11 research outputs found

    [Mg-Al]-LDH and [Zn-Al]-LDH as Matrices for Removal of High Loadings of Phosphate

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    <div><p>Eutrophication is an undesirable environmental process that occurs in water bodies affected by high concentrations of phosphate. Different economic sectors are responsible for discharge effluents with extremely high phosphate content. Therefore, is important to develop technologies capable of remove phosphate from these effluents, before that reach other and larger water bodies. This work proposes the use of layered double hydroxide (LDH) as an adsorbent matrix for phosphate removal from aqueous solution. Different isomorphic structure of LDH ([Mg-Al]-LDH and [Zn-Al]-LDH) were employed to incorporate loadings of phosphate by ion exchange. The obtained materials were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), and thermal analysis (TG/DTG). The crystalline structure of [Mg-Al]-LDH was preserved after phosphate adsorption, however the performance was low in comparison to [Zn-Al]-LDH, for which a high phosphate removal efficiency of 116.07 mg P. g-1 of LDH was achieved. The [Zn-Al]-LDH material showed good potential for use as matrix for the adsorption of phosphate in effluents.</p></div

    Nanocomposite PAAm/Methyl Cellulose/Montmorillonite Hydrogel: Evidence of Synergistic Effects for the Slow Release of Fertilizers

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    In this work, we synthesized a novel series of hydrogels composed of polyacrylamide (PAAm), methylcellulose (MC), and calcic montmorillonite (MMt) appropriate for the controlled release of fertilizers, where the components presented a synergistic effect, giving very high fertilizer loading in their structure. The synthesized hydrogel was characterized in relation to morphological, hydrophilic, spectroscopic, structural, thermal, and kinetic properties. After those characterizations, the application potential was verified through sorption and desorption studies of a nitrogenated fertilizer, urea (COĀ­(NH<sub>2</sub>)<sub>2</sub>). The swelling degree results showed that the clay loading considerably reduces the water absorption capability; however, the hydrolysis process favored the urea adsorption in the hydrogel nanocomposites, increasing the load content according to the increase of the clay mass. The FTIR spectra indicated that there was incorporation of the clay with the polymeric matrix of the hydrogel and that incorporation increased the water absorption speed (indicated by the kinetic constant <i>k</i>). By an X-ray diffraction technique, good nanodispersion (intercalation) and exfoliation of the clay platelets in the hydrogel matrix were observed. Furthermore, the presence of the montmorillonite in the hydrogel caused the system to liberate the nutrient in a more controlled manner than that with the neat hydrogel in different pH ranges. In conclusion, excellent results were obtained for the controlled desorption of urea, highlighting the hydrolyzed hydrogels containing 50% calcic montmorillonite. This system presented the best desorption results, releasing larger amounts of nutrient and almost 200 times slower than pure urea, i.e., without hydrogel. The total values of nutrients present in the system show that this material is potentially viable for application in agriculture as a nutrient carrier vehicle

    Growth of BiVO<sub>4</sub> Nanoparticles on a Bi<sub>2</sub>O<sub>3</sub> Surface: Effect of Heterojunction Formation on Visible Irradiation-Driven Catalytic Performance

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    Heterostructured materials composed of different semiconductors can be used to decrease rapid charge carrier recombination in photocatalysts, but the development of efficient synthesis methods for these materials remains a challenge. This work describes a novel strategy for tailoring heterostructures that is based on the solubility difference between two semiconductors with at least one metal in common. The growth of BiVO<sub>4</sub> on a preformed Bi<sub>2</sub>O<sub>3</sub> particle was used as a model for heterojunction formation. The number of Bi<sub>2</sub>O<sub>3</sub>/ā€‹BiVO<sub>4</sub> heterojunctions was tuned using synthesis variables (temperature and V concentration) and the particle size of the preformed Bi<sub>2</sub>O<sub>3</sub>. The synthesis of the Bi<sub>2</sub>O<sub>3</sub>/ā€‹BiVO<sub>4</sub> heterostructures using Bi<sub>2</sub>O<sub>3</sub> nanoparticles resulted in a larger quantity of heterojunctions due to the higher solubility of the nanoparticles compared to micrometric Bi<sub>2</sub>O<sub>3</sub>, which led to a classical heterogeneous precipitation on the preformed surfaces. The proposed growth mechanism was effective for obtaining heterostructured Bi<sub>2</sub>O<sub>3</sub>/ā€‹BiVO<sub>4</sub> semiconductors with enhanced photocatalytic performances compared to the isolated phases. The greater photoactivity of the heterostructures could be explained by the increased spatial separation in the photogenerated electron/hole pairs due to the formation of a type-II heterostructure and was observed by time-resolved photoluminescence analysis. In this case, the photogenerated electrons were transferred from the conduction band of the p-type semiconductor (Bi<sub>2</sub>O<sub>3</sub>) to the n-type (BiVO<sub>4</sub>) semiconductor, while the photogenerated holes were transferred from the valence band of the n-type semiconductor to the p-type semiconductor

