Hybrid photocatalysts for the degradation of trichloroethylene in air

Hybrid photocatalysts based on an adsorbent SiMgOx and a photocatalyst TiO(2) were developed in a plate shape. The ceramic surface was coated with TiO(2) by the slip-casting technique. The effect of the support in the photocatalytic degradation of trichloroethylene (TCE) was analyzed by modifying TiO(2) loading and the layer thickness. Photocatalysts were characterised by N(2) adsorption-desorption, mercury intrusion porosimetry, SEM, UV-vis spectroscopy and XRD. A direct relationship between the TiO(2) content and the photocatalytic activity was observed up to three layers of TiO(2) (0.66 wt.%). Our results indicate that intermediate species generated on the TiO(2) layer can migrate through relatively long distances to react with the OH(-) surface groups of the support. By increasing the TiO(2) loading of the photocatalyst two effects were observed: trichloroethylene conversion is enhanced, while the efficiency of the oxidation process is decreased at expenses of increasing the selectivity to COCl(2) and dichloroacetylchloride (DCAC). The results are discussed in terms of the layer thickness, TiO(2) amount, TCE conversion and CO(2), and COCl(2) selectivity. (C) 2009 Elsevier B.V. All rights reserved.

SnO(2)-based materials for pesticide degradation

This study presents the results of the degradation of the pesticide atrazine using electrochemical and photo-assisted electrochemical degradation techniques using SnO(2)-containing electrode of nominal composition electrodes of composition Ti/Ru(x)Sni-(x)O(2) (where X = 0.10, 0.15, 0.20, 0.25 and 0.30). The materials were characterized ex situ and in situ in order to correlate the observed atrazine removal rates with electrode morphology/composition. The results obtained demonstrate the effectiveness of the photo-assisted electrochemical degradation. Using purely electrochemical methods the rate of atrazine removal is almost zero at all the electrodes studied. However, the application of photo-assisted degradation results in almost complete atrazine removal in 1 h of electrolysis. The efficiency of atrazine degradation does not seem to be greatly affected by the electrode material or by SnO(2) content, but the overall COD removal is dependent on the SnO(2) content. Overall, the SnO(2)-containing electrodes do not reach the level of COD removal (maximum similar to 21%) seen for the Ti/Ru(0.3)Ti(0.2)O(2) electrode. An interesting correlation between the morphology factor (phi) and chemical oxygen demand removal is observed. (C) 2010 Elsevier B.V. All rights reserved.

Study of photo-assisted electrochemical degradation of carbaryl at dimensionally stable anodes (DSA (R))

This paper presents the results concerning the degradation of the pesticide carbaryl comparing two methods: electrochemical (EC) and photo-assisted electrochemical (PAEC). The experimental variables of applied current density, electrolyte flow-rate and initial carbaryl concentration were investigated. The results demonstrate that the electrochemical degradation of carbaryl was greatly enhanced when simultaneous UV light was applied. The greatest difference between the PAEC and EC method was apparent when lower current densities were applied. The extent of COD removal was much enhanced for the combined method, independent of the applied current density. It should be noted that the complete removal of carbaryl was achieved with out the need to add NaCl to the reaction mixture, avoiding the risk of chlorinated organic species formation. (C) 2009 Elsevier B.V. All rights reserved.

Heterogeneous photocatalytic degradation of acid dyes in aqueous TiO2 suspensions: Kinetics and toxicity

This work assesses the photocatalytic (TiO2/UV) degradation of a simulated acid dye bath (Yellow 3, Red 51, Blue 74, and auxiliary chemicals). Color and phytotoxicity removal were monitored by spectrophotometry and lettuce (Lactuca sativa) seeds as the test organism, respectively. Mineralization was determined by DOC analyses. Photocatalytic, photolytic, and adsorption experiments were performed, showing that adsorption was negligible. After 240 minutes of irradiation, it was achieved 96% and 78% of color removal with photocatalysis and photolysis, respectively. 37% of mineralization occurred with photocatalysis only. The dye bath was rendered completely non-toxic after 60 minutes of photocatalytic treatment; the same result was only achieved with photolysis after 90 minutes. A kinetic model composed of two first-order in series reactions was used. The first photocatalytic decolorization rate constant was k(1) = 0.062 min(-1) and the second k(2) = 0.0043 min(-1), approximately two times greater than the photolytic ones.

