Pharmaceuticals and their by-products are recalcitrant contaminants in water. Moreover, the high consumption of these drugs has many detrimental effects on body waters and ecosystems. In this timely ...review, the advances in molecular engineering of layered double hydroxides (LDH) that have been used for the removal of pharmaceutical pollutants are discussed. The approach starts from the strategies to obtain homogeneous synthesis of LDH that allow the doping and/or surface functionalization of different metals and oxides, producing heterojunction systems as well as composites with carbon and silica-based materials with high surface area. Adsorption is considered as a traditional removal of pharmaceutical pollutants, so the kinetic and mechanism of this phenomenon are analyzed based on pH, temperature, ionic strength, in order to obtain new insights for the formation of multifunctional LDH. Advanced oxidation methodologies, mainly heterogeneous photocatalysis and Fenton-like processes, stand out as the more efficient even to obtain the mineralization of the drugs. The LDH have the advantage of structural memory that favors regeneration processes. The reconstruction of calcined LDH can be used to improve drug removal, through a combination of adsorption capacity/catalytic activity. A meticulous analysis of the persistence, toxicity and bioaccumulation of the most common pharmaceuticals has allowed us to highlight the ability of the LDH to remove recalcitrant drugs at relatively low concentrations (ppm, ppb), in contrast to other mixed oxide nanostructures and homogeneous oxidation processes. In this sense, the mechanism of drug removal by LDH is discussed based on the importance of the use of composites, scavenger agents, Fenton and electro-Fenton processes, membranes, thin films and coatings, among others. In addition, the ecotoxicity of LDH is also reviewed to indicate that these layered structures can exhibit biocompatibility or high toxicity depending on the adsorbed drug and ions/metals that compose them. Undoubtedly, the LDH have a unique flexible structure with adsorption capacity and catalytic activity, facts that explain the important reasons for their extensive use in the environmental remediation of pharmaceutical pollutants from water.
•LDH nanomaterials can resolve the actual emerging pharmaceutical pollutants issues.•The use of LDH positively affects the water cycle to overcome toxic waste.•LDH can work as an adsorbent/catalytic agent for removal of pharmaceuticals.•Reconstruction of calcined LDH can be used to improve drug removal.
•Dy-doped metal oxides are obtained by calcination of ZnAlDy-LDH.•Mixed metal oxides exhibit catalytic activity in photodegradation of sulfamethoxazole.•Layer structure is reconstructed by memory ...effect during photocatalysis.•ZnAlDy-LDH exhibits better catalytic activity than derived metal oxides.
In this work, layered double hydroxides (LDHs) containing 1, 2, and 5% Dy were successfully prepared by the precipitation method. The partial substitution of Zn by Dy cations resulted in highly crystalline LDH structures, as a single crystalline phase, with a predominant 3R1 stacking favored by the intercalation of carbonate anions. The ZnAlDy-LDHs were calcined at 500 °C and produced a mixed metal oxides (MMOs), mainly ZnO and amorphous Al species. The catalytic activity of the ZnAlDy-MMOs was evaluated in the photodegradation of the antibiotic sulfamethoxazole (SMX) as pharmaceutical pollutant model. The ZnAlDy-MMO containing 2% Dy exhibited the best catalytic activity with 98% of degradation efficiency under UV light irradiation after 90 min. The catalyst reusability and stability study revealed that the ZnAlDy-MMO was restored to the LDH structure as a result of the structural memory effect triggered by hydration. According to our results, 98% of SMX was degraded by the ZnAlDy-LDH containing 2% Dy within 45 min of irradiation; this degradation efficiency was higher than that achieved by commercial ZnO and P-25 TiO2 photocatalysts (∼85%). Therefore, ZnAlDy2-LDH is a promising eco-friendly catalyst for the photodegradation of pharmaceutical pollutants since its synthesis is simple and does not require a calcination treatment to promote an improved catalytic response.
