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1.
Molecules ; 26(5)2021 Mar 03.
Artigo em Inglês | MEDLINE | ID: mdl-33802397

RESUMO

Ti(C,N)-reinforced alumina-zirconia composites with different ratios of C to N in titanium carbonitride solid solutions, such as Ti(C0.3,N0.7) (C:N = 30:70) and Ti(C0.5,N0.5) (C:N = 50:50), were tested to improve their mechanical properties. Spark plasma sintering (SPS) with temperatures ranging from 1600 °C to 1675 °C and pressureless sintering (PS) with a higher temperature of 1720 °C were used to compare results. The following mechanical and physical properties were determined: Vickers hardness, Young's modulus, apparent density, wear resistance, and fracture toughness. A composite with the addition of Ti(C0.5,N0.5)n nanopowder exhibited the highest Vickers hardness of over 19.0 GPa, and its fracture toughness was at 5.0 Mpa·m1/2. A composite with the Ti(C0.3,N0.7) phase was found to have lower values of Vickers hardness (by about 10%), friction coefficient, and specific wear rate of disc (Wsd) compared to the composite with the addition of Ti(C0.5,N0.5). The Vickers hardness values slightly decreased (from 5% to 10%) with increasing sintering temperature. The mechanical properties of the samples sintered using PS were lower than those of the samples that were spark plasma sintered. This research on alumina-zirconia composites with different ratios of C to N in titanium carbonitride solid solution Ti(C,N), sintered using an unconventional SPS method, reveals the effect of C/N ratios on improving mechanical properties of tested composites. X-ray analysis of the phase composition and an observation of the microstructure was carried out.


Assuntos
Óxido de Alumínio/química , Materiais Biocompatíveis/química , Cerâmica/química , Gases em Plasma/química , Titânio/química , Zircônio/química , Dureza , Teste de Materiais , Fenômenos Mecânicos , Propriedades de Superfície , Temperatura
2.
Artigo em Inglês | MEDLINE | ID: mdl-33720803

RESUMO

Measurement of skin exposure to particles using interception (e.g., cotton gloves) and removal (e.g., wiping) sampling techniques could be inaccurate because these substrates do not have the same topography and adhesion characteristics as skin. The objective of this study was to compare particle transfer and adherence to cotton gloves, cotton gloves with artificial sebum, and a pre-moistened polyvinyl alcohol (PVA) material with bare human skin (fingertip, palm). Experiments were performed with aluminum oxide powder under standardized conditions for three types of surfaces touched, applied loads, contact times, and powder mass levels. In the final mixed model, the fixed effects of substrate, surface type, applied load, and powder mass and their significant two-way interaction terms explained 71% (transfer) and 74% (adherence) of the observed total variance in measurements. For particle mass transfer, compared with bare skin, bias was -77% (cotton glove with sebum) to +197% (PVA material) and for adherence bias ranged from -40% (cotton glove) to +428% (PVA material), which indicated under- and over-sampling by these substrates, respectively. Dermal exposure assessment would benefit from sampling substrates that better reflect human skin characteristics and more accurately estimate exposures. Mischaracterization of dermal exposure has important implications for exposure and risk assessment.


Assuntos
Exposição Ambiental/análise , Pele/metabolismo , Manejo de Espécimes , Adesividade , Óxido de Alumínio/análise , Óxido de Alumínio/química , Óxido de Alumínio/metabolismo , Fibra de Algodão , Humanos , Álcool de Polivinil/química , Pós/análise , Pós/química , Pós/metabolismo , Absorção Cutânea
3.
Molecules ; 26(3)2021 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-33525515

RESUMO

Polymer templates play an essential role in the robust infiltration-based synthesis of functional multicomponent heterostructures with controlled structure, porosity, and composition. Such heterostructures are be used as hybrid organic-inorganic composites or as all-inorganic systems once the polymer templates are removed. Using iron oxide/alumina heterostructures formed by two-step infiltration of polystyrene-block-polyvinyl pyridine block copolymer with iron and aluminum precursors from the solution and vapor-phases, respectively, we show that the phase and morphology of iron oxide nanoparticles dramatically depend on the approach used to remove the polymer. We demonstrate that thermal and plasma oxidative treatments result in iron oxide nanoparticles with either solid or hollow morphologies, respectively, that lead to different magnetic properties of the resulting materials. Our study extends the boundaries of structure manipulations in multicomponent heterostructures synthesized using polymer infiltration synthesis, and hence their properties.


