RESUMO

BACKGROUND: In this work, a detector based on optical fiber covered with Multi-Wall Carbon Nanotubes (MWCNTs) was used for sensing and removal of Alizarin from wastewaters. Alizarin is a strong anionic red dye that is part of the anthraquinone dye group. As a rule, this dye is used in the textile industry as a coloring agent. Experiments showed a good efficiency of wastewater treatment. This development could resolve the problem of water contamination with Alizarin red dye. METHODS: We used a single-mode fiber SMF-28e with a core diameter of 8.2 µm and a cladding diameter of 125 µm as a base for the tapered optical fiber detector. An MWCNTs array was synthesized on the tapered optical fiber detector surface by spray pyrolysis Chemical Vapor Deposition (CVD) method at 800oC for 20 min inside a tubular furnace, using ferrocene solution in toluene as a catalyst precursor. The formed structure was applied for Alizarin detection in water. RESULTS: According to the patent studies, the nanotubes completely covered the optical fiber surface and the array had a high density with minimal distance between nearby nanotubes. Carbon nanotubes were oriented along the radius of the optical fiber. The average diameter of carbon nanotubes was 24 nm. The optical absorbance levels increased as the Alizarin concentration increased from 50 mg/L to 1000 mg/L. MWCNTs on the optical fiber tapered section adsorbed the dye molecules from aqueous solution. Three intensive absorption bands with the wavelength of the 700, 714 and 730 nm appeared and their intensity increased as the Alizarin concentration increased. The accumulated Alizarin can be recovered by multiple immersing clean water. This property may make tapered optical fiber detector reusable and increase the economic expediency of the sensor application. CONCLUSION: The study showed higher Alizarin adsorption efficiency of the tapered optical fiber detector compared with relative detectors. This structure can be reusable for dye detection. Removal efficiency for Alizarin reached 98.6%, which makes the tapered optical fiber detector promising for wastewater treatment and dye elimination.

RESUMO

AIMS: The purpose of this work was to obtain a hydrophobic sorbent material with potential applications in oil spill remediation. BACKGROUND: The accidents due to oil spills cause long-term ecological damage, especially in the aquatic environment. The cleaning of oil spills can be carried out by many methods and techniques, being absorbents the most attractive due to the possibility of recovery and complete elimination of the hydrocarbons in situ from the water surface. In recent years, interest in polymeric materials for oil spill remediation has increased due to its low cost, high stability, and recyclability. OBJECTIVE: The objective of this work was the development of sorbent materials based on polymer wastes, such as Polyethylene Terephthalate (PET), obtained from recycled bottles, and recycled Polyurethane (PU), for its application in the recovery of oil spills. METHODS: Sorbent materials were prepared from polymer wastes, using salt molds for the formation of porous materials with a composition of PU of 5, 10 and 15%, which were subsequently hydrophobized using carbon nanotubes or silica nanoparticles by dip-coating technique. RESULTS AND DISCUSSION: The obtained hydrophobic sorbent materials were characterized by Scanning Electron Microscopy (SEM) and Infrared Spectroscopy (FTIR). The resulting absorbent has shown capacity to separate oil from water; the best result was obtained by the sponge of PET-PU (10% PU) hydrophobized with a suspension with low multi-wall carbon nanotubes (MWCNTs) concentration, obtaining an absorption capacity of 2.01 g/g. CONCLUSION: Besides the standard sorption capacity, these cheap sorbent materials had interesting properties like low density, high hydrophobicity and buoyancy, which could be applied in other applications related to solving oil spills.

