Here, using water as the only solvent, we report the first green approach to the morphological controlled synthesis of robust ambient dried polyimide aerogels composed of interconnected hollow spheres. The addition of graphene oxide can direct the growth of polyimide into nanofibers and form 1D–2D nanohybrid aerogels. The mechanism behind is a soft/hard template directed dissolution-polymerization-reprecipitation process. After carbonization, a monolith carbon aerogel with monodisperse micropores could be formed. Such a green approach for the morphology controlled synthesis of robust polyimide aerogels and their carbon aerogels should be of great value for their environmental and energy related applications.

In this study, using a sequential polyamic acid (PAA) gelation and solvothermal imidization, we demonstrate a scalable one-pot solvothermal approach for the preparation of polyimide (PI) aerogels having a three-dimensional network composed of uniform microspheres. PI aerogels prepared by this approach were mechanically robust can be directly dried in oven without considerable contraction. More importantly, the PI aerogels showed morphology-enhanced water droplet contact angles from 98° to as high as 146°, which makes them nearly superhydrophobic. Such hydrophobic/oleophilic monolithic aerogels could rapidly and continuously separate oil from oil/water mixtures and even from water-in-oil emulsions.In this study, we demonstrate a scalable one-pot solvothermal approach for the preparation of mechanically robust polyimide (PI) aerogels that can be directly dried in oven without considerable contraction. More importantly, PI aerogels prepared by this approach showed morphology-enhanced contact angles from 98° to as high as 146°; therefore, these aerogels could be used in novel pumping strategy for a continuous and rapid separation of oil from oil/water mixtures and emulsions.Download high-res image (137KB)Download full-size image

In this study, we demonstrate the synthesis of dynamic polysulfide networks through the solution polycondensation of pentaerythritol tetra(3-mercaptopropionate) (PTMP) with elemental sulfur by a reverse vulcanization process. Elemental sulfur content as high as 51% can be incorporated into the dynamic polysulfide networks. An important feature of the resulted polysulfide networks is their catalytic-free malleability, which implies that they have both thermo- and photo-induced solid-state plasticities to obtain a complex permanent shape due to the exchange of dynamic SS bonds. These dynamic polysulfide networks have great potentials in fabricating complex three-dimensional shape memory devices for biological and mechanical applications.Download high-res image (95KB)Download full-size image

Triptycene-based porous organic frameworks (POFs) with high BET (Brunauer–Emmett–Teller) surface areas and tailored micropore environments were prepared using a facile external knitting strategy. The functionalized POFs exhibited very high aliphatic amine vapor uptakes of up to 5 times their own weight and more than 30 times selectivity for aliphatic amines over n-hexane; thus, they provide new opportunities for environment-related applications.

Polymeric aerogels have great potential in numerous fields because of their unique combination of thermal and electrical properties, and lightweight porous structures. However, the laborious supercritical CO2 drying method required for making these aerogels limits their commercial availability. Here we demonstrate a green and scalable method for preparing high-performance polyimide (PI) aerogels using a low-boiling-point solvent mixture of tetrahydrofuran/methanol, and especially using sublimation drying instead of laborious supercritical CO2 drying. The monolithic and powder polyamic acid aerogels can be prepared easily; after thermal imidization, PI aerogels with nanofibrous morphology, low density and high thermal stability can be obtained. This green, scalable and cost-effective process will facilitate the application of high-performance PI aerogel materials in many fields, in particular those in which high-temperature resistance is important.

The past decades have witnessed significant advance in the synthesis of covalent organic frameworks (COFs), however, their formation and morphology revolution mechanism have been rarely reported. Here, through an acid modulated dynamic covalent chemistry approach, pure and uniform micro-octahedral covalent imine frameworks were obtained for the first time. Formation mechanism based on the stacking of initially formed two-dimensional nanoplates followed by surface smoothing enabled by the dynamic nature of imine bonding was proposed. Furthermore, we revealed for the first time that nonstoichiometric method can be applied to the synthesis of covalent organic frameworks. Thus we provide novel strategy for the morphology control COFs which will surely facilitate their application in energy-related area.

