Deep Oxidation Processes Research Articles

Application of Fenton's Reaction for Removal of Organic Matter from Groundwater.

In this study, the effectiveness of the Fenton process in removing natural organic matter (NOM) from groundwater was investigated. The subject of this study is groundwater characterised by increased content of NOM and iron (II) compounds. In laboratory-scale studies, the influence of the ratio of concentrations of Fe(II) ions, which are naturally occurring in groundwater, to hydrogen peroxide (H2O2) as well as oxidation time and pH on the removal efficiency of organic matter was determined. Indicators such as total organic carbon (TOC), dissolved organic carbon (DOC), UV absorbance at 254 nm (UV254), UV absorbance at 272 nm (UV272), and specific UV absorbance (SUVA254) were used to quantitatively and qualitatively assess the organic substances present in the raw water and after oxidation with Fenton's reagent. Analysis of the results obtained showed that the highest removal efficiency of organic substances in the deep oxidation process using the Fenton reaction was obtained for a concentration ratio of Fe(II) to H2O2 = 1:5. Acidification of the water samples to a pH of about 4 and extending the oxidation time to 30 min significantly increased the removal efficiency of organic substances including mainly dissolved organic substances containing aromatic rings. The organic substances containing aromatic rings, determined at a wavelength of 254 nm, were degraded to other organic intermediates.

Insights into the PMS activation towards phenol removal mechanism by a Ti3C2-MXene doped BiVO4 photocatalyst

In the field of water treatment, photocatalysis and the peroxomonosulfate (PMS) deep oxidation process have emerged as potential solutions for the degradation of refractory organic pollutants. In this study, a novel BiVO4/Ti3C2 composite photocatalytic material was successfully synthesized using a hydrothermal method. The energy band structure of this material was utilized to establish Schottky barriers, enhancing the separation of photogenerated carriers. This, in turn, facilitated the activation of PMS under visible light, generating reactive species that effectively degraded phenol. The results demonstrate that in the BT-3/PMS system, the degradation rate of phenol reached 87.2 % within 60 min, with a maximum degradation rate constant of 0.02537 min−1. This represents an 8.8-fold improvement compared to pure BiVO4 and a 5.2-fold improvement compared to pure PMS. Free radical tests indicated that SO4·- was the primary reactive species involved in the degradation process. This study offers a promising approach for the design of efficient and stable Schottky junction photocatalysts that can be activated by visible light and PMS to effectively degrade organic pollutants.

Atomically Dispersed Pt-Doped Co3 O4 Spinel Nanoparticles Embedded in Polyhedron Frames for Robust Propane Oxidation at Low Temperature.

This study adopts a facile and effective in situ encapsulation-oxidation strategy for constructing a coupling catalyst composed of atomically dispersed Pt-doped Co3 O4 spinel nanoparticles (NPs) embedded in polyhedron frames (PFs) for robust propane total oxidation. Benefiting from the abundant oxygen vacancies and more highly valent active Co3+ species caused by the doping of Pt atoms as well as the confinement effect, the optimized 0.2Pt-Co3 O4 NPs/PFs catalyst exhibits excellent propane catalytic activity with low T90 (184 °C), superior apparent reaction rate (21.62×108 (mol gcat -1 s-1 )), low apparent activation energy (Ea = 17.89kJ mol-1 ), high turnover frequency( 811×107 (mol gcat -1 s-1 )) as well as good stability. In situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory calculations indicate that the doping of Pt atoms enhances the oxygen activation ability, and decreases the energy barrier required for CH bond breaking, thus improving the deep oxidation process of the intermediate species. This study opens up new ideas for constructing coupling catalysts from atomic scale with low cost to enhance the activation of oxygen molecules and the deep oxidation of linear short chain alkanes at low temperature.

