Morphology design of microporous organic polymers and their potential applications: an overview

Room-Temperature Synthesis of Covalently Bridged MOP@TpPa-CH3 Composite Photocatalysts for Artificial Photosynthesis

The conversion of CO2 into useful chemicals via photocatalysts is a promising strategy for resolving the environmental problems caused by the addition of CO2. Herein, a series of composite photocatalysts MOP@TpPa-CH3 based on MOP-NH2 and TpPa-CH3 through covalent bridging have been prepared via a facile room-temperature evaporation method and employed for photocatalytic CO2 reduction. The photocatalytic performances of MOP@TpPa-CH3 are greater than those of TpPa-CH3 and MOP-NH2, where the CO generation rate of MOP@TpPa-CH3 under 10% CO2 still reaches 119.25 μmol g-1 h-1, which is 2.18 times higher than that under pure CO2 (54.74 μmol g-1 h-1). To investigate the structural factors affecting the photocatalytic activity, MOP@TBPa-CH3 without C═O groups is synthesized, and the photoreduction performance is also evaluated. The controlling experimental results demonstrate that the excellent photoreduction CO2 performance of MOP@TpPa-CH3 in a 10% CO2 atmosphere is due to the presence of C═O groups in TpPa-CH3. This work offers a new design and construction strategy for novel MOP@COF composites.

Composite Flame Retardants Based on Conjugated Microporous Polymer Hollow Nanospheres with Excellent Flame Retardancy

The development of polymer materials with excellent flame retardancy has been paid increasing attention for their valuable applications in saving energy in modern architecture. Herein, conjugated microporous polymers hollow nanospheres (CMPs-HNS) were prepared by Sonogashira-Hagihara cross-coupling reaction with 1,3,5-triacetylenebenzene, 3-amino-2,6-dibromopyridine, and 2,4,6-tribromoaniline as building blocks using SiO2 nanoparticles as hard templates. To enhance the flame-retardant performance of the CMPs-HNS, antimony pentoxide solution (Sb2O5) and bisphenol A-bis (diphenyl phosphate) (BDP) were coated onto the as-prepared CMP-HNS (CMPs-HNS-BSb) by a simple immersion method. The peak heat release (pHRR) from microscale combustion colorimeter (MCC) of CMPs-HNS-BSb was 76.5 and 73.05 W g-1, respectively. By introducing CMPs-HNS-BSb into the epoxy resin (EP) matrix, the CMP2-HNS-BSb/EP (0.5) composites show that the pHRR values were 809.3 and 645.2 kW m-2, reduced by 21% as measured by conical calorimetry (CC), and total heat release (THR) reduced by 29.7%, going from 101 to 70.8 MJ/m2 when compared to the pure sample. Besides, total smoke production (TSP) reduced about 23.7%. The hollow structure can enhance the thermal insulation performance. As measured, the thermal conductivity of CMP1-HNS-BSb and CMP2-HNS-BSb is 0.044 and 0.048 W m-1 K-1. Based on the advantages of simple manufacture, superior thermal insulation, and flame retardancy, our CMPs-HNS-BSb/EP composites may find useful applications in various aspects such as building energy saving in future development.

Microporous organic nanotube assisted design of high performance nanofiltration membranes

Microporous organic nanotubes (MONs) hold considerable promise for designing molecular-sieving membranes because of their high microporosity, customizable chemical functionalities, and favorable polymer affinity. Herein, we report the use of MONs derived from covalent organic frameworks to engineer 15-nm-thick microporous membranes via interfacial polymerization (IP). The incorporation of a highly porous and interpenetrated MON layer on the membrane before the IP reaction leads to the formation of polyamide membranes with Turing structure, enhanced microporosity, and reduced thickness. The MON-modified membranes achieve a remarkable water permeability of 41.7 L m^-2 h^-1 bar^-1 and high retention of boron (78.0%) and phosphorus (96.8%) at alkaline conditions (pH 10), surpassing those of reported nanofiltration membranes. Molecular simulations reveal that introducing the MONs not only reduces the amine molecule diffusion toward the organic phase boundary but also increases membrane porosity and the density of water molecules around the membrane pores. This MON-regulated IP strategy provides guidelines for creating high-permeability membranes for precise nanofiltration.

Oriented Halide Perovskite Nanostructures and Thin Films for Optoelectronics

Oriented semiconductor nanostructures and thin films exhibit many advantageous properties, such as directional exciton transport, efficient charge transfer and separation, and optical anisotropy, and hence these nanostructures are highly promising for use in optoelectronics and photonics. The controlled growth of these structures can facilitate device integration to improve optoelectronic performance and benefit in-depth fundamental studies of the physical properties of these materials. Halide perovskites have emerged as a new family of promising and cost-effective semiconductor materials for next-generation high-power conversion efficiency photovoltaics and for versatile high-performance optoelectronics, such as light-emitting diodes, lasers, photodetectors, and high-energy radiation imaging and detectors. In this Review, we summarize the advances in the fabrication of halide perovskite nanostructures and thin films with controlled dimensionality and crystallographic orientation, along with their applications and performance characteristics in optoelectronics. We examine the growth methods, mechanisms, and fabrication strategies for several technologically relevant structures, including nanowires, nanoplates, nanostructure arrays, single-crystal thin films, and highly oriented thin films. We highlight and discuss the advantageous photophysical properties and remarkable performance characteristics of oriented nanostructures and thin films for optoelectronics. Finally, we survey the remaining challenges and provide a perspective regarding the opportunities for further progress in this field.

