Preparation Of Magnetic Bamboo Char And Its Effects On The Adsorption Performance Of Heavy Metal Ions

Heavy metal ions are non-degradable and will endanger human health along with the food chain enrichment in the human body,when the ion concentration exceeds a certain value.So it's imminent to solve the problem of the heavy metal pollution.A commonly method used to remove water pollutant is adsorption,in which activated biochar is a frequently-used adsorbent.Bamboo has a natural pore structure,and the bamboo char pyrolyzed at a certain temperature has high specific surface area and resistance to acid and alkali corrosion,which can be used as an excellent pollutant adsorption material.When used to adsorb pollutants in water,the activated biochar adsorbent is usually separated and recovered from the liquid phase by filtration after adsorption ended.The filtration method can easily cause plugging of the filter,and if the recycle is not complete,the secondary pollution is likely to occur.The above problem restricted practical application of active biochar.When loading the magnetic medium on the carbon matrix material,the adsorbent can be separated from the liquid phase by the external magnetic field after the adsorption is completed,and the recycled magnetic carbon can be in desorption and recovered to reuse.The secondary pollution and production costs will be greatly reduced.Thus it is a hot spot in the development of biological activated carbon materials in recent years.Compared with wood resources,bamboo has a short growth cycle.It is more economical to use bamboo as a raw material for biomass to prepare magnetic biological activated carbon materials.This is in line with the theme of sustainable development of green environmental protection.And at the same time,it is also possible to develop new ways to apply bamboo materials and increase the added value of them.In this paper,two different carbon sources were selected:hydrothermal and commercial bamboo char as carbon precursor materials,and ferric chloride hexahydrate and ferric nitrate nonhydrate as magnetic media sources,KOH as an activator.After co-precipitation,16 kinds of magnetic bamboo char composites with high saturation magnetization were prepared by one-step activated and magnetized at high cabornization temperature.The characteristics of each magnetic bamboo char product were characterized by X-ray diffraction(XRD),Raman spectroscopy(Raman),etc.And then a further study was conducted to investigate the influence of different parameters on the adsorption performance.The parameters included pH value,adsorbent dosage,temperature,time,and adsorbate concentration.The two kinds of heavy metal ions were Cu(?)and Pb(?),respectively.Main conclusions were listed as follows:(1)The physicochemical properties of the prepared 16 types of bamboo char were clearly evaluated:the SEM images clearly showed that the new pore generated on the char wall and the spherical aggregates attached to the surface of the bamboo char;the presence of Fe element on the magnetic bamboo char by EDX assisted.The magnetic bamboo char which added the activator KOH had higher Fe content than the untreated sample;the XPS figures proved the presence of carbon(Cls),oxygen(Ols),and iron(Fe2p)elements.The results of multiple peak splitting indicated that the Fe2p peak envelope could be fitted by the Fe(?)peaks corresponding to 709.8,722.8 eV and the Fe(?)peaks corresponding to 711.2 and 724.3 eV;FTIR results showed that the number of functional groups of magnetic bamboo char greatly reduced compared to the original bamboo powder,and the functional groups was determined by the final carbonization temperature.XRD figures showed that there are Fe3O4,?-Fe and FeO in the crystal structure of Fe in the samples.The Raman results showed that extending the carbonization time and using the activator would increase the degree of graphitization of the magnetic bamboo char;VSM test data indicated that all samples have superparamagnetic properties,and the saturation magnetization sample could reach 46.6 emu/g;the specific surface area and pore size analysis found that the specific surface area of activated bamboo char was approximately 2 times of the unactivated one,the sample with the largest specific surface area has a value of 554.637 m2/g for AH1C1-Cl,and the average pore diameter calculated by the BJH method was about 2 nm.(2)For adsorption properties of magnetic bamboo char on heavy metal ions,the adsorption effect was best with AH1C1-Cl among the eight kinds of magnetic bamboo char;it was found that two kinds of heavy metal ions had the optimum adsorption performance at pH=6 in the study of the effect of pH on adsorption process.Adsorbent dosage had different effects on the adsorption performance for two heavy metal ions,the adsorption of Pb(?)was positively related to the amount of adsorbent;The change of adsorption rate of Cu(?)firstly increased and then decreased and droped sharply when the adsorbent dosage reaches 95 mg;Pb(?)adsorption was spontaneous,exothermic,and the degree of disorder was decreasing in the adsorption process,the adsorption of Cu(?)was also a spontaneous and exothermic process,but the degree of disorder increased;the adsorption behavior of the two heavy metal ions wais more consistent with the pseudo-second-order kinetic model,indicating that the entire adsorption behavior was chemical adsorption under rate control,and the adsorption could achieve more than 90%of the equilibrium adsorption capacity within 10 minutes.The fitting results of adsorbate concentration and adsorption amount showed that both heavy metal ions were closer to the Langmuir model,indicating that the adsorption behavior was mainly monomolecular adsorption.The maximum theoretical adsorption capacities of the two heavy metal ions were 125.06 mg/g and 153.85 mg/g,respectively;the N2 adsorption-desorption curve of the sample AH1C1-Cl was a typical type ? isotherm,which represented a unitary multilayer adsorption;the obtained average pore diameter was 1.92 nm calculated by BJH method.(3)The adsorption of magnetic bamboo char on two heavy metal ions belonged to chemical adsorption.The main manifestation was the chemical bonding between heavy metal ions and the surface functional groups of magnetic bamboo char.Activation could provide more effective adsorption sites.The introduction of iron source could also promote adsorption.The magnetic bamboo char prepared with hydrothermal carbon as a carbon source was more conducive to adsorption.(4)AH1C1-Cl had excellent regeneration and recycling.After 5 cycles,the regeneration efficiency of Cu(?)and Pb(?)was 92.4%and 94.1%,respectively.