Porous Aromatic Frameworks Materials Research Articles

Constructing porous aromatic frameworks from natural products for organic pollutant capture

Organic micropollutants in water have raised increasing concerns about aquatic ecosystems and human health. Porous aromatic frameworks (PAFs) with highly porosity and good stability are widely used as sewage treatment agents. However, most of the PAFs are constructed by laboratory-synthesized building units, which are much expensive and increase the total cost of PAFs. At the same time, it is also a potential threaten that these synthetic compounds may affect human health and environmental safety. These shortcomings limit the environmental application of PAF materials. In this work, a route that synthesizing a series of PAFs was developed by using polyphenolic natural products as building units. As a prototype, PAF-274 was constructed by resveratrol to give a permanently porous material, and used for extracting bisphenol A from water. PAF-274 possessed specific surface area of 242 m2/g, and dual pore size at 1.6 and 2.7 nm. The maximum adsorption capacity for bisphenol A was 897 mg/g, which exceeded many other adsorbents and retained the high removal efficiency after 10 cycles. A wide range of non-toxic and harmless natural products can be used to construct porous materials. This synthetic method of introducing natural products broadens the selection of building units for PAFs and opens a new way for the design of functional porous materials.

Ultrathin Free-Standing Porous Aromatic Framework Membranes for Efficient Anion Transport.

Porous aromatic frameworks (PAFs) show promising potential in anionic conduction due to their high stability and customizable functionality. However, the insolubility of most PAFs presents a significant challenge in their processing into membranes and subsequent applications. In this study, continuous PAF membranes with adjustable thickness were successfully created using liquid-solid interfacial polymerization. The rigid backbone and the stable C-C coupling endow PAF membrane with superior chemical and dimensional stabilities over most conventional polymer membranes. Different quaternary ammonium functionalities were anchored to the backbone through flexible alkyl chains with tunable length. The optimal PAF membrane exhibited an OH- conductivity of 356.6 mS ⋅ cm-1 at 80 °C and 98 % relative humidity. Additionally, the PAF membrane exhibited outstanding alkaline stability, retaining 95 % of its OH- conductivity after 1000 hours in 1 M NaOH. To the best of our knowledge, this is the first application of PAF materials in anion exchange membranes, achieving the highest OH- conductivity and exceptional chemical/dimensional stability. This work provides the possibility for the potential of PAF materials in anionic conductive membranes.

Ultrathin Free‐Standing Porous Aromatic Framework Membranes for Efficient Anion Transport

AbstractPorous aromatic frameworks (PAFs) show promising potential in anionic conduction due to their high stability and customizable functionality. However, the insolubility of most PAFs presents a significant challenge in their processing into membranes and subsequent applications. In this study, continuous PAF membranes with adjustable thickness were successfully created using liquid‐solid interfacial polymerization. The rigid backbone and the stable C−C coupling endow PAF membrane with superior chemical and dimensional stabilities over most conventional polymer membranes. Different quaternary ammonium functionalities were anchored to the backbone through flexible alkyl chains with tunable length. The optimal PAF membrane exhibited an OH− conductivity of 356.6 mS ⋅ cm−1 at 80 °C and 98 % relative humidity. Additionally, the PAF membrane exhibited outstanding alkaline stability, retaining 95 % of its OH− conductivity after 1000 hours in 1 M NaOH. To the best of our knowledge, this is the first application of PAF materials in anion exchange membranes, achieving the highest OH− conductivity and exceptional chemical/dimensional stability. This work provides the possibility for the potential of PAF materials in anionic conductive membranes.

Enhanced pore structure regulation in porous aromatic framework materials via montmorillonite templating

The specific regulation of pore structure in porous aromatic framework (PAF) materials is of paramount importance for achieving exceptional performance. In this study, we propose a novel approach by utilizing the two-dimensional layered mineral, montmorillonite, as a template for the synthesis of PAF-Mt. Through a meticulously designed hydrothermal method, the residual template is completely eliminated, resulting in the creation of a new porous aromatic framework material, termed PAF-Mt-Free. Our research findings demonstrate remarkable improvements in the morphology, surface area, and pore size of PAF-Mt-Free compared to classical PAFs. Specifically, the morphology of PAF-Mt-Free undergoes a transformation from spherical to smaller fragmented particles. The specific surface area （968.163 m2/g） is enhanced by 47.9% compared to PAF-Mt（654.784 m2/g） and by 68.3% compared to PAF-45（575.390 m2/g）. Moreover, the main pore size of PAF-Mt-Free increases from approximately 0.5 nm to 0.9 nm. Importantly, PAF-Mt-Free not only maintains the excellent photocatalytic performance of PAF-Mt but also exhibits significantly enhanced adsorption capacity, particularly for organic molecules with a size smaller than 1 nm. Notably, the adsorption efficiency for benzene, toluene, chlorobenzene, and bromobenzene increases by 10%, 18.4%, 11%, and 13.2%, respectively. These findings highlight the promising potential of utilizing montmorillonite templating for the precise control of pore structure in PAF materials, leading to enhanced adsorption performance. Our study contributes to the advancement of porous aromatic framework materials and their applications in various fields.

