Docking Strategy To Construct Thermostable,Single‐Crystalline,Hydrogen‐Bonded Organic Framework with High Surface Area

Enhancing thermal and chemical durability and increasing surface area are two main directions for the construction and improvement of the performance of porous hydrogen‐bonded organic frameworks (HOFs). Herein, a hexaazatriphenylene (HAT) derivative that possesses six carboxyaryl groups serves as a suitable building block for the systematic construction of thermally and chemically durable HOFs with high surface area through shape‐fitted docking between the HAT cores and interpenetrated three‐dimensional network. A HAT derivative with carboxybiphenyl groups forms a stable single‐crystalline porous HOF that displays protic solvent durability, even in concentrated HCl, heat resistance up to 305 °C, and a high Brunauer–Emmett–Teller surface area [SA_(BET)] of 1288 m² g⁻¹. A single crystal of this HOF displays anisotropic fluorescence, which suggests that it would be applicable to polarized emitters based on robust functional porous materials.     

An Ultra‐Robust and Crystalline Redeemable Hydrogen‐Bonded Organic Framework for Synergistic Chemo‐Photodynamic Therapy

The low structural stability of hydrogen‐bonded organic frameworks (HOFs) is a thorny issue retarding the development of HOFs. A rational design approach is now proposed for construction of a stable HOF. The resultant HOF (PFC‐1) exhibits high surface area of 2122 m² g⁻¹ and excellent chemical stability (intact in concentrated HCl for at least 117 days). A new method of acid‐assisted crystalline redemption is used to readily cure the thermal damage to PFC‐1. With periodic integration of photoactive pyrene in the robust framework, PFC‐1 can efficiently encapsulate Doxorubicin (Doxo) for synergistic chemo‐photodynamic therapy, showing comparable therapeutic efficacy with the commercial Doxo yet considerably lower cytotoxicity. This work demonstrates the notorious stability issue of HOFs can be properly addressed through rational design, paving a way to develop robust HOFs and offering promising application perspectives.     

An Ultrastable and Easily Regenerated Hydrogen‐Bonded Organic Molecular Framework with Permanent Porosity

A robust hydrogen‐bonded organic framework HOF‐TCBP (H₄TCBP=3,3′,5,5′‐tetrakis‐(4‐carboxyphenyl)‐1,1′‐biphenyl) has been successfully constructed and structurally characterized. It possesses a permanent 3D porous structure with a 5‐fold interpenetrated dia topological network. This activated HOF‐TCBP has a high BET surface area of 2066 m² g⁻¹ and is capable of highly selective adsorption and separation of light hydrocarbons under ambient conditions. It shows excellent thermal stability, as demonstrated by PXRD experiments and N₂ adsorption tests. Practical use of HOF‐TCBP is facilitated by the ease of its preparation and renewal through rotary evaporation.     

Experimental Confirmation of a Predicted Porous Hydrogen-Bonded Organic Framework

Hydrogen-bonded organic frameworks (HOFs) with low densities and high porosities are rare and challenging to design because most molecules have a strong energetic preference for close packing. Crystal structure prediction (CSP) can rank the crystal packings available to an organic molecule based on their relative lattice energies. This has become a powerful tool for the a priori design of porous molecular crystals. Previously, we combined CSP with structure-property predictions to generate energy-structure-function (ESF) maps for a series of triptycene-based molecules with quinoxaline groups. From these ESF maps, triptycene trisquinoxalinedione (TH5) was predicted to form a previously unknown low-energy HOF (TH5-A) with a remarkably low density of 0.374 g cm⁻³ and three-dimensional (3D) pores. Here, we demonstrate the reliability of those ESF maps by discovering this TH5-A polymorph experimentally. This material has a high accessible surface area of 3,284 m² g⁻¹, as measured by nitrogen adsorption, making it one of the most porous HOFs reported to date.     

