Chitosan-Based Molecularly Imprinted Polymers for Effective Trapping of the Nerve Agent Simulant Dimethyl Methylphosphonate

Abstract

A molecular imprinted polymer (MIP) fabricated from a biomaterial (chitosan) was successfully created for the selective trapping of dimethyl methylphosphonate (DMMP) in the thousands of parts per million. DMMP is an organophosphorus compound that can be used in the production of chemical weapons and is the accepted surrogate to test filters and protective clothing designed to trap organophosphorus compounds. Computational calculations (density functional theory: B3LYP/6-31G) were used to calculate the optimum ratio of chitosan to DMMP that would produce the most energetically stable template−monomer complex. Gas chromatography mass spectrometry was used to model the DMMP concentration in the gas phase and to determine the DMMP trapped by the MIP, non-imprinted polymer (NIP), and activated charcoal. The MIP trapped 4554 (±227) ppm (4.55 mg/g) DMMP and outperformed both the NIP (156 (±20) ppm (0.16 mg/g)) and activated charcoal (82 (±17) ppm (0.08 mg/g)). Acetic acid, ammonium hydroxide, acetone, ethanol, and 2-propanol were introduced into the system as interferents and did not significantly affect the amount of DMMP trapped by the MIP: 4286 (±74) ppm (4.29 mg/g). Reusability of the MIP is affected by the extraction process but does not significantly affect the intended use as a filter for hazardous materials. Scanning electron microscopy was used to study the surface morphology of the MIP, and after MeOH extraction, the surface of the MIP became coarser, illustrating the alteration of the material. Overall, the trapping capabilities of the MIP are far superior to activated charcoal 50-fold and can be used as a filling agent in gas masks or gas filters.