Jairo Tronto

Hidróxidos duplos lamelares: nanopartículas inorgânicas para armazenamento e liberação de espécies de interesse biológico e terapêutico

Studies about the inorganic nanoparticles applying for non-viral release of biological and therapeutic species have been intensified nowadays. This work reviews the preparation strategies and application of layered double hydroxides (LDH) as carriers for storing, carrying and control delivery of intercalated species as drugs and DNA for gene therapy. LDH show low toxicity, biocompatibility, high anion exchange capacity, surface sites for functionalization, and a suitable equilibrium between chemical stability and biodegradability. LDH can increase the intercalated species stability and promote its sub-cellular uptake for biomedical purposes. Concerning the healthy field, LDH have been evaluated for clinical diagnosis as a biosensor component.

Biopolymer-clay nanocomposites: cassava starch and synthetic clay cast films

Polymer-clay nanocomposites (PCN) based on cassava starch, synthetic hectorite clay and inverted sugar cane syrup (plasticizer) were prepared by solvent-assisted (casting) process producing transparent and homogeneous films. Small amounts of clay (5-15 wt.%) resulted mainly in exfoliated nanocomposites while large amounts (30 wt.%) promote the intercalated nanocomposites formation. FT-Raman bands sensitive to hydrogen bonding in starch granules are progressively shifted to lower wavenumbers as the clay content is raised. Nanocomposites show a similar thermal behavior up to 320 oC while the biomolecule decomposition at about 500 oC is dependent on the clay content. CO2 release at about 300 oC (non-oxidative decomposition of polymeric chains) decreases if compared to the gas delivery at ca. 500 oC, as the clay content is increased. Films with clay content higher than 10 wt.% show no substantial benefit for either elongation or resistance properties.

Thermal decomposition and recovery properties of ZnAl–CO3 layered double hydroxide for anionic dye adsorption: insight into the aggregative nucleation and growth mechanism of the LDH memory effect.

The thermal decomposition of carbonate-intercalated layered double hydroxide (ZnAl–CO3-LDH) and recovery induced by water and dye solution addition were studied in situ by time-resolved wide angle X-ray scattering (WAXS) and time-resolved X-ray absorption spectroscopy (XAS), providing insights into the mechanisms of these structural transformations. LDH nanostructure recovery was driven by an aggregative nucleation and growth mechanism, which is limited by the steric hindrance caused by the adsorption of the Acid Blue 113 azo dye (AB) on the external surface of both the nanocrystalline tactoids and the exfoliated layers. The recovery behaviour in dye solution is consistent with the hypothesis of the LDH-recovery by a direct synthesis process, generating nanosized LDH particles with thickness about four times lower than those induced by water addition. These findings explain the higher AB adsorption capacity (1587 mg g−1) of calcined LDH, compared to pristine ZnAl–CO3-LDH (261.8 mg g−1) and also the efficient recycling of the spent adsorbent.

Extraction and concentration of biogenic calcium oxalate from plant leaves

O objetivo deste estudo foi extrair e concentrar cristais de oxalato de calcio (CaOx) a partir de folhas de plantas que formam os cristais mencionados. Os estudos quimicos e fisicos de CaOx de plantas a serem realizados demandam uma massa adequada dos cristais. A planta usada neste estudo foi o croton (Codiaeum variegatum). As folhas foram trituradas por um liquidificador industrial e peneiradas em peneira de 0,20 mm. Ao suco obtido foi adicionada agua destilada. Os cristais foram concentrados no fundo da proveta. E necessario manter a lavagem dos cristais ate que o sobrenadante fique livre de pigmentos de plantas e outras substâncias orgânicas. Os cristais de CaOx apresentaram picos bem formados e estreitos, indicando que sua cristalinidade e muito alta; alem disso, esses cristais nao foram danificados durante o procedimento de extracao, o que pode ser visto observando-se as fotos obtidas pelo microscopio eletronico de varredura. O metodo apresentado pode ser considerado eficiente para extrair e concentrar cristais de oxalato de calcio biogenico.

Native defects as sources of optical transitions in MgAl2O4 spinel

The outstanding physical and chemical properties of the magnesium aluminate (MgAl2O4) spinel makes it an important material for novel technological applications. Considering that a presence of native defects can promote important changes in those properties, in this work we present a study of the structural, electronic and thermodynamic properties of the MgAl2O4 spinel. The calculated formation energy for isolated defects, such as the vacancies of magnesium (V Mg), aluminum (V Al) and oxygen (V O), oxygen interstitial (Oi), magnesium and aluminum antisites (MgAl, AlMg), as well as some complex defects (V O + Oi, V O + AlMg, V O + MgAl, MgAl + AlMg) in the most stable charge states are shown. Through experimental data, we obtained that complex defects centers, such as V O , V O + Oi, V O + AlMg and VO + MgAl at different charge states are good candidates for the observed optical transitions at 4.75, 5.3, and 6.4 eV. Our findings were obtained from ab initio electronic structure calculations performed by using density functional theory. The Perdew–Burke–Ernzerhof generalized gradient approximation was used for the exchange-correlation potential. Furthermore, a modified Becke-Johnson exchange potential (GGA-mBJ) correction to the exchange potential were used to obtain a suitable value for the band gap energy, 7.40 eV, in accordance with the experimental one of 7.8 eV.

