11 research outputs found
[Mg-Al]-LDH and [Zn-Al]-LDH as Matrices for Removal of High Loadings of Phosphate
<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
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
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>/āBiVO<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>/āBiVO<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>/āBiVO<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
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>ā1</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>
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 ItafoĢs 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
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>ā1</sup> of nanocomposite and 7.29 g of
boron g<sup>ā1</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
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
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 SulfurāPhosphate Composites: Synergy among Materials in a Structure with Multiple Fertilization Roles
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
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