Photocatalytic Degradation Of Diuron Research Articles

Facile synthesis of a TiO2-Al2O3-GnPs compound and its application in the photocatalytic degradation of Diuron

New ternary materials TiO 2 -Al 2 O 3 -GnPs (TAG) were prepared by using an innocuous sol-gel method with a slight modification for the addition of graphene nanoplatelets (GnPs), under room temperature and atmospheric pressure. The materials TiO 2 -Al 2 O 3 -GnPs were prepared with variations of concentration between 0.05 and 1 wt % of GnPs. In this study, we analyzed the physicochemical properties by X-ray diffraction (XRD) and UV-Vis spectroscopy, textural properties by N 2 physisorption, morphology by scanning and transmission electron microscopy (SEM, TEM) and a chemical species analysis was carried out by X-ray photoelectron spectroscopic (XPS). The photocatalytic activity of each material was evaluated in the degradation of a model molecule, Diuron, a carcinogenic and cytotoxic herbicide used in farm fields. To determine reaction selectivity and mineralization degree, the photocatalytic reaction was monitored by using UV-Vis spectroscopy and total organic carbon (TOC). In samples with higher GnPs’ concentration, a good enough specific surface area of up to 379 m 2 /g was observed, and reduced band gap energy (2.8 eV) with respect to TiO 2 and mixed oxide (3.2 and 3.1 eV respectively), was obtained. These resulting properties were the key indicator so that the materials could be applied as photocatalysts. In the photocatalytic activity determination, TAG-0.75 was the sample that showed the best results with respect to the mixed oxide; the highest photocatalytic conversion, the reduced average life time, and increased mineralization and reaction selectivity.

Effects of catalyst surfaces on adsorption revealed by atomic force microscope force spectroscopy: photocatalytic degradation of diuron over zinc oxide.

Controlling adsorption of a heterogeneous catalyst requires a detailed understanding of the interactions between reactant molecules and the catalyst surface. Various characteristics relevant to adsorption have been theoretically predicted but have yet to be experimentally quantified. Here, we explore a model reaction based on diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] photo-degradation over a ZnO particle catalyst. We used atomic force microscope (AFM)-based force spectroscopy under ambient conditions to investigate interactions between individual functional groups of diuron (NH2, Cl, and CH3) and surfaces of ZnO particles (polar Zn and O-terminated, and nonpolar Zn-O terminated). We were able to distinguish and identify the two polar surfaces of conventional ZnO particles and the nonpolar surface of ZnO nanorods based on force-distance curves of functionalized probe/surface pairs. We posit that the reaction involved physisorption and could be described in terms of Hamaker constants. These constants had an order-of-magnitude difference among the probe/surface interacting pairs based on polarity. Hence, we confirmed that van der Waals interactions determined the adsorption behavior. We interpreted the electronic distribution models of the probe-modifying molecules. The functional group configurations inferred the diuron adsorption configurations during contact with each ZnO facet. The adsorption affected characteristics of the reaction intermediates and the rate of degradation.

Facile synthesis of Cu-doped ZnO nanoparticle in triethyleneglycol: photocatalytic activities and aquatic ecotoxicity

ABSTRACT A new synthetisis method of Cu-doped ZnO nanoparticles is presented in this work, this novel approach allow one to produce Zinc oxide nanocristal owing to a modified Polyol process that makes use of triethyleneglycol (TREG) as a solvent. The structure and morphology of the nanoparticles were characterized by high-resolution transmission electron microscopy (HRTEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), N2 adsorption study, UV-Vis diffuse reflectance spectroscopy, inductively coupled plasma optical emission spectroscopy and Raman spectroscopy. The lightly doped Zn1-xCuxO photocatalysts consisted in a novel nanorods structure of Zn0.9990Cu0.0010O nanoparticles. Taking the photocatalytic degradation of diuron under solar light as liquid phase test reaction, the lightly doped Zn0.9990Cu0.0010O nanorods photocatalysts showed strongly enhanced photocatalytic activity when compared to the bare ZnO counterpart. The apparent rate constant value of Zn0.9990Cu0.0010O was 22 times higher than that of pure ZnO. In order to study the environmental risk of Cu-ZnO, clams Ruditapes decussatus were exposed to Cu-ZnOC1 = 0.5 mg/L, Cu-ZnOC2 = 1 mg/L and Cu-ZnO C3 = 5 mg/L. Catalase (CAT) activities, malondialdehyde (MDA) content and acetylcholinesterase (AChE) activity were determined in gills and digestive gland of treated and untreated clams. Thus, no significant effects were detected in the gills of exposed clams after 7 days compared to control. Thus, MDA level and CAT activity showed significant differences in digestive glands of groups treated by the highest concentration of Cu-ZnO NPs compared to the control. No adverse effects on AChE activity was detected after Cu-ZnO NPs exposure. These results demonstrated that, although Cu-ZnO NPs is not acutely toxic to Ruditapes decussatus, it does exert oxidative stress on clams. These results are encouraging for the Cu-ZnO NPs use in variety of applications due to its high photocatalytic and low environmental toxicity.