An Ionic Liquid on a Porous Organic Framework Support: A Recyclable Catalyst for the Knoevenagel Condensation in an Aqueous System.

Porous aromatic frameworks (PAFs) that feature a high density of phenyl rings in their robust frameworks are attractive platforms for catalysis because of their extremely high stability, high surface area, and adjustable pore size. In this paper, two PAF-supported ionic liquids were constructed by introducing ionic liquid units onto the framework of a PAF material PAF-111 using a series of stepwise post-synthetic modifications. The basic PAF-supported ionic liquid with a hydroxy anion exhibited high catalytic activity and high stability, and could undergo at least 10 cycles without any activity loss when catalyzing Knoevenagel condensation reaction under aqueous conditions. It is expected that our study will further promote the development of designing and applying functional PAF materials for catalysis in aqueous systems.

Band structure tunable synthesis of photocatalytic porous aromatic frameworks via Scholl reaction

Porous aromatic framework (PAF) materials with π-π conjugation system based on Scholl reaction were found to exhibit satisfying photocatalytic performance, that can successfully degrade Rhodamine B (RhB) and colorless phenol. By selecting different multiple-phenyl building blocks, six kinds of PAF materials named as P-BP materials were successfully constructed by Scholl reaction, which exhibit not only photocatalytic ability, but also moderate specific surface areas, wide solar spectrum coverage, and good thermal and chemical stabilities. Depending on their different building block selections, the photocatalytic performance can be adjusted. The P-BP-DPA was found to exhibit the highest photocatalytic performance with 100% and 50% degradation rate for RhB and phenol in 300 min, respectively. Free radical trapping experiments showed that the photocatalytic activity originated from the strong oxidation capability of photogenerated holes. The band structure of such group of materials can be readily adjusted. With different monomers, their band gaps can be tuned from 1.87 to 2.36 eV, and their valence band positions were adjusted from 1.93 to 3.44 eV (vs NHE).

Facile Synthesis of Ultrastable Porous Aromatic Frameworks by Suzuki-Miyaura Coupling Reaction for Adsorption Removal of Organic Dyes.

Porous aromatic frameworks (PAFs) with robust structure, high stability, and high surface area have attracted intense interest from scientists in diverse fields. However, there are still very few reports on the adsorption of organic dyes by PAFs. In this work, four new PAFs have been facilely synthesized by the polymerization of a tetrahedral-shaped (four-node) monomer with a series of three-node monomers through Suzuki-Miyaura coupling reactions. All the obtained materials possess hierarchical porous structures and show high thermal and chemical stability. The Brunauer-Emmett-Teller (BET) surface areas of these PAFs were determined to be 857 m2 g-1 for PAF-111, 526 m2 g-1 for PAF-112A, 725 m2 g-1 for PAF-112B, and 598 m2 g-1 for PAF-113. Rhodamine B was selected as a model organic dye to test the adsorption capacities of the obtained PAF materials. PAF-111 showed a maximum adsorption capacity of 1666 mg g-1 (167 wt %) for Rhodamine B, which is among the highest values reported to date for porous organic materials. It is noteworthy that PAF-111 could be reused in at least ten cycles under the adsorption conditions without any loss of adsorption capacity. Our study has revealed the great potential and advantages of PAFs as ultrastable adsorption materials for the removal of organic dyes.

Porous aromatic frameworks derived from tetrahedral units

Porous aromatic frameworks (PAFs), an important class of porous materials, have gained worldwide attentions and been greatly developed since the first PAF material PAF-1 was successfully designed and synthesized in 2009. More than 100 PAF materials with specific functionalities were synthesized and reported in the last decade. The high surface areas, light skeleton densities and high thermal and chemical stabilities make PAF materials good candidates in various applications, such as gas sorption and separation, catalysis, sensor and host-guest chemistry. The design of PAF-1 came from the structure of diamond, the most stable substance exiting in the nature at present. The carbon atoms in diamond are covalently bonded with four adjacent carbon atoms by sp3 hybridization to form tetrahedral units. This special structure makes diamond the hardest material. However, the short length of C–C bond results in a compact structure of diamond. Conceptually, if the C–C bonds were replaced with rigid linear units, the resulting material should not only retain the diamond structure but also present increasing internal surface area. By employing Ullmann coupling reaction of tetrakis(4-bromophenyl)methane, PAF-1 with ultrahigh surface area as well as high thermal and chemical stability was synthesized. The structural information of PAF-1 was obtained by various characterizations, which is consistent with P2 model structure simulated from diamond topology. Thus, tetrahedral building units are good candidates to construct PAFs with high surface area and high stabilities. Reticular chemistry was introduced into the design of porous materials in the end of 20th century, and has been well developed and employed with the concept of topology. Via the bottom-up and top-down ways, PAF materials derived from tetrahedral units may possess diamond-like structure thus they would exhibit high thermal stabilities. By adjusting the length of linkages between tetrahedral units, PAFs with tunable pore sizes can be targeted synthesized, which might even extend to mesopore range. In-situ synthesis and post-modification methods bring more possibilities for the functionalization of PAF materials. Various functional groups such as –NH2, –COOH, –OH can be embedded in PAFs skeletons. Metal cations can be introduced in the pores of PAF materials by ion-exchange method. Besides, metal nanoparticles would also be encapsulated in PAF materials with large pore size and specific interaction sites. In this review, we summarized the targeted synthesis of PAF materials derived from tetrahedral units with the guide of reticular chemistry and demonstrated the functionalization strategy. Meanwhile, the applications of PAF materials, including CO2 sorption and separation, small liquid molecule adsorption, iodine capture, catalysis and sensor were presented and the effect factors were discussed in detail. In addition, cost-effective PAF materials were synthesized with cheap catalysts such FeCl3 and AlCl3 to expand their applications in practice. The above achievements opened up new avenues for the targeted synthesis of porous materials with high surface areas and high stabilities and provided insights for the materials design with specific functionalities.

