Cultural and technology elucidation of the Tupi-Guarani tradition through analysis of potsherds from Travessão do Rio Vermelho site (Santa Catarina - Brazil) by spectroscopy, SEM-EDS and chemometrics.

Ceramic fragments can provide an insight into the ancient culture and practices of groups of humans and their way of life (technology, cultural identity, social organization, habitation and economy). Scientific analysis can be used to obtain information on the ceramic production process, as well as the specificities of the material employed. In this research, all samples of archaeological potsherd from the Tupi-Guarani tradition were analyzed in order to identify and to characterize the structures, morphologies and the elemental composition by using by scanning electron microscopy (SEM-EDS) and multivariate statistical methods (PCA and HCA). FTIR spectroscopy revealed the presence of an organic residue in three samples along with carbonates, clay minerals, quartz and hematite. In addition, the presence of the stretching attributed to water molecules in crystalline systems was observed. Also, the presence of TiO2 in the anatase polymorphic form was detected using µ-Raman spectroscopy. These results indicate a firing temperature of between 800 and 1000 °C. In relation to the morphology, all samples revealed amorphous structures presenting isolated and heterogenic particles of different forms and sizes, and the EDS spectrum confirmed the elements present in the molecular structures elucidated by vibrational spectroscopy. The multivariate analysis has confirmed the correlation between the elemental compositions of ceramics collected from two different sites: a mountain region and a coastal area in Santa Catarina State, Brazil.

Upgrading from batch to continuous flow process for the pyrolysis of sugarcane bagasse: Structural characterization of the biochars produced.

The waste from agriculture can be used for biochar production by the pyrolysis process. The present work aimed was to produce sugarcane bagasse biochars using different temperatures and processes (batch and pilot-scale continuous flow). The samples were characterized by FTIR, functional group pKa, elemental analysis, zeta potential, Raman spectroscopy, EPR, and SEM. The FTIR spectra showed bands around 1400-1650 cm-1 corresponded to vibrations of CC bonds and pKa revealed the presence of carboxylic acids (pKa ≤5) and lactones (pKa ~5-9). The elemental analyses (H/C ~ 0.31) and Raman spectra (ID/IG ~ 0.55) confirmed greater carbonization and less structural disorder of the material produced using the continuous flow process. SEM images showed that the biochar morphologies were similar to that of the precursor biomass, with the formation of pores. The continuous flow process is a promising technique for the production of biochars with high carbon contents and aromatic structures, as well as lower defect degrees, compared to biochars produced using a batch process.

Pre-colonial culture and technology through elemental and molecular analysis of ceramics with decorative paintings found at Tapera beach, Florianópolis, Brazil.

The chemical analysis of archaeological ceramic artifacts can help archaeologists to characterize the technology used in the manufacturing process, and to elucidate aspects related to the way of life of past peoples. In this context, six ceramic fragments found at Tapera Beach in Florianópolis were analyzed. FTIR spectroscopy was used to identify carbonates and oxalic acid originating from the biodegradation process. In the pictorial regions of the ceramics, iron oxides, manganese and chromium were present, along with calcium carbonate, which were used as pigments. In addition, the absence of characteristic bands for kaolinite suggests low firing temperatures (up to 900 °C). EDS confirmed the elements of the molecules identified by FTIR and showed the presence of Al and Si in the primary structure and Fe in the secondary structure of the ceramics. In addition, there were traces of rare earth elements in samples A3 and A5, which may be related to the geochemistry at the site from which the raw material was excavated. The GC-MS results showed the presence of lipids and the profile of the fatty acids detected suggested that the source of the oils adsorbed in the ceramic structure is vegetable.

Relationship of the physicochemical properties of novel ZnO/biochar composites to their efficiencies in the degradation of sulfamethoxazole and methyl orange.

