Microporous polymers (MOPs) belong to a relatively new class of polymers that could find applications in gas separation processes, both as adsorbents and as polymer membranes. These polymers are ...constructed from purely organic building blocks by covalent bonds. It is possible to synthesize them by a range of different reactions that are either catalyzed with or without metal centers. Recently, these polymers have been researched in detail as potential sorbents, or membrane materials for a separation of CO2 from flue gas. Both adsorption driven and membrane driven separation of CO2 from flue gas could offer more cost effective alternatives to the methods currently in use. Here, we review recent papers and present our view on the opportunities and challenges when it comes to the use of MOPs in carbon capture and storage (CCS).
In general, the post-combustion capture of CO2 is costly; however, swing adsorption processes can reduce these costs under certain conditions. This review highlights the issues related to ...adsorption-based processes for the capture of CO2 from flue gas. In particular, we consider studies that investigate CO2 adsorbents for vacuum swing or temperature swing adsorption processes. Zeolites, carbon molecular sieves, metal organic frameworks, microporous polymers, and amine-modified sorbents are relevant for such processes. The large-volume gas flows in the gas flue stacks of power plants limit the possibilities of using regular swing adsorption processes, whose cycles are relatively slow. The structuring of CO2 adsorbents is crucial for the rapid swing cycles needed to capture CO2 at large point sources. We review the literature on such structured CO2 adsorbents. Impurities may impact the function of the sorbents, and could affect the overall thermodynamics of power plants, when combined with carbon capture and storage. The heat integration of the adsorption-driven processes with the power plant is crucial in ensuring the economy of the capture of CO2, and impacts the design of both the adsorbents and the processes. The development of adsorbents with high capacity, high selectivity, rapid uptake, easy recycling, and suitable thermal and mechanical properties is a challenging task. These tasks call for interdisciplinary studies addressing this delicate optimization process, including integration with the overall thermodynamics of power plants.
Microporous materials such as zeolites, metal organic frameworks, activated carbons and aluminum phosphates are suitable for catalysis and separation applications. These high surface area materials ...are invariably produced in particulate forms and need to be transformed into hierarchically porous structures for high performance adsorbents or catalysts. Structuring of porous powders enables an optimized structure with high mass transfer, low pressure drop, good heat management, and high mechanical and chemical stability. The requirements and important properties of hierarchically porous structures are reviewed with a focus on applications in gas separation and catalysis. Versatile powder processing routes to process porous powders into hierarchically porous structures like extrusion, coatings of scaffolds and honeycombs, colloidal processing and direct casting, and sacrificial approaches are presented and discussed. The use and limitations of the use of inorganic binders for increasing the mechanical strength is reviewed, and the most important binder systems, e.g. clays and silica, are described in detail. Recent advances to produce binder-free and complex shaped hierarchically porous monoliths are described and their performance is compared with traditional binder-containing structured adsorbents. Needs related to better thermal management and improved kinetics and volume efficiency are discussed and an outlook on future research is also given.
Predictions of future climate change have triggered a search for ways to reduce the release of greenhouse gases into the atmosphere. Carbon capture and storage (CCS) assists this goal by reducing ...carbon dioxide emissions, and CO
2
adsorbents in particular can reduce the costs of CO
2
capture. Here, we review the nanoscale sorbent materials that have been developed and the theoretical basis for their function in CO
2
separation, particularly from N
2
-rich flue gases.
Here, we review the nanoscale sorbent materials that have been developed and the theoretical basis for their function in CO
2
separation, particularly from N
2
-rich flue gases.
Calcium orthophosphates (CaPs) are important in geology, biomineralization, animal metabolism and biomedicine, and constitute a structurally and chemically diverse class of minerals. In the case of ...dicalcium phosphates, ever since brushite (CaHPO
·2H
O, dicalcium phosphate dihydrate, DCPD) and monetite (CaHPO
, dicalcium phosphate, DCP) were first described in 19
century, the form with intermediary chemical formula CaHPO
·H
O (dicalcium phosphate monohydrate, DCPM) has remained elusive. Here, we report the synthesis and crystal structure determination of DCPM. This form of CaP is found to crystallize from amorphous calcium hydrogen phosphate (ACHP) in water-poor environments. The crystal structure of DCPM is determined to show a layered structure with a monoclinic symmetry. DCPM is metastable in water, but can be stabilized by organics, and has a higher alkalinity than DCP and DCPD. This study serves as an inspiration for the future exploration of DCPM's potential role in biomineralization, or biomedical applications.
Sustainable composite materials, including carnauba wax, can store energy in the form of latent heat, and containing the wax may allow form-stable melting and crystallization cycles to be performed. ...Here, it is shown that carnauba wax in the molten state and the abundant nanoclay montmorillonite form stable composites with mass ratios of 50-70% (
/
). Transmission electron microscopy analysis reveals the inhomogeneous distribution of the nanoclay in the wax matrix. Analyses with infrared and multinuclear solid-state nuclear magnetic resonance (NMR) spectroscopy prove the chemical inertness of the composite materials during preparation. No new phases are formed according to studies with powder X-ray diffraction. The addition of the nanoclay increases the thermal conductivity and prevents the leakage of the phase change material, as well as reducing the time intervals of the cycle of accumulation and the return of heat. The latent heat increases in the row 69.5 ± 3.7 J/g, 95.0 ± 2.5 J/g, and 107.9 ± 1.7 J/g for the composite materials containing resp. 50%, 60% and 70% carnauba wax. Analysis of temperature-dependent
C cross-polarization solid-state NMR spectra reveal the enhanced amorphization and altered molecular dynamics of the carnauba wax constituents in the composite materials. The amorphization also defines changes in the thermal transport mechanism in the composites compared to pure wax at elevated temperatures.
