Designing Internal Hierarchical Porous Networks in Polymer Monoliths that Exhibit Rapid Removal and Photocatalytic Degradation of Aromatic Pollutants

Monolithic Catalysts Supported by Emulsion-Templated Porous Polydivinylbenzene for Continuous Reduction of 4-Nitrophenol

A monolithic catalyst was fabricated through an emulsion-templating method, postpolymerization modification, and in situ loading of active constituents. To achieve a high specific surface area, divinylbenzene (DVB) was solely employed as the monomer, while the porous structure was adjusted with the porogen content and the types of initiators. Then, anchor points were introduced on the pore wall through nitration and amination of the polymeric scaffold. Using a controlled "silver mirror reaction", monolithic catalysts were obtained after loading of silver nanoparticles (Ag NPs), which was verified from morphological and crystallinity characteristics. The catalytic performance of the resultant monolithic catalyst was determined with the model reduction of 4-nitrophenol (4-NP). In static catalysis, the monolithic catalyst was proved to have a reactively high apparent rate constant and a good reusability. Furthermore, a flow reactor was fabricated with the monolithic catalyst, showing a high efficiency and long-term durability for the continuous reduction of 4-NP. This work broadened the adjustment of porous structures and the subsequent application for emulsion-templated monoliths.

Covalent organic frameworks based hierarchical porous hybrid monolithic capillary: Synthesis, characterization, and applications in trace metals analysis

The preparation of hierarchical porous monolithic column with high covalent organic frameworks (COF) loading and micropores accessibility is challenging due to the easy aggregability and sedimentation of COFs. Herein, a novel strategy based on high internal phase emulsion (HIPE) polymerization was proposed for preparing COF hybrid capillary monolithic column with hierarchical porosity. COFs with different frameworks including imine COFs (COF-OMe, COF-F and COF-SH), triazine COF (CTF-1) and boron-based COF (COF-5) were selected to investigate the universality of the preparation strategy. The presence of COF in the monolithic capillary was confirmed by scanning electron microscope, X-ray diffraction and fourier transform infrared spectroscopy. Nitrogen adsorption/desorption experiments and thermogravimetric analysis showed that the prepared COF hybrid monolithic capillary exhibited high COF loading (e.g., 28.7% for COF-SH) and accessibility (e.g., 98.5% for COF-SH), mainly due to the thin walls of void-window structures originated from polymerization of HIPE. The successful preparation of water-stable COF-F, COF-OMe, COF-SH and CTF-1 hybrid monolithic columns demonstrated the proposed synthesis strategy is universal to water-stable COF without tedious optimization of dispersion system, effectively avoiding the sedimentation of COF in pre-polymerization solution. Then, the sulfhydryl-modified COF hybrid polymer (poly(COF-SH-HIPE)) monolithic column was evaluated for the extraction of heavy metal ions, and a method based on poly(COF-SH-HIPE) monolithic capillary microextraction on-line coupled with inductively coupled plasma mass spectrometry detection was developed for analysis of trace Cd, Hg and Pb in human fluid samples.

Highly Porous Polymer Beads Coated with Nanometer-Thick Metal Oxide Films for Photocatalytic Oxidation of Bisphenol A

Highly porous metal oxide-polymer nanocomposites are attracting considerable interest due to their unique structural and functional features. A porous polymer matrix brings properties such as high porosity and permeability, while the metal oxide phase adds functionality. For the metal oxide phase to perform its function, it must be fully accessible, and this is possible only at the pore surface, but functioning surfaces require controlled engineering, which remains a challenge. Here, highly porous nanocomposite beads based on thin metal oxide nanocoatings and polymerized high internal phase emulsions (polyHIPEs) are demonstrated. By leveraging the unique properties of polyHIPEs, i.e., a three-dimensional (3D) interconnected network of macropores, and high-precision of the atomic-layer-deposition technique (ALD), we were able to homogeneously coat the entire surface of the pores in polyHIPE beads with TiO2-, ZnO-, and Al2O3-based nanocoatings. Parameters such as nanocoating thickness, growth per cycle (GPC), and metal oxide (MO) composition were systematically controlled by varying the number of deposition cycles and dosing time under specific process conditions. The combination of polyHIPE structure and ALD technique proved advantageous, as MO-nanocoatings with thicknesses between 11 ± 3 and 40 ± 9 nm for TiO2 or 31 ± 6 and 74 ± 28 nm for ZnO and Al2O3, respectively, were successfully fabricated. It has been shown that the number of ALD cycles affects both the thickness and crystallinity of the MO nanocoatings. Finally, the potential of ALD-derived TiO2-polyHIPE beads in photocatalytic oxidation of an aqueous bisphenol A (BPA) solution was demonstrated. The beads exhibited about five times higher activity than nanocomposite beads prepared by the conventional (Pickering) method. Such ALD-derived polyHIPE nanocomposites could find wide application in nanotechnology, sensor development, or catalysis.

