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  • 1. Nugroho, Ferry A. A.
    et al.
    Xu, Chao
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Langhammer, Christoph
    UV-Visible and Plasmonic Nanospectroscopy of the CO2 Adsorption Energetics in a Microporous Polymer2015In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 87, no 20, p. 10161-10165Article in journal (Refereed)
    Abstract [en]

    In the context of carbon capture and storage (CCS), micro- and mesoporous polymers have received significant attention due to their ability to selectively adsorb and separate CO2, from gas streams. The performance of such materials is critically dependent on the isosteric heat of adsorption (Q(st)) of CO2, directly related to the interaction strength between CO2, and the adsorbent. Here, we show using the microporous polymer PIM-1 as a model system that its Q(st) can be conveniently determined by in situ UV-vis optical transmission spectroscopy directly applied on the adsorbent or, with higher resolution, by indirect nanoplasmonic sensing based on localized surface plasmon resonance in metal nanoparticles. Taken all together, this study provides a general blueprint for efficient optical screening of micro- and mesoporous polymeric materials for CCS in terms of their CO2, adsorption energetics and kinetics.

  • 2.
    Xu, Chao
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Imine/azo-linked microporous organic polymers: Design, synthesis and applications2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Microporous organic polymers (MOPs) are porous materials. Owing to their high surface area, tunable pore sizes and high physicochemical stability, they are studied for applications including gas capture and separation and heterogeneous catalysis. In this thesis, a series of imine/azo-linked MOPs were synthesized. The MOPs were examined as potential CO2 sorbents and as supports for heterogeneous catalysis.

    The MOPs were synthesized by Schiff base polycondensations and oxidative couplings. The porosities of the imine-linked MOPs were tunable and affected by a range of factors, such as the synthesis conditions, monomer lengths, monomer ratios. All the MOPs had ultramicropores and displayed relatively high CO2 uptakes and CO2-over-N2 selectivities at the CO2 concentrations relevant for post-combustion capture of CO2. Moreover, the ketimine-linked MOPs were moderately hydrophobic, which might increase their efficiency for CO2 capture and separation.

    The diverse synthesis routes and rich functionalities of MOPs allowed further post-modification to improve their performance in CO2 capture. A micro-/mesoporous polymer PP1-2, rich in aldehyde end groups, was post-synthetically modified by the alkyl amine tris(2-aminoethyl)amine (tren). The tethered amine moieties induced chemisorption of CO2 on the polymer, which was confirmed by the study of in situ infrared (IR) and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. As a result, the modified polymer PP1-2-tren had a large CO2 capacity and very high CO2-over-N2 selectivity at low partial pressures of CO2.

    Pd(II) species were incorporated in the selected MOPs by means of complexation or chemical bonding with the imine or azo groups. The Pd(II)-rich MOPs were tested as heterogeneous catalysts for various organic reactions. The porous Pd(II)-polyimine (Pd2+/PP-1) was an excellent co-catalyst in combination with chiral amine for cooperatively catalyzed and enantioselective cascade reactions. In addition, the cyclopalladated azo-linked MOP (Pd(II)/PP-2) catalyzed Suzuki and Heck coupling reactions highly efficiently.

  • 3.
    Xu, Chao
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Afewerki, Samson
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Córdova, Armando
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    A Cyclopalladated Microporous Azo-linked Polymer as a Heterogeneous Catalyst for Eco-friendly Suzuki and Heck Coupling ReactionsManuscript (preprint) (Other academic)
  • 4.
    Xu, Chao
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bacsik, Zoltan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Adsorption of CO2 on a micro-/mesoporous polyimine modified with tris(2-aminoethyl)amine2015In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 3, no 31, p. 16229-16234Article in journal (Refereed)
    Abstract [en]

