ZnO Nanoparticle Fortified Highly Permeable Carbon/Silica Monoliths as a Flow-Through Media

We demonstrate a facile one-pot synthesis of porous "flow-through" ZnO nanoparticle impregnated carbon/silica monoliths with high mechanical strength and interconnected end-to-end pores decorated with functional and catalytic nanoparticles. The materials and conditions for the synthesis were tailored to achieve the desired properties of high mechanical strength, good flow-through permeability, and crack-free morphology. Monoliths were prepared from a resorcinol formaldehyde rout but with the addition of tetraethyl-orthosilicate and a metal oxide precursor, ZnCl₂. The monoliths were ambient dried and carbonized under optimized conditions to suppress cracks. Compressive tests of both the resin and carbonized monoliths were performed to examine the effect of the metal oxide precursor on the mechanical properties. The permeability of the monoliths was determined to verify their utility as a flow-through material. The monoliths exhibited a high compressive modulus of ∼30 MPa compared with conventional carbon aerogels and a permeability of ∼10^-12 m². Various characterization techniques were used to analyze the surface morphology, pore texture, and chemical composition of the monoliths. Finally, Ag nanoparticles were incorporated in the monoliths to demonstrate an example of a "flow-through" catalysis application where controlled catalytic conversion of para-nitrophenol into para-aminophenol could be achieved in a continuous flow reactor mode.