Bimodal Porous Materials Research Articles

Microcell morphology evolution and mechanical performance of UHMWPE/PEG porous materials with bimodal cell structure

The bimodal cell structure with both large and small cells has been reported to have more excellent thermal insulation, vibration damping and mechanical properties. In this work, UHMWPE/PEG porous materials with bimodal cell structure were prepared by a simple one-step decompression micro-foaming technology using only supercritical carbon dioxide (sc-CO2). The effects of PEG content, molecular weight of PEG, saturation temperature, pressure and time on the evolution of cell morphology were investigated. The results show that when the content of PEG is 7%, the UHMWPE/PEG composite porous material exhibits stable bimodal cell morphologies in most process range, and a mechanism for the formation of bimodal cell is proposed. Moreover, UHMWPE/PEG porous materials with bimodal cell structure show higher mechanical properties. When the relative densities are similar, the anti-compression properties of bimodal porous materials are significantly better than those of unimodal porous materials.

Confrontation of various adsorption models for assessing the porous structure of activated carbons

Herein, a comprehensive analysis of DFT methods as a tool for evaluating the impact of the nature of the activating agent on the porous structure of activated carbons derived from hazelnut shells is given. The study was based on the use of NLDFT, QSDFT, and 2D-NLDFT methods applied to nitrogen adsorption isotherms, and the results were compared with those formerly obtained by using DR, BET, and LBET methods. Analyses conducted with NLDFT, QSDFT, and 2D-NLDFT revealed a very strong dependence of the results on assumptions about the specific pore model, which calls into question the reliability and credibility of these methods. However, if one takes into account the measurement errors that may during the determination of the adsorption isotherms, as well as the difficulty of selecting a representative sample in a batch of materials (most often non-homogeneous) to be analysed, some imperfections of the DFT methods become acceptable. The analyses in question revealed some limitations of the LBET method which became obvious when the analysis concerned bimodal porous materials with a considerable proportion of mesopores. In such cases, the LBET method, which was formerly designed for analysing microporous materials, may become less reliable.

Morphological study on the pore growth profile of poly(ε-caprolactone) bi-modal porous foams using a modified supercritical CO2 foaming process

Bi-modal porous material is considered to have superior physical and tissue-inducing properties. This study reports on the fabrication of bi-modal porous poly(ε-caprolactone) (PCL) scaffolds using two-step depressurization supercritical CO2 foaming process. In a single process, large pores over 100 μm nucleated in the slow depressurization step, and coalesced during holding stage; small pores below 40 μm were formed in the rapid depressurization step. Investigation on foaming parameters demonstrated that soaking time longer than 0.5 h was necessary to produce bi-modal pores. It was noted that the holding stage had a significant impact on the final pores. In particular, intermediate pressure would affect the plasticizing capabilities of CO2 to increase (5–7 MPa) or decrease (7–12 MPa) pore size. In all, bi-modal porous PCL foams with around 80% porosity were produced, and this work provided a potential reference to efficient design of bone tissue engineering scaffolds.

New non-covalent functionalized phenyl-methyl-silica for biomolecules immobilization: Experimental and theoretical insights of interactions

A new strategy for functionalization of porous silica with phenyl-methyl groups is developed and demonstrated in this work. Bare silica, a hierarchical bimodal porous material, was functionalized with non-hydrolysable alkylsilane (trimethylphenylsilane) by liquid phase grafting, without the use of additional catalyst. The analyses carried out by FTIR, zeta potential and 29Si NMR of modified material indicating that the silane is efficiently and stably adsorbed on silica surface. Computational simulations showing the interaction between silane and silica is by formation of bridges between phenyl ring of silane and silanol groups of silica, with interaction energies similar to those found for hydrogen bridges. Additionally, this modification generates a change on hydrophobicity of silica (11% more hydrophobic than bare silica) that allows the success immobilization of lipase from Thermomyces lanuginosus, used as probe biomolecule. This biocatalyst exhibits a specific activity of 45.7 IU (50% more than those obtained with bare silica) and a half-life of 89.9 h at 45 °C in acetone, which is 5-fold higher than for the biocatalyst prepared with the bare silica. These results could contribute to the preparation of new and efficient materials to be used as supports for biocatalysts, delivery drugs and remediation.