RESUMO

BACKGROUND: In this work, various carbon nanotubes (MWCNTs) were synthetized by the spray pyrolysis method. Resulting nanoforest-like and bamboo-like carbon nanotubes, as well as Yjunctions of carbon nanotubes, possess different shapes and morphology, depending on the kind of carbon source used and on the number of iron particles on the furnace tube surface, which derives from various concentrations of ferrocene catalyst. METHODS: We used the spray pyrolysis method, using different carbon sources (n-pentane, n-hexane, nheptane, and acrylonitrile) as precursors and two different concentrations of ferrocene as a catalyst. Reactions of hydrocarbon decomposition were carried out at 800oC. The solution (hydrocarbon and catalyst) was introduced with a syringe, with a flow of 1 mL/min and the synthesis time of 20 min. Argon was used as carrier gas (1000 L/min). Preheater and oven temperatures were selected 180°C and 800°C, respectively, for each carbon source. The solution passed into a quartz tube placed in an oven. RESULTS: According to the studies of carbon nanostructures, obtained from different precursors, it can be proposed that the structures synthesized from n-pentane, n-hexane and n-heptane are formed by the root growth method. The growth mechanism of MWCNTs was studied, confirming that the root growth formation of products takes place, whose parameters also depend on furnace temperature and gas flow rate. Dependence of interlayer distance (0.34-0.50 nm) in the formed MWCNTs on precursors and reaction conditions is also elucidated. The formation of carbon nanotubes does not merely depend on carbon precursors but also has strong correlations with such growth conditions as different catalyst concentrations, furnace temperature and gas flow rate. Such parameters as the amount of catalyst and synthesis time are also needed to be considered, since they are important to find minor values of these parameters in the synthesis of forest-like carbon nanotubes and other structures such as bamboo-like carbon nanotubes and Y-junctions in carbon nanotubes. CONCLUSION: As a result of the evaluation of interlayer distance in CNTs formed from different carbon sources, a standard value of interlayer distance normally for CNTs is 0.34 nm and for pentane A (0.5 wt.%), hexane B (1 wt.%), toluene A (0.5 wt.%) the range is from 0.33 to 0.35 nm. In case of pentane and acrylonitrile, under an increase of the catalyst concentration, an increase of the value of interlayer distance takes place from 0.35 and 0.4 to 0.4 and 0.5 nm, respectively, but for hexane, heptane and cyclohexane, an increase of the catalyst concentration maintains the same interlayer distance. This involves the use of lower quantities of raw materials and, therefore less cost for obtaining these materials.

RESUMO

Modern trends in the greener synthesis and fabrication of inorganic, organic and coordination compounds, materials, nanomaterials, hybrids and nanocomposites are discussed. Green chemistry deals with synthesis procedures according to its classic 12 principles, contributing to the sustainability of chemical processes, energy savings, lesser toxicity of reagents and final products, lesser damage to the environment and human health, decreasing the risk of global overheating, and more rational use of natural resources and agricultural wastes. Greener techniques have been applied to synthesize both well-known chemical compounds by more sustainable routes and completely new materials. A range of nanosized materials and composites can be produced by greener routes, including nanoparticles of metals, non-metals, their oxides and salts, aerogels or quantum dots. At the same time, such classic materials as cement, ceramics, adsorbents, polymers, bioplastics and biocomposites can be improved or obtained by cleaner processes. Several non-contaminating physical methods, such as microwave heating, ultrasound-assisted and hydrothermal processes or ball milling, frequently in combination with the use of natural precursors, are of major importance in the greener synthesis, as well as solventless and biosynthesis techniques. Non-hazardous solvents including ionic liquids, use of plant extracts, fungi, yeasts, bacteria and viruses are also discussed in relation with materials fabrication. Availability, necessity and profitability of scaling up green processes are discussed.