Porous Cyclodextrin Polymer Enables Dendrite-Free and Ultra-Long Life Solid-State Zn-I2 Batteries

Zn-I2 batteries have attracted attention due to their low cost, safety, and environmental friendliness. However, their performance is still limited by the irreversible growth of Zn dendrites, hydrogen evolution reactions, corrosion, and shuttle effect of polyiodide. In this work, we have prepared a new porous polymer (CD-Si) by nucleophilic reaction of β-cyclodextrin with SiCl4 , and CD-Si is applied to the solid polymer electrolyte (denoted PEO/PVDF/CD-Si) to solve above-mentioned problems. Through the anchoring of the CD-Si, a conductive network with dual transmission channels was successfully constructed. Due to the non-covalent anchoring effect, the ionic conductivity of the solid polymer electrolytes (SPE) can reach 1.64×10-3  S cm-1 at 25 °C. The assembled symmetrical batteries can achieve highly reversible dendrite-free galvanizing/stripping (stable cycling for 7500 h at 5 mA cm-2 and 1200 h at 20 mA cm-2 ). The solid-state Zn-I2 battery shows an ultra-long life of over 35,000 cycles at 2 A g-1 . Molecular dynamics simulations are performed to elucidate the working mechanism of CD-Si in the polymer matrix. This work provides a novel strategy towards solid electrolytes for Zn-I2 batteries.

Natural Amphiphilic Shellac Nanoparticle-Stabilized Novel Pickering Emulsions with Droplets and Bi-continuous Structures

Shellac is a natural amphiphilic substance, and its nanoparticles can be used to stabilize Pickering emulsions with droplets and bi-continuous structures. In this study, shellac nanoparticles (SNPs) were produced through the anti-solvent method, and these SNPs were used to produce a series of Pickering emulsions. Fourier transform infrared results showed that SNPs were generated through hydrogen bonding and hydrophobic effects. The contact angle of SNPs was 122.3°, indicating that hydrophobicity was their dominant characteristic. According to the results of confocal laser scanning microscopy, the Pickering emulsions stabilized by SNPs showed oil-in-water, bi-continuous structure, and water-in-oil characteristics, which were dependent on the oil-phase content. The resistance value of the emulsified part of these Pickering emulsion systems significantly increased at an oil-phase ratio of 80-90% (more than 10⁵ MΩ), as compared with the 10-70% oil-phase content (around 1 MΩ). The viscosity of SNP-stabilized Pickering emulsions with bi-continuous structures was highest at 40% oil-phase content. The porous material prepared by using Pickering emulsions with bi-continuous structures as a template had an interconnected structure and was able to absorb both water and oil. This study indicated that these amphiphilic SNPs readily form bi-continuous structures and effectively stabilize Pickering emulsions with droplets. These SNPs are expected to have increased application in food and pharmaceutical industries.

Organo-macrocycle-containing hierarchical metal-organic frameworks and cages: design, structures, and applications

Developing hierarchical ordered systems is challenging. Using organo-macrocycles to construct metal-organic frameworks (MOFs) and porous coordination cages (PCCs) provides an efficient way to obtain hierarchical assemblies. Macrocycles, such as crown ethers, cyclodextrins, calixarenes, cucurbiturils, and pillararenes, can be incorporated within MOFs/PCCs and they also endow the resultant composites with enhanced properties and functionalities. This review summarizes recent developments of organo-macrocycle-containing hierarchical MOFs/PCCs, emphasizing applications and structure-property relationships of these hierarchically porous materials. This review provides insights for future research on hierarchical self-assembly using macrocycles as building blocks and functional ligands to extend the applications of the composites.