A series of microporous polyimide networks with porphyrin units (Pr-MPIs) were facilely synthesized through a one-step solution polymerization process. Of particular interest is that Pr-MPI-1 containing distorted spirobisindane unit revealed the highest BET surface area (953 m2/g), total pore volume (0.75 cm3/g), and extreme hysteresis between the N2 adsorption and desorption isotherm. Further study revealed the prepared Pr-MPI-1 exhibited a synergistic structural effect on exceptional uptake of volatile organic compounds (VOCs) due to the high porosity and highly distorted spirobisindane structure enabled large interface and the swellability. This new approach would open up a facile approach toward the preparation of highly swellable high performance polymeric microporous materials, which are deeply wanted for environment-related applications such as VOCs adsorption and oil/water separation.

Here we demonstrate a novel solid-state approach for the facile, green and scalable synthesis of covalent organic frameworks (COFs) in the presence of relatively small amounts of solvent vapors. Rarely observed uniform nanofibrous morphologies could be obtained through fine-tuning the solvent composition. When graphene oxide was added, hierarchically 1D–2D graphene oxide based nanohybrids could be obtained.

A constitutional dynamic chemistry process is developed to synthesize novel cactus-like nanostructured carbon microspheres with high specific surface areas and catalytic activities. Polyazomethine microspheres have been firstly synthesized from two representative monomers of 1,4-terephthalaldehyde and 3,5-diamino-1,2,4-triazole and then carbonized to produce the desired carbon nanomaterials. The morphologies of the surfaces on the carbon microspheres can be controlled with tunable roughness by introducing 2-aminopyridine. As an application demonstration, these nanostructured carbon microspheres are used as counter electrodes to fabricate efficient dye-sensitized solar cells with energy conversion efficiencies up to 7.5%.

A green approach to the synthesis and morphological control of high performance polyimides and their nanohybrid shish-kebabs in glycerol through reaction-induced crystallization of nylon-salt-type monomers was reported. Crystalline polyimide nanoplates can be observed by direct polycondensation of pyromellitic acid with various kinds of aliphatic or aromatic diamines. With the existence of carbon nanotubes, the polyimides can be successfully decorated on the surface of CNTs through a reaction-induced hetero-epitaxial crystallization process, and resulted in novel polyimide/CNT nanohybrid shish-kebabs (NHSKs) structures. The morphologies of the NHSKs can be fine-tuned through changing the concentration of monomers or the reaction temperature, especially through the introduction of dynamic imine chemistry, the formation process of NHSKs can be attributed to a soft epitaxy mechanism. Thus a green approach for the synthesis of high performance polyimides and their CNT based nanohybrid structures was explored, which should be of great value for their applications in high performance reinforced nanocomposites.

This paper reports a facile solvothermal approach for the design and synthesis of novel crystalline COF nanofibers with amazing properties. An interesting morphological transformation from microsphere to nanofibers was observed, which could be supported by the unique dissolution-recrystallization mechanism due to the reversible nature of dynamic imine bonding. Interestingly, it was also found that the COF nanofibers could epitaxial grow on the aramid microfiber surface. This functional nanocomposite showed an interesting colorimetric humidity-responsive behavior. Our study provides a general methodology for the fabrication of COFs with designated micronanostructures and has more implications on their applications in catalyst and sensors.Keywords: covalent organic frameworks; dissolution−recrystallization; nanofibers; nanohybrid; solvothermal synthesis;

Dynamic covalent chemistry has attracted much attention in recent decades. Here we report a facile one-pot solvothermal synthesis of anisotropic polyazomethine particles using Pickering emulsions formed in situ as templates. An unexpected morphological transformation from nanoparticles to anisotropic particles and finally to complex anisotropic yolk-shell structures was observed. The underlying mechanism is a controlled chemical etching process enabled by the dynamic imine bonding and the inhomogeneous nature of the resulting anisotropic particles. The generalizability of this process was further proved by fine tuning the initial solvent composition, through which an interesting morphological transformation from hollow spheres to worm-like tubes and finally to microtubes with a smooth surface was observed, thus providing a novel template-free strategy for the synthesis of polymeric materials with complex hollow interiors, which has rarely been reported in polymeric systems.