Assuntos
Nanopartículas/química , Nanoestruturas/química , Polímeros/química , Óxido de Alumínio/química , Compostos Férricos/química , Magnetismo/métodos , Nanotecnologia/métodos , Poliestirenos/química , Piridinas/química
4.
Molecules ; 26(4)2021 Feb 04.
Artigo em Inglês | MEDLINE | ID: mdl-33557389

RESUMO

Ionic liquids (ILs) have attracted great interest in the field of extractive metallurgy mainly because they can be utilized in low temperature leaching processes where they exhibit selectivity and recyclability. A major drawback in mixed aqueous-IL systems, is IL dissolution in the aqueous phase, which leads to IL losses, increasing the overall processing cost. This study advances the method for recovering scandium (Sc) from bauxite residue (BR) using as leaching agent the IL betainium bistriflimide, [Hbet][Tf2N] mixed with water, which has been reported in previous publications. Ionic liquid leachate (IL-PLS) was prepared by leaching BR with a mixture of [Hbet][Tf2N]-H2O and subjected to different stripping experiments using hydrochloric acid. The advancement, presented in this work, is related with the optimization of the metal extraction (stripping) from the IL-PLS, where an aqueous solution with high Sc concentration and minimum metal impurities and minimum IL co-extraction is produced. It is further proven that the metal cation extraction is defined by the stoichiometry of the acidic solution and the dissolution (losses) of the IL in the aqueous phase can be minimized by adjusting the volume ratio and the acid concentration. A two-step stripping process described, achieves the selective increase of Sc concentration by 8 times in the aqueous solution, while maintaining cumulative IL losses to similar levels as the optimum 1 step non-Sc selective stripping process.


Assuntos
Óxido de Alumínio/química , Líquidos Iônicos/química , Reciclagem , Escândio/química , Fenômenos Mecânicos , Água/química
5.
Molecules ; 26(4)2021 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-33562208

RESUMO

MgAl2O4-spinel has wide industrial and geological applications due to its special structural and physical-chemical features. It is presumably the most important endmember of complex natural spinel solid solutions, and therefore provides a structural model for a large group of minerals with the spinel structure. There exists a well known but still inadequately understood phenomenon in the structure of MgAl2O4-spinel, the Mg-Al cations readily exchanging their positions in response to variations of temperature, pressure, and composition. A large number of experiments were performed to investigate the Mg-Al cation order-disorder process usually quantified by the inversion parameter x (representing either the molar fraction of Al on the tetrahedral T-sites or the molar fraction of Mg on the octahedral M-sites in the spinel structure), and some thermodynamic models were thereby constructed to describe the x-T relation. However, experimental data at some key T were absent, so that the different performance of these thermodynamic models could not be carefully evaluated. This limited the interpolation and extrapolation of the thermodynamic models. By performing some prolonged annealing experiments with some almost pure natural MgAl2O4-spinel plates and quantifying the x values with single-crystal X-ray diffraction technique, we obtained some critical equilibrium x values at T down to 773 K. These new x-T data, along with those relatively reliable x values at relatively high T from early studies, clearly indicate that the CS94 Model (a model constructed by Carpenter and Salje in 1994) better describes the Mg-Al cation order-disorder reaction in MgAl2O4-spinel for a wide range of T. On the basis of the CS94 Model, a geothermometer was established, and its form is T-closure = 21362 × x3 - 12143 × x2 + 6401 × x - 10 (T-closure standing for the closure temperature of the Mg-Al cation exchange reaction). This geothermometer can be used to constrain the thermal history of the geological bodies containing MgAl2O4-spinel.


