Research On The Adsorption Performance And Mechanism Of 17?-estradiol Onto Graphene-like Magnetic Biochar In Aqueous Solution

In recent years,the level of environmental estrogens(EEs)in water has continuously surge due to the frequent use of medicine,personal care products,plastic products and the unreasonable discharge of wastewater from animal husbandry,hospitals and domestic living.Studies have shown that EEs has been widely present in the water environment around the world,and has caused great harm to the healthy reproduction of humans,animals and plants.The harmful effects of EEs are mainly manifested in interfering with the normal hormone synthesis,secretion and metabolic processes of the organism,destroying the organism's reproductive system,nervous system,immune system,and inducing tumor diseases.Therefore,how to remove EEs from water effectively has become a hot topic in the scientific community.Adsorption has been considered to be the most potential method for removing various pollutants in water due to its advantages of simple operation,high treatment efficiency,low cost,easy reuse and low energy consumption.Meanwhile,biochar has been a hot research direction in the field of adsorption because of its unique structural characteristics,low material cost,and simple preparation operations in recent years.Based on the above considerations,17?-estradiol(E2)was selected as the representative EEs.The adsorption ability and its mechanism of E2 onto biochar that prepared by different methods,which including the different modification order and pyrolysis temperature was studied.Given the complexity of natural environment,the effects of the common(pH,inoic strength,humic acid and background electrolyte)and the new(inorganic nanoparticles:Al₂O₃ and microplastics)water environment conditions on E2 removal has been discussed.In order to avoid the secondary pollution that caused by the modified biochar material,A green and graphene-like magnetic biochar that produced by LSP and wood dust was synthesis by potassium ferrate for 17?-estradiol removal.Meanwhile,the impact of external environmental conditions was explored.The specific research work and results of this paper are summarized in the following four parts:In the first part,the adsorption performance and related mechanism of E2 in water by unmodified LSP biochar and KOH activated LSP biochar that prepared based on different modification sequences were studied.The scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR)and automatic specific surface area analyzer were used to investigate the morphology,compositions and structure of LSP-derived biochar.The effect of initial solution pH,humic acid,contact time and temperature,ionic strength onto LSP-derived biochar were studied.Meanwhile,the adsorption mechanisms were explored by combine the experimental data and the adsorption kinetic and isotherm model.The results showed that the modification reagent KOH can effectively increase the specific surface area of biochar and contribute to the formation of graphitized structure of biochar.The order of the KOH activation step has significant influence on the morphology structure,specific surface area,element composition,crystal structure and surface functional groups of the LSP-derived biochar,and ultimately affects the ability of the sample to remove E2.Compared to the pre-treatment and unmodified biochar,the post-treatment biochar possesses a better adsorption capacity.The order of sample biochar adsorption capacity for estradiol is:LSPB-K(post-treated biochar)>KLSP-B(pre-treated biochar)>LSPB(direct pyrolysis biochar).The efficiency of E2 removal increased with increasing E2concentration and decreased with the increase of ionic strength.E2 adsorption on LSP-derived biochar(BCs)was influenced little by humic acid,and slightly affected by the solution pH when its value ranged from 4.0 to 9.0,but considerably affected at pH 10.0.Low environmental temperature is favorable for E2 adsorption.The pseudo second-order dynamic model and Langmuir isotherm model could better simulate the experimental data and the adsorption process.to fit the kinetic E2adsorption results.Results also showed that chemisorption,?–?interactions,monolayer adsorption and electrostatic interaction might be possible the main adsorption mechanisms.In the second part,based on the results of the first chapter,the adsorption behavior of E2 by KOH-modified lotus biochar that prepared by two-step pyrolysis were studied.The morphological characteristics and physical and chemical properties of the prepared biochar were investigated through the characterization techniques of SEM,XPS,XRD,FTIR and automatic specific surface area analyzer.Meanwhile,the adsorption ability of biochar that prepared at different pyrolysis temperatures(the first pyrolysis temperature was 400?and 500?,respectively)to E2 pollutants in water was compared.The effect of common environmental factors,such as initial