Optimizing spatial pore-size and porosity distributions of adsorbents for enhanced adsorption and desorption performance

Bicontinuous interfacially jammed emulsion gels with nearly uniform sub-micrometer domains via regulated co-solvent removal

Porous materials possess numerous useful functions because of their high surface area and ability to modulate the transport of heat, mass, fluids, and electromagnetic waves. Unlike highly ordered structures, disordered porous structures offer the advantages of ease of fabrication and high fault tolerance. Bicontinuous interfacially jammed emulsion gels (bijels) are kinetically trapped disordered biphasic materials that can be converted to porous materials with tunable features. Current methods of bijel fabrication result in domains that are micrometers or larger, and non-uniform in size, limiting their surface area, mechanical strength, and interaction with electromagnetic waves. In this work, scalable synthesis of bijels with uniform and sub-micrometer domains is achieved via a two-step solvent removal process. The resulting bijels are characterized quantitatively to verify the uniformity and sub-micrometer scale of the domains. Moreover, these bijels have structures that resemble the microstructure of the scale of the white beetle Cyphochilus. We find that such bijel films with relatively small thicknesses (<150 μm) exhibit strong solar reflectance as well as high brightness and whiteness in the visible range. Considering their scalability in manufacturing, we believe that VIPS-STRIPS bijels have great potential in large-scale applications including passive cooling, solar cells, and light emitting diodes (LEDs).

Adsorption Properties of Anionic Dyes on Quaternized Microcrystalline Cellulose

Efficient removal of dyes in the wastewater of dyeing and printing industries is challenging, especially the anionic dyes with strong stability, serious environmental pollution, and difficult degradation. In the present work, a novel cationic adsorbent was synthesized through the quaternization of 2,3-epoxypropyltrimethylammonium chloride (GTA) onto microcrystalline cellulose and characterized by Fourier transform infrared spectroscopy, X-ray diffraction, specific surface and pore size analysis, and scanning electron microscopy. Acid Yellow 128 (AY-128) and Acid Red 1 (AR-1) were selected to investigate their adsorption on quaternized microcrystalline cellulose (QMCC). The experimental adsorption results indicated that (1) the adsorption kinetics of AY-128 and AR-1 on QMCC could be consistent with the pseudo-second-order and Freundlich models, respectively; (2) the adsorption process was spontaneous and feasibly endothermic. The removal efficiency of AY-128 and AR-1 was up to 99 and 95%, respectively. After five times of reuse, the removal efficiency of AY-128 and AR-1 was still 97 and 95%. In conclusion, quaternized microcrystalline cellulose was a promising adsorbent for AY-128 and AR-1.

Magnetic phenolic resin core-shell structure derived carbon microspheres for ultrafast magnetic solid-phase extraction of triazine herbicides

In this study, monodisperse magnetic carbon microspheres were successfully synthesized through the carbonization of phenolic resin encapsulated Fe₃ O₄ core-shell structures. The magnetic carbon microspheres showed high performance in ultrafast extraction and separation of trace triazine herbicides from environmental water samples. Under optimized conditions, both the adsorption and desorption processes could be achieved in 2 min, and the maximum adsorption capacity for simazine and prometryn were 387.6 and 448.5 μg/g. Coupled with HPLC-UV detection technology, the detection limit of triazine herbicides was in the range of 0.30-0.41 ng/mL. The mean recoveries ranged from 81.44 to 91.03% with relative standard deviations lower than 7.47%. The excellent magnetic solid phase extraction performance indicates that magnetic carbon microspheres are promising candidate adsorbent for the fast analysis of environmental contaminants. This article is protected by copyright. All rights reserved.

Highly Robust MOF Polymeric Beads with a Controllable Size for Molecular Separations

Shaping metal-organic frameworks (MOFs) into robust particles with a controllable size is of large interest to the field of adsorption. Therefore, a method is presented here to produce robust MOF beads of different sizes, ranging from 250 μm to several millimeters, which, moreover, preserve the adsorption properties of the unformulated MOF. A simple, mild, and flexible method is demonstrated with the zeolitic imidazolate framework-8 (ZIF-8)/polyvinyl formal composite material. The properties of the composite material are determined via optical imaging, scanning electron microscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma mass spectrometry, X-ray diffraction, mercury intrusion, argon porosimetry and pycnometry as well as thermogravimetric analysis/differential scanning calorimetry, crush strength tests, and immersion experiments. The proposed method allows the production of resistant particles with a high MOF loading (up to 85 wt %) and remarkable structural and textural properties required for adsorptive separation processes, including a preserved ZIF-8 crystalline structure, microporosity, and a narrow macropore size distribution (1.27 μm average). The particles show a spherical shape with an average aspect ratio of 0.85. The stability tests demonstrated that the composite MOF material exhibits a high mechanical strength (3.09 N/Pc crushing strength) almost equivalent to that of a widely used commercial zeolite material. Furthermore, the material remains stable up to 200 °C and in most solvents. The adsorption properties are explored via static and dynamic experiments in the vapor and liquid phases. The results show that the adsorption capacities are only reduced in proportion to the binder content compared with the pristine material, indicating no binder intrusion in the ZIF-8 pores. Fixed-bed experiments demonstrate the remarkable separation performance in the vapor phase, whereas mass transfer limitations arise in the liquid phase with increasing flow rate. The mass transfer limitations are attributed to the diffusion in the macropores or through the ZIF-8 crystal outer layer.

Hierarchical Porous Zeolite Structures for Pressure Swing Adsorption Applications

Porous adsorbents with hierarchical structured macropores ranging from 1 to 100 μm are prepared using a combination of freeze casting and additional sacrificial templating of polyurethane foams, with a zeolite 13X powder serving as adsorbent. The pore system of the prepared monoliths features micropores assigned to the zeolite 13X particle framework, interparticular pores of ∼1-2 μm, lamellar pores derived from freeze casting of ∼10 μm, and an interconnected pore network obtained from the sacrificial templates ranging from around 100 to 200 μm with a total porosity of 71%. Gas permeation measurements show an increase in intrinsic permeability by a factor of 14 for monoliths prepared with an additional sacrificial templated foam compared to monoliths solely providing freeze casting pores. Cyclic CO2 adsorption and desorption tests where pressure swings between 8 and 140 kPa reveal constant working capacities over multiple cycles. Furthermore, the monoliths feature a high volumetric working capacity of ∼1.34 mmol/cm(3) which is competitive to packed beds made of commercially available zeolite 13X beads (∼1.28 mmol/cm(3)). Combined with the faster CO2 uptake showing an adsorption of 50% within 5-8 s (beads ∼10 s), the monoliths show great potential for pressure swing adsorption applications, where high volumetric working capacities, fast uptakes, and low pressure drops are needed for a high system performance.

Diffusion in nanoporous materials: fundamental principles, insights and challenges

The increasing complexity of nanoporous catalysts and adsorbents presents a challenge to both the experimental measurement and theoretical modeling of transport behavior.

Nature-inspired optimization of hierarchical porous media for catalytic and separation processes

Nature-inspired structuring at the meso-scale: broad macropores separate the mesoporous catalyst grains.