Pyridine-Based Covalent Organic Frameworks with Pyridyl-Imine Structures for Boosting Photocatalytic H2O2 Production via One-Step 2e- Oxygen Reduction.

Bipyridine-based covalent organic frameworks (COFs) have emerged as promising contenders for the photocatalytic generation of hydrogen peroxide (H2O2). However, the presence of imine nitrogen alters the mode of H2O2 generation from an efficient one-step two-electron (2e-) route to a two-step 2e- oxygen reduction pathway. In this work, we introduce 3,3'-bipyridine units into imine-based COF skeletons, creating a pyridyl-imine structure with two adjacent nitrogen atoms between the pyridine ring and imine linkage. This unique bipyridine-like architecture can effectively suppress the two-step 2e- ORR process at the single imine-nitrogen site, facilitating a more efficient one-step 2e- pathway. Consequently, the optimized pyridyl-imine COF (PyIm-COF) exhibits a remarkable H2O2 production rate of up to 5850 µmol h-1 g-1, nearly double that of pristine bipyridine COFs. This work provides valuable insight into the rational design of functionalized COFs for enhanced H2O2 production in photocatalysis.

Nanofibrous Porous Organic Polymers and Their Derivatives: From Synthesis to Applications.

Engineering porous organic polymers (POPs) into 1D morphology holds significant promise for diverse applications due to their exceptional processability and increased surface contact for enhanced interactions with guest molecules. This article reviews the latest developments in nanofibrous POPs and their derivatives, encompassing porous organic polymer nanofibers, their composites, and POPs-derived carbon nanofibers. The review delves into the design and fabrication strategies, elucidates the formation mechanisms, explores their functional attributes, and highlights promising applications. The first section systematically outlines two primary fabrication approaches of nanofibrous POPs, i.e., direct bulk synthesis and electrospinning technology. Both routes are discussed and compared in terms of template utilization and post-treatments. Next, performance of nanofibrous POPs and their derivatives are reviewed for applications including water treatment, water/oil separation, gas adsorption, energy storage, heterogeneous catalysis, microwave absorption, and biomedical systems. Finally, highlighting existent challenges and offering future prospects of nanofibrous POPs and their derivatives are concluded.

Photothermal Conversion Porous Organic Polymers: Design, Synthesis, and Applications.

Solar energy is a primary form of renewable energy, and photothermal conversion is a direct conversion process with tunable conversion efficiency. Among various kinds of photothermal conversion materials, porous organic polymers (POP) are widely investigated owing to their controllable molecular design, tailored porous structures, good absorption of solar light, and low thermal conductivity. A variety of POP, such as conjugated microporous polymers (CMP), covalent organic frameworks (COF), hyper-crosslinked porous polymers (HCP), polymers of intrinsic microporosity (PIM), porous ionic polymers (PIP), are developed and applied in photothermal conversion applications of seawater desalination, latent energy storage, and biomedical fields. In this review, a comprehensive overview of the recent advances in POP for photothermal conversion is provided. The micro molecular structure characteristics and macro morphology of POP are designed for applications such as seawater desalination, latent heat energy storage, phototherapy and photodynamic therapy, and drug delivery. Besides, a probe into the underlying mechanism of structural design for constructing POP with excellent photothermal conversion performance is methodicalized. Finally, the remaining challenges and prospective opportunities for the future development of POP for solar energy-driven photothermal conversion applications are elucidated.

Bioinspired Gradient Covalent Organic Framework Membranes for Ultrafast and Asymmetric Solvent Transport.

