Destruction of chlorinated pesticides in TiO2-enhanced photochemical process (original) (raw)
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Environmental Science and Pollution Research, 2014
The objective of this work is double-firstly to explore the photocatalytic efficiency of five different commercial TiO 2 catalysts in the photodegradation of a mixture of pesticides classified by the EU as priority pollutants and secondly to analyze the correlation between their physicochemical properties and the inhibition of the studied photocatalytic process when natural water was employed. Photocatalytic efficiencies when ultrapure water was used seem to point out that surface area was not a prerequisite for the photodegradation of the selected mixture of pesticides. On the other hand, significant differences in total organic carbon (TOC) conversions were obtained with the two studied water compositions. On one side, Evonik materials appear to be mostly inhibited when natural water was employed, whereas on the other, it should be remarked that anatase Sigma-Aldrich (SA) and, particularly, Hombikat UV100 (HBK) materials presented a very limited photo-efficiency inhibition or even a higher initial rate of TOC removal when a natural water matrix was used, probably due to their specific surface properties (PZC, S BET ). Therefore, heterogeneous photocatalysis has proved to be a promising technology for the degradation of the selected mixture of pesticides where the final photoefficiency of the five commercial titania catalysts studied here responds to a complex balance between its surface and structural properties.
BACKGROUND: The presence of pesticides in surface and ground waters can trigger serious environmental problems, particularly in those areas where agriculture is the major economic activity. In this respect, photochemical advanced oxidation processes may be employed to decontaminate such matrices. RESULTS: Semiconductor photocatalysis was employed to treat a mixture of four commercial pesticides (oxydemethon-methyl, methidathion, carbaryl and dimethoate at 25 mg L −1 each). Laboratory scale experiments under UV-A irradiation were performed to evaluate the relative activity of six commercially available titania samples at 0.5 g L −1 concentration, with Evonik P25 (a 75:25 mixture of anatase:rutile) being the most effective one in terms of pesticides degradation. Experiments were then performed in a pilot plant reactor under natural sunlight leading to quantitative removal of pesticides in less than 300 min; this was accompanied by a substantial reduction of acute toxicity to Vibrio fischeri (i.e. from an initial value of 50% to 15%), as well as moderate mineralization, i.e. 40% COD and 25% DOC removal.
Titanium Dioxide - Material for a Sustainable Environment, 2018
The photocatalytic degradation of five selected organophosphorus pesticides (OPPs), azinphos methyl, azinphos ethyl, disulfoton, dimethoate, and fenthion, has been investigated using TiO 2 (photocatalyst) and UV irradiation. The addition of H 2 O 2 (oxidant agent) into the illuminated aquatic suspensions was also surveyed. The degradation kinetics was studied under different experimental conditions such as pesticides' and catalyst's concentration. Experiments were performed in a Pyrex UV laboratory-constructed photoreactor equipped with 4 × 18 W low-pressure Hg lamps emitting at 365 nm (maximum intensity 14.5 mW cm −2 at distance 15 cm). The concentration of pesticides was determined by GC-NPD means. The extent of pesticide mineralization was assessed through TOC measurements. The results demonstrated that photolysis of target organophosphates in the absence of catalyst or oxidant is a slow process resulting in incomplete mineralization. Contradictory, studied pollutants were effectively degraded in the presence of TiO 2 ; evolution of inorganic heteroatoms (SO 4 2− , PO 4 3− , NO 2 − , NO 3 − , and NH 4 +) as final products provided evidence that pesticide deterioration occurred. The photolysis efficiencies decreased in the order: disulfoton > azinphos ethyl > azinphos methyl > fenthion > dimethoate. Furthermore, a synergistic effect was observed with the addition of H 2 O 2 in the pesticide-TiO 2 suspensions. In all cases examined, reduction process appeared to follow pseudo first-order kinetics (Langmuir-Hinshelwood model). In conclusion, both catalytic systems investigated (UV-TiO 2 and UV-TiO 2-H 2 O 2) have good potential for small-scale applications.
