UV Irradiation Of Aqueous Solutions Research Articles

Гибридный фотокатализатор нано-диоксид титана/диатомит для удаления токсичных органических загрязнителей из воды с помощью эффективных окислительных процессов (АОPs)

В статье представлены результаты изучения фотокаталитической активности гибридной каталитической системы диатомит/диоксид титана, представляющей собой композит на основе наноразмерного диоксида титана, привитого на поверхность диатомита, которая была применена для разложения фенола в водном растворе под действием УФ излучения, как пример эффективных окислительных процессов типа AOPs (Advanced Oxidation Processes). Катализатор был синтезирован методом модифицированного гетерогенного гидролиза в присутствии диатомита с использованием четыреххлористого титана в качестве прекурсора диоксида титана. Фотокатализатор показал высокую активность в разложении фенола в водном растворе: так, степень деградации фенола достигала 90% в течение 180 мин процесса в зависимости от исходной концентрации загрязняющего вещества. Кинетика процесса фоторазложения хорошо описывается моделью адсорбции Ленгмюра-Хиншельвуда. Полученный композитный катализатор при дозе 2 г/л и исходном содержании фенола 10 г/л удаляет загрязнитель из водного раствора, достигая значений ПДК по фенолу в сточных водах (~5 мг/л) в течение 54 мин фотокатализа. Photocatalytic activity of the hybrid photocatalyst (diatomite/titanium dioxide, DTD) based on nano-sized titanium dioxide grafted on the diatomite surface was tested in advanced oxidation processes (AOPs) by measuring degradation of phenol in model contaminated aqueous solutions under UV illumination. The hybrid catalytic system was synthesized via a modified heterogeneous hydrolysis procedure in the presence of diatomite by using titanium tetrachloride as titania precursor. The photocatalyst showed high activity in photocatalytic decomposition of phenol in aqueous solution. The degradation degree was up to 90% in 180 min depending on initial phenol concentration. The experimental results obtained for the photodegradation kinetics of phenol showed a good agreement with the Langmuir-Hinshelwood model of adsorption with the external diffusion as the determining step of the process. The prepared DTD composite at a loading of 2g/L was able to mineralize phenol under UV irradiation in aqueous solution at initial phenol concentration of 10g/L within 54 min of photocatalytic process up to the maximum allowable concentration level (MAC) for phenol in wastewater (~5 mg/L).

Photodegradation of Hexafluoropropylene Oxide Trimer Acid under UV Irradiation

As a novel alternative to traditional perfluoroalkyl substances (PFASs), including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), hexafluoroproplyene oxide trimer acid (HFPO-TA) has been detected worldwide in surface water. Moreover, recent researches have demonstrated that HFPO-TA has stronger bioaccumulation potential and higher hepatotoxicity than PFOA. To treat these contaminants e.g. PFOA and PFOS, some photochemical techniques by adding exogenous substances had been reported. However, there is still no report for the behavior of HFPO-TA itself under direct UV irradiation. The current study investigated the photo-transformation of HFPO-TA under UV irradiation in aqueous solution. After 72 hr photoreaction, 75% degradation ratio and 25% defluorination ratio were achieved under ambient condition. Reducing active species, i.e., hydrated electrons and active hydrogen atoms, generated from water splitting played dominant roles in degradation of HFPO-TA, which was confirmed by different effects of reaction atmospheres and quenching experiments. A possible degradation pathway was proposed based on the products identification and theoretical calculations. In general, HFPO-TA would be transformed into shorter-chain PFASs, including hexafluoropropylene oxide dimer acid (HFPO-DA), perfluoropropionic acid (PFA) and trifluoroacetate (TFA). This research provides basic information for HFPO-TA photodegradation process and is essential to develop novel remediation techniques for HFPO-TA and other alternatives with similar structures.

