Macroporous Alumina Research Articles

PH Modulation of Super-Assembled Heteromembranes for Sustainable Chiral Sensing.

Enantioselective sensing and separation represent formidable challenges across a diverse range of scientific domains. The advent of hybrid chiral membranes offers a promising avenue to address these challenges, capitalizing on their unique characteristics, including their heterogeneous structure, porosity, and abundance of chiral surfaces. However, the prevailing fabrication methods typically involve the initial preparation of achiral porous membranes followed by subsequent modification with chiral molecules, limiting their synthesis flexibility and controllability. Moreover, existing chiral membranes struggle to achieve coupled-accelerated enantioseparation (CAE). Here, we report a replacement strategy to controllably produce mesoscale and chiral silica-carbon (MCSC) hybrid membranes that comprise chiral pores by interfacial superassembly on a macroporous alumina (AAO) membrane, in which both ion- and enantiomers can be effectively and selectively transported across the membrane. As a result, the heterostructured hybrid membrane (MCSC/AAO) exhibits enhanced selectivity for cations and enantiomers of amino acids, achieving CAE for amino acids with an isoelectric point (pI) exceeding 7. Interestingly, the MCSC/AAO system demonstrates enhanced pH-sensitive enantioseparation compared to chiral mesoporous silica/AAO (CMS/AAO) with significant improvements of 78.14, 65.37, and 14.29% in the separation efficiency, separation factor, and permeate flux, respectively. This work promises to advance the synthesis of two or more component-integrated chiral nanochannels with multifunctional properties and allows a better understanding of the origins of the homochiral hybrid membranes.

Hard-templated macroporous alumina with thick mesoporous walls: The key factors of pore formation

This paper focuses on the key factors contributing to pore formation in hard-templated macroporous alumina. Special attention is paid to the formation of a connected pore structure. Two series of samples were prepared, each with different content of the polymeric template. The pore structure of alumina was designed using polystyrene and acrylic copolymers as hard templates. Alumina differed in crystallite morphology (round-like and rod-like) and pore structure (bottleneck-like and slit-like). The templates differed in particle size (100 and 250 nm) and physical state (powder and suspension). All the samples were characterized by N2 adsorption, Hg porosimetry, XRD, and SEM. The data obtained indicate that a hard template made of polymeric particles has the following functions: fixing the pore size and shape, sintering small pores of the material, and creating additional channels to connect macropores. Regardless of the type of polymeric template and Al2O3 precursor, a connected pore system can be formed by adding more than 20 wt% of the template.

Preparation of macroporous alumina ceramics by ice templating without freeze drying using natural rubber latex binder

Preparation of macroporous alumina ceramics by ice templating without freeze drying using natural rubber latex binder

Engineering 2D Aligned Nanowires Assembled Porous Hetero-Membrane for Smart Ion Transport.

Engineering 2D nanosheets with well-defined porous structures and their assembled heterostructure membrane is a promising method to improve osmotic energy conversion. However, it is still a great challenge to directly fabricate 2D nanosheets with regular parallel nanochannels in aqueous media. Here, the desired functional nanosheets and heterostructure membrane device are successfully prepared through a simple interfacial assembly strategy. In this method, monolayer cylindrical monomicelles closely arrange and assemble on the surfaces of graphene oxide, and the resulting nanosheets with monolayered aligned nanowire polymer arrays parallel to the substrate surfaces are then obtained. Subsequently, a heterostructured membrane is constructed by assembling these 2D nanosheets on macroporous alumina. The nanofluidic membrane device with asymmetric geometry and charge polarity exhibits smart ion transport properties, and the output osmotic power density is ≈1.22 and 1.63 times over the reported pure 2D graphene oxide and biomass-derived membranes, respectively. In addition, theoretical calculations are carried out to reveal the mechanisms for ion selectivity and salinity gradient energy conversion. This monolayered interfacial assembly approach can open up new avenues for the synthesis of functional porous low-dimensional nanomaterials and membrane devices, and expand the palette of materials selection for many applications.