A semi-empirical model relating micro structure to acoustic properties of bimodal porous material

Complex morphology of open cell porous media makes it difficult to link microstructural parameters and acoustic behavior of these materials. While morphology determines the overall sound absorption and noise damping effectiveness of a porous structure, little is known on the influence of microstructural configuration on the macroscopic properties. In the present research, a novel bimodal porous structure was designed and developed solely for modeling purposes. For the developed porous structure, it is possible to have direct control on morphological parameters and avoid complications raised by intricate pore geometries. A semi-empirical model is developed to relate microstructural parameters to macroscopic characteristics of porous material using precise characterization results based on the designed bimodal porous structures. This model specifically links macroscopic parameters including static airflow resistivity (σ), thermal characteristic length (Λ′), viscous characteristic length (Λ), and dynamic tortuosity (α∞) to microstructural factors such as cell wall thickness (2t) and reticulation rate (Rw). The developed model makes it possible to design the morphology of porous media to achieve optimum sound absorption performance based on the application in hand. This study makes the base for understanding the role of microstructural geometry and morphological factors on the overall macroscopic parameters of porous materials specifically for acoustic capabilities. The next step is to include other microstructural parameters as well to generalize the developed model. In the present paper, pore size was kept constant for eight categories of bimodal foams to study the effect of secondary porous structure on macroscopic properties and overall acoustic behavior of porous media.

Synthesis of highly ordered macro-mesoporous anatase TiO 2 film with high photocatalytic activity

Highly ordered macro-mesoporous anatase TiO 2 film was synthesized by sol–gel method in an acidic medium, using polystyrene (PS) colloidal crystal and triblock copolymer P123 (EO 20PO 70EO 20) as dual templating. The resulting film was characterized by Raman spectroscopy, X-ray diffraction (XRD), N 2 adsorption–desorption analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photocatalytic activity of the porous TiO 2 film was evaluated by characterizing its photocatalytic effect on the photodegradation process of Rhodamine B (RhB). The results reveal that the bimodal porous material is in anatase phase, and the three-dimensionally ordered macroporous walls are composed of highly ordered mesopores. The average size of the mesopores and the BET surface area are 6.70 nm and 143.37 m 2 g −1, respectively. The obtained TiO 2 film shows a higher photocatalytic activity than commercial photocatalyst Degussa P25.

Catalytic Cracking of Methylcyclohexane on FAU, MFI, and Bimodal Porous Materials: Influence of Acid Properties and Pore Topology

Catalytic cracking of methylcyclohexane has been studied on eight commercially available zeolites, five FAUs and three MFIs, and on two newly developed zeotype materials with bimodal porous structure, BIPOMs. Both BIPOMs are composed of an MFI ultramicropore (<1 nm) network and a different supermicropore (1.5−2.0 nm) network. Site time yields obtained on FAU and MFI zeolites with varying acid properties are in the same range, showing that mass transfer limitations inside the pores of both zeolite frameworks are absent. Site time yields obtained on BIPOM3 are comparable to those on commercial MFI with similar Si/Al ratio, while BIPOM1 is significantly less active. Within a given framework type, the zeolite acid properties determine its activity in methylcyclohexane cracking, while the pore topology controls its selectivity. On FAU, methylcyclohexane isomerization, followed by ring opening and subsequent cracking, is the main reaction pathway, while on MFI, protolytic scission, followed by cracking, is pred...

Catalytic Cracking of 2,2,4-Trimethylpentane on FAU, MFI, and Bimodal Porous Materials: Influence of Acid Properties and Pore Topology

Cracking experiments using 2,2,4-trimethylpentane as a model component have been performed on five FAU and three MFI zeolites. In addition to these eight commercially available catalysts, two newly developed zeotype materials with bimodal pore structure, BIPOMs, have been investigated. Both BIPOMs possess an MFI ultramicropore (<1 nm) network but a different ordered supermicropore (1.5−2.0 nm) network. Site time yields are lower on MFI than on FAU because of the slower diffusion of the reactant inside the pores. The site time yield obtained on the BIPOMs is comparable to commercial MFI with similar Al content. Within one framework type, the zeolite acid properties determine its activity in catalytic cracking of 2,2,4-trimethylpentane, while the framework topology controls its selectivity. The main reaction route on FAU is hydride transfer followed by β-scission leading to mainly C4 species, while on MFI protolytic scission is responsible for the formation of high amounts of C1−C3 species. This points to t...

