The removal of metallic single-walled carbon nanotubes using an aqueous two-phase system

Extractive Fermentation for Process integration and amplified pullulan production by A. pullulans in Aqueous Two Phase Systems

Extractive fermentation technique or in situ product recovery process is a novel technique to segregate the desired product simultaneously in a fermentation process. For economic and high yield production of pullulan, Extractive fermentation process was applied fermentation process of A. pullulans. Aqueous Two Phase system (ATPS) systems were designed with various molecular mass of PEG (400, 600, 4000 and 6000) and dextran or mono/bi-sodium phosphate salts. Systems with short Tie Line length (TLL) 6.7 and 7.5% w/w for PEG-Salt and PEG-dextran respectively were chosen. Volume ratio for all the systems was kept constant at 1.0 and pH 7.0 for PEG-dextran and PEG-NaH2PO4 was maintained, whereas pH 9.0 was kept for PEG-Na2HPO4. A. pullulans, was found to be viable with PEG-NaH2PO4 and PEG-dextran systems. The biomass partitioned in the PEG rich top phase and the exopolysaccharide pullulan shown affinity towards the bottom phase. A maximum yield (36.47 g/L) was found with PEG 4000-Dextran 500 system of extractive fermentation process. The proposed process aptly integrates upstream and downstream process for continuous production and recovery of pullulan from the biomass, thus reducing the time quotient of the whole process.

Exploring the upper limit of single-walled carbon nanotube purity by multiple-cycle aqueous two-phase separation

Ultrahigh purity semiconducting single-walled carbon nanotubes (S-SWCNTs) are required for high-performance transistors. Aqueous two-phase (ATP) separation is an attractive method to obtain such SWCNTs due to its simplicity and scalability. This work targeted two questions; namely what is the upper limit of S-SWCNT purity that can be achieved by multiple cycles of ATP separation from the most commonly used polyethylene glycol and dextran system and how accurately can commonly used methods characterize the improvement in purity? SWCNT purity in nanotube dispersions obtained by multi-cycle ATP separation (2, 4, 6 and 8 cycles) was evaluated by three methods, including UV-vis-NIR absorption spectroscopy analysis, performance of thin-film field effect transistors (FETs) prepared by drop casting and short-channel FET devices prepared by dielectrophoresis deposition. Absorption spectroscopic analysis and the performance of the thin-film FET devices can hardly differentiate metallic SWCNT residues in the dispersions obtained after 4 cycles with the purity above 99.5%, and the short channel FET devices prepared by dielectrophoresis deposition are more sensitive towards tiny metallic SWCNT residues. A new method was also demonstrated to visualize the minor metallic content in the nanotube suspension using voltage contrast imaging in a scanning electron microscope, which enables rapid screening of many devices and the accurate obtainment of metallic content without performing a large number of individual transconductance measurements.

Solution-Processable High-Purity Semiconducting SWCNTs for Large-Area Fabrication of High-Performance Thin-Film Transistors

For the large-area fabrication of thin-film transistors (TFTs), a new conjugated polymer poly[9-(1-octylonoyl)-9H-carbazole-2,7-diyl] is developed to harvest ultrahigh-purity semiconducting single-walled carbon nanotubes. Combined with spectral and nanodevice characterization, the purity is estimated up to 99.9%. High density and uniform network formed by dip-coating process is liable to fabricate high-performance TFTs on a wafer-scale and the as-fabricated TFTs exhibit a high degree of uniformity.

Metallic and semiconducting carbon nanotubes separation using an aqueous two-phase separation technique: a review

It is known that carbon nanotubes show desirable physical and chemical properties with a wide array of potential applications. Nonetheless, their potential has been hampered by the difficulties in acquiring high purity, chiral-specific tubes. Considerable advancement has been made in terms of the purification of carbon nanotubes, for instance chemical oxidation, physical separation, and myriad combinations of physical and chemical methods. The aqueous two-phase separation technique has recently been demonstrated to be able to sort carbon nanotubes based on their chirality. The technique requires low cost polymers and salt, and is able to sort the tubes based on their diameter as well as metallicity. In this review, we aim to provide a review that could stimulate innovative thought on the progress of a carbon nanotubes sorting method using the aqueous two-phase separation method, and present possible future work and an outlook that could enhance the methodology.