Gradients play a pivotal role in membrane technologies, e.g., osmotic energy conversion, desalination, biomimetic actuation, selective separation, and more. In these applications, the compositional gradients are of great relevance for successful function implementation, ranging from solvent separation to smart devices; However, the construction of functional gradient in membranes is still challenging both in scale and directions. Inspired by the specific function-related, graded porous structures in glomerular filtration membranes, a general approach for constructing gradient covalent organic framework membranes (GCOMx) applying poly (ionic liquid)s (PILs) as template is reported here. With graded distribution of highly porous covalent organic framework (COF) crystals along the membrane, GCOMx exhibts an unprecedented asymmetric solvent transport when applying different membrane sides as the solvent feed surface during filtration, leading to a much-enhanced flux (10-18 times) of the "large-to-small" pore flow comparing to the reverse direction, verified by hydromechanical theoretical calculations. Upon systematic experiments, GCOMx achieves superior permeance in nonpolar (hexane ≈260.45 LMH bar-1) and polar (methanol ≈175.93 LMH bar-1) solvents, together with narrow molecular weight cut-off (MWCO, 472 g mol-1) and molecular weight retention onset (MWRO, <182 g mol-1). Interestingly, GCOMx shows significant filtration performance in simulated kidney dialysis, revealing great potential of GCOMx in bionic applications.

Carbon Nanotube Template-Assisted Synthesis of Conjugated Microporous Polytriphenylamine with High Porosity for Efficient Supercapacitive Energy Storage.

Engineering of conjugated microporous polymers (CMPs) with high porosity, redox activity, and electronic conductivity is of significant importance for their practical applications in electrochemical energy storage. Aminated-multiwall carbon nanotubes (NH2 -MWNT) are utilized to modulate the porosity and electronic conductivity of polytriphenylamine (PTPA), which is synthesized via Buchwald-Hartwig coupling reaction of tri(4-bromophenyl)amine and phenylenediamine as constitutional units in a one-step in situ polymerization process. Compared to PTPA, the specific surface area of core-shell PTPA@MWNTs has been greatly improved from 32 to 484 m2  g-1 . The PTPA@MWNTs exhibites an improved specific capacitance, with the highest value 410 F g-1 in 0.5 M H2 SO4 at a current of 10 A g-1 achieve for PTPA@MWNT-4 due to the hierarchical meso-micro pores, high redox-activity and electronic conductivity. Symmetric supercapacitor assemble by PTPA@MWNT-4 has a capacitance of 216 F g-1 of total electrode materials and retains 71% of initial capacitance after 6000 cycles. This study gives new insights into the role of CNT templates in the adjustment of molecular structure, porosity, and electronic property of CMPs for the high-performance electrochemical energy storage.

High-Performance Nonfused Electron Acceptor with Precisely Controlled Side Chain Fluorination.

Modification of the molecular packing of nonfullerene acceptors through fluorination represents one of the most promising strategies to achieve highly efficient organic solar cells (OSCs). In this work, three nonfused electron acceptors, namely, DTCBT-Fx (x = 0, 5, 9) with precisely controlled amounts of fluorine atoms in the side chains are designed and synthesized, and the effect of side chain fluorination is systematically studied. The results demonstrate that the light absorption, energy levels, molecular ordering, and film morphology could be effectively tuned by precisely controlling the side chain fluorination. DTCBT-F5 with an appropriate fluorine functionalization exhibits suitable miscibility with the donor polymer (PM6), leading to diminished charge recombination and improved charge carrier mobility. Consequently, a promising power conversion efficiency of 12.7% was obtained for DTCBT-F5-based solar cells, which outperforms those OSCs based on DTCBT-F0 (11.4%) and DTCBT-F9 (11.6%), respectively. This work demonstrates that precise control of the fluorine functionalization in side chains of nonfused electron acceptors is an effective strategy for realizing highly efficient OSCs.

Innovative Long-Lasting Catalytic Hydrothermal Reaction for High Efficient Energy Harvest and Carbon Capture from Recalcitrant Wastewater.