Photochemical synthesis of nano- and micro-crystalline particles in aqueous solutions

UV irradiation of aqueous solutions containing various metal ions (Ag, Rh, Cu, Pb, Ba, …) and sensitizers was performed in order to synthesize a large variety of solid nano- or microcrystalline materials in the irradiated solutions and illustrate the chemical and photochemical reactions leading to their formation. Acetone was shown to be a very effective sensitizer and photoreducing agent when coupled with propan-2-ol, whereas formate HCOO– was introduced either mainly as a reducing agent in deaerated solution or as a source of nascent CO2 in the presence of air. It was shown that UV irradiation allows for the preparation of a wide variety of inorganic materials. Moreover, reactions mechanisms discussed may occur during Laser Ablation in Liquid processes.

Photocatalytic Activity of Ag-TiO2 Composites Deposited by Photoreduction under UV Irradiation

In this work, we synthesized Ag nanoparticles on TiO2 thin films deposited on soda lime glass substrates. Ag nanoparticles were synthesized by photoreduction under UV irradiation silver nitrate solution. X-ray diffraction, Raman spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) measurements were used for physicochemical characterization. The structural study showed that all samples were polycrystalline, main phases were anatase and rutile, and no additional signals were detected after surface modification. Raman spectroscopy suggested that silver aggregates deposited on the TiO2 films could exhibit the surface plasmon resonance (SPR) phenomenon; XPS and SEM analysis confirmed TiO2 film morphological modification after photoreduction process. Photocatalytic degradation of methylene blue (MB) was studied under UV irradiation in aqueous solution, and, besides, pseudo-first-order model was used to obtain kinetic information about photocatalytic degradation. Results indicated that Ag-TiO2 showed an important increase in photocatalytic activity under UV (from 20% to 35%); finally, Ag-TiO2 thin films had kapp value 2.4 × 10−3 ± 0.003 min−1 of 1.8 times greater than the kapp value 1.3 × 10−4 ± 0.0004 min−1 of TiO2 thin films.

Photochemical Polymerization of N-Phenyl Mono-1,3-benzoxazines in Aqueous Media

Some N-phenyl monosubstituted mono-1,3-benzoxazines can be polymerized under appropriate UV irradiation in aqueous solutions at room temperature. Photoinduced intramolecular electron transfer from the amine to the phenyl ring in aqueous media produces the mesolitic O–alkyl bond cleavage governed by “topologically controlled Coulombic interactions”. Irradiation of EWG-substituted benzoxazines produces opening of the oxazine ring as expected, but no propagation of the polymerization is observed probably due to the low nucleophilicity of the intermediate phenolic species. However, with more nucleophilic electron-donor substituted benzoxazines the photopolymerization proceeds smoothly, with excellent conversions and modest degrees of polymerization. The produced materials show a similar degree of polymerization to the observed in the non-cross-linked fraction when monobenzoxazines are polymerized under thermal conditions (>150 °C) but having a lower dispersity.

Phototransformation of 2,4,6-tribromophenol in aqueous solution: Kinetics and photolysis products

ABSTRACTIn this research, we studied the phototransformation of 2,4,6-tribromophenol (TBP) by UV irradiation in aqueous solution. Effects of typical environmental factors (i.e., pH and the initial concentration of TBP, Fe3+ and NO2−) were also investigated. Results showed that the transformation process followed pseudo-first-order kinetics. The transformation rate constant of TBP decreased with increasing initial concentration and increased with increasing Fe3+ and NO2− concentrations as well as increasing pH. Ten photoproducts were tentatively identified after irradiation of TBP, according to HPLC-LTQ-Orbitrap MS and GC/MS analysis. Among them, two dihydroxylated dibromobenzene compounds (di-OH-DBB) were found to be predominant over the reaction time, indicating that hydrodebromination of TBP could be the main phototransformation mechanism. In addition, the identification of eight OH-PBDEs and di-OH-PBBs suggested that photodimerization might also be a reaction pathway for TBP photochemical reactions.

