Biodegradation of Benzene-d6 Associated with Various Black Carbon Materials by Pseudomonas putida strain F1: A 2H NMR study.

Black carbon materials vary in their composition and structural homogeneity (e.g., particle geometry, surface area, and porosity) and these variables may strongly influence the interaction mechanisms and bioavailability of HOC associated with black carbon materials. Using static, solid-state 2H nuclear magnetic resonance spectroscopy (NMR), this study investigates the effect of graphite, soot, multi-walled carbon nanotubes, carbon nanoparticles, and activated carbon on the biodegradation of benzene-d6 by the benzene-degrading microbe Pseudomonas putida strain F1 in the aqueous phase. Results indicate that benzene-d6 bioavailability in the aqueous phase is strongly related to the adsorption capacity of these materials. 2H NMR experiments characterized the molecular motion and the corresponding thermodynamic parameters of the benzene-d6 molecules upon association with black carbon materials before and after incubation with Pseudomonas putida strain F1. Changes in the benzene-d6 molecular motion after inoculation and biodegradation were observed. Highly homogeneous black carbon materials such as graphite had benzene associated primarily with the planar surface and as such were fairly accessible for biodegradation. At the other structural extreme with heterogenous activated carbon, benzene was found to have more than one binding interaction. The low energy binding sites, presumably those associated with planar surface areas, were preferentially biodegraded, while benzene associated with higher energy binding sites were selectively preserved. These 2H NMR results provide a molecular-scale view of the diverse interactions occurring between benzene and various black carbon materials and how these interactions control the accessibility of benzene to microbial degradation.