Chlorophenols in tap water from wells and surface sources in Rio de Janeiro, Brazil: method validation and analysis

Two analytical methods were validated for determination of trichlorophenols, tetrachlorophenols and pentachlorophenol in drinking water. Limits of quantification were at least ten times lower than maximum permissible levels set by the Brazilian legislation, which are 200 ng mL-1 for 2,4,6-trichlorophenol and 9 ng mL-1 for pentachlorophenol. Chlorophenol levels were determined in tap water collected in the Municipality of Rio de Janeiro. 2,4,6-Trichlorophenol residues were detected in 36% of the samples, varying from 0.008 to 0.238 ng mL-1. All other analytes were below the limit of quantification. The validated methods showed to be suitable for application in routine quality control.

Hidrogeles microestructurados de acrilamida y determinación de su capacidad de absorber agua y etanol

This paper reports the synthesis of nanostructured hydrogels of acrylamide by a two-step polymerisation process. The first step is performed by inverse microemulsion polymerization (water-in-oil) of N-isopropylacrylamide (NIPA), with these particles then added to aqueous solutions of acrylamide (AM), adding a crosslinking agent. The polymerization reaction is then initiated, thereby producing nanostructured hydrogels. We determined the capacity to absorb water, water and / or ethanol when nanostructured hydrogels were immersed in aqueous solutions with different concentrations of ethanol. It was found that the hydrogels were selective in absorbing water in all cases increasing with the ethanol concentration of the solutions.

Occurrence of agrochemicals in surface waters of shallow soils and steep slopes cropped to tobacco

Tobacco cultivation in shallow soils and steep landscape under intense use of agrochemicals contributes to environment degradation. In this study, we assessed the concentration of agrochemicals in draw wells used for human consumption and a creek in a small catchment predominantly cropped to tobacco. Chlorpyrifos, flumetralin, and iprodione were determined by gas chromatography with electron capture detection, while imidalcloprid, atrazine, simazine, and clomazone were quantified by high-performance liquid chromatography with UV detection. Considering all sampling sites, all agrochemicals were detected at least once, except for flumetralin. The occurrence of agrochemicals in tobacco crops is a consequence of their fast transfer to surface water.

Catálise básica usando sílica mesoporosa estabilizada por acrilatos encapsulados

The synthesis of new type of silicas, with structures akin to that of MCM-41, containing polyacrylate-encapsulated micelles in their mesopores is reported. Initially, the monomers were inserted in the aqueous micelles of cetyltrimethylammonium cations. MCM-41 was then prepared in this microemulsion. Finally, the polymerization of the acrylates was initiated by UVC radiation. The presence of monomers and polymers in the interior of micelles in aqueous media were characterized by IR spectroscopy and small-angle Xray scattering. The presence of this polymer increased the stability of these new materials in catalytic transesterification.

METHANE DRY REFORMING OVER Ni SUPPORTED ON PINE SAWDUST ACTIVATED CARBON: EFFECTS OF SUPPORT SURFACE PROPERTIES AND METAL LOADING

The influence of metal loading and support surface functional groups (SFG) on methane dry reforming (MDR) over Ni catalysts supported on pine-sawdust derived activated carbon were studied. Using pine sawdust as the catalyst support precursor, the smallest variety and lowest concentration of SFG led to best Ni dispersion and highest catalytic activity, which increased with Ni loading up to 3 Ni atoms nm-2. At higher Ni loading, the formation of large metal aggregates was observed, consistent with a lower "apparen" surface area and a decrease in catalytic activity. The H2/CO ratio rose with increasing reaction temperature, indicating that increasingly important side reactions were taking place in addition to MDR.

SIMULTANEOUS DETERMINATION OF PROTOCATECHUIC ALDEHYDE AND PROTOCATECHUIC ACID USING THE LOCALIZED SURFACE PLASMON RESONANCE PEAK OF SILVER NANOPARTICLES AND CHEMOMETRIC METHODS

A simple and sensitive spectrophotometric method is proposed for the simultaneous determination of protocatechuic acid and protocatechuic aldehyde. The method is based on the difference in the kinetic rates of the reactions of analytes with [Ag(NH3)2]+ in the presence of polyvinylpyrrolidone to produce silver nanoparticles. The data obtained were processed by chemometric methods using principal component analysis artificial neural network and partial least squares. Excellent linearity was obtained in the concentration ranges of 1.23-58.56 µg mL-1 and 0.08-30.39 µg mL-1 for PAC and PAH, respectively. The limits of detection for PAC and PAH were 0.039 and 0.025 µg mL-1, respectively.