Fluorine‐Doped Porous Single‐Crystal Rutile TiO2 Nanorods for Enhancing Photoelectrochemical Water Splitting

Fluorine‐doped hierarchical porous single‐crystal rutile TiO₂ nanorods have been synthesized through a silica template method, in which F^? ions acts as both n‐type dopants and capping agents to make the isotropic growth of the nanorods. The combination of high crystallinity, abundant surface reactive sites, large porosity, and improved electronic conductivity leads to an excellent photoelectrochemical activity. The photoanode made of F‐doped porous single crystals displays a remarkably enhanced solar‐to‐hydrogen conversion efficiency (≈0.35 % at ?0.33 V vs. Ag/AgCl) under 100 mW cm^?2 of AM=1.5 solar simulator illumination that is ten times of the pristine solid TiO₂ single crystals.     

Preparation of a Yb(III)‐Incorporated porous polymer by post‐Coordination: Enhancement of gas adsorption and catalytic activity

We synthesized a Yb(III)‐incorporated microporous polymer (Yb‐ADA) and studied its gas adsorption property and catalytic activity. The adamantane‐based porous polymer (ADA) was obtained from an ethynyl‐functionalized adamantane derivative and 2,5‐dibromoterephthalic acid through Sonogashira–Hagihara cross‐coupling. ADA had two carboxyl groups which were used for Yb(III) coordination under basic conditions. The Brunauer‐Emmett‐Teller (BET) surface area of ADA was 970 m² g^?1. As Yb(III) ions were incorporated into ADA, the surface area of the polymer (Yb‐ADA) was reduced to 885 m² g^?1. However, Yb‐ADA exhibited a significantly enhanced CO₂ adsorption capacity despite the reduction of surface area. The CO₂ uptakes of ADA and Yb‐ADA were 1.56 and 2.36 mmol g^?1 at 298 K, respectively. The H₂ uptake of ADA also increased after coordination with Yb(III) from 1.15 to 1.40 wt % at 77 K. Yb‐ADA showed high catalytic activity in the acetalization of 4‐bromobenzaldehyde and furfural with trimethyl orthoformate and could be reused after recovery without severe loss of activity. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5291–5297     

Designing Hydrogen‐Bonded Organic Frameworks (HOFs) with Permanent Porosity

Designing organic components that can be used to construct porous materials enables the preparation of tailored functionalized materials. Research into porous materials has seen a resurgence in the past decade as a result of finding of self‐standing porous molecular crystals (PMCs). Particularly, a number of crystalline systems with permanent porosity that are formed by self‐assembly through hydrogen bonding (H‐bonding) have been developed. Such systems are called hydrogen‐bonded organic frameworks (HOFs). Herein we systematically describe H‐bonding patterns (supramolecular synthons) and molecular structures (tectons) that have been used to achieve thermal and chemical durability, a large surface area, and functions, such as selective gas sorption and separation, which can provide design principles for constructing HOFs with permanent porosity.     

A Template‐Free Method for Preparation of Cobalt Nanoparticles Embedded in N‐Doped Carbon Nanofibers with a Hierarchical Pore Structure for Oxygen Reduction

Designing and preparing porous materials without using any templates is a challenge. Herein, single‐nozzle electrospinning technology coupled with post pyrolysis is applied to prepare cobalt nanoparticles embedded in N‐doped carbon nanofibers with a hierarchical pore structure (HP‐Co‐NCNFs). The resultant HP‐Co‐NCNFs have lengths up to several millimeters with an average diameter of 200 nm and possess abundant micro/meso/macropores on both the surface and within the fibers. Such a microstructure endows the surface area as high as 115 m² g^?1. When used as an electrocatalyst for the oxygen reduction reaction (ORR), the HP‐Co‐NCNFs exhibit outstanding electrochemical performance in terms of activity, methanol tolerance, and durability. The hierarchically porous structure and high surface area can effectively decrease the mass transport resistance and increase the exposed ORR active sites. The sufficient amount of exposed ORR active sites along with accessible transport channel and enhanced electrical conductivity may be responsible for the good electrocatalytic performance.     

Cooperative Capture of Uranyl Ions by a Carbonyl‐Bearing Hierarchical‐Porous Cu–Organic Framework

To efficiently capture the toxic uranyl ions (UO₂²⁺), a new hierarchical micro‐macroporous metal–organic framework was prepared under template‐free conditions, featuring interconnected multi‐nanocages bearing carbonyl groups derived from a semi‐rigid ligand. The material exhibits an unusually high UO₂²⁺ sorption capacity of 562 mg g^?1, which occurs in an intriguing two‐steps process, on the macropore‐based crystal surface and in the inner nanocages. Notably, the latter is attributed to the cooperative interplay of the shrinkage of the host porous framework induced by uranyl accommodation and the free carbonyl coordination sites, as shown by both single‐crystal X‐ray diffraction and a red‐shift of the infrared [O=U^VI=O]²⁺ antisymmetric vibration band.     