Nanoarchitectonics of High‐Performance Bis(triethoxysilyl)methane (BTESM) Hybrid‐Silica Membrane for Pervaporative Desalination Applications

AbstractAs an emerging technology, desalination by pervaporation (PV) has excellent potential in freshwater supply from saline waters. However, the investigation of stable membrane materials needs still to address separation issues such as fouling in desalination applications. Ceramic membranes, especially hybrid‐silica membranes, possess the required properties for pervaporation desalination and remain potentially tolerant to various saline waters which conventional membranes cannot withstand. Herein, we report the preparation of a thin, short‐chain BTESM hybrid‐silica membrane on cheap macroporous alumina supports for desalination applications through pervaporation. The fabricated membrane delivered water flux of 9.1 kg m−2 h−1 and 6.7 kg m−2 h−1 at 60 °C for simulated and real based sampled seawater, respectively, with a high rejection of >99.5 %. The fabricated membrane delivers excellent separation for various salt ranges and different salt solutions, including KCl, MgCl2, and CaCl2. Further, the PV performance of fabricated membranes implies that hybrid silica based membranes can be potential candidates for commercial desalination markets.

A New Insight into the Role of Silicate-Type Binders on the Crushing Strength of Alumina Foams

Semi-closed cell macroporous alumina foams with relative densities ranging from 0.26 to 0.35 have been produced by the well-established replication method based on the coating of a polyurethane (PU) template foam by a ceramic slurry, followed by burnout of the PU template, and sintering of the ceramic skeleton. Collapse of the three-dimensional structure upon the volatilisation of the PU sponge can only be prevented using appropriate binders. Scarce data are available on the slurry formulations of commercial alumina foams. The aim of this study was to investigate the influence of silicate-type binders, namely kaolin and bentonite additives, on the crushing strength of alumina foams. The highest crushing strength of around 10 MPa was observed at a porosity of 66 ± 2%. The open-cell model is inadequate to fit the crushing strength data of such semi-closed cell type structures. Both microscopic and macroscopic flaws resulting from the foam processing method contribute to the wide scatter of the strength, thereby explaining the Weibull modulus ranging from 4 to 7. Both flaw populations require further improvement to maximise the crushing strength of these foams with high potential for the design of structured catalyst carriers and molten aluminium filters.

Metal oxide-based macroporous ordered double affinity molecularly imprinted polymer for specific separation and enrichment of glycoprotein from food samples: a co-modification of DMSA and boronate affinity.

Metal oxide-based macroporous ordered double affinity molecularly imprinted polymers (D-MIPs) were developed as solid phase extraction (SPE) adsorbents for the specific identification of ovalbumin (OVA) under physiological pH conditions prior to ultraviolet visible (UV-vis) spectrophotometric detection. Herein, macroporous alumina (MA) was used as a matrix; dimercaptosuccinic acid (DMSA) and 3-aminophenylboric acid (APBA) were employed as dual-functional monomers; APBA is a self-polymerizing monomer. The effects of synthesis conditions, SPE conditionsas well as selectivity, reproducibility, and reusability were studied. The co-modification of DMSA and boronate affinity renders the adsorbent exhibiting a high adsorption capacity (114.4mgg-1) and short equilibrium time (30min). The surface imprinting technology causes the adsorbent to have high selectivity towards OVA. The OVA recovery range is 91.1-99.6%. This study provides a promising method for the enrichment of OVA and other cis-diol-containing analytes in complex biological samples. A novel metal oxide-based macroporous ordered nanoparticle with a combination of DMSA and boronate affinity was successfully prepared for specific separation and enrichment of glycoprotein from complex biological samples.

Fabrication of low cost and high performance NaA zeolite membranes on 100-cm-long coarse macroporous supports for pervaporation dehydration of dimethoxymethane

• High performance NaA zeolite membrane was prepared on 100-cm-long coarse macroporous supports. • A simple sandpaper polishing method effectively improved membrane separation selectivity. • These membranes exhibited a superior long-term stability for a 96 wt% DMM/H 2 O mixture. • The permeation flux was almost recovered using a 15 wt% H 2 O/MeOH PV test cleaning method for 4 h. Low cost and high performance NaA zeolite membranes have been successfully prepared on 100-cm-long coarse macroporous alumina supports using industrial grade reagents and chemicals. A simple and efficient sandpaper polishing method can effectively reduce the support surface roughness and the formation process of NaA zeolite membranes was investigated on inexpensive coarse supports by secondary growth, which was more conducive to the preparation of high performance membranes. For separation of a 90 wt% EtOH/H 2 O mixture at 348 K, the scaled-up NaA zeolite membrane showed a permeation flux of 4.67 kg m −2 h −1 and a high separation factor of more than 10,000. Simultaneously, these membranes were used for pervaporation (PV) dehydration of a dimethoxymethane/water (DMM/H 2 O) mixture for the first time, which exhibited a permeation flux of 0.89 kg m −2 h −1 and together with a separation factor of more than 23,000 at 313 K for dehydration of a 96 wt% DMM/H 2 O mixture. Moreover, the membrane also showed a superior long-term stability for running over 10 d. Importantly, the study on the recovery of permeation flux of scaled-up NaA zeolite membranes after long-term PV experiment to produce high-concentration DMM product (water content was less than 0.1%) found that the permeation flux was recovered to more than 85% of the fresh membranes after the membranes was cleaned using PV test with a methanol aqueous solution. These 100-cm-long NaA zeolite membranes with low cost and high performance demonstrated a promising industrial application prospects for PV dehydration of DMM/H 2 O mixtures and other organic water mixtures.

