J. Kiwi

Antibacterial textiles prepared by RF-plasma and vacuum-UV mediated deposition of silver

The bacterial inactivation efficiencies of silver metal and oxides and their combinations on textile fabrics was investigated to evaluate the disinfectant action on airborne bacteria. The inactivation performance was seen to depend on the amount of silver on the textile surface. The preparation of the polyester-polyamide Ag-loaded textiles was carried out by RF-plasma and vacuum-UV (V-UV) surface activation followed by chemical reduction of silver salts. The rate of bacterial inactivation by the silver loaded textile was tested on Escherichia coli K-12 and showed long lasting residual effect. Specular reflectance has been employed to assess the optical properties of the Ag-loaded fabrics. By elemental analysis it was found that levels of Ag loading >0.118% (w/w) for the vacuum-UV samples lead to complete inhibition of bacterial growth. X-ray photoelectron spectroscopy (XPS) shows that for textiles activated by RF or V-UV methods, the silver in the topmost layer increases with increasing concentration of the Ag used in the precursor solution. The exact determination of the oxidation state of the Ag-clusters on the textile is difficult because of the variation of particle size and electrostatic charging of the supported particles. Ag metal was found to be the main component of the Ag-clusters and not Ag2O and AgO as identified by the binding peak energies (BE). By transmission electron spectroscopy (TEM) it was seen that the Ag-clusters were deposited on the two polymer components of the textile fabric but having widely different sizes

Effect of Fenton and photo-Fenton reactions on the degradation and biodegradability of 2 and 4-nitrophenols in water treatment

Abstract Photo-Fenton, Fenton and biodegradation reactions have been investigated in detail during the degradation of 2 and 4-nitrophenols. Fenton-type reactions accelerated nitrophenols degradation in comparison with direct photolysis using pyrex flasks (λ > 290 nm). The influence of Fe3+, H2O2, light, temperature, reactant concentration and gas atmosphere was systematically studied. Experimental techniques used involved total organic carbon determination (TOC), high pressure liquid chromatography (HPLC), nuclear magnetic resonance (NMR) and spectroscopy (OD). A solution containing 3.6·10−1M of 2-nitrophenol was degraded in ca. 3 h (30°C) in the dark and in ca. 1 h (30°C) under light where continuous photoproduction of the Fenton reagent is achieved. This study shows that the hydrolxylation of the phenol ring is fast as compared to the slower concomitant decrease in DOC in dark or light processes. Using NMR an explanation is proposed in terms of pathways involving direct oxidation of the nitrophenols under study by hydroxy type radicals. Chemical insight is provided why the photo-Fenton degradation observed for 2-nitrophenol proceeds at about half the rate than his homologue 4-nitrophenol. Biodegradability of 2-nitrophenol was monitored before and after photo-Fenton treatment by biochemical oxygen demand (BOD) and dissolved organic carbon (DOC) and indicated the formation of substances which are non-biodegradable during photo-Fenton pretreatment.

Degradation of 2,4-dichlorophenol by immobilized iron catalysts.

The degradation of 2,4-Dichlorophenol (from now on 2,4-DCP) has been carried out on Nafion-Fe (1.78%) in the presence of H2O2 under visible light irradiation. A solution containing 2,4-DCP (TOC 72 mg C/L)) is seen to be mineralized in approximately 1 h in the presence of H2O2 (10 mM) under solar simulated visible light (80 mW cm-2) at pH values between 2.8 and 11. Homogeneous photo-assisted Fenton reactions were capable of mediating 2,4-DCP degradation only up to pH 5.4. The degradation kinetics of 2,4-DCP on Nafion-Fe membranes was more favorable than the one observed during Fenton photo-assisted processes at pH 2.8. The degradation of 2,4-DCP was investigated as a function of the substrate, oxidant concentration and applied light intensity. The Nafion-Fe was seen to be effective over many cycles during the photo-catalytic degradation of 2,4-DCP showing an efficient and stable performance during 2,4-DCP degradation without leaching out Fe(3+)-ions into the solution. Evidence is presented that the degradation at the surface of the Nafion-Fe membrane seems to be controlled by mass transfer and not by chemical reaction of the species in solution. The approach used to degrade 2,4-DCP is shown to be valid for other chloro-carbons like 4-chlorophenol, 2,3-chlorophenol and 2,4,5-trichlorophenol.

