Favorable Porous Structure Research Articles

Adsorption Behavior of Metal Ions by Amidoxime Chelating Resins

AbstractIn this work, the acrylonitrile (AN) – divinylbenzene (DVB) –methylacrylate (MA) resin was synthesized via suspension polymerization in the presence of toluene as diluent, and benzoylperoxide (BPO) as initiator. The effect of MA, toluene and alkaline treatment on the exchange capacity of the resin were investigated. The results showed that the anion exchange capacity decreased with an increase in the amount of MA, while alkaline treatment had no significant effect. Also, the cation exchange capacity increased with an increase in the amount of hydrophilic agent and reached a maximum point. The sorption equilibrium was achieved relatively fast within 40 mins, and the resin exhibited affinity towards lead (II), copper (II) and in particular uranium (VI). The adsorption of uranium was directly depended up on the pH value. Furthermore, the macroreticular chelating resin, containing amidoxime group had higher adsorption of uranium (VI) in comparison to other metal ions studied. Finally, the alkaline treatment enhanced the potential for much faster adsorption characteristics and the highly porous chelating resin provided a more favorable pore structure for the rapid rate of diffusion of metal ions.

Adsorption properties of amidoxime resins for separation of metal ions from aqueous systems

In this study, the acrylonitrile (AN)–divinylbenzene (DVB)–methylacrylate (MA) resin was synthesized via suspension polymerization in the presence of toluene as diluent, and benzoylperoxide (BPO) as initiator. The effects of MA as a hydrophilic agent and toluene as a diluent on the anion and cation exchange capacity of the synthesized amidoxime resins were investigated before and after alkaline treatment. The results showed that the anion exchange capacity decreased with an increase in the amount of MA while alkaline treatment had no significant effect. Also, the cation exchange capacity increased with an increase in the amount of hydrophilic agent and reached a maximum point. The sorption equilibrium was achieved relatively fast within 40 min, and the resin exhibited affinity towards lead (II), copper (II) and in particular U(VI), and the order of adsorption affinity were UO 2 2 + > Pb 2+ ≫ Co 2+ > Cu 2+ ≫ Cd 2+. The adsorption of uranium was directly depended up on the pH value. Furthermore, the macroreticular chelating resin, containing amidoxime group had higher adsorption of uranium (VI) than other metal ions studied. Finally, the alkaline treatment enhanced the potential for much faster adsorption and the highly porous chelating resin provided a more favorable pore structure for the rapid rate of diffusion of metal ions.

Characterisation of Calcium Phosphate Cement-Derived Hydroxyapatite Scaffolds with a PLGA-Bioactive Glass Composite Coating

The limitations of autogenic, allogenic and xenogenic grafting methods have led to the development of synthetic grafts as an alternative. The aim of this study was to manufacture highly porous and well interconnected hydroxyapatite scaffolds and modify them with a poly(lactic-co-glycolic acid) (PLGA)-bioactive glass composite coating to achieve mechanical properties close to those of natural cancellous bones. In this study, hydroxyapatite scaffolds were prepared from a calcium phosphate cement (CPC) powder and cell culture using fibroblast cells was done to examine the cytotoxicity of the materials used for the scaffolds. The average pore size of the scaffolds was found to be 650μm and the total porosity was about 80%. The hydroxyapatite scaffolds without the coating had a mean compressive strength and a mean compressive modulus of 0.74 MPa and 20.46 MPa, respectively, which were in contrast to those of the scaffolds coated with the PLGA-bioacitve glass composite material (1.36 MPa and 24.58 MPa, respectively). The fibroblast cells were observed to proliferate well on the PLGA-bioactive glass coated scaffolds. The cells had also penetrated into the scaffold to a depth of approximately 2mm. Thus the scaffolds fabricated in this study exhibited a favourable porous structure and good cell response which are desirable for bone tissue engineering.

