Photodegradation of a herbicide derivative, 2,4-dichlorophenoxy acetic acid in aqueous suspensions of titanium dioxide

The photocatalytic degradation of a herbicide derivative, 2,4-dichlorophenoxy acetic acid (2,4-D, 1), has been investigated in aqueous suspensions of titanium dioxide. The degradation was studied by monitoring the change in substrate concentration employing UV spectroscopic analysis and decrease in Total Organic Carbon (TOC) content as a function of irradiation time in the presence of UV light source. The degradation kinetics was investigated under a variety of conditions, such as different types of TiO₂, pH, catalyst and substrate concentrations. Higher photonic efficiencies were observed with Degussa P25 as compared with other photocatalysts. The degradation products were analysed by GC-MS and probable pathways for the formation of different products were proposed.     

Enhanced photocatalytic activities of ZnO thin films: a comparative study of hybrid semiconductor nanomaterials

Nanostructure single ZnO, SnO₂, In₂O₃ and composite ZnO/SnO₂, ZnO/In₂O₃ and ZnO/SnO₂/In₂O₃ films were prepared using sol?Cgel method. The obtained composite films were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV?CVis spectroscopy. The photocatalytic activities of composite films were investigated using phenol (P), 2,4-dichlorophenol (2,4-DCP), 4-chlorophenol (4-CP) and 4-aminophenol (4-AP) as a model organic compounds under UV light irradiation. Hybrid semiconductor thin films showed a higher photocatalytic activity than single component ZnO, SnO₂ and In₂O₃ films. The substituted phenols degrade faster than phenol. The ease of degradation of phenols is different for each catalyst and the order of catalytic efficiency is also different for each phenol. The use of multiple components offered a higher control of their properties by varying the composition of the materials and related parameters such as morphology and interface. It was also found that the photocatalytic degradation of phenolic compounds on the composite films and single films followed pseudo-first order kinetics.     

Destruction of 2,4 Dichlorophenol in an Atmospheric Pressure Dielectric Barrier Discharge in Oxygen

The processes of degradation of 2,4-dichlorophenol (2,4-DCP) under the action of atmospheric pressure of dielectric barrier discharge (DBD) in oxygen were studied. It was shown that the degradation of 2,4-DCP proceeds efficiently. Degree of decomposition reaches 90%. The degradation kinetics of 2,4-DCP obeys the formal first-order kinetic law on concentration of 2,4-DCP. The effective rate constants depend weakly on the experimental conditions and are equal to ~0.2 s^?1. Based on experimental data, the energy efficiency of decomposition of 2,4-DCP was determined. Depending on the conditions, the energy efficiency was in the range of (8–90) × 10^?3 molecules per 100 eV. The composition of the products was studied by gas chromatography (GC), gas chromatography–mass spectrometry (GC–MS), energy-dispersive X-ray spectroscopy (EDX), attenuated total reflection-fourier transform infrared (ATR-FTIR) spectroscopy, electron spin resonance (ESR) spectroscopy and UV/Visible spectroscopy. It was shown that about ~20% of 2,4-DCP is converted to CO₂, while the other part forms an organic film on the reactor wall. The substance formed is close to the carboxylic acids in chemical composition and exhibits electrical conductivity and paramagnetic properties. Almost all of the chlorine contained in the 2,4-DCP is released into the gas phase. The active species of the afterglow react with liquid hexane, forming the products of its oxidation. Some assumptions regarding the pathway of the process are discussed.     

Photodegradation of dye pollutants on TiO<Subscript>2</Subscript> pillared bentonites under UV light irradiation

TiO₂ pillared bentonite samples dried under different conditions are used to degrade 2,4-dichlorophenol and orange II under UV light irradiation. The supercritical dried sample exhibits a high activity for the photodegradation of 2,4-dichlorophenol and orange II due to its structural features. TOC and COD are measured during the degradation of 2,4-dichlorophenol under UV light irradiation using P25 and TiO₂ pillared bentonite samples dried under different conditions. The clay-based catalysts can be readily separated by filtration or sedimentation.     

