Synthesis Of Cobalt-based Nanocomposites And Their Catalytic Performance For Reduction Of 4-Nitrophenol

Environmental pollution,especially water pollution,seriously threatens the ecological balance and human health.Among the common water pollutants,4-nitrophenol?4-NP?as a bioaccumulative refractory toxic substance will cause great harm along with the food chain,and 4-aminophenol?4-AP?is an important intermediate for the synthesis of various pharmaceutical and plastic products,so the conversion of 4-NP to 4-AP is an important way to protect water.How to efficiently and conveniently reduce 4-NP to 4-AP has attracted wide attention of researchers.Catalysts for efficient,low-cost and easy-to-recover catalysts for the hydrogenation of4-nitrophenol are important for practical production.Metal cobalt,a non-noble metal in transition metals,is a potentially efficient catalyst.This paper aims to find a variety of methods to prepare different cobalt-based catalysts for reducing 4-nitrophenol,and improve the catalytic activity and recyclability of the catalysts.The main contents of this paper are as follows:1.Graphene-based cobalt-nickel alloy composites with different proportions were synthesized by one-step hydrothermal method.SEM images show that the alloy particles were uniformly dispersed on the graphene lamellae.The catalytic activity and cycling performance of the composites for 4-NP reduction were studied using NaBH₄ as hydrogen source.The experimental results show that graphene as the substrate inhibits the agglomeration of nanoparticles,facilitates their uniform dispersion,exposes the catalytically active sites of the material maximally,and makes the composite exhibit good catalytic performance in the reduction of 4-NP.The catalytic rate is 0.414 min^-1 when Co₂Ni/RGO as catalyst,which is much higher than other catalysts.Cobalt and nickel are magnetic metals,which make them have an advantage in recycling,which further improves the recyclability of the catalyst.2.3D RGO/ZIF-67 bulk phase composites were synthesized by hydrothermal self-assembly method.SEM characterization shows that ZIF-67 was uniformly attached to the holes of 3D RGO.Due to its high mechanical strength,the material has a certain load-bearing capacity,so the material has the potential as a bulk catalyst.Further study on its catalytic activity for 4-NP reduction,the experimental results show that the catalytic rate of 3D RGO/ZIF-67?5 mg?is 0.315 min^-1,which is higher than ZIF-67?1 mg?(0.034 min_-1),3D RGO/ZIF-67?1 mg?(0.064 min^-1)and 3D RGO/ZIF-67?3 mg?(0.204 min^-1),demonstrates that macroscopic three-dimensional porous block structure could not only enrich 4-NP,but also improve its catalytic reduction.The rate also makes the recycling and reuse of catalyst more convenient.3.The modification of Fe₃O₄ by PVP stabilizes Fe₃O₄ in the reaction solution,and the affinity of the nanoparticles to the coordination polymer sphere is enhanced due to the weak coordination interaction between the pyrrolidone ring and the cobalt atom,which making ZIF-67 successfully coating Fe₃O₄.Fe₃O₄@PVP@ZIF-67composite was synthesized by adsorbing PVP-modified Fe₃O₄ onto the continuously growing surface of ZIF-67 to coat Fe₃O₄ successfully.TEM characterization shows that Fe₃O₄ was uniformly coated in ZIF-67,which was further confirmed by BET analysis.Thermogravimetric analysis shows that the thermal stability of ZIF-67 did not decrease significantly after Fe₃O₄ was coated.Infrared analysis further shows that the internal structure of ZIF-67 was not destroyed.The composite material was used to catalyze the reduction of 4-NP.It was found that the synergistic effect between ZIF-67 and Fe₃O₄ greatly enhanced the catalytic activity,its catalytic rate is 0.614min^-1,which is much higher than single material,and the magnetic Fe₃O₄ facilitates magnetic separation.A series of data such as activation energy?Ea?,pre-exponential factor?A?and entropy change?S?of Fe₃O₄@PVP@ZIF-67 and ZIF-67 were also studied,which provided theoretical support for the design and synthesis of highly catalytic catalysts.4.ZIF-67 was synthesized by a simple method,and then amorphous sulfide CoS_x was formed by hydrothermal sulfidation of ZIF-67 by using ZIF-67 as self-sacrificing template.The derivate Co_1-xS of ZIF-67 which has the hollow structure was prepared by annealing in argon atmosphere.At the same time,Co_1-xS NPs were prepared as a control by the traditional two-steps method.The prepared materials were characterized and used to catalyze the reduction of 4-NP.The experimental results show that the catalytic rate of the derivative Co_1-xS(0.548 min^-1)is almost 7 times higher than Co_1-xS NPs(0.079 min^-1).This is because the derivative has hollow structure,the specific surface area is greatly increased,and the substrates can be enriched,so it is more conducive to the catalytic reaction.Then the recycling performance of Co_1-xS was tested.It was found that after four cycles,the catalytic efficiency of Co_1-xS remained above 90%.