Dependence of Catalyst Surface in Photocatalytic Degradation of Phenyl Urea Herbicides

Photocatalytic degradations of various contaminants using in-house synthesized catalysts have been generally reported, but the degradation intermediates formed are normally inconsistent. This issue is particularly important for the degradation of toxic compounds which may form intermediates with increased toxicity. This work resolves this issue by systematically investigating adsorption and photocatalytic degradation of diuron, linuron, and 3,4-dichloroaniline (DCA) on two forms of zinc oxide (ZnO), i.e., conventional particles with zinc- and oxygen-terminated polar surfaces, and nanorods with mixed-terminated non-polar surfaces. Experimental results indicate that both rate of degradation and degradation pathway depend upon the adsorption configuration of the compound undergoing the degradation onto the surface of the catalyst. The adsorption configuration is surface dependent. On polar surfaces, both aliphatic and aromatic sides of diuron and linuron molecules adsorb on the surface, allowing the attack of hydroxyl radicals on both ends. On the other hand, on non-polar surface, only the aliphatic chain adsorbs onto the surface, resulting in the hydroxyl radicals attack only on the aliphatic side. The structure of the catalyst is therefore a crucial factor determining the dominant degradation pathway.

Fabrication of zinc oxide nanorod incorporated carboxylic graphene/polyaniline composite and its photocatalytic activity for the effective degradation of diuron from aqueous solutions

A novel zinc oxide nanorod incorporated carboxylic graphene/polyaniline (ZnR@CGR/PANI) composite was synthesized for the effective removal and subsequent photodegradation of the pesticide diuron (DU) from aqueous solutions. The photocatalyst was characterized by FTIR, XRD, SEM, TEM, Surface Area Analyzer, Raman spectroscopy AFM, DRS, PL and Cyclic voltammetry. The photocatalytic performance of ZnR@CGR/PANI composite was evaluated by the degradation of DU under visible light irradiation. The band gap of the photocatalyst was found to be 2.77 eV. The maximum adsorption occurs at pH 4.0. The adsorption kinetic and isotherm data were described using pseudo-second-order kinetic model and Sips isotherm model, respectively. Adsorption capacity increases with increase of temperature indicates the endothermic nature of adsorption. The maximum adsorption capacity was found to be 13.40 mg/g. The photocatalytic degradation of DU was found to follow first-order kinetics and optimum pH for degradation was found to be 3.0. The regeneration of the adsorbent-cum-photocatalyst was also examined upto five cycles that confirmed the relative stability of the photocatalyst.

One-pot synthesis of lightly doped Zn1-x Cu x O and Au-Zn1-x Cu x O with solar light photocatalytic activity in liquid phase.

We report on the facile and low-temperature one-pot chemical synthesis of lightly doped Zn1-x Cu x O and hybrid Au-Zn1-x Cu x O photocatalysts with low Cu molar content (0<x<0.7%) using 1,3-propanediol polyol simultaneously as solvent, reducing and a stabilizing agent, without any final thermal treatment. The photocatalysts have been characterized by X-ray diffraction, N2 adsorption study, UV-vis diffuse reflectance spectroscopy, inductively coupled plasma optical emission spectroscopy, and transmission electron microscopy. The lightly doped hybrid Au-Zn1-x Cu x O photocatalysts consisted in faceted quasi-spherical large-size Au nanoparticle cores surrounded by closely packed small-size Zn1-x Cu x O nanoparticles. Taking the photocatalytic degradation of Diuron under solar light as liquid-phase test reaction, the lightly doped Au-Zn1-x Cu x O hybrid photocatalysts with optimized x=0.09% Cu content showed strongly enhanced photocatalytic activity when compared to the bare ZnO counterpart. The observed 16-fold higher degradation rate constant resulted jointly from the light doping of ZnO with Cu to form Zn1-x Cu x O photocatalyst and further from the addition of gold nanoparticles allowing interfacial oxide-to-metal electron transfer within the hybrid Au-Zn1-x Cu x O photocatalyst.

Effect of W doping level on TiO2 on the photocatalytic degradation of Diuron.

In the present study, three compositions of W-doped titania nano-photocatalyst are synthesized via the sol-gel method. The powders obtained were characterized by X-ray diffraction, Raman spectroscopy and UV-visible diffuse reflectance spectroscopy. The photocatalytic performances of the different photocatalysts are tested with respect to the degradation of Diuron in water solutions under simulated solar light and visible light irradiation. The W0.03Ti0.97O2 catalyst exhibits better photoactivity than the pure TiO2 even under simulated solar light and visible light. This improvement in activity was attributed to photoelectron/hole separation efficiency.

