Teng Ben

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.

Porous Organic Materials: Strategic Design and Structure–Function Correlation

Porous organic materials have garnered colossal interest with the scientific fraternity due to their excellent gas sorption performances, catalytic abilities, energy storage capacities, and other intriguing applications. This review encompasses the recent significant breakthroughs and the conventional functions and practices in the field of porous organic materials to find useful applications and imparts a comprehensive understanding of the strategic evolution of the design and synthetic approaches of porous organic materials with tunable characteristics. We present an exhaustive analysis of the design strategies with special emphasis on the topologies of crystalline and amorphous porous organic materials. In addition to elucidating the structure-function correlation and state-of-the-art applications of porous organic materials, we address the challenges and restrictions that prevent us from realizing porous organic materials with tailored structures and properties for useful applications.

Selective adsorption of carbon dioxide by carbonized porous aromatic framework (PAF)

A series of carbonized PAF-1s were obtained with enhanced gas storage capacities and isosteric heats of adsorption (Qst for short). Especially, PAF-1-450 can adsorb 4.5 mmol g−1 CO2 at 273 K and 1 bar. Moreover, it also exhibits excellent selectivity over other gases. On the basis of single component isotherm data, the dual-site Langmuir–Freundlich adsorption model-based ideal adsorption solution theory (IAST) prediction indicates that the CO2/N2 adsorption selectivity is as high as 209 at a 15/85 CO2/N2 ratio. Also, the CO2/CH4 adsorption selectivity is in the range of 7.8–9.8 at a 15/85 CO2/CH4 ratio at 0 < p < 40 bar, which is highly desirable for landfill gas separation. The calculated CO2/H2 adsorption selectivity is about 392 at 273 K and 1 bar for 20/80 CO2/H2 mixture. Besides, these carbonized PAF-1s possess excellent physicochemical stability. Practical applications in capture of CO2 lie well within the realm of possibility.

Ultrahigh Gas Storage both at Low and High Pressures in KOH-Activated Carbonized Porous Aromatic Frameworks

The carbonized PAF-1 derivatives formed by high-temperature KOH activation showed a unique bimodal microporous structure located at 0.6 nm and 1.2 nm and high surface area. These robust micropores were confirmed by nitrogen sorption experiment and high-resolution transmission electron microscopy (TEM). Carbon dioxide, methane and hydrogen sorption experiments indicated that these novel porous carbon materials have significant gas sorption abilities in both low-pressure and high-pressure environments. Moreover the methane storage ability of K-PAF-1-750 is among the best at 35 bars, and its low-pressure gas adsorption abilities are also comparable to the best porous materials in the world. Combined with excellent physicochemical stability, these materials are very promising for industrial applications such as carbon dioxide capture and high-density clean energy storage.

Fabrication of COF-MOF Composite Membranes and Their Highly Selective Separation of H2/CO2

The search for new types of membrane materials has been of continuous interest in both academia and industry, given their importance in a plethora of applications, particularly for energy-efficient separation technology. In this contribution, we demonstrate for the first time that a metal-organic framework (MOF) can be grown on the covalent-organic framework (COF) membrane to fabricate COF-MOF composite membranes. The resultant COF-MOF composite membranes demonstrate higher separation selectivity of H2/CO2 gas mixtures than the individual COF and MOF membranes. A sound proof for the synergy between two porous materials is the fact that the COF-MOF composite membranes surpass the Robeson upper bound of polymer membranes for mixture separation of a H2/CO2 gas pair and are among the best gas separation MOF membranes reported thus far.

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.

Electrochemical Synthesis of a Microporous Conductive Polymer Based on a Metal–Organic Framework Thin Film

A new approach to preparing 3D microporous conductive polymer has been demonstrated in the electrochemical synthesis of a porous polyaniline network with the utilization of a MOF thin film supported on a conducting substrate. The prepared porous polyaniline with well-defined uniform micropores of 0.84 nm exhibits a high BET surface area of 986 m(2) g(-1) and a high electric conductivity of 0.125 S cm(-1) when doped with I2, which is superior to existing porous conducting materials of porous MOFs, CMPs, and COFs.

Ultrahigh iodine adsorption in porous organic frameworks

We present two porous organic frameworks (POFs), PAF-1 and JUC-Z2, with ultrahigh iodine capture capacity. The iodine vapor uptake of PAF-1 and JUC-Z2 were 1.86 g g−1 and 1.44 g g−1 respectively at 298 K per 40 Pa, which is extremely high for such low pressure sorption conditions. In addition, PAF-1 and JUC-Z2 could adsorb iodine over water with the selectivity of 5.1 and 6.5 respectively. The isosteric enthalpy at zero surface coverage, calculated by a virial equation with the iodine vapor sorption isotherms at 298 K and 313 K of JUC-Z2, reached −51.1 kJ mol−1, which was much higher than the coverage of PAF-1 (−14.9 kJ mol−1). Raman measurement confirmed the polyiodide to be I5− in POFs. Furthermore, solvents with different polarities, such as n-hexane, chloroform, and methanol, were chosen to conduct iodine binding measurements on PAF-1 and JUC-Z2. The formation constant Kf for POFs in n-hexane, chloroform and methanol drastically decreased with the increase in polarity, thus illustrating the important role of solvents in iodine binding.

Molecular Rotors in Porous Organic Frameworks

Porous organic frameworks perform a variety of functions, owing to their extremely large surface areas, but the dynamics of the structural elements have never been explored. Our discovery of ultra-fast molecular rotors (10(6)  Hz at 225 K) in their architectures allows us to look at them from a new perspective. The constructive elements are robust struts and rapid rotors, resulting in a dynamic material whose motion can be frozen or released at will. The rotational motion can be actively regulated in response to guests. As the temperature is increased, the rotors spin ever faster, approaching free-rotational diffusion at 550 K. The unusual combination of remarkable nanoporosity with fast dynamics is intriguing for engineering oscillating dipoles and producing responsive materials with switchable ferroelectricity, and for applications spanning from sensors to actuators, which capture and release chemicals on command.