There have been extensive efforts to synthesize crystalline covalent triazine‐based frameworks (CTFs) for practical applications and to realize their potential. The phosphorus pentoxide ...(P2O5)‐catalyzed direct condensation of aromatic amide instead of aromatic nitrile to form triazine rings. P2O5‐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 P2O5‐catalyzed condensation reaction of both benzamide and benzonitrile to form 1,3,5‐triphenyl‐2,4,6‐triazine in high yield.
A covalent triazine‐based framework was synthesized by phosphorus pentoxide (P2O5)‐catalyzed direct condensation of aromatic amides to form a triazine ring. Highly crystalline covalent triazine frameworks (pCTF‐1) were produced with high specific surface area (2034.1 m2 g−1). At low pressure, pCTF‐1 shows a high carbon dioxide (CO2) uptake capacity of 21.9 wt % at 273 K and a hydrogen (H2) uptake capacity of 1.75 wt % at 77 K.
Recent graphene research has triggered enormous interest in new two-dimensional ordered crystals constructed by the inclusion of elements other than carbon for bandgap opening. The design of new ...multifunctional two-dimensional materials with proper bandgap has become an important challenge. Here we report a layered two-dimensional network structure that possesses evenly distributed holes and nitrogen atoms and a C2N stoichiometry in its basal plane. The two-dimensional structure can be efficiently synthesized via a simple wet-chemical reaction and confirmed with various characterization techniques, including scanning tunnelling microscopy. Furthermore, a field-effect transistor device fabricated using the material exhibits an on/off ratio of 10(7), with calculated and experimental bandgaps of approximately 1.70 and 1.96 eV, respectively. In view of the simplicity of the production method and the advantages of the solution processability, the C2N-h2D crystal has potential for use in practical applications.
The formation of 2D polyaniline (PANI) has attracted considerable interest due to its expected electronic and optoelectronic properties. Although PANIwas discovered over 150 y ago, obtaining an ...atomically well-defined 2D PANI framework has been a longstanding challenge. Here, we describe the synthesis of 2D PANI via the direct pyrolysis of hexaaminobenzene trihydrochloride single crystals in solid state. The 2D PANI consists of three phenyl rings sharing six nitrogen atoms, and its structural unit has the empirical formula of C₃N. The topological and electronic structures of the 2D PANI were revealed by scanning tunneling microscopy and scanning tunneling spectroscopy combined with a first-principle density functional theory calculation. The electronic properties of pristine 2D PANI films (undoped) showed ambipolar behaviors with a Dirac point of −37 V and an average conductivity of 0.72 S/cm. After doping with hydrochloric acid, the conductivity jumped to 1.41 × 10³ S/cm, which is the highest value for doped PANI reported to date. Although the structure of 2D PANI is analogous to graphene, it contains uniformly distributed nitrogen atoms for multifunctionality; hence, we anticipate that 2D PANI has strong potential, from wet chemistry to device applications, beyond linear PANI and other 2D materials.
Hierarchically structured nitrogen‐doped carbon nanotube (NCNT) composites, with copper (Cu) nanoparticles embedded uniformly within the nanotube walls and cobalt oxide (CoxOy) nanoparticles ...decorated on the nanotube surfaces, are fabricated via a combinational process. This process involves the growth of Cu embedded CNTs by low‐ and high‐temperature chemical vapor deposition, post‐treatment with ammonia for nitrogen doping of these CNTs, precipitation‐assisted separation of NCNTs from cobalt nitrate aqueous solution, and finally thermal annealing for CoxOy decoration. Theoretical calculations show that interaction of Cu nanoparticles with CNT walls can effectively decrease the work function of CNT surfaces and improve adsorption of hydroxyl ions onto the CNT surfaces. Thus, the activities of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are significantly enhanced. Because of this benefit, further nitrogen doping, and synergistic coupling between CoxOy and NCNTs, Cu@NCNT/CoxOy composites exhibit ORR activity comparable to that of commercial Pt/C catalysts and high OER activity (outperforming that of IrO2 catalysts). More importantly, the composites display superior long‐term stability for both ORR and OER. This simple but general synthesis protocol can be extended to design and synthesis of other metal/metal oxide systems for fabrication of high‐performance carbon‐based electrocatalysts with multifunctional catalytic activities.
Nitrogen‐doped carbon nanotubes (NCNTs), with copper (Cu) nanoparticles embedded uniformly within their walls and cobalt oxide (CoxOy) nanoparticles decorated on their surfaces, are controllably synthesized via a rationally designed multistep procedure. The resultant Cu@NCNT/CoxOy composites exhibit electrocatalytic activity comparable to that of commercial Pt/C catalysts for the oxygen reduction reaction and activity higher than that of IrO2 catalysts for the oxygen evolution reaction.
