Waterborne Colloidal Polymer/Silica Hybrid Dispersions and Their Assembly into Mesoporous Poly(melamine-formaldehyde) Xerogels

The acid-catalyzed polycondensation of oligo­(melamine-formaldehyde) in aqueous phase and in the presence of silica nanoparticles leads to a stable dispersion of coexisting silica and polymer nanoparticles. The dispersion can be processed into mesoporous xerogels (<i>S</i>_BET ≈ 200 m² g^–1), whose porosity can be enhanced by etching of silica up to specific surface areas of >400 m² g^–1. The formation mechanism and the characteristics of the hybrid dispersion are crucial to the materials derived from it and analyzed in detail using a variety of experimental techniques (electron and force microscopy, light and X-ray scattering, ultracentrifugation, and spectroscopy). The transformation of the dispersion into xerogels by electrostatic destabilization is described. Furthermore, the obtained materials are characterized with regard to their porosity and morphology using microscopy and porosimetry. The impact of selected synthesis parameters on the obtained properties is discussed, and it was found (most interestingly) that stable porosity was only observed if silica nanoparticles were present within the dispersion

Versatile Postmodification of Conjugated Microporous Polymers Using Thiol-yne Chemistry

Radical thiol-yne chemistry is used for the modification of microporous networks with aliphatic alcohols. The degree of functionalization can be tuned by varying the reacted amount of thiol. Porosity analysis indicates that the microporosity can be preserved within a certain range, however, a decrease in pore size is observed

Restricted Access: On the Nature of Adsorption/Desorption Hysteresis in Amorphous, Microporous Polymeric Materials

The phenomenon of low-pressure adsorption/desorption hysteresis, which is commonly observed in microporous polymers, is investigated by detailed gas adsorption studies. Diffusional limitations by pore blocking effects, which arise as a consequence of the micropore morphology and connectivity, are discussed as the origin of the hysteresis rather than swelling effects, which have been suggested previously. Micropores with narrow openings, which cannot be filled easily, are expected to be present next to open pores. Those pores are termed restricted-access pores and are only filled in the course of the adsorption process as a consequence of the increasing solvation pressure exhibited from already filled micropores. As a consequence of the results presented here, it is suggested to use the desorption branch in addition to the adsorption branch for the extraction of the porosity characteristics, such as specific surface area, pore volume, and pore size distribution. The magnitude of the low-pressure hysteresis might hence give an idea of the micropore connectivity, which is important information for potential applications

Teaching New Tricks to an Old Indicator: pH-Switchable, Photoactive Microporous Polymer Networks from Phenolphthalein with Tunable CO₂ Adsorption Power

Switchable, organic microporous networks were synthesized by Sonogashira coupling of tetrabromophenolphthalein with 1,4-diethynylenebenzene using optimized reaction conditions. The resulting networks are microporous and have specific surface areas exceeding 800 m² g^–1. The microporosity and the pore polarity are sensitive to the pH value as evidenced by nitrogen and carbon dioxide physisorption experiments. The switching between the open and closed form of the lactone ring is reversible, but some porosity is lost throughout the process. The colored, alkaline salts of these networks are photochemically active, as shown by the effective heterogeneous photosensitization of the photopolymerization of methyl methacrylate with visible light

Enhanced Carbon Dioxide Adsorption by a Mesoporous Poly(ionic liquid)

The synthesis of a mesoporous poly­(ionic liquid) network via a hard-templating pathway is presented. Structure analysis was carried out using gas adsorption, small-angle X-ray scattering, and electron microscopy. The mesoporous poly­(ionic liquid) showed a significantly faster CO₂ adsorption than its nonporous counterpart. We found the adsorption is accompanied by strong interactions, which are also reflected in a high CO₂ over N₂ selectivity

Covalent Triazine Frameworks Prepared from 1,3,5-Tricyanobenzene

A novel covalent triazine framework (CTF-0) was prepared by trimerization of 1,3,5-tricyanobenzene in molten ZnCl₂. The monomer/ZnCl₂ ratio, the reaction time, and temperature significantly influence the structure and porosity of such networks. XRD measurements revealed that crystalline frameworks can be formed with surface areas around 500 m²·g^–1 and high CO₂ uptakes. Increasing the reaction temperature yielded an amorphous material with an enlarged surface area of 2000 m²·g^–1. This material showed good catalytic activity for CO₂ cycloaddition

