The behavior of novel pellet-shaped bulky titania-kaolin photocatalysts is herein evaluated for its application in the solar-assisted photocatalytic treatment of a bio-recalcitrant pesticide mix (imidacloprid, pyrimethanil and methomyl) in solar lab-scale and semi-pilot scale raceway pond photoreactors. The photocatalyst consists of 1 cm long titania-kaolin macro-composites that combine some advantages of both nanoparticulate and supported catalysts without being either. This opening the opportunity to extend the use of this photocatalyst to complex wastewater effluents. In addition, their stability and reusability potential was also evaluated, and reactive species leading to the solar-degradation of each pesticide were also identified using radical scavengers. Total removal of pesticides (2 mg L-1 each) with an optimal pellets dosage of 34.8 g L-1 was addressed, whether in ultrapure water (180-270 min of solar irradiation) or in two basic pH Municipal Wastewater Treatment Plant (MWWTP) effluents (<= 300 min of solar irradiation) where methomyl was always the most recalcitrant pesticide. Lower Total Organic Carbon (TOC) removal (approximate to 53-56%) was also found under the effect of these complex MWWTP effluents than in ultrapure water (>60%). Those results are very promising when comparing to the almost negligible TOC removal achieved with the Titania powder under basic MWWTP effluents due to the strong effect of particle aggregation. Very good photocatalyst stability and durability was shown along three consecutive cycles after applying a low-cost recovery protocol consisting of several washing and drying cycles without addressing a significant photoefficiency loss (TOC approximate to 60-56%). The application of scavengers revealed that hydroxyl radical generated from photoinduced holes was the dominant species in the degradation of pyrimethanil and methomyl whereas reactive oxygen species formed from conduction band electrons were mainly involved in the photo-oxidation of imidacloprid.

An innovative bulky photocatalyst for water decontamination has been developed. The semiconductor (TiO2) is homogeneously distributed in an aggregating material through the whole piece. This design prevents the activity reduction usually observed in supported catalysts due to the loss of the photoactive layer, and facilitates its recovery for an easy reuse, which is a recurrent problem dealing with nanoparticles. The photocatalyst combines the excellent properties of TiO2 with those of a natural clay, which serves as binder, slows down the phase transition of anatase to rutile upon calcination, and has a synergetic function. The photocatalyst has been pre-pared in the form of small pellets with an Ecuadorian clay and TiO2 in the commercial form of P25 by evenly dry mixing, forming a paste with water, and subsequent extrusion, drying and calcination at 600 degrees C. The photo-degradation of phenol, as a model pollutant, has been achieved by using this aggregate material in a flow reactor with artificial UVA-Vis radiation, and reused without any significant loss of activity. The photocatalyst showed an optimum activity at a 40% clay / 60% P25 ratio, while higher calcination temperatures had a negative effect on its performance.

The removal of emerging pollutants from municipal wastewater was studied for the first time using a three-step pilot-scale system: 1) hybrid digester (HD) as first step, 2) subsurface vertical flow constructed wetland (VF) as second step, and 3) photodegradation (PD) unit as third step or post-treatment. The HD and VF units were built and operated in series with effluent recirculation at pilot scale. For the PD post-treatment, three alternatives were studied at lab-scale, i) UVC irradiation at 254 nm (0.5 h exposure time), ii) UVA irradiation at 365 nm using a TiO2-based photocatalyst and iii) sunlight irradiation using a TiO2-based photocatalyst, the last two for 1 and 2 h. Alternative iii) was also tested at pilot-scale. Degradation of nine compounds was evaluated: acetaminophen (ACE), caffeine (CAF), carbamazepine (CBZ), ketoprofen (KET), ibuprofen (IBU), diclofenac (DCL), clofibric acid (ACB), bisphenol A (BPA), and sotalol (SOT). Overall, the HD-VF-UVC system completely removed (>99.5 %) ACE, CAF, KET, IBU, DCL and ACB, and to a lesser extent SOT (98 %), BPA (83 %) and CBZ (51 %). On the other hand, the HD-VF-UVA/TiO2 system (at 2 h) achieved >99.5 % removal of ACE, CAF, KET, IBU and DCL while ACB, BPA, CBZ and SOT were degraded by 83 %, 81 %, 78 % and 68 %, respectively. Working also at 2 h of exposure time, in summer conditions, the HD-VF-Sol/TiO2 system achieved >99.5 % removal of ACE, CAF, KET, IBU, DCL and ACB, and to a minor extent BPA (80 %), SOT (74 %) and CBZ (69 %). Similar results, although slightly lower for SOT (60 %) and CBZ (59 %), were obtained in the pilot sunlight plus TiO2 catalyst unit. However, the use of sunlight irradiation with a TiO2-based photocatalyst clearly showed lower removal efficiency in autumn conditions (i.e., 47 % SOT, 31 % CBZ).

