Design And Environmental Applications Of γ-Fe₂O₃ Nanosheets/Au₃Fe Intermetallic Compounds Dual-loaded Self-healing Pd Catalyst

Chlorophenols（CPs）,a group of halogenated chemicals containing several homologues,is the main component of flame retardants,insecticides and wood preservatives,which has good application value.However,a large number of research results show that CPs is potentially harmful to the environment and human health.As one of the representative chemicals in CPs,4-chlorine phenol（4-CP）is usually discharged continuously in the form of solid waste and waste water,especially as the ingredient of pesticide and fertilizer,which is widely used and then discharged into the environment,which further increases the risk of harm to people and the environment.Therefore,it is necessary to study the transformation and degradation of 4-CP.Based on the recent research that Pd containing nano-catalysts have good effects on the catalytic fracture of carbon halogen bonds,especially in terms of crystal and electronic structure,this work focused on the preparation of Pd containing nano-catalysts and studied their catalytic effects on 4-CP containing carbon halogen bonds in the environment.At present,the catalytic degradation of 4-CP mainly includes advanced oxidation and electrochemical catalytic reduction.However,these two methods still have some problems,such as low degradation efficiency,complex products,easy to produce secondary pollutants,high cost and poor stability.Therefore,it is very important to construct a synthesis method of catalysts with high catalytic efficiency,lasting catalytic activity,low cost and strong resistance to poisoning.Based on this,in the second chapter of this paper,we designed a synthesis method of Au₃Fe@Pd/γ-Fe₂O₃ heterogeneous nano-catalyst with nanocluster embedded structure.The method has the characteristics of mild synthesis conditions and less precious metals content.Further study on the structure of the catalyst showed that the Au₃Fe nanocluster core could not only serve as the deposition site of Pd atom,but also as an electronic structure modifier to change the filling state of Pd atom d orbital and improve the stability of the catalyst.In the third chapter,we further use the synthesized Au₃Fe@Pd/γ-Fe₂O₃ nano-catalyst for the catalytic experiment of 4-CP to explore its catalytic performance.The results show that the catalytic activity of Au₃Fe@Pd/γ-Fe₂O₃ nano-catalyst to 4-CP reaches up to 80.0%in a short time（20 min）due to the addition of Pd atom.In the further cyclic catalytic performance test,Au₃Fe@Pd/γ-Fe₂O₃ nano-catalyst showed good stability,the catalytic effect of 4-CP reached 85.0%in the fifth cycle.Then,the sulfur poisoning and regeneration of the active site of Au₃Fe@Pd/γ-Fe₂O₃ nano-catalyst were investigated.We first found that the catalyst after sulfur poisoning showed extremely weak activity to 4-CP,but after adding hydrogen peroxide or persulfate solution to react with the catalyst,the generation of hydroxyl radical（·OH）could remove S on the active site of Pd,and due to the strong adsorption of Pd by Au₃Fe nanoclusters.The results showed that Au₃Fe@Pd/γ-Fe₂O₃catalyst had good catalytic activity,regeneration ability and lasting stability in the degradation process of 4-CP.Finally,in the fourth chapter,we prepared Au₃Fe@Pd/γ-Fe₂O₃ nano-catalyst and quartz sand into a water treatment fluidized bed to explore the actual environmental application of the catalyst.In the catalytic experiment of simulated 4-CP polluted environmental water sample,it was found that 1000 bed volume of water sample could be treated by the catalyst in situ regeneration.Furthermore,we applied the catalyst for the catalytic degradation of waste water from flame retardant factory.The experimental results show that the content of organic bromine in wastewater containing complex organic matter is significantly reduced after catalyst treatment.These results indicate that Au₃Fe@Pd/γ-Fe₂O₃ nano-catalyst exhibits high activity and durable stability in the wastewater treatment process containing 4-CP.In conclusion,for the degradation of 4-CP in the environment,we developed a nano catalyst Au₃Fe@Pd/γ-Fe₂O₃ with simple preparation method and mild conditions.The catalyst exhibits persistent catalytic activity and detoxification regeneration ability,which provides a reference for the design and environmental application of nano catalyst in the future.