Macrocycle-Based Porous Organic Polymers for Separation, Sensing, and Catalysis

With the rapid development of materials science, porous organic polymers (POPs) have received remarkable attentions because of their unique properties such as the exceptionally high surface area and flexible molecular design. The ability to incorporate specific functions in a precise manner makes POPs promising platforms for a myriad of applications in molecular adsorption, separation, and catalysis. Therefore, many different types of POPs have been rationally designed and synthesized to expand the scope of advanced materials, endowing them with distinct structures and properties. Recently, supramolecular macrocycles with excellent host-guest complexation abilities are emerging as powerful crosslinkers for developing novel POPs with hierarchical structures and improved performance, which can be well-organized at different spatial scales. Macrocycle-based POPs could have unusual porous, adsorptive, and optical properties when compared to their nonmacrocycle-incorporated counterparts. This cooperation provides valuable insights for the molecular-level understanding of skeletal complexity and diversity. Here, the research advances of macrocycle-based POPs are aptly summarized by showing their syntheses, properties, and applications in terms of separation, sensing, and catalysis. Finally, the current challenging issues in this exciting research field are delineated and a comprehensive outlook is offered for their future directions.

Facile synthesis of novel multifunctional β-cyclodextrin microporous organic network and application in efficient removal of bisphenol A from water

Here, a novel multifunctional β-cyclodextrin microporous organic network (CD-MON) has been successfully synthesized and used to remove bisphenol A (BPA) from water. The morphology and composition of the synthesized CD-MON were confirmed. The combination of hydrophobic interaction, π-π interaction inclusion mechanism and hydrogen bonding endowed CD-MON to exhibit superior adsorption capacity toward BPA. The adsorption kinetics and isotherms of BPA and other four model aromatic pollutants on CD-MON were studied. CD-MON could maintain adsorption efficiency toward BPA over wide pH ranges and without being affected by the ionic strengths, co-existing inorganic ions and humic acid. The optimal conditions and removal efficiency of BPA were screened by response surface analysis. In addition, nearly unchanged in the adsorption efficiency toward BPA was observed after five regeneration cycles on CD-MON. CD-MON can adsorb about 80% of five model aromatic pollutants from the water within 40 s in the flow-through experiments. This novel adsorbent gives great promise for practical wastewater remediation.

Macrocycle-derived hierarchical porous organic polymers: synthesis and applications

Porous organic polymers (POPs), as a new category of advanced porous materials, have received broad research interests owing to the advantages of light-weight, robust scaffolds, high specific surface areas and good functional tailorability. According to the long-range ordering of polymer skeletons, POPs can be either crystalline or amorphous. Macrocycles with inherent cavities can serve as receptors for recognizing or capturing specific guest molecules through host-guest interactions. Incorporating macrocycles in POP skeletons affords win-win merits, e.g. hierarchical porosity and novel physicochemical properties. In this review, we focus on the recent progress associated with new architectures of macrocycle-based POPs. Herein, these macrocycles are divided into two subclasses: non-planar (crown ether, calixarene, pillararene, cyclodextrin, cyclotricatechylene, etc.) and planar (arylene-ethynylene macrocycles). We summarize the synthetic methods of each macrocyclic POP in terms of the functions of versatile building blocks. Subsequently, we discuss the performance of macrocyclic POPs in environmental remediation, gas adsorption, heterogeneous catalysis, fluorescence sensing and ionic conduction. Although considerable examples are reported, the development of macrocyclic POPs is still in its infancy. Finally, we propose the underlying challenges and opportunities of macrocycle-based POPs.

Hierarchical Design of Functional, Fibrous, and Microporous Polymer Monoliths for the Molecular Recognition of Diethylstilbestrol

This paper demonstrates the hierarchical design of functional, fibrous polymer monoliths. The monoliths are composed of conjugated microporous polymers that not only are embedded with heteroatoms but also feature fibrous yet compressible structures due to the in situ self-assembly process that occurs during the polymerization process. Therefore, the doped nitrogen atoms can allow the growth of zeolitic imidazolate framework (ZIF) nanocrystals, which causes the homogeneous encapsulation of individual fibers. The resulting hybrid monoliths exhibit enhanced physical properties as well as catalytic activity, allowing the formation of an additional coating layer via a thiol-epoxy reaction. The deliberate inclusion of template molecules during the reaction forms molecularly imprinted sites on the fibers to afford functional monoliths. As a proof of concept, the hierarchically designed materials are able to show effective recognition properties toward diethylstilbestrol, an endocrine disruptor, taking advantage of the binding sites that selectively capture the analyte molecules and the fibrous morphology that increases the accessibility of these binding sites. We envisage that the incorporation of various heteroatoms or nanocrystals will bring about the bespoke design of advanced monoliths with autonomous functions, leading to smart textile systems.

