Hierarchically porous MOF@COF structures with ultrafast gas diffusion rate for C2H6/C2H4 separation

For ethylene purification, C2H6-selective metal-organic frameworks (MOFs) show great potential to directly produce polymer-grade C2H4 from C2H6/C2H4 mixtures. Most C2H6-traping MOFs are ultra-microporous structures so as to strengthen multiple supramolecular interactions with C2H6. However, the narrowed pore channels of C2H6-traping MOFs cause large guest diffusion barriers, greatly hampering their practical applications. Herein, we present a feasible strategy by precisely constructing hierarchically porous MOF@COF core-shell structures to address this issue. Additional mesoporous diffusion channels were incorporated between MOF crystals through the construction of the COF shell, thereby enhancing the gas adsorption kinetics. Notably, designing a core-shell MOF@COF structure with an optimal coating amount of mesoporous COF shell will further improve the gas diffusion rate. Breakthrough experiments reveal that the tailored MOF@COF composites can effectively achieve C2H6/C2H4 separation and maintain its separation performance over five continuous measurement cycles. This investigation opens up a new avenue to solve the diffusion/transfer issues and provides more opportunities and potentials for MOF@COF composites in practical separation applications.

Regulating defective sites for pharmaceuticals selective removal: Structure-dependent adsorption over continuously tunable pores

Developing efficient adsorbents with proper pore size for pharmaceutical removal is challenging. Water stable metal-organic frameworks (MOFs) are crystalline materials within the three-dimensional frameworks, which have already aroused increasing attention for their potential advantages with high surface area and abundant channels. However, whether or not the existing ones are performing their full capacities needs to be seriously considered. Herein, we precisely designed a series of fine-tuning hierarchically porous materials based on the water-stable Zr-based MOFs. The adsorption capacity and uptake rate of as-synthesized materials for pharmaceuticals are significantly improved. Fifteen isostructural frameworks with increasing finely tuned pore structures were successfully constructed with seven monocarboxylic modulators of increasing alkyl chain lengths. A strong correlated relationship between the mesoporous proportion and trapping kinetics can be found. Adsorption performance of 17 pharmaceuticals with various typical categories has been systematically studied over these as-synthesized materials. Competitors in natural wastewater were studied systematically. The competitive adsorption can selectively trap the target compounds in HA (humic acid), BSA (bovine serum albumin), and BHB (bovine hemoglobin) by an efficient size exclusion effect. Thus, this study offers helpful guidance for MOF modification to enhance the removal of micropollutants in natural wastewater and a fundamental understanding of the porosity-performance relationships.

Polyelectrolyte aerogels with regeneration capacity for efficient removal of particulate matters

HYPOTHESIS

With the rapid development of economy and global industrialization, the problem of air pollution has become a worldwide topic. The efficient filtration of airborne particulate matters (PMs) is critical for human health and environmental sustainability.

EXPERIMENTS

Herein, self-supporting bio-based polyelectrolyte aerogels were prepared and acted as the advanced filters for efficient removal of PMs. The natural choline cation (Ch⁺) or the organic cation, 1-butyl-3-methylimidazolium (Bmim⁺), are introduced into alginate (Alg^-) to form the polyelectrolytes of ChAlg or BmimAlg due to the electrostatic interaction. By the directional freeze-drying in liquid N₂, hierarchically porous aerogels with mechanical robustness, flexibility and thermo-stability were prepared. This specific structure may permit the polluted air to pass adequately through the aerogel channels, which are conducive to intercept various PMs with different diameters.

FINDINGS

As an example, the removal efficiency of ChAlg aerogels for PM₁₀, PM_2.5 and PM_0.3 are respectively up to (99.24 ± 0.03)%, (99.22 ± 0.02)%, and (93.41 ± 0.22)% within 15 h durability test. One outstanding character lies in ensuring high removal efficiency, while achieving a good balance with the low pressure drop (10 Pa), which is driven by synergistic effect of passive trapping and electrostatic capture. Moreover, the polyelectrolyte aerogels exhibit excellent antimicrobial activity and regenerated capacity. These properties endow the aerogels of polyelectrolyte ChAlg or BmimAlg with remarkable potential as new advanced filters for masks and other personal protective equipment.