    Amine-modified sorbents are relevant to the capturing of dilute carbon dioxide from gas mixtures, and micro-/mesoporous polymers are promising substrates due to their rich chemistry. Here, we prepared an aldehyde-rich polyimine with micro- and mesoporesby a Schiff-base condensation of 1,3,5-tris(4-aminophenyl)benzene and 1,3,5-benzenetricarboxaldehyde using an excess of aldehyde. The micropores were crucial to the physisorption of CO2, while the mesopores provided space for the post-modification with tris(2-aminoethyl) amine (tren) that induced the chemisorption of CO2. The amine modified polymer showed a high uptake of CO2 at low pressures (1.13 mmol g(-1) at 0.05 bar and 273 K) and a high estimated CO2-over-N-2 selectivity (1.04 x 10(3) at 273 K for 5 v%/95 v% CO2/N-2 mixture). CO2 both physisorbed and chemisorbed on the amine-modified polyimine, which we confirmed by studying the CO2-amine chemistry using in situ FTIR spectroscopy and solid state C-13 NMR spectroscopy. Carbamic acid formed during the chemisorption of CO2, as the CO2 reacted with the amine groups. Due to the formation of carbamic acid, the isosteric heat of adsorption was high, with values up to 80 kJ mol(-1) at a low coverage of CO2. It appears that amine-modified porous polymers could be relevant to the removal of CO2 from gas streams with low concentrations.

  • 5.
    Xu, Chao
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Deiana, Luca
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Afewerki, Samson
    Incerti-Pradillos, Celia
    Córdova, Oscar
    Guo, Peng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Córdova, Armando
    Stockholm University, Faculty of Science, Department of Organic Chemistry. Mid-Sweden University, Sweden.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    The Use of Porous Palladium(II)-polyimine in Cooperatively-catalyzed Highly Enantioselective Cascade Transformations2015In: Advanced Synthesis and Catalysis, ISSN 1615-4150, E-ISSN 1615-4169, Vol. 357, no 9, p. 2150-2156Article in journal (Refereed)
    Abstract [en]

    Porous organic polymers have prospects as functional substrates for catalysis, with quite different molecular properties from inorganic substrates. Here we disclose for the first time that porous palladium(II)-polyimines are excellent catalysts for cooperatively catalyzed and enantioselective cascade reactions. In synergy with a chiral amine co-catalyst, polysubstituted cyclopentenes and spirocyclic oxindoles, including the all-carbon quaternary stereocenter, were synthesized in high yields. High diastereo- and enantioselectivities were achieved for these dynamic kinetic asymmetric transformations (DYKAT) of enals with propargylic nucleophiles.

  • 6.
    Xu, Chao
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Dinka, Ermiase
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hydrophobic Porous Polyketimines for the Capture of CO22016In: ChemPlusChem, ISSN 2192-6506, Vol. 81, no 1, p. 58-63Article in journal (Refereed)
    Abstract [en]

    A new type of porous polymers is presented. Polyketimines (PPKs) were synthesized by condensing 1,3,5-tris(4-aminophenyl)benzene with aromatic diketones usingp-toluenesulfonic acid catalyst. They were characterized by infrared spectroscopy and solid-state 13C{1H} nuclear magnetic resonance spectroscopy, and their porosities were probed through the adsorption of N2 and CO2. The PPKs had low uptakes of N2 (at −196 °C), which was attributed to diffusion limitations and/or a shrinking of the polymer. They had relatively high uptakes of CO2 (at 0 °C; up to 1.26 mmol g−1 at 0.15 bar and 2.99 mmol g−1 at 1 bar), which was related to ultramicropores (6–9 Å). The PPKs had high estimated CO2-over-N2 selectivities (30–40 at 0 °C). Studies on the vapor adsorption of water and ethanol showed the PPKs to be moderately hydrophobic and had a high uptake of ethanol at low partial pressures.

  • 7.
    Xu, Chao
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Microporous adsorbents for CO2 capture - a case for microporous polymers?2014In: Materials Today, ISSN 1369-7021, E-ISSN 1873-4103, Vol. 17, no 8, p. 397-403Article, review/survey (Refereed)
    Abstract [en]

    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).

