Covalent organic frameworks (COFs) are an emerging class of porous crystalline polymers with broad potential applications. So far, the availability of three-dimensional (3D) COFs is limited and more importantly only one type of covalent bond has been successful used for 3D COF materials. Here, we report a new synthetic strategy based on dual linkages that leads to 3D COFs. The obtained 3D COFs show high specific surface areas and large gas uptake capacities, which makes them the top COF material for gas uptake. Furthermore, we demonstrate that the new 3D COFs comprise both acidic and basic sites, and act as excellent bifunctional catalysts for one-pot cascade reactions. The new synthetic strategy provides not only a general and versatile approach to synthesize 3D COFs with sophisticated structures but also expands the potential applications of this promising class of porous materials.

A series of in situ hot stage experiments using transmission electron microscopy (TEM) were studied to directly observe the transition of a Ni-MOF to Ni nanoparticles wrapped in carbon (Ni-NPC) over temperatures ranging from ambient temperature to 700 °C. Ni-NPC-600 displays high catalytic activity in 4-nitrophenol reduction and high conversion, even after 10 cycles.

•Co@N-C nanocatalyst series were obtained by direct carbonization of MOF precursor.•Direct carbonization method provide an efficient and controllable pathway in generating nanocatalyst with desired properties.•Catalytic performance was assessed through catalytic reduction of 4-NP to 4-AP with remarkable performance.•Co@N-C 700 sample showed the highest catalytic activity in performing 6 time consecutive catalytic reactions.The Co@N-C nanocatalysts derived by direct carbonization of Co-containing metal organic framework (MOF) structure under N2 flow have been prepared for their application as catalyst in reducing 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) assisted by NaBH4. Under inert gas treatment, we obtained Co0 phase-based nanocatalyst which inherited their former MOF precursor morphology. The resultant nanocatalysts were denoted as Co@N-C 600, 700, 800 corresponding to the respective carbonization temperatures and each was characterized using powder X-Ray diffraction (PXRD), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), surface area-porosity and transmission electron microscopy (TEM). We found that Co@N-C 700 presented the desired properties with largest surface area (262.800 m2/g), high crystallinity with better Co nanoparticle dispersed on the C-N matrix and sufficient amount of Co per gram of nanocatalyst without obvious particle aggregation. All of the nanocatalysts could catalyze 1.25 mM 4-NP to 4-AP per mg catalyst per second which is comparatively remarkable performance compared to previous reposts. Most importantly, as predicted Co@N-C 700 possessed the highest catalytic activity with 6 times consecutive catalytic reactions in successfully reducing 100% 4-NP to 4-AP. The catalytic activity was speculated due to the Co nanoparticle as catalytic active site worked synergistically with C-N matrix as conductive layer which could provide and transport electrons for catalytic reduction reaction.

A series of in situ hot stage experiments using transmission electron microscopy (TEM) were studied to directly observe the transition of a Ni-MOF to Ni nanoparticles wrapped in carbon (Ni-NPC) over temperatures ranging from ambient temperature to 700 °C. Ni-NPC-600 displays high catalytic activity in 4-nitrophenol reduction and high conversion, even after 10 cycles.