Hybrid Porous Materials with High Surface Area Derived from Bromophenylethenyl-Functionalized Cubic Siloxane-Based Building Units

Direct cross-linking of silyl-functionalized cage siloxanes via nonhydrolytic siloxane bond formation for preparing nanoporous materials

Bottom-up synthesis of siloxane-based nanoporous materials from siloxane oligomers is promising for constructing well-defined structures at a molecular level. Herein, we report the synthesis of nanoporous materials consisting of cage-type siloxanes through the nonhydrolytic siloxane bond formation reaction. Cage siloxanes with double-n-ring geometries (n = 4 or 6) modified with dimethylsilyl and dimethylethoxysilyl groups are synthesized and directly cross-linked using a B(C6F5)3 catalyst, resulting in the formation of porous networks composed of alternating cage siloxane nodes and tetramethyldisiloxane (-SiMe2OSiMe2-) linkers. Compared with conventional hydrolysis and polycondensation reactions of alkoxysilyl-modified cage siloxanes under acid conditions, the non-hydrolytic condensation reaction was found favorable for the formation of porous siloxane networks without unwanted cleavage of the siloxane bonds.

Porous organic polymers (POPs) for environmental remediation

Modern global industrialization along with the ever-increasing growth of the population has resulted in continuous enhancement in the discharge and accumulation of various toxic and hazardous chemicals in the environment. These harmful pollutants, including toxic gases, inorganic heavy metal ions, anthropogenic waste, persistent organic pollutants, toxic dyes, pharmaceuticals, volatile organic compounds, etc., are destroying the ecological balance of the environment. Therefore, systematic monitoring and effective remediation of these toxic pollutants either by adsorptive removal or by catalytic degradation are of great significance. From this viewpoint, porous organic polymers (POPs), being two- or three-dimensional polymeric materials, constructed from small organic molecules connected with rigid covalent bonds have come forth as a promising platform toward various leading applications, especially for efficient environmental remediation. Their unique chemical and structural features including high stability, tunable pore functionalization, and large surface area have boosted the transformation of POPs into various macro-physical forms such as thick and thin-film membranes, which led to a new direction in advanced level pollutant removal, separation and catalytic degradation. In this review, our focus is to highlight the recent progress and achievements in the strategic design, synthesis, architectural-engineering and applications of POPs and their composite materials toward environmental remediation. Several strategies to improve the adsorption efficiency and catalytic degradation performance along with the in-depth interaction mechanism of POP-based materials have been systematically summarized. In addition, evolution of POPs from regular powder form application to rapid and more efficient size and chemo-selective, "real-time" applicable membrane-based application has been further highlighted. Finally, we put forward our perspective on the challenges and opportunities of these materials toward real-world implementation and future prospects in next generation remediation technology.

Zn(II)-Siloxane Clusters as Versatile Building Blocks for Carboxylate-Based Metal-Organic Frameworks

Siloxanes have long been known for their highly desirable properties suited for a wide range of practical applications; however, their utilization as modular building blocks for crystalline open frameworks has been limited. In this study, a simple solvothermal pathway has been found to synthesize unprecedented Zn(II)-siloxane clusters supported by acetate ligands, [(RSiO2)8Zn8(CH3CO2)8] (R = Me or Ph). The same reaction using a dicarboxylate ligand such as 1,4-benzenedicarboxylate or 2,6-naphthalenedicarboxylate produces a new type of metal-organic framework, named SiMOF here, based on the [Si8Zn8] units. With the maximum connectivity of 8, the building block is shown to form topologically interesting structures such as octahedral supercages or uninodal 8-connected frameworks. All SiMOFs synthesized possess permanent porosity and high thermal stability and are naturally hydrophobic, as demonstrated by adsorptions of toluene, ethanol, methanol, and water vapor as well as water contact angle measurements. These promising characteristics for well-defined porous solids are attributed to metal-bound siloxane groups in the structural building units.

