly recalcitrant. Δ14C aging of DOC corresponded with increased DOC concentrations, slower degradation rates, changes in isotope ratios and optical properties, all suggesting that photochemical and microbial degradation processes contributed to recalcitrance. Young DOC degradation was stimulated by phosphorus, but older DOC was not, suggesting an important role for nutrients early in degradation. Photochemical processing coupled with decreased habitat diversity in hydrologically isolated systems may enable recalcitrant DOC to accumulate with important implications for Earth's carbon and oxygen cycles.

Synergistic effect of nitrate on UV-chlorine photochemical degradation of carbamazepine.

We investigated the use of UV-chlorine advanced oxidation process for the removal and transformation of carbamazepine (CBZ), and its photochemical synergy with NO3- for the production of .OH towards enhancing CBZ removal in aqueous solution. Production of .OH by UV-chlorine system with/without NO3- was studied under different conditions, by using salicylic acid (SA) as the chemical probe for .OH. Initial concentration of 30 mg/L SA, 5 and 10 mg/L chlorine, and 0-10 mg/L NO3- under irradiation at 254 nm (3.026 W/L) in a photochemical reactor was used. Aqueous solutions containing 10 mg/L chlorine and spiked with 4 mg/L NO3- gave the highest reproducible generation of .OH. Using initial concentrations of 10 mg/L CBZ and 10 mg/L chlorine, 60 % CBZ was removed after 10 min of irradiation without NO3-, while 72 % CBZ was removed with 4 mg/L NO3- added. There was no noticeable CBZ removal after 10 min of irradiation in the presence of NO3- without chlorine. Corresponding dark reactions were also conducted, with no noticeable degradation of CBZ. Samples were analyzed via UHPLC, LC-MS, and TOC (total organic carbon) analyzer for CBZ and TOC concentrations respectively. Although, there was significant reduction in CBZ concentrationduring both photochemical degradation processes, the was low TOC removal (~10%) in each case. The two photochemical degradation processes also seem to generate similar degradation products indicating that the addition NO3- of the UV-chlorine process might not have changed the degradation mechanism. The results indicate that NO3- could act synergistically in a UV-chlorine system to increase CBZ removal and reduce the quantity of free chlorine required to achieve a target removal efficiency. This could facilitate reduction in the potential production of chlorinated byproducts in the system.

Photochemical degradation of β-hexachlorocyclohexane in snow and ice.

Hexachlorocyclohexane (HCH), a typical organochloride pesticide, is one of the persistent organic pollutants. Despite the ban on technical grade HCH, it has been continuously observed at a steady level in the environment. The photochemical degradation of β-HCH in snow and ice under ultraviolet (UV) irradiation was investigated in this study. The effects of pH as well as common chemical components in snow on the degradation kinetics were investigated. In addition, the photodegradation products were determined and the reaction mechanism was hypothesized. The results showed that under UV irradiation, β-HCH can be photolyzed in snow and ice, with the photochemical degradation process conforming to the first-order kinetic equation. Changing the pH and adding Fe2+ had minimal effect on the photochemical degradation kinetics, while the presence of acetone, NO2-, NO3- and Fe3+ significantly inhibited the process. The addition of hydrogen peroxide slightly inhibited the photochemical degradation of β-HCH. Finally, the reaction rate, products and degradation mechanism of β-HCH in snow were compared with those in the ice phase. The photochemical degradation rate of β-HCH in snow was approximately 24 times faster than that in the ice phase. The photolysis product of β-HCH in snow was α-HCH, produced by the isomerization of β-HCH. However, in ice, in addition to α-HCH, pentachlorocyclohexene was produced by dechlorination. The results of this study are helpful in understanding the transformation of organochlorine pesticides in snow and ice, as well as in providing a theoretical basis for snow and ice pollution prevention and control.

Hydroxyl-Terminated Saponified Natural Rubber Based on the H2O2/P25-TiO2 Powder/UVC-Irradiation System.

Natural rubber (NR), a long-chain hydrocarbon polymer mostly consisting of cis-1,4-polyisoprene units, has a high molecular weight (MW) and viscosity, enabling it to show excellent physical properties. However, NR has no reactive functional group, making it difficult to react with other molecules, especially in manufacturing processes. The functionalized low-molecular-weight NR (FLNR) is a requirement to disperse ingredients into the rubber adequately. Here, the FLNR was prepared by a photochemical degradation process under UVC-irradiation in the presence of H2O2 using P25-titanium oxide (TiO2) powder as a photocatalyst. The optimum condition for the preparation of FLNR was the use of 2.0 g of TiO2 powder per 100 g of rubber and H2O2 at 20% w/w under UVC-irradiation for 5 h. The hydroxyl groups were found on the NR chains due to the chain-scission of polyisoprene chains and hydroxyl radicals in the system. The weight average MW of NR decreased from 12.6 × 105 to 0.6 × 105 gmol−1, while the number average MW decreased from 3.3 × 105 to 0.1 × 105 gmol−1.