Simultaneous recovery of energy and carbon from recalcitrant wastewater has attracted ever-growing interest for water management. However, the existing technologies to break down recalcitrant pollutants are mainly energy and chemical intensive. Here, a novel hydrothermal reaction amended with activated carbon (AC) was demonstrated to enable an unprecedented 99.5% removal of an exemplar difficult-to-degrade contaminant, polyvinyl alcohol (PVA), from wastewater. Meanwhile, an easy-separated hydrochar (C6H7.08O0.99) with an abundance of unsaturated aromatic rings was produced, exhibiting 118.46% of energy yield with a high heating value of 32.9 MJ/kg, outperforming the hydrochar(s) reported to date. The retrieved energy from the hydrochar was able to entirely offset the energy needs for this hydrothermal process. Interestingly, the AC catalyst can sustain in situ reuse over 125 cycles with no evidence of irreversible deactivation. The adjacent carbonyl groups on AC were revealed to provide active sites for dehydrogenation from either the C-H (1.24 Å) or O-H (1.40 Å) bond in PVA, forming hydroxyl groups on AC and highly reactive intermediates (ΔG0 = -11.5 kcal/mol). It was further proved that the free oxygen in the headspace extracted H atoms from the newly formed hydroxyl groups on AC (ΔG0 = -4.7 kcal/mol), thus regenerating the carbonyl sites on AC for the next catalytic hydrothermal dehydrogenation cycles. The long-lasting catalyst reusability and energy self-sufficient approach offer a sustainable route to carbon neutrality in recalcitrant wastewater treatment.

Poly (Ionic Liquid)-Metal Organic Framework-Derived Nanoporous Carbon Membranes: Facile Fabrication and Ultrahigh Areal Capacitance.

With the rapid development of energy storage technology, the operation of portable and wearable devices is inseparable from high energy density power supplies. However, the demand for high performance supercapacitors in movable smart electronics is still restrained by their insufficient areal capacitance and limited power/energy densities. In addition, some electroactive materials, including metal oxides, conductive polymers, graphene, porous carbons, etc., are inevitable to use extra adhesives for the preparation of electrode materials. In this work, integrated hierarchical graphitic porous carbon membranes used as the electrodes without adhesives are successfully synthesized, via pyrolyzing poly(ionic liquid)s (PILs)-metal organic frameworks (MOFs) composite membranes. The asymmetric supercapacitor is assembled by the carbonized PIL-MOF composite membrane and PILs-derived porous carbon membrane, and exhibits significant areal capacitance with remarkable power and energy densities. In the two-electrode system, the areal capacitance can reach 9.5 F cm-2 with an energy density of 1.91 mWh cm-2 . In the fabricated all-solid-state supercapacitors, the areal capacitance and energy density achieved 3.2 F cm-2 and 0.65 mWh cm-2 , respectively, exceeding most reported ones. Therefore, the integrated carbon membrane electrodes with high areal capacitance reveal great potential in miniaturized devices, and further show a wider application scope through regulating PILs.

Competitive proton-trapping strategy enhanced anti-freezing organohydrogel fibers for high-strain-sensitivity wearable sensors.

Stretchable organohydrogel fibers are attracting considerable interest for next-generation flexible and wearable soft strain sensors due to their excellent stability in harsh environments. However, due to the uniformly distributed ions and reduced number of carriers in the whole material, the sensitivity of organohydrogel fibers under subzero temperature is not desirable, which significantly hinders their practical application. Herein, a newly competitive proton-trapping strategy was designed to obtain anti-freezing organohydrogel fibers for high-performance wearable strain sensors via a simple freezing-thawing process, in which tetraaniline (TANI), serving as the proton trapper, and representing the shortest repeated structural unit of polyaniline (PANI), was physically crosslinked with polyvinyl alcohol (PVA) (PTOH). The as-prepared PTOH fiber exhibited an outstanding sensing performance at -40 °C due to the unevenly distributed ion carriers and the highly breakable proton-migration pathways, with a high gauge factor of 24.6 at a strain of 200-300%. Moreover, the existence of hydrogen bonds between the TANI and PVA chains endowed PTOH with a high tensile strength (1.96 MPa) and toughness (8.0 MJ m-3). Accordingly, strain sensors made from PTOH fibers and knitted textiles could monitor human motions rapidly and sensitively, demonstrating their potential as wearable anti-freezing anisotropic strain sensors.

Porous organic polycarbene nanotrap for efficient and selective gold stripping from electronic waste.