Facile preparation of composite flame retardantbased on conjugated microporous polymer hollow spheres

The development of functional materials with better flame-retardant and thermal insulation properties has attracted considerable attention for energy storage applications in modern society. Here, we describe a facile approach for the preparation of conjugated microporous polymer hollow spheres (CMP-HSs) by using SiO₂ nanoparticles as a template via the Sonogashira-Hagihara cross-coupling reaction. The as-synthesized CMP-HSs have good thermal stability with a thermal decomposition temperature of up to 281 °C, high porosity (the BET specific surface area is measured to be approximately 666 m² g^-1) along with lipophilic and hydrophobic characteristics. To further improve their flame retardancy, CMP-HSs were treated with dimethyl phosphonate (DMMP) though an immersion method to prepare the CMP-HSs composite (CMP-HSs-DMMP) flame-retardants. By introducing CMP-HSs-DMMP into the epoxy resin (EP) matrix, the as-prepared EP composites showed excellent flame-retardant properties, e.g., the peak heat release rate (pHRR) and total heat release (THR) value of EP composites containing only 0.2% CMP-HSs-DMMP flame-retardant were 650.9 kW m^-2 and 79.4 MJ m^-2 respectively, in the range of 0 °C - 650 °C, which are 19.6 ± 2% and 19.1 ± 5% lower than that of pure EP within the same temperature range. Considering the significant enhancement of its flame retardancy with only a slight dosage of CMP-HSs-DMMP, such CMP hollow sphere-based flame-retardant composites may have great potential as functional bulk materials or coatings in a variety of fireproofing applications.

Efficient Synthesis of Folate-Conjugated Hollow Polymeric Capsules for Accurate Drug Delivery to Cancer Cells

This study presents an efficient and systematic approach to synthesize bioapplicable porous hollow polymeric capsules (HPCs). The hydroxyl-functionalized nanoporous polymers with hollow capsular shapes could be generated via the moderate Friedel-Crafts reaction without using any hard or soft template. The numerous primitive hydroxyl groups on these HPCs were further converted to carboxyl groups. Owing to the abundance of highly branched carboxyl groups on the surface of the HPCs, biomolecules [such as folic acid (FA)] could be covalently decorated on these organic capsules (FA-HPCs) for drug delivery applications. The intrinsic hollow porosities and specific targeting agent offered a maximum drug encapsulation efficiency of up to 86% and drug release of up to 50% in 30 h in an acidic environment. The in vitro studies against cancer cells demonstrated that FA-HPCs exhibited a more efficient cellular uptake and intracellular doxorubicin release than bare HPCs. This efficient approach to fabricate carbonyl-functionalized hollow organic capsules may open avenues for a new type of morphological-controlled nanoporous polymers for various potential bioengineering applications.

Fe3O4@Void@Microporous Organic Polymer-Based Multifunctional Drug Delivery Systems: Targeting, Imaging, and Magneto-Thermal Behaviors

Multifunctional drug delivery systems were designed and engineered by template synthesis of a microporous organic polymer (MOP) and by postsynthetic modification. Hollow MOP spheres bearing Fe₃O₄ yolks (Fe₃O₄@Void@MOP) were prepared by the synthesis of MOP on Fe₃O₄@SiO₂ nanoparticles and by successive silica etching. In addition to the magneto-thermal function of Fe₃O₄ yolks, an aggregation-induced emission (AIE) feature was incorporated into the Fe₃O₄@Void@MOP through a homocoupling of tetra(4-ethynylphenyl)ethylene to form Fe₃O₄@Void@MOP-TE. Folate groups were further introduced into Fe₃O₄@Void@MOP-TE through the postsynthetic modification based on the thiol-yne click reaction. The resultant Fe₃O₄@Void@MOP-TE-FA showed multifunctionality in antitumoral therapy via folate receptor targeting, doxorubicin delivery, AIE-based imaging, and the magneto-thermal feature.