Coupling fullerene into porous aromatic frameworks for gas selective sorption.

A lot of investigations calculate that fullerene would be an excellent unit for porous adsorbents for gas sorption and separation. Although the conjugated structure and symmetrical shape of fullerene makes it an ideal building block, there is no facile strategy to achieve fullerene-based porous materials. Herein, we adopt a novel acid catalyzed coupling reaction to bind the fullerene molecules together in a one-step synthesis. After synthesizing the adducts as models, the atomic connectivity between the fullerene molecules is determined clearly. We then prepared a series of fullerene-based porous aromatic frameworks (PAFs). The targeted products adsorb H2 and CO2, and they exhibit some selectivity of CO2 over N2 and CH4. The good performance of the PAFs indicates that we could combine the gas binding ability of the building block and the porous nature of PAF materials together to give a better adsorbent.

Highly Efficient Enrichment of Volatile Iodine by Charged Porous Aromatic Frameworks with Three Sorption Sites

AbstractThe targeted synthesis of a series of novel charged porous aromatic frameworks (PAFs) is reported. The compounds PAF‐23, PAF‐24, and PAF‐25 are built up by a tetrahedral building unit, lithium tetrakis(4‐iodophenyl)borate (LTIPB), and different alkyne monomers as linkers by a Sonogashira–Hagihara coupling reaction. They possess excellent adsorption properties to organic molecules owing to their “breathing” dynamic frameworks. As these PAF materials assemble three effective sorption sites, namely the ion bond, phenyl ring, and triple bond together, they exhibit high affinity and capacity for iodine molecules. To the best of our knowledge, these PAF materials give the highest adsorption values among all porous materials (zeolites, metal–organic frameworks, and porous organic frameworks) reported to date.

Highly Efficient Enrichment of Volatile Iodine by Charged Porous Aromatic Frameworks with Three Sorption Sites.

The targeted synthesis of a series of novel charged porous aromatic frameworks (PAFs) is reported. The compounds PAF-23, PAF-24, and PAF-25 are built up by a tetrahedral building unit, lithium tetrakis(4-iodophenyl)borate (LTIPB), and different alkyne monomers as linkers by a Sonogashira-Hagihara coupling reaction. They possess excellent adsorption properties to organic molecules owing to their "breathing" dynamic frameworks. As these PAF materials assemble three effective sorption sites, namely the ion bond, phenyl ring, and triple bond together, they exhibit high affinity and capacity for iodine molecules. To the best of our knowledge, these PAF materials give the highest adsorption values among all porous materials (zeolites, metal-organic frameworks, and porous organic frameworks) reported to date.

Robust tri(4-ethynylphenyl)amine-based porous aromatic frameworks for carbon dioxide capture

We report here the synthesis and carbon dioxide capture of a series of porous aromatic framework (PAF) materials assembled using tri(4-ethynylphenyl)amine and various aryl halides via Sonogashira–Hagihara coupling reactions. These PAF materials show moderate surface areas ranging from 370 m2 g−1 to 953 m2 g−1. The functional groups, such as –COOH, –NH2 and –OH, are incorporated into the backbone of the PAF materials. The isosteric heats of CO2 and CO2/N2 selectivities for these PAFs are calculated based on the CO2 and N2 adsorption isotherms measured at 273 and 298 K. It is found that the –NH2 functionalized network shows the highest isosteric heat of CO2 and CO2/N2 selectivity. In addition, the –COOH functionalized network displays the highest CO2 uptake in terms of per unit areas (4.37 μmol m−2, 273 K). The results indicate the incorporation of functional groups is effective for synthesizing CO2-philic PAF networks with enhanced interaction with CO2 molecules.