Low-pressure Hg Lamp Research Articles

Photodegradation of micropollutants using V-UV/UV-C processes; Triclosan as a model compound

Non-potable reuse of treated wastewater is becoming widespread as means to address growing water scarcity. Removal of micropollutants (MPs) from such water often requires advanced oxidation processes using OH radicals. OH can be generated in-situ via water photolysis under vacuum-UV (λ<200nm) irradiation.The aim of this study was to investigate the potential of unmasking V-UV radiation from low pressure Hg lamps (emitting at 185 and 254nm), commonly used in decentralized treatment systems, for enhancing MPs removal efficiency. Triclosan, a biocide of limited biodegradability, served as a model compound for MPs that are not very biodegradable. Its degradation kinetics and identification of intermediate products were investigated under 254nm and under combined 254/185nm irradiation both in dry thin films and in aqueous solutions. In the latter, degradation was faster under combined 254/185nm radiation, although the 185nm radiation accounted for only 4% of the total UV light intensity. In contrast, triclosan photodegradation in dry film did not show significant differences between these irradiation wavelengths, suggesting that the enhanced degradation of dissolved triclosan under combined radiation is mainly due to oxidation by OH formed via water photolysis under V-UV. This conclusion was supported by slower TCS degradation in aqueous solution when methanol was added as OH scavenger. Under both irradiation types (254, 254/185nm) three transformation products (TPs) were identified: 2,8-dichlorodibenzo-p-dioxin, 5-chloro-2-(4- or 2-chlorophenoxy)phenol, and 2-hydroxy-8-chlorodibenzodioxin. In-silico QSAR toxicity assessment predicted potential toxicity and moderate-to-low biodegradability of these TPs. Removal of these TPs was faster under 254/185nm irradiation.Considering the low cost, simple operation (i.e. no chemicals addition) and small size of such low-pressure mercury lamps, this is a promising direction. Further investigation of the process in flow-through reactors and real wastewater/greywater effluent is needed for its future implementation in small on-site systems for post-treatment of persistent pollutants.

Effect of temperature on photochemical and thermal changes in calf skin collagen solutions at physiological pH

Effect of temperature on photochemical and thermal changes in calf skin collagen solutions at physiological pH

Impact of the Ultraviolet Photolysis of Monochloramine on 1,4-Dioxane Removal: New Insights into Potable Water Reuse

Although chloramines are ubiquitously present during ultraviolet-driven advanced oxidation processes (UV/AOP) that are becoming increasingly important for potable water reuse, the photochemistry of chloramines in treated wastewater, and the associated effects on trace chemical contaminant degradation, are unknown. This study investigated the fundamental radical chemistry involved in monochloramine (NH2Cl) photolysis and its efficiency in degrading 1,4-dioxane using a low-pressure Hg lamp (λ = 254 nm). These results showed that the UV fluence-normalized rate of 1,4-dioxane degradation in UV/NH2Cl ranged between 1.1 × 10–4 and 2.9 × 10–4 cm2·mJ–1. The photolysis of NH2Cl produced NH2• and Cl•, which further transformed to a series of reactive radical species. An optimal NH2Cl dosage for 1,4-dioxane degradation was observed at a NH2Cl/1,4-dioxane concentration ratio of 8.0, while excess NH2Cl scavenged reactive radicals and decreased the treatment efficiency. Scavenging experiments and probe compound calcula...

On the unexpected reproductive impacts of metformin: A need for support and new directions for the evaluation of the impacts of pharmaceuticals in the environment