MoS2-Embedded, Interpenetrating Network Composite Hydrogels that Show Controlled Release of Dyes and Tunable Strength

This paper describes a conceptual design of hierarchical composite hydrogels. The hydrogel materials comprise MoS2 flakes and interpenetrating polymer networks, and further exhibit controlled release and tunable strength that are caused by the synergistic combination of select components. In terms of design, MoS2 flakes initiate radical polymerization of chosen monomers and simultaneously provide physical cross-linking points, both of which afford a primary composite network. Then, the sequential formation of additional networks results in functional, hierarchical, composite hydrogels. Therefore, we were able to demonstrate double-network hydrogels as a stimuli-responsive vector for programmed release of cargo molecules in response to heat or light or to form triple-network hydrogels showing tunable mechanical strength owing to intermolecular interaction between charged monomers and MoS2 flakes. The design concept would be expanded by incorporating other chalcogenides or functional monomers, which advance the properties and functionalities of materials and broadens the versatility of nanocomposite hydrogels.

Recent Progress on Molecular Photoacoustic Imaging with Carbon-Based Nanocomposites

For biomedical imaging, the interest in noninvasive imaging methods is ever increasing. Among many modalities, photoacoustic imaging (PAI), which is a combination of optical and ultrasound imaging techniques, has received attention because of its unique advantages such as high spatial resolution, deep penetration, and safety. Incorporation of exogenous imaging agents further amplifies the effective value of PAI, since they can deliver other specified functions in addition to imaging. For these agents, carbon-based materials can show a large specific surface area and interesting optoelectronic properties, which increase their effectiveness and have proved their potential in providing a theragnostic platform (diagnosis + therapy) that is essential for clinical use. In this review, we introduce the current state of the PAI modality, address recent progress on PAI imaging that takes advantage of carbon-based agents, and offer a future perspective on advanced PAI systems using carbon-based agents.

Enhancement of wastewater treatment by underwater superelastic fiber-penetrated lamellar monolith

During the removal of pollutants from wastewater, the underwater compressibility of three-dimensional biomass materials is the main factor determining their properties and service life. To construct a chitosan (CS)-based material with underwater superelasticity, a bidirectional freezing technique was used to introduce bamboo fibers (BFs) as bridges between CS lamellae to form a biomimetic CS/BFs monolith with an architecture similar to Thalia dealbata stems. BFs completely penetrated CS lamellae from the top down, which served as springs to dampen the elastic deformation during compressive cycles. After 10,000 underwater compressive cycles at 60% strain, the plastic deformation was negligible, and after 100 cycles at 90% strain, the monolith retained 93.8% of the maximum stress. Moreover, the CS/BFs monolith was loaded with CaCO₃ nanoparticles via compression-release-compression to obtain a CS/BFs/CaCO₃ monolith that exhibited excellent water purification capabilities. The CS/BFs/CaCO₃ monolith removed water-soluble dyes, heavy-metal ions, and emulsified oils from water with a high separation efficiency by simple squeezing and pumping methods. The novel pumping technology using the CS/BFs/CaCO₃ monolith provides a facile and rapid method to separate oil-in-water emulsions (maximum water flux of 11,776.9 L m^-2 h^-1). Therefore, the CS/BFs/CaCO₃ monolith with underwater superelasticity has great potential applications for wastewater treatment.

Magnetic-responsive Pickering emulsion and its catalytic application at the water–oil interface

Schematic diagram of interfacial catalysis reactions by MRGO–Pd Pickering emulsion.

Fibrous mesoporous polymer monoliths: macromolecular design and enhanced photocatalytic degradation of aromatic dyes

A bottom-up design provides polymer monoliths comprising two monomers that form mesoporous, compressible, random fiber networks, as in marine sponges.

Cavitand and Molecular Cage-Based Porous Organic Polymers

Supramolecular cavitands and organic cages having a well-defined cavity and excellent host-guest complexing ability have been explored for a myriad of applications ranging from catalysis to molecular separation to drug delivery. On the other hand, porous organic polymers (POPs) having tunable porosity and a robust network structure have emerged as advanced materials for molecular storage, heterogeneous catalysis, water purification, light harvesting, and energy storage. A fruitful marriage between guest-responsive discrete porous supramolecular hosts and highly porous organic polymers has created a new interface in supramolecular chemistry and materials science, confronting the challenges related to energy and the environment. In this mini-review, we have addressed the recent advances (from 2015 to the middle of 2020) of cavitand and organic cage-based porous organic polymers for sustainable development, including applications in heterogeneous catalysis, CO2 conversion, micropollutant separation, and heavy metal sequestration from water. We have highlighted the "cavitand/cage-to-framework" design strategy and delineated the future scope of the emerging new class of porous organic networks from "preporous" building blocks.