Development and numerical modelling of a novel UV/H2O2 rotating flow reactor for water treatment.

The ultraviolet photochemical degradation process is widely applied in wastewater treatment due to its low cost, high efficiency and sustainability. In this study, a novel rotating flow reactor was developed for UV-initiated photochemical reactions. The reactor was run in a continuous flow mode, and the tangential installation of the inlet and outlet on the annular reactor improved reaction rates. Numerical modelling, which combined solute transport, radiation transfer and photochemical kinetic degradation processes, was conducted to evaluate improvement compared to current reactor designs. Methylene Blue (MB) decomposition efficiency from the modelling results and the experimental data agreed well with each other. The model results showed that a rotational motion of fluid was well developed inside the designed reactor for a wide range of inflow rates; the generation of ·OH radicals significantly depended on UV irradiation dose, and thus the degradation ratio of MB showed a strong correlation with the UV irradiation distribution. In addition, the comprehensive numerical modelling showed promising potential for the simulation of UV/H2O2 processes in rotating flow reactors.

Computational Fluid Dynamics Modeling of Rotating Annular VUV/UV Photoreactor for Water Treatment

The ultraviolet photochemical degradation process is widely recognized as a low-cost, environmentally friendly, and sustainable technology for water treatment. This study integrated computational fluid dynamics (CFD) and a photoreactive kinetic model to investigate the effects of flow characteristics on the contaminant degradation performance of a rotating annular photoreactor with a vacuum-UV (VUV)/UV process performed in continuous flow mode. The results demonstrated that the introduced fluid remained in intensive rotational movement inside the reactor for a wide range of inflow rates, and the rotational movement was enhanced with increasing influent speed within the studied velocity range. The CFD modeling results were consistent with the experimental abatement of methylene blue (MB), although the model slightly overestimated MB degradation because it did not fully account for the consumption of OH radicals from byproducts generated in the MB decomposition processes. The OH radical generation and contaminant degradation efficiency of the VUV/UV process showed strong correlation with the mixing level in a photoreactor, which confirmed the promising potential of the developed rotating annular VUV reactor in water treatment.

Mixing behavior, biological and photolytic degradation of dissolved organic matter in the East China Sea and the Yellow Sea

Optical properties of dissolved organic matter (DOM) were used as an indicator of the quantitative and qualitative changes occurring in marine DOM. The spatiotemporal distribution, bioavailability, and photoreactivity of chromophoric DOM (CDOM) and dissolved organic carbon (DOC) were investigated in the East China Sea (ECS) and the Yellow Sea (YS) during spring and summer using absorption spectroscopy and fluorescence excitation-emission matrix–parallel factor analysis. Over a 4-month laboratory study, we measured changes in six commonly used optical indices, including spectral slope (S275–295), slope ratio (SR: S275–295/S350–400), specific ultraviolet absorbance (SUVA254), ratio of the sum of protein-like components to the sum of humic-like components (Cprotein/Chumic), biological index (BIX), and humification index (HIX) to determine their changes following biological and photochemical degradation processes. Significant seasonal variations were observed in the spectral characteristics of CDOM in the ECS and the YS, indicating a stronger influence of the terrestrial origin and highly aromatic content of DOM in summer than in spring; this result was likely the consequence of an increase in the Changjiang River discharge, phytoplankton production, and biological activity, resulting in an increase in DOM production. Significant correlation between salinity and optical parameters (SUVA254, S275–295, S350–400, Cprotein/Chumic) indicated that water mixing strongly influenced the distributions of these optical parameters. The bioreactivity and photoreactivity of DOM varied depending on the source material, and the autochthonous protein-like DOM was more prone to biodegradation than the terrestrial DOM. The photodegradation processes acted preferentially on the CDOM than the colorless DOM. These results demonstrated that the optical parameters exhibited distinct changes during the mixing and the biodegradation and photodegradation processes and explained the seasonal distribution of DOM in the ECS and the YS.