Metformin consumption for diabetes treatment is increasing, leading to its presence in wastewater treatment plants where conventional methods cannot remove it. Therefore, this work aims to analyze the performance of advanced oxidation processes using sulfate radicals in the degradation of metformin from water. Experiments were performed in a photoreactor provided with a low-pressure Hg lamp, using K2S2O8 as oxidant and varying the initial metformin concentration (CA0), oxidant concentration (Cox), temperature (T), and pH in a response surface experimental design. The degradation percentages ranged from 26.1 to 87.3%, while the mineralization percentages varied between 15.1 and 64%. Analysis of variance (ANOVA) showed that the output variables were more significantly affected by CA0, Cox, and T. Besides, a reduction of CA0 and an increase of Cox up to 5000 μM maximizes the metformin degradation since the generation of radicals and their interaction with metformin molecules are favored. For the greatest degradation percentage, the first order apparent rate constant achieved was 0.084 min−1. Furthermore, while in acidic pH, temperature benefits metformin degradation, an opposite behavior is obtained in a basic medium because of recombination and inhibition reactions. Moreover, three degradation pathways were suggested based on the six products detected by HPLC-MS: N-cyanoguanidine m/z = 85; N,N-dimethylurea m/z = 89; N,N-dimethyl-cyanamide m/z = 71 N,N-dimethyl-formamide m/z = 74; glicolonitrilo m/z = 58; and guanidine m/z = 60. Finally, it was shown that in general the toxicity of the degradation byproducts was lower than the toxicity of metformin toward Chlamydomonas reinhardtii.

Degradation and fate of N-nitrosamines in water by UV photolysis

Carcinogenic nitrosamines have received much attention due to their formation in CO2 capture processes and probable emission into the atmosphere. Fortunately, nitrosamines are decomposed by exposure to UV irradiation. This may be an effective strategy to degrade nitrosamines, forming more benign products in the process. In this work, UV photolysis was used to examine the degradation kinetics and fate of nitrosamines (i.e., N-nitrosodiethylamine (NDEA), N-nitrosodibutylamine (NDBA), N-nitrosodimethylamine (NDMA), N-nitrosodiethanolamine (NDELA), and N-nitrosopyrrolidine (NPYR)) in water at 40°C. Nearly all nitrosamines were decomposed within the first 10min of photodegradation using 4W, low pressure Hg lamp. Pseudo-first order reaction rate constants were 1.8×10−2, 2.6×10−2, 2.6×10−2, 2.3×10−2, and 1.4×10−2L/W-min for NDEA, NDBA, NDMA, NDELA, and NPYR, respectively. There was minimal change in total organic carbon (TOC) and total nitrogen (TN), suggesting negligible loss of nitrosamines and photodegradation products by evaporation.

Non-OH chemistry in oxidation flow reactors for the study of atmospheric chemistry systematically examined by modeling

Abstract. Oxidation flow reactors (OFRs) using low-pressure Hg lamp emission at 185 and 254 nm produce OH radicals efficiently and are widely used in atmospheric chemistry and other fields. However, knowledge of detailed OFR chemistry is limited, allowing speculation in the literature about whether some non-OH reactants, including several not relevant for tropospheric chemistry, may play an important role in these OFRs. These non-OH reactants are UV radiation, O(1D), O(3P), and O3. In this study, we investigate the relative importance of other reactants to OH for the fate of reactant species in OFR under a wide range of conditions via box modeling. The relative importance of non-OH species is less sensitive to UV light intensity than to water vapor mixing ratio (H2O) and external OH reactivity (OHRext), as both non-OH reactants and OH scale roughly proportionally to UV intensity. We show that for field studies in forested regions and also the urban area of Los Angeles, reactants of atmospheric interest are predominantly consumed by OH. We find that O(1D), O(3P), and O3 have relative contributions to volatile organic compound (VOC) consumption that are similar or lower than in the troposphere. The impact of O atoms can be neglected under most conditions in both OFR and troposphere. We define “riskier OFR conditions” as those with either low H2O (&lt; 0.1 %) or high OHRext ( ≥ 100 s−1 in OFR185 and &gt; 200 s−1 in OFR254). We strongly suggest avoiding such conditions as the importance of non-OH reactants can be substantial for the most sensitive species, although OH may still dominate under some riskier conditions, depending on the species present. Photolysis at non-tropospheric wavelengths (185 and 254 nm) may play a significant (&gt; 20 %) role in the degradation of some aromatics, as well as some oxidation intermediates, under riskier reactor conditions, if the quantum yields are high. Under riskier conditions, some biogenics can have substantial destructions by O3, similarly to the troposphere. Working under low O2 (volume mixing ratio of 0.002) with the OFR185 mode allows OH to completely dominate over O3 reactions even for the biogenic species most reactive with O3. Non-tropospheric VOC photolysis may have been a problem in some laboratory and source studies, but can be avoided or lessened in future studies by diluting source emissions and working at lower precursor concentrations in laboratory studies and by humidification. Photolysis of secondary organic aerosol (SOA) samples is estimated to be significant (&gt; 20 %) under the upper limit assumption of unity quantum yield at medium (1 × 1013 and 1.5 × 1015 photons cm−2 s−1 at 185 and 254 nm, respectively) or higher UV flux settings. The need for quantum yield measurements of both VOC and SOA photolysis is highlighted in this study. The results of this study allow improved OFR operation and experimental design and also inform the design of future reactors.