Assuntos
Alumínio/química , Magnésio/química , Óxidos/química , Óxido de Alumínio/química , Óxido de Magnésio/química , Minerais/química , Modelos Moleculares , Soluções/química , Temperatura , Termodinâmica , Difração de Raios X
6.
Nat Commun ; 12(1): 140, 2021 01 08.
Artigo em Inglês | MEDLINE | ID: mdl-33420061

RESUMO

Solid-state nanopores allow high-throughput single-molecule detection but identifying and even registering all translocating small molecules remain key challenges due to their high translocation speeds. We show here the same electric field that drives the molecules into the pore can be redirected to selectively pin and delay their transport. A thin high-permittivity dielectric coating on bullet-shaped polymer nanopores permits electric field leakage at the pore tip to produce a voltage-dependent surface field on the entry side that can reversibly edge-pin molecules. This mechanism renders molecular entry an activated process with sensitive exponential dependence on the bias voltage and molecular rigidity. This sensitivity allows us to selectively prolong the translocation time of short single-stranded DNA molecules by up to 5 orders of magnitude, to as long as minutes, allowing discrimination against their double-stranded duplexes with 97% confidence.


Assuntos
DNA de Cadeia Simples/metabolismo , Ensaios de Triagem em Larga Escala/métodos , Nanoporos , Imagem Individual de Molécula/métodos , Óxido de Alumínio/química , Ensaios de Triagem em Larga Escala/instrumentação , Polímeros/química , Imagem Individual de Molécula/instrumentação , Propriedades de Superfície
7.
Food Chem ; 347: 129040, 2021 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-33484960

RESUMO

An Ultra High-Performance Liquid chromatography method quadruple time-of-flight mass spectrometry has been developed for the analysis of 11 cyclic polyesters oligomers, following a modified QuEChERS clean-up with alumina/primary secondary amine, in pasta. Target analytes were polyethylene terephthalate (PET) 1st series cyclic dimer to heptamer, polybutylene terephthalate (PBT) dimer to pentamer and a polyurethane oligomer. Standard addition method was applied for the calibration, and the limits of quantification ranged from 3.2 to 17.2 ng g-1. Recoveries ranged from 86.4 to 109.8%, RSDs were lower than 12% for all analytes, and matrix effect never exceeded ± 2.5%. The method was successfully applied to real commercial pasta samples, where the PET 1st series cyclic trimer was the most abundant oligomer, being found in all tested samples. The 1st series PET cyclic dimer and tetramer, as well as 1,4,7-trioxacyclotridecane-8,13-dione, were found in considerable amounts. Traces of the 2nd and 3rd series PET cyclic dimers were also found.


Assuntos
Análise de Alimentos/métodos , Espectrometria de Massas/métodos , Poliésteres/química , Polietilenotereftalatos/química , Óxido de Alumínio/química , Cromatografia Líquida de Alta Pressão , Dimerização , Farinha/análise , Poliésteres/análise , Polietilenotereftalatos/análise , Polimerização , Dióxido de Silício/química
8.
Artigo em Inglês | MEDLINE | ID: mdl-33499727