Single Crystal to Single Crystal (SC‐to‐SC) Transformation from a Nonporous to Porous Metal–Organic Framework and Its Application Potential in Gas Adsorption and Suzuki Coupling Reaction through Postmodification

A new amino‐functionalized strontium–carboxylate‐based metal–organic framework (MOF) has been synthesized that undergoes single crystal to single crystal (SC‐to‐SC) transformation upon desolvation. Both structures have been characterized by single‐crystal X‐ray analysis. The desolvated structure shows an interesting 3D porous structure with pendent ?NH₂ groups inside the pore wall, whereas the solvated compound possesses a nonporous structure with DMF molecules on the metal centers. The amino group was postmodified through Schiff base condensation by pyridine‐2‐carboxaldehyde and palladium was anchored on that site. The modified framework has been utilized for the Suzuki cross‐coupling reaction. The compound shows high activity towards the C?C cross‐coupling reaction with good yields and turnover frequencies. Gas adsorption studies showed that the desolvated compound had permanent porosity and was microporous in nature with a BET surface area of 2052 m² g^?1. The material also possesses good CO₂ (8 wt %) and H₂ (1.87 wt %) adsorption capabilities.     

A Hydrogen‐Bonded Organic Framework (HOF) with Type IV NH3 Adsorption Behavior

An S‐shaped gas isotherm pattern displays high working capacity in pressure‐swing adsorption cycle, as established for CO₂, CH₄, acetylene, and CO. However, to our knowledge, this type of adsorption behavior has not been revealed for NH₃ gas. Herein, we design and characterize a hydrogen‐bonded organic framework (HOF) that can adsorb NH₃ uniquely in an S‐shape (type IV) fashion. While conventional porous materials, mostly with type I NH₃ adsorption behavior, require relatively high regeneration temperature, this platform which has significant working capacity is easily regenerated and recyclable at room temperature.     

Porphyrin‐based covalent triazine frameworks: Porosity,adsorption performance,and drug delivery

Two porous porphyrin‐based covalent triazine frameworks (PCTFs), in which porphyrin is incorporated as building block, have been synthesized by the Friedel–Crafts reaction. The copolymer PCTFs show large Brunauer–Emmett–Teller specific surface area of up to 1089 m² g^?1, high CO₂ uptake capacity reaching 139.9 mg g^?1 at 273 K/1.0 bar, and good selectivity for CO₂/CH₄ adsorption attaining 6.1 at 273 K/1.0 bar. The resulting porous solids also can be used as matrices for drug delivery of ibuprofen in vitro. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 2594–2600     

Hydrogen‐Bonded Organic Frameworks (HOFs): A New Class of Porous Crystalline Proton‐Conducting Materials

Two porous hydrogen‐bonded organic frameworks (HOFs) based on arene sulfonates and guanidinium ions are reported. As a result of the presence of ionic backbones appended with protonic source, the compounds exhibit ultra‐high proton conduction values (σ) 0.75× 10^?2 S cm^?1 and 1.8×10^?2 S cm^?1 under humidified conditions. Also, they have very low activation energy values and the highest proton conductivity at ambient conditions (low humidity and at moderate temperature) among porous crystalline materials, such as metal–organic frameworks (MOFs) and covalent organic frameworks (COFs). These values are not only comparable to the conventionally used proton exchange membranes, such as Nafion used in fuel cell technologies, but is also the highest value reported in organic‐based porous architectures. Notably, this report inaugurates the usage of crystalline hydrogen‐bonded porous organic frameworks as solid‐state proton conducting materials.     