Preparation and Charaterization of the Electrode Catalyst Supported on Mesoporous Carbons for the Dmfc Application

Mesoporous carbon (MCs) was synthesized using mesoporous silica as a template. Prepared mesoporous carbon materials were found to have high surface area and large pore volume with uniform pore size. Resulting materials showed a different pore arrangement from mesoporous silica templates. Pt catalysts supported on mesoporous carbon prepared were applied to an anode catalyst for Direct Methanol Fuel Cell (DMFC). Results indicate that a mesoporous carbon having 3-dimensional pore system (3D-MC) had higher catalytic activity than 2-dimensional one (2D-MC) due to a favorable pore structure in methanol electro-oxidation.

Characterization of some physical and chromatographic properties of monolithic poly(styrene–co-divinylbenzene) columns

Monolithic capillary columns were prepared by copolymerization of styrene and divinylbenzene inside a 200μm i.d. fused silica capillary using a mixture of tetrahydrofuran and decanol as porogen. Important chromatographic features of the synthesized columns were characterized and critically compared to the properties of columns packed with micropellicular, octadecylated poly(styrene–co-divinylbenzene) (PS–DVB–C18) particles. The permeability of a 60mm long monolithic column was slightly higher than that of an equally dimensioned column packed with PS–DVB–C18 beads and was invariant up to at least 250bar column inlet pressure, indicating the high-pressure stability of the monolithic columns. Interestingly, monolithic columns showed a 3.6 times better separation efficiency for oligonucleotides than granular columns. To study differences of the molecular diffusion processes between granular and monolithic columns, Van Deemter plots were measured. Due to the favorable pore structure of monolithic columns all kind of diffusional band broadening was reduced two to five times. Using inverse size-exclusion chromatography a total porosity of 70% was determined, which consisted of internodule porosity (20%) and internal porosity (50%). The observed fast mass transfer and the resulting high separation efficiency suggested that the surface of the monolithic stationary phase is rather rough and does not feature real pores accessible to macromolecular analytes such as polypeptides or oligonucleotides. The maximum analytical loading capacity of monolithic columns for oligonucleotides was found to be in the region of 500fmol, which compared well to the loading capacity of the granular columns. Batch-to-batch reproducibility proved to be better with granular stationary phases compared to monolithic stationary phase, in which each column bed is the result of a unique column preparation process.

Isobutane/2-Butene Alkylation Using Large-Pore Zeolites: Influence of Pore Structure on Activity and Selectivity

The alkylation of isobutane with 2-butene was performed in the liquid phase at 80°C and 300 psi. This study constitutes a detailed comparison under identical conditions of 12-membered pore zeolites with different dimensionalities, namely USY, mordenite, beta, LTL, and ZSM-12 zeolite. Particular attention was paid to the role of the structural characteristics of the catalysts. In the mechanism studies, very-low-olefin feed (i/o molar ratio of 1000, olefin WHSV of 0.01 h −1) was used to keep real alkylation without undesirable oligomerizations. For selectivity toward the individual TMP and DMH compounds, pore structure plays a significant role. At the initial stage (5 min on stream), it was found that the relative value for TMP selectivities described by the configurational ratio of 2,2,4-/2,2,3-TMP to 2,3,3-/2,3,4-TMP decreased in the following order: beta ≥ ZSM-12 > mordenite > USY ≥ LTL. Beta and ZSM-12 showed higher values due to their specific pore structure (the absence of large expansions at either the channel intersections or within the channel itself), in which bulky TMPs could diffuse out without structural restriction. In order to support this, the ratio of diffusivity for selected TMP isomers (2,2,4- to 2,3,4-TMP) was obtained. The value of diffusivity ratio of 2,2,4-TMP to 2,3,4-TMP decreased in the sequence beta > USY > LTL. This difference was reflected clearly in the different distribution of TMP isomers. The comparable trends were also observed for the selectivity of DMHs, ratio of 2,5-/2,4-/2,3-DMH to 3,4-DMH. Most of cracking products, 2-methyl butane, 2,3-dimethyl butane, and 2,3- and 2,4-dimethly pentane, were formed by type A β-scissions from [C 12H 25] + and [C 16H 33] +. For other studies with different feed conditions (i/o molar ratio of 98, olefin WHSV of 0.1 h −1), it was also observed that the pore structure of zeolites plays a significant role in the activity of olefin conversion. Beta and ZSM-12 were shown to outperform other zeolites because their favorable pore structures limited the accumulation of carbonaceous compounds that lead to pore plugging. This is in contrast to the common belief that three-dimensional zeolites are less susceptible to pore plugging than one-dimensional zeolites; we observed dramatically better coke tolerance over ZSM-12 (one dimensional) than USY (three dimensional). It was observed that samples synthesized with low Si/Al ratios resulted in higher activity and selectivity to the desired products. This was mainly because of the high hydrogen transfer (HT) capability of the low Si/Al samples. However, the dealumination procedure used strongly affected the catalyst performance; samples dealuminated with ammonium hexafluorosilicate were significantly less active and selective to TMPs than samples either dealuminated with HCl or synthesized directly. This was primarily because of the ability of the latter dealuminating agent to remove surface aluminum as well as partial pore blocking by the silicate salts deposited.

