UV Photodegradation Research Articles

Water matrix effect on UV photodegradation of perfluorooctanoic acid

The widespread detection of perfluorinated compounds (PFCs) in the water environment has been a concern for the last several years, while effluents from wastewater treatment facilities are the major sources of these compounds. Even advanced oxidation technologies (AOTs) are not useful for mineralization of the compounds due to their very high stability. Photochemical techniques using particularly vacuum UV (VUV) have been found to be very promising in this regard. But the use of VUV in UV-based AOTs has still not progressed much. Moreover, the impact of water quality on PFCs photomineralization is unknown. This investigation aimed to assess photomineralization potentials of perfluorooctanoic acid (PFOA) in ultrapure water (UPW), tap water (TW), surface water and treated wastewater effluent using a reactor setup enabling maximum utilization of VUV emission of low pressure lamp in laboratory batch experiments. Neya River water (NRW) and the Nakahama Wastewater Treatment Plant Effluent (NWWTPE) represented surface water and treated wastewater effluent respectively. Also, tests were carried out in 50% diluted NRW and NWWTPE. PFOA photomineralization in terms of PFOA removal, defluorination and total organic carbon (TOC) removal are discussed. The usefulness of the method for PFOA mineralization in organic-rich wastewaters, and further research needs are also highlighted.

Recovery of biological removal of gaseous alpha-pinene in long-term vapor-phase bioreactors by UV photodegradation

Excessive biomass accumulation and bio-activity loss in biofilter (BF) and biotrickling filter (BTF) can lead to unreliable long-term operation. In this study, UV photodegradation was developed as a strategy of controlling biomass accumulation to recover BF and BTF for the treatment of gaseous alpha-pinene (α-pinene) over long-term period. With the addition of UV, an overall efficiency of more than 85% was re-achieved in BTF since excessive biomass was removed. Due to continuous positive effects by UV photodegradation, biomass concentration in the BTF was kept at a normal level (9.25–9.58 kg m −3 dry carrier), and the maximum elimination capacity and CO 2 production increased by 4.2 and 6.2 times that achieved by the deteriorated BTF. Microbial analysis revealed that microbial community structure in BTF became more complicated with the addition of UV photodegradation. Kinetic analysis indicated that photodegradation could improve the removal process of α-pinene in BTF. Contrarily, UV photodegradation could not recover BF based on similar experiments. These findings provided a potential use of UV photodegradation for maintenance of biotrickling filtration efficient for gaseous pollutants removal over long-term operation.

Effects of Adding UV and H2O2on the Degradation of Pharmaceuticals and Personal Care Products during O3Treatment

The degradation of 30 pharmaceuticals and personal care products (PPCPs) subjected to O3, O3/UV, and O3/H2O2 treatments were investigated using semi-batch tests and evaluated by their pseudo-first-order rate constants. The additional application of UV or H 2 O 2 during O3 treatment significantly improved the degradation rate of most of the PPCPs. At the same O 3 feed rate, O3/UV treatment exhibited much higher PPCP degradation efficiency than that of O 3 treatment. This was probably due to degradation of the PPCPs by O3, direct UV photodegradation, and OH radicals that formed from the photodegradation of O3 during O3/UV treatment. PPCP degradation by O 3 was also promoted by adding H 2 O 2 during the O 3 treatment. However, when the initial H 2 O 2 concentration was high during O3 treatment, OH radicals were likely to be scavenged by excess H2O2, leading to low PPCP degradation. Therefore, it is important to determine the appropriate H 2 O 2 dosage during O 3 treatment to improve PPCP degradation when adding H 2 O 2 during O 3 treatment.

Photodegradation of emamectin benzoate and its influence on efficacy against the rice stem borer, Chilo suppressalis

