Hybridization of metal–organic framework and monodisperse spherical silica for chromatographic separation of xylene isomers

Metal–organic frameworks(MOFs) packed in the column have been a promising candidate as the stationary phase for high performance liquid chromatography(HPLC). However, the direct packing of irregular MOF powder could raise some problems like high back pressure and low column efficiency in the HPLC separation. In this work, UiO-66 capable of separating xylenes was supported effectively on the surface of the monodisperse spherical silica microspheres by one-pot method. The hybridization of Ui O-66 and silica microspheres(termed UiO-66@SiO_2 shell–core composite) was prepared by stirring the suspension of the precursors of Ui O-66 and\\COOH terminated silica in the N,N-dimethylformamide with heating. The shell–core composite material UiO66@SiO_2 was characterized by SEM, TEM, PXRD and FTIR. Then, it was used as a packing material for the chromatographic separation of xylene isomers. Xylene isomers including o-xylene, m-xylene and p-xylene were efficiently separated on the column with high resolution and good reproducibility. Moreover, the Ui O-66@SiO_2 shell–core composites packed column still remained reverse shape selectivity as Ui O-66 possessed, and the retention of xylenes was probably ascribed to the hydrophobic effect between analytes and the aromatic rings of the Ui O-66 shell. The Ui O-66@SiO_2 shell–core composites obtained in this study have some potential for the separation of structural isomers in HPLC.     

Studying the structure of the vapor–liquid equilibrium diagram of the butyl propionate–propionic acid–butyl butyrate–butyric acid system

This article deals with specific structural features of the vapor–liquid equilibrium diagram of the butyl propionate–propionic acid–butyl butyrate–butyric acid four-component system, which is of industrial importance and contains biazeotropic ester–acid constituents. The positions of some isomanifolds in the concentration tetrahedron and in its constituents are reported.     

Design and synthesis of zero–zero-birefringence polymers in a quaternary copolymerization system

We designed and synthesized quaternary copolymers of methyl methacrylate (MMA), 2,2,2-trifluoroethyl methacrylate (TFEMA), benzyl methacrylate (BzMA), and 3,3,5-trimethylcyclohexyl methacrylate (TMCHMA) and we investigated their birefringence, thermal properties, and other optical properties. When the copolymer composition was MMA/TFEMA/BzMA/TMCHMA = 50:38:8:4, 40:30:7:23, or 30:21:7:42 (wt%), a zero–zero-birefringence polymer that exhibited neither orientational nor photoelastic birefringence was obtained. We demonstrated that such zero–zero-birefringence polymers with a variety of compositions could be successfully prepared in the quaternary system by using the same compensation method as applied in ternary random copolymerization. We also demonstrated that the glass-transition temperature (T_g) and refractive index (n_D) of these copolymers could be controlled with high accuracy while retaining their zero–zero-birefringence property. We can therefore predict the type of birefringence, the T_g, and the n_D of a particular copolymer before polymerization. Zero–zero-birefringence polymers with the most appropriate characteristics can then be synthesized selectively by quaternary copolymerization.     

Thermodynamic assessment within the Zr–B–C–O quaternary system

Thermodynamic modeling of Zr–B–C–O quaternary system is conducted within the CALPHAD framework by employing data obtained from first-principle calculations and literature. The lower order binary B–O is assessed in this work by estimating the thermodynamic properties of stable solid phases of B₂O₃ and B₆O and by estimating the gas and liquid phases. First-principle calculations, in conjunction with special quasirandom structure were used to predict enthalpies of mixing for the ternary solid-solution phase of FCC-Zr(C, O). The calculated results were used to optimize the model parameters pertaining to the cubic phase, which is described by a two-sublattice model. The modeled Zr–C–O ternary phase diagrams calculated at 1923 and 2273 K under ambient pressure and 4 Pa, respectively, are in agreement with experimental phase diagrams.     