Removal of Sodium Dodecylbenzenesulphonate and Cetyltrimethylammonium Bromide Using a Carbon Composite Derived from Modified Zn–Al-Layered Double Hydroxide

We describe the synthesis of a composite carbon derived from zinc–aluminium-layered double hydroxides. The material was characterized by powder X-ray diffraction, Fourier transform infrared/attenuated total reflectance spectroscopy, thermogravimetric analysis–differential scanning calorimetry–mass spectrometry, measurement of BET specific surface area, zeta-potential analysis and scanning electron microscopy. The resulting material was used for adsorption studies with an anionic surfactant, sodium dodecylbenzenesulphonate, and a cationic surfactant, cetyltrimethylammonium bromide, as adsorbates. The adsorption of the surfactants was well described by the typical Langmuir pattern. An investigation of the influence of initial pH of a medium on surfactant adsorption showed that high pH values decrease the adsorption capacity of the adsorbent. The adsorption processes were exothermic. The results also showed that the adsorption of the two surfactants was chemical and that the kinetic models were best described by a pseudo-second-order model.

A flow injection procedure using Layered Double Hydroxide for on line pre-concentration of fluoride

This work showed a flow system designed with solenoid valves for preconcentration of fluoride using SPADNS method in water samples. The analyte was preconcentrated in a mini-column coated with Layered Double Hydroxides (LDH) used as adsorbent. Then, the fluoride ions were eluted with 0.5molL-1 sodium hydroxide and determined by spectrophotometry. The variables that affect the system such adsorbent mass, type of eluent, solutions flow rate, reagent concentration and pH effect were critically evaluated. Under optimized conditions, the detection limit, coefficient of variation, linear range and preconcentration factor were estimated at 15µgL-1 (99.7% confidence level), 0.8% (500µgL-1, n = 10), 50-500µgL-1 and 10, respectively. The accuracy of the method was evaluated by analysis of ALPHA APS 1076 (Simulated Rain Water) certified material, the values were not significantly different at a 95% level of confidence. The method was applied for fluoride determination in water samples and the levels found were below the maximum values established by Brazilian environmental and health legislations.

Starch, cellulose acetate and polyester biodegradable sheets: Effect of composition and processing conditions

The production of biodegradable plastic materials using natural resources has aroused increased attention due to environmental concerns. This study aimed to manufacture novel, commercially feasible, biodegradable sheets by flat die extrusion-calendering process produced with thermoplastic starch/plasticized cellulose acetate (TPS/PCA) and thermoplastic starch/plasticized cellulose acetate/poly (butylene adipate-co-terephthalate) (TPS/PCA/PBAT) blends, and to investigate the effects of composition and processing conditions, morphological characteristics, and thermal properties. The results showed that TPS/PCA and TPS/PCA/PBAT biodegradable sheets properties were highly dependent upon both composition and processing temperature. The morphological characteristics and thermal properties of the sheets demonstrated the good compatibility between TPS and PCA in TPS/PCA blends, mainly at higher processing temperatures, whereas TPS/PCA/PBAT sheets present a heterogeneous structure due to the poor compatibility between the components. TPS/PCA biodegradable sheets presented suitable processability and handleability characteristics that allow them to be considered as a novel eco-friendly, economically feasible alternative to conventional plastic materials.

Characterization of biochars from different sources and evaluation of release of nutrients and contaminants

The biochar, product of pyrolysis of organic waste, has been used as a soil conditioner and alternative on solid waste management. However, the raw material and pyrolysis temperature used influence the quantity and dynamics of release of nutrients and contaminants from the biochar. The objective wasto evaluate the use of waste sugarcane bagasse, eucalyptus and sewage sludge for production of biochar and determine the chemical, physical, mineralogical properties and acid extraction of these materials produced at 350 °C and 500 °C. Were evaluated the proportion of C, H, N, O; ashes; macro and micronutrients, plus some contaminants; characterization of mineral phases by diffractometry of X- rays; functional groups by infrared absorption spectroscopy (FTIR). Moreover, it was determined the release of nutrients and contaminants for the extraction in increasing concentration of HNO3 (0,01 - 2,0 mol L-1). The O/C and H/C relations decreased with increasing temperature of pyrolysis, which define a greater stability of the C of biochars. Sewage sludge biochar (BC-L) had the highest nutrient release rates and contaminant metals (Cd, Cr, Ni and Pb). Acid extraction of other biocarvoes was very low (<20% of the total content). The results indicate that the carbon fraction of biochar contributes to the low rateof release of the elements in acid place.

Caracterização química e mineralógica de carvões vegetais coletados em diferentes ambientes

The increased emissions of greenhouse gases have motivated researches about capture and sequestration of C. The use of biochar in soils is an efficient way to maintain the C in the biochar stabilized and benefit the crop yield. The objective of this research was to characterize charcoals collected at different places.It was determined: total and organic C contents; elementary analysis by calcination; characterization of the samples by X-ray diffractometry, absorption spectroscopy and scanning electron microscopy. The samples in contact with soil showedhigher TOC contents, while total C contents were higher in the charcoals without contact with soil. The pH-H2O values of charcoal samples in contact with soil ranged between 4,42-7,24, average 6,8, while pH-KCl values ranged between 2,91-6,88, average 4,68. All samples presented low nutrient contents. In the samples of charcoal in contact with soil,kaolinite, quartz, graphite and gibbsitewere detected.The main functional groups identified were O-H, C=O, C=C and C-O. In the SEM of thesamples 1 and 2,wood structures were less evident and there was influence of the soil components and organisms in these charcoals.