A NOVEL POLYACRYLAMIDE-BASED HYDROGEL CROSSLINKED WITH CELLULOSE ACETATE AND PREPARED BY PRECIPITATION POLYMERIZATION

The synthesis of polyacrylamide-cellulose acetate hydrogels by precipitation polymerization in acetone solution is reported herein. These hydrogels exhibit smaller swelling ratios and larger compression moduli than homo polyacrylamide hydrogels. For cellulose acetate concentrations above 20 wt.%, hydrogels with N,N'-methylenebisacrylamide as a crosslinker exhibit swelling ratios and compression moduli similar to those of the hydrogels without the crosslinker. A possible explanation for this behavior is that cellulose acetate crosslinks polyacrylamide via free-radical reaction. The hydrogels obtained without the N,N'-methylenebisacrylamide crosslinker exhibit compression moduli up to 1.7 MPa, making them suitable for tissue engineering applications such as cartilage replacement.

Surface Modification of Ceramics

Ceramics are widely used in industrial applications due to their advantageous thermal and mechanical stability. Corrosion of ceramics is a great problem resulting in significant costs. Coating is one method of reducing adversities of corrosion. There are several different thin film deposition processes available such as sol-gel, Physical and Chemical Vapour Deposition (PVD and CVD). One of the CVD processes, called Atomic Layer Deposition (ALD) stands out for its excellent controllability, accuracy and wide process capability. The most commonly mentioned disadvantage of this method is its slowness which is partly compensated by its capability of processing large areas at once. Several factors affect the ALD process. Such factors include temperature, the grade of precursors, pulse-purge times and flux of precursors as well as the substrate used. Wrongly chosen process factors may cause loss of self-limiting growth and thus, non-uniformities in the deposited film. Porous substrates require longer pulse times than flat surfaces. The goal of this thesis was to examine the effects of ALD films on surface properties of a porous ceramic material. The analyses applied were for permeability, bubble point pressure and isoelectric point. In addition, effects of the films on corrosion resistance of the substrate in aqueous environment were investigated. After being exposured to different corrosive media the ceramics and liquid samples collected were analysed both mechanically and chemically. Visual and contentual differences between the exposed and coated ceramics versus the untreated and uncoated ones were analysed by scanning electron microscope. Two ALD film materials, dialuminium trioxide and titanium dioxide were deposited on the ceramic substrate using different pulse times. The results of both film materials indicated that surface properties of the ceramic material can be modified to some extent by the ALD method. The effect of the titanium oxide film on the corrosion resistance of the ceramic samples was observed to be fairly small regardless of the pulse time.

The Li+, Na+ and K+ ion exchange reaction process on the surface of mixed oxide SiO2/TiO2/Sb2O5 surface prepared by the sol-gel processing method

The porous mixed oxide SiO2/TiO2/Sb2O5 obtained by the sol-gel processing method presented a good ion exchange property and a high exchange capacity towards the Li+, Na+ and K+ ions. In the H+/M+ ion exchange process, the H+ / Na+ could be described as presenting an ideal character. The ion exchange equilibria of Li+ and K+ were quantitatively described with the help of the model of fixed tetradentate centers. The results of simulation evidence that for the H+ / Li+ exchange the usual situation takes place: the affinity of the material to the Li+ ions is decreased with increasing the degree of ion exchange. On the contrary, for K+ the effects of positive cooperativity, that facilitate the H+ / K+ exchange, were revealed.

A water soluble 3-n-propyl-1-azonia-4-azabicyclo[2.2.2]octanechloride silsesquioxane grafted onto Al/SiO2 surface: chromium adsorption study

The water soluble material, 3-n-propyl-1-azonia-4-azabicyclo[2.2.2]octanechloride silsesquioxane (dabcosil silsesquioxane) was obtained. The dabcosil silsesquioxane was grafted onto a silica surface, previously modified with aluminum oxide. The resulting solid, dabcosil-Al/SiO2, presents 0.15 mmol of dabco groups per gram of material. The product of the grafting reaction was analyzed by infrared spectroscopy and N2 adsorption-desorption isotherms. The dabcosil-Al/SiO2 material was used as sorbent for chromium (VI) adsorption in aqueous solution.

Immersion enthalpy variation of surface-modified mineral activated carbon in lead (II) aqueous solution adsorption: the relation between immersion enthalpy and adsorption capacity

An activated carbon was obtained by chemical activation with phosphoric acid, CM, from a mineral carbon. Afterwards, the carbon was modified with 2 and 5 molL-1, CMox2 and CMox5 nitric acid solutions to increase the surface acid group contents. Immersion enthalpy at pH 4 values and Pb2+ adsorption isotherms were determined by immersing activated carbons in aqueous solution. The surface area values of the adsorbents and total pore volume were approximately 560 m².g-1 and 0.36 cm³g-1, respectively. As regards chemical characteristics, activated carbons had higher acid sites content, 0.92-2.42 meq g-1, than basic sites, 0.63-0.12 meq g-1. pH values were between 7.4 and 4.5 at the point of zero charge, pH PZC. The adsorbed quantity of Pb2+ and the immersion enthalpy in solution of different pH values for CM activated carbon showed that the values are the highest for pH 4, 15.7 mgg-1 and 27.6 Jg-1 respectively. Pb2+ adsorption isotherms and immersion enthalpy were determined for modified activated carbons and the highest values were obtained for the activated carbon that showed the highest content of total acid sites on the surface.