Strengthening chlorobenzene catalytic degradation rate over LaxSr1-xMnO3±δ by anchoring interfacial oxygen vacancy

Surficial lattice oxygen in perovskite compounds is a common participant during chloroaromatic catalytic degradation. Herein, we proposed a facile oxygen vacancy construction strategy for preparing high active LaxSr1-xMnO3±δ (LSMO) via NaBH4 treatment. Results reveal that LSMO composites are not only reduced by NaBH4 under mild condition, but also triggering a significant Sr segregation effect, which plays a key role in oxygen vacancy formation accounting to the electron donation from Sr to Mn acceptor and subsequent lattice oxygen activation. Moreover, the concentration of interfacial active oxygen species can be regulated by taming the La-Sr interaction with different Sr substitution proportions. The anchored oxygen vacancies (OVs) take advantage of electron capture or transfer and induce molecule oxygen into active oxygen species to react with chlorobenzene molecules, resulting in a preferential catalytic oxidation capacity. Amongst, reduced La0.5Sr0.5MnO3±δ catalyst displays superior chlorobenzene destruction efficiency with 90% of which converted as low as 236 °C, which also exhibits a stable performance in long-time operation. However, the OVs would be refilled by H2O molecules and results in a weaker water resistance for OVs anchored catalyst. In summary, the annihilation of OVs is the most important factor for catalyst deactivation. The research offers a new avenue to construct interfacial oxygen species in perovskite oxides during the chlorobenzene deep oxidation process.

A direct relationship between the sensitivity of the sensors and the intensity of IR CO2 peak in in situ FTIR-LCR meter chemi-impedance SnO2–carbon nanoparticles polymer-based sensors in the detection of organic compounds vapor

Three sensors were prepared with SnO2, carbon nanoparticles (CNPs), and cellulose acetate (CA) composites, and each sensor containing different amounts of SnO2 powder were prepared for the detection of n-dodecane, 2-hexanone, and 3-methylcyclopentanone vapor at room temperature. Sensors with a combination of CNP:CA, SnO2:CA, SnO2:CNPs, and SnO2 composites were used as control, and their performance was compared with that of the sensor based on SnO2:CNPs:CA toward a wide range of 2-hexanone and 3-methylcyclopentanone vapor concentrations. Sensors based on CNPs:CA and SnO2:CNPs:CA selectively responded very well to 3-methylcyclopentanone and 2-hexanone, respectively. The in situ FTIR study revealed that both sensors undergo a deep oxidation process during sensing and the sensitivity of the sensors directly relates to the IR intensity of the CO2 peak at 668 cm−1, and for highly sensitive sensors, the CO2 peak at 668 cm−1 is found to be very intense. The gradient area under the curve of the IR CO2 band at 668 cm−1 against time for more sensitive sensors toward the analyte is larger than that for less sensitive ones. The effect of the amount of SnO2 in the composites indicated that the sensors based on three sensing materials combined at a mass ratio of 1:1:3 were highly selective toward 3-methylcyclopentanone and less selective toward the other two analytes. Sensors based on the composition of SnO2:CNPs:CA at a mass ratio of 1.5:1:3 and those based on the composition of SnO2:CNPs:CA at a mass ratio of 2:1:3 were selective toward 2-hexanone and n-dodecane, respectively. All the fabricated sensors were found to have their sensing ability regenerated after the analytes were removed from the system without losing their sensing and recovery abilities.

Catalytic oxidation of CO in gases emitted by industrial processes and vehicle exhaust

A new type of catalysts not containing noble metal oxides have been developed and the possibilities of their application both for the complete neutralization of carbon monoxide in exhaust gases and the process of deep oxidation of volatile hydrocarbons are studied. It has been foundthatthe activity of catalysts based on vanadiumandphosphorus oxides supported on Al2O3, SiO2, TiO2by and their modification withof 1–3% oxides of Cu, Cr, Co, Zn enhanced the conversion of the deep oxidation process to 95–100% at the temperatures of 673–693K and volumetric velocities of 5000–10000 h–1. During the simultaneous oxidation of CO and C3H8at a CO conversion of 90%, the C3H8conversionwas 70%. It has been established that oxidation of CO and C1–C4 hydrocarbons, and especially propane, with the participation of synthesized catalytic series, occurs by stepwise and associative mechanisms. The oxidation of CO and C3H8required a high oxygen content of 1:20–25 mol. Besides utilizing carbon monoxide in exhaust gases from motor vehicles, these catalytic systems can be successfully used to neutralize industrial gases, especially those emitted from oil refineries and thermal power plants. Preliminary research has shown that these catalytic systems can operate for about 50000 hours without changing the activity.

