Porous Polyurea Research Articles

Flexible and High-Strength Porous Graphene/Polyurea Composite Film for Multifunctional Applications

Porous composites possess distinctive structural features and performance advantages, making them promising for applications in various domains such as sensing, energy storage, and acoustics. A simple, efficient, and environmentally friendly method was employed to prepare porous polyurea materials, which were then modified with graphene nanosheets. The resulting graphene/polyurea porous composites demonstrated enhanced mechanical properties, with a 35.04% increase in tensile strength at a graphene content of 5 wt%. These composites exhibited exceptional multifunctionality, achieving a specific capacitance of 35.74 F/g when used as capacitor electrodes. Additionally, they displayed high sensitivity to resistance and capacitance changes under various mechanical loads, such as tensile, torsional, and bending stresses, with a resistance change rate of 57.72% under 180-degree torsion, highlighting their potential as resistive and capacitive sensors. Compared to traditional materials, the multifunctional composites maintained a resistance change rate below 40% and a capacitance retention rate above 95.07% after 10,000 cycles, underscoring their durability and reliability. Moreover, the developed graphene/polyurea porous composites exhibited good corrosion resistance and an impressive sound absorption rate of 30.68% for high-decibel noise, reducing environmental limitations for their applications. These properties position the composite as a durable, high-sensitivity, multifunctional material with significant potential in sensing, energy storage, and noise reduction applications.

Facile one-pot strategy to fabricate polyurea-based palladium for flow-through catalytic reduction of harmful hexavalent chromium from water

Developing facile approaches for fabrication of supported metallic nanoparticle (NPs) catalysts, and nascent technologies for their efficient application are highly desired. Herein, one-pot approach is developed for anchoring of palladium (Pd) nanoparticles on porous polyurea (PPU). In this process, tolylene-2,4-diisocyanate was poured to a mixture of water, acetone and palladium acetate at a fixed rate. After that, NaBH4 was added to the reaction mixture to obtain Pd/PPU with highly porous morphology. The obtained hybrid composite Pd/PPU was characterized by NMR, BET, SEM, XRD, TEM, ICP-OES, and XPS techniques. The outcomes revealed the efficacious anchoring and uniform dispersion of Pd with average size of 7.81 nm onto PPU containing highly porous structure with surface area of 115.51 m2/g. A packed-bed reactor was designed by using Pd/PPU for flow-through catalytic reduction of harmful hexavalent chromium (Cr(VI)) to benign trivalent (Cr(III)) with formic acid as reducer from water. A good permeation flux of 20,000 L/m2/h with > 99% of Cr(VI) reduction efficiency were obtained. Moreover, it was observed that Pd/PPU was a highly stable (>96% efficiency for 15 h used) catalyst for flow-through transformation of Cr(VI) to Cr(III). This report therefore proposes a facile approach for synthesis of PPU-based Pd, for continuous flow catalytic remediation of wastewaters, an emerging technology.

Immobilization of cobalt oxide nanoparticles on porous nitrogen-doped carbon as electrocatalyst for oxygen evolution

Highly efficient and robust electrocatalysts have been in urgent demand for oxygen evolution reaction (OER). For this purpose, high-cost carbon materials, such as graphene and carbon nanotubes, have been used as supports to metal oxides to enhance their catalytic activity. We report here a new Co 3 O 4 -based catalyst with nitrogen-doped porous carbon material as the support, prepared by pyrolysis of porous polyurea (PU) with Co(NO 3 ) 2 immobilized on its surface. To this end, PU was first synthesized, without any additive, through a very simple one-step precipitation polymerization of toluene diisocyanate in a binary mixture of H 2 O-acetone at room temperature. By immersing PU in an aqueous solution of Co(NO 3 ) 2 at room temperature, a cobalt coordinated polymer composite, Co(NO 3 ) 2 /PU, was obtained, which was heated at 500 °C in air for 2 h to get a hybrid, Co 3 O 4 /NC, consisting of Co 3 O 4 nanocrystals and sp 2 -hybridized N-doped carbon. Using this Co 3 O 4 /NC as a catalyst in OER, a current density of 10 mA·cm −2 was readily achieved with a low overpotential of 293 mV with a Tafel slope of 87 mV·dec −1 , a high catalytic activity. This high performance was well retained after 1000 recycled uses, demonstrating its good durability. This work provides therefore a facile yet simple pathway to fabrication of a new transition metal oxides-based N-doped carbon catalyst for OER with high performance.