Photocatalytic degradation of pesticides using TiO2 nanoparticles
2013
The problem of water pollution has been an environmental concern for many years. Numerous researchers are looking for an effective method to solve this issue. Heterogeneous photocatalysis, using a semiconductor as a catalyst, is a promising method for the destruction of water polluting pesticides. This method has been called the Advanced Oxidation Process (AOP) which is one of the techniques for water treatment. Titanium dioxide (TiO 2) is the most widely accepted photocatalyst because it is non-toxic, stable to photocorrosion, low cost and can potentially work using sunlight rather than artificial sources of light. When titanium dioxide is illuminated by UV radiation, the absorption of photons of energy is then equal to or greater than its band gap width. This artefact leads to the formation of conduction-band electrons and valence-band holes on the surface of TiO 2, which yield hydroxyl radicals, the primary oxidising species needed for the photocatalytic degradation of pollutants. Supercritical water hydrothermal synthesis (ScWHS) is one of novel approaches for nanoparticle manufacture which involves the mixing of an aqueous metal salt stream with a supercritical water stream to produce nanosized metal oxide particles. The engineering design for the mixing of these CONTENTS ABSTRACT i ACKNOWLEDGEMENTS iii CONTENTS iv LIST OF FIGURES xvi LIST OF TABLES xxxvii Chapter 1 INTRODUCTION 1 1.1 Introduction 1 1.1.1 Examples of common water pollutants 1 1.1.2 Definition of pesticides (in general view) 2 1.1.3 Group of pesticides (categorised by Ministry of 3 Environment, Ontario, Canada) 1.1.4 Water pollution from pesticides: the pesticides usually 8 found in wastewater 1.1.5 Selected pesticides used in this thesis 1.1.6 Legislation of pesticides in respect to human consumption 1.2 Research objectives 1.3 Thesis structure Chapter 2 BACKGROUND AND REVIEW OF LITERATURE 2.1 Introduction to background and review of literature v 2.2 The photolysis or photodissociation process 2.3 The principle of photocatalysis 2.3.1 Homogeneous photocatalytic reactions 2.3.2 Heterogeneous photocatalytic reactions 2.4 The photo-Fenton reaction 2.5 Advanced Oxidation Processing (AOP) 2.6 Photocatalytic materials 2.7 Mechanism/reactions of TiO 2 photocatalyst 2.8 Photocatalytic degradation pathways and intermediates 2.9 Degradation pathways of isoproturon, simazine and propazine 2.10 The toxicity assessment of isoproturon, simazine and propazine using % inhibition of bacteria 2.11 Factors affecting the photocatalytic kinetics 2.11.1 Crystal phase of photocatalyst 2.11.2 Organic pollutant concentration 2.11.3 TiO 2 concentration 2.11.4 O 2 initial concentration 2.11.5 pH 2.11.6 Reaction temperature 2.11.7 Irradiation wavelength 2.11.8 Light intensity vi 2.11.9 Additional oxidants 2.11.10 Mode of the catalyst application: the suspended or immobilized system 2.12 Photocatalytic reactor 2.12.1. Reactors using suspended solid photocatalysts 2.12.1.1 Annular reactors with horizontal flow 2.12.1.2 Thin-film slurry photocatalytic reactor (TFS) 2.12.2 Fixed catalyst systems 2.12.2.1 Thin Film Fixed Bed Reactor (TFFBR) 2.12.2.2 Packed Bed Reactor (PBR), fixed bed reactor and fluidised bed reactor 2.12.2.3 Fibre Photoreactor (FP) and Optical Fibre Photoreactor (OFP) 2.12.2.4 Rotating Disc Reactor (RDR) 2.12.2.5 Photocatalytic Membrane Reactors (PMRs) 2.13 Key elements of reactor design for photocatalytic reaction 2.13.1 Mass transfer and contact between chemical compounds and photocatalyst 2.13.2 Photocatalyst activation 2.13.3 Oxygen content in two phases? systems 2.14 Supercritical water hydrothermal synthesis (ScWHS) vii 2.15 The ScWHS process 2.16 Conclusions from review of literature Chapter 3 EXPERIMENTAL 3.1 Introduction to experimental 3.2 Chemicals and materials 3.3 Procedure for supercritical water synthesis of TiO 2 3.4 Thin Film Fixed Bed Reactor