Preparation Of Cobalt-containing Metal Compounds Porous Nanomaterials Using ZIF-67 As A Precursor And Their Application In Catalysis

Porous metal compounds nanomaterials were acknowledged to be excellent catalysts due to their porous structure and high activity of metal compounds.MOFs could be precursors to syntheze porous metal compounds nanomaterials because of their unique morphology,ordered porous structures,rich metal and organic species.Despite the rapid development has been achieved using MOFs as precursors to synthesize metal compounds with complex structures and compositions,there is still lack of universal synthetic approaches.This dissertation focuses on the synthesis of a series of cobalt-containing metal compounds using ZIF-67 as a precursor,providing a common method for designing and fabricating porous metal compounds with complex structures and compositions and investigates the properties of synthesized products as heterocatalysts.1.Hollow CeO2 dodecahedrons:template synthesis and catalytic performance for CO oxidationHollow CeO2 dodecahedrons were synthesized using ZIF-67 nanocrystals as templates via liquid phase reaction for the first time.The structure,composition,morphology,and surface chemical states of the as-prepared hollow CeO2 dodecahedrons were thoroughly investigated with XRD,SEM,TEM,HR-TEM,XPS,Raman,and ICP-AES.The hollow structures,with a specific BET surface area as high as 128 m2·g-1，are composed of small Ce02 particles with diameter less than 5 nm.The formation mechanism of hollow CeO2 were proposed that Ce02 nanoshell deposited on the template due to the hydrolysis of cerium nitrate in ethanol,during which the template was dissolved as H+ released from the hydrolysis.The CO oxidation catalytic activities of hollow Ce02 dodecahedrons revealed a good performance with complete CO conversion at about 170℃,which can be attributed to its large surface area,small crystallites,hollow structure,large amount of oxygen vacancies,as well as the containing Co species.This work provides a rapid and cost-efficient approach to synthesize a new dodecahedral CeO2 hollow structure,which broadens the way to synthesize crystalline metal oxide with controllable morphologies in mild solution conditions.2.Synthesis of Co-based multimetal hydroxide/CeO2 dodecahedral nanocages with enhanced oxygen evolution reaction activityZIF-67@CeO2 core-shell structure was prepared by ZIF-67 template reacting with cerium nitrate.The core-shell structure then reacted with mixed metal nitrates in ethanol,resulting in a series Co-based multimetal hydroxide/CeO2 composites with porous dodecahedral nanocage structure.The composites well replicated the morphology of ZIF-67 template with sandwiched shell:Co-based hydroxide outer layer intimately in contact with CeO2 inner layer.All of the three composites exhibited enhanced oxygen evolution reaction activity with lower overpotential,Tafel slope,larger TOF and increased electro conductivity,which was due to the porous hollow structure,the excellent oxygen storage ability and good conductivity of ceria,the interactivity between ceria and hydroxide.Among them,the CoNiFe ternary hydroxide/Ce02 hollow structure exhibited best OER performance because of the synergistic effect of multiple metal elements.This robust strategy provides not only a new way for preparing hollow nanostructures with tailored shell architectures but also opens up more opportunities for the development of efficient Co-based composite electrocatalysts by compositional and structural engineering.3,Synthesis of porous CoF2-C composite for highly efficient water oxidationThe well dispersed cobalt nanoparticles in porous carbon matrix were synthesized by annealing ZIF-67 nanocrystals in inert atmosphere first and then reacted with HF gas,producing porous CoF2-C composite.This is the first time using MOFs as precursor to prepare cobalt fluoride nanocomposites,and the organic linkers in ZIF-67 converted to carbon increasing the electroconductivity of cobalt fluoride.The porous CoF2-C composite exhibited good OER activity and excellent stability because of increased electroconductivity and large electrochemically active surface area.