Adsorption of hidrogen peroxide on the surface of silica - titania mixed oxide obtained by the sol-gel processing method

This work describes the sol-gel mixed oxide SiO2/TiO2 property, ST, as prepared, and submitted to heat treatment a 773 K, STC. SEM and EDS images show, within magnification used, a uniform distribution of the TiO2 particles in SiO2/TiO2 matrix. Both, ST and STC adsorb hydrogen peroxide on the surface and through EPR and UV-Vis diffuse reflectance spectra, it was possible to conclude that the species on the surface is the peroxide molecule attached to the Lewis acid site of titanium particle surface, alphaTi(H2O2)+. As the material is very porous, presumably the hydrogen peroxide molecule is confined in the matrix pores on the surface, a reason why the adsorbed species presents an exceptional long lived stability.

Lanthanum based high surface area perovskite-type oxide and application in CO and propane combustion

The perovskite-type oxides using transition metals present a promising potential as catalysts in total oxidation reaction. The present work investigates the effect of synthesis by oxidant co-precipitation on the catalytic activity of perovskite-type oxides LaBO3 (B= Co, Ni, Mn) in total oxidation of propane and CO. The perovskite-type oxides were characterized by means of X-ray diffraction, nitrogen adsorption (BET method), thermo gravimetric and differential thermal analysis (ATG-DTA) and X-ray photoelectron spectroscopy (XPS). Through a method involving the oxidant co-precipitation it's possible to obtain catalysts with different BET surface areas, of 33-44 m²/g, according the salts of metal used. The characterization results proved that catalysts have a perovskite phase as well as lanthanum oxide, except LaMnO3, that presents a cationic vacancies and generation for known oxygen excess. The results of catalytic test showed that all oxides have a specific catalytic activity for total oxidation of CO and propane even though the temperatures for total conversion change for each transition metal and substance to be oxidized.

Biosynthesis of Yersinia enterocolitica serotype O:3 lipopolysaccharide outer core

Lipopolysacharide (LPS) present on the outer leaflet of Gram-negative bacteria is important for the adaptation of the bacteria to the environment. Structurally, LPS can be divided into three parts: lipid A, core and O-polysaccharide (OPS). OPS is the outermost and also the most diverse moiety. When OPS is composed of identical sugar residues it is called homopolymeric and when it is composed of repeating units of oligosaccharides it is called heteropolymeric. Bacteria synthesize LPS at the inner membrane via two separate pathways, Lipid A-core via one and OPS via the other. These are ligated together in the periplasmic space and the completed LPS molecule is translocated to the surface of the bacteria. The genes directing the OPS biosynthesis are often clustered and the clusters directing the biosynthesis of heteropolymeric OPS often contain genes for i) the biosynthesis of required NDP-sugar precursors, ii) glycosyltransferases needed to build up the repeating unit, iii) translocation of the completed O-unit to the periplasmic side of the inner membrane (flippase) and iv) polymerization of the repeating units to complete OPS. The aim of this thesis was to characterize the biosynthesis of the outer core (OC) of Yersinia enterocolitica serotype O:3 (YeO3). Y. enterocolitica is a member of the Gram-negative Yersinia genus and it causes diarrhea followed sometimes by reactive arthritis. The chemical structure of the OC and the nucleotide sequence of the gene cluster directing its biosynthesis were already known; however, no experimental evidence had been provided for the predicted functions of the gene products. The hypothesis was that the OC biosynthesis would follow the pathway described for heteropolymeric OPS, i.e. a Wzy-dependent pathway. In this work the biochemical activities of two enzymes involved in the NDP-sugar biosynthesis was established. Gne was determined to be a UDP-N-acetylglucosamine-4-epimerase catalyzing the conversion of UDP-GlcNAc to UDP-GalNAc and WbcP was shown to be a UDP-GlcNAc- 4,6-dehydratase catalyzing the reaction that converts UDP-GlcNAc to a rare UDP-2-acetamido- 2,6-dideoxy-d-xylo-hex-4-ulopyranose (UDP-Sugp). In this work, the linkage specificities and the order in which the different glycosyltransferases build up the OC onto the lipid carrier were also investigated. In addition, by using a site-directed mutagenesis approach the catalytically important amino acids of Gne and two of the characterized glycosyltranferases were identified. Also evidence to show the enzymes involved in the ligations of OC and OPS to the lipid A inner core was provided. The importance of the OC to the physiology of Y. enterocolitica O:3 was defined by determining the minimum requirements for the OC to be recognized by a bacteriophage, bacteriocin and monoclonal antibody. The biological importance of the rare keto sugar (Sugp) was also shown. As a conclusion this work provides an extensive overview of the biosynthesis of YeO3 OC as it provides a substantial amount of information of the stepwise and coordinated synthesis of the Ye O:3 OC hexasaccharide and detailed information of its properties as a receptor.