RESUMO

In the present study, the adsorption behavior of ciprofloxacin (CIP) from aqueous solution onto MWCNTs/Al2O3 was studied using batch experiments. Physical characterization of MWCNTs/Al2O3 was determined by SEM, XRD, and BET. The effective parameters investigated included: initial CIP concentration, contact time, MWCNTs/Al2O3 mass, and temperature. Based on experimental results and correlation coefficients, the rate of CIP adsorption followed the pseudo-second-model kinetics. Complete compatibility of the adsorption isotherm process was achieved with the Langmuir model, and the maximum adsorption capacity reached 41.73 mg/g under the optimized conditions (pH = 7, MWCNTs/Al2O3 dose = 1.2 g/L, contact time = 60 min, initial concentration = 10 mg/L, and temperature= 45 °C). The adsorption capacities based on the Langmuir model at different temperatures, 273, 288, 303, and 318 K, were equal to 72.18, 75.92, 79.65, and 83.47 mg/g, respectively. The determined parameters of the thermodynamic studies demonstrated the endothermic and spontaneous nature of the biosorption. The mean free energy was estimated from D-R isotherm model to be 0.316-0.707 KJ/mol, which clearly proved that the adsorption experiment followed a physical process. The data suggest that MWCNTs/Al2O3 could be used as a highly effective adsorbent material with a high capacity for the removal of antibiotics from water and wastewater.


Assuntos
Óxido de Alumínio/química , Antibacterianos/química , Ciprofloxacina/química , Nanotubos de Carbono/química , Poluentes Químicos da Água/química , Adsorção , Concentração de Íons de Hidrogênio , Cinética , Temperatura , Termodinâmica , Águas Residuárias , Purificação da Água/métodos
9.
Chemosphere ; 254: 126608, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32957262

RESUMO

Al2O3 Nanoparticles (Al2O3-NPs) have been widely used because of their unique physical and chemical properties, and Al2O3-NPs can be released into the environment directly or indirectly. Our previous research found that 13 nm Al2O3-NPs can induce neural cell death and autophagy in primarily cultured neural cells in vitro. The aim of this study was to determine where Al2O3-NPs at 13 nm particle size can cause neural cells in vivo and assess related behavioural changes and involved potential mechanisms. Zebrafish from embryo to adult were selected as animal models. Learning and memory as functional indicators of neural cells in zebrafish were measured during the development from embryo to adult. Our results indicate that Al2O3-NPs treatment in zebrafish embryos stages can cause the accumulation of aluminium content in zebrafish brain tissue, leading to progressive impaired neurodevelopmental behaviours and latent learning and memory performance. Additionally, oxidative stress and disruption of dopaminergic transmission in zebrafish brain tissues are correlated with the dose-dependent and age-dependent accumulation of aluminium content. Moreover, the number of neural cells in the telencephalon tissue treated with Al2O3-NPs significantly declined, and the ultramicroscopic morphology indicated profound autophagy alternations. The results suggest that Al2O3-NPs has dose-dependent and time-dependent progressive damage on learning and memory performance in adult zebrafish when treated in embryos. This is the first study of the effects of Al2O3-NPs on learning and memory during the development of zebrafish from embryo to adult.


Assuntos
Óxido de Alumínio/toxicidade , Aprendizagem/efeitos dos fármacos , Memória/efeitos dos fármacos , Nanopartículas/toxicidade , Alumínio/farmacologia , Óxido de Alumínio/química , Animais , Embrião não Mamífero , Nanopartículas Metálicas , Estresse Oxidativo/efeitos dos fármacos , Tamanho da Partícula , Peixe-Zebra/embriologia
10.
J Vis Exp ; (160)2020 06 25.
Artigo em Inglês | MEDLINE | ID: mdl-32658181

RESUMO

This protocol demonstrates a method for graphene-assisted quick growth and coalescence of AlN on nano-pattened sapphire substrate (NPSS). Graphene layers are directly grown on NPSS using catalyst-free atmospheric-pressure chemical vapor deposition (APCVD). By applying nitrogen reactive ion etching (RIE) plasma treatment, defects are introduced into the graphene film to enhance chemical reactivity. During metal-organic chemical vapor deposition (MOCVD) growth of AlN, this N-plasma treated graphene buffer enables AlN quick growth, and coalescence on NPSS is confirmed by cross-sectional scanning electron microscopy (SEM). The high quality of AlN on graphene-NPSS is then evaluated by X-ray rocking curves (XRCs) with narrow (0002) and (10-12) full width at half-maximum (FWHM) as 267.2 arcsec and 503.4 arcsec, respectively. Compared to bare NPSS, AlN growth on graphene-NPSS shows significant reduction of residual stress from 0.87 GPa to 0.25 Gpa, based on Raman measurements. Followed by AlGaN multiple quantum wells (MQWS) growth on graphene-NPSS, AlGaN-based deep ultraviolet light-emitting-diodes (DUV LEDs) are fabricated. The fabricated DUV-LEDs also demonstrate obvious, enhanced luminescence performance. This work provides a new solution for the growth of high quality AlN and fabrication of high performance DUV-LEDs using a shorter process and less costs.