The role of N-heterocyclic carbene, a well-known reactive site, in chemical catalysis has long been studied. However, its unique binding and electron-donating properties have barely been explored in other research areas, such as metal capture. Herein, we report the design and preparation of a poly(ionic liquid)-derived porous organic polycarbene adsorbent with superior gold-capturing capability. With carbene sites in the porous network as the "nanotrap", it exhibits an ultrahigh gold recovery capacity of 2.09 g/g. In-depth exploration of a complex metal ion environment in an electronic waste-extraction solution indicates that the polycarbene adsorbent possesses a significant gold recovery efficiency of 99.8%. X-ray photoelectron spectroscopy along with nuclear magnetic resonance spectroscopy reveals that the high performance of the polycarbene adsorbent results from the formation of robust metal-carbene bonds plus the ability to reduce nearby gold ions into nanoparticles. Density functional theory calculations indicate that energetically favourable multinuclear Au binding enhances adsorption as clusters. Life cycle assessment and cost analysis indicate that the synthesis of polycarbene adsorbents has potential for application in industrial-scale productions. These results reveal the potential to apply carbene chemistry to materials science and highlight porous organic polycarbene as a promising new material for precious metal recovery.

Hierarchical meso-micro porous FeNC derived from tripolycyanamide-based microporous polymer as efficient electrocatalyst for oxygen reduction reaction.

Designing porous FeNC nanomaterials with highly efficient active sites is an effective strategy for constructing high-performance oxygen reduction reaction (ORR) electrocatalysts. N-containing porous organic polymers (POPs) have emerged as promising candidates for the preparation of porous FeNC catalysts. Here, N-rich tripolycyanamide-based microporous polymer (TCAMP)-coated SiO2 nanospheres (SiO2@TACMP) were prepared as the precursors of an Fe-N doped hierarchical meso-micro porous carbon (Fe-N-HMC) electrocatalyst for the ORR. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) characterizations demonstrated that the Fe-N-HMC catalyst possessed a higher content percentage of Fe-Nx active sites and a better distribution of Fe nanoparticles than its Fe-N doped microporous carbon (Fe-N-MC) counterpart. N2 adsorption-desorption isotherm analysis showed that Fe-N-HMC catalyst exhibited a hierarchical meso-micro porous system, with a Brunauer-Emmett-Teller (BET) surface area (SBET) of 733 m2 g-1 (∼2 times of Fe-N-MC's SBET). As a result, Fe-N-HMC catalyst presented a highly efficient ORR performance with a half-wave potential of 0.856 mV, which is similar to the commercial grade 20 wt% Pt/C catalyst and superior to the Fe-N-MC catalyst. Moreover, the as-synthesized Fe-N-HMC catalyst displayed a better durability and methanol tolerance than the commercial Pt/C catalyst. Therefore, Fe-N-HMC shows great promise as an ORR catalyst for fuel batteries and metal-air cells due to its low-cost, high activity, and good stability.

Functionalization of Mesoporous Semiconductor Metal Oxides for Gas Sensing: Recent Advances and Emerging Challenges.

With the emerging of the Internet of Things, chemiresistive gas sensors have been extensively applied in industrial production, food safety, medical diagnosis, and environment detection, etc. Considerable efforts have been devoted to improving the gas-sensing performance through tailoring the structure, functions, defects and electrical conductivity of sensitive materials. Among the numerous sensitive materials, mesoporous semiconductor metal oxides possess unparalleled properties, including tunable pore size, high specific surface area, abundant metal-oxygen bonds, and rapid mass transfer/diffusion behavior (Knudsen diffusion), which have been regarded as the most potential sensitive materials. Herein, the synthesis strategies for mesoporous metal oxides are overviewed, the classical functionalization techniques of sensitive materials are also systemically summarized as a highlight, including construction of mesoporous structure, regulation of micro-nano structure (i.e., heterojunctions), noble metal sensitization (e.g., Au, Pt, Ag, Pd) and heteroatomic doping (e.g., C, N, Si, S). In addition, the structure-function relationship of sensitive materials has been discussed at molecular-atomic level, especially for the chemical sensitization effect, elucidating the interface adsorption/catalytic mechanism. Moreover, the challenges and perspectives are proposed, which will open a new door for the development of intelligent gas sensor in various applications.

Fabrication of polyaniline/poly(vinyl alcohol)/montmorillonite hybrid aerogels toward efficient adsorption of organic dye pollutants.