Porous Silica Coated Ceria as a Switch in Tandem Oxidative Dehydrogenation and Dry Reforming of Ethane with CO2

AbstractThe oxidative dehydrogenation of ethane using CO2 as soft oxidant for the production of ethylene, possesses the features of valorization of light alkane and utilization of greenhouse gas. Although a significant challenge, the control of the reaction extent can provide a potential on‐purpose ethylene technology. In the present paper, CeO2 is proposed to be a promising catalyst, while the deep oxidation process of dry reforming is preferred. The SiO2 coated CeO2 catalyst can render the reaction more selective towards ethylene. Through high sensitivity low energy ion scattering spectroscopy, findings were made that SiO2 only partially covered CeO2 in the Si0.1CeO2 sample, in which the ethylene selectivity was 2.7 times as high as that of the bulk CeO2 based on the same conversion level. Further, density functional theory calculations also demonstrated that the presence of the SiO2 layer was more conducive to the desorption of ethylene.

Different reactive behaviours of dichloromethane over anatase TiO2 supported RuO2 and V2O5

Abstract Three catalysts with RuO2 and V2O5 as the active components loaded on anatase TiO2 were prepared and used for the catalytic decomposition of dichloromethane (DCM). The V2O5/TiO2 showed higher CO selectivity and lower CH3Cl selectivity than RuO2/TiO2. Further characterization of these samples demonstrated that the V2O5 loading can promote the acidity of TiO2, which is beneficial for the adsorption of DCM and cleavage of C-Cl bonds, thus leading to a higher low temperature catalytic activity than RuO2/TiO2. Meanwhile, the EDS-mapping and XRD results indicated that RuO2 agglomerated over the surface of anatase TiO2. Therefore, a portion of the DCM directly decomposed over the bare surface of TiO2 and led to the production of CH3Cl, which is more stable than CH2Cl2 and difficult to decompose. However, the loading of RuO2 greatly enhanced the redox properties of the catalyst by enriching the surface oxygen species and promoted the deep oxidation processes to improve the selectivity of the product to CO2. Finally, the RuO2&V2O5/TiO2 catalyst was synthesized and used for the decomposition of DCM. The results demonstrated that the RuO2&V2O5/TiO2, which coupled the oxidation centre (RuO2) with the acid centre (V2O5), shows wonderful prospects for application in DCM decomposition.

Principles of the progress of reactions involving deep oxidation of isopropyl alcohol under conditions of aerosol nanocatalysis technology

We studied the process of deep oxidation of isopropyl alcohol under conditions of aerosol nanocatalysis technology. The process was carried out in a reactor with a vibro-fluidized bed of a catalytic system, which consists of powder of a catalytically active Fe2O3 substance and dispersing material. We performed a study for the further development of an environmentally friendly catalytic heat generator, which would operate in accordance with principles of nanotechnology. It was noted that the main controlling factors in the applied method of aerosol nanocatalysis are temperature and mechanical-and-chemical activation of a catalyst. Mechanical-and-chemical activation makes it possible to adjust a mode of vibro-fluidization to obtain the required reaction products. We modernized the laboratory unit to study the processes by the method of aerosol nanocatalysis in a vibro-fluidized bed of a catalytic system for tasks of deep catalytic oxidation of isopropanol.We carried out experimental studies into the effect of temperature on carbon monoxide content in oxidation gases, a degree of isopropanol transformation, and selectivity of the deep oxidation process. It has been shown that it is possible to achieve almost 100 % oxidation of isopropanol to СО2 in aerosol of nanoparticles of iron oxide at temperatures below 630 °C. The mentioned fact makes it possible to use low-alloyed steels and to reduce equipment costs in future technology. The results of the study give a possibility to determine a direction of the further research to optimize parameters of the process of control of oxidation of isopropyl alcohol for its deep oxidation and to obtain free energy for further use. We performed comparison of some technical-and-economic parameters of the process being developed with the processes based on heterogeneous catalysis.