2. Sensitized degradation of chlorophenols on iron oxides induced by visible light: Comparison with titanium oxide

Abstract The sensitized photocatalytic degradation of mono-, di- and trichlorophenols on iron oxides aqueous suspensions of α-Fe 2 O 3 and α-FeOOH is reported in detail. The degradation of these compounds followed pseudo-first-order kinetics when α-Fe 2 O 3 was used as photocatalyst. α-FeOOH was found to be inactive for chlorophenols degradation with the exception of 2,4-dichlorophenol (2,4-DCP) where a modest effect was observed. The formation of a surface complex by the chlorophenols with the iron oxide and the solubility of the particular chlorophenol in aqueous solution were observed to be the controlling parameters during the photodegradation. The results obtained with the most active catalyst α-Fe 2 O 3 are compared with TiO 2 . Total mineralization of chlorophenols was observed on TiO 2 while on α-Fe 2 O 3 only partial mineralization was observed. In either case, the intermediates produced in solution during the photodegradation were found to be significantly more biodegradable than the initial compound. For mono-, di- and trichlorophenols the overall photocatalytic degradation was observed to increase in the order: 2,4,6-trichlorophenol (2,4,6-TCP) 3- DCP ) chlorophenol (2- CP) ,4-DCP. The former sequence shows that the recalcitrant 2,4-DCP degrades more rapidly than other chlorophenols tested during this study. The photodegradation of chlorophenols on α-Fe 2 O 3 and TiO 2 proceeds mechanistically through para -hydroxylation of the initial compound as suggested by the intermediates found by high-pressure liquid chromatography HPLC during the course of the degradation.

Degradation/decoloration of concentrated solutions of Orange II. Kinetics and quantum yield for sunlight induced reactions via Fenton type reagents

Abstract Light and thermal processes involving Fenton reagent are shown to be effective in the mineralization/decoloration of concentrated Orange II solutions. Light activation accelerates the observed degradation and the UV component of natural sunlight is sufficient to promote the reaction leading to the azo-dye abatement. The degradation involves dark and light steps. Kinetic information on these steps is reported. The results obtained in this study suggests that the thermodynamic potential for the redox couple in a Fenton-like reagent is not the most important factor controlling ther degradation of this dye. A quantum yield of 0.10 was observed for Orange II disappearance. Decoloration of a 2.9 mM dye solution (450 mg Cl−1) is achieved in less than 2 h via photo-Fenton reactions and mineralization is completed to 95% in less than 8 h. A turnover number of 4.7 was estimated for light induced processes in the model system used. Cyanuric acid added to the Fenton system suggests that besides the OH radicals, highly stable Fe-complexes in combination with H2O2 are active in the abatement of this azo-dye. Near surface radical formation is shown to be important during the observed photocatalysis. No activation energy was detected during the mineralization suggesting a radical mechanism for this reaction. The quantum yields observed as a function of wavelength during Orange II disappearance corresponds in experimental error to the point-by-point addition of the absorbance of the Fe3+ and H2O2 solutions used in the photolysis.

Accelerated mineralization of the drug Diclofenac via Fenton reactions in a concentric photo-reactor.

The complete mineralization of concentrated solutions of Diclofenac (2-[(2,6-dichlorophenyl) amino] benzene-acetic acid) sodium salt C14H10C12NO2Na was carried out in a concentric cylindrical immersion photoreactor in batch mode operation. Irradiation with a lamp emitting light at 254 nm (400 W) achieved total mineralization of Diclofenac solutions (0.062 mM or TOC 20 mg C l(-1)) in times under an hour. The mineralization was carried out via Fenton photo-assisted treatment. A determination of the solution parameters was carried out to optimize the time of the Diclofenac pretreatment, the type and intensity of the light source, the effect of the concentrations of Fe-ions and the oxidant added in solution and the reactor recirculation rate. Diclofenac disappearance was monitored by high liquid pressure chromatography (HPLC). Concomitantly, the aromatic and aliphatic intermediates were also monitored under low-energy (36 W) light irradiation at 366 nm in order to be able to detect the intermediates by HPLC in the minute time scale. The decrease of the chemical oxygen demand was followed during Diclofenac degradation. The activation energy for the mineralization of Diclofenac was determined to be 4.02 Kcal mol(-1).

