Search

Fused aromatic networks (FANs) have been studied in efforts to overcome the low physicochemical stability of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), while preserving crystallinity. Herein, we describe the synthesis of a highly stable and crystalline FAN (denoted as Pz-FAN) using pyrazine-based building blocks to form porphyrazine (Pz) linkages via an irreversible reaction. Unlike most COFs and FANs, which are synthesized from two different building blocks, the new Pz-FAN is formed using a single building block by self-cyclotetramerization. Controlled and optimized reaction conditions result in a highly crystalline Pz-FAN with physicochemical stability. The newly prepared Pz-FAN displayed a high magnitude (1.16×10

One-dimensional (1D) ladder-like poly(benzoimidazobenzophenanthrolines) (BBLs) have attracted great interest due to their outstanding features, including thermal and chemical stability, electrical conductivity, and optical and electronic properties. Nevertheless, layered conjugated porous BBL structures have not yet been reported to date. Here, we introduce two-dimensional (2D) layered BBL structures via the polycondensation of mellitic anhydride (MTA) as an A3 monomer with 1,2,4,5-tetraaminobenzene (TAB) as the B2 monomer, or hexaaminobenzene (HAB) as the B3 monomer in polyphosphoric acid (PPA). The porous 2D BBL network structures are constructed of robust fused aromatic rings and thus exhibit high thermal stability and high Brunauer–Emmett–Teller (BET) surface areas with different pore diameters and permanent microporosities. The 2D BBL networks demonstrated high gas uptake capacities for hydrogen (H2, 1.65 wt% at 77 K, 1 bar) and carbon dioxide (CO2, 15.6 wt% at 273 K, 1 bar) with unusually high Qst values.

Single-atom catalysts have recently attracted considerable attention because of their highly efficient metal utilization and unique properties. Finding a green, facile method to synthesize them is key to their widespread commercialization. Here we show that single-atom catalysts (including iron, cobalt, nickel and copper) can be prepared via a top-down abrasion method, in which the bulk metal is directly atomized onto different supports, such as carbon frameworks, oxides and nitrides. The level of metal loading can be easily tuned by changing the abrasion rate. No synthetic chemicals, solvents or even water were used in the process and no by-products or waste were generated. The underlying reaction mechanism involves the mechanochemical force in situ generating defects on the supports, then trapping and stably sequestering atomized metals.

Fused aromatic networks (FANs) are attracting considerable interest in the scientific community because of their intriguing electronic properties and superior physiochemical stability due to their fully fused aromatic systems. Here, a three-dimensional (3D) cage-like organic network (3D-CON) and a vertical two-dimensional (2D) layered ladder structure (designated as V2D-BBL structure) were studied as materials for gas hydrate inhibitors because of their outstanding stability in high-pressure/low-temperature and periodically incorporated molecular building blocks. The V2D-BBL structure demonstrated remarkable performance, inhibiting the formation of both methane (CH4) and carbon dioxide (CO2) hydrates, comparable to conventional lactam-based polymers. It was determined that the designed perinone moiety in the V2D-BBL structure enables synergistic interactions with the host (water) and guest (CH4) molecules involved in hydrate nucleation. Given their pre-designability and inherent stability, the FANs hold enormous potential as gas hydrate inhibitors for industrial applications.

There have been extensive efforts to synthesize crystalline covalent triazine-based frameworks (CTFs) for practical applications and to realize their potential. The phosphorus pentoxide (P2 O5 )-catalyzed direct condensation of aromatic amide instead of aromatic nitrile to form triazine rings. P2 O5 -catalyzed condensation was applied on terephthalamide to construct a covalent triazine-based framework (pCTF-1). This approach yielded highly crystalline pCTF-1 with high specific surface area (2034.1 m2 g-1 ). At low pressure, the pCTF-1 showed high CO2 (21.9 wt % at 273 K) and H2 (1.75 wt % at 77 K) uptake capacities. The direct formation of a triazine-based COF was also confirmed by model reactions, with the P2 O5 -catalyzed condensation reaction of both benzamide and benzonitrile to form 1,3,5-triphenyl-2,4,6-triazine in high yield.

