Manipulation of Conducting Polymer Hydrogels with Different Shapes and Related Multifunctionality.

Maneuver of conducting polymers (CPs) into lightweight hydrogels can improve their functional performances in energy devices, chemical sensing, pollutant removal, drug delivery, etc. Current approaches for the manipulation of CP hydrogels are limited, and they are mostly accompanied by harsh conditions, tedious processing, compositing with other constituents, or using unusual chemicals. Herein, a two-step route is introduced for the controllable fabrication of CP hydrogels in ambient conditions, where gelation of the shape-anisotropic nano-oxidants followed by in-situ oxidative polymerization leads to the formation of polyaniline (PANI) and polypyrrole hydrogels. The method is readily coupled with different approaches for materials processing of PANI hydrogels into varied shapes, including spherical beads, continuous wires, patterned films, and free-standing objects. In comparison with their bulky counterparts, lightweight PANI items exhibit improved properties when those with specific shapes are used as electrodes for supercapacitors, gas sensors, or dye adsorbents. The current study therefore provides a general and controllable approach for the implementation of CP into hydrogels of varied external shapes, which can pave the way for the integration of lightweight CP structures with emerging functional devices.

Selective Growth of Metal-Free Metallic and Semiconducting Single-Wall Carbon Nanotubes.

A major obstacle for the use of single-wall carbon nanotubes (SWCNTs) in electronic devices is their mixture of different types of electrical conductivity that strongly depends on their helical structure. The existence of metal impurities as a residue of a metallic growth catalyst may also lower the performance of SWCNT-based devices. Here, it is shown that by using silicon oxide (SiOx ) nanoparticles as a catalyst, metal-free semiconducting and metallic SWCNTs can be selectively synthesized by the chemical vapor deposition of ethanol. It is found that control over the nanoparticle size and the content of oxygen in the SiOx catalyst plays a key role in the selective growth of SWCNTs. Furthermore, by using the as-grown semiconducting and metallic SWCNTs as the channel material and source/drain electrodes, respectively, all-SWCNT thin-film transistors are fabricated to demonstrate the remarkable potential of these SWCNTs for electronic devices.

Growth of semiconducting single-wall carbon nanotubes with a narrow band-gap distribution.

The growth of high-quality semiconducting single-wall carbon nanotubes with a narrow band-gap distribution is crucial for the fabrication of high-performance electronic devices. However, the single-wall carbon nanotubes grown from traditional metal catalysts usually have diversified structures and properties. Here we design and prepare an acorn-like, partially carbon-coated cobalt nanoparticle catalyst with a uniform size and structure by the thermal reduction of a [Co(CN)6](3-) precursor adsorbed on a self-assembled block copolymer nanodomain. The inner cobalt nanoparticle functions as active catalytic phase for carbon nanotube growth, whereas the outer carbon layer prevents the aggregation of cobalt nanoparticles and ensures a perpendicular growth mode. The grown single-wall carbon nanotubes have a very narrow diameter distribution centred at 1.7 nm and a high semiconducting content of >95%. These semiconducting single-wall carbon nanotubes have a very small band-gap difference of ∼0.08 eV and show excellent thin-film transistor performance.

In Situ TEM Observations on the Sulfur-Assisted Catalytic Growth of Single-Wall Carbon Nanotubes.

The effect of sulfur on the catalytic nucleation and growth of single-wall carbon nanotubes (SWCNTs) from an iron catalyst was investigated in situ by transmission electron microscopy (TEM). The catalyst precursor of ferrocene and growth promoter of sulfur were selectively loaded inside of the hollow core of multiwall CNTs with open ends, which served as a nanoreactor powered by applying a voltage inside of the chamber of a TEM. It was found that a SWCNT nucleated and grew perpendicularly from a region of the catalyst nanoparticle surface, instead of the normal tangential growth that occurs with no sulfur addition. Our in situ TEM observation combined with CVD growth studies suggests that sulfur functions to promote the nucleation and growth of SWCNTs by forming inhomogeneous local active sites and modifying the interface bonding between catalysts and precipitated graphitic layers, so that carbon caps can be lifted off from the catalyst particle.