Jianhui Lan

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

Lithium‐Doped 3D Covalent Organic Frameworks: High‐Capacity Hydrogen Storage Materials

Quick on the uptake: A multiscale theoretical method predicts that the gravimetric adsorption capacities of H(2) in Li-doped covalent organic frameworks based on the building blocks shown (Li violet, H white, B pink, C green, O red, Si yellow) can reach nearly 7 % at T=298 K and p=100 bar, suggesting that these Li-doped materials are promising adsorbents for hydrogen storage.

Doping of Alkali, Alkaline-Earth, and Transition Metals in Covalent-Organic Frameworks for Enhancing CO2 Capture by First-Principles Calculations and Molecular Simulations

We use the multiscale simulation approach, which combines the first-principles calculations and grand canonical Monte Carlo simulations, to comprehensively study the doping of a series of alkali (Li, Na, and K), alkaline-earth (Be, Mg, and Ca), and transition (Sc and Ti) metals in nanoporous covalent organic frameworks (COFs), and the effects of the doped metals on CO2 capture. The results indicate that, among all the metals studied, Li, Sc, and Ti can bind with COFs stably, while Be, Mg, and Ca cannot, because the binding of Be, Mg, and Ca with COFs is very weak. Furthermore, Li, Sc, and Ti can improve the uptakes of CO2 in COFs significantly. However, the binding energy of a CO2 molecule with Sc and Ti exceeds the lower limit of chemisorptions and, thus, suffers from the difficulty of desorption. By the comparative studies above, it is found that Li is the best surface modifier of COFs for CO2 capture among all the metals studied. Therefore, we further investigate the uptakes of CO2 in the Li-doped COFs. Our simulation results show that at 298 K and 1 bar, the excess CO2 uptakes of the Li-doped COF-102 and COF-105 reach 409 and 344 mg/g, which are about eight and four times those in the nondoped ones, respectively. As the pressure increases to 40 bar, the CO2 uptakes of the Li-doped COF-102 and COF-105 reach 1349 and 2266 mg/g at 298 K, respectively, which are among the reported highest scores to date. In summary, doping of metals in porous COFs provides an efficient approach for enhancing CO2 capture.

Multiscale simulation and modelling of adsorptive processes for energy gas storage and carbon dioxide capture in porous coordination frameworks

Computational modelling is a powerful tool for the study of gas–solid interactions, and can be used both to complement experiment and design new materials. For the modelling of gas adsorption by nanoporous media, a multiscale approach can be used, in which the molecular force fields required for Grand Canonical Monte Carlo (GCMC) simulations are derived from first-principles calculations. This can result in significantly enhanced accuracy, in comparison with conventional empirical force field-based GCMC methods. In this article, we review the application of this multiscale approach to the simulation of the adsorption of hydrogen, methane and carbon dioxide in Porous Coordination Frameworks (PCFs) for the purpose of gas storage for energy transportation and Carbon Capture and Storage (CCS) technology. We also define a scheme for the design of new materials with improved adsorption performance for the storage of these gases through the combination of multiscale simulation and experimental work, and discuss some of the issues regarding gas adsorption measurement accuracy in the context of the validation of simulation results using experimental data.

High uptakes of methane in Li-doped 3D covalent organic frameworks.

By using a multiscale theoretical method, which combines the first-principles calculation and grand canonical Monte Carlo (GCMC) simulation, we studied storage capacities of methane in 3D covalent organic frameworks (COFs) and their Li-doped compounds at T = 243 and 298 K. Our results predicted that, at T = 298 K and 35 bar, the excess gravimetric capacities of COF-102 and COF-103 reach 17.72 and 16.61 wt % (corresponding to 302 and 285 cm(3) (STP)/g)), which are in good agreement with experimental data, while the excess volumetric capacities of COF-102 and COF-103 reach 127 and 108 v (STP)/v, respectively. The high methane storage capacity of the COFs can be attributed to their ultrahigh surface areas and low densities. To further enhance the methane capacity, we investigated the impact of Li-doping on the methane storage performance of the COFs. Our first-principles calculations show that the Li cation doped in the COFs can enhance the binding of methane to the substrate significantly because of the London dispersion and the induced dipole interaction, due to the strong affinity of Li cation to methane molecules. At T = 298 K and relatively low pressures (p < 50 bar), the Li-doping method nearly doubles the methane uptakes of the COFs, compared to the nondoped materials. In particular, at T = 298 K and p = 35 bar, the methane volumetric uptakes of Li-doped COF-102 and COF-103 reach 303 and 290 v (STP)/v, respectively, which is more than 2 times those in the nondoped (127 and 108 v (STP)/v). To the best of our knowledge, the Li-doped 3D COFs show the largest methane storage uptakes at room temperature to date.

Li 12 Si 60 H 60 Fullerene Composite: A Promising Hydrogen Storage Medium

By using the first-principles DFT calculations, we design a novel hydrogen storage material, Li(12)Si(60)H(60) composite, and validate its geometric stability. It is found that the adsorbed Li atoms do not cluster on the Si(60)H(60) fullerene unlike other metals such as Ti, owing to the relatively low Li-Li binding energy and the inhibition of Si-H bonds. Our results show that the Li-doping enhances the hydrogen adsorption ability of Si(60)H(60) significantly, owing to the charge transfer from the doped Li atoms to the host material and the polarization of the adsorbed H(2) molecules. By combining the first-principles calculation and grand canonical Monte Carlo simulation, we further investigate the hydrogen storage capacity of the simulation-synthesized exohedral Li(12)Si(60)H(60) composite at T = 77 K. As the vdW gap (i.e., the separation between the surfaces of two Li(12)Si(60)H(60) fullerenes) is equal to 8.2 A, the total hydrogen uptake of the square-arranged Li(12)Si(60)H(60) array reaches 12.83 wt % at p = 10 MPa, while the excess hydrogen uptake shows a maximum of 7.46 wt % at p = 6 MPa. Impressively, at T = 298 K and p = 10 MPa, the Li(12)Si(60)H(60) array still exhibits a total hydrogen uptake of 3.88 wt % at the vdW gap of 8.2 A. These results clearly indicate that the composite, Li(12)Si(60)H(60) fullerene, is a promising candidate for hydrogen storage.

Semiconducting and conducting transition of covalent-organic polymers induced by defects

The chemical doping method is often adopted to obtain metal-free conducting materials. To date, it is still a great challenge to controllably prepare metal-free semiconducting and conducting materials by tuning the inherent structure of a material. In this work, a class of novel one-dimensional (1D) covalent-organic polymer (COP) has been designed, whose cross-sections are triangular, tetragonal, pentagonal and hexagonal, and their electronic properties are explored. The tetragonal 1D COP exhibits unique phenomena in electronic properties, i.e. the tetragonal COPs with mono- or trilayer defects (odd defects) show semiconducting properties, while they become conductors for the two cases of non- or bilayer defects (even defects). This observation indicates that they comply with the characteristics of semiconducting and conducting switches induced by the odd-even defects. Therefore, we infer that for the tetragonal configuration, the odd-even defects could potentially manipulate the electrical behavior of the COP material. The discovery provides a new direction for the targeted synthesis of semiconducting and conducting materials by tuning the inherent structure of materials, which is entirely different from the chemical doping method yielding metal-free conducting materials.