Emamectin benzoate, a novel insecticide with characteristics of translaminar movement into plant leaf tissue, was derived from the avermectin family with improved thermal stability, greater water solubility and a broader spectrum of insecticidal activity than avermectin. To quantify UV photodegradation of emamectin benzoate, HPLC analysis was conducted to quantify residues of MAB1a, the major component in emamectin benzoate, after exposure to UV light for different lengths of time. Results showed both MAB1a concentration and length of UV light exposure (0–120 h) had significant impacts on photodegradation rate. The degradation rate increased as exposure duration increased, but decreased as initial MAB1a concentration increased. Four UV protectants, kojic acid, sodium ligninsulfonate, soybean lecithin and milk, were evaluated for their effect on UV degradation. Results showed that kojic acid could effectively reduce the photodegradation of MAB1a. In addition, the photodegradation of emamectin benzoate was also examined for its influence on the efficacy against the rice stem borer, Chilo suppressalis. The results of the bioassays were consistent with those of HPLC analysis. The initial concentration of emamectin benzoate and exposure duration to UV light both had significant influences on the efficacy against C. suppressalis. As the UV exposure time increased, the efficacy of emamectin benzoate against C. suppressalis decreased. The results indicated that UV photodegradation has a significant effect on the efficacy of emamectin benzoate against C. suppressalis and the effect is concentration-dependant. In addition to understanding the critical factor of UV exposure length, this study also showed that maintaining emamectin benzoate concentration above a certain level in the formulation and the application solution, and applying UV protectants may reduce photodegradation and increase efficacy against target pests.

Self-Cleaning Tests of Zn-Fe/Anatase-Coated Glass Plates under Direct and Diffuse Sunlight

Thin films of anatase (TiO2) doped with 1 wt. percent of zinc ferrite (ZnFe2O4) were formed on glass plates by deposition of a sol-gel mixture using an ultra-spinning technique. After the preparation, the TiO2 films with a thickness of 168-232 nm were investigated with respect to their UV absorption capability and photo-degradation of organic molecules. Microscope observations of the surface of TiO2 films showed that they exhibit a micro-granular surface. To test the self-cleaning properties of the doped TiO2 films, a layer of fluoranthene of around 6.5 mg was sprayed over the glass and then exposed to direct or diffuse solar radiation. While the coated-glass transparency was totally recovered at 88 h of direct solar exposure for the undoped anatase film, the covering of fluoranthene on the 1 wt. percent ZnFe2O4-doped TiO2 film was degraded totally at 52 h of exposure time. As complementary experiments, the same glass plates with metal oxide-doped anatase films, after spraying with a similar layer of the organic contaminant, were placed under diffuse sunlight. In a typical experiment, the covering of fluoranthene was degraded almost 100 percent at an exposure time of 48 days and the transparency of glass plates was recovered totally at 55 days of indirect solar exposure. A correlation was found between the weight losses of the solid contaminant and the intensity of the Raman vibration at 672 cm-1. It was found that under diffuse solar irradiation is possible to remove completely a fluoranthene layer generating an expected application of these active surfaces under extreme conditions.

Self-Cleaning Tests of Zn-Fe/Anatase-Coated Glass Plates under Direct and Diffuse Sunlight

Thin films of anatase (TiO2) doped with 1 wt. percent of zinc ferrite (ZnFe2O4) were formed on glass plates by deposition of a sol-gel mixture using an ultra-spinning technique. After the preparation, the TiO2 films with a thickness of 168-232 nm were investigated with respect to their UV absorption capability and photo-degradation of organic molecules. Microscope observations of the surface of TiO2 films showed that they exhibit a micro-granular surface. To test the self-cleaning properties of the doped TiO2 films, a layer of fluoranthene of around 6.5 mg was sprayed over the glass and then exposed to direct or diffuse solar radiation. While the coated-glass transparency was totally recovered at 88 h of direct solar exposure for the undoped anatase film, the covering of fluoranthene on the 1 wt. percent ZnFe2O4-doped TiO2 film was degraded totally at 52 h of exposure time. As complementary experiments, the same glass plates with metal oxide-doped anatase films, after spraying with a similar layer of the organic contaminant, were placed under diffuse sunlight. In a typical experiment, the covering of fluoranthene was degraded almost 100 percent at an exposure time of 48 days and the transparency of glass plates was recovered totally at 55 days of indirect solar exposure. A correlation was found between the weight losses of the solid contaminant and the intensity of the Raman vibration at 672 cm-1. It was found that under diffuse solar irradiation is possible to remove completely a fluoranthene layer generating an expected application of these active surfaces under extreme conditions.

