RESUMO
This research focuses on developing MIL-53-type compounds with Fe obtained with ligands derived from PET waste, followed by the controlled addition of hydrofluoric acid (HF). Incorporating HF into the MOF structure induced substantial changes in the material textural properties, resulting in a significant change in CO2 adsorption. Furthermore, a distinctive structural alteration (breathing effect) was observed in the CO2 isotherms at different temperatures; these structural changes have not been observed by X-ray diffraction (XRD) because this characterization has been performed at room temperature, whereas the adsorption experiments were conducted at 260, 273, and 303 K and different pressures. Subsequently, DFT studies were performed to investigate the CO2-filling mechanisms and elucidate the material respiration effect. This approach offers promising opportunities for sustainable materials with improved gas adsorption properties.
RESUMO
We report on a detailed textural analysis of mechanochemically synthesized MOF-199 including N2 adsorption-desorption and CO2 adsorption isotherms data at 77â K and 273â K (up to atmospheric pressure), respectively, and CH4 adsorption data at 298â K (up to 35â bar). We used the isotherm adsorption data to determine the micropore volume of the MOF-199 structures, to establish their methane uptake capacity and to understand how these properties depended on the Ethanol/BTC ratio used during the synthesis. The maximum methane uptake capacity for our specimens was recorded at 130â v/v at 35â bars. These results open an avenue for a better understanding of alternative manufacturing processes of MOF structures for gas storage applications.
RESUMO
SBA-15 and KIT-6 materials have been synthesized and modified with iron salts by the wet impregnation method with different metal loadings. The different mesostructures obtained were characterized by N2 adsorption-desorption at 77 K, X-ray diffraction, temperature-programmed reduction, and ultraviolet-visible spectroscopy. These iron-containing mesostructured materials have been successfully tested for the heterogeneous photo-Fenton degradation of aqueous solutions of dangerous herbicides, such as atrazine, using UV-visible light irradiation, at room temperature and close to neutral pH. The results showed that the Fe/SBA-15 (10%) and Fe/KIT-6 (5%) catalysts exhibited the highest activities. However, the Fe/KIT-6 (5%) catalyst with minor Fe loading than Fe/SBA-15 (10%) presented a higher degradation of atrazine (above 98% in a reaction time of 240 min). Therefore, the interconnectivity of the cage-like mesopores had an important influence on the catalytic activity, favoring probably mass-transfer effects. Thus, the high performance of these materials indicates that the heterogeneous via of photo-Fenton process can also be efficiently employed to treat wastewaters containing pollutants such as herbicides, in order to reduce them to simplest and less toxic molecules.
Assuntos
Atrazina/análise , Peróxido de Hidrogênio/química , Ferro/química , Dióxido de Silício/química , Poluentes Químicos da Água/análise , Purificação da Água/métodos , Adsorção , Catálise , Concentração de Íons de Hidrogênio , Luz , Processos Fotoquímicos , Porosidade , Propriedades de Superfície , Águas Residuárias/químicaRESUMO
In this study, natural and modified clays were evaluated as catalysts in an esterification reaction to obtain bio-based lubricants. The biolubricants are environmentally preferred to petroleum-based lubricants because they are biodegradable and non-toxic. Other advantages include very low volatility due to the high molecular weight and excellent viscosity properties with temperature variations. Modifications in natural clay were performed intending to obtain materials with different textural properties that could improve the reaction under study. The modified clays were obtained in two ways: by pillarization using Al13 Keggin polyoxocations or by acid treatments with H2SO4, HCl and HNO3. All samples were evaluated for the esterification reaction of fatty acids from castor oil (FACO) using 2-ethyl-hexanol. During the reaction step, a zeolite-based adsorbent was used for water removal to increase the reaction equilibrium conversion. Gas chromatography and nuclear magnetic resonance were performed to ensure the formation of the products. The highest conversion of fatty acids to esters was obtained using pillared clays. Adding adsorbent in the reaction medium (10 g of 3A zeolite to 100 g of FACO), the conversion improved from 74â»88 wt % after 6 h at 50 °C.
RESUMO
We demonstrate morphology and pore size dependence of silica nanoparticles (SNPs) synthesized via control of the iron oxidation state. In the absence of any Fe species, only spherical SNPs are produced, whereas in the presence of Fe³âº and Fe²âº ions, SNPs with rod-like and nanosheet morphologies, respectively, are formed. The average pore size increases from 1.7 nm in the absence of iron to 3.2 and 5.9 nm as Fe³âº and Fe²âº, respectively, were used during the synthesis. Both samples of SNPs synthesized in the presence of Fe²âº and Fe³âº have 0.2 wt% of tetrahedral iron in the silica framework, whereas most of the iron is in the silica extraframework, as verified by Mössbauer spectroscopy, UV-vis diffuse reflectance, FTIR, XRD data and TPR analysis. These Fe²âº and Fe³âº cations play a fundamental role in controlling these properties because they change the curvature and the surface charge density of CTAB micelles, thus favoring the spherical to rod-like transition. The rod-like shape was retained in Fe-containing samples, whereas a nanosheet-like morphology was produced in Fe²âº-containing samples due to the breakage of silica walls during the thermal treatment to remove the template. The control of the textural properties is interesting to allow the fabrication of selective photocatalysts for oxidation of different organic substrates.