HO&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt; radical chemistry in oxidation flow reactors with low-pressure mercury lamps systematically examined by modeling

Abstract. Oxidation flow reactors (OFRs) using OH produced from low-pressure Hg lamps at 254 nm (OFR254) or both 185 and 254 nm (OFR185) are commonly used in atmospheric chemistry and other fields. OFR254 requires the addition of externally formed O3 since OH is formed from O3 photolysis, while OFR185 does not since O2 can be photolyzed to produce O3, and OH can also be formed from H2O photolysis. In this study, we use a plug-flow kinetic model to investigate OFR properties under a very wide range of conditions applicable to both field and laboratory studies. We show that the radical chemistry in OFRs can be characterized as a function of UV light intensity, H2O concentration, and total external OH reactivity (OHRext, e.g., from volatile organic compounds (VOCs), NOx, and SO2). OH exposure is decreased by added external OH reactivity. OFR185 is especially sensitive to this effect at low UV intensity due to low primary OH production. OFR254 can be more resilient against OH suppression at high injected O3 (e.g., 70 ppm), as a larger primary OH source from O3, as well as enhanced recycling of HO2 to OH, make external perturbations to the radical chemistry less significant. However if the external OH reactivity in OFR254 is much larger than OH reactivity from injected O3, OH suppression can reach 2 orders of magnitude. For a typical input of 7 ppm O3 (OHRO3 = 10 s−1), 10-fold OH suppression is observed at OHRext ~ 100 s−1, which is similar or lower than used in many laboratory studies. The range of modeled OH suppression for literature experiments is consistent with the measured values except for those with isoprene. The finding on OH suppression may have important implications for the interpretation of past laboratory studies, as applying OHexp measurements acquired under different conditions could lead to over a 1-order-of-magnitude error in the estimated OHexp. The uncertainties of key model outputs due to uncertainty in all rate constants and absorption cross-sections in the model are within ±25 % for OH exposure and within ±60 % for other parameters. These uncertainties are small relative to the dynamic range of outputs. Uncertainty analysis shows that most of the uncertainty is contributed by photolysis rates of O3, O2, and H2O and reactions of OH and HO2 with themselves or with some abundant species, i.e., O3 and H2O2. OHexp calculated from direct integration and estimated from SO2 decay in the model with laminar and measured residence time distributions (RTDs) are generally within a factor of 2 from the plug-flow OHexp. However, in the models with RTDs, OHexp estimated from SO2 is systematically lower than directly integrated OHexp in the case of significant SO2 consumption. We thus recommended using OHexp estimated from the decay of the species under study when possible, to obtain the most appropriate information on photochemical aging in the OFR. Using HOx-recycling vs. destructive external OH reactivity only leads to small changes in OHexp under most conditions. Changing the identity (rate constant) of external OH reactants can result in substantial changes in OHexp due to different reductions in OH suppression as the reactant is consumed. We also report two equations for estimating OH exposure in OFR254. We find that the equation estimating OHexp from measured O3 consumption performs better than an alternative equation that does not use it, and thus recommend measuring both input and output O3 concentrations in OFR254 experiments. This study contributes to establishing a firm and systematic understanding of the gas-phase HOx and Ox chemistry in these reactors, and enables better experiment planning and interpretation as well as improved design of future reactors.