Enhancement of Desulfurization Capacity with Cu-Based Macro-Porous Sorbents for Hydrogen Production by Gasification of Petroleum Cokes

Macro-porous alumina was used as a support for a pellet-type Cu-based desulfurization sorbent in the gas purification process for producing blue hydrogen by the gasification of petroleum coke. The effects of the macro-porous alumina on the pellet-type sorbents in reducing the gas diffusion resistance into the pores were investigated. The results showed that the macro-porous alumina enhances the diffusion resistance, resulting in an improved sulfur capacity of CuO absorbents. Such effects were more significant on the pellet type CuO absorbents than the powder type. In addition, CO production was observed experimentally during the desulfurization reaction of carbonyl sulfide (COS) at low temperatures (~473 K). Density functional theory calculations were also performed to understand the kinetics of desulfurization and CO production. The simulation results predicted that the kinetics of desulfurization is strongly affected by the local surface environment. The CO generated from C–O bond breaking from COS had a lower adsorption energy than the CO2 formation. These results suggest that the Cu-based desulfurization sorbent has potential catalytic activity for producing CO from COS dissociation.

Gas permeation and thermomechanical properties for macroporous alumina focused on necking size at grain boundaries

AbstractThe gas permeation and thermomechanical properties of macroporous alumina used as a support substrate for microporous ceramic permselective membranes were investigated. The porosity, pore size, and apparent necking size between grains of macroporous alumina were systematically varied, and the relationships between the porous microstructure and material properties were examined. The grain necking size at alumina grain boundaries was evaluated by microstructural observations. The nitrogen gas permeance of the porous alumina increased with increasing pore size. All the measured thermal and mechanical properties decreased with increasing porosity. The properties of porous alumina samples with extensive grain necking showed higher values even in samples with the largest pore size. The high thermal conductivity of porous alumina with extensive grain necking was due to the low interfacial thermal resistance at grain boundaries. Porous alumina with extensive grain necking had high thermal shock strength due to the higher thermal conductivity. It was demonstrated that a porous structure combining high gas permeability and excellent fracture resistance could be successfully achieved.

Synthesis of Macro-Porous De-NOx Catalysts for Poly-Tetra-Fluoro-Ethylene Membrane Bag Filter.

This study examined the effects of the porosity of catalytic bag-filter materials for applications to the SNCR (selective noncatalytic reduction)-SCR (selective catalytic reduction) hybrid process for highly treating nitrogen Oxides (NOx) in the exhaust gas of a combustion process. A V₂O5/TiO₂ catalyst was dispersed in a PTFE (poly-tetra-fluoro-ethylene) used as the catalytic bag-filter material to remove particulate matter and nitrogen oxides contained in the combustion exhaust gas. Macroporous alumina was added into a V₂O5/TiO₂-dispersed PTFE to improve the catalytic activity of V₂O5/TiO₂ dispersed in the PTFE material. In this study, the textural properties and denitrification performances of the V₂O5/TiO₂-dispersed PTFE materials were examined according to the addition of macro-porous alumina. When the denitrification catalyst was solely dispersed in the PTFE material, the catalyst inside the PTFE backbone had low gas-solid contact efficiency owing to the low porosity of the PTFE materials, resulting in low denitrification efficiency. On the other hand, the catalytic activity of V₂O5/TiO₂ dispersed inside the macro-porous PTFE material was significantly enhanced by adding macro-porous alumina into the PTFE matrix. The enhanced textural properties of the macro-porous PTFE material where V₂O5/TiO₂ was uniformly dispersed proved the facilitated diffusion of combustion exhaust gas into the PTFE material.

Sequential Superassembly of Nanofiber Arrays to Carbonaceous Ordered Mesoporous Nanowires and Their Heterostructure Membranes for Osmotic Energy Conversion.