    Controlled Release of Phosphate from Layered Double Hydroxide Structures: Dynamics in Soil and Application as Smart Fertilizer

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    A route is proposed to produce a hydrotalcite-like layered double hydroxide structure ([Mg-Al]-LDH) for phosphate fertilization. The mechanism of controlled phosphate release from the structure was investigated. The preparation strategy resulted in a phosphorus content of around 40 mgĀ·g<sup>ā€“1</sup> LDH, which was higher than previously reported for related fertilizers. The release of phosphate into water from [Mg-Al-PO<sub>4</sub>]-LDH continued over a 10-fold longer period, compared to release from KH<sub>2</sub>PO<sub>4</sub>. Analysis using <sup>31</sup>P NMR elucidated the nature of the interactions of phosphate with the LDH matrix. In soil experiments, the main interaction of P was with Fe<sup>3+</sup>, while the Al<sup>3+</sup> content of LDH had no effect on immobilization of the nutrient. Assays of wheat (<i>Triticum aestivum</i>) growth showed that [Mg-Al-PO<sub>4</sub>]-LDH was able to provide the same level of phosphate nutrition as other typical sources during short periods, while maintaining higher availability of phosphate over longer periods. These characteristics confirmed the potential of this preparation route for producing controlled release fertilizers, and also revealed fundamental aspects concerning the interactions of phosphate within these structures

    A Fed-Batch Strategy Integrated with Mechanical Activation Improves the Solubilization of Phosphate Rock by <i>Aspergillus niger</i>

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    Solubilization of phosphate rock (PR) by microorganisms is an environmentally sustainable alternative to chemical processing for production of phosphate fertilizers. The effectiveness of this PR biological solubilization process is driven by the microbial production of organic acids that chelate the cations (mainly calcium) bound to phosphate. However, the biological solubilization efficiency has been limited by the PR solids content of cultivation systems and is still low for practical applications. Here, we propose a fed-batch strategy coupled with mechanical activation to improve the biological solubilization of PR by <i>Aspergillus niger</i>. An initial systematic study of the effect of the particle size of ItafoĢs phosphate rock (IPR), a low reactivity phosphate mineral (P<sub>2</sub>O<sub>5</sub>, 20%), on the biological solubilization of phosphorus revealed that the particle size played a key role in IPR solubilization. Increases of available phosphate of up to 57% under submerged cultivation and 45% for solid-state culture were observed for rocks that had been milled for only 10 min. A fed-batch procedure was proposed in order to increase the solids content while maintaining the P-solubilization efficiency, resulting in a remarkable increase of 78% in P-solubilization, compared to the conventional process. This proposed strategy could potentially contribute to the future development of biotechnological processes for the large-scale industrial production of phosphate fertilizers that are environmentally sustainable

    Macro- and Micronutrient Simultaneous Slow Release from Highly Swellable Nanocomposite Hydrogels

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    Clay-loaded hydrogels have been arousing great interest from researchers and academics due to their unique properties and broad applicability range. Here we developed hydrogel-based nanocomposites intended for slow/controlled release of macro- and micronutrients into independent or concurrent systems. The produced nanocomposites underwent a hydrolysis treatment that improved their physicochemical properties. We obtained materials capable of absorbing water contents 5000 times greater than their weights, an outcome that makes them promising, particularly if compared with commercially available materials. Though swelling degree was affected by the presence of calcium montmorillonite (MMt), MMt has increased nutrient (urea and boron) loading capacity and, as a consequence of its interaction with the studied nutrients, has led to a slower release behavior. By evaluating the simultaneous release behavior, we observed that both the ionic (sodium octaborate) and the nonionic (urea) sources competed for the same active sites within the nanocomposites as suggested by the decreased loading and release values of both nutrients when administrated simultaneously. Because of its great swelling degree, higher than 2000 times in water, the nanocomposites formulated with high MMt contents (approximately 50.0% wt) as well as featuring high loading capacity and individual (approximately 74.2 g of urea g<sup>ā€“1</sup> of nanocomposite and 7.29 g of boron g<sup>ā€“1</sup> of nanocomposite) and simultaneous release denote interesting materials for agricultural applications (e.g., carriers for nutrient release)

    Mechanochemical Activation of Elemental Sulfur Increases Its Bioavailability in the Forage Species Brachiaria Production