Determination of amitraz and its degradation products and monitoring degradation process in quince and cucumber

Amitraz is a non-systemic acaracide and insecticide. Current maximum residue limits for amitraz are stated as ‘Amitraz including the metabolites containing the 2,4-dimethylaniline moiety’. Therefore, determination of amitraz and its all degradation products are important. In this study, we develop a gas chromatography/mass spectrometry (GC/MS) method for determination of amitraz and its degradation products 2,4 dimethylaniline (DMA), 2,4 dimethylformamidine (DMF) and N-(2,4-dimethyl phenyl)-N’-methylformamidine (DMPF) in cucumber and quince. The mechanism of the degradation process was monitored at different temperatures. Amitraz and its degradation products were extracted using the QuEChERS method. To determine amitraz and its degradation products, we used GC/MS. Quantification was carried out by using selected ion monitoring, and total ion chromatogram was used to monitor additional degradation products. The method was validated by studying linearity, limit of detection (LOD) and limit of quantification (LOQ), recovery and precision. The mechanism of the degradation process was monitored at different temperatures. Degradation of amitraz mainly to three degradation products, namely DMA, DMF and DMPF, increased with temperature. Besides these three main degradation products, two other new degradation products were detected.     

Photocatalytic Degradation of Ethyl tert‐Butyl Ether in Aqueous Solution Mediated by TiO2 Suspensions: Parameter and Reaction Pathway Investigations

Degradation of ethyl tert‐butyl ether (ETBE) with UV/TiO₂ was studied by solid‐phase microextraction and gas chromatography‐mass spectrometry. The complete removal of 0.1 g L^?1 of ETBE was achieved after 20 h of treatment. Factors such as pH of the system, catalyst and substrate concentration, and the presence of anions influenced the degradation rate. Establishment of the degradation pathway was made possible by a thorough analysis of the reaction mixture, which identified the main intermediate products generated. The possible degradation pathways were proposed and discussed in this research. The attack on the C–H bond in ETBE by ·OH forms an alkyl radical, which consequently produces a peroxyl radical upon reaction with oxygen. Peroxyl radicals react with one another and produce an alkoxy radical. The β‐bond fragmentation of the alkoxy radical produces different intermediates.     

Destruction Kinetics of 2,4 Dichlorophenol Aqueous Solutions in an Atmospheric Pressure Dielectric Barrier Discharge in Oxygen

The processes of degradation of 2,4-dichlorophenol (2,4-DCP) aqueous solutions under the action of atmospheric pressure of DBD in oxygen were studied. The degradation of 2,4-DCP proceeds efficiently, the degree of decomposition reaching 100%. The degradation kinetics of 2,4-DCP obeys a formal first-order kinetic law on concentration of 2,4-DCP. The effective rate constants depend weakly on the experimental conditions and are equal to ~ 2 s^?1. Based on experimental data, the energy efficiency of 2,4-DCP decomposition was determined to be in the range of 0.039–0.173 molecules per 100 eV depending on the experimental conditions. The composition of the products was studied by gas chromatography, chromatography-mass spectrometry, UV/visible spectroscopy, fluorescent methods and some chemical methods. The main decomposition products present in the solution were found to be carboxylic acids, aldehydes and chloride ions, whereas carbon dioxide and molecular chlorine appear in the gas. The results obtained are compared with similar data from other advanced oxidation processes (AOP’s) methods.     

Heterogeneous photocatalyzed degradation of a pesticide derivative, 3-chloro-4-methoxyaniline, in aqueous suspensions of titania

The photocatalyzed degradation of a pesticide derivative, 3-chloro-4-methoxyaniline (1), has been investigated in aqueous suspensions of titanium dioxide (TiO₂) and air as a function of irradiation time under a variety of conditions using UV?CVis spectroscopic and HPLC analysis techniques. The degradation kinetics were studied under different conditions such as types of TiO₂ powders, reaction pH, catalyst loading, substrate, and H₂O₂ concentrations. The photocatalyst Degussa P25 showed better photocatalytic activity for the degradation of the compound 1. Addition of hydrogen peroxide as an electron acceptor in addition to oxygen greatly enhanced the degradation rate of the compound 1. Higher degradation rates were observed at lower and higher pH values, i.e., 3.15 and 9.15, respectively. The optimal substrate concentration and catalyst loading for the degradation was found to be 0.6?mM with 1.5?g?L^?1. A probable pathway for the decomposition of compound 1 is proposed.     