We propose a general reaction induced hetero-epitaxial crystallization strategy for the preparation of high performance aromatic polymers/CNT nanohybrid shish-kebab structures, typical aromatic polymers such as polyazomethine and polyimide have been successfully decorated on the surface of CNTs through this novel approach. It is interesting to note that the introduction of dynamic imine chemistry can enhance the kinetic control of this process and helps perfectionization of NHSK structures. Beside CNTs, this approach can be further extended to the epitaxial crystallization of aromatic polymer on the surface of microscale aramid fibers, thus opened a new gateway for the surface modification of CNTs and fibers using high performance aromatic polymer, which are of great value for the fabrication of complex hybrid nanoarchitectures or nanocomposites.

Here, we present a novel constitutional dynamic chemistry controlled reaction induced crystallization strategy for the morphological controlling of aromatic polyazomethines. Complex nanostructured polyazomethines with sphere, elliptic, discus and disk-like morphologies can be readily fine tuned by varying the ratio of reagents in the dynamic imine exchange reaction. After pyrolysis, hierarchically nanostructured carbons can be obtained. The study revealed the concert of constitutional dynamic chemistry and reaction induced crystallization could provide a powerful strategy for the complex morphological control of aromatic polymers.

Hierarchical polyimide hollow spheres consisting of crystalline nanoparticles were synthesized by a novel gas bubble templated transimidization induced crystallization process. The morphologies of the hollow spheres can be fine-tuned by changing the concentrations and the chemical structure of the monomers. Based on the experimental results, a possible formation mechanism of these polyimide hollow spheres was proposed based on the aggregation of the primary crystalline polyimide nanoparticles on the in situ formed gas bubbles as soft templates to minimize the interfacial energy.

Realizing the vast technological potential of patternable block copolymers requires both the precise controlling of the orientation and long-range ordering, which is still a challenging topic so far. Recently, we have demonstrated that ordered nanoporous thin film can be fabricated from a simple supramolecular assembly approach. Here we will extend this approach and provide a general route to fabricate large areas of highly ordered polymeric nanodot and nanowire arrays. We revealed that under a mixture solvent annealing atmosphere, a near-defect-free nanoporous thin film over large areas can be achieved. Under the direction of interpolymer hydrogen bonding and capillary action of nanopores, this ordered porous nanotemplate can be properly filled with phenolic resin precursor, followed by curation and pyrolysis at middle temperature to remove the nanotemplate, a perfect ordered polymer nanodot arrays replication was obtained. The orientation of the supramolecular assembly thin films can be readily re-aligned parallel to the substrate upon exposure to chloroform vapor, so this facile nanotemplate replica method can be further extend to generate large areas of polymeric nanowire arrays. Thus, we achieved a successful sub-30 nm patterns nanotemplates transfer methodology for fabricating polymeric nanopattern arrays with highly ordered structure and tunable morphologies.

Here we demonstrate a novel solid-state approach for the facile, green and scalable synthesis of covalent organic frameworks (COFs) in the presence of relatively small amounts of solvent vapors. Rarely observed uniform nanofibrous morphologies could be obtained through fine-tuning the solvent composition. When graphene oxide was added, hierarchically 1D–2D graphene oxide based nanohybrids could be obtained.

A constitutional dynamic chemistry process is developed to synthesize novel cactus-like nanostructured carbon microspheres with high specific surface areas and catalytic activities. Polyazomethine microspheres have been firstly synthesized from two representative monomers of 1,4-terephthalaldehyde and 3,5-diamino-1,2,4-triazole and then carbonized to produce the desired carbon nanomaterials. The morphologies of the surfaces on the carbon microspheres can be controlled with tunable roughness by introducing 2-aminopyridine. As an application demonstration, these nanostructured carbon microspheres are used as counter electrodes to fabricate efficient dye-sensitized solar cells with energy conversion efficiencies up to 7.5%.