UV photo-chlorination and -bromination of single-walled carbon nanotubes

Abstract

Fabrication of thermochromic composite films using transition temperature controlled VO&lt;sub&gt;2&lt;/sub&gt; fine particles

mixing ratios of 0.2vol%. The mixture wasdegassed under a pressure of 1kPa for 1h to expel the dissolvedair introduced during the mixing process. The mixed precursorslurry was placed between flat slide glasses, controlling the pre-cursor film thickness to 80¯m. The composite was cured byirradiation with a 1kW low-pressure Hg lamp (UV­visible light)and VO

Reductive Bromine Atom-Transfer Reaction

Atom-transfer radical (ATR) reactions of alkenes with R-X usually give products having new C-C and C-X bonds at the adjacent carbons. However, when the reaction was carried out under irradiation using a low-pressure Hg lamp, addition/reduction products were obtained in good yield. Hydrogen bromide, formed by H-abstraction of a bromine radical from alkenes, is likely to play a key role in the reductive ATR reaction.

Raman spectroscopy study on the reactions of UV-generated oxygen atoms with single-layer graphene on SiO2/Si substrates

Successful application of graphene requires development of various tools for its chemical modification. In this paper, we present a Raman spectroscopic investigation of the effects of UV light on single layer graphene with and without the presence of <TEX>$O_2$</TEX> molecules. The UV emission from a low pressure Hg lamp photolyzes <TEX>$O_2$</TEX> molecules into O atoms, which are known to form epoxy on the basal plane of graphene. The resulting surface epoxy groups were identified by the disorder-related Raman D band. It was also found that adhesive residues present in the graphene samples prepared by micro-mechanical exfoliation using adhesive tape severely interfere with the O atom reaction with graphene. The UV-induced reaction was also successfully applied to chemical vapor deposition-grown graphene. Since the current method can be readily carried out in ambient air only with UV light, it will be useful in modifying the surfaces of graphene and related materials.

Solar-blind photodetectors based on polycrystalline MgZnO thin films

Photoconductive metal-semiconductor-metal ultraviolet detectors were fabricated based on the polycrystalline MgZnO films, which were grown on SiO2/Si substrates by radio frequency magnetron sputtering. The peak response of the detector was at 300 nm, which lay in the solar-blind spectrum range (220 to 300 nm). And the peak responsivity was 34.02 A/W. The ratio of Iph/Id was as high as 2659.7 at 5 V bias under a low pressure Hg lamp illumination. And a rise time of 44.48 μs (90%) and fall time of 120.2 ms (10%) of the detector were acquired.

Microwave discharge electrodeless lamps (MDELs). VI. Performance evaluation of a novel microwave discharge granulated electrodeless lamp (MDGEL)—Photoassisted defluorination of perfluoroalkoxy acids in aqueous media

Novel microwave discharge granulated electrodeless lamps (MDGELs; 5 mm × 10 mm), fabricated using vacuum-UV (VUV) transparent quartz envelopes, have been examined for the treatment of model contaminated wastewaters. Evaluation of these MDGELs was performed through the self-ignition of the lamps at low microwave power levels and by the photoassisted decomposition and defluorination of trifluoroacetic acid (TFA), heptafluorobutyric acid (HFBA) and perfluorooctanoic acid (PFOA) in aqueous solutions in a flow-through microwave photoreactor (MW/Photo) containing 20 such MDGELs. A conventional single rod-shaped microwave discharge electrodeless lamp (MDEL) and a low-pressure electrode Hg lamp were also used to compare the performance of these novel MDGELs. The dominant performance of the MDGELs was established by the defluorination kinetics per surface area of the light source immersed in the solutions and by the applied electric power of the lamps. At pH 10, the kinetics correlated with the carbon chain length and with the number of C–F bonds in the three fluorinated acids. Microwave irradiation of the single rod-shaped MDEL device achieved a defluorination level of 51% (TFA), 67% (HFBA), and 37% (PFOA) for a 240-min VUV/UV irradiation of solutions at initial pHs = 4.7–5.2, whereas at pH = 10 defluorination of TFA and HFBA was 100% complete within 120–135 min of irradiation; defluorination of PFOA was ca. 80% complete after 200 min. With the 20 MDGEL system, 100% defluorination of TFA and HFBA was achieved after 105 min, whereas 100% defluorination of PFOA required ca. 400 min of irradiation. A decomposition/defluorination pathway is described for PFOA on the basis of intermediates identified by LC–MS techniques that involved initial VUV/UV irradiation (185 nm and 254 nm) of the PFOA contaminant followed by subsequent losses of CO 2 and –CF 2 units to complete defluorination and degradation.

