Study On The Controlled Preparation,Composite Modification And Catalytic Performance Of New Transition Metal Co/Ni-based Materials

The sustainability of energy and ecological and environmental issues constitute an increasingly severe global crisis today,which seriously restricts the harmony and development of human society.The development of green,clean,efficient,and renewable new energy is an inevitable demand for social development.These new energy technologies include hydrogen production by electrolysis of water,fuel cells,and metal-air batteries,especially hydrogen production by electrolysis of water.However,the oxygen evolution reaction(OER)occurring at the anode in the hydrogen production technology by electrolysis is the bottleneck of technology transformation.Noble metal-based materials have good electrocatalytic performance,and Ru O₂ is a commercial catalyst for OER and is used in large quantities.However,precious metals are rare in surface content,expensive in price,and easy to be poisoned and inactivated,which are the main restricting factors for the development of the industry.Therefore,because of this technical bottleneck,this paper uses the following methods to solve the above problems:(i)Select the transition metal(cobalt and nickel)with abundant and cheap surface content as the basis to synthesize new metal-organic framework(MOFs)catalyst materials;(ii)To improve the catalytic performance and stability of MOFs materials by changing the dimension of MOFs materials and modifying and modifying the substrate;(iii)In the process of analyzing MOFs with good OER performance,it is found that metal ions in MOFs are active centers and can easily combine with oxygen potentials,and then the MOFs@CS/O₃ composite catalytic system is constructed,which can be applied to the pretreatment and deep treatment system of pollutant degradation and coking wastewater treatment process.The specific research contents include the following aspects:(1)The transition metal(cobalt and nickel)was selected as the metal center,and 1,2,4,5-Benzenetetracarboxylic acid was used as the organic ligand,and a series of three-dimensional columnar MOFs were synthesized by the hydrothermal method.3D-Co/NiMOFs can be used as an efficient and stable OER catalyst in 0.1 M KOH solution,where?₁₀ is 377 m V,and?=110.5 m V dec^-1.3D-Co/NiMOFs can be synthesized in situ and uniformly distributed on iron foam without bonding.The porosity of the foam material is conducive to gas desorption,and the composite with the conductive substrate can further improve the catalytic performance.Compared with single metals,the OER activity of 3D-Co/NiMOFs@Fe(?₁₀=264 m V,?=54.3m Vdec^-1)is significantly enhanced,and has good stability.According to XPS analysis,the binding energy of Co/Niin bimetallic MOFs moves to a higher direction after Co/Nibimetallic doping,in which the increment of Co 2p_3/2 is 0.4 e V and that of Ni2p_3/2 is 0.3 e V.The synergistic effect of electrons after bimetal doping can improve the OER performance of MOFs materials.In MOFs,the performance of the material can be improved by modifying the active center of the metals,increasing the types of metal ions,and the in-situ composite of conductive substrate materials.(2)1,4,5,8-naphthalenetetracarboxylic acid was selected as the organic ligand,the triclinic crystal system[Ni₂(NTC)(H₂O)₈]·4H₂O crystal was synthesized by low-temperature hydrothermal method for the first time,and its crystal structure was analyzed by X-Ray single crystal diffractometer.The ultra-thin nanosheets(2D-MOFs)with coordinated unsaturated metal sites were successfully prepared at low temperatures combined with ultrasonic peeling technology,and the thickness of 2D-Co MOFs,2D-NiMOFs,and 2D-Co/NiMOFs was 3.45 nm,8.84 nm,and 5.26 nm,respectively.In 0.1 M KOH solution,the OER catalytic performance of2D-Co/NiMOFs(?₁₀=317 m V,?=59.44 m Vdec^-1)is higher than that of 3D-Co/NiMOFs,and it is also better than single metal ultra-thin nanosheets.In the synthesis of efficient catalysts,heteroatom doping and ultra-thin nanosheets are an effective strategy to promote MOFs as OER catalysts.(3)High-temperature calcination of metal-organic framework materials(MOFs)in an inert(Ar)atmosphere converts them into carbon nanostructured composite materials.The 3D-Co/NiMOFs were doped with in-situ heterogeneous elements(carbon,nitrogen,oxygen,phosphorus,sulfur,and selenium).The carbon-based material formed after high-temperature carbonization can still maintain the 3D-Co/NiMOFs original morphology(three-dimensional columnar),while the electrical conductivity of the material has been improved.The Co/NiMOFs@Se and 3D-Co/NiMOFs@P materials have excellent OER performance(?₁₀=238 m V,?=109.2 m Vdec^-1)and HER performance(?₁₀=194 m V,?=58.3 m Vdec^-1),with dual functionality.Furthermore,3D-Co/NiMOFs@Se and 3D-Co/NiMOFs@P were assembled into an electrolytic cell for the overall water splitting,showing excellent electrocatalytic water decomposition activity(?₁₀=1.59 V),and stable operation.Improve the properties of carbon-based materials by adjusting the MOFs derived charge distribution strategy on the surface.(4)Green,non-toxic,carbon-based spherical materials were prepared using glucose as the substrate,and 3D-Co/NiMOFs@CS composite was obtained by in-situ packaged/encapsulated of 3D-Co/NiMOFs,with a specific surface area of 100.6 m²/g.With the assistance of a variety of characterization techniques,the performance of 3D-CO/NiMOFss@CS composite material as catalytic ozonation was investigated,and the research objects were Levofloxacin,raw water from coking wastewater,and effluent from OHO biological process.(i)Analyze the three degradation pathways of levofloxacin in the 3D-Co/NiMOFs@CS/O₃ system.Since the metal active center in 3D-Co/NiMOFs is the oxygen binding site,it can promote ozone to produce a variety of free radicals(O₂^-·,¹O₂,and·OH),and analyze the transformation law of nitrogen in levofloxacin.(ii)Based on the fact that residual COD and total nitrogen(TN)are the constraints of water treatment technology,and combined with the actual experience of coking wastewater treatment projects.The 3D-Co/NiMOFs@CS/O₃ system was applied to the coking wastewater project.The removal effect of COD and the migration and transformation rule of nitrogen elements in the pretreatment system and deep treatment system of coking wastewater by 3D-Co/NiMOFs@CS/O₃ system were preliminarily discussed.In short,this article systematically studied new Co/Nicatalyst materials(Co/Ni-MOFs)and achieved the improvement of the electrocatalytic performance of the catalyst by qualitatively and quantitatively controlling the structure,morphology,and composition of the material.On the one hand,the combination of MOFs material rich in oxygen binding sites and advanced oxidation technology has been realized,which is a preliminary exploration in actual coking wastewater treatment projects.It provides an experimental basis and theoretical reference for the practical application of MOFs materials.