Low-cost, high-yield production of graphene nanosheets (GNs) is essential for practical applications. We have achieved high yield of edge-selectively carboxylated graphite (ECG) by a simple ball ...milling of pristine graphite in the presence of dry ice. The resultant ECG is highly dispersable in various solvents to self-exfoliate into single-and few-layer (<5 layers) GNs. These stable ECG (or GN) dispersions have been used for solution processing, coupled with thermal decarboxylation, to produce large-area GN films for many potential applications ranging from electronic materials to chemical catalysts. The electrical conductivity of a thermally decarboxylated ECG film was found to be as high as 1214 S/cm, which is superior to its GO counterparts. Ball milling can thus provide simple, but efficient and versatile, and eco-friendly (CO₂-capturing) approaches to low-cost mass production of high-quality GNs for applications where GOs have been exploited and beyond.
A series of edge-selectively halogenated (X = Cl, Br, I) graphene nanoplatelets (XGnPs = ClGnP, BrGnP, IGnP) were prepared simply by ball-milling graphite in the presence of Cl2, Br2 and I2, ...respectively. High BET surface areas of 471, 579 and 662 m(2)/g were observed for ClGnP, BrGnP and IGnP, respectively, indicating a significant extent of delamination during the ball-milling and subsequent workup processes. The newly-developed XGnPs can be well dispersed in various solvents, and hence are solution processable. Furthermore, XGnPs showed remarkable electrocatalytic activities toward oxygen reduction reaction (ORR) with a high selectivity, good tolerance to methanol crossover/CO poisoning effects, and excellent long-term cycle stability. First-principle density-functional calculations revealed that halogenated graphene edges could provide decent adsorption sites for oxygen molecules, in a good agreement with the experimental observations.
A three‐dimensional (3D) cage‐like organic network (3D‐CON) structure synthesized by the straightforward condensation of building blocks designed with gas adsorption properties is presented. The ...3D‐CON can be prepared using an easy but powerful route, which is essential for commercial scale‐up. The resulting fused aromatic 3D‐CON exhibited a high Brunauer–Emmett–Teller (BET) specific surface area of up to 2247 m2 g−1. More importantly, the 3D‐CON displayed outstanding low pressure hydrogen (H2, 2.64 wt %, 1.0 bar and 77 K), methane (CH4, 2.4 wt %, 1.0 bar and 273 K), and carbon dioxide (CO2, 26.7 wt %, 1.0 bar and 273 K) uptake with a high isosteric heat of adsorption (H2, 8.10 kJ mol−1; CH4, 18.72 kJ mol−1; CO2, 31.87 kJ mol−1). These values are among the best reported for organic networks with high thermal stability (ca. 600 °C).
A shape‐persistent cage‐like organic network structure using a rigid building block derived from triptycene hexamine was design and synthesized. This robust structure is thermally stable, ultramicroporous, and displays outstanding gas‐adsorption properties. The cage‐like organic network structure exhibits a BET surface area up to 2247 m2 g−1 and high gas‐adsorption capacity.
Nitrogen fixation is essential for the synthesis of many important chemicals (e.g., fertilizers, explosives) and basic building blocks for all forms of life (e.g., nucleotides for DNA and RNA, amino ...acids for proteins). However, direct nitrogen fixation is challenging as nitrogen (N₂) does not easily react with other chemicals. By dry ball-milling graphite with N₂, we have discovered a simple, but versatile, scalable and eco-friendly, approach to direct fixation of N₂ at the edges of graphene nanoplatelets (GnPs). The mechanochemical cracking of graphitic C--C bonds generated active carbon species that react directly with N₂ to form five- and six-membered aromatic rings at the broken edges, leading to solution-processable edge-nitrogenated graphene nanoplatelets (NGnPs) with superb catalytic performance in both dye-sensitized solar cells and fuel cells to replace conventional Pt-based catalysts for energy conversion.
Challenging precious Pt‐based electrocatalysts for dye‐sensitized solar cells (DSSCs), graphene nanoplatelets that are N‐doped at the edges (NGnPs) are prepared via simply ball‐milling graphite in ...the presence of nitrogen gas. DSSCs based on specific nanoplatelets designated “NGnP5” display superior photovoltaic performance (power conversion efficiency, 10.27%) compared to that of conventional Pt‐based devices (9.96%). More importantly, the NGnP counter electrode exhibits outstanding electrochemical stability and electrocatalytic activity with a cobalt‐complex redox couple.
Ordered graphitic carbon nanosheets (GCNs) were, for the first time, synthesized by the direct condensation of multifunctional phenylacetyl building blocks (monomers) in the presence of phosphorous ...pentoxide. The GCNs had highly ordered structures with random hole defects and oxygenated functional groups, showing paramagnetism. The results of combined structural and magnetic analyses indicate that the hole defects and functional groups are associated with the appearance and stabilization of unpaired spins. DFT calculations further suggest that the emergence of stabilized spin moments near the edge groups necessitates the presence of functionalized carbon atoms around the hole defects. That is, both hole defects and oxygenated functional groups are essential ingredients for the generation and stabilization of spins in GCNs.
Ordered graphitic carbon nanosheets (GCNs) were prepared by the direct dehydration of phenylacetyl units using powerful dehydrating agent, phosphorous pentoxide (P2O5). The GCNs, with random hole defects and remnant oxygenated groups, displayed paramagnetism. The correlation between structure and magnetism was manifested by experiments and calculations.
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