Preparation Of Magnetic Biochar For The Removal Of Heavy Metals From Aqueous Solution

Forest waste,as an important biomass resource,has become a hot point in recent years.The classic approach for biomass was used to produce into biochar.Biochar as an adsorbent has high specific surface area,rich surface functional groups and stable structure,which is benefical to the treatment of heavy metal pollutants from wastewater.However,it is difficult to recycle,resulting in high-cost and second pollution.To solve the above problem,in this study,the biochar was prepared by magnetizing,dipping and high-temperature pyrolysising method.Meanwhile,the in-situ growth of metal and metal oxide nanoparticles was realized.It has large specific surface area,excellent adsorption-photocatalysis performance.What’s more,it is recyclable.With Pb（II）and Cr（VI）as target pollutant,the performance of the samples was investigated,and the mechanism of adsorption-photocatalysis has been explored.The main research results are as follows:1.With different biomass（PS,FS,BS,CS,QS,WS）as raw material,the biochar（BC）was synthesized at different temperatures（300℃,500℃,700℃）by high-temperature pyrolysising.The biochar from PS has abundant surface functional groups,pore structure,large specific surface area and strong surface electronegativity by SEM image,FTIR and other characterizations.At the same time,it has a higher p H and conductivity.With Pb（II）as the target pollutant,PS700 has better adsorption performance（92.31%）,which is higher than FS700（88.20%）,BS700（15.84%）,QS700（10.35%）,and WS（7.16%）and CS700（7.05%）.Therefore,biochar from PS was used to remove Pb（II）and Cr（VI）in the water.2.BC/MgO/Fe₃O₄ with magnetic and recyclable was prepared by the high-temperature pyrolysising.SEM image showed that MgO with the hexagonal aggregated spherical structure（40 nm）and Fe₃O₄ with octahedral structure（600-800 nm）were uniformly distributed on the surface of BC.BC/MgO/Fe₃O₄ has a large specific surface area(337.82 m²g^-1).With Pb（II）as the target pollutant,the saturated adsorption capacity of BC/MgO/Fe₃O₄ can reach 639 mg g^-1,which is significantly higher than that of BC/Fe₃O₄(352 mg g^-1).The removal rate of Pb（II）can still remain86%after 10 cycles.However,it has high leaching of iron(33.13 mg L^-1after 14 days).To reduce the leaching of iron,BC/GO/Fe₃O₄ was prepared by self-assembly method.After 10 minutes,BC/GO/Fe₃O₄ can adsorb 98%of Pb（II）.The key is that BC/GO/Fe₃O₄ has excellent stability.Under weak acidity（p H=4）,high salinity and high humic acid environment,the adsorption of Pb（II）is 80%.After 14 days,the concentration of iron ions leaching in the BC/GO/Fe₃O₄ system(7.78 mg L^-1)is much lower than that of BC/MgO/Fe₃O₄(33.13 mg L^-1).Importantly,the leaching of iron ions in the BC/GO/Fe₃O₄ system(45.89 mg L^-1)at p H 2.0 has reduced compared with BC/MgO/Fe₃O₄ system(167.12 mg L^-1).3.The in-situ growth of plasmonic-bismuth（Bi）combined with magnetic ferroferric（Fe₃O₄）nanoparticles on biochar was realized by high-temperature pyrolysising.Bi and Fe₃O₄ nanoparticles was unifirmly distributed on the BC.BC/Bi/Fe₃O₄ has large specific surface area(43.4638m² g^-1)and exhibits broad and strong light absorption from 400 nm to 2000nm.Under visible light,with Cr（VI）as the target pollutant,BC/Bi/Fe₃O₄has excellent removal efficiency for Cr（VI）（95%）,which is high than BC/Bi（60%）,BC/Fe₃O₄（72%）and Bi/Fe₃O₄（56%）.In addition,the photoelectrocatalytic removal efficiency of Cr（VI）（97%,160 min）was high than photocatalytic（95%,180min）.BC/Bi/Fe₃O₄ was also stability and recyclability.