Water as the Key to Proto-Aragonite Amorphous CaCO3 Farhadi-Khouzani, Masoud; Chevrier, Daniel M.; Zhang, Peng ...
Angewandte Chemie (International ed.),
July 4, 2016, Letnik:
55, Številka:
28
Journal Article
Recenzirano
Temperature and pH value can affect the short‐range order of proto‐structured and additive‐free amorphous calcium carbonates (ACCs). Whereas a distinct change occurs in proto‐vaterite (pv) ACC above ...45 °C at pH 9.80, proto‐calcite (pc) ACC (pH 8.75) is unaffected within the investigated range of temperatures (7–65 °C). IR and NMR spectroscopic studies together with EXAFS analysis showed that the temperature‐induced change is related to the formation of proto‐aragonite (pa) ACC. The data strongly suggest that the binding of water molecules induces dipole moments across the carbonate ions in pa‐ACC as in aragonite, where the dipole moments are due to the symmetry of the crystal structure. Altogether, a (pseudo‐)phase diagram of the CaCO3 polyamorphism in which water plays a key role can be formulated based on variables of state, such as the temperature, and solution parameters, such as the pH value.
The binding of water molecules above 45 °C at pH 9.80 induces dipole moments across carbonate ions in proto‐aragonite amorphous CaCO3 as in the anhydrous crystalline polymorph aragonite, where the dipole moments are due to the crystal structure. This key role of water was inferred from IR (see picture) as well as NMR spectroscopy in combination with Ca K‐edge EXAFS analysis.
Abstract Microporous organic polymers that have three-dimensional connectivity stemming from monomers with tetrahedral or tetrahedron-like geometry can have high surface areas and strong ...fluorescence. There are however few examples of such polymers based on hindered biaryls, and their fluorescence has not been studied. Hypothesizing that the contortion in a hindered biphenyl moiety would modulate the optical properties of a polymer built from it, we synthesized a meta-enchained polyphenylene from a 2,2ʹ,6,6ʹ-tetramethylbiphenyl-based monomer, in which the two phenyl rings are nearly mutually perpendicular. The polymer was microporous with S BET = 495 m 2 g −1 . The polymer absorbed near-UV light and emitted blue fluorescence despite the meta-enchainment that would have been expected to break the conjugation. A related copolymer, synthesized from 2,2ʹ,6,6ʹ-tetramethylbiphenyl-based and unsubstituted biphenyl-based monomers, was microporous but not fluorescent.
Spherical mesoporous carbon (with a particle size in the range of 40–75 μm) was synthesized by nanoreplication of a hard silica template using sucrose as the carbon precursor. The mesoporous carbon ...with BET surface areas higher than 1200 m2/g was doped with N by a treatment in an aqueous solution of nitric acid and/or in a flow of gaseous ammonia. The highest N content (3.2 wt % of N in bulk) was obtained when both modification methods were combined. Complementary physicochemical characterization techniques, including scanning electron microscopy (SEM), low-temperature N2 adsorption, powder X-ray diffraction (XRD), and Raman spectroscopy revealed the morphology, structure, and textural properties of the synthesized N-loaded carbon materials. For the identification of the detailed chemical structure on the surface of the carbons, 1H, 13C, and 15N solid-state nuclear magnetic resonance (NMR) measurements were performed, and the data were supported by chemical shift calculations with accurate quantum chemistry methods and X-ray photoelectron spectroscopic (XPS) analyses. All NMR experiments were performed at natural isotope abundance. The verified experimental data clearly showed that after the introduction of the N-containing moieties by the combined methods of treatment, a high concentration of pyridinic N at the edge, and pyrrolic N being external to the edge, was achieved for the mesoporous carbon. The distributed N surface species promoted the catalytic activity in the oxidative dehydrogenation of ethylbenzene to styrene but did not significantly influence the efficiency of the carbon materials in the electrochemical reduction of nitrate ions.
Piezoelectric semiconductors have emerged as redox catalysts, and challenges include effective conversion of mechanical energy to piezoelectric polarization and achieving high catalytic activity. The ...catalytic activity can be enhanced by simultaneous irradiation of ultrasound and light, but the existing piezoelectric semiconductors have trouble absorbing visible light. A piezoelectric catalyst is designed and tested for the generation of hydrogen peroxide (H2O2). It is based on Nb‐doped tetragonal BaTiO3 (BaTiO3:Nb) and is sensitized by carbon quantum dots (CDs). The photosensitizer injects electrons into the conduction band of the semiconductor, while the piezoelectric polarization directed electrons to the semiconductor surface, allowing for a high‐rate generation of H2O2. The piezoelectric polarization field restricts the recombination of photoinduced electron–hole pairs. A production rate of 1360 µmol gcatalyst−1 h−1 of H2O2 is achieved under visible light and ultrasound co‐irradiation. Individual piezo‐ and photocatalysis yielded lower production rates. Furthermore, the CDs enhance the piezocatalytic activity of the BaTiO3:Nb. It is noted that moderating the piezoelectricity of BaTiO3:Nb via microstructure modulation influences the piezophotocatalytic activity. This work shows a new methodology for synthesizing H2O2 by using visible light and mechanical energy.
Carbon quantum dots sensitized Nb‐doped tetragonal BaTiO3 nanopiezoelectrics are considerably effective in simultaneously utilizing visible light and vibration energy, thus achieving high hydrogen peroxide yields from ethanol and water suspensions. This is because the sensitized piezoelectrics‐mediated polarization field accelerates the migration of photoinduced charge carriers.
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