Self-healing mixed matrix membranes containing metal-organic frameworks

Mixed-matrix membranes (MMMs) provide a means to formulate metal-organic frameworks (MOFs) into processable films that can help to advance their use in various applications. Conventional MMMs are inherently susceptible to craze or tear upon exposure to impact, cutting, bending, or stretching, which can limit their intended service life and usage. Herein, a simple, efficient, and scalable in situ fabrication approach was used to prepare self-healing MMMs containing Zr(iv)-based MOFs. The ability of these MMMs to self-heal at room temperature is based on the reversible hydrolysis of boronic-ester conjugates. Thiol-ene 'photo-click' polymerization yielded robust MMMs with ∼30 wt% MOF loading and mechanical strength that varied based on the size of MOF particles. The MMMs could undergo repeated self-healing with good retention of mechanical strength. In addition, the MMMs were catalytically active toward the degradation of the chemical warfare agent (CWA) simulant dimethyl-4-nitrophenyl phosphate (DMNP) with no change in activity after two damage-healing cycles.

Synthesis of (Deoxy)difluoromethylated Phosphines by Reaction of R2P(O)H with TMSCF3 and Their Application in Cu(I) Clusters in Sonogashira Coupling

R₂PCF₂H ligands and their R₂P(O)CF₂H precursors were synthesized from R₂P(O)H with TMSCF₃ by simply modulating the H₂O concentration via deoxydifluoromethylation and difluoromethylation. The air sensitive R₂PCF₂H phosphines can be stabilized in Cu(I) clusters as ligands. Within these Cu(I) clusters, the Sonogashira cross-coupling reaction can proceed fast and efficiently using terminal alkynes and aryl iodides within 15 min at room temperature under air to give a variety of diaryl(alkyl)acetylenes in good yields (49 examples, yields of ≤99%). Six of the internal alkynes present in drug precursors can be obtained using this protocol in good yields. The mechanism is proposed on the basis of control experiments.

Variation of counter quaternary ammonium cations of anionic cage germanoxanes as building blocks of nanoporous materials

Double-four ring (D4R)-type cage germanoxanes, having a fluoride anion in the cage, contain organic ammonium cations as counter cations outside the cage, and they are attractive as unique nano-building blocks of anionic porous materials. Although the variety of counter cations directly included in the cage germanoxane synthesis is limited, this study demonstrates that other tetraalkylammonium cations can be introduced by cation exchange in both discrete and cross-linked states. Tetraethylammonium (TEA) of a discrete cage germanoxane was replaced with tetrabutylammonium (TBA) in an organic solvent, which provides another starting material. TEA and TBA cations in cross-linked networks formed by hydrosilylation reactions of dimethylvinylsilylated cage germanoxanes with various oligosiloxanes as linkers were exchanged with tetramethylammonium (TMA) cations. The variation in the pore volume, which depends on the type of introduced counter cations and oligosiloxane linkers, is verified. In terms of bottom-up synthesis of nanoporous materials from cage-type germanoxanes, the selection of both the counter cation and cross-linker is important to vary the porosity.

Double-Decker Silsesquioxanes Self-Assembled in One-Dimensional Coordination Polymeric Nanofibers with Emission Properties

The urgent needs for photoactive materials in industry drive fast evolution of synthetic procedures in many branches of chemistry, including the chemistry of silsesquioxanes. Here, we disclose an effective protocol for the synthesis of novel double-decker silsesquioxanes decorated with two (styrylethynylphenyl)terpyridine moieties (DDSQ_Ta-b). The synthesis strategy involves a series of silylative and Sonogashira coupling reactions and is reported for the first time. DDSQ_Ta-b were employed as nanocage ligands to promote self-assembly in the presence of transition metals (TM), i.e., Zn2+, Fe2+, and Eu3+ ions, to form one-dimensional (1D) coordination polymeric nanofibers. Additionally, ultraviolet-promoted and reversible E-Z isomerization of the C═C bond within the ligand structures may be exploited to tune their emission properties. These findings render such complexes promising candidates for applications in materials chemistry. This is the first example of 1D coordination polymers bearing DDSQ-based nodes with TM ions.

Porous silsesquioxane cage and porphyrin nanocomposites: sensing and adsorption for heavy metals and anions

A porous silsesquioxane cage/porphyrin nanocomposite was designed as a dual fluorescent probe for the sensing and adsorption of both heavy metal ions and anions.

