Ranking Biochar-Fluorinated Contaminant Interactions Using Dynamic Signatures

Understanding how fluorinated contaminants interact with porous carbonaceous materials requires to gain insights beyond macroscopic uptake metrics, particularly when heterogeneous pore networks and surface chemistries imply multiple mobility states. Here, we introduce a dynamic-signature approach to rank biochar-fluorinated liquid interactions based on molecular mobility states probed by ¹⁹F fast field-cycling (FFC) NMR relaxometry. Two fluorinated model systems, a perfluoropolyether mixture (Galden HT70) and the small-molecule perfluorodecalin (PFD), were investigated as neat liquids and after contact with two activated biochars (APN1 and LP39) characterized by diverse pore architectures and surface chemistries. Inverse Laplace transform (ILT) analysis of selected relaxation decays reveals the emergence of interfacial and confinement-related heterogeneity upon biochar contact, whereas quantitative analysis of ¹⁹F nuclear magnetic relaxation dispersion (NMRD) profiles using a two-term rotational-translational model yields effective dynamic parameters that encode these interactions. APN1, a predominantly microporous and alkaline carbon, induces moderate perturbations consistent with partial interfacial exchange and confinement, whereas LP39, a high-surface area, mesopore-richer and acidic carbon, produces strongly dispersive NMRD signatures indicative of restricted diffusion and enhanced surface-driven relaxation. These trends are consistent across both fluorinated probes, demonstrating that the observed dynamic signatures primarily reflect biochar physicochemical properties rather than probe-specific chemistry. Overall, the results show that activated biochars can be mechanistically typified by their ability to redistribute fluorinated molecules among bulk-like, interfacial, and confined dynamic states. The dynamic-signature approach presented here provides a complementary, mechanistically grounded perspective to conventional adsorption metrics and offers a pathway toward rational selection of biochars for fluorinated-contaminant retention.