Synthesis and characterization of UV photocrosslinkable hydrogels with poly(N-vinyl-2-pyrrolidone): Determination of the network mesh size distribution

ABSTRACTHydrogels of poly(n-vinyl-2-pyrrolidone) were produced by UV irradiation of aqueous solutions of the polymer in presence of hydrogen peroxide, used as initiator. The mechanical and the nanostructural properties of the gels were characterized by a combination of experimental techniques including rheology, low field nuclear magnetic resonance spectroscopy (LF-NMR), and small angle X-ray scattering. Different irradiation doses as well as polymer and initiator concentrations were tested in the characterization. The study elucidates the relationship between different methods to estimate the mesh size of the gel polymeric network. Moreover, a novel correlation model was developed based on Chui and Scherer theories for the interpretation of LF-NMR dataset of polymer solutions and networks.

Oxidative etching of MoS2/WS2 nanosheets to their QDs by facile UV irradiation.

Oxidative etching has been proved to be an efficient top-down method to prepare quantum dots (QDs) of layered transition-metal dichalcogenides which possess unique properties and have potential applications in various areas. Here, one facile and green oxidative etching method induced by UV irradiation is reported to prepare the QDs of MoS2/WS2 in aqueous solution, respectively. A prominent morphology change occurred to the nanosheets of MoS2/WS2 after irradiation and finally they were etched to ultrasmall nanoparticles which were proved to be the QDs. Insight into the etching mechanism was discussed in detail and hydroxyl free radicals (˙OH) were conclusively demonstrated to play the main role in etching nanosheets. From another point of view, this work also proves the crucial long-term photo instability of MoS2/WS2 since there are increasing photo-related applications of them and points out an easy way to degrade their nanosheets.

Composite nanofibers for highly efficient photocatalytic degradation of organic dyes from contaminated water

In this study highly efficient photocatalyst based on composite nanofibers containing polyacrylonitrile (PAN), carbon nanotubes (CNT), and surface functionalized TiO2 nanoparticles was developed. The composite nanofibers were fabricated using electrospinning technique followed by chemical crosslinking. The surface modification and morphology changes of the fabricated composite nanofibers were examined through SEM, TEM, and FTIR analysis. The photocatalytic performance of the composite nanofibers for the degradation of model molecules, methylene blue and indigo carmine, under UV irradiation in aqueous solutions was investigated. The results demonstrated that high photodegradation efficiency was obtained in a short time and at low power intensity compared to other reported studies. The effective factors on the degradation of the dyes, such as the amount of catalyst, solution pH and irradiation time were investigated. The experimental kinetic data were fitted using pseudo-first order model. The effect of the composite nanofibers as individual components on the degradation efficiency of MB and IC was evaluated in order to understand the overall photodegradation mechanism. The results obtained showed that all the components possess significant effect on the photodegradation activity of the composite nanofibers. The stability studies demonstrated that the photodegradation efficiency can remain constant at the level of 99% after five consecutive cycles.

The combined treatment of bisphenol A (BPA) by coagulation/flocculation (C/F) process and UV irradiation in aqueous solutions

The coagulation characteristics of bisphenol A (BPA) with polyaluminum chloride (PACl) as a coagulant and the influence of UV irradiation as a complementary process were investigated. The influences of various coagulation parameters such as coagulant dose, pH, solution turbidity, and initial BPA concentrations were analyzed. The possible dominate mechanisms, formation, and performance of flocs over coagulation process were discussed. A coagulant dose of 17.5 mg/L was chosen as optimum dosage. Compared with other ranges of the pH, it can be seen that pH 8 was more effective. It was indicated that turbidity 16 NTU and BPA initial concentration 0.25 mg/L were as optimum conditions in the coagulation process. In this study, elimination mechanism of BPA included colloids entrapment and sweep flocs, predominantly. The results showed that the contact time of UV irradiation was an important factor in the removal efficiency of the BPA residual supernatant. The combination of C/F followed by UV irradiation showed an efficient removal method for treatment of water solutions containing BPA.