Application of impinging jet atomization in UV/H2O2 reactor operation: Design, evaluation, and optimization

The concept of augmenting UV/H2O2 reactor with impinging jet atomization to achieve highly efficient mixing and thin fluid sheet formation capability was investigated. The collision of two jets forming a free-standing thin liquid sheet allowed the establishment of an effective UV/ H2O2 advanced oxidation setting. The response surface methodology (RSM) was applied to model and optimize the photochemical degradation process, which provides three level designs for RSM fitting. Three variables namely, Re (15000–31000), impingement angle (60–120 degree) and H2O2 dosage (1000−3000 mg L-1) were applied in BBD to model and optimize the effects of three key operational parameters. The optimum methyl orange (MO) removal percentage (after 90 min) and the apparent first order rate constant were 93.6% and 2.438 min-1, respectively. The influences of initial dye concentration, UV radiation power, and jet diameter were also investigated as the other main operating parameters. ANOVA analysis indicated that the Re number has the highest impact of the three considered parameters and additional experiments showed that the jet diameter does not have any significant effect on MO degradation. A pseudo-first-order kinetic model was applied for the prediction of contaminant degradation and rate coefficients. The good agreements between the model predictions and experimental results indicate that the proposed model could successfully describe the effectiveness of the augmented UV/H2O2 reactor due to the maximum degradation of the model contaminant.

Microbial response to oil enrichment in Gulf of Mexico sediment measured using a novel long-term benthic lander system

Weathered crude oil sank to the seafloor following the Deepwater Horizon disaster in 2010, removing this oil from further physical and photo-chemical degradation processes and leaving benthic processes as the mechanisms for altering and remediating this hydrocarbon source. To quantify potential microbial oil degradation rates at the seafloor, and associated changes in sediment microbial community structure and pore fluid composition, we used a benthic lander system to deploy novel sediment flow-through chambers at a natural hydrocarbon seep in the Gulf of Mexico (at a depth of 1226 m in lease block GC600) roughly 265 km southwest of the Deepwater Horizon wellhead (at 1500 m depth). Sediment amended with 20% unweathered crude oil had elevated rates of sulfate reduction over the course of the 5-month-long experiment as compared to an unamended control, yielding potential rates of sulfate reduction (600–800 mmol m–2 d–1) among the highest measured in hydrocarbon-influenced seafloor sediment. Oil amendment also stimulated methane production towards the end of the experiment, and led to slightly higher cell densities without significant changes in microbial community structure, based on 16S rRNA gene sequence libraries and fatty acid profiles. Assuming a link between sulfate reduction and hydrocarbon degradation, these results suggest that electron acceptor availability may become limiting in heavily oiled deep-sea environments, resulting in minimal degradation of deposited oil. This study provides unique data on seafloor sediment responses to oil deposition, and reveals the value of using observatories to fill the gap in understanding deep-sea microbial processes, especially for ephemeral and stochastic events such as oil spills.

Photochemical degradation of isoprene-derived 4,1-nitrooxy enal

Abstract. In isoprene-impacted environments, carbonyl nitrates are produced from NO3-initiated isoprene oxidation, which constitutes a potentially important NOx reservoir. To better understand the fate of isoprene carbonyl nitrates, we synthesized a model compound, trans-2-methyl-4-nitrooxy-2-buten-1-al (4,1-isoprene carbonyl nitrate, or 4,1-isoprene nitrooxy enal), and investigated its photochemical degradation process. The measured OH and O3 oxidation rate constants (298 K) for this nitrooxy enal are 4.1(±0.7) × 10−11 cm3 molecules−1 s−1 and 4.4(±0.3) × 10−18 cm3 molecules−1 s−1, respectively. Its UV absorption spectrum was determined, and the result is consistent with TDDFT calculations. Based on its UV absorption cross section and photolysis frequency in a reaction chamber, we estimate that the ambient photolysis frequency for this compound is 3.1(±0.8) × 10−4 s−1 for a solar zenith angle of 45°. The fast photolysis rate and high reactivity toward OH lead to a lifetime of less than 1 h for the isoprene nitrooxy enal, with photolysis being a dominant daytime sink. The nitrate products derived from the OH oxidation and the photolysis of the nitrooxy enal were identified with an iodide-based chemical ionization mass spectrometer. For the OH oxidation reaction, we quantified the yields of two nitrate products, methyl vinyl ketone nitrate and ethanal nitrate, which together contributed to 36(±5) % of the first-generation products.

Photochemical transformation of flufenamic acid by artificial sunlight in aqueous solutions

In the present article, we have studied the photochemical behavior of a common non-steroidal anti-inflammatory drug (NSAIDs) namely flufenamic acid (FLUA) in aqueous solution. The absorption spectrum of such compound shows a significant absorption beyond 290 nm and the photochemical irradiation within the range 300–450 nm leads to its complete transformation in roughly 6 h. The quantum yield of FLUA transformation measured at 290 and 310 nm was evaluated to about 1.1 × 10−4 without any significant effect of the excitation wavelength. The degradation process was inhibited in acidic solutions owing to the sharp increment in the absorption of FLUA in the wavelength region between 300 and 350 nm. The quantum yield was estimated to 1.2 × 10−4 at pH 7. The effect of oxygen on the photochemical behavior of FLUA has also been investigated. The obtained results clearly indicate that oxygen is not significantly involved in the photochemical degradation process. The phototransformation of the flufenamic acid appears to occur through one pathway that involves the photohydrolysis of trifluoromethyl group, and thus leads to the formation of one specific photoproduct, namely 2,3′-imino-dibenzoic acid. This result was confirmed by the formation of the fluoride ions after irradiation during the irradiation of flufenamic acid. A mechanistic scheme for such transformation of flufenamic acid was proposed.