We report on the degradation of aqueous propranolol (PRO) in a heterogeneous system with natural iron oxide (N.I.O.) and oxalic acid (OAA) under near UV-Vis irradiation. Photolysis experiments showed ca. 65% degradation of PRO after 2 h irradiation, and a similar degradation in the presence of N.I.O. A more efficient PRO removal was obtained upon irradiation within a mixture of N.I.O. and OAA. Under the best conditions considered, complete degradation (> 95%) was observed in less than 10 min, and TOC decreased by 60% after 3 h irradiation. The observed processes were adequately fitted by pseudo-first-order kinetics, the corresponding rate constants were determined, and the effect of different variables analyzed. Photodegradation of PRO is accelerated under acidic conditions, and neutralization takes place along the reaction. Hydroxyl radicals play a predominant role in the photodegradation reaction, as shown by the dramatic inhibition observed upon t-butanol addition. Furthermore, HO center dot formation is strongly dependent on the pH of the medium. LC-MS identification of ten different intermediates leads to the proposal of a degradation mechanism. This photocatalytic system has also proven effective, for the first time, in different real aqueous matrices (river water > distilled water > sewage >> > seawater, revealing quite efficient in the former) and also employing sunlight, where PRO photodegradation was slower. The results obtained show that N.I.O.-oxalate complexes are a green, cheap choice for removing organic pollutants in aqueous solution.

Replacement of classical tertiary water treatment by chemical-free sunlight-driven photocatalytic units has been often proposed. Photocatalysts are required to be cost-effective, inert, chemically stable, reusable, and easy to separate and also that they are mechanically stable. The effect of mechanical stress on a photoactive TiO 2 layer, and on its effectivity for degradation of phenol as a model pollutant, has been studied during photocatalytic water treatment using NUV–vis light. Sol–gel (SG) and liquid phase deposition (LPD) methods have been used to coat spherical glass beads with the photocatalyst (TiO 2 ). Physicochemical characterization of coated glass beads has been performed by N 2 adsorption–desorption isotherms, SEM, EDXS, and AFM. Phenol photocatalyzed degradation was carried out both in stirred batch and flow reactors irradiated with a medium-pressure Hg-vapor lamp ( λ > 350 nm). Phenol concentration was determined by HPLC, and its photoproducts were identified using HPLC/MS. In the stirred batch reactor, all LPD-coated glass beads displayed higher catalytic activity than SG-coated ones, which increased with calcination temperature, 700°C being the most efficient temperature. Preliminary etching of the glass beads surface yielded dissimilar results; whereas, phenol photodegradation with SG-coated etched glass beads is twice faster than with unetched SG ones, the rate reduces to one-third using LPD etched instead of unetched LPD glass beads. Phenol photodegradation using LPD is similar both in stirred batch and flow reactors, despite the latter uses a lower catalyst load. LPD-etched catalyst was recovered and reused in the stirred batch reactor; its activity reduced sharply after the first use, and it also lost activity in successive runs, ca . 10% of activity after each “use and recover” cycle. In the flow reactor, activity loss after the first experiment and recycling (ca. 30%) was much larger than in the following runs, where the activity remained rather constant through several cycles. LPD is more adequate than SG for TiO 2 immobilization onto glass beads, and their calcination at 700°C leads to relatively strong and reactive photocatalytic films. Still, TiO 2 -coated glass beads exhibited very low photoactivity compared to TiO 2 -P25 nanoparticles, though their separation is much easier and almost costless. The durability of the catalytic layer increases when using a flow reactor, with the pollutant solution flowing in a laminar regime through the photocatalyst bed. In this way, the abrasion of the photocatalytic surface is largely reduced and its photoactivity is better maintained.

The authors wish to make the following corrections to this paper: [...].

The authors wish to make the following corrections to this paper: [...]