Assuntos
Óxido de Alumínio/química , Grafite/química , Nanoestruturas/química , Semicondutores , Raios Ultravioleta , Compostos de Alumínio/química , Catálise , Gálio/química , Gases/química , Luminescência , Volatilização
11.
Food Chem ; 331: 127312, 2020 Nov 30.
Artigo em Inglês | MEDLINE | ID: mdl-32619907

RESUMO

Growing interest in the health benefits of soy isoflavones has led to research in the isolation of individual isoflavone species for further application. Herein, we develop a new strategy to isolate daidzein, genistein, daidzin and genistin in soybean. We investigated the impact of solvents used and the extraction time on the extracted isoflavone contents from soybean. A 30-min extraction with 65% aqueous methanol gave a total isoflavone yield of 345 mg/100 g soybean, the highest value among tested conditions. Further, we proposed a two-stage adsorption/desorption chromatography comprising macroporous resin and aluminium oxide to isolate isoflavone. First, HP-20 resin was used to separate the glucosidic and aglyconic forms of isoflavone, then individual species of isoflavone could be isolated using aluminium oxide by specific retention of 5-hydroxy isoflavone. This process achieved overall high recovery (82-97%) and purity (92-95%) of the four isoflavones, which confirms a high separating efficiency for isoflavones from soybean.


Assuntos
Óxido de Alumínio/química , Isoflavonas/isolamento & purificação , Resinas Sintéticas/química , Solventes/química , Soja/química , Isoflavonas/análise , Isoflavonas/química , Porosidade , Resinas Vegetais
12.
Chemosphere ; 260: 127568, 2020 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-32683011

RESUMO

Nowadays millions of oil tons are spilled into the environment causing important damage. Therefore, the development of new technologies and materials are needed to remediate this problem. In this study, hydroxyethyl cellulose alumina-based aerogels are synthesized by an environmentally friendly freeze-drying process to be used as sorbents for oil spills. It is demonstrated that the oil retention coefficient depends on the viscosity of the oil and the amount of hydroxyethyl cellulose contained in the aerogel, being 10% the optimal proportion. The aerogel synthetized with this content of hydroxyethyl cellulose displays the most favourable physicochemical and morphological properties to retain different oil spills, achieving 5.5 times its weight in comparison to its dry state. In addition, reusability experiments washing the aerogel with acetone or ethanol after the oil retention are carried out. Results show an improvement after a long washing of the sorbent with acetone, resulting in an oil weight gain of 38.7%.


Assuntos
Recuperação e Remediação Ambiental/métodos , Géis/química , Poluição por Petróleo , Adsorção , Óxido de Alumínio/química , Celulose/análogos & derivados , Celulose/química , Liofilização
13.
Ecotoxicol Environ Saf ; 203: 110995, 2020 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-32678763