Three different composites were produced, based on zinc oxide and biochar (ZnO/biochar), varying the type of biomass (Salvinia molesta: SM; exhausted husk of black wattle: EH; and sugarcane bagasse: SB), with pyrolysis under mild conditions at 350 and 450 °C. Evaluation was made of the capacities of the composites for photocatalytic degradation of sulfamethoxazole antibiotic (SMX) and methyl orange dye (MO). The properties of the prepared composites were influenced by the biomass source, with larger crystallite size (SB), lower band gap energy (SM), higher specific surface area (SB), and larger pore size (SM) resulting in higher photocatalytic efficiency. Good degradation results were obtained using these innovative photocatalysts prepared at low temperatures, when compared to ZnO/biochar materials reported in previous studies. The best degradation capacities were obtained for the composites produced at 450 °C from SB and SM, with 99.3 and 97% degradation of SMX after 45 min, and 90.8 and 88.3% degradation of MO after 120 min, respectively.

Clay mineralogy affects the efficiency of sewage sludge in reducing lead retention of soils.

Recent studies have shown the feasibility of using of sewage sludge for the remediation of heavy metal-contaminated soils. However, there are no researches to check the influence of clay mineralogy on the efficiency of the sewage sludge to remediation of contaminated soils with heavy metals. For this purpose, we use two contrasting soils: Oxisol rich in hematite and gibbsite and Inceptisol rich in kaolinite. Thermal-treated sludge was applied to Pb-contaminated soil samples and incubated for 40 days. The soil samples were submitted to seven sequential extractions: soluble-Pb, exchangeable-Pb, precipitated-Pb, organic matter-Pb, Fe and Mn oxide-Pb, gibbsite and kaolinite-Pb, and residual-Pb. The reduction of soluble Pb forms by thermal sludge application was more pronounced in the Oxisol than in the Inceptisol because of the conversion of soluble-Pb into more stable forms, such as precipitated-Pb and oxides-Pb. For Inceptisol was necessary to apply high rates of thermal sludge to reach a significant reduction in soluble-Pb contents. The addition of humic fractions in the form of thermal sludge increased the concentration of organic matter-Pb. In confined area, the use of sewage sludge to reduce the heavy metals levels in soils must be better considered, mainly in more weathered soils.

Activated biochar: Preparation, characterization and electroanalytical application in an alternative strategy of nickel determination.

This work reports for the first time the use of chemically activated biochar as electrode modifier for nickel determination. The biochar activation was performed by refluxing with HNO3, which promoted a higher nickel preconcentration compared to unmodified and modified biochar precursor electrodes. Morphological and structural characterization revealed the increase of surface acid groups, surface area and porosity of biochar after activation. Nickel determination was investigated adopting an alternative voltammetric methodology based on monitoring the Ni(II)/Ni(III) redox couple. In the proposed method, it was not necessary to use a complexing agent and the biochar itself was responsible for the analyte preconcentration. A linear response for Ni(II) concentration range from 1.0 to 30 µmol L-1 and a limit of detection of 0.25 µmol L-1 were obtained. The method was successfully applied for Ni(II) determination in spiked samples of bioethanol fuel and discharge water, with recoveries values between 103 and 109%.

Biochar prepared from castor oil cake at different temperatures: A voltammetric study applied for Pb(2+), Cd(2+) and Cu(2+) ions preconcentration.

Biochar is a carbonaceous material similar produced by pyrolysis of biomass under oxygen-limited conditions. Pyrolysis temperature is an important parameter that can alters biochar characteristics (e.g. surface area, pore size distribution and surface functional groups) and affects it efficacy for adsorption of several probes. In this work, biochar samples have been prepared from castor oil cake using different temperatures of pyrolysis (200-600°C). For the first time, a voltammetric procedure based on carbon paste modified electrode (CPME) was used to investigate the effect of temperature of pyrolysis on the adsorptive characteristics of biochar for Pb(II), Cd(II) and Cu(II) ions. Besides the electrochemical techniques, several characterizations have been performed to evaluate the physicochemical properties of biochar in function of the increase of the pyrolysis temperature. Results suggest that biochar pyrolized at 400°C (BC400) showed a better potential for ions adsorption. The CPME modified with BC400 showed better relative current signal with adsorption affinity: Pb(II)>Cd(II)>Cu(II). Kinetic studies revealed that the pseudo-second order model describes more accurately the adsorption process suggesting that the surface reactions control the adsorption rate. Values found for amount adsorbed were 15.94±0.09; 4.29±0.13 and 2.38±0.39µgg(-1) for Pb(II), Cd(II) and Cu(II) ions, respectively.