Novel properties of PES fabrics modified by corona discharge and colloidal TiO2 nanoparticles

AbstractThe objective of this study was to highlight the potential application of the corona discharge at atmospheric pressure for the surface activation of polyester (PES) fabrics in order to improve the binding efficiency of colloidal TiO2 nanoparticles. The obtained nanocomposite textile materials provide desirable level of UV protection, self‐cleaning properties, and photodegradation activity. The measured UV protection factor (UPF) of fabrics corresponds to UPF rating of 50+, designating the maximum UV protection. Additionally, the total photodegradation of methylene blue in aqueous solution was achieved after 24 hr of UV illumination and this capability was preserved and even improved after four repeated cycles. The results showed that the corona treated PES fabrics loaded with TiO2 nanoparticles had considerably enhanced the overall efficiency compared to PES fabrics loaded only with TiO2 nanoparticles. Copyright © 2009 John Wiley & Sons, Ltd.

Tetrakis-2,3-[5,6-di-(2-pyridyl)-pyrazino]porphyrazine, and its Cu(II) complex as sensitizers in the TiO 2-based photo-degradation of 4-nitrophenol

The tetrapyrrolic macrocycle tetrakis-2,3-[5,6-di-(2-pyridyl)-pyrazino]porphyrazine, [Py 8TPyzPzH 2], and its copper(II) derivative, [Py 8TPyzPzCu] were used as sensitizers adsorbed on TiO 2 (anatase) particles for the UV (300–400 nm) photo-degradation of 4-nitrophenol (4-NP) in water suspensions. A 3.5-fold increase of photocatalytic power over bare TiO 2-anatase has been observed in the case of the Cu(II) complex and of more than a factor of two for the free base. Compared with previous data obtained with anatase samples impregnated with some structurally similar porphyrins and phthalocyanines derivatives, these results represent a significant improvement. On the contrary, upon impregnation with [Py 8TPyzPzCu], both TiO 2-rutile and TiO 2-Degussa P25 did not show any improvement of their photocatalytic efficiency. Experimental evidences indicate that formation of singlet oxygen does not contribute to the beneficial effect of the macrocycles. Hydrogen peroxide was found not to participate to the 4-NP depletion. Some photo-bleaching of the adsorbed dye has also been observed.

Morphology and photocatalysis of mesoporous titania thin films annealed in different atmosphere for degradation of methyl orange

The effect of different annealing atmosphere on the morphology and photocatalytic activity of mesoporous TiO2 thin films by dip-coating technique is investigated. The annealing temperature and atmosphere causes significant change of the morphology, thermal stability, photoluminescence, and photocatalytic properties of mesoporous TiO2 films. As-prepared mesoporous thin films have an amorphous structure that is transformed to crystalline TiO2 with well-maintained mesoporous structure at 450°C in various annealing atmosphere except that the mesoporous structure is fully destroyed for films annealed in air. Films annealed in N2 show the enhanced UV photodegradation of methyl orange (MO) resulting from the enhanced crystallinity in these films evidenced by XRD and Raman spectra. These findings can be used to tailor the structure and morphology of mesoporous TiO2 films and thus improve their photocatalytic activity for efficient removal of dye effluents in wastewater.

Spectroscopic evidence of photodegradation by ultraviolet exposure of tris(8-hydroxyquinoline) aluminum (Alq3) thin films

The extrinsic degradation of organic light emitting diodes (OLEDs) remains a critical issue especially concerning degradation due to exposure to light. Very few studies exist and little is known about the related photodegradation products and mechanisms, responsible for quenching of luminescence. In order to gain insight into the degradation mechanisms caused by light exposure of Alq3 thin films, used successfully as electron transport layer and emissive material in the fabrication of OLEDs, we have monitored UV photodegradation through synchrotron radiation-based photoabsorption and photoemission techniques at the carbon, nitrogen, and oxygen 1s edges as well as at the aluminum 2s and 2p edges. The influence of light exposure was simulated using three different wavelengths, namely 254, 365 and 307 nm, the first two nearly corresponding to absorption maxima in the UV spectrum of Alq3. After exposure all spectra show decrease of the photoabsorption and photoemission signals. However, while irradiation at 307 nm causes lesser changes in the total electron yield NEXAFS spectra, strong spectral modifications are observed for 254 and 365 nm exposures. Core level photoemission measurements from non-irradiated and irradiated Alq3 thin films at 307 nm were also performed. While the Al peaks maintained almost intact, changes in peak intensities as well as shifts for carbon, nitrogen and oxygen are much more dramatic.

