Sang Hyun Je

Unprecedented high-temperature CO2 selectivity in N2-phobic nanoporous covalent organic polymers

Post-combustion CO(2) capture and air separation are integral parts of the energy industry, although the available technologies remain inefficient, resulting in costly energy penalties. Here we report azo-bridged, nitrogen-rich, aromatic, water stable, nanoporous covalent organic polymers, which can be synthesized by catalyst-free direct coupling of aromatic nitro and amine moieties under basic conditions. Unlike other porous materials, azo-covalent organic polymers exhibit an unprecedented increase in CO(2)/N(2) selectivity with increasing temperature, reaching the highest value (288 at 323 K) reported to date. Here we observe that azo groups reject N(2), thus making the framework N(2)-phobic. Monte Carlo simulations suggest that the origin of the N(2) phobicity of the azo-group is the entropic loss of N(2) gas molecules upon binding, although the adsorption is enthalpically favourable. Any gas separations that require the efficient exclusion of N(2) gas would do well to employ azo units in the sorbent chemistry.

Elemental-Sulfur-Mediated Facile Synthesis of a Covalent Triazine Framework for High-Performance Lithium–Sulfur Batteries

A covalent triazine framework (CTF) with embedded polymeric sulfur and a high sulfur content of 62 wt % was synthesized under catalyst- and solvent-free reaction conditions from 1,4-dicyanobenzene and elemental sulfur. Our synthetic approach introduces a new way of preparing CTFs under environmentally benign conditions by the direct utilization of elemental sulfur. The homogeneous sulfur distribution is due to the in situ formation of the framework structure, and chemical sulfur impregnation within the micropores of CTF effectively suppresses the dissolution of polysulfides into the electrolyte. Furthermore, the triazine framework facilitates electron and ion transport, which leads to a high-performance lithium-sulfur battery.

Charged Covalent Triazine Frameworks for CO2 Capture and Conversion

The quest for the development of new porous materials addressing both CO2 capture from various sources and its conversion into useful products is a very active research area and also critical in order to develop a more sustainable and environmentally-friendly society. Here, we present the first charged covalent triazine framework (cCTF) prepared by simply heating nitrile functionalized dicationic viologen derivatives under ionothermal reaction conditions using ZnCl2 as both solvent and trimerization catalyst. It has been demonstrated that the surface area, pore volume/size of cCTFs can be simply controlled by varying the synthesis temperature and the ZnCl2 content. Specifically, increasing the reaction temperature led to controlled increase in the mesopore content and facilitated the formation of hierarchical porosity, which is critical to ensure efficient mass transport within porous materials. The resulting cCTFs showed high specific surface areas up to 1247 m2 g-1, and high physicochemical stability. The incorporation of ionic functional moieties to porous organic polymers improved substantially their CO2 affinity (up to 133 mg g-1, at 1 bar and 273 K) and transformed them into hierarchically porous organocatalysts for CO2 conversion. More importantly, the ionic nature of cCTFs, homogeneous charge distribution together with hierarchical porosity offered a perfect platform for the catalytic conversion of CO2 into cyclic carbonates in the presence of epoxides through an atom economy reaction in high yields and exclusive product selectivity. These results clearly demonstrate the promising aspect of incorporation of charged units into the porous organic polymers for the development of highly efficient porous organocatalysts for CO2 capture and fixation.

Effect of N-substitution in naphthalenediimides on the electrochemical performance of organic rechargeable batteries

We have demonstrated that even small structural variations on the imide nitrogens of naphthalenediimides bearing identical Li-ion binding sites can cause dramatic effects in the performance of organic rechargeable batteries. In particular, naphthalenedimide dilithium salt showed excellent cycling with a capacity of 130 mA h g−1 at potentials as high as 2.5 V vs. Li/Li+.

Ordered supramolecular gels based on graphene oxide and tetracationic cyclophanes.

A new strategy to form ordered hierarchical supramolecular gels that incorporate graphene oxide (GO) sheets and cationic rigid macrocyles under mild conditions via self-assembly is demonstrated. These ordered gels are stabilized by a series of non-covalent - donor-acceptor, π-π stacking, cation-π - interactions. These theoretical studies indicate that cationic macrocycles are positioned in between GO layers with a substantial binding energy.

Systematic Investigation of the Effect of Polymerization Routes on the Gas‐Sorption Properties of Nanoporous Azobenzene Polymers

Functional-group-oriented polymerization strategies have contributed significantly to the initial development of porous polymers and have led to the utilization of several well-known organic transformations in the synthesis of these polymers. Because there are multiple polymerization routes that can be used to introduce the same chemical functionality, it is very important to demonstrate the effect of different polymerization routes on the gas-sorption properties of these chemically similar polymers. Herein, we have studied the rich chemistry of azobenzenes and synthesized four chemically similar nanoporous azobenzene polymers (NABs) with surface areas of up to 1021 m(2)  g(-1) . The polymerization routes have a significant impact on the pore-size distributions of the NABs, which directly affects the temperature dependence of the CO2 /N2 selectivity. A pore-width maximum of 6-8 Å, narrow pore-size distribution, and small particle size (20-30 nm) were very critical for high CO2 /N2 selectivity and N2 phobicity, which is associated with azo linkages and realized at warm temperatures. Our findings collectively suggest that an investigation of different polymerization routes for the same chemical functionalization is critical to understand fully the combined effect of textural properties, local environment, and chemical functionalization on the gas-sorption properties of nanoporous polymers.

Bottom-up synthesis of fully sp2 hybridized three-dimensional microporous graphitic frameworks as metal-free catalysts

We report on the bottom-up synthesis of a fully sp2-hybridized nitrogenated three-dimensional microporous graphitic framework (3D-MGF) starting from a highly preorganized, saddle-shaped tetraphenylene derivative under ionothermal reaction conditions. The 3D-MGF showed high stability and a surface area of 928 m2 g−1 along with a narrow pore size distribution. Our approach enabled template-free inclusion of the third dimension into the graphitic frameworks while retaining π-conjugation and conductivity, which was verified by their activity as metal-free electrocatalysts for the hydrogen evolution reaction.