Xiaofei Jing

Targeted Synthesis of a Porous Aromatic Framework with High Stability and Exceptionally High Surface Area

Porous materials have been of intense scientific and technological interest because of their vital importance in many applications such as catalysis, gas separation, and gas storage. Great efforts in the past decade have led to the production of highly porous materials with large surface areas. In particular, the development of metal–organic frameworks (MOFs) has been especially rapid. Indeed, the highest surface area reported to date is claimed for a recently reported MOF material UMCM-2, which has a N2 uptake capacity of 1500 cm g at saturation, from which a Langmuir surface area of 6060 m g (Brunauer–Emmett–Teller (BET) surface area of 5200 m g) can be derived. Unfortunately, the high-surface-area porous MOFs usually suffer from low thermal and hydrothermal stabilities, which severely limit their applications, particularly in industry. These low stability issues could be resolved by replacing coordination bonds with stronger covalent bonds, as observed in covalent organic frameworks (COFs) or porous organic polymers. However, the COFs and porous organic polymers reported to date have lower surface areas compared to MOFs; the highest reported surface area for a COF is 4210 m g (BET) in COF103. Thus, further efforts are required to explore various strategies to achieve higher surface areas in COFs. Herein, we present a strategy that has enabled us to achieve, with the aid of computational design, a structure that possesses by far the highest surface area reported to date, as well as exceptional thermal and hydrothermal stabilities. We report the synthesis and properties of a porous aromatic framework PAF-1, which has a Langmuir surface area of 7100 m g. Besides its exceptional surface area, PAF-1 outperforms highly porous MOFs in thermal and hydrothermal stabilities, and demonstrates high uptake capacities for hydrogen (10.7 wt % at 77 K, 48 bar) and carbon dioxide (1300 mgg 1 at 298 K, 40 bar). Moreover, the super hydrophobicity and high surface area of PAF-1 result in unprecedented uptake capacities of benzene and toluene vapors at room temperature. It is well known that one of the most stable compounds in nature is diamond, in which each carbon atom is tetrahedrally connected to four neighboring atoms by covalent bonds (Figure 1a). Conceptually, replacement of the C C covalent bonds of diamond with rigid phenyl rings should not only retain a diamond-like structural stability but also allow sufficient exposure of the faces and edges of phenyl rings with the expectation of increasing the internal surface areas. By employing a multiscale theoretical method, which

Gas storage in porous aromatic frameworks (PAFs)

A series of porous aromatic frameworks (PAFs) were synthesized via a Yamamoto-type Ullmann reaction containing quadricovalent Si (PAF-3) and Ge (PAF-4). These PAFs are thermally stable up to 465 °C for PAF-3 and 443 °C for PAF-4, corresponding to a 5% weight loss according to the TG pattern. As PAF-1, they exhibit high surface areas (up to 2932 m2 g−1) and excellent adsorption ability to hydrogen, methane and carbon dioxide. Low pressure gas uptake experiments on PAFs show PAF-3 has the highest heat of adsorption (Qst) of hydrogen (6.6 kJ mol−1) and carbon dioxide (19.2 kJ mol−1), while PAF-4 has the highest Qst for methane adsorption (23.2 kJ mol−1) among PAFs. Gas molecule recognition at 273 K was performed and results show only greenhouse gases such as carbon dioxide and methane could be adsorbed onto PAFs.

Targeted synthesis of a porous aromatic framework with a high adsorption capacity for organic molecules

Tetrakis(4-bromophenyl)methane (TBPM) as a tetrahedral unit and a diboronic acid as a linker were selected to couple the phenyl rings into a porous aromatic framework, PAF-11. PAF-11 was polymerized via a Suzuki coupling reaction. A TG analysis showed that PAF-11 is thermally stable up to 400 °C in air. PAF-11 also has a high chemical stability and cannot be dissolved or decomposed in common solvents or concentrated hydrochloric acid. A N2 sorption measurement on activated PAF-11 revealed a surface area of 952 m2 g−1 in the Langmuir model. PAF-11 also shows a considerable adsorption capacity for H2. Interestingly, PAF-11 is a highly hydrophobic material but with a high methanol uptake (654 mg g−1 at saturated vapour pressure and room temperature). PAF-11 also exhibits high adsorption abilities for small aromatic molecules such as benzene and toluene (874 and 780 mg g−1, respectively, at saturated vapour pressure and room temperature) due to its aromatic framework. This ability of PAF-11 could be very useful to eliminate harmful small aromatic molecules produced by industry.

Synthesis of a porous aromatic framework for adsorbing organic pollutants application

Porous organic frameworks (POFs) have attracted considerable attention due to their high surface areas and good mechanical properties. A series of vivid characteristics in POFs, such as their plentiful phenyl rings texture, their high surface area, uniform pore size distribution and permanent porosity, make themselves suitable adsorbents to adsorb organic pollutants. To synthesize a new porous aromatic framework being composed of only phenyl rings, a monomer 1,3,5-tris(4-bromophenyl)benzene was employed. PAF-5 has been synthesized successfully using the Yamamoto-type Ullmann reaction. This material was characterized by Fourier transform infrared spectroscopy (FT-IR), 13C solid-state NMR, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and N2 gas sorption. PAF-5 displaying high stability and high surface area exhibits excellent abilities to adsorb organic chemical pollutants at saturated vapour pressure and room temperature.