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    Although sulfur is an essential macronutrient for plants, its supply through elemental S0 is not efficient, demanding its oxidation by soil microbiota before plant uptake. Thus, we demonstrate that a simple reactive mechanochemical route, using anhydrous KOH as a reactant with no need for water addition, can convert S0 to bio-absorbable oxidized forms, leading to residual K+ as a plant nutrient in the final composition. The powdery products obtained by 1 h (S-1 h) or 8 h (S-8 h) milling have been fully converted to HSO3ā€“, SO32ā€“, and SO42ā€“, also suggesting different amounts of these sulfur oxides according to the milling. S-1 h and S-8 h were efficient for S and K fertilization, as probed by the successful growing of the forage crop Brachiaria ssp. in a greenhouse trial, with similar biomass yields observed for K2SO4 (positive control) and superior to S0 + KCl (negative control). These data suggest that the mechanochemical process provides a sustainable route to increase sulfur plant bioavailability, suggesting a simple alternative that can be easily implemented in forage plant production sites such as Brachiaria ssp

    Mechanochemically Synthesized Nitrogen-Efficient Mg- and Zn-Ammonium Carbonate Fertilizers

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    New scalable methods are needed to provide sustainable solutions for nutrient recovery in the form of solid fertilizer materials and their environmental stabilization from anaerobic digestion liquid byproducts. In this work, two nutrient metal containing double salts, Mg(NH4)2(CO3)2Ā·4H2O and Zn(NH3)CO3, were synthesized using naturally abundant Mg- and Zn-carbonate minerals and ammonium (bi)carbonate salts. This constituted a conceptually new synthetic approach, different from the previous work in which the aqueous solution was utilized. We also showed that the materials could be easily scaled to 20 g quantities sufficient for soil testing. The crystalline structure of the resulting materials was confirmed using powder XRD and thermal analysis showed properties distinctly different from those of parent ammonium (bi)carbonates. Accordingly, a reduction in NH3 volatilization in soil was measured with up to 20% more NH4+ recovered after the soil experiments at 80% water holding capacity. Further, inhibition of the agriculture-beneficial bacteria Bacillus subtillis in a nutrient medium was dramatically reduced when compared to the ammonium bicarbonate alone, suggesting decreased negative effects on soil biota. Finally, Mg(NH4)2(CO3)2Ā·4H2O and Zn(NH3)CO3 matched the kinetic nitrogen need of lettuce plants better than the ammonium carbonate control while also keeping it in a form that will be available in the future. The utility of magnesium and zinc double salts in agriculture is paramount if environmentally benign and nutrient-efficient fertilizers from liquid digestate waste are to be enabled

    Smart Fertilization Based on Sulfurā€“Phosphate Composites: Synergy among Materials in a Structure with Multiple Fertilization Roles

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    Sulfur is currently a bottleneck for agronomic productivity. Many products are based on the application of elemental sulfur (SĀ°), but the ability of the soil to oxidize them is variable and dependent on the presence of oxidizing microorganisms. In this work, a composite was designed based on a matrix of SĀ° prepared by low-temperature extrusion, reinforced by rock phosphate particles acting as P fertilizer, and with encapsulation of <i>Aspergillus niger</i> as an oxidizing microorganism. This structure was shown to be effective in significantly increasing SĀ° oxidation while providing P by rock phosphate dissolution in an acid environment. X-ray absorption near-edge structure (XANES) spectra provided information about P fixation in the soil after dissolution, showing that the composite structure with <i>A. niger</i> modified the nutrient dynamics in the soil. This fully integrated material (a smart fertilizer) is an innovative strategy for eco-friendly agronomic practices, providing high nutrient delivery with minimal source preprocessing

    Self-Assembly of Metal and Metal Oxide Nanoparticles and Nanowires into a Macroscopic Ternary Aerogel Monolith with Tailored Photocatalytic Properties

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    Self-assembly processes represent the most powerful strategy to produce complex materials with unique structural and compositional sophistication. Here we present such a self-assembly route to a three-component aerogel from preformed nanoparticle building blocks. Starting with a mixture of gold and anatase nanoparticles and tungsten oxide nanowires, controlled cogelation resulted in the formation of a macroscopic aerogel monolith with high specific surface area and porosity, remarkable transparency, and excellent crystallinity. The modular approach enables us to fine-tune the composition of the aerogels, and thus their properties, by choosing the appropriate building blocks and their relative concentration ratios. As an illustrative example, we show the targeted tailoring of the photocatalytic activity: the gold nanoparticles and the tungsten oxide nanowires both add their specific beneficial effects to the anatase aerogel matrix, leading to a superior performance of the three-component system
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