Materiais SiO2-TiO2 para a degradação fotocatalítica de diuron

SiO2-TiO2 materials prepared by sol-gel method were evaluated in the photocatalytic degradation of diuron. The materials were prepared with and without surfactant cetyltrimethylammonium chloride at different temperatures (25, 50 and 100 oC). The samples were characterized by N2 adsorption-desorption measurements, scanning electron microscopy, X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy and infrared diffuse reflectance spectroscopy. The results showed that the materials synthesized with the surfactant had higher surface areas and band-gap values similar to anatase. All materials were more active than the commercial catalyst P-25 and better performance was achieved using the surfactant in the material synthesis.

Photocatalytic degradation of diuron in aqueous solution by platinized TiO 2

The photocatalytic degradation of diuron, which is one of phenylurea herbicides, was carried out in the presence of platinized TiO 2 photocatalyst. Platinization was found to increase the rate of diuron degradation. When 0.2 wt.% of platinum was deposited onto the surface of TiO 2, an initial diuron concentration of 10 mg L −1 was completely degraded after 20 min. Furthermore, the first-order rate constant for diuron degradation by Pt–TiO 2 was ca. 4 times higher than P-25 TiO 2. In addition, the photocatalytic activity of Pt–TiO 2 was appeared under visible light. The decrease of TOC as a result of mineralization of diuron was observed during the photocatalytic process. The degree of diuron mineralization was about 97% under UV irradiation after 8 h. The formations of chloride, nitrate and ammonium ions as end-products were observed during the photocatalytic system. The decomposition of diuron gave four kinds of intermediate products. The degradation mechanism of diuron was proposed on the base of the evidence of the identified intermediates. Based on these results, the photocatalytic reaction by Pt–TiO 2 could be useful technology for the treatment of wastewater containing diuron.

Photocatalytic Degradation of Diuron: Experimental Analyses and Simulation of HO° Radical Attacks by Density Functional Theory Calculations

The photocatalytic oxidation of diuron has been performed in presence of TiO(2) suspensions. To better understand the mechanistic details of the hydroxyl radical attack on diuron, computational methods were carried out. The combination of experimental and computational methods has been employed to establish the main degradation pathways of diuron. After identification of the majority of first byproduct, the experimental study underlined that substitution of chlorines and hydroxylation by hydroxyl radicals are the main diuron degradation pathways, in agreement with MOPAC and DFT simulations carried out in the gas phase. In addition, these calculations revealed that the aromatic ring attack is led by a HO degrees addition and not a hydrogen abstraction and the main first byproduct, monochlorohydroxylated compounds, are obtained by concerted reactions.

Photocatalytic degradation of diuron in aqueous solution in presence of two industrial titania catalysts, either as suspended powders or deposited on flexible industrial photoresistant papers

In the present paper, the practical elimination of pesticides from water by photocatalysis has been studied by using two commercial titania photocatalysts (Degussa P25 (50m2/g) and Millennium PC500 (340m2/g)) and by choosing diuron as a model molecule. These two catalysts have been tested and compared in suspension in a slurry reactor. Their activities have been based on the rates of diuron disappearance diuron. In particular, comparisons have been made on their initial activities, which is independent of the influence of intermediates formed. Under identical conditions, Degussa P25 appeared substantially more active than Millennium PC500. However, since the final filtration of titania powders in suspension for the release of cleaned water and the recovery of the catalysts is a tedious process, titania has been successfully deposited on flexible photo-inert supports to be easily removed and recycled. The binding agent was an amorphous silica, transparent to UV. Depending on the nature of the industrial paper support used, both industrial titania photocatalysts behaved oppositely: for the same quantity of deposited titania samples, Degussa P25 was as active as in suspension when deposited on paper KN47 and substantially (20%) less active when deposited on NW10 whereas Millennium PC-500 behaved oppositely.

Mechanisms of Direct and TiO2‐Photocatalysed UV Degradation of Phenylurea Herbicides