Fabrication of adsorbents with excellent adsorption capacity, outstanding stability, easy separation ability, excellent recyclability and widely generality for organic dyes removal from wastewater remains challenging. Herein, three-dimensional polyaniline/poly(vinyl alcohol)/montmorillonite (PANI/PVAL/MMT) hybrid aerogels with easy separation performance and highly effective reusable adsorption on both anionic and cationic dyes were fabricated by a simple in-situ polymerization method. As-prepared hybrid aerogels were characterized via infrared and Raman spectra, scanning electron microscopy, energy dispersive spectra mapping, small and wide-angle X-ray scattering, thermogravimetric analysis, mercury intrusion porosimetry and elemental analysis. The results showed that MMT particles were successfully incorporated into aerogel matrix. Well-defined hierarchical structure, where PANI nanofibers are coated on the skeleton wall, can be observed for PANI/PVAL/MMT when the incorporation amount of MMT was around 11.1 wt%. The adsorption performance of as-prepared hybrid aerogels on both anionic and cationic dyes was systemically carried out at different solution pH, adsorbent dosage and initial dye concentration. The data analysis showed that the adsorption process for PVAL/PANI/MMT aerogel for Reactive Black 5, methyl orange and safranin followed Freundlich isotherm and the maximum experimental adsorption capacities were found to be 199, 251 and 57.0 mg g-1 at 25 °C, respectively. Mechanism studies indicated that the electrostatic interaction is the main driving force for the adsorption of dyes. The results demonstrated that the fabricated hybrid aerogel is an efficient adsorbent for the removal of both anionic and cationic organic dyes.

Macroscale Conjugated Microporous Polymers: Controlling Versatile Functionalities Over Several Dimensions.

Since discovered in 2007, conjugated microporous polymers (CMPs) have been developed for numerous applications including gas adsorption, sensing, organic and photoredox catalysis, energy storage, etc. While featuring abundant micropores, the structural rigidity derived from CMPs' stable π-conjugated skeleton leads to insolubility and thus poor processability, which severely limits their applicability, e.g., in CMP-based devices. Hence, the development of CMPs whose structure can not only be controlled on the micro- but also on the macroscale have attracted tremendous interest. In conventional synthesis procedures, CMPs are obtained as powders, but in recent years various bottom-up synthesis strategies have been developed, which yield CMPs as thin films on substrates or as hybrid materials, allowing to span length scales from individual conjugated monomers to micro-/macrostructures. This review surveys recent advances on the construction of CMPs into macroscale structures, including membranes, films, aerogels, sponges, and other architectures. The focus is to describe the underlying fabrication techniques and the implications which follow from the macroscale morphologies, involving new chemistry and physics in such materials for applications like molecular separation/filtration/adsorption, energy storage and conversion, photothermal transformation, sensing, or catalysis.

Scalable Fabrication of Conjugated Microporous Polymer Sponges for Efficient Solar Steam Generation.

Seawater evaporation realized by solar-thermal conversion represents one of the most sustainable and effective strategies to obtain fresh water. Many approaches have been proposed to achieve high efficiencies of solar-thermal conversion, but their practical applications are limited by the low scalability. Herein, novel porphyrin/aniline-based conjugated microporous polymers (PACMPs) are synthesized via a Buchwald-Hartwig coupling reaction, which are then integrated with polyurethane sponges via a simple dip-coating technique. The PACMP-modified sponges (PACSs) retain the high porosity of the sponge substrate and excellent solar-thermal conversion properties of PACMPs. Under standard solar irradiation (1 kW m-2), PACSs achieve a high seawater evaporation rate of 1.31 kg m-2 h-1 with a solar-thermal conversion efficiency of 86.3%. PACSs show no salt accumulation and high performance of desalination and dye decolorization, removing >99.9% salt and >99.2% dye, respectively. The self-floating characteristic, recyclability, and durable solar-thermal evaporation efficiencies enable PACSs to be promising candidate materials for seawater desalination and sewage purification.

