Characterization of carbonized polydopamine nanoparticles suggests ordered supramolecular structure of polydopamine

Polydopamine is not only a multifunctional biopolymer with promising optoelectronic properties but it is also a versatile coating platform for different surfaces. The structure and formation of polydopamine is an active area of research. Some studies have supposed that polydopamine is composed of covalently bonded dihydroxyindole, indoledione, and dopamine units, but others proposed that noncovalent self-assembly contributes to polydopamine formation as well. However, it is difficult to directly find the details of supramolecular structure of polydopamine via self-assembly. In this study, we first report the graphite-like nanostructure observed in the carbonized polydopamine nanoparticles in nitrogen (or argon) environment at 800 °C. Raman characterization, which presents the typical D band and G band, confirmed the existence of graphite-like nanostructures. Our observation provides clear evidence for a layered-stacking supramolecular structure of polydopamine. Particularly, the size of graphite-like domains is similar to that of disk-shaped aggregates hypothesized in previous study about the polymerization of 5,6-dihydroxyindole [ Biomacromolecules 2012 , 13 , 2379 ]. Analysis of the hierarchical structure of polydopamine helps us understand its formation.

Thermal transformation of carbon hybrid materials to graphene films

We demonstrate a simple approach to grow graphene films on polycrystalline nickel (Ni) foils, in which polycrystalline carbon hybrid materials (CHMs) were used in sandwich structures (molybdenum-CHMs-Ni-molybdenum) as a carbon source for graphene, and pressure was then applied to the sandwich. The CHMs were transformed into single as well as few layer graphene by a segregation-precipitation process. The applied pressure not only increased the density of the graphene films but also reduced the vaporization of dissociated carbon molecules of the CHMs. We have explored the possibility to grow graphene films in low vacuum (5 × 10(-1) Pa) at relatively low temperatures (≤750 °C). The formation of the graphene films at 750 °C is simple and cost-effective and can be scaled up.

Highly selective and stable carbon dioxide uptake in polyindole-derived microporous carbon materials

Adsorption with solid sorbents is considered to be one of the most promising methods for the capture of carbon dioxide (CO₂) from power plant flue gases. In this study, microporous carbon materials used for CO₂ capture were synthesized by the chemical activation of polyindole nanofibers (PIF) at temperatures from 500 to 800 °C using KOH, which resulted in nitrogen (N)-doped carbon materials. The N-doped carbon materials were found to be microporous with an optimal adsorption pore size for CO₂ of 0.6 nm and a maximum (Brunauer-Emmett-Teller) BET surface area of 1185 m(2) g(-1). The PIF activated at 600 °C (PIF6) has a surface area of 527 m(2) g(-1) and a maximum CO₂ storage capacity of 3.2 mmol g(-1) at 25 °C and 1 bar. This high CO₂ uptake is attributed to its highly microporous character and optimum N content. Additionally, PIF6 material displays a high CO₂ uptake at low pressure (1.81 mmol g(-1) at 0.2 bar and 25 °C), which is the best low pressure CO₂ uptake reported for carbon-based materials. The adsorption capacity of this material remained remarkably stable even after 10 cycles. The isosteric heat of adsorption was calculated to be in the range of 42.7-24.1 kJ mol(-1). Besides the excellent CO₂ uptake and stability, PIF6 also exhibits high selectivity values for CO₂ over N₂, CH₄, and H₂ of 58.9, 12.3, and 101.1 at 25 °C, respectively, and these values are significantly higher than reported values.