Preparation Of Iron-based LDH And Its Adsorption And Degradation Of Bisphenol A

Bisphenol A?BPA?is an important raw material for the synthesis of polycarbonate and epoxy resin,and is also a typical endocrine disruptor.Because BPA is extremely difficult to degrade in the natural environment,it can also be enriched in living organisms through the food chain.More and more studies have shown that BPA has spread all over the world and adversely affects the natural environment and human health.Traditional methods for removing BPA include biological methods,physical adsorption methods,chemical oxidation methods,and the like.Among them,the adsorption method has been widely studied and applied due to its simple operation,low cost and good removal effect.Layered double hydroxide?LDH?is a typical anionic layered clay mineral as a representative of layered double hydroxide.Its unique ion exchange performance and structural memory benefits make it a good adsorption performance and can be recycled.But adsorption simply transfers contaminants and does not remove the contaminants fundamentally.The catalytically active Fe²⁺is introduced into the laminate by the controllability of the ionic layer ions of the LDHs,and a heterogeneous iron-based catalyst having catalytic activity can be obtained.In this paper,the widely used magnesium-aluminum hydrotalcite?Mg-Al-LDH?and iron-based hydrotalcite?Fe-Al-LDH?were synthesized.The synthesized materials were calcined,and the materials before and after calcination were characterized by XRD,FTIR,SEM and TG.The results show that the materials before calcination have a good crystal structure and have the characteristics of typical LDHs.The calcined materials are typical metals of oxide structure.The resulting material was applied to the adsorption of BPA and its derivative bisphenol AF?BPAF?.The results showed that only Mg-Al-CLDH could effectively adsorb BPA and BPAF,and the removal efficiency reached 96.16%and 96.96%at 48h,respectively,and the adsorption accorded with the Langmuir isotherm model.The maximum adsorption capacities of Mg-Al-CLDH for BPA and BPAF were 216.5 mg/g and 337.6 mg/g,respectively.On the one hand,the adsorption mechanism of Mg-Al-CLDH is restored to the previous layered structure due to the structural memory effect during the hydration process,and adsorbs BPA and BPAF in the water;on the other hand,the layered structure of Mg-Al-CLDH is restored.Mg-Al-CLDH also removes BPA and BPAF by surface electrostatic adsorption.In addition,the initial p H,temperature,different coexisting anions and ionic strength will affect the adsorption capacity of Mg-Al-CLDH to varying degrees.The Mg-Al-CLDH regenerated by calcination can effectively remove BPA and BPAF from water,and although Fe-Al-LDH can not effectively adsorb BPA and BPAF,the ferrous iron contained in it can be used in Fenton system to degrade organic pollutants.The second part of the thesis uses this property to study the new homogeneous and heterogeneous systems of Fe-Al-LDH and H2O2.The experimental results show that the system can completely degrade BPA within 30 minutes and overcome the traditional Fenton.The disadvantage of high acidity in the system is the ability to degrade BPA over a wide p H range.Through a series of characterization results,a new synergistic effect of homogeneous and heterogeneous Fenton systems was proposed as the reaction mechanism.The dissolved Fe²⁺from Fe-Al-LDH and the ion exchange caused by the dissolution reprecipitation process release Fe²⁺as a homogeneous Fenton catalyst.In addition,undissolved and newly formed?by dissolution reprecipitation process?LDH forms a heterogeneous Fenton system with H2O2.The two systems achieve rapid and efficient degradation of BPA through synergy.In the cycle experiment,Fe-Al-LDH was proven to be used multiple times and achieved a degradation rate of more than 95%for BPA.Sulfate radicals ionized by persulfate?PMS?possess more powerful oxidizing ability than hydroxyl radicals.In addition,the properties of PMS are relatively stable,and the reaction rate is slow at normal temperature.Once activated,the reaction rate can be greatly increased.Therefore,the third part of the paper uses Fe-Al-LDH and PMS to synergistically degrade BPA.The system is capable of degrading more than 92%of BPA in 5 minutes and BPA could be degradated over a wide p H range.By analyzing the characterization results of the products after reaction,the reaction mechanism of surface activation to generate hydroxyl radicals and sulfate radicals and oxygen-transformed superoxide radicals in the crystal lattice,and three kinds of free radicals synergistically degrading BPA was proposed.The dissolved Fe²⁺from Fe-Al-LDH,Fe²⁺in the crystal lattice and Fe³⁺which have been oxidized can be used to activate PMS.The oxygen in the crystal lattice acts as an electron transfer agent,which reduces some Fe³⁺and generates superoxide radicals,all improve the efficiency of the reaction.Moreover,the concentration of Fe-Al-LDH can be appropriately reduced without affecting the degradation efficiency of BPA,thereby obtaining a lower cost.