Molecular Simulation And Adsorption Mechanism Of Carbamazepine Imprinted Adsorbent

Molecular imprinted technology is expected to make up for the shortcomings of existing water treatment process which cannot specifically remove the targeted pollutants.Functional monomers,as the part of imprinted adsorbents,have a great impact on the performance of adsorbents.Computer molecular simulation provides valuable theoretical guidance for rapid selection of functional monomers and helps to explain the mechanism of specific recognition.In this study,the imprinting recognition system of targeted pollutant carbamazepine(template molecule)and 15 functional monomers was constructed.Simulated annealing method was used to search low-energy conformations.This overcame the shortcomings of the existing searching method by which the conformations were prone to fall into local potential wells.Molecular simulation showed that the binding capacity of functional monomer itaconic acid(IA)to carbamazepine was the strongest.The adsorption experiments showed that the adsorption capacity of imprinted adsorbent prepared with itaconic acid as functional monomer was 9.280 mg/g,which was higher than that of the adsorbent prepared with methacrylic acid,the most-widely used monomer in previous study.Kinetic experiments demonstrated that the equilibrium could be reached in 20 minutes.Competitive adsorption experiments with a highly similar substance oxcarbazepine as interference pollutant were carried out both in pure water and filtration effluent from drinking water treatment plant.The results showed that the imprinted adsorbent could show high selectivity in the actual water sample.The imprinting factor was 3.83 and the selective factor was 3.98.The adsorbent regeneration experiment showed that the adsorption capacity of imprinted adsorbent did not decrease significantly(1.3%)after10 "elution-adsorption" cycles.Molecular simulation calculation showed that the binding capacity of traditional functional monomer methacrylic acid(MAA)to carbamazepine was not ideal.The adsorption capacity of the adsorbent prepared by MAA was only 5.558 mg/g in aqueous solution.The adsorption equilibrium could also be achieved within 20 minutes.Competitive experiments showed that the imprinting factor was 2.31 and the selective factor was 2.14.After 10 times of regeneration,the adsorption capacity decreased by 5.7%.The adsorption process of the two adsorbents accorded with Freundlich adsorption model and the adsorption kinetics of the adsorbent conforms to the pseudo-second-order kinetics model.Scatchard analysis showed thatthere existed adsorption sites with different adsorption abilities in the two adsorbents.Generally speaking,the adsorbent prepared with IA as functional monomer had better absorption capacity,specific recognition ability and regenerative performance than the adsorbent prepared with MAA.Molecular simulation and spectroscopic analysis were used to investigate the microscopic mechanism of the specific adsorption process.Energy calculation and hydrogen bond analysis suggested that van der Waals force and electrostatic interaction including hydrogen bond played a major role in the recognition process,and the recognition sites were located between the carboxylic group of itaconic acid and carbamazepine amide.Hydrogen bonds could also be observed between IA molecules,which made the structure of the adsorbent more stable,so it had better regeneration performance.The ultraviolet spectra of the imprinted system were calculated theoretically and then measured practically.The experimental results showed that a new interaction system was formed between itaconic acid and carbamazepine.The theoretical calculation could accurately predict the ultraviolet spectra of the itaconic acid and carbamazepine in aqueous solution,but the prediction of the ultraviolet spectra of the interaction system between them was not ideal,which suggested that a variety of binding conformations were formed between itaconic acid and carbamazepine.Further study of infrared analysis confirmed the existence of hydrogen bonds in the imprinting system,which was consistent with the results of molecular simulation.