RESUMO

BACKGROUND: The addition of nanoparticles to cellulose paper can improve its mechanical strength, chemical stability, biocompatibility and hydrophobic properties. Silica nanoparticles are known to be inert, hydrophobic, biocompatible, biodegradable and have a good distribution being deposited on surfaces. The main characteristics of 20 nm SiO2 nanoparticles are good chemical and thermal stability with a melting point of 1610-1728°C, a boiling point of 2230°C with a purity of 99.5%. OBJECTIVE: To carry out the hydrophobization of paper based on Kraft cellulose and on cellulose obtained from soybean husk with 20-nm size SiO2 nanoparticles and to study hydrophobicity, morphology and topography of the prepared composites. Few relevant patents to the topic have been reviewed and cited. METHODS: The ground and roasted soybean husk was treated with a NaOH, washed and dried. Hydrophobization of paper was carried in aqueous medium by SiO2 addition in weight ratios "paper-SiO2 " of 0.01-0.05 wt.%, stirring, filtration and drying. The obtained cellulose sheet composites were characterized by Scanning Electron Microscopy (SEM), Transmisión Electron Microscopy (TEM), FTIRspectroscopy, Mullen proofs of hydrophobicity, and contact angle measurements. RESULTS: The mechanical properties of paper nanocomposites (tensile strength and compression) increased considerably by varying the concentrations. The tensile strength increased by 41-46% and the compressive strength increased by 55-56%. The existence of fiber nanofoils, good adhesion of 20-nm SiO2 nanoparticles to the paper surface, and their homogeneous distribution were observed. CONCLUSION: Cellulose was successfully obtained from soybean husk, applying the alkaline-based extraction method. A good reinforcement of cellulose fibers is observed due to the outstanding characteristics of the silicon dioxide nanoparticles.

RESUMO

BACKGROUND: The addition of nanoparticles to cellulose paper can improve its mechanical strength, chemical stability, biocompatibility and hydrophobic properties. Silica nanoparticles are known to be inert, hydrophobic, biocompatible, biodegradable and have a good distribution in being deposited on surfaces. The main characteristics of 20 nm SiO2 nanoparticles are good chemical and thermal stability with a melting point of 1610-1728°3C, a boiling point of 2230°C with a purity of 99.5%. OBJECTIVE: To carry out the hydrophobization of paper based on Kraft cellulose and on cellulose obtained from soybean husk with 20-nm size SiO2 nanoparticles and to study hydrophobicity, morphology and topography of the prepared composites. METHODS: The ground and roasted soybean husk was treated with a NaOH, washed and dried. Hydrophobization of paper was carried in aqueous medium by SiO2 addition in weight ratios "paper-SiO2" of 0.01-0.05 wt.%, stirring, filtration and drying. The obtained cellulose sheet composites were characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), FTIRspectroscopy, Mullen proofs of hydrophobicity, and contact angle measurements. RESULTS: The mechanical properties of paper nanocomposites (tensile strength and compression) increased considerably by varying the concentrations. The tensile strength increased by 41-46% and the compressive strength increased by 55-56%. The existence of fiber nanofoils, good adhesion of 20-nm SiO2 nanoparticles to the paper surface, and their homogeneous distribution were observed. CONCLUSION: Cellulose was successfully obtained from soybean husk, applying the alkaline-based extraction method. A good reinforcement of cellulose fibers is observed due to the outstanding characteristics of the silicon dioxide nanoparticles.

RESUMO

BACKGROUND: Synthesis and applications of Ag-coated carbon nanotubes are currently under intensive research, resulting in a series of recent patents. Silver nanoparticles are normally obtained from silver nitrate. However, there are also other silver-containing compounds that can facilitate the production of silver nanoparticles, such as silver(I) acetate and silver(II) oxide. Being combined with carbon nanotubes, silver nanoparticles can transfer to them some of their useful properties, such as conductivity and antibacterial properties, and contribute to improving their dispersion in solvents. OBJECTIVE: To apply three different silver-containing precursors of Ag nanoparticles for the decoration of carbon nanotubes and study the morphology of formed composites by several methods. METHOD: Three different silver compounds were used as Ag source to carry out the functionalization and decoration of carbon nanotubes under ultrasonic treatment of the reaction system, containing, commercial carbon nanotubes, organic peroxides as oxidants or hydrazine as a reductant, and a surfactant. Resulting samples were analyzed by XRD and XPS spectroscopy, as well as TEM and SEM microscopy to study the morphology of formed nanocomposites. RESULTS: Silver nanoparticles can be produced without the presence of a reducing agent. Applying hydrazine, as a reducing agent, it is possible to obtain functionalized carbon nanotubes doped with silver nanoparticles, in which their sizes are smaller (1-5 nm) compared to those obtained without using hydrazine. CONCLUSION: Silver nanoparticles having a size range between 2-60 nm can be produced without the presence of a reducing agent. The use of a reducing agent, such as hydrazine, affects the size of silver nanoparticles.