Sensitive voltammetric determination of lead released from ceramic dishes by using of bismuth nanostructures anchored on biochar.

A simple and sensitive electroanalytical method was developed for determination of nanomolar levels of Pb(II) based on the voltammetric stripping response at a carbon paste electrode modified with biochar (a special charcoal) and bismuth nanostructures (nBi-BchCPE). The proposed methodology was based on spontaneous interactions between the highly functionalized biochar surface and Pb(II) ions followed by reduction of these ions into bismuth nanodots which promote an improvement on the stripping anodic current. The experimental procedure could be summarized in three steps: including an open circuit pre-concentration, reduction of accumulated lead ions at the electrode surface and stripping step under differential pulse voltammetric conditions (DPAdSV). SEM images revealed dimensions of bismuth nanodots ranging from 20 nm to 70 nm. The effects of main parameters related to biochar, bismuth and operational parameters were examined in detail. Under the optimal conditions, the proposed sensor has exhibited linear range from 5.0 to 1000 nmol L(-1) and detection limit of 1.41 nmol L(-1) for Pb(II). The optimized method was successfully applied for determination of Pb(II) released from overglaze-decorated ceramic dishes. Results obtained were compared with those given by inductively coupled plasma optical emission spectroscopy (ICP-OES) and they are in agreement at 99% of confidence level.

Electrochemical determination of copper ions in spirit drinks using carbon paste electrode modified with biochar.

This work describes for first time the use of biochar as electrode modifier in combination with differential pulse adsorptive stripping voltammetric (DPAdSV) techniques for preconcentration and determination of copper (II) ions in spirit drinks samples (Cachaça, Vodka, Gin and Tequila). Using the best set of the experimental conditions a linear response for copper ions in the concentration range of 1.5 × 10(-6) to 3.1 × 10(-5) mol L(-1) with a Limit of Detection (LOD) of 4.0 × 10(-7) mol L(-1). The repeatability of the proposed sensor using the same electrode surface was measured as 3.6% and 6.6% using different electrodes. The effect of foreign species on the voltammetric response was also evaluated. Determination of copper ions content in different samples of spirit drinks samples was also realized adopting inductively coupled plasma optical emission spectroscopy (ICP-OES) and the results achieved are in agreement at a 95% of confidence level.

An electroanalytical approach for evaluation of biochar adsorption characteristics and its application for lead and cadmium determination.

This work describes for first time the use of electroanalytical techniques for evaluation of adsorptive proprieties of biochar using it as electrode modifier and its application for preconcentration and determination of Lead(II) and Cadmium(II) under differential pulse adsorptive voltammetric conditions (DPAdSV). Samples of biochars were obtained from castor oil cake using a predefined set of experimental conditions varying the heating rate (V), final temperature (T) and warm-up period (P) and subsequently used for carbon paste modified electrode (CPME) preparation. The proposed method was applied for Lead(II) and Cadmium(II) determination in spiked simulated industrial effluents and the limit of detection obtained for both metals were adequated for determination of these evaluated ions taking into account the limits established by Brazilian legislation. For all samples analyzed, recoveries ranged from 95% to 104% were obtained and no significative interferences were observed for common cations in water samples.

Study of copper(II) ternary complexes with phosphocreatine and some polyamines in aqueous solution.

Ternary systems of Cu(II) with phosphocreatine (PCr) and the polyamines (PAs), ethylenediamine (en), 1,3-diaminopropane (tn), putrescine (Put), spermidine (Spd), and spermine (Spm), were investigated in aqueous solution through potentiometry, ultraviolet-visible, EPR and Raman spectroscopy. The binary complex CuPCr was also studied by Raman spectroscopy, and the calculation of the minimum stabilization energy was done assuming this molecule in aqueous solution. The stability constants of the CuPCrPA ternary complexes were determined by potentiometry (T=25°C, I=0.1 mol L(-1), KNO(3)). The stability order determined was CuPCrSpm>CuPCrSpd>CuPCren>CuPCrtn>CuPCrPut, the same order of the corresponding binary complexes of Cu(II) with these polyamines. The evaluation of intramolecular PA-PCr interactions in protonated and deprotonated species of ternary complexes was carried out using the equation Δlog K=log ß(CuPCrPAHq+p)-(log ß(CuPAHq)+log ß(CuPCrHp)). All of the CuPCrPA ternary complexes have a square planar structure and are bonded to PCr through the nitrogen atom of the guanidine group and the oxygen atom of the phosphate group, and to the PAs through two nitrogen atoms of the amine groups. The structure of the complex CuPCrSpm is planar with distortion towards tetrahedral. Calculation of the minimum stabilization energy for the CuPCr and CuPCrenH complexes confirmed the proposed coordination mode.