The capture of sustainable energy from a salinity gradient, in particular, using renewable biomass-derived functional materials, has attracted significant attention. In order to convert osmotic energy to electricity, many membrane materials with nanofluidic channels have been developed. However, the high cost, complex preparation process, and low output power density still restrict the practical application of traditional membranes. Herein, we report the synthesis of highly flexible and mechanically robust nanofiber-arrays-based carbonaceous ordered mesoporous nanowires (CMWs) through a simple and straightforward soft-templating hydrothermal carbonization approach. This sequential superassembly strategy shows a high yield and great versatility in controlling the dimensions of CMWs with the aspect ratio changes from about 3 to 39. Furthermore, these CMWs can be used as novel building blocks to construct functional hybrid membranes on macroporous alumina. This nanofluidic membrane with asymmetric geometry and charge polarity exhibits low resistance and high-performance energy conversion. This work opens a solution-based route for the one-pot preparation of CMWs and functional heterostructure membranes for various applications.

Simple and efficient method for functionalizing photocatalytic ceramic membranes and assessment of its applicability for wastewater treatment in up-scalable membrane reactors

A photocatalytically active layer composed of TiO2 (Evonik P25) was successfully deposited on the macroporous (3 µm pore size) permeate side of an asymmetric porous alumina membrane with the aid of a smectite (a synthetic hectorite, Sumecton SWF) by dipping the membranes into an aqueous suspension containing P25 and the smectite. After the heat treatment at 400 °C, the coated hybrid was adhered on the macroporous support enough to be applied for the photocatalytic decomposition of organics (methylene blue and phenol as model molecules) in water. The water permeance of the membranes after the coating with the P25-smectite hybrid was reduced by only 24% compared with that of the pristine membrane, showing that the advantages of the present method for the preparation of the photocatalyst layer on the surface of the macroporous alumina without significant infiltration of the suspension into the support pores. The amount of MB and phenol degraded using the P25-SWF hybrid was equal to 0.007 and 0.023 mmol.L−1, respectively, when the reaction was carried out using the four single-channel tubular membrane reactor at transmembrane pressures of 250 mbar. The implemented photocatalytic membrane reactor can easily be up-scaled by increase the size of the membrane module, with more tubes and longer tubes (lengths up to 1 m are commercially available), paving the way to potential technological applications for the continuous treatment of polluted waters.

Dynamically capped hierarchically porous microneedles enable post-fabrication loading and self-regulated transdermal delivery of insulin

Glucose-responsive microneedle (MN) patches are of great interest for painless self-regulated insulin delivery in diabetic patients to improve their quality of life. This work is aimed to develop a smart MN-based insulin delivery system with potential for post-fabrication loading of insulin and a fast, repeatable response to glucose fluctuations without sacrificing its structural constituents. A hierarchically porous inorganic MN array is developed, consisting of a macroporous alumina core to provide an external access and a large capacity for insulin loading and a mesoporous shell to control insulin release by glucose-responsive gating of its nanopores that are dynamically capped with an enzyme-loaded chitosan (CS) hydrogel. The capped MNs doff their caps to blood sugar quickly and reversibly via swelling/deswelling of the CS cap. As a result, insulin release can be repeatedly regulated during sequential cycles of hyperglycemia/normoglycemia with short intervals of 40 min. In a type 1 diabetic mouse model, application of the smart MN system quickly causes normoglycemia within 1 h, which is prolonged for 5 h. Diabetic mice treated by the smart MN system behave similarly to the healthy mice in terms of controlled blood glucose levels during the in vivo glucose tolerance test. The “cap doffing” approach can aid the development of more safe, long-lasting MN systems for smart transdermal delivery of insulin and other drugs.

Synthesis and Characterization of Multi‐Modal γ‐Al2O3: A Systematic Investigation on the Optimization of Hydrodemetallization Catalyst Preparation

AbstractThe pore structure of hydrodemetallization catalysts plays a vital role in their lifetime and thus, on the process economy. In this investigation, a multi‐modal meso and macroporous alumina has been prepared by using aluminum alkoxides. To tune the alumina properties to the desired values, a systematic design of experiments was applied to propose correlations between the synthesis parameters and catalyst properties. Several factors, which are effective on the specifications of the prepared multi‐modal alumina, were analyzed and the dominant factors were identified. The results predicted by the model were in agreement with the experimental data. The analysis of the results showed that the prepared optimal sample had an average pore diameter and specific surface area of 21.2 nm and 341 m2/gr, respectively. For the prepared catalyst, N2 adsorption/desorption measurements showed a multimodal pore structure ranging from 2 to 100 nm in size.Finally, an HDM catalyst was prepared based on optimum alumina. The activity and performance of the prepared catalyst were compared with those of the commercial catalyst. At low space times, V‐TPP conversion for commercial and prepared catalysts were 38.9 and 49.5 percent, respectively, showing a higher activity for the prepared catalyst.