Photocatalyzed degradation of phenol in aqueous solution over surface impregnated TiO2 (M = Cu, Cr, V) under UV-Vis (366 nm) and UV (254 nm) irradiation is described. Nanosized photocatalyts were prepared from TiO2-P25 by wet impregnation, and characterized by X-ray diffraction, X-ray fluorescence, transmission electron microscopy, UV-Vis diffuse reflectance spectroscopy, Raman spectroscopy, and adsorption studies. No oxide phases of the metal dopants were found, although their presence in the TiO2-P25 lattice induces tensile strain in Cu-impregnated TiO2-P25, whereas compressive strain in Cr- and V-impregnated TiO2-P25. Experimental evidences support chemical and mechanical stability of the photocatalysts. Type IV N2 adsorption–desorption isotherms, with a small H3 loop near the maximum relative pressure were observed. Metal surface impregnated photocatalysts are mesoporous with a similar surface roughness, and a narrow pore distribution around ca. 25 Å. They were chemically stable, showing no metal lixiviation. Their photocatalytic activity was followed by UV-Vis spectroscopy and HPLC–UV. A first order kinetic model appropriately fitted the experimental data. The fastest phenol degradation was obtained with M (0.1%)/TiO2-P25, the reactivity order being Cu > V >> Cr > TiO2-P25 under 366 nm irradiation, while TiO2-P25 > Cu > V > Cr, when using 254 nm radiation. TOC removal under 366 nm irradiation for 300 min showed almost quantitative mineralization for all tested materials, while 254 nm irradiation for 60 min led to maximal TOC removal (ca. 30%). Photoproducts and intermediate photoproducts were identified by HPLC–MS, and appropriate reaction pathways are proposed. The energy efficiency of the process was analysed, showing UV lamps are superior to UVA lamps, and that the efficiency of the surface impregnated catalyst varies in the order Cu > V > Cr.

•Small changes in the rates of the aromatic compounds were observed in both TiO2.•Photodegradation starts with HO addition to the aromatic ring in a two-step process.•A photo-mechanism mediated by HO radicals was the most significant with Hombikat.•CB electrons and ROS generated from CB electrons played a major role with P25.•Ions enhanced photoactivity and faster HO radical formation with Hombikat.

The efficiency of 2-mercaptobenzothiazole (MBT) degradation by heterogeneous photo-Fenton process using local natural clay powder (NCP) is described. Experiments were conducted at natural pH with a batch reactor equipped with a medium-pressure Hg lamp emitting mainly at 366 nm. The natural clay was characterized by SEM-EDS, UV-vis diffuse reflectance spectroscopy, XRF and XRD analysis. The specific BET surface area of the clay was 30.2 m(2) g(-1). The photodegradation of MBT follows first order (for direct photolysis) and pseudo-first order kinetics (for photocatalysis). Direct photolysis of MBT showed a negligible effect both upon 254 and 365 nm irradiation, while 42.5% and 62% of MBT was eliminated in three hours under 310 nm irradiation in the presence of H2O2 and under sunlight irradiation (using NCP), respectively. Kinetic runs carried out with 5.0.10(-5)M MBT and 0.5 g L(-1)clay showed both higher MBT conversion and photodegradation rate at basic pH (10) and in oxygen saturated media. The presence of oxalic acid and H2O2 significantly enhanced MBT photodegradation. The photodegradation of MBT is mainly attributed to reaction with HO%, leading to different intermediates that have been identified by HPLC-MS. A reaction mechanism is proposed. The highest TOC removals were obtained using UVA at low pHs (2.6), and in the absence of O-2 with 68% and 65% TOC removal respectively in two hours, whereas MBT transformation is faster (t 1/2 = 7 min) and higher (90%) at pH = 10. The obtained results strongly support the use of natural clay rich in iron oxides as inexpensive, clean and efficient photocatalysts for water pollutants abatement using heterogeneous photo-Fenton process.

A mont-La (6%)-Cu0.6Cd0.4S nanocomposite was prepared by a simple cation exchange and impregnation method and its application for the phenol removal from wastewater was studied. The photocatalyst was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (XEDS) and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). Phenol in aqueous solution was used as a model compound for evaluation of near UV-vis (filter cut-off for lambda >= 366 nm) photocatalytic activity. We have studied the following parameters: load of photocatalyst, load of phenol, pH, [O-2], and irradiation wavelength. Within 240 min, heterogeneous suspensions of 1 g.L-1 of mont-La (6%)-Cu0.6Cd0.4S nanocomposite allowed removal of ca. 86% of 20 mg.L-1 solution of phenol at pH = 5.44, with dissolved oxygen from air, with 77.8% TOC removal. The kinetics of photocatalytic transformation followed the Langmuir-Hinshelwood kinetic model. Pseudo-first-order kinetics adequately fitted the experimental data and the obtained rate constants are reported. With the mont-La (6%)-Cu0.6Cd0.4S catalyst 84% removal of phenol degradation efficiency was achieved after five consecutive photocatalytic cycles. Twelve main photoproducts were observed from phenol photodegradation, using HPLC-MS. The used photocatalyst is promising for green chemistry use in abatement of persistent organic pollutants. (C) 2017 Elsevier B.V. All rights reserved.

