Hierarchically Porous Carbon Materials from Self-Assembled Block Copolymer/Dopamine Mixtures

Hierarchically porous carbon materials with interconnected frameworks of macro- and mesopores are desirable for electrochemical applications in biosensors, electrocatalysis, and supercapacitors. In this study, we report a facile synthetic route to fabricate hierarchically porous carbon materials by controlled macro- and mesophase separation of a mixture of polystyrene-block-poly(ethylene) and dopamine. The morphology of mesopores is tailored by controlling the coassembly of PS-b-PEO and dopamine in the acidic tetrahydrofuran-water cosolvent. HCl addition plays a critical role via enhancing the charge-dipole interactions between PEO and dopamine and suppressing the clustering and chemical reactions of dopamine in solution. As a result, subsequent drying can produce interpenetrated PS-b-PEO/DA mixtures without forming dopamine microsized crystallites. Dopamine oxidative polymerization induced by solvent annealing in NH₄OH vapor enables the formation of percolating macropores. Subsequent pyrolysis to selectively remove the PS-b-PEO template from the complex can produce hierarchically porous carbon materials with interconnected frameworks of macro- and mesopores when pyrolysis is implemented at a low temperature or when DA is a minor component.

Block-Copolymer-Templated Hierarchical Porous Carbon Nanostructures with Nitrogen-Rich Functional Groups for Molecular Sensing

The self-assembly of a block copolymer offers access to micellar nanodomains with tunable dimensions and structural diversity through control of such molecular parameters as the volume fraction and molecular mass. We fabricated hierarchical porous carbon (HPC) nanostructures with bundles of aggregated nanospheres and with nitrogen-rich functional groups through pyrolysis of diblock copolymer micelles in multiple layers. The resultant HPC nanostructures with a considerable specific surface area serve as an excellent substrate for surface-enhanced Raman spectroscopy (SERS), coupled with fluorescence quenching, for molecular sensing of physically adsorbed Rhodamine 6G. The abundant nitrogen atoms terminating on the surface of HPC nanostructures play a critical role in promoting a large Raman enhancement generated via a chemical mechanism. Most importantly, the observed enhancement factors show a clear dependence on the mesoscale porosity within HPC nanostructures, indicating that the chemical enhancement can be steadily tuned with control over the interfacial areas as a function of the nanosphere size. The unique architecture of HPC nanostructures based on the construction of a building block of a well-defined network of core-shell nanospheres provides a new design strategy for fabricating SERS substrates.

Tailoring Carbon Nanostructure with Diverse and Tunable Morphology by the Pyrolysis of Self-Assembled Lamellar Nanodomains of a Block Copolymer

The pyrolysis of a block copolymer thin film, the free surface of which was in contact with air or a capping layer of SiO₂, produced four carbon nanostructures. Thin films of a diblock copolymer having perpendicularly oriented lamellar nanodomains served as carbon and nitrogen precursors. Before pyrolysis, the lamellar nanodomains were cross-linked with UV irradiation under nitrogen gas (UVIN). Without a capping layer, pyrolysis caused a structural transformation from lamellar nanodomains to short carbon nanowires or to dropletlike nanocarbons in a row via Rayleigh instability, depending on the duration of pyrolysis. When capped with a layer of SiO₂ followed by pyrolysis, the lamellar nanodomains were converted to pod-like, spaghetti-like, or long worm-like carbon nanostructures. These carbon nanostructures were driven by controlling the surface or interface tension and the residual yield of solid carbonaceous species.