Dehydrated halloysite intercalated mechanochemically with urea: thermal behavior and structural aspects.

Urea has been intercalated mechanochemically into dehydrated halloysite and analyzed by X-ray powder diffraction (XRPD), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance ultraviolet/visible spectroscopy (DRUV-VIS), thermal analysis (TGA/DTA), transmission electron microscopy (TEM), and electron paramagnetic resonance (EPR). The basal distance expands from 7.4 to 10.7 A and the interaction of urea to adjacent layers of halloysite through hydrogen bonds increases the structural order of the matrix. After heat treatment in air at different temperatures, decomposition products begin to appear starting from 100 degrees C. Although the basal distance remains constant up to 160 degrees C and collapses to the original value at 200 degrees C, urea and the decomposition products are still present in the sample. Starting from 125 degrees C, urea decomposition products reduce halloysite structural Fe3+ centers to Fe2+, as indicated by DRUV-VIS and EPR spectroscopy.

Chemical modification of zinc hydroxide nitrate and Zn-Al-layered double hydroxide with dicarboxylic acids.

A zinc hydroxide nitrate (ZHN), Zn5(OH)8(NO3)2.2H2O, and a layered double hydroxide (LDH), Zn/Al-NO3 were doped with 0.2 mol% of Cu2+ during alkaline chemical precipitation. Both compounds were intercalated with adipate ((-)OOC(CH2)4COO(-)), azelate ((-)OOC(CH2)7COO(-)), and benzoate (C6H5COO(-)) ions through ion exchange reactions. Solid state 13C nuclear magnetic resonance spectroscopy showed only one signal of carboxylic carbon for adipate and azelate intercalated into LDH, indicating that the carboxylic ends of both acids were equivalent, whereas the signal split when the intercalation was into the ZHN matrix. The electron paramagnetic resonance (EPR) spectrum of copper in octahedral cation sites of LDH layers showed a Hamiltonian parameter ratio g ||/A ||=170 cm and, after intercalation of adipate, the change was not significant: g ||/A ||=174 cm. This result indicates that the carboxylate ions did not coordinate with copper centers. Nonetheless, the intercalation of azelate increased the ratio to g ||/A ||=194 cm, similar to the spectra of ZHN modified with adipate, g ||/A ||=199 cm, and azelate, g ||/A ||=183 and 190 cm, which are associated with the coordination of copper by weak carboxylate anion ligands. Copper occupies octahedral or tetrahedral sites in ZHN layers, and the EPR spectra indicate that the dicarboxylate anions reacted preferentially with octahedral sites, whereas benzoate reacted with both sites.

Cu2+ ions as a paramagnetic probe to study the surface chemical modification process of layered double hydroxides and hydroxide salts with nitrate and carboxylate anions.

A layered zinc hydroxide nitrate (Zn5(OH)8(NO3)2.2H2O) and a layered double hydroxide (Zn/Al-NO3) were synthesized by coprecipitation and doped with different amounts of Cu2+ (0.2, 1, and 10 mol%), as paramagnetic probe. Although the literature reports that the nitrate ion is free (with D3h symmetry) between the layers of these two structures, the FTIR spectra of two zinc hydroxide nitrate samples show the C2v symmetry for the nitrate ion, whereas the g ||/A || value in the EPR spectra of Cu2+ is high. This fact suggests bonding of some nitrate ions to the layers of the zinc hydroxide nitrate. The zinc hydroxide nitrate was used as matrix in the intercalation reaction with benzoate, o-chlorobenzoate, and o-iodobenzoate ions. FTIR spectra confirm the ionic exchange reaction and the EPR spectroscopy reveals bonding of the organic ions to the inorganic layers of the zinc hydroxide nitrate, while the layered double hydroxides show only exchange reactions.

