Preparation Of ZnCl₂ Activated Straw Based Biochar And Experimental Study On Adsorption Of Gaseous Formaldehyde

Indoor formaldehyde poses a great danger to the environment and human health,and the adsorption method has become a effective way for the desorption of indoor formaldehyde because of it has the advantages of low cost and high efficiency.Therefore,the search for economical,safe and efficient adsorbents is an important task at present.In this study,straw-based biomass carbon（BACs）was prepared from agricultural straw by ZnCl₂activation of agricultural straw waste,and the materials were characterized by industrial and elemental analysis,BET,SEM,and FTIR characterization.A systematic experimental study was conducted to investigate the factors affecting the adsorption performance of straw-based biomass carbon with gaseous formaldehyde as the research object,and desorption and regeneration experiments were conducted to investigate their safety,and finally,the adsorption kinetics,adsorption thermodynamics and adsorption mechanism of straw-based biomass carbon on formaldehyde were investigated.The following results were obtained.（1）Preparation and characterization of ZnCl₂ activated straw-based biomass carbon:Corn,rice and wheat straw-based biomass carbon was prepared by soaking activated straw in ZnCl₂solution at different activation temperature and time with different dosage of ZnCl₂.The straw based biochar samples prepared under the optimal activation conditions were characterized.The characterization results showed that there were more volatile substances and rich elements in the straw materials,and the specific surface area and porosity of the straw based biochar were enhanced by activation.Moreover,there were many functional groups on the surface of the straw based biochar,which was conducive to the adsorption of formaldehyde.（2）ZnCl₂ activated straw based biochar adsorption of formaldehyde experiment:The effects of activation conditions,O₂concentration and HCHO concentration on the adsorption performance of straw-based biomass carbon were investigated.The results showed that the adsorption effect of the straw-based biomass carbon obtained by activation reached 99%at the activation temperature of 750°C,the activation time of 2h and the mass ratio of activator to raw material of1:1.5,and the adsorption performance was inhibited by O₂,and the decrease of adsorption performance was accelerated when the concentration of HCHO increased.The superior pore properties of straw-based biomass carbon were confirmed by penetration experiments,which can achieve efficient adsorption of formaldehyde mainly by physical action.The desorption and regeneration experiments demonstrated the safety of the straw-based biomass carbon prepared in this study,and the adsorption capacity was still higher than 95%after two regenerations.（3）Study on the adsorption mechanism of ZnCl₂ activated straw based biochar to formaldehyde:The quasi-primary kinetics can better reflect the adsorption process,indicating that the adsorption of straw-based biomass carbon on formaldehyde is mainly controlled by physical effects,and the temperature rise is conducive to the adsorption reaction in this study.The Langmuir model can better fit the adsorption process of straw-based biomass carbon,indicating that the adsorption process is dominated by monolayer adsorption.The adsorption mechanism of ZnCl₂activated straw-based biomass carbon was investigated,and the results showed that its adsorption performance depends largely on the porosity and surface functional groups.