solution pH,humic acid were discussed.Besides,this part has carried on comparative analysis of the lotus biochar that prepared by two-step pyrolysis with the lotus biochar that prepare by direct,pre or post-treatment in first chapter on E2 pollutants adsorption capacity.The results showed that the biochar prepared by the two-step pyrolysis method has the largest specific surface area,and the E2 adsorption capacity was better than that of the direct pre or post-treatment biochar samples.During the two-step pyrolysis preparation process,the elemental composition of biochar is less affected by the pyrolysis temperature of the first step,and the higher the pyrolysis temperature of the first step(500?)would contribute to the increase of the specific surface area.At a temperature of 290 K,the maximum adsorption capacity of LSP500K-B for E2 was 100.60 mg/g,indicating that biochar produced through the two-step pyrolysis process has great application potential.The adsorption process of E2 by LSP400K-B and LSP500K-B could be well described by the pseudo second-order dynamic model and Langmuir isotherm,demonstrating the adsorption is mainly controlled by chemical adsorption.When the initial solution pH value was 10 or the existence of Na Cl(0-0.1M)in E2 solution,The adsorption ability of E2 on LSP400K-B?LSP500K-B would decrease,however,humic acid had little effect on E2adsorption.In the third part,a novel graphene-liked magnetic biochar(GLMB)was successfully synthesized by one-step method using biomass-derived biochar as a precursor and K₂Fe O₄ as activator and was applied for E2 pollution removal.The graphene-like structure and magnetic property of GLMB have been confirmed by various characterization techniques,including SEM,TEM,HRTEM,XRD,Raman,XPS,atomic force microscope(AFM),vibrating sample magnetometer(VSM)and automatic specific surface area analyzer.Several common(solution pH,ionic strength,humic acid and foreign ions)and new(Al₂O₃nanoparticles and microplastics(MPs))water experiment conditions were investigated.Results exhibited that GLMB was successfully prepared and it possessed a larger surface area(828.37 m₂/g).The E2adsorption onto GLMB fitted better to the pseudo-second-order kinetics and Langmuir isotherm models better describe the isothermal adsorption data,and the adsorption capacity of GLMB at 288 K was 98.73 mg/g.Humic acid and background electrolyte(Na⁺,K⁺,Ca²⁺,Mg²⁺,Cl^-,NO^3-,PO₄^3-)showed a negligible effect,but the adsorption capacity was affected by solution pH,and SO₄^2-ions for the removal of E2 onto GLMB.The presence of Al₂O₃/MPs reduced the adsorption equilibrium time.However,at equilibrium time,the increased ratio of Al₂O₃/GLMB or MPs/GLMB did not show obvious improve or inhibit effect on E2 removal.Multiple mechanisms may act simultaneously for E2 adsorption onto GLMB,including?-?interactions,micropore filling effects,electrostatic interaction,etc.The regeneration experiments showed that GLMB possessed a good regeneration performance.Based on the experimental results and comparative analysis with other adsorbents,GLMB was an economical,high-efficiency,green and recyclable ideal adsorbent for E2 removal.In order to understand the impact of different biomass types of biochar and the different pyrolysis temperatures,and the ratio of biochar to potassium ferrate during the preparation process,in the fourth part six kinds of sawdust biochar that modified by potassium ferrate have been prepared.Studies have shown that when the mass ratio of biochar to potassium ferrate is 1:1 and the pyrolysis temperature is 900?,the sample biochar has the best performance of E2 adsorption.Through SEM?HRTEM?XRD?XPS?VSM and Raman,the morphology,such as the specific surface area,pore volume and the graphene-like properties of sample biochar were investigated.The results showed that the surface morphology of the potassium ferrate modified sawdust biochar prepared under different ratio conditions and different pyrolysis temperatures was quite different.The specific surface area and pore structure of sawdust biochar increased with the increasing of potassium ferrate.However,the pyrolysis temperature of biochar is not the higher,the better,as the surface area of sawdust biochar tends to rise first and then decrease with the increase of pyrolysis temperature,and the disorder structure would increase.The solid-liquid separation of sawdust biochar can be achieved by a magnet,which provides convenience for the recycling of sawdust biochar.The adsorption data of graphene-like magnetic sawdust biochar could be well fitted by pseudo first-order model and Langmuir model,indicating that the adsorption process is mainly controlled by the diffusion step and is monolayer adsorption.Besides,Low temperature conditions and the presence of humic acid are more conducive to the removal of E2 by graphene-like magnetic sawdust biochar but the initial pH of the solution was go against to E2 adsorption in the water environment.