Compositing Amorphous TiO2 with N‐Doped Carbon as High‐Rate Anode Materials for Lithium‐Ion Batteries

Compositing amorphous TiO₂ with nitrogen‐doped carbon through Ti? N bonding to form an amorphous TiO₂/N‐doped carbon hybrid (denoted a‐TiO₂/C? N) has been achieved by a two‐step hydrothermal–calcining method with hydrazine hydrate as an inhibitor and nitrogen source. The resultant a‐TiO₂/C? N hybrid has a surface area as high as 108 m² g^?1 and, when used as an anode material, exhibits a capacity as high as 290.0 mA h g^?1 at a current rate of 1 C and a reversible capacity over 156 mA h g^?1 at a current rate of 10 C after 100 cycles; these results are better than those found in most reports on crystalline TiO₂. This superior electrochemical performance could be ascribed to a combined effect of several factors, including the amorphous nature, porous structure, high surface area, and N‐doped carbon.     

Synthesis of a Rigid C3v‐Symmetric Tris‐salicylaldehyde as a Precursor for a Highly Porous Molecular Cube

The development of a synthetic approach to a C_3v‐symmetric tris‐salicylaldehyde based on triptycene is presented. The tris‐salicylaldehyde is a versatile precursor for porous molecular materials, as demonstrated in the [4+4] condensation reaction with a triptycene triamine to form a molecular shape‐persistent porous cube. The amorphous material of the molecular porous cube shows a very high surface area of 1014 m² g^?1 (BET model) and a high uptake of CO₂ (18.2 wt % at 273 K and 1 bar). Furthermore, during the multistep synthesis of the tris‐salicylaldehyde precursor, a relatively rare (twofold) addition of the aryne to the anthracene in the 1,4‐ and 1,4,5,8‐positions have been found during a Diels–Alder reaction, as proven by X‐ray structure analysis.     

Hyperporous‐Carbon‐Supported Nonprecious Metal Electrocatalysts for the Oxygen Reduction Reaction

Highly porous carbonaceous nonprecious metal catalysts for the oxygen reduction reaction are prepared by carbonization of low‐cost metalloporphyrin‐based hyper‐crosslinked polymers (MPH‐X). With high surface area (2768 m² g⁻¹), hierarchical porous structure, and high metal loading (9.97 wt %), the obtained hyperporous carbon MPH‐Fe/C catalyst exhibits high oxygen reduction reaction (ORR) activity with a half‐wave potential (0.816 V) that is comparable to the 0.819 V of commercial Pt/C. Stability tests reveal that MPH‐Fe/C also exhibits outstanding long‐term durability and methanol tolerance. Our findings may offer an alternative approach to produce nonprecious metal ORR catalysts on a large scale owing to the low‐cost MPH‐X precursors with diverse metal types.     

Computational study of energetic nitrogen‐rich derivatives of 1,1′‐ and 5,5′‐bridged ditetrazoles

Density functional theory method was used to study the heats of formation (HOFs), electronic structure, energetic properties, and thermal stability for a series of bridged ditetrazole derivatives with different linkages and substituent groups. The results show that the ? N₃ group and azo bridge (? N?N? ) play a very important role in increasing the HOF values of the ditetrazole derivatives. The effects of the substituents on the HOMO–LUMO gap are combined with those of the bridge groups. The calculated detonation velocities and detonation pressures indicate that the ? NO₂, ? NF₂, ? N?N? , or ? N(O)?N? group is an effective structural unit for enhancing the detonation performance for the derivatives. An analysis of the bond dissociation energies for several relatively weak bonds suggests that the N? N bond in the ring or outside the ring is the weakest one and the N? N cleavage is possible to happen in thermal decomposition. Overall, the ? CH₂? CH₂? or ? NH? NH? group is an effective bridge for enhancing the thermal stability of the bridged ditetrazoles. Because of their desirable detonation performance and thermal stability, five compounds may be considered as the potential candidates of high‐energy density materials (HEDMs). These results provide basic information for the molecular design of novel HEDMs. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011     

Synthesis of High‐Surface‐Area Nitrogen‐Doped Porous Carbon Microflowers and Their Efficient Carbon Dioxide Capture Performance