Use of Fe(3+) ion probe to study the stability of urea-intercalated kaolinite by electron paramagnetic resonance.

The effect of mechanical and chemical activation in processes of urea intercalation in the interlayer spacing of kaolinite and the effect of varying the temperature of the intercalation product between 100 and 200 degrees C were studied using Fe(3+) ions as a probe in electron paramagnetic resonance (EPR) spectroscopy. Other techniques were also used to characterize the samples. Monitoring the heating of urea-intercalated kaolinite, FTIR, and XRD revealed that the product obtained was stable up to a temperature of 150-160 degrees C. The EPR data indicated that the intercalation process promoted an approximation and increase of the magnetic interactions among the Fe(3+) ions. The DRUV-vis analysis of the product before heating showed an absorption band at 680 nm that was absent in the raw kaolinite. This band was attributed to the transition A(1)6-->T(2)4(G4) in the adjacent Fe(3+) ions, intensified by magnetic coupling among these ions. We suggest that intercalated urea forms hydrogen bonds between the carbonyl's oxygen and the hydroxyls bound to the Fe(3+) ions of the kaolinite structure. This would cause the approximation of the Fe(3+) ions, maximizing magnetic couplings and intensifying concentrated centers of Fe(3+), as was visible by EPR spectroscopy.

Sequestered carbon on clay mineral probed by electron paramagnetic resonance and X-ray photoelectron spectroscopy.

This paper describes the interaction among soil organic matter components with kaolinite, an important clay mineral present in tropical soils, especially in Brazil. XPS data show that the soil organic matter adsorbed on kaolinite has aromatic and aliphatic structures, with phenolic and/or alcoholic functions and carbonyl carbons (CO) of amide and/or carboxylic groups. The N1s spectrum of the kaolinite shows an asymmetric peak that is assigned to amide and protonated ammines probably from humin. The interaction between them is strong enough to resist chemical oxidative or reductive attack besides loose amide functionalities. EPR data show that reductive treatment reduces some Fe3+ of the kaolinite structure, loosing organic components. A schematic representation of the reduction of structural Fe3+ in the concentrated domains and consequently increased concentration of Fe3+ ions in diluted domains of the spectrum is presented. This reinforces the hypothesis that humin is a stable carbon sink in soils when adsorbed to clays.

Effects of citrinin on iron-redox cycle.

The ability of the mycotoxin citrinin to act as an inhibitor of iron-induced lipoperoxidation of biological membranes prompted us to determine whether it could act as an iron chelating agent, interfering with iron redox reactions or acting as a free radical scavenger. The addition of Fe3+ to citrinin rapidly produced a chromogen, indicating the formation of citrinin-Fe3+ complexes. An EPR study confirms that citrinin acts as a ligand of Fe3+, the complexation depending on the [Fe3+]:[citrinin] ratios. Effects of citrinin on the iron redox cycle were evaluated by oxygen consumption or the o-phenanthroline test. No effect on EDTA-Fe2+-->EDTA-Fe3+ oxidation was observed in the presence of citrinin, but the mycotoxin inhibited, in a dose-dependent manner, the oxidation of Fe2+ to Fe3+ by hydrogen peroxide. Reducing agents such as ascorbic acid and DTT reduced the Fe3+-citrinin complex, but DTT did not cause reduction of Fe3+-EDTA, indicating that the redox potentials of Fe3+-citrinin and Fe3+-EDTA are not the same. The Fe2+ formed from the reduction of Fe3+-citrinin by reducing agents was not rapidly reoxidized to Fe3+ by atmospheric oxygen. Citrinin has no radical scavenger ability as demonstrated by the absence of DPPH reduction. However, a reaction between citrinin and hydrogen peroxide was observed by UV spectrum changes of citrinin after incubation with hydrogen peroxide. It was also observed that citrinin did not induce direct or reductive mobilization of iron from ferritin. These results indicate that the protective effect on iron-induced lipid peroxidation by citrinin occurs due to the formation of a redox inactive Fe3+-citrinin complex, as well as from the reaction of citrinin and hydrogen peroxide.