Synthesis And Charaterization Of The Magnetic Biochar Composites Derived From Bamboo

Biochar is an excellent adsorption material used in contamiant treatment because of its porous structure,high specific surface area,good acid and caustic corrosion resistance and other characteristics.However,filtration,the main method of conventional separation of biochar from aqueous solution,is generally facing some thorny issues,such as clogging of the filter and loss of the adsorbent.By loading magnetic particles to biochar surface,simple magnetic solid-liquid phase separation can be easily achieved,which is a new hot spot in the development of biochar material.Using bamboo as the biomass feedstock to prepare magnetic biochar composites is an important way to extend the utlization of bamboo and develop the high value-added products.In this work,Moso bamboo was used as the raw material to prepare the precursor firstly through crushing,drying,pyrolysis under low temperature,impregnation with iron salt and other steps.Then the magnetic bamboo charcoal composites with high saturation magnetization were fabricated by one-step carbonization of the resulting precursor under high temperatures.All the bamboo-based products were characterized by X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),Raman spectroscopy,Fourier transform infrared spectroscopy(FT-IR),environmental scanning electron microscopy(ESEM),transition electronic microscopy(TEM),superconducting quantum interference device(SQUID),etc.The results were summarized as follows:(1)The advances of magnetic biochar composites were described.Its preparation methods and correlative process parameters were emphatically introduced.In addition,the applications of magnetic biochar in pollution treatment were also briefly mentioned.(2)Carbonized samples were obtained through pyrolyzing 70-meshes bamboo powder for one hour under different low temperature,i.e.300,450 and 600 °C,which were referred to as BC300,BC450 and BC600,respectively.Then BC600 was used as the carbon source to obtain the precursor of magnetic biochar through impregnation with hexahydrated ferric chloride(the mass ratio of charcoal to salt was 1: 10),mixing,dring and grinding,which was referred to as BC600 P.Characterization results indicated that,BC300 remained some functional groups stemed from the raw bamboo powder and did not be fully carbonized.BC450 and BC600 were carbonized entirely,but the latter possessed a slightly higher degree of graphite.For BC600 P,the charcoal matrix was covered with ironbased derivatives domoninated by chlorides and oxides,which provided a guarantee for the subsequent charcoal magnetization.(3)Magnetic bamboo charcoal composites were fabricated by carbonizing BC600 P for one hour under high temperatures(800,1000 and 1200 °C),which were referred to as MBC800,MBC1000 and MBC1200,respectively.All the products were of high saturation magnetization,though there were some differnces in structure and morphology.Two magnetic media existed in MBC800,i.e.Fe3O4 and ?-Fe2O3,made up lots of spherical aggregates(about 5 ?m in diam)attached into the charcoal matrix surface.However,only zerovalent iron was detected in both MBC1000 and MBC1200.The iron particles in MBC1000 with a diameter ranging from nano level to micron level were partically embedded in charcoal matrix,while most iron particles in MBC1200 aggregated into quasi spherical particles with a diameter of tens of micrometers and isolated from the charcoal matrix.The saturation magnetization of such three samples were 63.6,118.1 and 122.7 emu g-1,respectively,and the last two were superparamagnetic due to their low coercivity.Excellent magnetic properties showed that they had a great potential for development in magnetic materials.(4)Based on the characterization results obtained at the stages covered from raw material to final products,the formation mechanism of magnetic bamboo charcoal composites was discussioned.After ferric chloride was dissolved in the charcoal suspensions,iron oxides or hydroxides were uniformly distributed on the charcoal matrix,which were formed in the process of mixing,drying and grinding.During the high temperature carbonization,the iron-based compounds in the precursor were reverted to iron oxides such as Fe3O4 followed by zerovalent iron with the rise of temperature.Finally,most metallic iron particles aggregated and formed sphericle particles with a higher volume,which were isolated from the charcoal.Therefore,in order to obtain zerovalent iron/bamboo charcoal composites with stable physical and chemical properties,carbonization temperature should be controlled within a reasonable range.