System (TFFBR) 3.4.1 Surface coating method 3.4.2 Experimental procedures for the TFFBR 3.4.3 Operating conditions 3.5 Stirred photoreactor 3.5.1 Operating conditions 3.6 Fluidised bed photoreactor system 3.6.1 Experimental procedure for fluidised bed photoreactor 3.7 Analytical Techniques 3.7.1 High Performance Liquid Chromatography (HPLC) 3.7.2 Ultraviolet-visible Spectroscopy (UV-Vis) 3.7.3 Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDAX) 3.7.4 Transmission Electron Microscope (TEM) 3.7.5 X-Ray Diffraction (XRD) viii 3.8 Calibration curves for pesticides quantification 3.9 Conclusions of the Experimental Chapter Chapter PHOTOCATALYTIC DEGRADATION OF PESTICIDES USING THIN FILM FIXED BED REACTOR 4.1 Introduction to TFFBR results 4.2 Aims and objectives for TFFBR experiments 4.3 Characterisation of the TiO 2 photocatalysts: Scanning Electron Microscope (SEM) image and Energy Dispersive X-ray Spectroscopy (EDAX) data 4.4 Control experiments to determine the difference between photolysis and photocatalytic reaction 4.4.1 Determination of the pesticides degradation rate in the absence of UV excitation but the presence of TiO 2 4.4.2 Determination of the rate of loss of pesticides in the presence of UV irradiation without a TiO 2 catalyst. 4.5 Photocatalytic degradation, effect of TiO 2 and the feed flow rate 120 4.6 Influence of initial pesticides concentration 4.7 Influence of photocatalyst type (the commercial VS the synthesised) 4.8 Conclusions of TFFBR experiments
Journal of the Serbian Chemical Society
In this paper the efficiency of photocatalytic degradation of different pesticides was investigated using bare TiO2 and TiO2 nanoparticles modified with polyaniline under simulated solar irradiation. Sulcotrione showed the highest percentage degradation and further experiments were related to this herbicide. Mineralization and cytotoxicity of the starting compound and intermediate species formed during the decomposition in double distilled water (DDW), as well as the efficiency of removal from various environmental waters were studied. The contents of the most abundant ions present in the River Danube were simulated in DDW and their influence was evaluated. It was found that cytotoxicity was in all cases below 11 % and the efficiency of photocatalytic degradation in environmental waters was decreased compared with DDW. Furthermore, addition of different scavengers revealed that the main path of degradation is through holes, while the presence of H2O2 decreased and KBrO3 increased th...
Degradation of pesticides chlorpyrifos, cypermethrin and chlorothalonil in aqueous solution by TiO 2 photocatalysis under UVA (365 nm) irradiation was examined. Enhancement of degradation and improvement in biodegradability index (BOD 5 /COD ratio) by H 2 O 2 addition were also evaluated. UVA irradiation per se produced insignificant degradation of the pesticides. In UV/TiO 2 photocatalysis (TiO 2 1.5 g L À1 , pH 6 and 300 min irradiation), COD and TOC removal were 25.95 and 8.45%, respectively. In UV/ TiO 2 /H 2 O 2 photocatalysis (TiO 2 1.5 g L À1 , H 2 O 2 100 mg L À1 , pH 6 and 300 min irradiation), COD and TOC removal were 53.62 and 21.54%, respectively and biodegradability index improved to 0.26. Ammonianitrogen (NH 3 eN) decreased from 22 to 7.8 mg L À1 and nitrate-nitrogen (NO À 3 eN) increased from 0.7 to 13.8 mg L À1 in 300 min, indicating mineralization. Photocatalytic degradation followed pseudo-first order kinetics with rate constant (k) of 0.0025 and 0.0008 min À1 for COD and TOC removal, respectively. FTIR spectra indicated degradation of the organic bonds of the pesticides. UV/TiO 2 /H 2 O 2 photocatalysis is effective in degradation of pesticides chlorpyrifos, cypermethrin and chlorothalonil in aqueous solution. UV/TiO 2 /H 2 O 2 photocatalysis may be applied as pretreatment of a chlorpyrifos, cypermethrin and chlorothalonil pesticide wastewater at pH 6, for biological treatment.