Thermal stability and safety of dimethoxymethane oxidation at low temperature

In this work, thermal oxidation reaction of dimethoxymethane (DMM) at low temperature was investigated with a custom-designed mini closed pressure vessel test (MCPVT) employed. The initial auto-oxidation, thermal decomposition and deep radical oxidation processes were revealed by analyzing the behavior of oxidation temperature (T) and pressure (P) in the process of MCPVT monitoring. Peroxides generated from DMM auto-oxidation were measured by iodimetry and thin-layer chromatography (TLC). The dominant peroxide was separated from oxidation products via column chromatography, with structure characterized by mass spectrometry (MS), 1H and 13C nuclear magnetic resonance (NMR). The thermal decomposition characteristics were determined by differential scanning calorimeter (DSC). Results show that the oxidation was mainly initiated by hydrogen abstraction on the methylenedioxy (O-CH2-O) of DMM when temperature was above about 310 K. The primary product of hydroperoxide, hydroperoxy(methoxymethoxy)methane was found in DMM oxidation for the first time, with a high level. Its exothermic onset temperature (T0) and decomposition heat (QDSC) are 372.87 K and 2431.37 J·g−1, respectively. The thermal decomposition could lead to thermal runaway of oxidation, and further transform into an explosion. In most cases, the release of radical pool after peroxides decomposition would induce a rapidly radical oxidation of DMM through an endothermic reaction at about 410 K.

Compact, flexible conducting polymer/graphene nanocomposites for supercapacitors of high volumetric energy density

Graphene is extensively utilized in energy storage devices because of its high surface area and electronic conductivity as well as ease of electrode fabrication. But graphene sheets often stack themselves in polymeric matrices leading to poor capacitive performance. This problem was addressed herein by developing and inserting respectively two types of nano-sized conducting polymers into graphene interlayer spacing. The resulting hydrogel composite electrodes demonstrated efficient electron transfer for fast and reversible Faradaic reactions at the interface. Theoretical modelling by the density functional theory suggested that the reduction involve 2H+ transfer steps from polyaniline to graphene oxide: the first step would be an epoxy-ring opening process after activation of the C–O bond, and the second step would be C–O rupture leading to a de-epoxidation process. This binder-free electrode demonstrated high cycling performance and ultrahigh volumetric capacitance of 612 F cm−3, being 10 times higher than the activated carbon used in the current industry. The study represents a step forward towards the fabrication of flexible, high-energy density supercapacitors.