UV photocatalytic oxidation of paint solvent compounds in air using an annular TiO2-supported reactor

BACKGROUND: One of the most important industrial sources of volatile organic compounds (VOCs) is related to coating and painting applications. In this sense, photocatalytic oxidation can become an innovative and promising alternative for the remediation of air polluted by VOCs. In this study the UV photodegradation of m-xylene, toluene and n-butyl acetate, as representative compounds of paint solvents, was carried out in an annular reactor using a TiO2–glass wool supported catalyst. RESULTS The removal of each component and their mixture, simulating an industrial emission, was evaluated under different operational conditions. A maximum elimination capacity of 12, 18 and 80 mg C m−3 s−1 was reached for m-xylene, toluene and n-butyl acetate, respectively. A simple Langmuir–Hinshelwood kinetic model was used to match the experimental data. Photocatalytic oxidation was found to be more effective for all compounds when humidified air was used. CONCLUSIONS: No mass transfer limitation was found under the experimental conditions. n-butyl acetate was the easiest to degrade and m-xylene the most recalcitrant. In the abatement of the mixture, competitive adsorption between the pollutants was observed, with the degradation of toluene especially hindered. A nearly linear correlation was found between the UV light intensity and kinetic constants. Copyright © 2010 Society of Chemical Industry

Photocatalytic degradation activity of titanium dioxide sol–gel coatings on stainless steel wire meshes

Stainless steel wire meshes have been functionalised with multiple titanium dioxide (TiO 2) coatings deposited by the sol–gel technique, using titanium isopropoxide as precursor and titanium dioxide nanopowders dispersed in the colloidal solution. After the thermal conversion of the amorphous fraction of the coating into anatase, the functionalised stainless steel wire meshes were tested for the UV photodegradation of aqueous solutions of methylene blue, solid stearic acid and nitrogen oxides in air. The addition of TiO 2 nanopowders in the colloidal deposition solution enhanced the photocatalytic performance of the deposited TiO 2 layers in all the tested conditions. Moreover, increasing the number of coatings (from 1 to 4) improves the photocatalytic efficiency. The catalyst did not show reduced photoreactivity after four repeated cycles in water decontamination from methylene blue, and after up to 10 repeated cycles in nitrogen oxides photodegradation. Complete regeneration of the catalyst could be achieved by rinsing it with warm deionised water and was observed in the case of experiments for NO x abatement.

Protein Patterning by UV-Induced Photodegradation of Poly(oligo(ethylene glycol) methacrylate) Brushes

The UV photodegradation of protein-resistant poly(oligo(ethylene glycol) methacrylate) (POEGMA) bottle-brush films, grown on silicon oxide by surface-initiated atom radical transfer polymerization, was studied using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Exposure to light with a wavelength of 244 nm caused a loss of polyether units from the brush structure and the creation of aldehyde groups that could be derivatized with amines. An increase was measured in the coefficient of friction of the photodegraded polymer brush compared to the native brush, attributed to the creation of a heterogeneous surface film, leading to increased energy dissipation through film deformation and the creation of new polar functional groups at the surface. Exposure of the films through a photomask yielded sharp, well-defined patterns. Analysis of topographical images showed that physical removal of material occurred during exposure, at a rate of 1.35 nm J(-1) cm(2). Using fluorescence microscopy, the adsorption of labeled proteins onto the exposed surfaces was studied. It was found that protein strongly adsorbed to exposed areas, while the masked regions retained their protein resistance. Exposure of the film to UV light from a scanning near-field optical microscope yielded submicrometer-scale patterns. These data indicate that a simple, rapid, one-step photoconversion of the poly(OEGMA) brush occurs that transforms it from a highly protein-resistant material to one that adsorbs protein and can covalently bind amine-containing molecules and that this photoconversion can be spatially addressed with high spatial resolution.

