Microporous Volumes from Nitrogen Adsorption at 77 K: When to Use a Different Standard Isotherm?

This work reviews the application of various standard isotherms to evaluate the micropore volume in a range of microporous materials. The selected materials have quite different surface chemistry, and are relevant due to their properties for adsorption and catalysis: zeolites, activated carbons, clay-based materials and MOFs. Some cases were analysed before and after being used as supports in the heterogenization of homogeneous catalysts. The discussion is centred, but not limited, to the three standard isotherms that are mostly employed in the literature (t-curve, non-porous carbon and non-porous hydroxylated silica) for the assessment of the micropore volume. For a given material the values of the micropore volumes from the different standard isotherms were compared, particularly against the values from the largely used t-curve. The cases where major discrepancies were found could normally be ascribed to samples that have a broad micropore size distribution.

Novel Mg-Incorporated Micro-Arc Oxidation Coatings for Orthopedic Implants Application

In this study, Ti-6Al-4V alloy samples were processed by micro-arc oxidation (MAO) in phytic acid (H12Phy) electrolytes with the addition of different concentrations of EDTA-MgNa2 (Na2MgY) and potassium hydroxide (KOH). The surface characterization and cytocompatibility of MAO-treated samples were evaluated systematically. H12Phy is a necessary agent for MAO coating formation, and the addition of Na2MgY and KOH into the electrolytes increases the surface roughness, micropore size and Mg contents in the coatings. The MAO coatings are primarily composed of anatase, rutile, MgO and Mg3(PO4)2. Magnesium (Mg) ions in the electrolytes enter into MAO coatings by diffusion and electromigration. The MAO coatings containing 2.97 at% Mg show excellent cell viability, adhesion, proliferation, alkaline phosphatase activity, extracellular matrix (ECM) mineralization and collagen secretion, but the cytocompatibility of the MAO coatings containing 6.82 at% Mg was the worst due to the excessively high Mg content. Our results revealed that MAO coatings with proper Mg contents improve the cytocompatibility of the Ti-6Al-4V alloys and have large potential in orthopedic applications.

Influence of Evaporation Drying on the Porous Properties of Carbon/Carbon Composite Xerogels

Carbon/carbon (C/C) composite xerogels dried by evaporation were prepared in this study to observe the change of their porous properties and their morphology by nitrogen sorption apparatus and a scanning electron microscope. Resorcinol and formaldehyde (RF) sols as a matrix phase and cotton fibers (CF) as a dispersed phase were mixed and gelated to be CF/RF composite hydrogels. The composite hydrogels were exchanged by t-butanol (TBA), dried by evaporation at 50 °C, and carbonized at 1000 °C to become the C/C composite xerogels. The results show that the CF addition does not decrease the mesoporous properties of the C/C composite xerogels. Moreover, the CF addition can alleviate the pore shrinkage, and it can maintain the mesopore structure. The mesopore size and the micropore size of C/C composites are insignificantly changed because the CF addition and the solvent exchange using TBA may suppress the pore shrinkage despite the gas-liquid interface existing during the evaporation drying.

Study on the microscopic pore structures of the four different kinds of lithological reservoirs in the basin of Western China

In the basin of western China, four different kinds of lithological reservoirs are developed, including low-permeability sandstone, sedimentary tuff, shale and volcanic rock. There is generally a large difference in the micropore structure characteristics and distribution laws due to different reservoirs. The reserving capacity as well as the porous flowability, mechanism and laws are determined by the micropore structure characteristics and distribution laws of hydrocarbon reservoirs. Low-temperature nitrogen adsorption and desorption technology, high-pressure mercury injection experiment and nuclear magnetic resonance (NMR) testing technology are applied to study the micropore size, quantity, structure and distribution laws of four different kinds of lithological reservoirs as well as their similarities and differences of corresponding relation with macroporosity–permeability physical parameters. This paper also studies the movable fluid and nonlinear seepage flow characteristics of four different kinds of lithological reservoirs.

Kraft Lignin Ethanolysis over Zeolites with Different Acidity and Pore Structures for Aromatics Production

To utilize its rich aromatics, lignin, a high-volume waste and environmental hazard, was depolymerized in supercritical ethanol over various zeolites types with different acidity and pore structures. Targeting at high yield/selectivity of aromatics such as phenols, microporous Beta, Y, and ZSM-5 zeolites were first examined in lignin ethanolysis, followed by zeolites with similar micropore size but different acidity. Further comparisons were made between zeolites with fin-like and worm-like mesoporous structures and their microporous counterparts. Despite depolymerization complexity and diversified ethanolysis products, strong acidity was found effective to cleave both C–O–C and C–C linkages of lignin while mild acidity works mainly in ether bond breakdown. However, when diffusion of gigantic molecules is severe, pore size, particularly mesopores, becomes more decisive on phenol selectivity. These findings provide important guidelines on future selection and design of zeolites with appropriate acidity and pore structure to promote lignin ethanolysis or other hydrocarbon cracking processes.

Microstructure and properties of rare earth CeO2-doped graphene composite coatings prepared by MAO on AA7050

In this paper, ceramic coatings were prepared on the surface of 7050 high strength aluminum alloy using a micro-arc oxidation process in a silicate electrolyte combined with the rare earth element cerium or graphene. To analyze the surface morphology, roughness, phase composition, and corrosion resistance, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectrometry, and electrochemical measurements were used, respectively. It was shown that the micropore size of the composite coatings, which mainly consisted of α-Al2O3 and γ-Al2O3, decreases and the density improved with the simultaneous addition of 4 g · L-1 of CeO2 and 10 g · L-1 of graphene to the electrolyte. In addition, with the addition of CeO2 and graphene, the roughness was the lowest and the corrosion resistance was significantly improved.

Calcium-Assisted Regulation of the Structures of Porous Carbons at the Micro-Nano Scale

Here a facile and effective method was investigated to regulate the microstructures of porous carbons by adjusting the contents of calcium in precursors. The carbonization characteristics of precursors were characterized by thermogravimetric analysis (TGA) and differential thermogravimetric (DTG), and the results show that the weight loss rates of precursors decrease with the increases of calcium contents. The structures of carbonized samples and their derived porous carbons at the micrometer scale were characterized by Scanning electron microscopy (SEM), and the results show that the structures of carbonized samples change regularly with the increases of calcium contents in precursors, and porous carbons can inherit the structures from their corresponding carbonized samples. The pore characteristics of porous carbons at the nanometer scale were characterized by N2 adsorption and desorption, Barrett Joyner and Halenda (BJH) method and Horvath-Kawazoe (HK) method, and the results show that the existence of calcium in precursors can greatly increase the total pore volumes and specific surface areas of porous carbons derived from precursors, and interestingly it can be noticed that the micropore size distributions of porous carbons in the range of 0.58–10 nm are quite similar.