Preparation And Adsorption Properties Of Biomass-Based Porous Materials

Biochar and cellulose aerogel are two kinds of porous materials which can be prepared from waste biomass materials.Improving their adsorption properties is an important content to realize high value recycling of solid waste.In this study,different waste biomass（waste paper,wheat straw,jade straw,rice straw,hemp and cotton）were pretreated with amino acid ionic liquid cysteine（[Gys][NO₃]）to obtain cellulose with high purity,and then prepared into biochar and cellulose aerogel respectively.The adsorption and removal rates of metal ions(Na⁺,Mg²⁺,Ca²⁺,Cd²⁺)and organic pollutants（bisphenol A,enrofloxacin,ciprofloxacin,tetracycline）in water and pollutants in the biochemical tail water of kitchen wastewater（hereafter referred to as removal rates）were tested.The effect of biochar activation temperature on the removal rate and the adsorption capacity of aerogel on oil were investigated.By comparing the adsorption performance with that of ordinary biochar,whether[Gys][NO₃]pretreatment can improve the adsorption performance of biochar was verified,and the mechanism of pretreatment to improve the adsorption performance of biochar was discussed.Finally,the adsorption properties,thermodynamics,kinetics and mechanism of the optimized wastepaper-based biochar（K-C-BC）on enrofloxacin（ENR）were studied.The main conclusions are as follows:（1）[Gys][NO₃]pretreatment of biomass removes part of C and O groups,making the biomass skeleton more stable and retaining more C in the heat treatment process.In addition,pretreatment can greatly increase the micropores of biochar,and N in ionic liquid can form chemical bonds with C and remain on the surface of biochar,ultimately improving the adsorption performance of biochar.（2）The removal rate of metal ions by biochar is generally lower than that of organic matter.The removal rates of Mg²⁺and Cd²⁺by paper-based activated at 850℃were 65.1%and 90.4%,while the removal rates of metal ions by biochar were generally lower than 43.2%.Compared to different biochar,The adsorption and removal rates of Na⁺,Mg²⁺and Cd²⁺on paper-based biochar were the highest,and the adsorption and removal rates of Ca²⁺on mac-based biochar and jade-based biochar were the highest.The removal rates of bisphenol A,enrofloxacin,ciprofloxacin and tetracycline for most biochar activated at 850℃were more than 99.7%.（3）[Cys][NO₃]pretreatment can improve the adsorption performance of biochar.Increasing activation temperature can improve the removal rates of organic matter and Mg²⁺by biochar,as well as the removal rates of Na⁺,Ca²⁺and Cd²⁺by some biochar.Except that the removal rates of Mg²⁺by hemp-based aerogel F-CA and paper-based aerogel K-CA were71.2%and 58.9%respectively,the removal rates of metal ions by six aerogels were generally lower than 49.7%.Among different adsorbents,F-CA had the highest removal rates of Na⁺and Mg²⁺,while rice-based aerogel P-CA had the highest removal rates of Ca²⁺and Cd²⁺.The adsorption capacity of aerogel on oil is 9.7～17.7 g/g,and P-CA is the highest.（4）Biochar and air gel were used to treat kitchen biochemical wastewater,the removal rates of Ca²⁺by different biochar and aerogels were higher than 69.6%and 87.6%,respectively,and the removal rates of Na⁺,Mg²⁺and TOC were lower than 15.1%and 16.3%,respectively.This is due to the high concentration of Na⁺in the wastewater,resulting in high adsorption amount of Na⁺on the adsorption material,and the adsorption site is covered.Ca²⁺concentration is relatively lowest,so the removal rate is highest.（5）K-C-BC,hemp-based biochar F-BC and cotton-based biochar C-BC were mainly micropores,while wheat-based biochar W-BC and jade-based biochar M-BC were mainly mesoporous and macropores.Paper-based biochar has the largest specific surface area and pore volume,the smallest average pore size,and has a crystal structure,which is conducive to the formation of chemical bonds by electron transport.Other biochar has amorphous structure.（6）The adsorption isotherm is a Langmuir isotherm model,and the adsorption process conforms to the quasi-second-order kinetic model,indicating that the adsorption of K-C-BC on ENR may be monolayer adsorption,mainly chemical adsorption.Adsorption is an endothermic,entropic and spontaneous process.The adsorption of enrofloxacin by K-C-BC is mainly through the formation of chemical bond between N and ENR,pore filling,π-πinteraction,etc.It is proved that the biochar prepared by[Gys][NO₃]pretreatment of recycled paper can efficiently remove pollutants.