Hybrid Clay: A New Highly Efficient Adsorbent for Water Treatment

New hybrid clay adsorbent based on kaolinite clay and <i>Carica papaya</i> seeds with improved cation exchange capacity (CEC), rate of heavy metal ion uptake, and adsorption capacity for heavy metal ions were prepared. The CEC of the new material is ca. 75 meq/100 g in spite of the unexpectedly low surface area (≈9 m²/g). Accordingly, the average particle size of the hybrid clay adsorbent decreased from over 200 to 100 μm. The hybrid clay adsorbent is a highly efficient adsorbent for heavy metals. With an initial metal concentration of 1 mg/L, the hybrid clay adsorbent reduces the Cd²⁺, Ni²⁺, and Pb²⁺ concentration in aqueous solution to ≤4, ≤7, and ≤20 μg/L, respectively, from the first minute to over 300 min using a fixed bed containing 2 g of adsorbent and a flow rate of ≈7 mL/min. These values are (with the exception of Pb²⁺) in line with the WHO permissible limits for heavy metal ions. In a cocktail solution of Cd²⁺, and Ni²⁺, the hybrid clay shows a reduced rate of uptake but an increased adsorption capacity. The CEC data suggest that the adsorption of Pb²⁺, Cd²⁺, and Ni²⁺ on the hybrid clay adsorbent is essentially due to ion exchange. This hybrid clay adsorbent is prepared from materials that are abundant and by a simple means that is sustainable, easily recovered from aqueous solution, nonbiodegradable (unlike numerous biosorbent), and easily regenerated and is a highly efficient alternative to activated carbon for water treatment

Effective Mercury Sorption by Thiol-Laced Metal–Organic Frameworks: in Strong Acid and the Vapor Phase

Free-standing, accessible thiol (−SH) functions have been installed in robust, porous coordination networks to provide wide-ranging reactivities and properties in the solid state. The frameworks were assembled by reacting ZrCl₄ or AlCl₃ with 2,5-dimercapto-1,4-benzenedicarboxylic acid (H₂DMBD), which features the hard carboxyl and soft thiol functions. The resultant Zr-DMBD and Al-DMBD frameworks exhibit the UiO-66 and CAU-1 topologies, respectively, with the carboxyl bonded to the hard Zr­(IV) or Al­(III) center and the thiol groups decorating the pores. The thiol-laced Zr-DMBD crystals lower the Hg­(II) concentration in water below 0.01 ppm and effectively take up Hg from the vapor phase. The Zr-DMBD solid also features a nearly white photoluminescence that is distinctly quenched after Hg uptake. The carboxyl/thiol combination thus illustrates the wider applicability of the hard-and-soft strategy for functional frameworks

Microwave-Assisted Synthesis of Defects Metal-Imidazolate-Amide-Imidate Frameworks and Improved CO₂ Capture

In this work, we report three isostructural 3D frameworks, named <b>IFP-11</b> (R = Cl), <b>IFP-12</b> (R = Br), and <b>IFP-13</b> (R = Et) (IFP = Imidazolate Framework Potsdam) based on a cobalt­(II) center and the chelating linker 2-substituted imidazolate-4-amide-5-imidate. These chelating ligands were generated <i>in situ</i> by partial hydrolysis of 2-substituted 4,5-dicyanoimidazoles under microwave (MW)-assisted conditions in DMF. Structure determination of these IFPs was investigated by IR spectroscopy and a combination of powder X-ray diffraction (PXRD) with structure modeling. The structural models were initially built up from the single-crystal X-ray structure determination of <b>IFP-5</b> (a cobalt center and 2-methylimidazolate-4-amide-5-imidate linker based framework) and were optimized by using density functional theory calculations. Substitution on position 2 of the linker (R = Cl, Br, and Et) in the isostructural <b>IFP-11</b>, <b>-12</b>, and <b>-13</b> allowed variation of the potential pore window in 1D hexagonal channels (3.8 to 1.7 Å). The potential of the materials to undergo specific interactions with CO₂ was measured by the isosteric heat of adsorption. Further, we resynthesized zinc based IFPs, namely <b>IFP-1</b> (R = Me), <b>IFP-2</b> (R = Cl), <b>IFP-3</b> (R = Br), and <b>IFP-4</b> (R = Et), and cobalt based <b>IFP-5</b> under MW-assisted conditions with higher yield. The transition from a nucleation phase to the pure crystalline material of <b>IFP-1</b> in MW-assisted synthesis depends on reaction time. <b>IFP-1</b>, <b>-3</b>, and <b>-5</b>, which are synthesized by MW-assisted conditions, showed an enhancement of N₂ and CO₂, compared to the analogous conventional electrical (CE) heating method based materials due to crystal defects