Nano-engineered Sorbent Materials for Chemical Sensing

Traditional sorbent materials trap all impinging compounds within a certain molecular weight fraction or polarity range until the sorbent capacity is exhausted. Functionality beyond this broad spectrum binary "trap to capacity" capability is left for design of the sampler, scrubber, or filter with which the sorbent is to be interfaced. The Intelligence Advanced Research Projects Activity (IARPA) Ithildin program is developing novel sorbent materials for chemical sampling and storage, enabled by material engineering at the molecular, nanoscale, and mesoscale level of the sorbent itself, independent of the sampler or filter design into which the sorbent is incorporated. Four specific capability enhancements are under development: (1) Selective Sorption (preferential adsorption of target chemicals or chemical classes of interest, while retaining the capability to collect broad-spectrum background); (2) Clutter Rejection (preferential rejection of high-abundance clutter materials, such as water or hydrocarbons); (3) Temporal Fidelity (a capability to activate/deactivate the sorbent material based on various trigger mechanisms); and (4) Remote Indicators (a remotely detectable signature indicative of adsorption of a specific target or target class). This paper describes advances in core sorbent materials (including transition metal carbide, boron nitride, and porous silica and silicon variants), sorbent functionalization, development of engineered hierarchical structures, and novel coatings that enable passive sorbents to function as active samplers. Highlights include biologically-produced Molecular Organic Frameworks (MOFs) used as a gatekeeper layer, porous silicon thin films with hierarchical pore structures, and novel classes of self-immolative polymers used as chemical triggers. Applications to wearable sensors are discussed.