Magnetic Solid-Phase Extraction of Organic Compounds Based on Graphene Oxide Nanocomposites

Graphene oxide (GO) is a chemical compound with a form similar to graphene that consists of one-atom-thick two-dimensional layers of sp²-bonded carbon. Graphene oxide exhibits high hydrophilicity and dispersibility. Thus, it is difficult to be separated from aqueous solutions. Therefore, functionalization with magnetic nanoparticles is performed in order to prepare a magnetic GO nanocomposite that combines the sufficient adsorption capacity of graphene oxide and the convenience of magnetic separation. Moreover, the magnetic material can be further functionalized with different groups to prevent aggregation and extends its potential application. Until today, a plethora of magnetic GO hybrid materials have been synthesized and successfully employed for the magnetic solid-phase extraction of organic compounds from environmental, agricultural, biological, and food samples. The developed GO nanocomposites exhibit satisfactory stability in aqueous solutions, as well as sufficient surface area. Thus, they are considered as an alternative to conventional sorbents by enriching the analytical toolbox for the analysis of trace organic compounds.

Guided Assembly of Well-Defined Hierarchical Nanoporous Polymers by Lewis Acid-Base Interactions

Three-dimensional hierarchical nanoporous polymers and carbon nanomaterials with well-defined superstructures are of great interest for various intelligent applications, whereas a facile and versatile approach to access those materials with a high surface area, stable well-defined morphology, and ordered pores still remains a significant challenge. Herein, we report a self-regulated Lewis acid-base interaction-mediated assembly strategy for the in situ synthesis of morphology-engineered hyper-cross-linked porous polymers and carbon materials. A series of functionalized aromatic compounds (FAC) is subjected to self-cross-linking via classic Friedel-Crafts chemistry to achieve stable porous polymers with a high surface area. Varying the monomer/catalyst combination had a dramatic effect on the acid-base interaction, facilitating the tailoring of the self-assembled morphologies from nanotubes to hollow nanospheres, and even nanosheets. A mechanistic study showed that the byproducts generated during cross-linking orchestrate the interactions between the catalyst (acid) and FAC (base) and simultaneously drive the self-assembly to yield specific morphologies. Based on the rigid hollow polymer framework and intrinsic hydroxyl functionality, the hyper-cross-linked hollow nanospheres were easily transformed to an acid-functionalized catalyst for efficient biodiesel production. Moreover, high-quality porous carbonaceous nanocounterparts such as carbon nanotubes, hollow carbon nanospheres, and carbon nanosheets could also be produced by direct pyrolysis of the corresponding polymer precursors. These findings may provide guidance for the facile design of morphology-controlled functionalized polymers and carbon nanomaterials for various applications.

Hyper-Cross-Linked Polymer on the Hollow Conjugated Microporous Polymer Platform: A Heterogeneous Catalytic System for Poly(caprolactone) Synthesis

This work shows that the shape-controlled microporous organic polymer (MOP) can be utilized for the morphological engineering of another class of MOP materials. The morphology of a hyper-cross-linked polymer (HCP) was successfully engineered on the hollow conjugated microporous polymer (CMP). Through the postsynthetic modification of HCP bearing BINOLs (HCP-B) on the hollow CMP-like material (H-CMPL), the HCP bearing BINOL phosphoric acid (HCP-BP) was engineered on the H-CMPL platform. The resultant H-CMPL@HCP-BP showed good catalytic performance as a heterogeneous catalytic system and excellent recyclability in the ring-opening polymerization of ε-caprolactones to poly(caprolactone).

Emerging porous materials in confined spaces: from chromatographic applications to flow chemistry

Porous materials confined within capillary columns/microfluidic devices are discussed, and progress in chromatographic and membrane separations and catalysis is reviewed.

Morphology engineering of a Suzuki coupling-based microporous organic polymer (MOP) using a Sonogashira coupling-based MOP for enhanced nitrophenol sensing in water

A hollow and hydrophilic Suzuki coupling-based microporous organic polymer was engineered using a Sonogashira coupling based MOP.

Covalent Organic Frameworks: Promising Materials as Heterogeneous Catalysts for C-C Bond Formations

Covalent organic frameworks (COFs) are defined as highly porous and crystalline polymers, constructed and connected via covalent bonds, extending in two- or three-dimension. Compared with other porous materials such as zeolite and active carbon, the versatile and alternative constituent elements, chemical bonding types and characteristics of ordered skeleton and pore, enable the rising large family of COFs more available to diverse applications including gas separation and storage, optoelectronics, proton conduction, energy storage and in particular, catalysis. As the representative candidate of next-generation catalysis materials, because of their large surface area, accessible and size-tunable open nano-pores, COFs materials are suitable for incorporating external useful active ingredients such as ligands, complexes, even metal nanoparticles deposition and substrate diffusion. These advantages make it capable to catalyze a variety of useful organic reactions such as important C-C bond formations. By appropriate pore-engineering in COFs materials, even enantioselective asymmetric C-C bond formations could be realized with excellent yield and ee value in much shorter reaction time compared with their monomer and oligomer analogues. This review will mainly introduce and discuss the paragon examples of COFs materials for application in C-C bond formation reactions for the organic synthetic purpose.

Heteropore covalent organic frameworks: a new class of porous organic polymers with well-ordered hierarchical porosities

This review highlights the development of heteropore covalent organic frameworks, a new class of porous organic polymers which exhibit well-ordered heterogeneous/hierarchical porosities.