Oxides with the perovskite type structure of formula LnCoO3, where Ln is a rare earth element, have unique physical and chemical properties. These materials are applied in catalysis, gas sensors, and ...electrodes for solid oxide fuel cells, among others. In this work, single-phase DyCoO3 was obtained at 900°C using the solution-polymerization method. The microstructure of this material corresponds to a dendritic-type shape, with grain size between 0.2 and 8 μm and abundant porosity. The ultraviolet (UV) sensing characterization was performed on sintered pellets made with the as-prepared DyCoO3 powder. The UV source was a light emitting diode (LED) of wavelength (λ) of 365 nm. The detection of this radiation, with constant optical irradiance (Ee), produced uniform and reproducible response patterns. When Ee was increased, the graphs revealed a quantitative detection of the light. Analogous results were obtained using light of larger wavelengths: λ = 400, 449, and 642 nm. The graphs display a decrease on the variation of the photocurrent by increasing λ, corresponding to a decrease on the energy of the incoming photons. On the other hand, the photocatalytic decomposition of malachite green under UV radiation was investigated using powder of DyCoO3. The results show a decrease of the absorbance by increasing the UV exposure time, indicating the degradation of the dye. Since DyCoO3 is a p-type semiconductor material, the generation of electrical charge carriers under UV radiation explains its photocurrent and photocatalytic properties. In general, these properties can be applied in UV sensors to prevent skin cancer, photoconductive materials for solar photocells, and photocatalysis to decompose organic dyes.
Layered or two-dimensional (2D) compounds have recently attracted the attention of the scientific community due to their potential industrial applications. Their importance lies on the possibility of ...controlling and modifying the interlayer space in order to confer different chemical properties to the 2D assemblies. Modifications can be carried out by exfoliation/intercalation, anion exchange and/or layer surface grafting reactions. The structure of the layered hydroxide salts (LHS) derives from the brucite-like structure, where a fraction of the structural hydroxide groups is replaced by water molecules and anions, resulting in compounds formulated as M(OH)
2−
x
(A
m−
)
x/
m
·
nH
2O. This paper describes the synthesis, characterization, properties and possible applications of this fascinating class of compounds.
The first 10 cm of sediment from Lake Chapala, Western Mexico are in constant activity related to the exchange and speciation of metal cations. Samples of this sediment were analyzed in electron ...paramagnetic resonance (EPR) equipment to study the paramagnetic metals. Assays indicated that only Fe
3+
was present in a detectable amount. This cation, along with chemical fractions of sediment obtained by sequential extraction, was analyzed by EPR. The analysis supported by infrared data revealed that Fe
3+
was present in diluted and concentrated domains. Easily exchangeable iron was retained by carbonyl groups in organic matter. The carbonate fraction and oxides contained iron in concentrated domains. The alumina-silicate fraction (that resisted the sequential extraction digestions) presented diluted domains of iron in the octahedral alumina sheet along with occlusions of concentrated domains. This last inference was obtained by comparing EPR results against the spectrum of iron in synthetic model clay.
A combination of density functional theory (DFT) with experimental methods was used to study the electronic and crystal structure of Sm3Fe5O12 (SmIG), which was synthesized using a modified sol-gel ...method. Computational studies were performed within the generalized gradient approximation (GGA), with and without the HubbardU correction ( DFT + U ), to analyze the influence of the on-site repulsion on the band structure and the density of states (DOS) of SmIG, as well as the structural parameters. The calculations were contrasted with experimental results from x-ray diffraction (XRD) and UV-Vis spectra. A Rietveld refinement returned a lattice parameter of 12.5231(3) Å. Synthesis methods seem to have a substantial effect in the band gap of SmIG, as our experimental value of 2.26–2.27 eV differs from the 2.02 eV value previously reported for samples prepared using the traditional solid-state method, despite similar lattice parameters. The DFT-calculated lattice parameters were within 1% of the experimental value. Analytically calculated effective HubbardU values were 4.3092 eV for tetrahedral iron, and 6.0926 eV for octahedral iron. A model is proposed to calculate the band gap in Sm3Fe5O12, taking into account the structure's ferrimagnetism and energy level distribution. A direct transition between minority spin states was found, resulting in a calculated band gap of 2.27 eV, close to the aforementioned value from sol-gel synthesis.
