Fabrication Of Nanoporous Bio-char By Coupling Nanocasting And Template Self-activation And Its Adsorption Behavior

This essay put forward a new way to fabricate hierarchical porous biochar by coupling nanocasting and template self-activation adopted Micro-powder as template to enhance the S_BET and porous volume.Nitrogen adsorption-desorption itotherm curves,SEM analysis were conducted to analysis the characteristics of pore structure,further investigating the pore fabricating mechanism by coupling nanocasting and template self-activation.The adsorption behavior to acid orange Ⅱ azo dye（AOII）wastewater and heavy metal contained Cr（Ⅵ）is conducted in batch experiments.Adsorption kinetics and thermodynamics were evolved to further evaluate the adsorption characteristics.The researches including:（1）The flour and CaCO₃ micropowder were conducted as carbon precursor and template,respectively.The flour and CaCO₃ were mixed in a varied mass ratio and impregnated into deionized water,further being dried to form gels.The dired mixtures were carbonized in a programmable tube electronic furnace at different temperature（500,600,800 ^oC）.And then washed by acid solution to remove the template.The specific surface area and pore structure of biochar were analyzed by nitrogen adsorption-desorption.CaCO₃-BC-1:1 carbonized under 800℃which has high surface area（BET）up to 441.2 m²/g,porous constructure,and much more mesoporous and micropores were cast;By Fourier transform infrared spectroscopy（FT-IR）analysis it has been found that CaCO₃-BC surface contains C=O,C-H and hydroxyl,carboxyl and other functional groups,with the increase of carbonization temperature,the types and quantities of functional groups decreased gradually;XRD analysis found that when the carbonization temperature was lower than 800℃,the CaCO₃ micropowder did not decompose,and high to 800℃,CaO could been detected in the material surface,indicating that the decomposition has happened;Through the SEM scanning electron microscope images,we can clearly see the porous morphology of the CaCO₃-BC.Surface images showed that CaCO₃-BC contains many channel,and the structure like tufted,flake,honeycomb on the surface of the porous morphology,and the porosity developed with the increase of CaCO₃ ratio.CaCO₃ produced CO₂ in the carbonization process and CaO can promote the formation of porous structure.In the carbonization process,the change of cellulose,sugar and CaCO₃ maintained the main transformation which promoted flour transforming into porous biochar.（2）The adsorption behavior of simulation acid orange Ⅱ dye waste water on the biochar prepared with varied CaCO₃ content and carbonization at varied temperatures were investigated.After adding 50%CaCO₃,adsorption capacity of acid orange Ⅱ raised to 380mg/g,the adsorption capacity of CaCO₃-BC-1:1-phy was only 28.99%of CaCO₃-BC-1:1.The difference of adsorption capacity between the two absorbents was more than 290mg/g.The results shown that template self activationcan can make an increase of 122 mg/g in the adsorption capacity.The adsorption properties of CaCO₃-BC-1:1,CaCO₃-BC-1:2 and CaCO₃-BC-1:8 on acid orange Ⅱ were studied.When the pH about 3,CaCO₃-BC particle size 60⁸0 mersh,adsobents feeding 1g/L,acid orange Ⅱ initial concentration 300mg/L,within 60 mins,the removal rate of acid orange Ⅱ above 90%.Dynamics research proved that the pseudo secondary dynamics model much better fit the description of the adsorption process of CaCO₃-BC on simulated acid Orange II.Adsorption mass transfer process was complicated and it’s adsorption mainly controlled by physical adsorption.Through thermodynamics study,we can see that Langmuir isothermal adsorption equation can describe the adsorption process better.Adsorption was a spontaneous exothermic process and increasing the temperature was not conducive to adsorption.（3）Adsorption properties of Cr（Ⅵ）were studied with different adsorbents called CaCO₃-BC-1:1,CaCO₃-BC-1:2,CaCO₃-BC-0:1.It has found that CaCO₃-BC has the best adsorption of Cr（Ⅵ）prepared by carbonization temperature at 800℃.The best adsorption condition proved to be that pH about5,CaCO₃-BC particle size 60⁸0mersh,adsobents feeding 1g/L,Cr（Ⅵ）initial concentration 50mg/L,within 300 mins could basically reach to balance,and adsorption capacity reached up to 41.38 mg/g,29.3 mg/g and 3.94 mg/g respectively.Adsorption kinetics and thermodynamic studies had found that the adsorption of CaCO₃-BC on Cr（Ⅵ）was in accordance with pseudo second order kinetic model and Langmuir isotherm equation,where the dynamics of R² were 0.9870,0.9975,0.9982 in order.Although the Langmuir isotherm equation and Freundlich isotherm equation for the adsorption process of the fitting degree of R² were more than 0.9,the Langmuir isotherm equation of R² was higher.The adsorption mechanism were controlled by the electrostatic force and the diffusion of the particles in the channel,where there obtained the electrostatic adsorption,and hydroxyl,carboxyl,and other functional groups involved in the complexation adsorption.There mainly occured on monolayer adsorption which was a spontaneous endothermic process.