Modeling of Hydrogen Storage Utilizing Silsesquioxane Cages: Adsorption and Quasi-Dynamic Simulations of Encapsulation of H2 Molecule into Silsesquioxane Cages

Solid-state hydrogen storage may be the only promising way for mobile applications of hydrogen energy since it is safe, quickly reversible, cost-efficient, and has a high volumetric energy density under standard conditions. Silsesquioxane and its derivatives seem well suited for solid-state hydrogen storage and have attracted many experimental and theoretical researchers. In the present work, we have systematically studied four cages of T8, T10, and T12 (D_2d and D_6h) for hydrogen storage including adsorption and encapsulation of hydrogen molecules. We find that silsesquioxane cages have up to about 4150 m²/g specific surface area (SSA) and 7.81 wt % for hydrogen storage. These calculated values are comparable to the highest hydrogen storage values of metal-organic frameworks, porous polymer networks, and covalent organic frameworks. In addition, we use the quasi-dynamic method to study the encapsulation of hydrogen molecules into these cages because of the timescale limitation of ab initio molecular dynamics. Thermodynamic parameters such as enthalpy and Gibbs free energy at different temperatures are calculated during the insertion processes. We find that the insertion process of a hydrogen molecule into the T12 (D_6h) cage is almost energy-conserved and its energy barriers of enthalpy and free energy are moderate under standard conditions.

Porous Aromatic Frameworks (PAFs)

Porous aromatic frameworks (PAFs) represent an important category of porous solids. PAFs possess rigid frameworks and exceptionally high surface areas, and, uniquely, they are constructed from carbon-carbon-bond-linked aromatic-based building units. Various functionalities can either originate from the intrinsic chemistry of their building units or are achieved by postmodification of the aromatic motifs using established reactions. Specially, the strong carbon-carbon bonding renders PAFs stable under harsh chemical treatments. Therefore, PAFs exhibit specificity in their chemistry and functionalities compared with conventional porous materials such as zeolites and metal organic frameworks. The unique features of PAFs render them being tolerant of severe environments and readily functionalized by harsh chemical treatments. The research field of PAFs has experienced rapid expansion over the past decade, and it is necessary to provide a comprehensive guide to the essential development of the field at this stage. Regarding research into PAFs, the synthesis, functionalization, and applications are the three most important topics. In this thematic review, the three topics are comprehensively explained and aptly exemplified to shed light on developments in the field. Current questions and a perspective outlook will be summarized.

Metalated-bipyridine-based porous hybrid polymers with POSS-derived Si–OH groups for synergistic catalytic CO2 fixation

ZnBr₂ metalated-bipyridine porous hybrid polymers with POSS-derived Si–OH as “all-in-one” heterogeneous catalysts for synergistic catalytic CO₂ fixation.

Diphenylphosphine-Substituted Ferrocene/Silsesquioxane-Based Hybrid Porous Polymers as Highly Efficient Adsorbents for Water Treatment

The study describes the synthesis of two porous hybrid polymers (abbreviated as DPPF-HPP and DPPOF-HPP) from the Friedel-Crafts reaction of octavinylsilsesquioxane with 1,1'-bis(diphenylphosphine)ferrocene (DPPF) and 1,1'-bis(diphenylphosphine oxide)ferrocene (DPPOF), respectively. DPPF-HPP and DPPOF-HPP possess surface areas of about 890 and 780 m² g^-1, respectively, as well as similar pore structures of the coexisting micropores and mesopores. They are excellent materials for high adsorption of different dyes with adsorption capacities of 2280 mg g^-1 for Congo Red and 1440 mg g^-1 for Crystal Violet. DPPF-HPP also shows a strong affinity to adsorb Hg²⁺ ions (300 mg g^-1). These materials show no sign of degradation under repeated cycles and thus offer potential for wastewater treatment.

Porous networks based on iron(ii) clathrochelate complexes

Microporous networks based on boronate ester-capped iron(ii) clathrochelate complexes are described. The networks were obtained by covalent cross-linking of tetrabrominated clathrochelate complexes via Suzuki-Miyaura polycross-coupling reactions with diboronic acids, or by Sonogashira-Hagihara polycross-coupling of clathrochelate complexes with terminal alkyne functions and 1,3,5-tribromobenzene. The networks display permanent porosity with apparent Brunauer-Emmett-Teller surface areas of up to SABET = 593 m2 g-1. A clathrochelate complex based on an enantiopure dioximato ligand was used to prepare chiral networks. One of these networks was shown to preferentially absorb d-tryptophan over l-tryptophan.

Constructing POSS and viologen-linked porous cationic frameworks induced by the Zincke reaction for efficient CO2 capture and conversion

POSS and viologen-linked porous cationic frameworks were constructed via the Zincke reaction towards efficient CO₂ capture and conversion under ambient conditions.