Photochemical degradation of typical halogenated herbicide 2,4-D in drinking water with UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript>/micro-aeration

UV/H₂O₂/micro-aeration is a newly developed process based on UV/H₂O₂. Halogenated pesticide 2,4-dichlorophenoxyacetic acid (2,4-D) photochemical degradation in aqueous solution was studied under various solution conditions. The UV intensity, initial 2,4-D concentrations and solution temperature varied from 183.6 to 1048.7 μW·cm⁻², from 59.2 to 300.0 μg·L⁻¹ and from 15 to 30°C, respectively. The concentration of hydrogen peroxide (H₂O₂) and pH ranged from 0 to 50 mg·L⁻¹ and 5 to 9, and different water quality solutions (tap water, distilled water and deionized water) were examined in this study. With initial concentration of about 100 μg·L⁻¹, more than 95.6% of 2,4-D can be removed in 90 min at intensity of UV radiation of 843.9 μW·cm⁻², H₂O₂ dosage of 20 mg·L⁻¹, pH 7 and room temperature. The removal efficiency of 2,4-D by UV/H₂O₂/micro-aeration process is better than UV/H₂O₂ process. The photodecomposition of 2,4-D in aqueous solution follows pseudo-first-order kinetics. 2,4-D is greatly affected by UV irradation intensity, H₂O₂ dosage, initial 2,4-D concentration and water quality solutions, but it appears to be slightly influenced by pH and temperature. There is a linear relationship between rate constant k and UV intensity and initial H₂O₂ concentration, which indicates that higher removal capacity can be achieved by the improvement of these factors. Finally, a preliminary cost analysis reveals that UV/H₂O₂/micro-aeration process is more cost-effective than the UV/H₂O₂ process in the removal of 2,4-D from drinking water.     

Studies on inclusion complexes of 2,4-dinitrophenol, 2,4-dinitroaniline, 2,6-dinitroaniline and 2,4-dinitrobenzoic acid incorporated with β-cyclodextrin used for a novel UV absorber for ballpoint pen ink

The inclusion complexes of β-cyclodextrin with different dinitrocompounds like 2,4-dinitrophenol, 2,4-dinitroaniline, 2,6-dinitroaniline and 2,4-dinitrobenzoic acid appears the UV absorption bands in different wavelength region below 400 nm, a combination of these dinitro aromatic compounds of inclusion complexes can improve the UV protection properties of ball point pen ink against photo degradation. The formation of inclusion complexes were characterized by FT-IR, ¹H NMR and 2D ROESY NMR spectroscopy. The UV protecting properties of these inclusion complexes were calculated their sun protection factor was discussed. The stability of the ballpoint pen ink has been confirmed by UV–visible spectroscopic method.     

γ-Radiolysis of aqueous 2-chloroanisole

The radiation-induced degradation of 2-chloroanisole (2-ClAn) is investigated under various experimental conditions in neutral aqueous media as a function of absorbed radiation dose. The initial yields (G_i-values) of substrate degradation as well as those of the resulting major products were determined by HPLC analysis. Probable reaction mechanisms are suggested.     

Synthesis of TiO2/CNT Composites and its Photocatalytic Activity Toward Sudan (I) Degradation

Semiconductor photocatalysis has the potential for achieving sustainable energy generation and degrading organic contaminants. In TiO₂, the addition of carbonaceous nanomaterials has attracted extensive attention as a means to increase its photocatalytic activity. In this study, composites of TiO₂ and carbon nanotubes (CNT) in various proportions were synthesized by the hydrothermal method. The crystalline structures, morphologies, and light absorption properties of the TiO₂/CNT photocatalysts were characterized by PXRD, TEM and UV–Vis absorption spectra. The photocatalytic efficiency of the composites was evaluated by the degradation of Sudan (I) in UV–Vis light. Introducing 0.1–0.5 wt% CNT was shown to substantially improve the photoactivity of TiO₂. The composite with 0.3 wt% CNT showed the best catalytic activity, and its reaction activation energy was calculated as 39.57 kJ mol^?1 from experimental rates. The degradation products of Sudan (I) with different irradiation durations were characterized by Fourier transform infrared spectroscopy, and a degradation reaction process was proposed.     