Self-transformation synthesis of hierarchically porous benzene-bridged organosilica nanoparticles for efficient drug delivery

Herein, a feasible outside-in hydrothermal self-transformation strategy is presented to fabricate hierarchically porous benzene-bridged organosilica nanoparticles (HPBONs), and detailed mechanistic investigations were performed to study the formation of hierarchically porous nanostructures. The obtained HPBONs consisted of a mesoporous core (2.3 nm) and a large mesoporous flocculent shell (12.6 nm), which corresponded to an overall diameter of ∼ 200 nm and good water dispersibility, respectively. Owing to the unique hierarchically porous structure and high surface area (877 m²/g), HPBONs showed a high coloading capacity for the hydrophilic drug doxorubicin (DOX) and the hydrophobic photosensitizer chlorin e6 (Ce6) (355 µg/mg, 38 µg/mg, respectively) and acid-responsive DOX drug release (42.62%), leading to precise chemo-photodynamic therapy in vitro, as the cytotoxicity assay revealed 70% killing of breast cancer (MCF-7) cells. This research provides a new method to construct hierarchically porous organosilica-based nanodelivery systems.

The construction of bio-inspired hierarchically porous graphene aerogel for efficiently organic pollutants absorption

Three-dimensional graphene aerogel shows a wide application in many frontier domains, which have attracted extensive research interest owing to its large specific surface area and high porosity. However, it is still a great challenge to construct the ideal hierarchical pore structure while guaranteeing excellent absorption and mechanical performance. In this paper, inspired by the bio-based porous material, a hierarchical graphene aerogel with inter-connected micro-/nano-scale pore structure was constructed. The micro and nano-scale pores are generated by the bubble and nanoparticles (NPs) template, respectively. The resulting graphene aerogel (GA) presents low density, increased interfacial areas, high mechanical performance, and excellent absorption performance towards a mass of organic solvents. In combination with its high compressibility, a diverse organic solvent can be absorbed efficiently and recycled by extrusion conveniently. Besides, owing to the scattered hydrophilic sites of functional groups and NPs on the surface of GA-b/NP, it shows high adhesion properties for water droplets, thus presents great potential in high-efficiency fog collecting materials. In a word, the proposed approach presents a novel strategy for the construction of the hierarchical aerogel with light-weight and elasticity, as well as the achievement of efficient functionalization, which has great potential for the preparation of diverse functional composites.

Supported growth of inorganic-organic nanoflowers on 3D hierarchically porous nanofibrous membrane for enhanced enzymatic water treatment

Organic-inorganic nanoflower is a new type of functional material that can effectively immobilize a wide range of enzymes to form flower-like structures for various enzymatic applications with enhanced catalytic performance and stability. In order to avoid the processing inconvenience and flower structure damage caused by the particular form of these hybrid nanoflowers during material fabrication and catalytic application, different substrates have been used to carry out supported growth of hybrid nanoflowers. However, all previously used substrates have only 2-dimensional feature and only incorporate hybrid nanoflowers on surface with limited nanoflower loading. In this study, three-dimensional (3D) hierarchically porous nanofibrous PVA-co-PE membranes (HPNM) are prepared by a simple template method for effectively immobilizing laccase-Cu₂(PO₄)₃•3H₂O hybrid nanoflowers. Compared with dense nanofibre membrane with only small sized pores (<1 micron), the coexistence of both small and large sized (30-80 microns) pores of HPNM could significantly increase the nanoflower density and allow the penetrated growth of hybrid nanoflowers into the inner structure of the membrane. The hybrid nanoflower containing hierarchically porous nanofibrous membranes (HNF-HPNM) show excellent catalytic performance in degrading different types of textile dyes (reactive blue 2, acid blue 25, acid yellow 76 and indigo carmine), with a degradation efficiency of ˜99.5% for indigo carmine. In addition, the HNF-HPNM could be reused at least 14 times for indigo carmine degradation, with a negligible degradation efficiency drop from 99.48% to 98.52%. These results indicate that hierarchically porous nanofibrous membrane can be a promising type of materials for supported hybrid nanoflower growth for practical applications such as waste water treatment, dye degradation and biosensing.

