Modification of Nanoporous Silicon Nitride with Stable and Functional Organic Monolayers

This study describes the formation of functional organic monolayers on thin, nanoporous silicon nitride membranes. We demonstrate that the vapor-phase carbene insertion into the surface C-H bonds can be used to form sub-5 nm molecular coatings on nanoporous materials, which can be further modified with monolayers of polyethylene glycol (PEG) molecules. We investigate composition, thickness, and stability of the functionalized monolayers and the changes in the membrane permeability and pore size distribution. We show that, due to the low coating thickness (~7 nm), the functionalized membrane retains 80% of the original gas permeance and 40% of the original hydraulic permeability. We also show that the carbene/PEG functionalization is hydrolytically stable for up to 48 h of exposure to water and that it can suppress nonspecific adsorption of the proteins BSA and IgG. Our results suggest that the vapor-phase carbenylation can be used as a complementary technology to the traditional self-assembly and polymer brush chemistries in chemical functionalization of nanoporous materials, which are limited in their ability to serve as stable coatings that do not occlude nanomembrane pores.