On the activation and physical degradation of boron-doped diamond surfaces brought on by cathodic pretreatments

The electrochemical activation and physical degradation of boron-doped diamond (BDD) electrodes with different boron doping levels after repeated cathodic pretreatments are reported. Galvanostatic cathodic pretreatment passing up to -14000 C cm(-2) in steps of -600 C cm(-2) using -1 A cm(-2) caused significant physical degradation of the BDD surface, with film detachment in some areas. Because of this degradation, a great increase in the electrochemically active area was observed in Tafel plots for the hydrogen evolution reaction (HER) in acid media. The minimum cathodic pretreatment needed for the electrochemical activation of the BDD electrodes without producing any observable physical degradation on the BDD surfaces was determined using electrochemical impedance spectroscopy (EIS) measurements and cyclic voltammetry: -9 C cm(-2), passed at -1 A cm(-2). This optimized cathodic pretreatment can be safely used when electrochemical experiments are carried out on BDD electrodes with doping levels in the range between 800 and 8000 ppm.

Photo-assisted electrochemical degradation of the commercial herbicide atrazine

This paper presents a degradation study of the pesticide atrazine using photo-assisted electrochemical methods at a dimensionally stable anode (DSA (R)) of nominal composition Ti/Ru(0.3)Ti(0.7)O(2) in a prototype reactor. The effects of current density, electrolyte flow-rate, as well as the use of different atrazine concentrations are reported. The results indicate that the energy consumption is substantially reduced for the combined photochemical and electrochemical processes when compared to the isolated systems. It is observed that complete atrazine removal is achieved at low current densities when using the combined method, thus reducing the energy required to operate the electrochemical system. The results also include the investigation of the phytotoxicity of the treated solutions.

Photo-assisted electrochemical degradation of real textile wastewater

In the present study, photo-assisted electrochemical degradation of real textile wastewater was performed. Degradation assays were performed at constant current (40 mA cm(-2)) in a combined electro/photochemical flow-cell using a Ti/Ru(0.3)Ti(0.7)O(2) DSA(R) type electrode. The results show that the method is capable of removing color and chemical oxygen demand (COD) from the effluent. Additionally, the effect of initial pH and type of supporting electrolyte (Na(2)SO(4) or NaCl) was investigated. The principal figures of merit used in this study were COD removal and color removal (605 nm). The results show that up to 72% color and up to 59% COD removal in 120 min is possible under the operating conditions employed. Studies of the phytotoxicity of the wastewater before and after the photo-assisted degradation assays are also presented and the results demonstrate that the toxicity of the effluent is dependent on the length of electrolysis time and the treatment procedure employed.

Degradation of alachlor herbicide by gamma radiation from cobalt-60 in aqueous and alcohol solution

Alachlor has been widely used in agriculture all over the world. It is suggested that it may be a carcinogen and an environmental estrogen. The aim of this work was to verify the degradation the alachlor by gamma radiation. Gamma radiation from (60)Co was used to degrade the alachlor herbicide in water and methanol solution. The alachlor in water and alcohol solution in the concentration of 100 mgL(-1) was irradiated with doses of 0.25-50 kGy, at dose rate 5-6 and 2.7 kGyh(-1). High performance liquid chromatography was used as an analytical technique to determine the degradation rate of herbicide studied.

Heterogeneous photocatalytic degradation of reactive dyes in aqueous TiO(2) suspensions: Decolorization kinetics

This work assesses the photocatalytic (TiO(2)/UV) degradation of a simulated reactive dye bath (Black 5, Red 239, Yellow 17, and auxiliary chemicals). Color removal was monitored by spectrophotometry. Mineralization was determined by DOC analyses. Photocatalytic, photolytic, and adsorption experiments were performed, showing that adsorption was negligible. After 30 min of irradiation, it was achieved 97% and 40% of color removal with photocatalysis and photolysis, respectively. No mineralization occurred within 30 min. A kinetic model composed of two, first-order in-series reactions was used. The first photocatalytic decolorization rate constant was k(1) = 2.6 min(-1) and the second k(2) = 0.011 min(-1). The fast decolorization of Reactive Black 5 dye is an indication that the number of azo and vinylsulfone groups in the dye molecule maybe a determining factor for the increased photolytic and photocatalytic color removal and degradation rates. (C) 2008 Elsevier B.V. All rights reserved.