Sustainable carbon materials have received particular attention in CO₂ capture and storage owing to their abundant pore structures and controllable pore parameters. Here, we report high‐surface‐area hierarchically porous N‐doped carbon microflowers, which were assembled from porous nanosheets by a three‐step route: soft‐template‐assisted self‐assembly, thermal decomposition, and KOH activation. The hydrazine hydrate used in our experiment serves as not only a nitrogen source, but also a structure‐directing agent. The activation process was carried out under low (KOH/carbon=2), mild (KOH/carbon=4) and severe (KOH/carbon=6) activation conditions. The mild activated N‐doped carbon microflowers (A‐NCF‐4) have a hierarchically porous structure, high specific surface area (2309 m² g^?1), desirable micropore size below 1 nm, and importantly large micropore volume (0.95 cm³ g^?1). The remarkably high CO₂ adsorption capacities of 6.52 and 19.32 mmol g^?1 were achieved with this sample at 0 °C (273 K) and two pressures, 1 bar and 20 bar, respectively. Furthermore, this sample also exhibits excellent stability during cyclic operations and good separation selectivity for CO₂ over N₂.     

Zeolitic Imidazolate Framework (ZIF)‐Derived,Hollow‐Core,Nitrogen‐Doped Carbon Nanostructures for Oxygen‐Reduction Reactions in PEFCs

The facile synthesis of a porous carbon material that is doped with iron‐coordinated nitrogen active sites (FeNC‐70) is demonstrated by following an inexpensive synthetic pathway with a zeolitic imidazolate framework (ZIF‐70) as a template. To emphasize the possibility of tuning the porosity and surface area of the resulting carbon materials based on the structure of the parent ZIF, two other ZIFs, that is, ZIF‐68 and ZIF‐69, are also synthesized. The resulting active carbon material that is derived from ZIF‐70, that is, FeNC‐70, exhibits the highest BET surface area of 262 m² g^?1 compared to the active carbon materials that are derived from ZIF‐68 and ZIF‐69. The HR‐TEM images of FeNC‐70 show that the carbon particles have a bimodal structure that is composed of a spherical macroscopic pore (about 200 nm) and a mesoporous shell. X‐ray photoelectron spectroscopy (XPS) reveals the presence of Fe‐N‐C moieties, which are the primary active sites for the oxygen‐reduction reaction (ORR). Quantitative estimation by using EDAX analysis reveals a nitrogen content of 14.5 wt. %, along with trace amounts of iron (0.1 wt. %), in the active FeNC‐70 catalyst. This active porous carbon material, which is enriched with Fe‐N‐C moieties, reduces the oxygen molecule with an onset potential at 0.80 V versus NHE through a pathway that involves 3.3–3.8 e^? under acidic conditions, which is much closer to the favored 4 e^? pathway for the ORR. The onset potential of FeNC‐70 is significantly higher than those of its counterparts (FeNC‐68 and FeNC‐69) and of other reported systems. The FeNC‐based systems also exhibit much‐higher tolerance towards MeOH oxidation and electrochemical stability during an accelerated durability test (ADT). Electrochemical analysis and structural characterizations predict that the active sites for the ORR are most likely to be the in situ generated N? FeN₂₊₂/C moieties, which are distributed along the carbon framework.     

A Polyhedron‐based Metal‐Organic Framework showing high CO2 Adsorption Capacity

A novel porous copper‐based metal‐organic framework {[Cu₂(TTDA)₂]*(DMA)₇}_n ( 1 ) (DMA = N,N‐dimethylacetamide) was designed and synthesized via the combination of a dual‐functional organic linker 5′‐(4‐(4H‐1,2,4‐triazol‐4‐yl)phenyl)‐[1,1′:3′,1′′‐terphenyl]‐4,4′′‐dicarboxylic acid (H₂TTDA) and a dinuclear Cu^II paddle‐wheel cluster. This MOF is characterized by elemental analysis, powder X‐ray diffraction (PXRD), thermo gravimetric analysis (TGA), and single‐crystal X‐ray diffraction. The framework is constructed from two types of cages (octahedral and cuboctahedral cages) and exhibits two types of circular‐shaped channels of approximate size of 5.8 and 11.4 Å along the crystallographic c axis. The gas sorption experiments indicate that it possesses a large surface area (1687 m² · g^–1) and high CO₂ adsorption capacities around room temperature (up to 172 cm³ · g^–1 at 273 K and 124 cm³ · g^–1 at 298 K).