Rational Construction of Hierarchically Porous Fe-Co/N-Doped Carbon/rGO Composites for Broadband Microwave Absorption

Developing lightweight and broadband microwave absorbers for dealing with serious electromagnetic radiation pollution is a great challenge. Here, a novel Fe-Co/N-doped carbon/reduced graphene oxide (Fe-Co/NC/rGO) composite with hierarchically porous structure was designed and synthetized by in situ growth of Fe-doped Co-based metal organic frameworks (Co-MOF) on the sheets of porous cocoon-like rGO followed by calcination. The Fe-Co/NC composites are homogeneously distributed on the sheets of porous rGO. The Fe-Co/NC/rGO composite with multiple components (Fe/Co/NC/rGO) causes magnetic loss, dielectric loss, resistance loss, interfacial polarization, and good impedance matching. The hierarchically porous structure of the Fe-Co/NC/rGO enhances the multiple reflections and scattering of microwaves. Compared with the Co/NC and Fe-Co/NC, the hierarchically porous Fe-Co/NC/rGO composite exhibits much better microwave absorption performances due to the rational composition and porous structural design. Its minimum reflection loss (RLmin) reaches - 43.26 dB at 11.28 GHz with a thickness of 2.5 mm, and the effective absorption frequency (RL ≤ - 10 dB) is up to 9.12 GHz (8.88-18 GHz) with the same thickness of 2.5 mm. Moreover, the widest effective bandwidth of 9.29 GHz occurs at a thickness of 2.63 mm. This work provides a lightweight and broadband microwave absorbing material while offering a new idea to design excellent microwave absorbers with multicomponent and hierarchically porous structures.

Surfactant-free synthesis of silica aerogel microspheres with hierarchically porous structure

In this work, we developed a new method to synthesize silica aerogel microspheres via ambient pressure drying (APD) process without applying any surfactants and mechanical stirring. An ethanol solution of partially hydrolyzed, partially condensed silica (CS) was used as precursor in the synthesis, the water-repellent n-Heptane as solvent, while the water-soluble ammonia gas (NH₃) as catalyst. After a fast sol-gel process and APD process, aerogel microspheres were obtained in the form of white powder with packing density ranged from 62 mg/cm³ to 230 mg/cm³ for different samples. The SEM images exhibited fine spherical morphology for these aerogel microparticles, and their statistical average particle diameter ranged from 0.8 μm to 1.5 μm. Besides, according to the analysis of N₂ adsorption-desorption isotherms, the BET surface area of these aerogel microspheres was in the range of 800-960 m²/g, and a considerable volume of micropores was detected along with the abundant mesospores in these microspheres, which was further confirmed by the TEM image and SAXS curve. Based on the very limited solubility of NH₃ in the reaction system, a non-emulsion formation mechanism was proposed to illustrate the formation of these aerogel microspheres.

Sodium carbonate-assisted synthesis of hierarchically porous single-crystalline nanosized zeolites

Hierarchically porous single-crystalline nanosized zeolites as heterogeneous catalysts show great potential in fine chemistry because they offer more rich hierarchically porous channels for the mass transfer and molecular diffusion. However, the synthesis of hierarchically porous nanosized zeolites generally requires the assistance of templates acting as the mesoporogens, which limits its popularity. Herein, we report a one-pot and template-free synthesis of hierarchically porous single-crystalline nanosized zeolite beta only by introducing sodium carbonate in precursor solution. The resulted sample features the extraordinary properties, including the uniform nanocrystal (200-300nm), high pore volume (0.65cm³g^-1) and the hierarchical pore-size distribution (e.g., 2-8 and 90-150nm). After slicing processing, it is interestingly found that a large number of interconnected mesopores penetrate throughout whole material, which enables the hierarchically porous nanosized zeolite beta remarkably superior catalytic activity than the conventional zeolite beta in condensation of benzaldehyde with ethanol at room temperature. More importantly, this one-pot sodium carbonate-assisted synthetic strategy is highly versatile, which has also been successfully developed to synthesize hierarchically porous nanosized single-crystalline zeolites ZSM-5 and TS.