Adsorption Performance Of Modified Pomelo Peel-based Biochar For Ammonia And Its Mechanism Research

Grapefruit peel is a common waste in life.Its surface is rich in biomass（such as cellulose,hemicellulose,lignin and minerals）and a large number of functional groups（such as phenolic hydroxyl,carbonyl,and carboxyl）.And ether group),and the pore size of grapefruit peel is small,which is conducive to the entry of macromolecular substances,so grapefruit peel is an ideal adsorbent raw material.Biochar has strong adsorption capacity and ion exchange capacity,and has the advantages of being cheap and easy to obtain,easy to operate,and environmentally friendly.It is widely used in the removal of various pollutants.In this paper,pomelo peel-based biochar is prepared from grapefruit peel,modified with different modifiers and applied to the adsorption and purification of gaseous pollutant ammonia（NH₃）,so as to achieve the purpose of"using waste to treat waste and turning waste into treasure",The main content and conclusions of this research are as follows.（1）Pomelo peel-based biochar（BC）was prepared using grapefruit peel as a raw material,and three oxidants of hydrogen peroxide（H₂O₂）,phosphoric acid（H₃PO₄）and nitric acid（HNO₃）were used as modifiers to modify the biochar.A variety of modified pomelo peel-based biochars（M-BC）were prepared for NH₃ dynamic adsorption experiments,and penetration time and penetration adsorption capacity were used as indicators,and the best modifier—nitric acid was selected.According to the SEM and FTIR results,this is because the pomelo peel-based biochar modified by nitric acid has more micropores,larger pore size,and richer types of functional groups.At the same time,it can be found that the order of the modification effect of the three modifiers is:HNO₃>H₂O₂>H₃PO₄.In addition,the modification effect of H₂O₂ and HNO₃ will increase with the increase of the concentration of the modifier within a certain range.However,H₃PO₄is the opposite.The optimal modification conditions were screened out through orthogonal experiments（mass fraction of nitric acid 50%,reaction time 6h,temperature50℃）.At this time,the starting time for the modified pomelo peel-based biochar to adsorb ammonia is nearly 20 minutes,which is more than The unmodified biochar has increased by about 35 times;the penetration adsorption capacity has reached 26.21 mg/g,which is nearly 10 times higher than that of the unmodified biochar（2.73 mg/g）.In addition,through the extreme analysis results of the influencing factors of the orthogonal experiment,it can be known that the order of the degree of influence on the effect of nitric acid modified pomelo peel-based biochar is:modifier concentration>reaction temperature>modification time.FTIR results show that the number and types of functional groups on the surface of the biochar under different modification conditions do not change much.The energy spectrum（EDS）analysis results show that the oxygen content on the surface of the best modified pomelo peel-based biochar reaches 25wt%,Is much higher than other modifiers and the oxygen content on the surface of modified carbon under other modified conditions,and is nearly 2.6 times higher than that of unmodified biochar（7wt%）.（2）The effects of different ammonia gas inlet concentrations（200ppm,500ppm,700ppm,1000ppm）and different experimental temperatures（273K,288K,298K,313K）on pomelo peel-based biochar（BC）and its optimal modified biochar were studied.（M-BC）The influence of the ammonia adsorption process can be seen from the dynamic adsorption curve.As the temperature increases,the adsorption rate increases,the breakthrough point moves forward,the breakthrough time is shortened,and the breakthrough adsorption capacity decreases.,That is,the increase in temperature is not conducive to the accumulation of ammonia adsorption capacity on the pomelo peel-based biochar;the difference is that as the concentration increases,the adsorption rate increases,the penetration time becomes shorter,and the penetration adsorption capacity increases.,This is just the opposite of the law of temperature changes.The quasi-first and quasi-secondary adsorption kinetic models were used to fit the equilibrium data of the grapefruit-based biochar adsorption of ammonia,and it was found that most of the correlation coefficients fitted by the two models were very high（R²>0.99）,which indicates Both models can well describe the entire process of adsorbing ammonia at different temperatures,but the R² fitted by the quasi-first-order kinetic model is generally more stable,and the fitted adsorption capacity qe value is closer to the actual experimental value.Therefore,the adsorption process is more in line with the quasi-first-order kinetic model,that is,the adsorption process of ammonia on the pomelo peel-based biochar is mainly physical adsorption.Similarly,two isothermal adsorption models of Freundlich and Langmuir were used to fit the equilibrium data of the adsorption of ammonia gas by the pomelo peel-based biochar at a specific temperature,and it was found that the correlation coefficients R² were all above 0.9,but the Langmuir model fitted the correlation coefficient R² is higher,so the model can better describe the adsorption law of ammonia on pomelo peel-based biochar.The adsorption process is a monolayer adsorption.The Langmuir model fits the single-layer maximum adsorption capacity Q_mto 95.05 mg/g;In addition,the Q_m,K_L,and K_f values all decrease with the increase of temperature,indicating that the equilibrium adsorption capacity,adsorption rate and adsorption strength of biochar for ammonia gas decrease with the increase of temperature,which further shows that the pomelo peel The adsorption behavior of ammonia-based biochar is an exothermic process.The thermodynamic results show that the?H values(-2.49～-3.33k J.mol^-1)of the adsorption reaction process of the two pomelo peel-based biochar before and after the modification are all negative numbers,indicating that the ammonia gas on the pomelo peel-based biochar The adsorption behavior is an exothermic reaction,and the?values(-13.6～-17.38k J.mol^-1)are all negative values,indicating that the adsorption behavior of pomelo peel-based biochar to ammonia is a spontaneous process.The higher the adsorption temperature,the higher the?The larger the absolute value of is,the higher the temperature is,the greater the spontaneous tendency of the adsorption process;the?S values(40.74～44.90J.mol^-1.k^-1)are all positive,which means that the ammonia is in the pomelo peel before and after the modification.The adsorption process on biochar is a process of entropy increase,the degree of freedom of the system increases,and the degree of disorder of the gas-solid interface increases.（3）The actual regeneration effect of the ultrasonic regeneration method on the modified pomelo peel-based biochar after the adsorption of ammonia gas was studied was studied.The dynamic adsorption experiment results proved the feasibility of this method.At the same time,the influence of different regeneration conditions（regeneration temperature,ultrasonic time,power intensity）on the regeneration efficiency of the saturated modified pomelo peel-based biochar was explored,and it was found that the order of the degree of influence of the three factors is:ultrasonic time>ultrasonic power>Regeneration temperature.In addition,the regeneration efficiency of pomelo peel-based biochar will decrease with the extension of the ultrasonic time,which indicates that too long ultrasonic time is not conducive to the regeneration process of biochar.The best regeneration conditions are:the ultrasonic temperature is 25℃,the super-generation time is 15min,and the ultrasonic power is 360W.At this time,the regeneration efficiency reaches more than 70%.SEM analysis results showed that the micropores of the pomelo peel-based biochar after adsorption saturation were partially blocked,and the micropores of the biochar re-opened after ultrasonic regeneration,which made the pomelo peel-based biochar regain a certain adsorption capacity.The results of FTIR analysis found that the number of functional groups on the surface of biochar after adsorption was reduced(mainly C=O groups around 1745cm^-1),while the number of functional groups on the surface of biochar after ultrasonic regeneration began to increase and the better the adsorption performance,the more abundant the types and number of functional groups on the surface of biochar.