RESUMO

In the present study, silver (Ag) atoms were chemically deposited on γ-alumina (Al2O3) nanospheres to be further functionalized with trithiocyanuric acid (TTC). The result was Al2O3@Ag@TTC composites, which were used for the selective extraction and preconcentration of Fe (III) and Pb (II) ions in seawater and river water samples. TTC is a potent scavenger of heavy metal ions with multiple nitrogen- and sulfur-containing functional groups. The concentrations of analytes were determined by flame atomic absorption spectrometry, and the structure of the synthetic adsorbent was characterized by spectral and microscopic techniques. Furthermore, the fundamental parameters influencing the extraction and desorption of the target ions were evaluated. Under optimized conditions, the calibration curve was linear in the range of 10-100 ng mL-1 for both analytes. The detection limits of the proposed method for Fe (III) and Pb (II) ions were 1.5 ng mL-1 and 0.8 ng mL-1, respectively, with a relative standard deviation of less than 6.1% (n = 7). Moreover, the proposed method tolerated salinities of up to 50.0 g L-1 without exhibiting any decrease in selectivity or recovery. The developed method was successfully applied to extract Fe (III) and Pb (II) ions from seawater and river water samples. The extraction recovery rates of the spiked ions were at least 93% for Fe (III) and 97 % for Pb (II).


Assuntos
Óxido de Alumínio/química , Ferro/análise , Chumbo/análise , Nanoconjugados/química , Prata/química , Triazinas/química , Poluentes Químicos da Água/análise , Água Doce/química , Concentração de Íons de Hidrogênio , Íons , Água do Mar/química , Extração em Fase Sólida/métodos
14.
Ecotoxicol Environ Saf ; 201: 110847, 2020 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-32554203

RESUMO

Bauxite residues (BR), commonly named red muds, are the saline-sodic waste produced during the extraction of alumina from bauxite. In this study, four kinds of BR were mixed at increasing concentrations with two soils in a mesososm experiment. Unamended BR from Provence (PRO) and Guinea (GUI) bauxite were selected, and Modified Bauxite Residues from PRO and GUI (MBR-PRO and MBR-GUI) were obtained by gypsum application and repeated leaching, in order to reduce their pH, electrical conductivity (EC) and exchangeable sodium percentage (ESP). Several indicators of microbial community functions and structure (growth of culturable bacteria; enzymatic activities; C-sourced substrates degradation (Biolog®); bacteria and fungi PCR-RFLP fingerprints) were measured after 35 days of incubation. Results showed that PRO residue had stronger negative effects than GUI on all the tested indicators. Residues modified by gypsum addition (MBR-PRO, MBR-GUI) were equally or sometimes less harmful compared to unamended residues. Microbial activities (bacterial growth and enzyme activities) were more inhibited than the diversity of microbial functions (Biolog®), and the structure of bacterial and fungal communities was not affected by increasing concentrations of bauxite residues. EC and ESP were the main factors explaining the inhibition of microbial activities, although the origin of bauxite residue is of great importance too.


Assuntos
Óxido de Alumínio/toxicidade , Sulfato de Cálcio/toxicidade , Microbiota/efeitos dos fármacos , Microbiologia do Solo , Poluentes do Solo/toxicidade , Solo/química , Óxido de Alumínio/análise , Óxido de Alumínio/química , Bactérias/efeitos dos fármacos , Bactérias/crescimento & desenvolvimento , Sulfato de Cálcio/análise , Sulfato de Cálcio/química , Fungos/efeitos dos fármacos , Fungos/crescimento & desenvolvimento , Poluentes do Solo/análise , Poluentes do Solo/química
15.
J Vis Exp ; (159)2020 05 24.
Artigo em Inglês | MEDLINE | ID: mdl-32510476

RESUMO

Aluminum-oxide (Al2O3) is a low cost, easily processable and high dielectric constant insulating material that is particularly appropriate for use as the dielectric layer of thin-film transistors (TFTs). Growth of aluminum-oxide layers from anodization of metallic aluminum films is greatly advantageous when compared to sophisticated processes such as atomic layer deposition (ALD) or deposition methods that demand relatively high temperatures (above 300 °C) such as aqueous combustion or spray-pyrolysis. However, the electrical properties of the transistors are highly dependent on the presence of defects and localized states at the semiconductor/dielectric interface, which are strongly affected by the manufacturing parameters of the anodized dielectric layer. To determine how several fabrication parameters influence the device performance without performing all possible combination of factors, we used a reduced factorial analysis based on a Plackett-Burman design of experiments (DOE). The choice of this DOE permits the use of only 12 experimental runs of combinations of factors (instead of all 256 possibilities) to obtain the optimized device performance. The ranking of the factors by the effect on device responses such as the TFT mobility is possible by applying analysis of variance (ANOVA) to the obtained results.