Heterogeneous Photocatalytic Degradation of Disulfoton in Aqueous TiO2 Suspensions: Parameter and Reaction Pathway Investigations

The photocatalytic degradation of organophosphorus insecticide disulfoton is investigated by having titanium dioxide (TiO₂) as a photocatalyst. About 99% of disulfoton is degraded after UV irradiation for 90 min. The effects of the solution pH, catalyst dosage, light intensity, and inorganic ions on the photocatalytic degradation of disulfoton are also investigated, as well as the reaction intermediates which are formed during the treatment. Eight intermediates have been identified and characterized through a mass spectra analysis, giving insight into the early steps of the degradation process. To the best of our knowledge, this is the first study reporting the degradation pathways of disulfoton. The results suggest that possible transformation pathways may involve in either direct electron or hole transfer to the organic substrate. The photodegradation of disulfoton by UV/TiO₂ exhibits pseudo‐first‐order reaction kinetics and a reaction quantum yield of 0.267. The electrical energy consumption per order of magnitude for photocatalytic degradation of disulfoton is 85 kWh/(m³ order).     

Photolysis and photocatalysis of ibuprofen in aqueous medium: characterization of by‐products via liquid chromatography coupled to high‐resolution mass spectrometry and assessment of their toxicities against Artemia Salina

The degradation of the pharmaceutical compound ibuprofen (IBP) in aqueous solution induced by direct photolysis (UV‐A and UV‐C radiation) and photocatalysis (TiO₂/UV‐A and TiO₂/UV‐C systems) was evaluated. Initially, we observed that whereas photocatalysis (both systems) and direct photolysis with UV‐C radiation were able to cause an almost complete removal of IBP, the mineralization rates achieved for all the photodegradation processes were much smaller (the highest value being obtained for the TiO₂/UV‐C system: 37.7%), even after an exposure time as long as 120 min. Chemical structures for the by‐products formed under these oxidative conditions (11 of them were detected) were proposed based on the data from liquid chromatography coupled to high‐resolution mass spectrometry (LC‐HRMS) analyses. Taking into account these results, an unprecedented route for the photodegradation of IBP could thus be proposed. Moreover, a fortunate result was achieved herein: tests against Artemia salina showed that the degradation products had no higher ecotoxicities than IBP, which possibly indicates that the photocatalytic (TiO₂/UV‐A and TiO₂/UV‐C systems) and photolytic (UV‐C radiation) processes can be conveniently employed to deplete IBP in aqueous media. Copyright © 2014 John Wiley & Sons, Ltd.     

Core-shell microgel stabilized silver nanoparticles for catalytic reduction of aryl nitro compounds

Silver nanoparticles loaded into shell of poly (styrene-N-isopropylmethacrylamide-co-acrylic acid) core shell [P (SNA-CS)] gel particles were synthesized and analyzed by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), ultraviolet–visible spectroscopy (UV–vis) and dynamic light scattering (DLS). Catalytic activity of Ag@P (SNA-CS) particles was investigated by reducing p-nitroaniline (p-NA) into p-aminoaniline (p-AA) in the presence of sodium borohydride (NaBH₄) reductant. Molecules of the substrate adsorbed on the surface of silver nanoparticles interact with borohydride ions (BH₄⁻) to form p-AA. Other nitroarenes like o-nitroaniline (o-NA), p-nitrophenol (p-NP) o-nitrophenol (o-NP), 2,4-dinitrophenol(2,4-DNP) were also reduced into their corresponding aryl amines using Ag@P (SNA-CS) composite microgels as catalyst. Reported catalyst efficiently reduced the nitro aromatic compounds individually as well as simultaneously at ambient temperature. Effect of different reaction conditions (catalyst dose, concentration of NaBH₄ and concentration of p-NA) on reaction completion time, value of apparent rate constant (k_app) and reduction efficiency of the catalyst for reduction of p-NA was also demonstrated. Ag@P (SNA-CS) catalyst was found to be able to retain activity up to four cycles.     

Photocatalysed degradation of a herbicide derivative, Dinoterb, in aqueous suspension

The photocatalytic degradation of a herbicide derivative, Dinoterb (1), has been investigated in aqueous micellar solution in the presence of titanium dioxide (TiO₂) and air as a function of irradiation time under a variety of conditions using UV and HPLC analysis techniques. The degradation kinetics was studied under different conditions such as different types of TiO₂, catalyst concentration, substrate concentration and reaction pH in the presence of air. The photocatalyst Degussa P25 was found to be more efficient catalyst as compared to other photocatalysts tested. The model compound was found to degrade more efficiently under neutral pH as compared to acidic and alkaline pH. GC/MS analysis of the irradiated samples indicate the formation of 2-isopropyl-4,6-dinitro-phenol as by-product which has been characterized on the basis of molecular ion and mass fragmentation pattern. A probable pathway for its formation has been proposed.     