RESUMO

Recent advances (during the 2007-2014 period) in the coordination and organometallic chemistry of compounds containing natural and artificially prepared radionuclides (actinides and technetium), are reviewed. Radioactive isotopes of naturally stable elements are not included for discussion in this work. Actinide and technetium complexes with O-, N-, N,O, N,S-, P-containing ligands, as well π-organometallics are discussed from the view point of their synthesis, properties, and main applications. On the basis of their properties, several mono-, bi-, tri-, tetra- or polydentate ligands have been designed for specific recognition of some particular radionuclides, and can be used in the processes of nuclear waste remediation, i.e., recycling of nuclear fuel and the separation of actinides and fission products from waste solutions or for analytical determination of actinides in solutions; actinide metal complexes are also usefulas catalysts forcoupling gaseous carbon monoxide,as well as antimicrobial and anti-fungi agents due to their biological activity. Radioactive labeling based on the short-lived metastable nuclide technetium-99m ((99m)Tc) for biomedical use as heart, lung, kidney, bone, brain, liver or cancer imaging agents is also discussed. Finally, the promising applications of technetium labeling of nanomaterials, with potential applications as drug transport and delivery vehicles, radiotherapeutic agents or radiotracers for monitoring metabolic pathways, are also described.

Assuntos

RESUMO

In this review, we examine 'greener' routes to nanoparticles of zerovalent metals, metal oxides, and salts with an emphasis on recent developments. Products from nature or those derived from natural products, such as extracts of various plants or parts of plants, tea, coffee, banana, simple amino acids, as well as wine, table sugar and glucose, have been used as reductants and as capping agents during synthesis. Polyphenols found in plant material often play a key role in these processes. The techniques involved are simple, environmentally friendly, and generally one-pot processes. Tea extracts with high polyphenol content act as both chelating/reducing and capping agents for nanoparticles. We discuss the key materials used in the field: silver, gold, iron, metal alloys, oxides, and salts.

Assuntos

RESUMO

Ni- and Cu/alumina powders were prepared and characterized by X-ray diffraction (XRD), scanning electronic microscope (SEM), and N2 physisorption isotherms were also determined. The Ni/Al2O3 sample reveled agglomerated (1 µm) of nanoparticles of Ni (30-80 nm) however, NiO particles were also identified, probably for the low temperature during the H2 reduction treatment (350 °C), the Cu/Al2O3 sample presented agglomerates (1-1.5 µm) of nanoparticles (70-150 nm), but only of pure copper. Both surface morphologies were different, but resulted in mesoporous material, with a higher specificity for the Ni sample. The surfaces were used in a new proposal for producing copper and nickel phthalocyanines using a parallel-plate reactor. Phthalonitrile was used and metallic particles were deposited on alumina in ethanol solution with CH3ONa at low temperatures; ≤60 °C. The mass-transfer was evaluated in reaction testing with a recent three-resistance model. The kinetics were studied with a Langmuir-Hinshelwood model. The activation energy and Thiele modulus revealed a slow surface reaction. The nickel sample was the most active, influenced by the NiO morphology and phthalonitrile adsorption.

RESUMO

Using molecular mechanics (MM+), semi-empirical (PM6) and density functional theory (DFT) (B3LYP) methods we characterized bismuth nanotubes. In addition, we predicted the bismuth clusters {Bi(20)(C(5V)), Bi(24)(C(6v)), Bi(28)(C(1)), B(32)(D(3H)), Bi(60)(C(I))} and calculated their conductor properties.

Assuntos

RESUMO

Recently reported patents and experimental articles on the synthesis, properties, and main applications of core-shell nanoparticles, containing iron or its oxides and gold, as well as trimetallic systems on their basis, are reviewed. These nanostructures were obtained by a series of methods, including reduction in reverse micelles, decomposition of organometallic compounds, electron-beam, laser and gamma-irradiation, sonolysis and electrochemical methods. (Fe or Fe(X)O(y))/Au nanoparticles are subject to be functionalized with organic moieties, may expand their main applications, which consist of catalysis, biological and biomedical uses.

Assuntos