Sorption Of Carbendazim In Solution By Activated Carbon Prepared From Rape Straw And Its Mechanism

The rapeseed planting area in our country exceeds 100 million mu every year,however,a large amount of rape straw is discarded or burned directly,which not only causes the waste of resources,but also causes serious pollution to the environment.At present,the excessive and repeated use of pesticides in agricultural production has caused serious pollution to the soil and water body,so it is urgent to reduce and control the use of pesticides.In order to solve this problem,rapeseed straw as precursor,phosphoric acid as activator,rapeseed straw activated carbon can be used to adsorb pesticide wastewater at different temperatures.Using rape straw activated carbon as adsorbent and carbendazim as adsorbent,the adsorption performance of rape straw activated carbon to carbendazim in solution was studied,and its adsorption mechanism was discussed,which could provide a reference for reducing environmental pollution of pesticides.The main works of this article are as follows:（1）The rape straw as precursor,and phosphoric acid as activating agent at different temperatures（300℃,400℃,500℃and 600℃）the activated carbon（ACx）was prepared.The sample AC600 was modified by specific functional group masking with anhydrous methanol and formaldehyde,and AC600-CGB and AC600-PGB were obtained.The physical and chemical properties of samples were analyzed by SEM,XRD,elemental analysis,FTIR,N₂ sorption-desorption,XPS,Raman,pHpzc and Boehm titration.The results show that with the increase of pyrolysis temperature,polarity index,activated carbon samples of hydrophobic and surface oxygen groups decreased,and the aromaticity increased.The pyrolysis temperature is too low,the pore structure of activated carbon were not fully developed,while pyrolysis temperature is too high,the pore structure of the samples will collapse or crosslinking.All the samples,specific surface area and the pore volume of the sample AC400 reaches the maximum,1490 m²/g and 1.17 cm³/g respectively.The sample AC600 was modified by anhydrous methanol and formaldehyde.After modification,two samples of AC600-CGB and AC600-PGB were successfully screened.The pore structure of AC600 was almost unchanged compared with that of AC600.（2）Carbendazim（CBD）was chosen as the target pesticide.The effect of initial pH on the sorption was investigated by using rape straw and activated carbon derived from rape straw as sorbent.The sorption mechanism was also discussed based on sorption isotherms,sorption kinetics models,sorption thermodynamics model and Dual-mode model also were discussed.The results show that the CBD sorption capacity in ACx reaches 80%of the equilibrium sorption capacity in the initial 5 min,which proves that the material is an ideal sorbent and pore filling is the most important mechanism of CBD sorption by activated carbon.The K_d value and the polarity index（O+N）/C significant correlation between atomic ratio of O/C was negative,which showed that the activated carbon surface owned rich polar functional groups,and inhibited the sorption of CBD on the surface of the sample at the same time.The K_d value and O/C atomic ratio also showed a significant negative correlation,it is further indicated that the adsorption of hydrophobicity of CBD on activated carbon accounts for a large proportion.When the initial pH is less than 3.0,the dominant sorption mechanism is electrostatic interaction.When initial pH is greater than 4.0,CBD sorption is affected by hydrophobic interaction,pore filling andπ-πEDA reaction.Different initial concentrations of CBD,surface adsorption and partition adsorption contribution ratio of CBD in the whole sample is different.At low concentrations,adsorption absolute contribution,with the increasing of concentration,the share distribution of the contribution is always increased gradually.（3）The sorption of CBD on samples is affected by three mechanisms,including pore filling,surface adsorption（electrostatic interaction,hydrophobic interaction andπ-πEDA reaction）and distribution.Surface adsorption plays a dominant role in the sorption.