Construction of Porous Polyureas and Polyamides via Domino Polymerization and Their High-Efficiency Au(III) Adsorption.

The adoption of new synthesis strategy and monomers significantly promotes the construction of porous organic polymers (POPs) and their promising applications. A fabricating method of porous polyimides is developed via sequential imidization and cross-linking reaction among self-condensable building blocks, as reported in the authors' previous manuscript. Herein, porous polyureas (A-POPs) are prepared starting from 4-ethynylaniline and diisocyanate monomers, while porous polyamides (B-POPs) are synthesized from 4-ethynylbenzoic acid and diisocyanate monomers. It is found that decreasing the monomer content in solvent can effectively inhibit the premature phase separation and facilitate the evolution of integrated network. Eventually, a maximum surface area of 425m2 g-1 is achieved for porous polyureas when the content of monomers is 10%. To the best knowledge, A-POPs are the porous polyureas with the highest surface areas reported up to now. The as-prepared porous polyurea (AN-POP) exhibits the maximum adsorption capacity of 1093.87 ± 5.23mgg-1 and removal rate of 99.96% for Au(III), due to its high surface area and the coordination between the heteroatoms (N and O) in A-POPs and metal ions. Besides, the porous polyurea also exhibits excellent renewable efficiency and high selectivity to Au(III).

Synthesis of porous polyurea microspheres for matting coating

Synthesis of porous polyurea microspheres for matting coating

Facile strategy to fabricate palladium-based nanoarchitectonics as efficient catalytic converters for water treatment

Developing facile strategies for anchoring transition-metal nanoparticles (M-NPs) on support materials to make their easy handling, and nascent technologies to advance their applications towards large scale sustainable catalysis are highly demanding. Herein, one-pot strategy is reported for the in-situ immobilization of palladium nanoparticles (Pd-NPs) on highly porous polyurea (PPU). In this approach, Pd acetate (PdAc) solution in tolylene-2,4-diisocyanate (TDI) was gradually added in H2O/acetone (3/7 wt%) mixture under stirring at ambient conditions, followed by the addition of NaBH4 to get Pd/PPU. The combined outcomes of characterizations of resulting Pd/PPU by NMR, SEM, ICP-OES, XRD, XPS, TEM, and BET techniques revealed the successful immobilization of uniformly dispersed Pd-NPs (dmean = 6.2 nm) on PPU having hierarchically porous morphology with specific surface area of 127.13 m2/g. The hybrid composite, Pd/PPU, was used in packed-bed reactor to evaluate its performance as the continuous flow catalytic converter for several toxic organic and inorganic pollutants, as well as their mixture in aqueous medium with the assistance of suitable reductants. The effects of Pd loading, feed concentrations, and permeation flux on the activity of Pd/PPU are discussed. A remarkable permeation flux of 21,000 Lm−2 h−1 (LMH) with > 99% of pollutant’s reduction efficiency and high stability (no change for 20 h used) of Pd/PPU in packed-bed continuous flow catalytic converter were obtained, far better (>10 times) to compare with reported results (2000 LMH) so far. This work therefore provides facile strategy to get PPU-based Pd, a high-performance catalyst for continuous flow reduction of toxic contaminants from wastewaters.