The discharges enriched with heavy metals, particularly Cr(VI), are a serious environmental problem. In this work, it is presented the use of biosorbents from eggshells membranes of ostrich, quail, ...duck and chicken; the membranes were easily prepared and studied for the removal of Cr(VI) from aqueous solutions. Maximum uptake of 1.41 mmol g−1 membrane permitted the identification of ostrich membrane as the material with the highest Cr(VI) uptake. N2 adsorption experiments permitted to classify ostrich membranes as mesoporous materials, since they had pore size of 14.8 nm. This represented an advantage on the nature of these membranes to be used as biosorbents with respect to other membranes. The adsorption isotherm models such as Langmuir and Freundlich were verified using experimental data. Langmuir model described the adsorption process satisfactorily at pH 1 and 2 whereas Freundlich model fitted data better at pH 3 and 5. The adsorption kinetic data were adjusted to a pseudo-second order kinetic model. TGA results permitted demonstrating a low thermal stability of ostrich membrane, since it starts decomposing at around 50°C due to the fact that membranes have about 60% protein. Through SEM microscopy was possible to observe the morphology of the membrane surfaces before and after Cr(VI) uptake which reflects the textural characteristics of the biosorbent. FTIR and XPS analyses suggested that Cr was adsorbed on ostrich membranes through the amine groups of proteins conforming the fibers of membranes. Despite the oxygen shows higher electronegativity than N, Cr shows more preference toward N due to fact that pH conditions favor the positive charges on the surface of the membrane. Our results make evident that this waste material is a novel and efficient option for the removal of Cr(VI) from aqueous solutions.
Nanoparticle-based delivery technologies have played a central role in a wide variety of applications, including cell therapy, gene transformation, and cellular delivery of molecular dyes. This work ...synthesized via ionic exchange a nanoparticle consisting of zinc-layered hydroxychloride coupled with yeast β-glucan (ZG), whose cellular immune response was evaluated using fish spleen leukocytes. Leukocytes from the marine Pacific red snapper (Lutjanus peru) were stimulated with zinc-layered hydroxychloride (ZHC) coupled with yeast β-glucan (GLU) and challenged with live Vibrio parahaemolyticus after 24 h. Structural characterization of this yeast glucan by proton nuclear magnetic resonance (NMR) indicated structures containing (1–6)-branched (1–3)-β-D-glucan. The ZHC and ZG were characterized with X-ray diffraction, infrared spectroscopy, scanning electron microscopy and thermogravimetric analysis. The results of the immunological study showed that ZHC, GLU or ZG were safe for leukocytes because cell viability was higher than 80% compared with DMSO or V. parahaemolyticus exposure. The ZG or GLU treatments enhanced nitric oxide production, superoxide dismutase, catalase and peroxidase activities. Induction of anti- and pro-inflammatory cytokine (IL-1β, IL-6, IL-8, IL-10, IL-12 and IL-17) genes was more pronounced in ZG or GLU treatments compared to the other groups. Based on the results, ZHC nanoparticles can be used as a delivery carrier of yeast β-glucan for enhancing immunity in fish and have great potential application in the aquaculture industry.
•Nanoparticle of zinc-layered hydroxychloride coupled with yeast β-glucan (ZG) was synthesized.•ZHC, G and ZG were safe because leukocyte viability was up to 80%.•ZG-stimulated leukocytes enhanced NO production and antioxidant enzymatic activities upon Vibrio parahaemolyticus challenge.•Anti- and pro-inflammatory cytokine gene expressions regulated differentially in ZHC, G and ZG treatments.•ZHC could serves as delivery carrier of yeast β-glucan to enhance fish immunity.
The aim of this work was to evaluate the concentrations of polycyclic aromatic hydrocarbons (PAHs) in soils to which solid shale materials (SSMs) were added as soil conditioners. The SSMs were ...derived from the Petrosix® pyrolysis process developed by Petrobras (Brazil). An improved ultrasonic agitation method was used to extract the PAHs from the solid samples (soils amended with SSMs), and the concentrations of the compounds were determined by gas chromatography coupled to mass spectrometry (GC-MS). The procedure provided satisfactory recoveries, detection limits, and quantification limits. The two-, three-, and four-ring PAHs were most prevalent, and the highest concentration was obtained for phenanthrene (978 ± 19 μg kg⁻¹in a pyrolyzed shale sample). The use of phenanthrene/anthracene and fluoranthene/pyrene ratios revealed that the PAHs were derived from petrogenic rather than pyrogenic sources. The measured PAH concentrations did not exceed national or international limit values, suggesting that the use of SSMs as soil conditioners should not cause environmental damage.
PDF