Comparison of four advanced oxidation processes for the removal of naphthenic acids from model oil sands process water

Four advanced oxidation processes (UV/TiO 2, UV/IO 4 −, UV/S 2O 8 2−, and UV/H 2O 2) were tested for their ability to mineralize naphthenic acids to inorganic carbon in a model oil sands process water containing high dissolved and suspended solids at pH values ranging from 8 to 12. A medium pressure mercury (Hg) lamp was used, and a Quartz immersion well surrounded the lamp. The treatment goal of 5 mg/L naphthenic acids (3.4 mg/L total organic carbon (TOC)) was achieved under four conditions: UV/S 2O 8 2− (20 mM) at pH 8 and 10, and UV/H 2O 2 (50 mM) at pH 8 (all with the Quartz immersion well). Values of electrical energy required to meet the treatment goal were about equal for UV/S 2O 8 2− (20 mM) and UV/H 2O 2 (50 mM) at pH 8, but three to four times larger for treatment by UV/S 2O 8 2− (20 mM) at pH 10. The treatment goal was also achieved using UV/S 2O 8 2− (20 mM) at pH 10 when using a Vycor filter that transmits light primarily in the mid and near UV, suggesting that that treatment of naphthenic acids by UV/S 2O 8 2− using low pressure Hg lamps may be feasible.

Aerosol Charging Using Pen-Type UV Lamps

A portable aerosol charger utilizing pen-type Hg lamps was constructed to investigate the particle charging process under UV irradiation. The charger primarily consisted of a quartz tube surrounded by four pen-type low-pressure Hg lamps and an ion trap located downstream of the quartz tube to remove excessive ions. The performance of the prototype UV charger at 5 L/min flow rate and with four UV lamps turned on using monodisperse silver (Ag) particles with diameters ranging from 7 to 30 nm was evaluated. As expected, the prototype UV charger provided higher particle charging efficiencies than corona-based unipolar chargers for Ag particles. To evaluate the effect of irradiation intensity on particle photocharging, the charging efficiencies and charge distributions for Ag particles ranged from 7 to 30 nm when the prototype was operated at an aerosol flow rate of 5 L/min for the cases of one, two, and four lamps turned on. The UV charging model with the photoemission based on the Fowler-Nordheim law was further applied to predict the charging performance of the UV charger at different operational conditions.

Modeling and experimental evaluation of vacuum-UV photoreactors for water treatment

Vacuum-UV (VUV) radiation is a promising and effective technology for the oxidation of organic contaminants. The VUV-induced degradation of a model pollutant, Formic Acid (FA), was modeled and experimentally investigated. Experimental work involved an annular flow-through reactor operated in batch mode with complete recycle of the reactants. Ozone-producing low-pressure Hg lamps were used as the source of VUV radiation. FA concentrations of up to 0.55 mmol L −1 were completely degraded after 40 min of irradiation. FA degradation was accompanied by the formation of H 2O 2 at concentrations of about 0.3 mmol L −1. Kinetic and radiation models were combined with the corresponding mass balances to describe the experimental results. The kinetic model accounted for the most important reactions occurring in the system, including photolysis of water and H 2O 2, side reactions between radicals, and degradation of FA. The radiation model, which was solved using the Monte Carlo method, described the propagation of photons in the reactor volume and took into account the optical properties of the solution and the emission power of the lamps, obtained by actimometry. Modeling simulations fit experimental data of FA degradation using VUV, H 2O 2/VUV, and H 2O 2/UV with a root mean square error of 7.4%. According to modeling and experimental results, the VUV-induced degradation of FA followed an apparent zero order kinetics, a fact that may suggest the reaction was limited by the availability of hydroxyl radicals (HO ).