Isobutane/2-Butene Alkylation Using Large-Pore Zeolites: Influence of Pore Structure on Activity and Selectivity

The alkylation of isobutane with 2-butene was performed in the liquid phase at 80°C and 300 psi. This study constitutes a detailed comparison under identical conditions of 12-membered pore zeolites with different dimensionalities, namely USY, mordenite, beta, LTL, and ZSM-12 zeolite. Particular attention was paid to the role of the structural characteristics of the catalysts. In the mechanism studies, very-low-olefin feed (i/o molar ratio of 1000, olefin WHSV of 0.01 h −1 ) was used to keep real alkylation without undesirable oligomerizations. For selectivity toward the individual TMP and DMH compounds, pore structure plays a significant role. At the initial stage (5 min on stream), it was found that the relative value for TMP selectivities described by the configurational ratio of 2,2,4-/2,2,3-TMP to 2,3,3-/2,3,4-TMP decreased in the following order: beta ≥ ZSM-12 > mordenite > USY ≥ LTL. Beta and ZSM-12 showed higher values due to their specific pore structure (the absence of large expansions at either the channel intersections or within the channel itself), in which bulky TMPs could diffuse out without structural restriction. In order to support this, the ratio of diffusivity for selected TMP isomers (2,2,4- to 2,3,4-TMP) was obtained. The value of diffusivity ratio of 2,2,4-TMP to 2,3,4-TMP decreased in the sequence beta > USY > LTL. This difference was reflected clearly in the different distribution of TMP isomers. The comparable trends were also observed for the selectivity of DMHs, ratio of 2,5-/2,4-/2,3-DMH to 3,4-DMH. Most of cracking products, 2-methyl butane, 2,3-dimethyl butane, and 2,3- and 2,4-dimethly pentane, were formed by type A β-scissions from [C 12 H 25 ] + and [C 16 H 33 ] + . For other studies with different feed conditions (i/o molar ratio of 98, olefin WHSV of 0.1 h −1 ), it was also observed that the pore structure of zeolites plays a significant role in the activity of olefin conversion. Beta and ZSM-12 were shown to outperform other zeolites because their favorable pore structures limited the accumulation of carbonaceous compounds that lead to pore plugging. This is in contrast to the common belief that three-dimensional zeolites are less susceptible to pore plugging than one-dimensional zeolites; we observed dramatically better coke tolerance over ZSM-12 (one dimensional) than USY (three dimensional). It was observed that samples synthesized with low Si/Al ratios resulted in higher activity and selectivity to the desired products. This was mainly because of the high hydrogen transfer (HT) capability of the low Si/Al samples. However, the dealumination procedure used strongly affected the catalyst performance; samples dealuminated with ammonium hexafluorosilicate were significantly less active and selective to TMPs than samples either dealuminated with HCl or synthesized directly. This was primarily because of the ability of the latter dealuminating agent to remove surface aluminum as well as partial pore blocking by the silicate salts deposited.