Photodegradation of norfloxacin in aqueous and organic solvents: A kinetic study

Abstract The kinetics of photodegradation of norfloxacin (NF) on UV irradiation in aqueous solution (pH 2–12) and in organic solvents has been studied using a validated HPLC method. The apparent first-order rate constants ( k obs ) for the reaction in aqueous solution range from 0.28 (pH 2) to 5.19 × 10 −3 min −1 (pH 10) and in organic solvents from 0.34 (1-butanol) to 0.80 × 10 −3 min −1 (acetonitrile). The rate–pH profile for the photodegradation of NF shows an initial slow increase in the rate up to pH 6, followed by a rise in the rate to form a bell-shaped curve with pH max around 10. It represents the involvement of cationic, zwitterionic and anionic species of NF undergoing photodegradation at variable rates in acid, neutral and alkaline regions. The increase in rate in the pH range 6–10 is due to the participation of zwitterionic and anionic species and may largely result from the hydrolytic degradation of piperazine side chain in the higher pH range. The decrease in rate above pH 10 is due to low reactivity of anionic species which are less susceptible to photodegradation. The role of excited triplet states of NF species to influence the rate of photodegradation has been highlighted. The photodegradation of NF in organic solvents is a linear function of the dielectric constant and an inverse function of the viscosity of the medium. Five photodegraded products of NF have been identified by LC–MS/MS analysis and schemes for the photodegradation pathways of NF in acid, neutral and alkaline solutions are presented.

DHPLC and MS studies of a photoinduced intrastrand cross-link in DNA labeled with 5-bromo-2′-deoxyuridine

It is well known that the replacement of thymidine with 5-bromo-2′-deoxyuridine (BrdU) in DNA sensitizes it to UVB light. Irradiation of a biopolymer substituted in such a way leads to manifold kinds of DNA damage, such as intrastrand cross-links, single- and double-strand breaks or alkali-labile sites that were studied in the past with a broad spectrum of analytical methods. Here, we demonstrate that completely denaturing high-performance liquid chromatography (DHPLC), underestimated so far in DNA damage studies, could act as an inexpensive, and high-resolution substitute for the commonly employed gel electrophoresis. We report on the DHPLC/mass spectrometry (MS) analyses of photolytes obtained with the UV irradiation of aqueous solutions containing 40 base pairs of a long, double-stranded oligonucleotide labeled with BrdU in one of its strands. The UV-product was detected by HPLC at a temperature of 70°C. Subsequent MS analysis with electrospray ionization (ESI-MS) of the photolyte, enzymatic digestion of the irradiated material and HPLC and MS analysis (LC–MS) of the digest demonstrated unequivocally that an intrastrand covalent dimer, involving adenine and uracil, is formed in the irradiated system.

Heteropolyacid Photocatalytical Degradation of Atrazine in Aqueous Solution under UV-Irradiation

The photodegradation of atrazine induced by UV-irradiation in aqueous solution was investigated initially. The affecting factors on the photodetradation were studied and described in details such as atrazine initial concentration, temperature, pH value, exposure intensity, oxidant and co-existing substances. It was found that the atrazine initial concentration had no obvious effect on the photodegradation. With the pH value increasing, photodegradation rates decreased. However, we also observed a positive correlation between the degradation rate of atrazine and temperature, exposure intensity and oxidant while the coexisting organic compounds may decelerate photodegradation of the atrazine in water. In this paper, the degradation products had also been confirmed by using LC-MS.

