Preparation Of Magnetic Biochar And Its Adsorption Characteristics For Organic Pollutions In Water

Compared to heavy metal,nitrogen,phosphorus,and dye pollution,Norfloxacin(NOR)and Bisphenol A(BPA)are emerging organic pollutants in recent years,and there are few reports on the removal of both from water.As a traditional sewage treatment process,the adsorption method is favored for its high efficiency,low cost and easy operation.Biochar is a carbonbased adsorption material that has been widely studied in recent years.However,the size of the biochar particles is generally small,which makes it difficult for the biochar after adsorption to be recovered from the water,which reduces its practical value.Therefore,this article is based on enhancing the recyclability of biochar,modifying biochar with iron oxide particles,preparing magnetic biochar,and applying it to remove organic pollutants in water:Norfloxacin,Bisphenol A and Methyl Orange.The main work and conclusions of this article are as follows:(1)Pomelo peel-based biochar(BC)was prepared at different pyrolysis temperatures using discarded grapefruit peels.The adsorption kinetics and adsorption isotherm models of Norfloxacin and Bisphenol A by pomelo peel-based biochar at different pyrolysis temperatures were explored.On this basis,the optimal pyrolysis temperature of pomelo peelbased biochar(400℃ BC)is selected,and the mixed solution of Fe(II)/Fe(III)is used as the magnetizing substance,through the chemical precipitation method without oxygen limitation,γ-Fe2O3@BC was prepared by loading γ-Fe2O3 onto the surface of pomelo peel-based biochar.The physical and chemical properties of the BC and γ-Fe2O3@BC were characterized,and the results showed that the introduced γ-Fe2O3 particles can significantly increase the specific surface area and pore volume of pomelo peel-based biochar.The surface of biochar modified with iron oxide particles has richer oxygen-containing functional groups.In addition,the introduction of γ-Fe2O3 particles reduces the electronegativity of the surface of the material,making it have a lower zero point charge,making γFe2O3@BC able to adsorption Norfloxacin and Bisphenol A in a wider pH range.The hysteresis loop of γ-Fe2O3@BC was measured with a vibrating sample magnetometer(VSM).The results show that the prepared γFe2O3@BC has superparamagnetism and saturation magnetization(Ms)as high as 30.60 emu/g,which can achieve rapid separation under the action of an external magnetic field.(2)The adsorption characteristics and mechanism of Norfloxacin and Bisphenol A in water by BC and γ-Fe2O3@BC were explored.The results show that the adsorption of Norfloxacin(Bisphenol A)by BC and γFe2O3@BC is a spontaneous endothermic(exothermic)process,and the adsorption process can be described by pseudo-second-order kinetic models and Sips(Langmuir)isothermal model.Compared with BC,γ-Fe2O3@BC has a larger adsorption capacity and applicable pH range for Norfloxacin and Bisphenol A.The analysis of the adsorption mechanism shows that the main force of BC adsorption of Norfloxacin is cation exchange and hydrogen bonding,and the hydrophobic effect is the main force of γFe2O3@BC adsorption of Norfloxacin.The adsorption mechanism of BC and γ-Fe2O3@BC for Bisphenol A is more complicated.The H bond interaction and π-π electron donor-acceptor(EDA)interaction are the main forces for BC and γ-Fe2O3@BC to adsorb Bisphenol A.(3)The performance of γ-Fe2O3@BC reused to adsorb Norfloxacin and Bisphenol A was explored.The adsorbed saturated γ-Fe2O3＠BC is separated by a magnet,followed by ethanol immersion and drying,and then the next adsorption test is continued.The results show that after 4 cicular adsorptions,the adsorption of Norfloxacin and Bisphenol A by yFe2O3@BC can still reach 61.43%and 80.01%of the initial adsorption capacity,demonstrating a good recycling performance.(4)Using water hyacinth stem biomass,Fe3O4 was loaded onto the surface of water hyacinth biomass biochar by impregnation-pyrolysis method,and Fe3O4@BC was prepared and characterized.The adsorption characteristics of Fe3O4@BC to the azo dye Methyl Orange(MO)were explored,and the preparation parameters of Fe3O4@BC were optimized by response surface methodology to enhance its adsorption capacity for Methyl Orange.The results show that the optimal preparation parameters of Fe3O4@BC are:Fe2+concentration=0.27 mol/L,pyrolysis temperature=405℃,pyrolysis time=3.2 h.The increase of Fe2+concentration and pyrolysis temperature can increase the specific surface area and pore volume of Fe3O4@BC,while the average pore size is only controlled by the pyrolysis temperature.Fe3O4@BC has superparamagnetism,and the preparation parameters have a significant effect on its saturation magnetization(2.57-18.49 emu/g).The optimal preparation parameters of Fe3O4@BC can achieve good separation within 3 minutes after applying a magnetic field.The kinetics and adsorption isotherms of Fe3O4@BC for Methyl Orange conform to pseudo-second-order kinetics and Sips model,respectively.Adsorption thermodynamics shows that the process of Fe3O4@BC adsorption of Methyl Orange is a spontaneous exothermic process.The mechanism analysis shows that electrostatic interaction and H bond formation are the main mechanisms for Fe3O4@BC to adsorb Methyl Orange.