Ammonia oxide ((+)NH(3)O(-)), a zwitterionic tautomer of hydroxylamine (NH(2)OH), has been proposed to explain the high reactivity of NH2OH with phosphate esters. The key parameter for kinetically significant reactions through (+)NH(3)O(-) is the value of the tautomeric constant K(T) = [(+)NH(3)O(-)]/[NH(2)OH], which it has so far proved elusive to measure experimentally. Thermodynamic cycles using CBS-QB3 and CPCM computed data have been used to estimate microscopic and macroscopic acid-base equilibria involving NH(2)OH, the latter in close agreement to the experimental ones, but those involving anions. Calculated K(T) is 2.6 x 10(-2), which indicates that although molecular NH(2)OH is favoured, there should be enough (+)NH(3)O(-) in aqueous solution to be a kinetically active species. (C) 2010 Elsevier B.V. All rights reserved.

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.

The title compounds, C20H20FNO6 and C20H19Cl2NO6, respectively, may exhibit bioactivity. In these compounds, the pyrrolidine ring adopts a conformation intermediate between envelope and half-chair. Only one of the two ethoxycarbonyl side chains is nearly planar. Centrosymmetric pairs are formed, and the crystal structure is stabilized by weak C-H...O hydrogen bonds and van der Waals interactions.

The base-assisted decomposition of (N-X),N-methylethanolamine (X = Cl, Br) takes place mainly through two concurrent processes: a fragmentation and an intramolecular elimination. The global process follows second order kinetics, first order relative to both (N-X),N-methylethanolamine and base. Interaction of the base with the ionizable hydroxylic hydrogen triggers the reaction. The intramolecular elimination pathway leads to formaldehyde and 2-aminoethanol as reaction products via base-assisted proton transfer from the methyl to the partially unprotonated hydroxylic oxygen, with loss of halide. Meanwhile, the fragmentation pathway leads to methylamine and two equivalents of formaldehyde via bimolecular base-promoted concerted breakage of the molecule into formaldehyde, halide ion and N-methylmethanimine. Kinetic evidences allow a crude estimation of the concertedness and characterization of the transition structure for both processes, which are slightly asynchronous, the proton transfer to the base taking place ahead of the rest of the molecular events. The degree of asynchroneity increases as the bases become weaker. Electronic structure calculations, at the B3LYP/6-31++G** level, on the fragmentation pathway support the proposed mechanism.

One-electron oxidation of 1,3,5-triazines is observed with both excited uranyl ion (*UO2(2+)) and sulfate radical anion (SO4.-) in aqueous solution, but not with Tl2+, indicating that the standard reduction potentials E degree of 1,3,5-triazine radical cations are = 2.3 +/- 0.1 V vs. NHE, consistent with theoretical calculations; this suggests that if triazines inhibit electron transfer during photosynthesis, they would need to act on the reductive part of the electron transport chain.

Atrazine (1), Atraton (2) and Ametryn (3) are photodegraded upon 254 nm irradiation, yielding 2-OH-atrazine (4) as a photoproduct. Dealkylation products are also generated, and 4-ethylamino-6-isopropylamino-(1,3,5)triazine was also found as a photoproduct of 3. The main photoreaction is proposed to be an addition-elimination, yielding 4, which subsequently photodegrades. The ease of photodegradation depends on the electron availability at position C-2, the observed order of photoreactivity being 1 > 3 > 4 > 2. Copyright (C) 2003 John Wiley Sons, Ltd.

The crystal structure of the monoclinic form of the title compound, C25H21N, is influenced by the presence of the alkyl chain, whose trans conformation leads to distortion of the aromatic moiety from planarity, the dihedral angle between the two outer rings being ca 20°. The C—C—C ring angles and C—C ring distances nearest to the n-butyl substituent are perturbed from typical values to minimize the steric effect.

The photodegradation of pesticides is reviewed, with particular reference to the studies that describe the mechanisms of the processes involved, the nature of reactive intermediates and final products. Potential use of photochemical processes in advanced oxidation methods for water treatment is also discussed. Processes considered include direct photolysis leading to homolysis or heterolysis of the pesticide, photosensitized photodegradation by singlet oxygen and a variety of metal complexes, photolysis in heterogeneous media and degradation by reaction with intermediates generated by photolytic or radiolytic means.