Assuntos
Óxido de Alumínio/química , Condutividade Elétrica , Eletrodos , Transistores Eletrônicos , Desenho de Equipamento
16.
Chemosphere ; 258: 127274, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32569956

RESUMO

The main aim of this work was to develop sustainable catalyst from geothermal waste by hydrothermal process for enhanced biohydrogen production. The effects of Si/Al ratio and pH neutralization on the catalyst were also investigated to provide further insight into the hydrogen production capability. Results have shown with increasing Si/Al ratio, a lower amount of catalyst was synthesized and smaller particle size was obtained. pH neutralization treatment resulted in higher conversion compared to non-neutralized ones. Meanwhile, the highest conversion of biohydrogen from ethanol through steam reforming process (95.19%) was obtained from catalyst with pH neutralization treatment and Si/Al ratio of 10. The catalyst developed in this study was concluded to be suitable for framework/supporting catalyst due to relatively low selectivity.


Assuntos
Biocombustíveis/análise , Etanol/química , Hidrogênio/análise , Resíduos Industriais/análise , Zeolitas/química , Óxido de Alumínio/química , Catálise , Temperatura Alta , Concentração de Íons de Hidrogênio , Dióxido de Silício/química , Vapor , Propriedades de Superfície
17.
Chemosphere ; 259: 127427, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32599385

RESUMO

Spinel oxides, e.g., NiCo2O4, is a promising catalyst for the catalytic oxidation of toluene. Understanding and designing versatile NiCo2O4 spinel is important for low-temperature toluene oxidation. Here, we investigated the surface-characteristic-dependent degradation activity of NiCo2O4 crystals through experiment and characterization. NiCo2O4 nanosheet using ethanol as solvent (named E--NiCo2O4) exposing {110} crystal planes exhibited the lowest temperature toluene oxidation. The T99 of toluene conversion was 256 °C, which is much lower than that of NiCo2O4 nanosheet using ethylene glycol as solvent (named EG--NiCo2O4), NiCo2O4 octahedron (named O--NiCo2O4) and NiCo2O4 truncated octahedron (named TO--NiCo2O4). Characterization using various techniques such as XRD, TEM, BET, XPS, H2-TPR and CO2-TPD showed that Co3+ and surface adsorbed oxygen (Osur) enriched surface, excellent redox properties and effective diffusion of the reaction product reasonably explain the enhancement in catalytic activity over the E--NiCo2O4. The research reveals that the effect of specific crystal planes and solvent was the key factor to govern the activity of low-temperature toluene oxidation.


Assuntos
Óxido de Alumínio/química , Óxido de Magnésio/química , Tolueno/química , Adsorção , Catálise , Temperatura Baixa , Oxirredução , Óxidos/química , Oxigênio/química , Solventes
18.
Chemosphere ; 257: 127256, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32531489

RESUMO

Five kinds of Al2O3 were characterized by SEM, TEM, FT-IR and BET surface area, and then used as carriers to investigate the photochemical removal of hexachlorobenzene (HCB) in aqueous system. The results showed that HCB coated on the surfaces of all Al2O3 could be photodegraded rapidly, and Neutral-Al2O3 presented the best performance. Meanwhile, the efficient removal of HCB in real water matrices, including tap water, river water and secondary clarifier effluent showed the potential practical application of Al2O3. EPR and theoretical calculation revealed the generation of hydroxyl radicals on Al2O3 surface under 500 W Xe lamp irradiation. Nine intermediates and a small amount of Cl- were identified by GC/MS, LC/MS and IC analysis, which was further verified by transition state calculations. These results can provide a new technique for HCB removal in water and wastewaters, and give more insights into the environmental ecological risk assessment of this pollutant.