Benign fabrication process of hierarchal porous polyurea microspheres with tunable pores and porosity: Their Pd immobilization and use for hexavalent chromium reduction

Developing new strategies for fabrication of porous materials with tunable morphology which have fewer environmental impacts is highly desired. Herein, conventional precipitation polymerization of polyurea (PU) synthesis is converted to interfacial polymerization via simple microfluidics and hierarchically porous and uniform PU microspheres (PPM) are prepared by the reaction of toluene diisocyanate and water, eliminating the use of toxic amines and organic solvents. The morphology and porosity of PPM are probed. The size of PPM is controlled by changing the diameter of flow channels of microfluidic device and their pore size and porosity are tuned by optimizing the polymerization conditions. Moreover, palladium (Pd) is immobilized on PPM by impregnation and subsequent reduction approach to get Pd@PPM. The hybrid composite, Pd@PPM, is used for catalytic reduction of toxic Cr6+ to benign Cr3+ by formic acid as a reductant along with sodium format as a promoter in aqueous system. Pd@PPM exhibited high catalytic activity and good stability for Cr6+ reduction and their large size with high uniformity eased their recovery to reuse them in subsequent Cr6+ reduction. Porous PU with controllable shape and morphology are rarely available. This work therefore provides new strategy to synthesis PPM with controllable porous morphology and their use as an effective support for catalysis.

Porous Polyurea Supported Pd Catalyst: Easy Preparation, Full Characterization, and High Activity and Reusability in Reduction of Hexavalent Chromium in Aqueous System

Porous Polyurea Supported Pd Catalyst: Easy Preparation, Full Characterization, and High Activity and Reusability in Reduction of Hexavalent Chromium in Aqueous System

Stoichiometric modulation of triazine based polyurea frameworks for carbon dioxide capture

Synergistic modulation of morphology, porosity and end functionalities in porous polyurea frameworks (PPFs) was accomplished via stoichiometry control in one pot facile strategy under catalyst free room temperature conditions. Monomer feed optimization of an aliphatic diisocyanate with melamine, employing 1,4-dioxane solvent, rendered PPF-1, PPF-2 and PPF-3 manifesting tailored terminal moieties and thermal profiles. FTIR spectral data corroborated the formation of urea linkages as well as the existence of tuned reactive capping for ensuing PPFs. A high thermochemical stability was attributed to the combined effect of heat resistant urea linkages, heterocyclic aromatic triazine rings and crosslinks between the binary monomer mixtures. Distinct morphologies and surface areas were established for individual PPFs, with PPF-3 exhibiting the highest BET surface area. PPF-3 was further probed for CO2 capture capacity at different temperatures and demonstrated a good CO2 adsorption in comparison with the existing porous polymers of comparable surface areas. Simultaneous modulation of multiple structural attributes and appreciable CO2 uptake provide an impetus to unlock the immense potential of these PPFs for carbon dioxide capture under extreme thermochemical milieu.

Constructing “Rigid-and-Soft” interlocking stereoscopic interphase structure of aramid fiber composites with high interfacial shear strength and toughness

High strength and toughness seems like intrinsic conflicts in mechanical properties of materials, including composites interfaces. To solve this problem, we constructed a hierarchically structured interphase in aramid composites via in-situ grafting and foaming of polyurea on fiber surface and penetrating epoxy resin into the pores. As differential scanning calorimeter (DSC) and atomic force microscopic (AFM) confirmed, soft porous polyurea filled rigid resin matrix generated numerous covalent bonded interfaces and formed “rigid-and-soft” interlocking stereoscopic interphase. Axial covalent bonds between fiber and polyurea, radial covalent bonds between polyurea and epoxy resin highly improved interfacial shear strength by 115.9%. Newly formed interfaces caused much higher energy consumption during interfacial failure is considered to enhance interfacial shear toughness (GⅠC) by 493.2%. Mathematical analysis and finite element analysis furtherly proved strengthening and toughening mechanisms, and we found the enhancement of GⅠC is also highly related to thickness of polyurea layer and pores’ sizes.

Nanogels Constituted of Polyurea Filled with an Ionic Liquid as an Electrolyte for Electric Double-Layer Transistors

An ionic liquid (IL)-containing porous polyurea (PU) nanogel electrolyte was synthesized from its constituent monomers and the IL 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide using...