Influence of acid–base property of support on the toluene combustion activity of palladium

Metal–support interaction in the catalytic combustion of toluene was studied, using metal oxides with different acid–base properties as supports. The combustion activity over Pd loaded on strong acidic or basic support was lower than over Pd on weak acidic or basic metal oxides. The study of Pd surface with X-ray photoelectron spectroscopy and reaction order measurement showed that the affinity for oxygen changed according to the acid–base property of support. It was considered that the combustion activity of Pd was controlled by the acid–base property of support through an electronic interaction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of solvent,Lewis acid–base complex,and nanoparticles on the morphology and gas separation properties of polysulfone membranes

A series of polysulfone (PSF) membranes were prepared using different solvents: dimethylformamide (DMF), tetrahydrofuran, dimethylacetamide, and n-methyl-2-pyrrolidone (NMP). The PSF membrane prepared by NMP showed the highest gas permeability. The influence of propionic acid as a Lewis acid on gas separation properties of the PSF was explored. The PSF membrane prepared by the casting solution containing 25 wt% PSF, 35 wt% propionic acid, and 40 wt% NMP showed a superior gas separation performance. The gas permeation measurements indicated that incorporating 30 wt% γ-alumina nanoparticles into the PSF matrix resulted in about the respective 43% and 41% increase in CO₂ and O₂ permeability together with a rise in CO₂/CH₄ and O₂/N₂ selectivities (13% and 7%, respectively). Furthermore, by rearranged modified Maxwell model, the role and nature of the interfacial layer in the PSF-based mixed matrix membranes were mathematically analyzed considering a reduced permeability factor.     

Use of the combined Lifshitz–van der Waals and Lewis acid–base approaches in determining the apolar and polar contributions to surface and interfacial tensions and free energies

Recently, a number of authors have been rearranging the various combinations and permutations of the different apolar and polar liquids with which contact angles can be measured on polar surfaces and in so doing have arrived at bizarre results. The rational order and procedures to be followed in the determination of the apolar and polar surface tension properties of polar materials, according to the van Oss-Chaudhury-Good components and parameters of the approach, are reiterated.     

Synthesis of acid–base bifunctional CaO/ITQ-2 zeolite catalyst for phosphorylation of dodecanol

A series of acid–base bifunctional CaO/ITQ-2 zeolite catalysts were prepared by introducing calcium into the ITQ-2 zeolite. The catalysts were characterized by X-ray diffraction, FT-IR, NH₃-TPD and CO₂-TPD. The characterization results proved that ITQ-2 zeolite was synthesized by delaminating the MCM-22 zeolite. After modification by CaO, the catalysts could simultaneously have alkaline and acidic sites with little structural change. We then studied the catalytic capabilities of the prepared catalysts in the phosphorylation of dodecanol to di-dodecyl phosphate (DAP). The results show that ITQ-2 catalyst has higher selectivity for DAP than MCM-22. Versus ITQ-2 zeolite, the CaO/ITQ-2 catalysts have excellent acid–base cooperativity. The conversion of phosphoric acid and the selectivity of di-dodecyl phosphate could reach 80.2% and 77.5%, respectively over 3 wt.%CaO/ITQ-2 at optimal conditions. The catalytic activity of CaO/ITQ-2 catalyst could be regenerated by roasting after four times of reusing.     

Plasma assisted novel production process of glass-ceramic spheres in the quaternary system CaO–SiO2–Al2O3–MgO

In this work, a novel transformation process of industrial byproducts into spherical glass-ceramic materials in the quaternary system CaO–SiO₂–Al₂O₃–MgO is presented. Byproducts used as precursor are blast furnace slags (BFS) generated by steelmaking industry located in northeastern Mexico. Several parameters for plasma projection process, such as Ar:He feeding flow and electric current were studied. Industrial Ar:He plasma projection equipment was used for vitrification and microstructural/morphological transformation of BFS. Precursor particles as well as produced glass-ceramic spheres were characterized by optical microscopy (OM), field emission scanning electron microscopy (FE-SEM), and X-ray diffraction (XDS). In addition, density measurements from the generated powders were obtained using a Helium pycnometer.These new materials have a highly amorphous structure, and their final properties, such as porosity, density and size can be controlled by process parameters and therefore they could be modified to obtain special features for specific applications.     