Fluorescence-Tuned Polyhedral Oligomeric Silsesquioxane-Based Porous Polymers

Two series of new polyhedral oligomeric silsesquioxane (POSS)-based fluorescent hybrid porous polymers, HPP-1 and HPP-2, have been prepared by the Heck reaction of octavinylsilsesquioxane with 2,2',7,7'-tetrabromo-9,9'-spirobifluorene and 1,3,6,8-tetrabromopyrene, respectively. Three sets of reaction conditions were employed to assess their effect on fluorescence. These materials exhibit tunable fluorescence from nearly no fluorescence to bright fluorescence both in the solid state and dispersed in ethanol under UV light irradiation by simply altering the reaction conditions. We speculated that the difference may be attributable to the fluorescence quenching induced by Et3 N, P(o-CH3 Ph)3 , and their hydrogen bromide salts employed in the reactions. This finding could give valuable suggestions for the construction of porous polymers with tunable/controllable fluorescence, especially those prepared by Heck and Sonogashira reactions in which these quenchers are used as organic bases or co-catalysts. In addition, the porosities can also be tuned, but different trends in porosity have been found in these two series of polymers, which suggests that various factors should be carefully considered in the preparation of porous polymers with tunable/controllable porosity. Furthermore, HPP-1 c showed moderate CO2 uptake and fluorescence that was efficiently quenched by nitroaromatic explosives, thereby indicating that these materials could be utilized as solid absorbents for the capture and storage of CO2 and as sensing agents for the detection of explosives.

Amine post-functionalized POSS-based porous polymers exhibiting simultaneously enhanced porosity and carbon dioxide adsorption properties

We provide a possibility for post-synthetic amine functionalization of porous polymers exhibiting enhanced CO₂ capacity and selectivity without compromising the porosity.

Preparation and preliminary application of 5-HMF@SiO2 micro-particles

We report an organic–inorganic hybrid composite of surface-modified silica gel with 5-hydroxymethylfurfural, which provided a new promising stationary phase for protein separation.

Controllable intramolecular interaction of 3D arranged π-conjugated luminophores based on a POSS scaffold, leading to highly thermally-stable and emissive materials

This manuscript describes the inorganic cubic core as an advantageous scaffold for realizing solid-state emissive materials with high thermal stability.

Construction of porous cationic frameworks by crosslinking polyhedral oligomeric silsesquioxane units with N-heterocyclic linkers

In fields of materials science and chemistry, ionic-type porous materials attract increasing attention due to significant ion-exchanging capacity for accessing diversified applications. Facing the fact that porous cationic materials with robust and stable frameworks are very rare, novel tactics that can create new type members are highly desired. Here we report the first family of polyhedral oligomeric silsesquioxane (POSS) based porous cationic frameworks (PCIF-n) with enriched poly(ionic liquid)-like cationic structures, tunable mesoporosities, high surface areas (up to 1,025 m(2) g(-1)) and large pore volumes (up to 0.90 cm(3) g(-1)). Our strategy is designing the new rigid POSS unit of octakis(chloromethyl)silsesquioxane and reacting it with the rigid N-heterocyclic cross-linkers (typically 4,4'-bipyridine) for preparing the desired porous cationic frameworks. The PCIF-n materials possess large surface area, hydrophobic and special anion-exchanging property, and thus are used as the supports for loading guest species PMo10V2O40(5-); the resultant hybrid behaves as an efficient heterogeneous catalyst for aerobic oxidation of benzene and H2O2-mediated oxidation of cyclohexane.

New mono- and diethynylsiloxysilsesquioxanes--efficient procedures for their synthesis

Ethynyl-substituted siloxysilsesquioxanes are promising building blocks for a wide range of substances based on a POSS/DDSQ core, especially for (oligo-)polymer syntheses and modifications (the formation of hybrid materials with interesting photophysical and mechanical properties). In this study, we report on a series of new mono- and diethynylsiloxysilsesquioxanes formed via an efficient and highly selective one-pot process from silsesquioxanes with reactive Si-OH groups based on sequential condensation, hydrolysis, chlorination and substitution reactions. All newly synthesized compounds were isolated and characterized by spectroscopic methods.

A novel pH-responsive POSS-based nanoporous luminescent material derived from brominated distyrylpyridine and octavinylsilsesquioxane

A novel porous material is prepared by octavinylsilsesquioxane and brominated distyrylpyridine via the Heck coupling reaction, which exhibits an excellent pH-responsive property in the pH range from 1 to 4.