Porous polyurea microspheres with Pd immobilized on surface and their catalytic activity in 4-nitrophenol reduction and organic dyes degradation

Transition-metal nanoparticles (NPs) have been widely used as high performance catalyst in organic reactions, and it is well recognized that these metal species are highly toxic, their handling is hazardous, and featured also by high-costing. Their incorporation in or immobilization on a support is one of the most opted strategies. We report here a facile two-step protocol to obtain composite microspheres (Pd@PPM2) of porous polyurea microspheres (PPM) and Pd-NPs: highly uniform PPM were prepared first by interfacial polymerization of toluene diisocyanate in water through a microfluid device, followed by Pd immobilization on their surface. Pd@PPM2 was characterized by NMR, XPS, and temperature-programmed reduction. The results indicated that Pd was immobilized on PPM surface through a coordination interaction with urea ligand. A parallel version of the composite microspheres, Pd@PPM1, was also prepared through one single step, by dissolving Pd(OAc)2 in the monomer in PPM preparation. The catalytic performance of the two composite microspheres, Pd@PPM1 and Pd@PPM2, was evaluated in the reduction of 4-nitrophenol (4-NP) and in degradation of several dyes, using NaBH4 as the reducer in both, and the results compared. In all the tested processes, Pd@PPM2 out-performed Pd@PPM1, thanks to their higher specific surface area of immobilized Pd-NPs and a larger number of active sites on the surface. The catalysts were shown also to have sustainable reusability in dyes degradation. In contrast, the catalytic activity was obviously deteriorated in its reuse in 4-NP reduction, owing to the formation of a complex between Pd-NPs and the reduction product of 4-NP, which resulted in the Pd active sites being covered by the complex, leading to the decrease in their catalytic performance. Their good reusability in dyes degradation confirmed that the decrease in catalytic activity was limited only to the processes where 4-aminophenol and similar amine containing compounds were involved. The high uniformity, easy recovery, high catalytic activity and sustainable reusability make Pd@PPM2 a great catalyst with good potential for applications in different fields.

Effective enhancement of Cu ions adsorption on porous polyurea adsorbent by carboxylic modification of its terminal amine groups

The pollution by metal ions has been a key issue in environmental protection. Amine-rich porous polyurea (PPU), prepared by a simple one-step precipitation copolymerization of diisocyanate and diamine, is highly selective for Cu2+ adsorption, but associated with a poor reusability. We report here a chemically modified PPU by simply turning the amine groups of PPU to aminoacetic carboxyls. The results indicate that this carboxylation is an easy and effective pathway to polymer adsorbent, with high performance for Cu2+ adsorption and reusability superior to most of the reported adsorbents. Cu2+ adsorption capacity on PPU-M, i.e. PPU after carboxylation, increased to 2.84 mmol/g, an increase by 22% in comparison with PPU. The chemical modification process was optimized. The porosity and morphology of PPU-M were characterized using N2 adsorption, mercury intrusion, and scanning electron microscopy. The high Cu2+ adsorption was interpreted through a complex coordination mechanism of Cu2+ based on XPS analysis. The high performance of reusability of PPU-M, thanks to enhanced desorption of 99.5% or more of the adsorbed Cu2+ after each recycled use, was also interpreted based on the stability constants of acid-base equilibrium of amine and carboxyl towards Cu2+ and protons. Adsorption kinetics modelling demonstrated this adsorption followed the pseudo-second-order model. The adsorption analysis by isothermal adsorption showed this adsorption was well fitted by Freundlich equation and in good agreement with the suggested adsorption mechanism.

Highly Uniform and Porous Polyurea Microspheres: Clean and Easy Preparation by Interface Polymerization, Palladium Incorporation, and High Catalytic Performance for Dye Degradation.

Owing to their high specific surface area and low density, porous polymer materials are of great importance in a vast variety of applications, particularly as supports for enzymes and transition metals. Herein, highly uniform and porous polyurea microspheres (PPM), with size between 200 and 500 μm, are prepared by interfacial polymerization of toluene diisocyanate (TDI) in water through a simple microfluidic device composed of two tube lines, in one of which TDI is flowing and merged to the other with flowing aqueous phase, generating therefore TDI droplets at merging. The polymerization starts in the tube while flowing to the reactor and completed therein. This is a simple, easy and effective process for preparation of uniform PPM. Results demonstrate that the presence of polyvinyl alcohol in the aqueous flow is necessary to obtain uniform PPM. The size of PPM is readily adjustable by changing the polymerization conditions. In addition, palladium is incorporated in PPM to get the composite microspheres Pd@PPM, which are used as catalyst in degradation of methylene blue and rhodamine B. High performance and good reusability are demonstrated. Monodispersity, efficient dye degradation, easy recovery, and remarkable reusability make Pd@PPM a promising catalyst for dye degradation.