TiO(2)-PHOTOCATALYZED DEGRADATION OF PHENOL IN SALINE MEDIA IN AN ANNULAR REACTOR: HYDRODYNAMICS, LUMPED KINETICS, INTERMEDIATES, AND ACUTE TOXICITY

The photocatalytic degradation of phenol in aqueous suspensions of TiO(2) under different salt concentrations in an annular reactor has been investigated. In all cases, complete removal of phenol and mineralization degrees above 90% were achieved. The reactor operational parameters were optimized and its hydrodynamics characterized in order to couple mass balance equations with kinetic ones. The photodegradation of the organics followed a Langmuir-Hinshelwood-Hougen- Watson lumped kinetics. From GC/MS analyses, several intermediates formed during oxidation have been identified. The main ones were catechol, hydroquinone, and 3-phenyl-2-propenal, in this order. The formation of negligible concentrations of 4-chlorophenol was observed only in high salinity medium. Acute toxicity was determined by using Artemia sp. as the test organism, which indicated that intermediate products were all less toxic than phenol and a significant abatement of the overall toxicity was accomplished, regardless of the salt concentration.

Photochemical degradation of 2,4-D and atrazine in well-defined media

Atrazine and 2,4-D are common herbicides used for crop, lawn, and rangeland management. Photochemical degradation has been proposed as one safe and efficient remediation strategy for both 2,4-D and Atrazine. In the presence of iron(llI) and hydrogen peroxide these herbicides decay by both thermal and light induced oxidation. Past studies have focused primarily on sun light as an energy source. This work provides a mechanistic description of herbicide degradation incorporating intermediate degradation products produced in the dark and under well-defined light conditions.

An improved and fast UHPLC-PDA methodology for determination of L-ascorbic and dehydroascorbic acids in fruits and vegetables: evaluation of degradation rate during storage

This study provides a versatile validated method to determine the total vitamin C content, as the sum of the contents of L-ascorbic acid (L-AA) and dehydroascorbic acid (DHAA), in several fruits and vegetables and its degradability with storage time. Seven horticultural crops from two different origins were analyzed using an ultrahigh-performance liquid chromatographic–photodiode array (UHPLC-PDA) system, equipped with a new trifunctional high strength silica (100% silica particle) analytical column (100 mm×2.1 mm, 1.7 μm particle size) using 0.1% (v/v) formic acid as mobile phase, in isocratic mode. This new stationary phase, specially designed for polar compounds, overcomes the problems normally encountered in HPLC and is suitable for the analysis of large batches of samples without L-AA degradation. In addition, it proves to be an excellent alternative to conventional C18 columns for the determination of L-AA in fruits and vegetables. The method was fully validated in terms of linearity, detection (LOD) and quantification (LOQ) limits, accuracy, and inter/intraday precision. Validation experiments revealed very good recovery rate of 96.6±4.4% for L-AA and 103.1±4.8 % for total vitamin C, good linearity with r2-values >0.999 within the established concentration range, excellent repeatability (0.5%), and reproducibility (1.6%) values. The LOD of the method was 22 ng/mL whereas the LOQ was 67 ng/mL. It was possible to demonstrate that L-AA and DHAA concentrations in the different horticulture products varied oppositely with time of storage not always affecting the total amount of vitamin C during shelf-life. Locally produced fruits have higher concentrations of vitamin C, compared with imported ones, but vegetables showed the opposite trend. Moreover, this UHPLC-PDA methodology proves to be an improved, simple, and fast approach for determining the total content of vitamin C in various food commodities, with high sensitivity, selectivity, and resolving power within 3 min of run analysis.

New bacterial cellulose nanocomposites prepared by in situ radical polymerization of methacrylate monomers

Bacterial cellulose/polymethacrylate nanocomposites have received attention in numerous areas of study and in a variety of applications. The attractive properties of methacrylate polymers and bacterial cellulose, BC, allow the synthesis of new nanocomposites with distinct characteristics. In this study, BC/poly(glycidylmethacrylate) (BC/PGMA) and BC/poly(ethyleneglycol)methacrylate (BC/PPEGMA) nanocomposites were prepared through in situ free radical polymerization of GMA and PEGMA, respectively. Ammonium persulphate (APS) was used as an initiator and N,N’methylenebisacrilamide (MBA) was used as a crosslinker in BC/PGMA. Chemical composition, morphology, thermal stability, water absorption, mechanic and surface properties were determined through specific characterization techniques. The optimal polymerization was obtained at (1:2) for BC/PGMA, (1:2:0.2) ratio for BC/GMA/MBA and (1:20) for BC/PPEGMA, with 0.5% of initiator at 60 ºC during 6 h. A maximum of 67% and 87% of incorporation percentage was obtained, respectively, for the nanocomposites BC/PGMA/MBA and BC/PPEGMA. BC/PGMA nanocomposites exhibited an increase of roughness and compactation of the three-dimensional structure, an improvement in the thermal and mechanical properties, and a decrease in their swelling ability and crystallinity. On the other hand, BC/PPEGMA showed a decrease of stiffness of three-dimensional structure, improvement in thermal and mechanical properties, an increase in their swelling ability and a decrease the crystallinity. Both BC/polymethacrylate nanocomposites exhibited a basic surface character. The acid treatment showed to be a suitable strategy to modifiy BC/PGMA nanocomposites through epoxide ring-opening reaction mechanism. Nanocomposites became more compact, smooth and with more water retention ability. A decrease in the thermal and mechanical proprieties was observed. The new nanocomposites acquired properties useful to biomedical applications or/and removal of heavy metals due to the presence of functional groups.