Photocatalytic degradation of organophosphorus pesticides using thin films of TiO2
Journal of Chemical Technology AND Biotechnology, 1995
This paper describes solar heterogeneous photocatalysis using immobilized TiO 2 applied in the treatment of agricultural waste resulting from the application of commercial formulations of methyl parathion. The disappearance of the insecticide, as well as the formation of its metabolite, was monitored by high-performance liquid chromatographytandem mass spectrometry (LC-MS/MS), while mineralization efficiency was monitored by measurements of total organic carbon (TOC). Toxicity studies were performed using the microcrustacean Artemia salina. The TOC removal efficiency by photocatalytic process was 48.5%. After 45 minutes of treatment, the removal efficiency of methyl parathion was 90%, being completely mineralized at the end of treatment. The formation and removal of the metabolite methyl paraoxon was observed during the photocatalytic process. The photocatalytic treatment resulted in increased microcrustacean mobility, indicating a reduction of acute toxicity.
Titanium-dioxide-mediated photocatalysis reaction of three selected pesticide derivatives
Research on Chemical Intermediates, 2004
The photocatalysis reaction of three selected pesticide derivatives, namely methoxychlor (1), chlorothalonil (2) and disulfoton (3), has been investigated in an acetonitrile/water mixture in the presence of titanium dioxide and oxygen. The change as a function of irradiation time has been monitored using the UV spectroscopic analysis technique. An attempt has been made to identify the product formed during the photooxidation process through GC/MS analysis technique. The photolysis of methoxychlor (1) led to the formation of methoxychlor olefin (4) and 4,4-dimethoxybenzophenone (9), whereas chlorothalonil (2) gave rise to 2,3,4,5-tetrachlorophenol (17) as the only product. On the other hand, the photolysis of disulfoton (3) under analogous conditions gave disulfoton sulfoxide (25) and phosphorodithioic acid (21). All the products have been identified by comparing the molecular ion and mass fragmentation peaks of the products with those reported in the library. A probable mechanism for the formation of the products has been proposed.
Combining TiO2-photocatalysis and wetland reactors for the efficient treatment of pesticides
Chemosphere, 2008
In the present work the photocatalytic and biological degradation of two commercial mixtures of pesticides (Folimat and Ronstar) and two fungicides (pyrimethanil and triadimenol) has been studied. The evolution of some components of these commercial products (dicofol, tetradifon and oxadiazon) and that of the two fungicides has been monitored by means of HPLC, GC-MS, TOC and toxicity (Lemna minor toxicity test) measurements. The photocatalytic method was able to degrade dicofol, tetradifon, pyrimethanil, triadimenol and the components of Ronstar with the exception of oxadiazon. In addition to this, the photocatalytic method eliminated pyrimethanil toxicity and reduced that of triadimenol by a 90%, Ronstar by a 78% and Folimat by an 87%. Nevertheless, the wetland reactors alone could reduce the toxicity of only the former. Finally, the proper dosage of the water containing the pesticides to a photocatalytic reactor followed by a wetland reactor resulted to be the most successful strategy for the detoxification of the studied compounds and their mixtures.
Photocatalytic degradation of lindane, p, p′DDT and methoxychlor in an aqueous environment
Journal of Photochemistry and Photobiology A-chemistry, 2000
Aqueous solutions containing 40 mg/dm 3 of lindane, p,p -DDT and methoxychlor were photodegraded in a UV/TiO 2 /O 2 system yielding different degradation products. Powdered anatase and rutile, and anatase supported on glass hollow microspheres served as photocatalysts. The destruction degree of pesticides was evaluated and oxidation products identified by gas chromatography with an electron capture detector (GC-ECD) and a mass spectroscopy detector (GC-MS). From 68 to 90% of pesticides investigated was eliminated after 30 min irradiation in the presence of anatase supported on glass microspheres. The lowest efficiency was obtained for rutile as a catalyst. One hundred and fifty minutes of processing resulted in 50% elimination for ␥-HCH, 85% for DDT and over 99% for methoxychlor.