Near‐net shape manufacture of macroporous nanosized alumina monolith by aqueous gel casting method

AbstractA potentially near‐net‐shape manufacturing procedure for macroporous alumina monoliths with 20%‐75% porosity was presented by gel casting of nano γ‐Al2O3. Although monolith obtained by nano alumina had a high surface area and low sintering temperature, an optimum fraction of micron alumina needed to be added to achieve the proper rheological and mechanical properties of slurries. The preparation parameters including alumina loading, sintering temperature, monomer concentration, and the fraction of nano alumina were investigated. The green densities ranging from 0.66 to 0.86 g cm−3 were obtained by raising alumina loading from 10 to 20 vol%. Depending on the monomer concentration and sintering temperature, the mean pore size ranging from 45 to 412 nm, total porosity (20%–75%), and open porosity varying from 12% to 89% were obtained. The sintered density (from 0.95 to 3.15 g cm−3) and compressive strength (CS) (from 4.2 to 31.46 MPa) were suitable for use in different fields.

Diffusion simulation based design and macroporous structure tailored preparation of FCC naphtha selective hydrodesulfurization catalyst

Aiming at the rational design and controllable preparation of highly selective fluid catalytic cracking (FCC) naphtha hydrodesulfurization (HDS) catalyst, a two-dimensional lattice Boltzmann method with multi-relaxation-time collision operator was developed to simulate the intraparticle diffusivities in alumina supports. The simulation results showed that, in a series of virtual alumina supports with the identical mesoporous structure but different macroporous structures, which were constructed via the random generation of macro-mesopores, the intraparticle diffusivity increases sharply with the increasing macropore volume and diameter, with the one having macropore volume 0.55 cm3/g and macropore diameter 500 nm simultaneously guaranteeing both satisfactory intraparticle diffusion performance and suitable crushing strength. Based on the simulation results, five γ-Al2O3 supports with the identical mesoporous structure but different macroporous structures were synthesized from the same pseudo-boehmite precursor by using sodium polyacrylate and different amounts of water during shaping, from which five CoMo/γ-Al2O3 catalysts were prepared. The HDS assessment results obtained using a real FCC naphtha showed that, compared with the reference catalyst prepared from an alumina without macropores, the catalysts prepared from the aluminas with different macroporous structures displayed higher HDS selectivity due to the enhanced diffusion in macropores. The systematic characterization results demonstrated that the enhanced HDS activities and selectivities of the macroporous alumina supported catalysts are mainly attributed to the enhanced diffusion in macropores.

Corrosion Resistance Properties of Porous Alumina–Mullite Ceramic Membrane Supports

Cost‐effective macroporous alumina–mullite membrane supports are fabricated by sintering coarse α‐alumina and colloidal silica, using cornstarch as the foaming agent at 1550 °C for 2 h in air atmosphere. To evaluate the corrosion resistance of such membrane supports, the corrosion behaviors of the supports before and after corroding in the H2SO4 and NaOH solutions (80 °C) are systematically investigated. Interestingly, with increasing Al2O3/SiO2 ratio, the support presents numerous alumina grains and little glass phases, resulting in excellent corrosion resistance especially in acidic media. Benefiting from the alumina grains and little glass phases among the grain boundaries, lower mass loss, less variations in pore size and porosity, high residual strength, and an almost unchanged gas flux are obtained for a higher Al2O3/SiO2 ratio support. The porous support, herein, is suitable for microfiltration membranes used in harsh environments.

Synthesis and Characterization of Robust γ-Alumina Monolith with Hierarchical Pore Structure, High Specific Surface Area and Novel Macropore Morphology

A three-dimensional interconnected macroporous alumina monolith was successfully prepared by phase separation combined with microwave-hydrothermal process in ammonia solution. The material calcined...

Synthesis, Structural Characteristics, and Adsorption Properties of Macroporous Alumina

Macroporous alumina is synthesized via precipitation with sulfuric acid from a sodium aluminate solution. It is established that introducing a coagulating agent (sodium chloride) preventing macrogel formation makes it possible to obtain highly porous samples of alumina with specific surface areas of ~100 m2/g, a large pore volume of 1.6–1.7 cm3/g, and an average pore diameter of 50–75 nm. According to the adsorption isotherms and the pH dependence of hemoglobin adsorption that such samples have a high capacity for protein macromolecules. The maximum adsorption of hemoglobin is ~500 mg/g, and is observed at pH 6–7. Adsorption falls substantially when the pH is reduced to 4 or increased to 9, and it is close to zero at pH 11.