Beneficial effects of homogeneous photo-Fenton pretreatment upon the biodegradation of anthraquinone sulfonate in waste water treatment

Homogeneous photo-oxidation of anthraquinone-2-sulfonic acid sodium salt (ASS) with H2O2 and Fe3+ was investigated. The continuous photoproduction of Fenton reagent can be achieved in this way. The behaviour of Fe3+ was similar to Fe2+ under the same experimental conditions and the photoactivity was favourably influenced in the presence of oxygen. The photo-Fenton reactions greatly accelerated ASS degradation in comparison with direct photolysis using Pyrex flasks (λ > 290 nm). The influence of Fe3+, Cu2+, H2O2 concentration, pH, temperature and gas atmosphere was systematically studied. A solution containing ASS 3·10−3 M was degraded up to ca. 90% under light (AM 1) at 60°C in 3 h and in ca. 5 h at 35°C. Complete oxidation was achieved after 15 h. About 90% of the total organic carbon was degraded to carbon dioxide when dearomatization was completed. Photo-Fenton systems could be used for initial treatment of waste waters containing ASS to obtain aliphatic and oxidized compounds susceptible to being more easily degraded in biological waste water treatment plants. Reaction products were characterized by total organic carbon (TOC); nuclear magnetic resonance (NMR); gas chromatography (GC) and spectroscopy (OD).

Chemical (photo-activated) coupled biological homogeneous degradation of p-nitro-o-toluene-sulfonic acid in a flow reactor

This study presents the combined photochemical (Fenton) and biological flow reactor degradation of p-nitrotoluene-ortho-sulfonic acid (p-NTS). p-NTS is a compound whose degradation is not possible by waste water bacteria. From this point of view it is considered as a non-biodegradable intermediate found in the manufacture of dyes, surfuctants and brighteners. By way of HPLC technique it is shown that the photochemical pretreatment of p-NTS induces dearomatization due to -OH radical attack. A concomitant 20–25% decrease in the initial carbon content during the photochemical pretreatment was observed along the abatement of the aromaticity. This study shows that the intermediates produced in the pretreatment stage are biodegradable. After pretreatment a minimum residual H2O2 (< 0.2 mg l−1) was attained. This level of oxidant did not interfere with the subsequent biological degradation. The influence of the reaction parameters such as: input concentration of p-NTS, rate of H2O2 addition, reactor flow rate, TOC reduction rate and BOD5/COD as a function of the time of photochemical pretreatment are reported. At a flow rate of 0.18 l h−1 (5.5. h residence time) a photochemical degradation efficiency of 75%, a biological degradation efficiency of 52% and an overall degradation efficiency for the coupled process of 88% was observed. The disappearance of p-NTS in the photochemical reactor, the growth and degradation of the benzoquinone like aromatic intermediate followed by the appearance short chain aliphatic compounds are reported as a function of pretreatment time. The increase in BOD/TOC as function of pretreatment time has been correlated to the p-NTS and aliphatic recalcitrants existing in the solution. The biological degradation was observed to be strongly dependent on the flow used and on the pollutant loading of the solution. These were the two main parameters affecting the degradation in the bioreactor.

I. Adsorption mechanism of chlorophenols on iron oxides, titanium oxide and aluminum oxide as detected by infrared spectroscopy

The adsorption of 2-chlorophenol, 2,3- and 2,4-dichlorophenols and 2,4,6-trichlorophenol in liquid and gas phase on iron, titanium and aluminum oxides seem to proceed in a similar way. Higher adsorption of chlorophenols either from gas phase or from aqueous solution was observed on α-Fe2O3 than on α-FeOOH. The low adsorption of chlorophenols from aqueous solution on oxide surfaces suggests that hydrophobic chlorophenols cannot effectively compete with water for the absorption on hydrophilic oxide surface sites. The adsorption of chlorophenols on iron, titanium and aluminum oxides was followed by the adsorption isotherm, HPLC and diffuse reflectance FT-IR (DRIFT) spectroscopy. The adsorption of the chlorophenols on the oxides under study is related to the amount of interfacial water content on the iron oxide. The alumina–chlorophenolate surface complex was found to be weak when compared with either the iron or titanium analogs as seen by the CO stretching vibrations, leading to a lower adsorption on alumina than on iron and titanium oxides.

Dynamics of oxidant addition as a parameter in the modelling of dye mineralization (Orange II) via advanced oxidation technologies

Light and dark processes involving Fenton reagent are effective in the degradation of Orange II solutions. The degradation time is shown to be strongly dependent on the initial pH of the solution used. Experimental results show that the mineralization rates for Orange II become significant only at pH H 2 O 2 added and O 2 evolved were monitored during the degradation cycles allowing optimization for the times for oxidant addition. About 88% dye mineralization in 40 minutes under light irradiation. A model for the degradation has been developed from the available kinetic rates for radical reactions. The model predicts an H 2 O 2 consumption time of ∼100 seconds consistent with the experimental results obtained. A turnover number of 4.7 was estimated for light induced processes in the model system used. Near surface radical formation is shown to be important during the observed photocatalysis. No activation energy was detected during the mineralization suggesting a radical mechanism for this reaction.