Assuntos
Óxido de Alumínio/química , Hexaclorobenzeno/química , Poluentes Químicos da Água/química , Cromatografia Gasosa-Espectrometria de Massas , Radical Hidroxila/química , Cinética , Espectroscopia de Infravermelho com Transformada de Fourier , Água
19.
Chemosphere ; 256: 127077, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32438124

RESUMO

The ultra-deep adsorptive desulfurization (ppb level) of benzene remains a challenging subject with the need to construct efficient adsorbent systems. Herein, a kind of ruthenium-based adsorbent functionalized with bimetallic Ru-Al was rationally designed using Al2O3 as support (denoted as 0.8%Ru-1.2%Al/Al2O3). It was found that the co-anchoring of Ru and Al species endows the Ru-based adsorbent unique adsorption capability, which is able to completely eliminate sulfur compounds in benzene, and exhibiting a much higher breakthrough sulfur capacity than that of the 0.8%Ru/Al2O3. Remarkably, under the industrial experiment conditions, 0.8%Ru-1.2%Al/Al2O3 exhibited excellent long-term stability for more than 1200 h, showing the potential for industrial application. Various characterization techniques, including BET, XRD, SEM, TEM, TPD-MS, TPR and XPS, were used to investigate the correlation between the adsorption performance and the microstructure of the adsorbents. Over 0.8%Ru-1.2%Al/Al2O3, the ultra-thin aluminum additive is beneficial to improve the dispersion of Ru species, which therefore exhibits desirable desulfurization efficiency. Moreover, the enhanced performance is also correlated to the presence of the suitable Ru active centers generated from the selective coverage by Al species. It leads to an optimal exposure of the Ru active centers, which would facilitate the interaction of S-Ru and the improvement of the desulfurization activity.


Assuntos
Benzeno/análise , Rutênio/química , Adsorção , Alumínio , Óxido de Alumínio/química , Espaços Confinados , Enxofre , Compostos de Enxofre
20.
Chemosphere ; 251: 126382, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32443238

RESUMO

A single metal Pd/γ-Al2O3 catalyst and a bimetallic Pd-Ce/γ-Al2O3 catalyst were prepared by the equal-volume impregnation method to investigate the effect of CeO2 loading on the catalytic oxidation of toluene. The specific surface area, surface morphology, and redox performance of the catalyst were characterized by N2 desorption, scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), H2-TPR, O2-TPD, and electron paramagnetic resonance (EPR). The results showed that bimetal catalysts loaded CeO2 had smaller nano-PdO particles than those of the Pd/γ-Al2O3 catalyst. Compared with the catalyst of 0.2Pd/γ-Al2O3 (percentage of mass, the same as below), the catalyst doped with 0.3CeO2 had a stronger reduction peak, which was shifted to the low-temperature zone by more than 80 °C. The results of XPS and O2-TPD showed that the introduction of CeO2 provided more surface oxygen vacancy for the catalyst and enhanced its catalytic oxidation ability, and the amount of desorbed O2 increased from 3.55 µmol/g to 8.54 µmol/g. The results of EPR were that the addition of CeO2 increased the content of active oxygen species and oxygen vacancies on the surface of the catalysts, which might be due to the supply of electrons to the O2 and PdO during the Ce3+toCe4+ conversion process. That could have accelerated the catalytic reaction process. Compared with the single precious metal catalyst, the T10 and T90 of the Pd-Ce/γ-Al2O3 catalyst were decreased by 22 °C and 40 °C, respectively.


Assuntos
Tolueno/química , Óxido de Alumínio/química , Catálise , Cério/química , Chumbo/química , Oxirredução , Oxigênio/química , Espectroscopia Fotoeletrônica
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