Investigation of the photochemical behaviour of pyrethroids lacking the cyclopropane ring by photo‐solid‐phase microextraction and gas chromatography/mass spectrometry

The characterization of by-products arising from the UV photodegradation of two insecticide pyrethroids lacking the cyclopropane ring (flucythrinate and fenvalerate) has been investigated by gas chromatography coupled with mass spectrometry (GC/MS). Twenty photoproducts were tentatively identified mainly based on the interpretation of the experimental mass spectra or by using reference mass spectra. Some of these compounds had not previously been detected. Furthermore, the generation of some of the photoproducts might be a matter for concern due to their potential toxicity. The corresponding photodegradation routes, including postulation of the intermediate radicals, have also been proposed. These photodegradation studies were performed by photo-solid-phase microextraction (photo-SPME) in which the SPME fibre was exposed to light after extraction of the target analytes from aqueous solutions. The degradation kinetics of the investigated pyrethroids and the photoformation-photodegradation curves of the photoproducts generated in situ were also monitored through the ion chromatograms obtained for different irradiation times and the corresponding mass spectra.

Experimental and model comparisons of H2O2 assisted UV photodegradation of Microcystin-LR in simulated drinking water

The degradation of Microcystin-LR (MC-LR) in water by hydrogen peroxide assisted ultraviolet (UV/H2O2) process was investigated in this paper. The UV/H2O2 process appeared to be effective in removal of the MC-LR. MC-LR decomposition was primarily ascribed to production of strong and nonselective oxidant-hydroxyl radicals within the system. The intensity of UV radiation, initial concentration of MC-LR, MC-LR purity, dosages of H2O2, the initial solution pH, and anions present in water, to some extent, influenced the degradation rate of MC-LR. A modified pseudo-first-order kinetic model was developed to predict the removal efficiency under different experimental conditions.

Advantages of combined UV photodegradation and biofiltration processes to treat gaseous chlorobenzene

A combined ultraviolet photodegradation and biofiltration (UV-BF) process was developed to treat gaseous chlorobenzene. The performance of this process was evaluated under various operating conditions, including different inlet concentrations, residence times, and transient loadings, and compared with a control biofiltration (BF) process. Furthermore, the acute biotoxicities of the photodegradation products, the bioaerosol emissions from biofilters, the biomass accumulation and pressure drop in biofilters were investigated. The experimental results showed that the UV-BF process provided higher removal efficiencies than those of the control BF process over an inlet concentration range of 250–1500 mg m −3 for residence times of 41–122 s inside the biofilters and 24–81 s inside the UV reactor. After UV pretreatment, removal rates of the subsequent biofilter increased linearly with biofilter inlet loading, even beyond 50 g m −3 h −1. Similar inlet loading resulted in a gradual decline of removal rates for the control process due to a substrate inhibition effect. These results suggested that UV pretreatment reduced the inhibitory effects of chlorobenzene on microorganisms inside biofilters. Transient loading conditions were tested by increasing the inlet concentration from 1000 to 2500 mg m −3 or shifting the gas flow rate from 0.1 to 0.3 m 3 h −1, which led to reduced outlet concentrations in the UV-BF process compared with those of the control BF process. The standalone UV photodegradation of chlorobenzene can produce products with significant acute biotoxicity. Acute biotoxicities as high as 12 mg-Zn 2+ L −1 were measured. Biotoxicity levels were reduced to less than 5 mg-Zn 2+ L −1 after the biofilter. Ozone, a by-product produced during the UV photodegradation process, contributed to a reduction in bioaerosol emission from the biofilters and helped to control the biomass, thus slowing down the pressure drop increase in the biofilters.

Di-(2-Ethylhexyl)Phthalate Leakage and Color Changes in Endotracheal Tubes after Application in High-Risk Newborns