Biomass-Derived, Highly Conductive Aqueous Inks for Superior Electromagnetic Interference Shielding, Joule Heating, and Strain Sensing.

Conductive composite inks are widely used in various applications such as flexible electronics. However, grand challenges still remain associated with their relatively low electrical conductivity and require heavy use of organic solvents, which may limit their high performance in broad applications and cause environmental concerns. Here, we report a generalized and eco-friendly strategy to fabricate highly conductive aqueous inks using silver nanowires (AgNWs) and biomass-derived organic salts, including succinic acid-chitosan (SA-chitosan) and sebacic acid-chitosan. SA-chitosan/AgNW composite coatings can be prepared by directly casting conductive aqueous inks on various substrates, followed by subsequently heating for cross-linking. The composite coatings exhibit an ultrahigh electrical conductivity up to 1.4 × 104 S/cm, which are stable after being treated with various organic solvents and/or kept at a high temperature of 150 °C, indicating their high chemical and thermal resistance. The flexibility and performance durability of these composite coatings were demonstrated by a suite of characterization methods, including bending, folding, and adhesion tests. Moreover, a high electromagnetic interference shielding (EMI) effectiveness of 73.3 dB is achieved for SA-chitosan/AgNW composite coatings at a thickness of only 10 µm due to the ultrahigh electrical conductivity. Additionally, we further demonstrated that such conductive composite inks can be used for fabricating functional textiles for a variety of applications with high performance, such as EMI shielding, Joule heating, and strain sensing. The robust and highly conductive inks prepared by this simple and environmental-friendly method hold great promise as important material candidates for the potential large-scale manufacturing of flexible and wearable electronics.

Solvothermal synthesis of porphyrin-ferrocenyl conjugated microporous polymer nanospheres for shape-stable phase change materials with improved latent heat and cyclability.

Organic phase change materials (PCMs) have attracted considerable attention for thermal energy storage applications because of their non-toxicity, suitable working temperature range and excellent thermal/chemical stability. However, most traditional organic PCMs have small molecular structures and are prone to leakage during fusion. To address this problem and enhance the shape-stability of organic PCMs, nanosphere-shaped porphyrin-ferrocenyl conjugated microporous polymers (PFCMPs) with high porosity (~ 650 m2/g) were solvothermally synthesized using a Diels-Alder reaction between 1,1'-ferrocenedicarboxaldehyde and pyrrole in the presence of glacial acetic acid and anhydrous Lewis acids (FeCl3, AlCl3, and CuCl2). The PFCMPs were then encapsulated with PCMs, that is, 1-octadecanol (ODA), to prepare the composite materials of ODA@PFCMPs. The optimized composite exhibited a high latent heat (up to 153.8 J/g), excellent reversibility (negligible change in latent heat upon 100 cycles of heating-cooling), good shape stability, and long heat storage durability (425 s), making it a promising candidate for solar thermal energy engineering and management.

High-Yield Synthesis of Pyridyl Conjugated Microporous Polymer Networks with Large Surface Areas: From Molecular Iodine Capture to Metal-Free Heterogeneous Catalysis.

Capturing volatile radioactive nuclides including iodine (I129 or I131 ) is one of the major problems to be solved for environmental sustainability. Multiple types of functional microporous materials such as metal organic frameworks and covalent organic frameworks have been constructed for iodine emission control. However, most of the microporous materials are limited by their weak binding force with iodine and low stability, leading to low capture efficiencies. Herein, the synthesis of pyridyl conjugated microporous polymer networks with large surface areas (PCMP-Y) up to 1304 m2 g-1 and high yields up to 95% via a simple Yamamoto cross-coupling reaction, is reported. The PCMP-Y carries amine and pyridine N groups which have stronger interactions with iodine molecules. The high specific surface areas and porosities of PCMP-Y facilitate iodine capture, delivering a maximum adsorption capacity of 4.75 g g-1 in a short time (3 h), which is superior to a majority of porous materials reported. Moreover, the reversible desorption nature of PCMP-Y capturing iodine imparts a platform for metal-free heterogeneous catalyst, which can be applied to synthesize aminobenzothiazole medicines via O2 -promoted cascade reactions.