РАЦИОНАЛЬНАЯ ДОЗА ИКОРНОГО КОМПОНЕНТА И ЛИМОННОЙ КИСЛОТЫ В РЕЦЕПТУРЕ ИКОРНОГО СОУСА НА ОСНОВЕ НЕКОНДИЦИОННОЙ ИКРЫ ЩУКИ

The article focuses on the investigation of four variants of the caviar sauce "Nezhnost" using mayonnaise, different doses of the caviar component (off-standard unscreened caviar of the pike caught in autumn) and citric acid. The idea of developing recipe variants is connected to changing percentage of off-standard caviar (minus 5%) and mayonnaise portion (plus 5%). Analysis of organoleptic and physico-chemical indices of caviar sauce samples with different doses of introducing the caviar component (76.5; 71.5; 66.5 и 61.5%) showed that only one sample with 71.5% of caviar component corresponded to the requirements of GOST 31761-2012 "Mayonnaises and mayonnaise causes". In order to eliminate bitterness in the caviar sauce samples, as well as to prevent the deep oxidation process of fat, citric acid was introduced into the formulation in different amounts: 0 (control), 0.1; 0.3 and 0.5%. According to organoleptic and physico-chemical indices, the only sample with citric acid dose 0.3% (caviar component dose - 71.5%) corresponded to the requirements of GOST 31761-2012. In order to determine the stage of product readiness there was studied the process of accumulation of fermolent titrated nitrogen in the caviar sauce samples. Introduction of citric acid was stated to inhibit the production process. Maturation period of caviar sauce with citric acid dose 0.3-0.5% made 20 days. Chemical composition of a sample with citric acid dose 0.3%, most correspondent to GOST requirements, was determined as following: content of water - 61.1%; protein - 12.4%; lipids - 22.6%; carbohydrates - 2.3%; minerals - 1.5%. Sample energy value made 241.6 kcal. According to such microbiological indices as amount of mesophilous aerobic and facultatively anaerobic microorganisms and bacteria belonging to a coli bacillus group, this sample of caviar sauce corresponded to the Sanitary-epidemiological requirements 2.3.6.1079-01. Using off-standard unscreened pike roe of autumn catch as raw material for producing the new protein caviar product has been found possible.

New C[sbnd]O isotopic data on supergene minerals from the Skorpion and Rosh Pinah ore deposits (Namibia): Genetic and paleoclimatic constraints

Skorpion and Rosh Pinah Zn-(Pb) deposits are hosted in Neoproterozoic rocks that are part of a volcano-sedimentary sequence within the Gariep Belt of southwest Namibia. Skorpion is the largest Zn-nonsulphide mineralization ever discovered. It formed from weathering and oxidation of a volcanic hosted massive sulphide (VMS) protore and mostly consists of Zn-oxidized minerals. Rosh Pinah is a hybrid Zn massive sulphide deposit, with some VMS and Broken Hill-type characteristics and partly weathered in the uppermost part of the massive sulphide lens.We compared the deep oxidation process that occurred at Skorpion with the limited weathering of the Rosh Pinah deposit by studying the carbon and oxygen isotope ratios of supergene carbonates minerals. Twenty three smithsonite samples from the Skorpion deposit and 6 gossanous samples (containing both host dolomite and smithsonite) from the uppermost levels of the Rosh Pinah mine have been analysed. The Skorpion smithsonites form botryoidal crusts overgrown by euhedral calcite crystals. At Rosh Pinah all sampled smithsonites occur in veins within the dolostone host rock. Skorpion smithsonite is characterized by δ13C values strongly variable between −9.1‰ and 0.1‰ VPDB and by a small range in δ18O from 28.0 to 29.9‰ VSMOW. Calcite shows a minor variation in δ13C with values being generally positive (0–1.6‰ VPDB) and δ18O values slightly lower than those of smithsonite (25.4–27.1‰ VSMOW). The analyses of the Rosh Pinah samples show that the host dolomite is characterized by δ18O values ranging from 18.7 to 22.0‰ VSMOW and by negative δ13C values (−5.9 to −2.7‰ VPDB). The carbon isotope ratios of smithsonite, as in Skorpion, are negative (−2.8 to −1.9‰ VPDB) and partly overlapping with those of the host dolomites. The δ18O values (26.7–29.0‰ VSMOW) are on average comparable with the values measured at Skorpion. The similar negative δ13C values of smithsonite and dolomite at Rosh Pinah point to the involvement of both re-oxidized organic carbon and host dolomite inorganic carbon during smithsonite formation, whereas at Skorpion a larger contribution of isotopically light organic carbon is considered more probable. The comparable δ18O compositions of smithsonite from the two deposits imply similar ore-forming fluids and/or similar temperatures conditions during formation. In agreement with former studies, we suggest that Skorpion smithsonite precipitated at an average temperature near 17 °C from fluids depleted in 13C due to a high contribution of soil organic carbon, either during the first (Late Cretaceous-Paleocene) or the last humid climatic stage (early-middle Miocene). Even if the similarity between the δ18O composition of Rosh Pinah and Skorpion smithsonites points to similar ore-forming fluids and/or similar conditions during formation, the relatively high δ13C values of the Rosh Pinah smithsonites suggest a minor influence of isotopically light organic carbon and the absence of soils over this deposit. Combining these data with the limited thickness of the supergene zone over the latter orebody, it is likely that the Rosh Pinah smithsonites, together with the gossan in which they occur, formed at the end of the early-middle Miocene semi-humid period.The δ18O and δ13C compositions of Skorpion calcite indicate that the precipitating supergene fluids remained roughly unchanged, but that the bicarbonate from the host rock became prevailing. This suggests that calcite formation occurred at the beginning of the last late Miocene-Pliocene semi-arid period, when the host marbles were uplifted and karstified, thus promoting a higher bicarbonate contribution from dissolving host rock.