Effect of the acid–base composition of water on the wettability of coals of different ranks (Short Communication)

The results of the experimental studies allowed us to assume that the process characteristics determined by the wettability of coal (dust suppression, hydraulic fracturing, coal washing, etc.) may be insensitive to the acid–base composition of utilized water in a range of pH 4.6–10.     

Comparison of the Lifshitz–van der Waals/acid–base and contact angle hysteresis approaches for determination of solid surface free energy

Total surface free energy, γ_S ^TOT, for several solids (glass, PMMA, duralumin, steel and cadmium) was calculated from the surface free energy components: apolar Lifshitz–van der Waals, γ_S ^LW, and acid–base electron–donor, γ_S ^-, and electron–acceptor, γ_S ⁺. Using van Oss and coworkers' approach (Lifshitz–van der Waals/acid–base (LWAB) approach), the components were determined from advancing contact angles of the following probe liquids: water, glycerol, formamide, diiodomethane, ethylene glycol, 1-bromonaphthalene and dimethyl sulfoxide. Moreover, receding contact angles were also measured for the probe liquids, and then applying the contact angle hysteresis (CAH) approach very recently proposed by Chibowski, the total surface free energy for these solids was calculated. Although the thus determined total surface free energy for a particular solid was expected to depend on the combination of three probe liquids used (LWAB approach), as well as on the kind of the liquid used (CAH approach), surprisingly the average values of the surface free energy from the two approaches agreed very well. The results obtained indicate that both approaches can deliver some useful information about the surface free energy of a solid.     

Deposition efficiency and uniformity of monodisperse solid particle deposition in the Vitrocell® 24/48 Air–Liquid-Interface in vitro exposure system

Abstract

A key to understanding biological response due to cell exposure to chemical constituents in aerosols is to accurately be able to determine the delivered dose. Deposition efficiency and uniformity of deposition was measured experimentally in the Vitrocell^® 24/48 air–liquid-interface (ALI) in vitro exposure system using monodisperse solid fluorescent particles with mass median aerodynamic diameters (MMAD) of 0.51, 1.1, 2.2 and 3.3?µm. Experimental results were compared with computational fluid dynamics (CFD; using both Lagrangian and Eulerian approaches) predicted deposition efficiency and uniformity for a single row (N?=?6) of cell culture inserts in the Vitrocell^® 24/48 system. Deposited fluorescent monodisperse particles were quantified using fluorescent microscopy and Image J software. Experiments were conducted using a suspension of two particle MMADs with each experiment being conducted a total of three times on different days. The average experimentally measured deposition efficiency ranged from a low of 0.013% for 0.51?µm MMAD particles to a maximum 0.86% for 3.3?µm MMAD particles. There was good agreement between the average experimentally measured and the CFD predicted particle deposition efficiency (regardless of approach) with agreement being slightly better at the smaller MMADs. Experimentally measured and CFD predicted average uniformity of deposition was >45% of the mean and within 15% of the mean for 0.51?µm and 2.2 MMAD µm particles, respectively. Experimentally measured average uniformity of deposition was between 15 and 45% of the mean while CFD predictions were within 15% of the mean for 1.1 and 3.3?µm MMAD particles. The deposition efficiency and uniformity across the cell culture inserts for solid particles should be considered when designing exposure regimens using the Vitrocell^® 24/48 ALI in vitro exposure system.

Copyright © 2019 American Association for Aerosol Research     

Enhancing the selectivity of Pare-dihydroxybenzene in hollow titanium silicalite zeolite catalyzed phenol hydroxylation by introducing acid–base sites

A facile and effective method for enhancing the selectivity of Pare-dihydroxybenzene in phenol hydroxylation has been developed by introducing acid–base sites (MgO–Al₂O₃ binary oxide) to the micropores of hollow titanium silicalite (HTS, Ti/Si = 25) zeolite. For MgO–Al₂O₃ modified HTS zeolites, the biggest ratio of para- to ortho-dihydroxybenzene is over 2, while that is close to 1 for conventional HTS zeolite. The high pare-dihydroxybenzene selectivity is ascribed to the steric hindrance and the synergistic effect between acid–base sites of mixed oxide and tetrahedral framework Ti species in HTS zeolite.     