Hybrid nanoporous polystyrene derived from cubic octavinylsilsesquioxane and commercial polystyrene via the Friedel–Crafts reaction

A series of POSS-based nanoporous materials were prepared from commercial polystyrene and octavinylsilsesquioxane via the Friede–Crafts reaction.

Octavinylsilsesquioxane-based luminescent nanoporous inorganic–organic hybrid polymers constructed by the Heck coupling reaction

A class of luminescent nanoporous inorganic–organic hybrid polymers has been synthesized by the Heck coupling of octavinylsilsesquioxane with aromatic bromide monomers. The resulting materials exhibit porous and luminescent features, and show picric acid sensing behaviour.

POSS-based luminescent porous polymers for carbon dioxide sorption and nitroaromatic explosives detection

Luminescent porous polymers based on octavinylsilsequioxane and triphenylamine units show tunable porosity and luminescence, a moderate uptake of CO₂ and high sensitivity for TNT.

Constructing hybrid porous polymers from cubic octavinylsilsequioxane and planar halogenated benzene

Hybrid porous polymers derived from cubic octavinylsilsequioxane and planar halogenated benzene monomers exhibit high thermal stability, tunable porosities and potential applications in carbon dioxide storage.

Organic-inorganic hybrid supermicroporous iron(III) phosphonate nanoparticles as an efficient catalyst for the synthesis of biofuels

Here we report a novel family of crystalline, supermicroporous iron(III) phosphonate nanomaterials (HFeP-1-3, HFeP-1-2, and HFeP-1-4) with different Fe(III)-to-organophosphonate ligand mole ratios. The materials were synthesized by using a hydrothermal reaction between benzene-1,3,5-triphosphonic acid and iron(III) chloride under acidic conditions (pH ≈ 4.0). Powder X-ray diffraction, N2 sorption, transmission and scanning electron microscopy (TEM and SEM) image analysis, thermogravimetric and differential thermal analysis (TGA-DTA), and FTIR spectroscopic tools were used to characterize the materials. The triclinic crystal phase [P1(2) space group] of the hybrid iron phosphonate was established by a Rietveld refinement of the PXRD analysis of HFeP-1-3 by using the MAUD program. The unit cell parameters are a = 8.749(1), b = 8.578(1), c = 17.725(3) Å; α = 104.47(3), β = 97.64(1), γ = 113.56(3)°; and V = 1013.41 Å(3). With these crystal parameters, we proposed an 24-membered-ring open framework structure for HFeP-1. Compound HFeP-1-3, with an starting Fe/ligand molar ratio of 3.0, shows the highest Brunauer-Emmett-Telller (BET) surface area of 556 m(2) g(-1) and uniform supermicropores of approximately 1.1 nm. The acidic surface of the porous iron(III) phosphonate nanoparticles was used in a highly efficient and recyclable catalytic transesterification reaction for the synthesis of biofuels under mild reaction conditions.

Conceptual design of large surface area porous polymeric hybrid media based on polyhedral oligomeric silsesquioxane precursors: preparation, tailoring of porous properties, and internal surface functionalization

We report on the preparation of hybrid, organic-inorganic porous materials derived from polyhedral oligomeric vinylsilsesquioxanes (vinylPOSS) via a single-step molding process. The monolithic, large surface area materials are studied with a particular focus on morphology and porous properties. Radical vinyl polymerization of the nanometer-sized POSS building blocks is therefore utilized via a thermally initiated route and in porogenic diluents such as tetrahydrofuran and polyethylene glycols of varying composition. Careful choice of these porogenic solvents and proper choice of initiator concentration lead to highly porous monolithic building entities which show a rigid, 3D-adhered, porous structure, macroscopically adapting the shape of a given mold. The described materials reflect Brunauer-Emmett-Teller (BET) surface areas of 700 m2/g or more and maximum tunable mesopore volumes of up to 2 cm3/g. Experimental investigations demonstrate the option to tailor nanoporosity and macroporosity in the single-step free-radical polymerization process. While studies on the influence of the used porogenic solvents reveal tuneability of pore sizes due to the unique pore formation process, tailored existence of residual vinyl groups allows facile postpolymerization modification of the highly porous, large surface area hybrid materials exploited via thiol-ene "click" chemistry. Our developed, simply realizable preparation process explores a new route to derive porous organic-inorganic hybrid adsorbents for a wide variety of applications such as extraction, separation science, and catalysis.