Microwave Discharge Electrodeless Lamps (MDEL). V. Microwave-assisted Photolytic Disinfection of Bacillus Subtilis in Simulated Electroplating Wash Wastewaters

This short article examines the microwave-assisted photolytic disinfection of aqueous solutions contaminated by Bacillus subtilis microorganisms using UV and vacuum-UV radiation emitted from a microwave discharge electrodeless lamp (MDEL), a device containing a Hg/Ar gas-fill that was proposed recently for use in Advanced Oxidation Processes (AOPs). Results of the disinfection are compared with those obtained from UV radiation emitted by a low-pressure electrode Hg lamp and by an excimer lamp. Also examined is the disinfection of B. subtilis aqueous media that contained Au3+ or Ni2+ ions, species often found in the treatment of electroplating wash wastewaters.

Factors influencing the photodegradation of N-nitrosodimethylamine in drinking water

In order to provide basic data for practical application, photodegradation experiment of N-nitrosodimethylamine (NDMA) in aqueous solution was carried out with a low-pressure Hg lamp. Effects of the initial concentration of NDMA, solution pH, dissolved oxygen, and the presence of humic acid on NDMA photodegradation were investigated. NDMA at various initial concentrations selected in this study was almost completely photodegraded by UV irradiation within 20 min, except that at 1.07 mmol/L, NDMA could be photodegraded almost completely in the acidic and neutral solutions, while the removal efficiency decreased remarkably in the alkaline solution. Dissolved oxygen enhanced the NDMA photodegradation, and the presence of humic acid inhibited the degradation of NDMA. Depending on the initial concentration of NDMA, NDMA photodegradation by UV obeyed the pseudo-first-order kinetics. Dimethylamine, nitrite, and nitrate were detected as the photodegradation products of NDMA. 1O2 was found to be the reactive oxygen species present in the NDMA photodegradation process by UV, based on the inhibiting experiments using tert-butanol and sodium azide.

Photoluminescence Properties of Ba3MgSi2O8 : Eu2 + Blue Phosphor and Ba3MgSi2O8 : Eu2 + , Mn2 + Blue-Red Phosphor under Near-Ultraviolet-Light Excitation

Photoluminescence (PL) properties of (BMS-E) blue phosphor and (BMS-EM) blue-red phosphor under near-UV-light excitation were investigated. BMS-E shows efficient blue-violet emission at under light excitation. The sample doped with shows PL peak intensity about twice higher than a commercial (BAM) for low-pressure Hg lamps. The PL integrated intensity of BMS-E below of Eu content is similar to that of BAM in magnitude of thermal quenching. BMS-EM shows strong red emission under light excitation because of the efficient energy transfer from to . The sample doped with and shows luminance about 12 and 3 times larger than and , respectively. Moreover, the PL integrated intensity of the BMS-EM shows less thermal quenching than that of and . These results indicate that BMS-E and BMS-EM are promising phosphors for white light-emitting diodes (LEDs) fabricated with near-UV LEDs.

Optimization of the removal efficiency of nitrogen oxides in the air using a low-pressure Hg lamp

The photo-oxidation of gaseous nitrogen oxide (NO x ) by a low-pressure Hg lamp (UV 254+185 nm ) irradiation was studied. Nitric oxide gas (NO) was rapidly converted to nitrogen dioxide (NO 2) to form nitric acid (HNO 3) by continuous reactions with ozone and hydroxyl radicals which are produced by UV 254+185 nm irradiation. Because HNO 3 is water-soluble, it can easily be removed by water spray. It was found that high removal efficiency of NO x was recorded at the reaction conditions of humidity above 40% and the reaction temperature below 100 °C. NO x removal efficiency increases with lower inlet concentration and longer residence time. The conversion of NO 2 to HNO 3 by UV 254+185 nm irradiation was easier than that of NO, which indicates that the pre-oxidation of NO to NO 2 might be effective for enhancing the amount of NO x removal.