  • 8.
    Xu, Chao
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Synthesis of microporous organic polymers with high CO2-over-N-2 selectivity and CO2 adsorption2013In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 1, no 10, p. 3406-3414Article in journal (Refereed)
    Abstract [en]

    A series of microporous organic polymers (MOPs) were synthesized by Schiff base condensation of 1,3,5-tris(4-aminophenyl)benzene and a number of dialdehyde monomers. The polymers were structurally characterized by in situ infrared and ex situ solid state C-13{H-1} nuclear magnetic resonance (NMR) spectroscopy. Synthesis conditions were optimized to enhance CO2 uptake by the MOPs. Synthesis at low temperatures results in the MOPs being linked by imine groups. Heating of the MOPs reduces the number of imine groups and after heating to >300 degrees C nitrile groups were found to be present in the MOPs. The MOPs have specific surface areas up to 614 m(2) g(-1) and narrow pore size distributions of similar to 4 to 8 angstrom. The selectivity of CO2-over-N-2 at 273 K and 1 bar was 56-77, which requires either an influence of chemisorption on CO2 or a molecular sieving (or kinetic selection) of CO2-over-N-2. The materials had also heats of adsorption typical for physisorption of CO2.

  • 9.
    Xu, Chao
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Ultramicroporous CO2 adsorbents with tunable mesopores based on polyimines synthesized under off-stoichiometric conditions2016In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 222, p. 80-86Article in journal (Refereed)
    Abstract [en]

    A series of porous polymers with ultramicropores and tunable mesopores were synthesized by condensation reaction (Schiff base) of triamine and trialdehyde monomers. They had specific surface areas and pore volumes of up to 694 m2/g and 0.67 cm3/g. The ultramicropores seemed to have been templated by the solvent (DMSO) primarily. The size of the mesopores depended strongly on the amine-to-aldehyde ratio used during synthesis. With a moderate aldehyde excess, the irregular mesopores of the porous polymers increased in size. The polymers’ capacities to adsorb CO2 were large (0.93–1.58 mmol/g at 0.15 bar and 2.20–3.28 mmol/g at 1 bar; 0 °C) due to their large ultramicropore volumes, and the estimated CO2-over-N2 selectivities were also relatively high (31-90 for CO2/N2 mixtures with 15v%/85v% at 0 °C). The uptake of CO2 on the polymers was quite rapid, and it appears advantageous to have a combination of meso- and ultramicropores in this class of polymers for applications in carbon capture and storage.

  • 10.
    Xu, Chao
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Anhui University of Technology, China.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shi, Hua-Tian
    Xina, ZhiFeng
    Zhang, Qian-Feng
    Stepwise assembly of a semiconducting coordination polymer [Cd8S(SPh)(14)(DMF)(bpy)](n) and its photodegradation of organic dyes2015In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 44, no 14, p. 6400-6405Article in journal (Refereed)
    Abstract [en]

    Chalcogenolate clusters can be interlinked with organic linkers into semiconducting coordination polymers with photocatalytic properties. Here, discrete clusters of Cd8S(SPh)(14)(DMF)(3) were interlinked with 4,4'-bipyridine into a one dimensional coordination polymer of [Cd8S(SPh)(14)(DMF)(bpy)](n) with helical chains. A stepwise mechanism for the assembly of the coordination polymer in DMF was revealed by an ex situ dynamic light scattering study. The cluster was electrostatically neutral and showed a penta-supertetrahedral structure. During the assembly each cluster was interlinked with two 4,4'-bipyridine molecules, which replaced the two terminal DMF molecules of the clusters. In their solid-state forms, the cluster and the coordination polymer were semiconductors with wide band gaps of 3.08 and 2.80 ev. They photocatalytically degraded rhodamine B and methylene blue in aqueous solutions. The moderate conditions used for the synthesis could allow for further in situ studies of the reaction-assembly of related clusters and coordination polymers.

  • 11.
    Xu, Chao
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Anhui University of Technology, People's Republic of China .
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shi, Hua-Tian
    Zhang, Qian-Feng
    A semiconducting microporous framework of Cd6Ag4(SPh)(16) clusters interlinked using rigid and conjugated bipyridines2014In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 50, no 28, p. 3710-3712Article in journal (Refereed)
    Abstract [en]

    Ternary supertetrahedral chalcogenolate clusters were interlinked with bipyridines into a microporous semiconducting framework with properties qualitatively different from those of the original clusters. Both the framework and the clusters were effective photocatalysts, and rapidly degraded the dye rhodamine B.

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