Controllable fluorescence via tuning the m-substituents of added aromatic molecules in a pyrene derivative-decorated porous skeleton.

A novel pyrene derivative based composite fluorescent material was developed by immobilizing the pyrene-1-carboxylic acid (PyCOOH) into the pores of porous polyurea microspheres (denoted as PyCOOH-decorated PPUM). Encouragingly, the fluorescence spectrum of this synthesized composite microsphere only exhibited monomer emission of guest PyCOOH, indicating that the porous skeleton PPUM has excellent isolation ability to separate the guest molecules from each other. This discovery will provide an effective strategy to design and synthesize pyrene based host–guest systems without excimer emission. Notably, the PyCOOH-decorated PPUM can keep good fluorescent stability when dispersed in many organic solvents. More excitingly, it was found for the first time that the fluorescence of such a material can be regulated by adding aromatic compounds containing different m-substituted groups. When m-cresol was added, the intensity of the monomer emission enhanced significantly due to the unusual dissolution of the host porous polyurea sphere. By adding the m-toluidine, the monomer emission without the fluorescence of unassociated PyCOOH increased owing to the connection of m-toluidine and PyCOOH which escaped from the pores. In the presence of m-methylacetophenone and m-toluic acid, the monomer emission showing different degrees of decline was observed respectively because of the different substitution process. This result will contribute to the exploration of more promising candidates for pyrene-based fluorescent sensors.

Easy preparation of porous polyurea through copolymerization of toluene diisocyanate with ethylenediamine and its use as absorbent for copper ions

Porous and functional polyurea (PPU) is prepared through a very simple one-step precipitation copolymerization of toluene diisocyanate and ethylenediamine in acetonitrile, and is shown to have high adsorption for Cu2+ ions with high selectivity among 5 ions tested. Effects of pH, adsorption time and initial ion concentration on the adsorption are studied. Compared with a group of reported porous adsorbents, this PPU is of high performance. Based on X-ray photoelectron spectroscopy on PPU before and after the adsorption, the high adsorption of Cu2+ ions is interpreted by the formation of multifunctional complexations of the ions not only with the terminal amines of PPU, but also with oxygen and nitrogen atoms of its carbamido units. Adsorption kinetics simulations by pseudo-first and pseudo-second-order models show that this adsorption follows the latter one; The adsorption analysis using isothermal adsorption equations shows that Freundlich equation is well fitted. All these results are in good agreement with the proposed mechanism for the adsorption process. Selective adsorption tests for different metal ions, i.e. Cu2+, Ni2+, Pb2+, Cd2+ and Cr3+, demonstrate that PPU is highly selective towards Cu2+. Reusability of PPU is also tested, which reveals that 82.5% of the initial adsorption capacity is retained at the fifth recycled use for Cu2+ adsorption.

Vapor Deposition Polymerization and Porous Structural Formation of Polyurea Thin Films via Nano-Ionic Liquid Films

Porous polyurea films were synthesized by vapor deposition polymerization via ionic liquid (IL) nano thin films with different thicknesses, and the water contact angles (WCAs) on the polyurea films...

