Graphical To activate peroxymonosulfate (PMS) and degrade dyes, composite catalysts containing cobalt, nitrogen-doped porous carbon and carbon nanotubes (CNTs) were prepared. The catalyst (CNT@ZIF-800) showed faster degradation rates towards congo red (98.5 %, 5 min) and slower rates towards rhodamine B (90.7 %, 30 min) than methylene blue (94.8 %, 30 min). It had 14.5 % more Co−Nx/pyridinic-N sites than C-ZIF-800. Such sites, together with cobalt and CNTs, had activated PMS into 1 O 2 , SO 4 − ⋅ and ⋅OH, which were primary and secondary dye degradation species. To activate peroxymonosulfate (PMS) and degrade methylene blue (MB), cobalt and nitrogen-doped porous carbon composite catalysts were prepared through pyrolysing zeolitic imidazolate framework ZIF-9 and dicyandiamide (DCDA) at 700–900 °C with various mass ratios. Powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Brunauer-Emmett-Teller results showed that Co, porous carbon and carbon nanotubes (CNTs) co-existed in the catalyst prepared at 800 °C with a ZIF-9/DCDA ratio of 1 : 3. Thermogravimetric analysis suggested that CNT@ZIF-800 had a higher ratio of graphitic to turbostratic carbon than CNT@ZIF-700. It had degraded 94.8 % MB within 30 min, which was about 1.9 times faster than its counterpart C-ZIF-800. It also showed faster degradation rates towards Congo red (98.5 %, 5 min) and slower rates towards rhodamine B (90.7 %, 30 min) than MB. Furthermore, XPS revealed that it had 14.5 % more Co−Nx/pyridinic-N active sites than C-ZIF-800. EPR suggested that 1 O 2 might be the primary catalytic species whereas the SO 4 − ⋅ and ⋅OH the secondary ones. The formation mechanism of such active species might be originated from the synergistic activation of PMS by CNTs, Co−Nx/pyridinic-N and abundant Co sites in the CNT@ZIF-800. This work not only provided efficient Fenton-like catalysts for MB degradation, but also clarified the catalytic mechanism.
Transition metal sulfides and their hybrids are promising alternative to precious metal catalyst for the oxygen evolution reaction (OER). Herein, the high-density Co 9 S 8 nanoparticles (NPs) embedded in N-doped carbon has been prepared by using surface-engineered zeolitic imidazolate framework-9 (ZIF-9) nanosheets as precursor. The surface of ZIF-9 was modified with TAA , which is able to create chemical barrier and prevents metal from aggregation in the subsequent pyrolysis , thus making small Co 9 S 8 NPs densely anchored on carbon layers . Arising from the unique structure, Co 9 S 8 @NC affords an optimized electronic structure and rich effective reactive sites for OER. As expected, Co 9 S 8 @NC exhibits small overpotential of 264 mV at 10 mA cm −2 , low Tafel slope of 68.4 mV dec −1 , and superior stability for alkaline OER (0.1 M KOH). The electrolysis cell , which was equipped with Co 9 S 8 @NC cathode and Pt/C anode, shows low water splitting voltage of 1.58 V at 10 mA cm −2 in 1.0 M KOH. This work employs an efficacious surface engineering strategy to design metal sulfide-based electrocatalysts for enhancing OER performance.
Yiqiang Deng,Ying Liu,Yaju Chen,Lihua Cheng,Weili Dai,Hongbing Ji
On the way toward a carbon–neutral future, anthropogenic chemical recycling of captured carbon dioxide (CO 2 ) into value-added chemicals and reusable materials provides an attractive and promising pathway. A multifunctional zeolitic imidazolate framework (ZIF-9-ImBr) consisting of electrophilic cobalt ions, CO 2 -philic nitrogen-rich units and nucleophilic imidazolium-based ionic liquids (ILs) was synthesized by simple substitution reaction of amino-functionalized ZIF (ZIF-9-NH 2 ) with 1-(4-bromobutyl)-3-methylimidazolium bromide ([BrBMIM]Br). The obtained ZIF-9-ImBr was employed as heterogeneous catalyst for the solvent-free synthesis of cyclic carbonates from CO 2 and epoxides in the absence of any cocatalyst. A certain amount of micropores and abundant nitrogen atoms could facilitate CO 2 enrichment and its activation, while the mesopores could enhance the mass transfer of reactant and product molecules. Moreover, the synergistic effect between Lewis-acid cobalt and Lewis-base bromine ions of ZIF-9-ImBr made it promising in the CO 2 cycloaddition reaction. As expected, ZIF-9-ImBr displayed good catalytic performance of 93.8 % yield and 98.9 % selectivity of propylene carbonate at 120 °C and 2.0 MPa for 3.5 h. Additionally, the reactions proceeded with a broad substrate scope and high selectivity to give the corresponding cyclic carbonates in good to excellent yields (77.9–95.8 %). Even for the challenging internal epoxide, cyclohexene oxide, a satisfactory 71.4 % yield was obtained by extending the reaction time to 24 h. More importantly, ZIF-9-ImBr can be easily recycled and maintains its reactivity and selectivity after five successive cycles. This work highlights the potential of functional ZIF-based materials for targeting CO 2 capture and conversion.
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