Iron-based polymetallic catalysts with a nanostructured surface for deep oxidation processes

A new class of highly active polymetallic catalysts for deep oxidation based on iron with admixtures of other d-metals and rare earths has been developed. The precursors of the catalysts are multicomponent intermetallides obtained by selfpropagating high-temperature synthesis (SHS). The XPA spectra, specific surface, and the morphology of the surface according to the SEM results are studied. The catalytic properties are studied using the example of deep oxidation processes of carbon monoxide and propane. It has been shown that two-level metal–oxide nanostructures are common features of the surface for the catalysts studied. The lowest level represents granules 10–30 nm in diameter, of which flat hexahedrons are built with a diameter of about 1 μm and a thickness of ≤100 nm.

Microstructural features of the La1−xCaxFeO3−δ solid solutions prepared via Pechini route

Solid solutions with La1−xCaxFeO3−δ (0≤x≤0.7) perovskite-like structure prepared via Pechini route have been investigated by using high resolution transmission electron microscopy and X-ray diffraction. Extended planar defects lying in (101) crystallographic planes and α-Fe2O3 nanoparticles on the surface of perovskite microcrystals are characteristic of the samples under investigation. It was found that testing of the samples in catalytic deep CH4 oxidation process results in partial destruction of solid solutions with formation of planar defects in the bulk and α-Fe2O3 particles on the surface.

Thermal oxidative degradation of styrene-butadiene rubber (SBR) studied by 2D correlation analysis and kinetic analysis

The thermal oxidation degradation of styrene–butadiene rubber (SBR) was investigated by in situ FTIR, 2D-FTIR, and programming heating DSC. The results of analyses suggest that the degradation reaction is an autocatalytic process and mainly occurs on the aliphatic part instead of benzene pendants. Based on the results of in situ FTIR and 2D-FTIR, the oxidation process can be divided into three stages. In stage one, just two carbonyl peaks appear, namely 1,697 cm−1 (conjugate carbonyls) and 1,727 cm−1 (saturated carbonyls), and the generation speed is 1,697 > 1,727 cm−1. Yet the peaks appearing at 1,777 cm−1 belonged to peresters and anhydrides generating in stages two and three. The generation sequences are: 1,698 > 1,727 > 1,777 cm−1 for stage two; and 1,698 < 1,727 < 1,777 cm−1 for stage three. According to DSC results, the thermal oxidation of SBR contains four steps. The first step is the generation of alkyl radicals and the accumulation of hydroperoxide species. The second step is initial oxidation stage mainly producing conjugate carbonyls. The third step is deep oxidation process generating diverse carbonyls. The fourth is chain termination reaction, in which step the generation rates of anhydrides and peresters are the fastest due to bi-radical termination of alkoxy radicals and the consumption of conjugate carbonyl. Furthermore, crosslinking reactions occur during the whole thermal oxidation.