Analysis of thermal degradation of diacetylene-containing polyurethane copolymers

This work investigates the thermal degradation of diacetylene-containing polyurethane (PUDA) copolymers that consist of 2,4-hexadiyene-1,6-diol (DA), 4,4′-diphenylmethane diisocyanate (MDI) and polytetramethylene glycol (PTMG), by thermogravimetric analysis (TGA) and TGA coupled with Fourier transform infra-red spectroscopy (TG-FTIR). The results of TGA at different heating rates and under various annealing conditions demonstrated that the PUBD and PUDA copolymers underwent three stages of degradation. These stages of degradation of PUBD copolymers differed from those in earlier works, in which two stages of degradation were proposed. The three stages of degradation of PUBD and PUDA copolymers involved four and five steps of degradation, respectively, as revealed by TG-FTIR, which identified the main decomposition products, CO₂, tetrahydrofuran and ether-containing olefin. The effect of the cross-linked network of diacetylene-containing hard segments on the degradation of PUDA copolymers was investigated under various annealed conditions. Annealing at a high temperature for a long time promote the PUDA TG and DTG curves shifting to a higher temperature region, but the effect on the temperature does not obviously increase as the annealing further performed at 80-160 °C for a long time. This event is caused by the cross-linked networks inhibiting further cross-polymerization in the diacetylene-containing hard-segmented domains.     

Rapid and solvent-free solid-state synthesis and characterization of Zn3V2O8 nanostructures and their phenol red aqueous solution photodegradation

Zinc vanadate (Zn₃V₂O₈) nanostructures have been successfully synthesized via simple, rapid and solvent-free solid-state method by using different complex precursors of Zn and NH₄VO₃ as novel starting materials. Effects of various zinc (II) Schiff base complex precursors and calcination temperatures were investigated to reach optimum condition. It was found that particle size and optical property of the as-prepared products could be greatly influenced via these parameters. The products were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, energy dispersive X-ray microanalysis (EDX), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Photoluminescence and ultraviolet-visible (UV–Vis) spectroscopy. The photocatalytic activity of zinc vanadate nano and bulk structures were compared by degradation of phenol red aqueous solution.     

Transformation of 2,4-dichlorophenol by H2O2/UV-C, Fenton and photo-Fenton processes: Oxidation products and toxicity evolution

In the present study, H₂O₂/UV-C, Fenton and photo-Fenton treatment of 2,4-dichlorophenol was compared in terms of oxidation products and acute toxicity. The oxidation products were identified by gas chromatography-mass spectroscopy, high performance liquid chromatography and ion chromatography, whereas changes in acute toxicity were evaluated by the Vibrio fischeri luminescence inhibition assay. H₂O₂/UV-C and photo-Fenton processes ensured complete 2,4-dichlorophenolremoval, detoxification and significant mineralization. Hydroquinone and formic acid were identified as the common oxidation products of the studied advanced oxidation processes investigated. 3,5-dichloro-2-hydroxybenzaldehyde, phenol, 4-chlorophenol and 2,5-dichlorohydroquinone were identified as the additional H₂O₂/UV-C oxidation products of 2,4-dichlorophenol. Acute toxicity decreased with decreasing 2,4-dichlorophenol and increasing chloride release.     

Photocatalytic membrane processes,and respective modelling,for removal of pharmaceutical residues in wastewaters. A case study with 2-[2,6-(dichlorophenyl)amino]phenyl acetic acid as model molecule

Non linear modelling of data in photomineralization kinetics of organic micropollutants, by photocatalytic membranes immobilizing semiconductors (TiO₂ particularly) has been previously applied to methane, phenol and to 2,4-dichlorophenol as model molecules, by using a four parameters kinetic modelling based on substrate disappearance and total organic carbon (TOC) in laboratory scale experiments, as a function of initial concentration of substrate and of irradiance.In the present paper, the photocatalytic degradation of diclofenac as model molecule was investigated in a pilot plant module, fitted with 2–3 concentric membranes. Maximum allowable quantum efficiencies corresponded to equal distances between 3 membranes immobilizing photocatalyst. This arrangement fully behaves as if a photocatalyst nanopowder would be homogeneously suspended in the reactor, but obviating all drawbacks of a nanopowder suspension.