Photodegradation of the endocrine-disrupting chemicals 4n-nonylphenol and triclosan by simulated solar UV irradiation in aqueous solutions with Fe(III) and in the absence/presence of humic acids

► Photodegradation of 4 n -NP and TCS were investigated using experimental design. ► Different pH, concentration of Fe(III) and humic acids were evaluated. ► The presence of Fe(III) and basic pH increases the oxidation rate for triclosan. ► Synergistic effect was observed for presence of Fe(III) and HAs for 4 n -nonylphenol. ► First publication reporting of endocrine-disrupting chemicals photodegradation in waters from Colombia. 4 n -Nonylphenol (4 n -NP) and triclosan (TCS) are endocrine disrupters that are used widely in personal care products. They are mainly transported in domestic sewage, which can eventually reach natural waters (rivers, lakes or reservoirs). In this work, the photodegradation of 4 n -NP and TCS using a solar simulator (300–800 nm) at two different pH levels, two different concentrations of ferric ion, Fe(III), and in the absence/presence of humic acids (HAs) were investigated. A Xe lamp (250 W m −2 ) was employed as the light source. The conditions were chosen to simulate a natural aquatic environment. The experiments were performed using a factorial design for three factors with eight combinations of the factors studied. Experiments performed in ultrapure water showed that the degradation of 4 n -NP was faster than that of TCS. The data showed that first-order reaction kinetics describe the degradation of both compounds well; the half-lives of TCS and 4 n -NP were 5.4 h and 2.3 h, respectively. For TCS, the results indicated that the oxidation rate increases in the presence of Fe(III) and at basic pH levels; however, the rate it decreased in the presence HAs. In the case of 4 n -NP, synergistic effect was observed for presence of Fe(III) and HAs. The best conditions were a basic medium (pH 9) and an Fe(III) concentration of 2 mg L −1 without HAs for TCS and a pH of 9, an Fe(III) concentration of 2 mg L −1 and a HAs concentration of 1 mg L −1 for 4 n -NP. The results of photodegradation of both compounds in water from two reservoirs showed that the photodegradation was highly dependent on the conditions of the aquatic environment.

SYNTHESIS, STRUCTURE AND PHOTOELECTROCHEMICAL ACTIVITY OF MIXED COPPER-COBALT OXIDE COATINGS

The aim of the current work was to obtain photoactive copper–cobalt oxide coatings on AISI 304 type stainless steel substrate. This work is relevant to the search of new photocatalysts suitable for water photosplitting. Mixed copper–cobalt oxide coatings were synthesized by heating for 3 h at 550 °C the mixtures of copper acetate hydrate Cu(CH 3 COO) 2 ∙H 2 O and cobalt acetate tetrahydrate Co(CH 3 COO) 2 ∙4H 2 O. The obtained coatings were characterized by X–ray diffraction (XRD), Fourier transform infrared (FT-IR), thermogravimetric–differential scanning microscopy (TG–DSC) and photovoltammetry. The experimental results revealed that mixed copper–cobalt oxide coatings are predominantly composed of spinel-type CuCo 2 O 4 phase. The average crystallite size of CuCo 2 O 4 particles was calculated to be in the range of 65–76 nm. The prepared coatings show a p -type semiconducting behavior. The value of photogenerated current depends on the molar ratio Cu:Co in the coatings. Unfortunately, photoelectrochemical measurements showed that these coatings are relatively unstable under UV irradiation in aqueous solutions. DOI: http://dx.doi.org/10.5755/j01.ct.60.2.1803

Nanocrystalline TiO2 based films onto fibers for photocatalytic degradation of organic dye in aqueous solution

Nanocrystalline titania (TiO2) synthesized via sol–gel, by using an alkoxide precursor were deposited onto commercially available silica and alumina fibers, namely E-Glass and Nextel 650, respectively. Different processing conditions and material preparation parameters, such as amount of TiO2, film composition and annealing temperature were tested in order to obtain nanocrystalline TiO2 with different morphological and structural characteristics. The materials were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and the Brunauer, Emmett, and Teller (BET) surface area measurements. The photocatalytic activity of the obtained coated fibers was investigated by monitoring the degradation of a model molecule, an azo dye (Methyl Red), under UV irradiation in aqueous solution. The detected photocatalytic performance of the sol–gel derived nanocrystalline TiO2 was explained on the basis of mechanism associated to the photocatalytic decomposition of organic molecules using semiconductor oxides and accounted for the structural and morphological characteristics of the TiO2 based coating. The materials with the most suited characteristics for photocatalysis were used to scale up the deposition onto a larger sample of fiber and then tested in a photocatalytic reactor. A commercially available TiO2 standard material (TiO2 P25 Degussa) was used as reference, in order to ultimately assess the viability of the coating process for real application.