Summary Fused aromatic networks (FANs) are a new generation of porous organic networks (PONs), which are thermodynamic products. FANs are also kinetic products with low crystallinity. Nevertheless, their high physicochemical stability suggests many potential applications. This work reports three structures with their fully fused aromatic units vertically (V), horizontally (H), and three-dimensionally (3D) linked to the growth direction, forming “standing” FAN (VS-FAN), “planar” FAN (HP-FAN), and 3D-FAN, respectively. Their performance as sorbent materials was evaluated. While the VS-FAN has the fastest kinetics for CH4 and I2 adsorption due to the highest segmental freedom, the HP-FAN exhibits the best separation selectivity of the CH4/N2 mixture due to the strongest segmental confinement. The 3D-FAN displays the highest adsorption capacity of CH4 because of the highest specific surface area. The results suggest that the different segmental arrangements may critically affect the sorbent performance of FANs.

Platinum (Pt) nanoparticles were stably anchored on triazine-functionalized graphene nanoplatelets (TfGnPs), which were prepared by a two-step reaction starting from carboxylic acid- (CGnPs), acyl chloride- (AcGnPs) and amide-functionalized graphene nanoplatelets (AfGnPs). The resulting Pt nanoparticles on TfGnPs (Pt/TfGnPs) exhibited outstanding electrocatalytic activity with significantly enhanced stability compared with commercial Pt-based catalysts for the oxygen reduction reaction (ORR) in fuel cells (FCs) and the iodine reduction reaction (IRR) in dye-sensitized solar cells (DSSCs). For the ORR in FCs, the onset and half-wave potentials of Pt/TfGnPs under acidic conditions displayed greater positive shifts to 0.58 and 0.53 V, respectively, than those of the commercial Pt/C catalyst (0.57 and 0.52 V). For the IRR in DSSCs, Pt/TfGnPs displayed a reduced charge transfer resistance (Rct) of 0.13 Ω cm2 at the CE/electrolyte interface. This value was much lower than the Pt CE of 0.52 Ω cm2. More importantly, Pt/TfGnPs exhibited profoundly improved electrochemical stability in both the ORR and IRR compared to the Pt-based catalysts. The combination of extraordinarily high electrocatalytic activity with stability could be attributed to the high specific surface area (963.0 m2 g−1) and the triazine units of the TfGnPs, respectively, which provided more active sites and stably anchored the Pt nanoparticles.

The dissociation of stable diatomic nitrogen molecules under mild conditions was realized via cyclic strain engineering., All quiet on the nitrogen front. The dissociation of stable diatomic nitrogen molecules (N2) is one of the most challenging tasks in the scientific community and currently requires both high pressure and high temperature. Here, we demonstrate that N2 can be dissociated under mild conditions by cyclic strain engineering. The method can be performed at a critical reaction pressure of less than 1 bar, and the temperature of the reaction container is only 40°C. When graphite was used as a dissociated N* receptor, the normalized loading of N to C reached as high as 16.3 at/at %. Such efficient nitrogen dissociation is induced by the cyclic loading and unloading mechanical strain, which has the effect of altering the binding energy of N, facilitating adsorption in the strain-free stage and desorption in the compressive strain stage. Our finding may lead to opportunities for the direct synthesis of N-containing compounds from N2.

Recently, studies of 2D organic layered materials with unique electronic properties have generated considerable interest in the research community. However, the development of organic materials with functional electrical transport properties is still needed. Here, a 2D fused aromatic network (FAN) structure with a C5 N basal plane stoichiometry is designed and synthesized, and thin films are cast from C5 N solution onto silicon dioxide substrates. Then field-effect transistors are fabricated using C5 N thin flakes as the active layer in a bottom-gate top-contact configuration to characterize their electrical properties. The C5 N thin flakes, isolated by polydimethylsiloxane stamping, exhibit ambipolar charge transport and extraordinarily high electron (996 cm2 V-1 s-1 ) and hole (501 cm2 V-1 s-1 ) mobilities, surpassing the performance of most pristine organic materials without doping. These results demonstrate their vast potential for applications in thin-film optoelectronic devices.

Heptene-functionalized graphitic nanoplatelets (HGNs) were prepared as a new reinforcing additive for linear low-density polyethylene (LLDPE). HGNs were synthesized using a mechanochemical reaction between graphite and 1-heptene. The formation of HGNs is confirmed using a variety of analytic techniques. Because HGNs were well dispersible in organic solvents, HGN/LLDPE composites were easily prepared using a solution process. Compared to neat LLDPE, the HGN/LLDPE composites showed significantly enhanced mechanical properties (i.e., tensile strength, yield strength, Young's modulus, and tensile toughness) and thermal stability. Considering cost, efficiency, and practicality, HGNs could become promising candidates for reinforcing additives for LLDPE.