Prevention of bacterial translocation using β-(1-3)-D-glucan in small bowel ischemia and reperfusion in rats

To investigate the role of β-(1-3)-D-glucan on 99mTc labelled Escherichia coli translocation and cytokines secretion in rats submitted to small bowel ischemia/reperfusion injury. Methods: Five groups (n=10 each) of Wistar rats were subjected to control(C), sham(S), group IR subjected to 45 min of bowel ischemia/60 min of reperfusion(I/R), and group I/R+glucan subjected to 45 min of bowel ischemia/60 min of reperfusion(I/R) and injected with 2mg/Kg intramuscular. Translocation of labelled bacteria to mesenteric lymph nodes, liver, spleen, lung and serum was determined using radioactivity/count and colony forming units/g(CFU/g). Serum TNFα, IL-1β, IL-6, IL-10 were measured by ELISA. Results: CFU/g and radioactivity/count were higher in I/R than in I/R+glucan rats. In C, S and S+glucan groups, bacteria and radioactivity/count were rarely detected. The I/R+glucan rats had enhancement of IL-10 and suppressed production of serum TNFα, IL-1β and, IL-6, compared to I/R untreated animals. Conclusion: The β-(1-3)-D-glucan modulated the production of pro-inflammatory and anti-inflammatory cytokines during bowel ischemia/reperfusion, and attenuated translocation of labelled bacteria

Bacterial translocation in rats nonfunctioning diverted distal colon

To investigate whether the alterations of the diverted colon segment mucosa, evidenced in fecal colitis, would be able to alter Bacterial Translocation (BT). Methods: Sixty-two Wistar male rats ranging from 220 to 320 grams of weight, were divided in two groups: A (Colostomy) and B (Control), with 31 animals each one. In group A, all animals underwent end colostomy, one stoma, in ascending colon; and in the 70th POD was injected in five rats, by rectal route – diverted segment - 2ml of a 0.9% saline solution in animals (A1 subgroup); in eight it was inoculated, by rectal route, 2ml of a solution containing Escherichia coli ATCC 25922 (American Type Culture Collection), in a concentration of 108 Colony Forming Unit for milliliters (CFU/ml) - A2 Subgroup; in ten animals the same solution of E. coli was inoculated, in a concentration of 1011 CFU/ml (A3 Subgroup); and in eight it was collected part of the mucus found in the diverted distal colonic segment for neutral sugars and total proteins dosage (A4 subgroup). The animals from the group B underwent the same procedures of group A, but with differences in the colostomy confection. In rats from subgroups A1, A2, A3, B1, B2, and B3 2ml of blood were aspirated from the heart, and fragments from mesenteric lymphatic nodule, liver, spleen, lung and kidney taken for microbiological analysis, after their death. This analysis consisted of evidencing the presence of E. coli ATCC 25922 CFU. Mann-Whitney and ANOVA Tests were applied as analytic techniques for association of variables. Results: The occurrence of BT was evidenced only in those animals in which inoculated concentration of E. coli ATCC 25922, reached levels of 1011CFU/ml, i.e. in Subgroups A3 and B3, although, being significantly greater (80%) in those animals without colostomy (subgroup B3) when compared to the ones with colostomy (20%) from the subgroup A3 (P <0.05). Lung, liver and mesenteric lymphatic nodules were the tissues with larger percentile of bacterial recovery, so much in subgroup A3, as in B3. Blood culture was considered positive in 60% of the animals from subgroup B3 and in 10% of those from subgroup A3 (p <0.05). There was greater concentration of neutral sugars, in subgroup A4 - mean 27.3mg/ml -, than in subgroup B4 - mean 8.4mg/ml - (P <0.05). Conclusion: The modifications in the architecture of intestinal mucosa in colitis following fecal diversion can cause alterations in the intestinal barrier, but it does not necessarily lead to an increased frequency of BT