Fabrication and Characterization of Gelatin Stabilized Silver Nanoparticles under UV-Light

Silver nanoparticles (Ag-NPs) were successfully synthesized using the UV irradiation of aqueous solutions containing AgNO3 and gelatin as a silver source and stabilizer, respectively. The UV irradiation times influence the particles’ diameter of the Ag-NPs, as evidenced from surface plasmon resonance (SPR) bands and transmission electron microscopy (TEM) images. When the UV irradiation time was increased, the mean size of particles continuously decreased as a result of photoinduced Ag-NPs fragmentation. Based on X-ray diffraction (XRD), the UV-irradiated Ag-NPs were a face-centered cubic (fcc) single crystal without any impurity. This study reveals that the UV irradiation-mediated method is a green chemistry and promising route for the synthesis of stable Ag-NPs for several applications (e.g., medical and surgical devices). The important advantages of this method are that it is cheap, easy, and free of toxic materials.

Living cationic polymerization of a coumarin-substituted vinyl ether and reversible photoinduced crosslinking of the resulting homopolymers and amphiphilic block copolymers

Living cationic polymerization of 4-methyl-7-(2-vinyloxyethoxy)coumarin (CMVE) was achieved using SnCl4 in the presence of nBu4NBr as an added salt at 0 °C. The number-average molecular weight of the resulting polymers increased in direct proportion to the monomer conversion while retaining relatively low polydispersity. Structural analysis revealed that the resulting polymers carried pendant coumarinyl moieties. These coumarinyl moieties were crosslinked by irradiation with UV light at λmax = 366 nm, and the crosslinked sites were then cleaved by irradiation with UV light at λmax = 254 nm. The crosslinking behaviors of the polymers were studied by UV and FTIR spectroscopic measurement. PolyCMVE was soluble in dichloromethane but was found to be insoluble upon UV light irradiation. We also synthesized amphiphilic block polymers bearing coumarinyl moieties by living cationic copolymerization with an amphiphilic vinyl ether. The resulting block polymers were soluble in an aqueous medium and also formed micelle-like aggregates. Upon UV irradiation of aqueous solutions above the critical micelle concentration, an efficient crosslinking reaction occurred. Photoinduced structural changes of these polymer aggregates in the solution state were further investigated. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Synthesis and Photochemical Behavior of the Tetrazolo Tautomer of 2-Azido-4-pyrimidinone-2′-deoxyriboside

The 2-azido analogue of 2'-deoxyuridine was prepared in three steps from 2'-deoxy-2-thiouridine. The sulfur atom of the 2-thio nucleoside was methylated and then displaced by hydrazine to furnish the corresponding 2-hydrazino derivative. After diazotization, the 2-azido compound that exists as its tetrazolo tautomer was obtained. Upon UV irradiation in aqueous solution, the title compound led to isocytosine.

Photochemical synthesis of cadmium sulfide nanoparticles

The formation of cadmium sulfide nanoparticles upon UV irradiation of aqueous solutions of cadmium thiosulfates was established on the basis of spectroscopic and macroscopic data. The yield and size of the cadmium sulfide nanoparticles depend on the ratio of cadmium to thiosulfate ions in solution, the concentration of the solution, and the irradiation duration. The cadmium sulfide nanoparticles with a diameter of 4 nm were obtained by the photolysis of solutions with a concentration of 10−3 mol L−1 at the ratio S2O32−: Cd2+ = 2: 1.