Background: Polyvinylchloride (PVC) is often adopted for making medical devices. Objective: Testing the hypothesis that materials degradation occurs in PVC endotracheal tubes during infant ventilation, thus releasing the known toxic plasticizer di-(2-ethylhexyl)phthalate (DEHP). Materials and Methods: Endotracheal tubes degradation was assessed by: (1) analysis of color and spectral changes in endotracheal tubes after use in the 400- to 700-nm range and compared to virgin samples. Color changes were expressed as euclidean distances in the Commission International de l’Eclairage Laboratory and Lightness-Chroma-Hue (Munsell’s) color spaces (i.e., ΔE, ΔL, Δa, Δb, ΔC, and ΔH units); (2) DEHP leakage was assessed by thermal characterization by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Data from used tubes were compared with those from either virgin devices or submitted to artificial aging, including O₂-induced oxidation, washing, UV photodegradation and exposition to acid solutions. Results: Significant color differences of 13.33 ± 0.85 ΔE were evidenced in used endotracheal tubes, as compared to virgin samples (p < 0.0001). Chromatic changes were independent from intubation duration. DSC and TGA analyses showed a loss of DEHP from used tubes, as indicated by increase of the glass transition temperature (Tg) and DEHP weight loss. In vivo application of tubes was associated with an aging process whose effects on the optical and spectral properties were similar to those observed following artificial aging processes. Conclusions: Our findings indicate that significant spectrocolorimetric, DSC and TGA changes occur in endotracheal tubes after application, thus demonstrating for the first time the occurrence of in vivomaterials degradation and DEHP leakage from medical devices worldwide used for neonatal ventilation.

Chemical identification and acute biotoxicity assessment of gaseous chlorobenzene photodegradation products

In order to evaluate the ecological safety and feasibility of UV photodegradation processes for the treatment of halogenated aromatic hydrocarbons, the chemical composition and acute biotoxicity of gaseous chlorobenzene photodegradation products were investigated. Results showed that the main products of chlorobenzene photodegradation included hydrochloric acid, acetic acid, formic acid, phenol and chlorophenol. Roughly 64% of the removed chlorobenzene was converted into phenol, making it the most significant product formed. The types of byproducts suggested that two distinct reaction pathways might compete during the photodegradation process. Interestingly, it appeared that one of these pathways did not involve the direct photocatalytic oxidation of chlorobenzene. An acute biotoxicity assay measuring the inhibition of bioluminescence indicated that gaseous exhaust with overall higher toxicity was emitted after UV irradiation. The acute toxicity of the UV reactor exhaust gas was as high as EC 50 = 13.5 mg-Zn 2+ m −3--gas. The increased toxicity mainly resulted from the conversion of chlorobenzene to more soluble toxic products and ozone production during the photodegradation process.

A novel integrated UV-biofilter system to treat high concentration of gaseous chlorobenzene

A novel integrated UV-biofilter system using UV reactor as the pretreatment process was setup to treat high concentration of gaseous volatile organic compounds (VOCs). Another control biofilter without the UV pretreatment was also established to compare the performance of the two systems. Chlorobenzene was selected as a model compound. The two systems were operated in parallel under different inlet chlorobenzene concentrations (500, 1000, 1600, mg · m−3). The experimental results indicate that the integrated system could eliminate chlorobenzene completely (100% removal efficiency) at the inlet concentration of 500 mg · m−3, whereas only 60% removal efficiency was achieved for the control biofilter. Also the elimination capacity for the organic carbon of the integrated system was much higher than that of the control biofilter. On the basis of intermediates analysis by Ion Chromatography and Gas Chromatography-Mass Spectrometry, the UV pretreatment has been proven to be able to enhance the performance of the following biofilter by transferring the recalcitrant target to some more biodegradable and soluble organic products (such as formic acid and chlorophenol). Furthermore, the produced ozone, a harmful by-product from UV photo-degradation, could be easily eliminated by the following biofiltration process.

Hydrogen peroxide-assisted UV photodegradation of Lindane

Aqueous solutions of γ-hexachlorocyclohexane (Lindane) were photolyzed ( λ = 254 nm) under a variety of solution conditions. The initial concentrations of hydrogen peroxide (H 2O 2) and Lindane varied from 0 to 20 mM and 0.21 to 0.22 μM, respectively, the pH ranged from 3 to 11, and several concentration ratios of Suwannee River humic acid and fulvic acid were dissolved in the irradiated solutions. Lindane rapidly reacted, and the maximum reaction rate constant (9.7 × 10 −3 s −1) was observed at pH 7 and initial [H 2O 2] = 1 mM. Thus, 90% of the Lindane is destroyed in ∼4 min under these conditions. In addition, within 15 min, all chlorine atoms were converted to chloride ion, indicating that chlorinated organic by-products do not accumulate. The reactor was characterized by measuring the photon flux (7.04 × 10 −6 E s −1) and the cumulative production of OH during irradiation. The cumulative OH production during irradiation was fastest at an initial [H 2O 2] = 5 mM ( k = 0.77 μM s −1).