Phenylurea herbicides undergo low-yield (phi(PI) <15 %) monophotonic photoionisation upon 193-nm laser flash excitation. The so-formed radical cations (phenylurea.+) are highly acidic (-1.5 < pKa <0.5) and deprotonate readily to yield the corresponding neutral radical (phenylurea.). Pulse radiolysis experiments allowed limitation of the reduction potential of phenylurea.+ within 2.22 V versus the normal hydrogen electrode (NHE) < E degrees (phenylurea.+/phenylurea) < 2.43 V versus NHE. The main photoproducts of UVC (lambda=193 nm) photodegradation of phenylureas correspond to a photo-Fries rearrangement. One-electron reduction with e-(aq) yields the corresponding radical anions (phenylurea.-), for which 4.3< pKa < 5.33. The rate constants for reaction with e-(aq) show that in photocatalysis the generation of phenylurea.- and O2.- on the surface of the photocatalyst may be competitive. High reactivity toward e-(aq) is predicted from linear free-energy relationships (LFER) for phenylureas bearing electron-withdrawing groups. Reaction with HO. takes place mainly via addition to the aromatic ring and/or H. abstraction from a saturated carbon atom (98 %), rather than one-electron oxidation (2 %). High reactivity toward oxidation by HO. is predicted from LFER for phenylureas bearing electron-donating groups. Adsorption studies for TiO2 in its polymorphic forms of rutile and anatase, as well as with the commercial mixture Degussa P-25, show photocatalysis is independent of the specific area of the catalyst. A variety of compounds are generated during the photocatalytic degradation of Diuron, while only two hydroxychloro derivatives are observed upon prolonged direct 365 nm irradiation. The photocatalytic degradation proceeds mainly by oxidation of the Me group of the side chain, hydroxylation of the aromatic ring, and dechlorination. The photoproducts of photocatalytic degradation differ from one polymorphic form of TiO2 to another.

Activity of nanosized titania synthesized from thermal decomposition of titanium (IV) n-butoxide for the photocatalytic degradation of diuron

Nanoparticles of anatase titania were synthesized by the thermal decomposition of titanium (IV) n-butoxide in 1,4-butanediol. The powder obtained was characterized by various characterization techniques, such as XRD, BET, SEM and TEM, to confirm that it was a collection of single crystal anatase with particle size smaller than 15 nm. The synthesized titania was employed as catalyst for the photodegradation of diuron, a herbicide belonging to the phenylurea family, which has been considered as a biologically active pollutant in soil and water. Although diuron is chemically stable, degradation of diuron by photocatalyzed oxidation was found possible. The conversions achieved by titania prepared were in the range of 70–80% within 6 h of reaction, using standard UV lamps, while over 99% conversion was achieved under solar irradiation. The photocatalytic activity was compared with that of the Japanese Reference Catalyst (JRC–TIO–1) titania from the Catalysis Society of Japan. The synthesized titania exhibited higher rate and efficiency in diuron degradation than reference catalyst. The results from the investigations by controlling various reaction parameters, such as oxygen dissolved in the solution, diuron concentration, as well as light source, suggested that the enhanced photocatalytic activity was the result from higher crystallinity of the synthesized titania.

Photocatalytic degradative oxidation of Diuron in organic and semi-aqueous systems over titanium dioxide catalyst

The photocatalytic degradation of Diuron in organic and semi-aqueous media is compared. The rates of disappearence fit Langmuir–Hinshelwood kinetics and the parameters k and K have been determined. A main intermediate was detected in all cases and its structure has been determined. This product is obtained by oxidation of a methyl group of the urea moiety. Several compounds [trichloroaniline, dichloronitrobenzene, N-(3,4-dichlorophenyl)formamide, dimethylurea . . .] were detected by GC-MS analysis in both media while hydroxylated compounds were only observed in the semi-aqueous medium.

Photocatalytic degradation of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] on the layer of TiO2 particles in the batch mode plate film reactor

The photocatalytic degradation of diuron in aqueous solution on TiO2 layer of a batch mode plate reactor irradiated with ultraviolet sun-bed tubes was investigated. Dependence of the reaction rate on the diuron concentration (in the range of 0·8–8·0×10−5 mol dm−3) and on the light intensity (0·8–2·7×10−9 einstein cm−2 s−1) but independence on the flow rate (2·5–3·6 dm3 min−1) were found. A reaction scheme was proposed following the main identified primary [3-(3,4-dichlorophenyl)-1-methyl-1-formylurea and 3-(3,4-dichlorophenyl)-1-methylurea] and secondary [3-(3,4-dichlorophenyl)-1-formylurea and 3,4-dichlorophenylurea] products. © 1998 SCI

Photocatalytic degradation of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] on the layer of TiO2 particles in the batch mode plate film reactor

The photocatalytic degradation of diuron in aqueous solution on TiO2 layer of a batch mode plate reactor irradiated with ultraviolet sun-bed tubes was investigated. Dependence of the reaction rate on the diuron concentration (in the range of 0·8–8·0×10−5 mol dm−3) and on the light intensity (0·8–2·7×10−9 einstein cm−2 s−1) but independence on the flow rate (2·5–3·6 dm3 min−1) were found. A reaction scheme was proposed following the main identified primary [3-(3,4-dichlorophenyl)-1-methyl-1-formylurea and 3-(3,4-dichlorophenyl)-1-methylurea] and secondary [3-(3,4-dichlorophenyl)-1-formylurea and 3,4-dichlorophenylurea] products. © 1998 SCI