Recent theoretical and experimental advancements in the application of the van Oss–Chaudhury–Good acid–base theory to the analysis of polymer surfaces II. Some peculiar cases

—According to the general guidelines presented in the accompanying paper, some relevant examples of common polymer surfaces are analysed and discussed; a number of polymers commercially available or laboratory synthesized have been analysed. In particular, the case of poly(vinyl chloride) (PVC), often considered as peculiar in the literature, is fully analysed on the basis of a new set of well-prepared samples, whose compositions were checked by high-vacuum spectroscopies. 'Equilibrium' contact angles, obtained by a new experimental technique, are presented. The results are, however, preliminary, because the final set of liquids used is not so 'well equilibrated' as possible, from the point of view of acid–base properties. The contact angle data obtained are analysed in a non-linear way to calculate the acid–base components of all the liquids and solids. The results are discussed and compared with those obtained from liquid–liquid interfaces presented in the accompanying paper. The physico-chemical features of these samples have also been compared with the adhesion properties of some bacterial cells, commonly found as infective agents on biomaterials surfaces of medical devices, in order to rationalize these results within the theoretical framework of acid–base theory.     

Recent theoretical and experimental advancements in the application of van Oss–Chaudury–Good acid–base theory to the analysis of polymer surfaces I. General aspects

The acid-base theory as developed by van Oss, Chaudury and Good is a powerful tool to analyze the surface free energy of polymeric materials; however, some problems are encountered in its application and some authors have shown that these problems can be theoretically solved considering this theory as an example of the so-called LFER theories. From this point of view, the definition of a well-defined scale of acid-base strength and the use of a wide and well-equilibrated, appropriate set of liquids is very important. In the present paper some recent results are presented which are based on the mathematical approach discussed by Della Volpe and Siboni in previous papers. The treatment is developed as a list of questions, Frequently Asked Questions (FAQs), whose theoretical implications are discussed using numerical examples chosen from the literature. Some literature data, collected by the opponents of the acid-base theory and recently published, are re-analysed using these methods, showing that they constitute a well-defined set to calculate, with a good precision, the acidbase components of the considered materials and the interfacial energies of liquids used. The present paper is the premise of a second one, in which a set of contact angles data collected by the authors and by other researchers will be analysed following the principles discussed here.     

Influence of surface acid–base properties of zirconia and titania based catalysts on the product selectivity in gas phase dehydration of glycerol

Acid–base properties of zirconia and titania based materials were investigated by adsorption microcalorimetry of NH₃ and SO₂ probe molecules. Catalytic performance of the catalysts was also tested in the gas phase dehydration of glycerol with the intention of finding correlations between catalytic activity and surface acid–base features. Results show that the number of basic sites directly affects the selectivity in gas phase dehydration of glycerol to produce acrolein. Therefore, in order to realize the target reaction it is necessary to control not only the strength and the amount of the desired sites (acidic ones), but also to hinder as much as possible the number/strength/action of the undesired ones (basic ones).     

An unprecedented acid/base stable Cu-based metal–organic framework with good catalytic activity for the reduction of 4-nitrophenol

A new 3D metal–organic framework with pcu topology {[Cu₂(TPOM)(ddpa)₂]}_n (1) was synthesized under solvothermal condition by employing flexible tetrakis(4-pyridyloxymethylene) methane (TPOM) and semirigid 4,4′-dicarboxydiphenylamine (H₂ddpa) as well as Cu(II) ion. Complex 1 exhibits good endurance in acid/base aqueous solutions and a high catalytic activity for the reduction of 4-nitrophenol in excess NaBH₄ solution.