Prospects for the development of oxidative catalysis (On the materials of the ninth international conference EuropaCat-IX, 2009 catalysis for a sustainable world)

This article is an overview of the main results of the section on oxidative catalysis, which is one of the most prospective and intensively developing spheres of catalysis. Basic tendencies and achievements in this field of catalysis are shown, results on the investigation of catalysts used in the synthesis of commercially important products including those of fine organic synthesis are analyzed, and the development of partial oxidation catalytic technologies, the search of new catalysts for these processes, and also the application of deep oxidation processes to the solution of environmental problems are considered. Works concerning the synthesis of catalytic systems based on gold nanoparticles are especially emphasized.

Production of intermetallic catalysts of deep CO and hydrocarbon oxidation

The possibility of producing (Ni, Co, Mn) Alx intermetallides using the technique of self-propagating high-temperature synthesis and their subsequent processing with the purpose of using them as catalysis in the process of complete oxidation of CO and hydrocarbons is considered. Phase composition, microstructure, and morphology of alloys and catalysts based on them are studied. Dependences of activity and stability on composition are determined. These catalysts are shown to possess high activity and their development is considered to be a promising direction in the catalysis of deep oxidation processes.

Sialon-supported catalysts for deep oxidation of carbon monoxide and hydrocarbons

Catalysts supported on a new class of supports—β-Sialons Si6 − zAlzOzN8 − z (z = 1, 3, 4) modified with transition-metal oxides—were synthesized and tested in the complete and partial oxidation of hydrocarbons and CO. These Sialons were prepared by self-propagating high-temperature synthesis (SHS). Catalytic activity in the test reactions appeared in systems that contain unary, binary, or ternary mixtures of metal oxides of the second half of the 3d row. Cobalt oxide-based catalysts showed the highest activity. Methods were proposed for activating Sialon supports with a considerable enhancement of the activity of a supported catalyst. More precise investigative tools are required for refining new data and understanding the nature and operation mechanism of Sialons. On account of their high thermal stability and wear resistance, Sialon-supported catalysts are proposed for use in deep oxidation processes in abrasive and acid solutions and at elevated temperatures.

UV radiation effects on pigments, photosynthetic efficiency and DNA of an Antarctic marine benthic diatom community

The impact of ultraviolet radiation (UVR) on a semi-natural, soft-bottom diatom commu- nity from Potter Cove, King Georg Island, Antarctica, was investigated. The objective was to estimate the impact of UV-B (280 to 320 nm) and UV-A (320 to 400 nm) on photosynthetic efficiency, pigments, DNA damage and repair. The diatom community was exposed to different doses of radiation treat- ments: PAR + UV-A + UV-B (PAB), PAR + UV-A (PA) and PAR (P). The most frequently observed spe- cies were Pleurosigma obscurum and Gyrosigma fasciola. Within the 0.7 mm substrate, UV radiation significantly reduced the Photosystem II (PS II) maximum efficiency (Fv/Fm). Complete recovery was observed after 6 h post-cultivation under dim white light. The accumulation of diatoxanthin increased with exposure time for the P and PA treatments, but not for the PAB treatment, indicating a UV-B-related blocking of the de-epoxidation process within the xanthophyll cycling process. The ratio of diatoxanthin:(diatoxanthin+diadinoxanthin) decreased again to initial values after 24 h of recovery. The amount of DNA damage, measured as accumulation of cyclobutane pyrimidine dimers (CPDs), was minimal and increased with increasing UV-B dose, but DNA lesions were completely repaired within 24 h under dim white light. Regardless of possible avoidance strategies, e.g. vertical migration, negative UV treatment effects were observed. However, these effects were transient, facilitated by the dynamic recovery of photoinhibition and an efficient DNA damage repair mecha- nism. Although results from laboratory experiments using artificial radiation can only be extrapolated to field conditions with great caution, we conclude that Antarctic marine benthic diatoms inoculated into a semi-natural habitat are resilient to unnaturally high UVR.