Formation and shape transition of porous polyurea of exotic forms through interfacial polymerization of toluene diisocyanate in aqueous solution of ethylenediamine and their characterization

Polyureas (PU) are of prime importance for a great number of applications from protective coatings and catalyst support to biomaterials for hydrogels and drug release. Novel physical and chemical methods of their synthesis have been great interests in order to obtain these materials of different morphologies with different surface and structural properties. Herein, PUs with exotic structures, including bead-skewer and string-form, are prepared through a very simple interfacial polymerization of toluene diisocyanate (TDI), by adding it into an aqueous solution of ethylenediamine (EDA) at constant rate. The effects of experimental conditions, including EDA/TDI ratio, polymerization temperature, pore size of syringe needle for TDI addition and the addition rate, on the morphology of PU materials were studied. The results showed that bead-skewer PU was obtained with EDA/TDI ratio at 1.43–1.51, and string-form PU achieved with the same ratio at 1.59–2.20. A hard shell was first formed on the surface of TDI once extruded out of the syringe needle. The size of bead-skewer and string-form PU was easily adjusted. Their chemical structure characterization by NMR confirmed that a PU shell was formed in the early stage of the polymerization, owing to the reaction of TDI with EDA. PU materials thus prepared are macroporous regardless of their shape. This paper provides therefore a novel and simple way to the preparation of porous PU with specific shapes, such as bead-skewer and string-form, along with the formation and shape transition mechanism of the materials.

팔라듐 담지 다공성 폴리우레아를 불균일 촉매로 활용한 Suzuki-Miyaura 커플링 반응

다공성 고분자(porous organic polymer, POPs)는 높은 표면적을 가지는 무정형의 고분자이다. 본 연구에서는 우레아 축합반응으로 UPOP라는 다공성 고분자를 합성하였다. UPOP는 Brunauer-Emmett-Teller(BET) 분석을 통해 다공성을 확인하였고, 불균일 촉매 활용성을 보기 위하여 팔라듐을 담지하여 Pd@UPOP를 합성하였다. Pd@UPOP는 XPS 분석을 통해 Pd 담지를 확인하였고, Suzuki-Miyaura 커플링 반응을 이용하여 촉매활성을 측정하였다. Pd@UPOP의 촉매활성은 물과 ethanol이 3:1이고 K₂CO₃를 사용하였을 때 가장 높았다. 특히 이 조건에서 Pd@UPOP를 촉매로 사용하여 공기 중에서 반응시켰을 때 Pd 함량은 0.1 mol%였음에도 불구하고 99% 이상의 수율을 보였다. 또한 5번 재사용하였을 때도 90%의 수율을 유지하였다.

Immobilization of Lipase from Pseudomonas fluorescens on Porous Polyurea and Its Application in Kinetic Resolution of Racemic 1-Phenylethanol.

A porous polyurea (PPU) was prepared through a simple protocol by reacting toluene diisocyanate with water in binary solvent of water-acetone. Its amine group was determined through spectrophotometric absorbance based on its iminization with p-nitrobenzaldehyde amines. PPU was then used as a novel polymer support for enzyme immobilization, through activation by glutaraldehyde followed by immobilization of an enzyme, lipase from Pseudomonas fluorescens (PFL), via covalent bonding with the amine groups of lipase molecules. Influences of glutaraldehyde and enzyme concentration and pH in the process were studied. The results revealed that the activity of the immobilized PFL reached a maximum at GA concentration of 0.17 mol/L and at pH 8. Immobilization rate of 60% or higher for PFL was obtained under optimized condition with an enzyme activity of 283 U/mg. The porous structure of PPU, prior to and after GA activation and PFL immobilization, was characterized. The activity of the immobilized PFL at different temperature and pH and its stability at 40 °C as well as its reusability were tested. The immobilized enzyme was finally used as enantioselective catalyst in kinetic resolution of racemic 1-phenylethanol (1-PEOH), and its performance compared with the free PFL. The results demonstrate that the enzyme activity and stability were greatly improved for the immobilized PFL, and highly pure enantiomers from racemic 1-PEOH were effectively achieved using the immobilized PFL. Noticeable deactivation of PFL in the resolution was observed by acetaldehyde in situ formed. In addition, the immobilized PFL was readily recovered from the reaction system for reuse. A total of 73% of the initial activity was retained after 5 repeated reuse cycles. This work provides a novel route to preparation of a polyurea porous material and its enzyme immobilization, leading to a novel type of immobilized enzyme for efficient kinetic resolution of racemic molecules.