Facile synthesis of cost-effective porous aromatic materials with enhanced carbon dioxide uptake

Porous aromatic frameworks (PAF-32s) derived from tetrahedral monomers as basic building units have been successfully synthesized via the Friedel–Crafts alkylation reaction in the presence of the inexpensive catalyst FeCl3. The resulting PAF-32 materials possess high stabilities and high surface areas up to 1679 m2 g−1. In particular, amino and hydroxyl functional groups have been introduced into the networks. The corresponding functionalized PAF materials (PAF-32-NH2 and PAF-32-OH) display enhanced CO2 adsorption capacities and higher heats of adsorption (Qst) than the non-functionalized PAF-32.

Targeted Synthesis of Porous Aromatic Frameworks and their Composites for Versatile, Facile, Efficacious, and Durable Antibacterial Polymer Coatings

Novel quaternary pyridinium-type porous aromatic frameworks, PAF-50, and their composites, AgCl-PAF-50, have been synthesized to effectively and efficiently inhibit the growth of bacteria. Most importantly, both PAF-50 and AgCl-PAF-50 have excellent compatibility with conventional polymers, which lead to great operation flexibility and versatility for antibactrial coatings on various medical devices simply via solution or spray coating.

Microwave-assisted crystallization inclusion of spiropyran molecules in indium trimesate films with antidromic reversible photochromism

An indium trimesate metal–organic framework (JUC-120) which possesses a cubic zeolitic MTN topology, as a new analogue to MIL-100(Al, Fe or Cr) compounds, has been successfully synthesized. Its structure exhibits a mesoporous cage (26 A) and high thermal stability. The assembly of nitrobenzospiropyran derivatives (BSP) into JUC-120 nanocrystals (BSP/JUC-120) is achieved by a microwave-assisted crystallization inclusion approach. The BSP/JUC-120 films have been prepared on quartz wafers by a spin-coating method. The successful encapsulation of BSP molecules into the mesopores of the JUC-120 structure has been verified by N2 adsorption and TGA measurements. The photochromic properties of BSP/JUC-120 films are studied by the UV-Vis and fluorescence spectroscopies. More interestingly, metastable open merocyanine (OMC) species are directly generated from the closed spiropyran form (CSP) without photoirradiation and stabilized for a long period in the BSP/JUC-120 film. The open merocyanine isomer bleaches to the closed spiropyran form by ultraviolet or visible light, and the coloration is regained upon standing in the dark, exhibiting antidromic photochromism. Moreover, the BSP/JUC-120 film shows high reversibility and thermal stability of photochromism. This highly efficient MOF film is expected to be promising in the applications of optical devices.

The Adsorption and Simulated Separation of Light Hydrocarbons in Isoreticular Metal-Organic Frameworks Based on Dendritic Ligands with Different Aliphatic Side Chains

Three isoreticular metal-organic frameworks, JUC-100, JUC-103 and JUC-106, were synthesized by connecting six-node dendritic ligands to a [Zn4O(CO2)6] cluster. JUC-103 and JUC-106 have additional methyl and ethyl groups, respectively, in the pores with respect to JUC-100. The uptake measurements of the three MOFs for CH4, C2H4, C2H6 and C3H8 were carried out. At 298 K, 1 atm, JUC-103 has relatively high CH4 uptake, but JUC-100 is the best at 273 K, 1 atm. JUC-100 and JUC-103 have similar C2H4 absorption ability. In addition, JUC-100 has the best absorption capacity for C2H6 and C3H8. These results suggest that high surface area and appropriate pore size are important factors for gas uptake. Furthermore, ideal adsorbed solution theory (IAST) analyses show that all three MOFs have good C3H8/CH4 and C2H6/CH4 selectivities for an equimolar quaternary CH4/C2H4/C2H6/C3H8 gas mixture maintained at isothermal conditions at 298 K, and JUC-106 has the best C2H6/CH4 selectivity. The breakthrough simulations indicate that all three MOFs have good capability for separating C2 hydrocarbons from C3 hydrocarbons. The pulse chromatographic simulations also indicate that all three MOFs are able to separate CH4/C2 H4/C2H6/C3H8 mixture into three different fractions of C1, C2 and C3 hydrocarbons.

Sensitive detection of hazardous explosives via highly fluorescent crystalline porous aromatic frameworks

A three-dimensional (3D) porous aromatic framework (PAF-14) with high fluorescence quantum yield was synthesized from luminescent monomer of tetra(4-dihydroxyborylphenyl)germanium (TBPGe) building blocks. The powder X-ray diffraction (PXRD) analysis of the experimental and simulated patterns indicate that PAF-14 is highly crystalline with ctn topology. The Argon sorption measurement indicates that PAF-14 possesses high surface area (Brunauer Emmet Teller surface area: 1288 m2 g−1). Significantly, the introduction of germanium into PAF-14 skeletons may bring about a low-lying lowest unoccupied molecular orbital (LUMO) and the crystalline polymeric backbones enhance the sensitivity of electron delocalization. Therefore the designed PAF-14 exhibits high fluorescence quenching ability for hazardous explosives, such as nitrobenzene, 2,4-DNT (2,4-dinitrotoluene) and TNT (2,4,6-trinitrotoluene).