Preparation Of Biomass-based Porous Activated Carbon And Its Adsorption Performance Of Cr(Ⅵ) Ions

The development of high efficiency,low cost and easily available adsorbent materials is an important research direction in the field of wastewater treatment.In view of the problem that heavy metal chromium ion in aqueous solution is highly toxic and difficult to degrade,this project plans to carry out the preparation of activated carbon material with high adsorption performance based on renewable biomass with low raw material price（and its adsorption performance of Cr（Ⅵ））.At present,the biomass based raw materials for the preparation of activated carbon show the characteristics of high specific surface area,large pore volume and excellent adsorption performance.This project plans to use corn stalk,beet residue and beet as raw materials,respectively,using different activation methods and activation reagents,to prepare multiple series of biomass-based activated carbon materials.The morphology and structure of the prepared activated carbon were characterized by SEM,TEM,N₂-adsorption,XRD,FT-IR and Raman methods.The prepared activated carbon was used in the adsorption experiment of Cr（Ⅵ）ion aqueous solution.The effects of the preparation methods on the structure and adsorption properties of the activated carbon were investigated.1.Corn straw was used as raw material and a new activation method was adopted,that is,KOH or H₃PO₄ dilute solution was used as activator after activation treatment,which did not participate in the roasting process.The activation process dissolved part of the tissue structure of corn straw and played the role of pore-building.When p H of Cr（Ⅵ）ionic solution was 4.5 and the amount of activated carbon was 2.5 g/L,the adsorption capacity of activated carbon prepared by 4 wt%KOH solution reached 89.5mg/g.The adsorption capacity of activated carbon prepared by activation of 1 wt%H₃PO₄ solution reached 98.5 mg/g,which was generally higher than the results reported in the literature.The Freundlich model of AC-KOH（4）has the highest fitting degree,indicating that the adsorption of corn stover based activated carbon is multi-molecular layer.The Langmuir model of AC-H₃PO₄（1.0）has the highest fitting degree,indicating that the adsorption process is monolayer adsorption.Through the kinetic model fitting of adsorption,the two series of corn stover based activated carbon meet the pseudo-second order kinetic model,indicating that the adsorption of corn stover based activated carbon is mainly chemisorption.2.Beet residue as raw material,three series of beet residue based multi-pore activated carbons were prepared by using KOH,H₃PO₄ and Zn Cl₂ as activators after the raw material was first carbonized.When the p H of Cr（Ⅵ）ionic solution is 4.5 and the amount of activated carbon is 2.0 g/L,the adsorption capacity of activated carbon prepared by activation with KOH/carbonization precursor ratio of 3,700°C reaches163.7 mg/g.The adsorption capacity of activated carbon prepared by H₃PO₄/carbonization precursor ratio at 2,600°C is 247.9 mg/g,and that of activated carbon prepared by Zn Cl₂/carbonization precursor ratio at 2,700°C is 166.5 mg/g.The Langmuir model of BR_KOH3.0-700 and BR_H3PO42.0-600 has the best fitting degree,indicating that the adsorption process is monolayer adsorption.The Freundlich model of BR_{Zn Cl2}2.0-700 has the highest fitting degree,which indicates that the activated carbon prepared from beet residue is adsorbed by multiple molecular layers.Through the kinetic model fitting of adsorption,the three series of beet residue based activated carbon have the highest degree of fitting to the pseudo-second order kinetic mode,indicating that the beet residue based activated carbon is mainly chemisorption.3.Beet as raw material,using KOH and H₃PO₄ as activators directly impregnated beet,roasted and fully washed to get beet based multi-pore activated carbon material.When the p H of Cr（Ⅵ）ionic solution is 4.5 and the amount of activated carbon is 2.0g/L,the adsorption capacity of activated carbon prepared by activation with KOH/beet ratio of 3,700°C reaches 219.0 mg/g.When the H₃PO₄/beet ratio is 0.5,the adsorption capacity of activated carbon prepared by 600°C activation reaches 233.7mg/g.The fitting degree of Cr（Ⅵ）adsorption for Beet _KOH3.0-700 samples to Freundlich model is the highest,which indicates that the adsorption of Beet _KOH3.0-700samples is multi-molecular layer adsorption.The Langmuir model of Beet _H3PO40.5-600has the highest fitting degree,indicating that the adsorption process is monolayer adsorption.Through the kinetic model fitting of adsorption,the beet-based activated carbon has the highest degree of fitting to the pseudo-second order kinetic mode,indicating that the beet-based activated carbon is mainly chemisorption.