Cytotoxicity on Allium cepa of the two main sulcotrione photoproducts, xanthene-1,9-dione-3,4-dihydro-6-methylsulphonyl and 2-chloro-4-mesylbenzoic acid

The cytotoxic effects of 2-chloro-4-mesylbenzoic acid (CMBA) and xanthene-1,9-dione-3,4-dihydro-6-methylsulphonyl (XDD), the two main photoproducts of sulcotrione, were investigated on Allium root meristematic cells at different concentrations. Degradation of sulcotrione was correlated to mitotic index decrease, together with increasing anomaly and c-mitosis frequencies. Mitotic index significantly decreased with increasing XDD and CMBA concentrations. Cell frequency with abnormal chromosomes increased with CMBA or XDD application rates. In contrast, CMBA induced a low micronucleus rate even for high concentrations while XDD increased the micronucleus ratio. C-mitoses, chromosomal aberrations due to an inactivation of the spindle, were enhanced by CMBA treatments but not by XDD. The photochemical degradation process of the pesticide can change the risk for the environment.

Photodegradation of E2 in the presence of natural montmorillonite and the iron complexing agent ethylenediamine-N,N′-disuccinic acid

In this work, the photochemical degradation process of 17β-estradiol (E2) in a suspension of natural montmorillonite (NM) has been studied. The addition of the iron complexing agent ethylenediamine-N,N'-disuccinic acid (EDDS) to the suspension was investigated and compared with the system without EDDS. The effects of the main physicochemical parameters (pH, EDDS, oxygen and NM concentrations) on E2 degradation in NM suspensions were also investigated. In order to better understand the photochemical process, experiments were carried out in the presence of 2-propanol. In general, the photochemical efficiency of the E2 degradation is better in EDDS-NM suspensions than in NM suspensions, especially at higher pH. This work demonstrated that the NM-EDDS system is an interesting and valuable research area and could be considered as a promising photochemical system for wastewater treatment.

Photochemistry of CF3(CH2)2CHO in air: UV absorption cross sections between 230 and 340 nm and photolysis quantum yields at 308 nm

This work constitutes the first study on the photochemical degradation process of CF3(CH2)2CHO. Firstly, the wavelength and temperature dependence of the UV absorption cross sections, σλ, was determined. The n → π* electronic transition band of CO chromophore was characterized between 230 and 340 nm in the 269–323 K range. A hyperchromic effect was observed in the structured part of the band when the temperature decreases. Maximum σλ = 283, 291 nm at 323 K is ca. 22% larger than those at 269 K. Secondly, the pulsed laser photolysis of a stationary mixture of CF3(CH2)2CHO/cyclohexane (OH-scavenger)/air or N2 was carried out at 308 nm. On-line Fourier transform infrared (FTIR) spectroscopy was employed to monitor the decay of CF3(CH2)2CHO and to obtain the photolysis quantum yield, Φλ = 308 nm, as a function of total pressure (20.5–760 Torr). A slight curvature in the Stern–Volmer plot was observed at pressures lower than 75 Torr. At high pressures, the pressure dependence of Φλ = 308 nm can be described by a Stern–Volmer relationship. Photodissociation of CF3(CH2)2CHO at 308 nm can produce HCO and CF3(CH2)2 radicals (1a), CF3CH2CH3 and CO (1b) and CF3(CH2)2CO radicals and H atoms (1c). HCO radicals are rapidly converted into CO in the presence of O2. Formation of CF3CH2CHO and CF3CH2CH2OH evidences the importance of secondary chemistry involving CF3(CH2)2 radicals formed in channel (1a). Further photodegradation of CF3CH2CHO yields mainly CF3CHO. Small quantities of HC(O)OH were also detected. CF3(CH2)2C(O)OH was only observed in the absence of OH-scavenger, implying that formation of CF3(CH2)2CO radicals in channel (1c) is not an important photolysis pathway. Consequently, photodissociation of CF3(CH2)2CHO in the actinic region is a source of shorter fluorinated oxygenated compounds, but it is not expected to be a source of fluorinated acids.