Selective Surface Functionalization and Metal Deposition in the Micropores of Mesoporous Silica SBA-15

A procedure for the selective surface functionalization of the mesopores and micropores of mesoporous silica SBA-15 has been developed. The resulting bifunctional material has been used to incorporate Pd nanoparticles in the micropores. The method described provides a general route for creating different local environments within the nanometer-sized pore structure and for the selective deposition of guest species in the micropores of this type of bimodal porous materials.

Photocatalytic Activity of a Hierarchically Macro/Mesoporous Titania

Light-harvesting macroporous channels have been successfully incorporated into a mesoporous TiO(2) framework to increase its photocatalytic activity. This bimodal porous material was characterized by X-ray diffractometry in both low-angle and wide-angle ranges, N(2) adsorption-desorption analysis, scanning and transmission electron microscopy, FT-IR, and diffuse reflectance spectroscopy. Ethylene photodegradation in gas-phase medium was employed as a probe reaction to evaluate the photocatalytic reactivity of the catalysts. The results reveal that sintering temperature significantly affects the structural stability and photocatalytic activity of titania. The catalyst which calcined at 350 degrees C possessed an intact macro/mesoporous structure and showed photocatalytic reactivity about 60% higher than that of commercial P25 titania. When the sample was calcined at 500 degrees C, the macroporous structure was retained but the mesoporous structure was partly destroyed. Further heating at temperatures above 600 degrees C destroyed both macro- and mesoporous structures, accompanied by a loss in photocatalytic activity. The high photocatalytic performance of the intact macro/mesoporous TiO(2) may be explained by the existence of macrochannels that increase photoabsorption efficiency and allow efficient diffusion of gaseous molecules.

Synthesis of Bimodal Nanostructured Silicas with Independently Controlled Small and Large Mesopore Sizes

We report on the synthesis of bimodal, structured silicas by a fully chemical, templating−scaffolding route that enables independent control over small and large mesopore sizes. Mesoporous MCM-41 nanoparticles, synthesized in a first step, are cross-linked in a second step, leading to a bimodal porous material. Triblock copolymer surfactants added during the second synthesis step form assemblies, around which the nanoparticles aggregate and cross-link, considerably influencing both the average and the width of the secondary pore size distribution, without affecting the primary pore size. By changing the conditions of the second step, one can easily synthesize a broad variety of silicas with a controlled bimodal nanopore size distribution. Textural and structural properties were characterized by X-ray diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, 29Si solid-state NMR spectroscopy, N2 adsorption and desorption, and thermogravimetric analysis.

Synthesis and characterization of composite molecular sieves with mesoporous and microporous structure from ZSM-5 zeolites by heat treatment

The commercial ZSM-5 zeolites (Si/Al=50 and 19 respectively) were treated for n hours at determinate temperatures. After the heat treatment under different conditions, a new kind of ZSM-5 with bimodal pore was developed, in which the part of original microporous structure in ZSM-5 was remained, but some of mesopores with narrow pore size distribution were formed in the same matrix. The experiments showed that the characteristics of the composite molecular sieves with mesopores and micropores strongly depended on the heat treatment conditions. To evaluate the new molecular sieves, microstructure and physical properties of the treated ZSM-5 were investigated by N 2 sorption, XRD, SEM and HRTEM. The process developed in the present work provides a convenient method to prepare bimodal porous material with advantages of low cost, easy control and good repeatability.

Synthesis of Macroporous Materials with Zeolitic Microporous Frameworks by Self-Assembly of Colloidal Zeolites

Abstract This study reports a novel and flexible technique to synthesize bimodal porous materials with ordered macropores whose walls are composed of microporous zeolites by self-assembly of nanocrystals of silicalite-1 and ZSM-5. The materials prepared by this novel technique are well crystalline and possess uniform macropores interconnected in three dimensions through windows.