Eco-Friendly Dispersant-Free Purification Method of Boron Nitride Nanotubes through Controlling Surface Tension and Steric Repulsion with Solvents.

Boron nitride nanotubes (BNNTs) were purified without the use of a dispersant by controlling the surface tension and steric repulsion of solvent molecules. This method effectively enhanced the difference in solubilities of impurities and BNNTs. The purification process involved optimizing the alkyl-chains of alcohol solvents and adjusting the concentration of alcohol solvent in water to regulate surface tension and steric repulsion. Among the solvents tested, a 70 wt% t-butylalcohol in water mixture exhibited the highest selective isolation of BNNTs from impurities based on differences in solubilities. This favorable outcome was attributed to the surface tension matching with BNNTs, steric repulsion from bulky alkyl chain structures, and differences in interfacial energy between BNNT-liquid and impurity-liquid interfaces. Through this optimized purification process, impurities were removed to an extent of up to 93.3%. Additionally, the purified BNNTs exhibited a distinct liquid crystal phase, which was not observed in the unpurified BNNTs.

Scalable, Highly Pure, and Diameter-Sorted Boron Nitride Nanotube by Aqueous Polymer Two-Phase Extraction.

Boron nitride nanotube (BNNT) has attracted recent attention owing to its exceptional material properties; yet, practical implementation in real-life applications has been elusive, mainly due to the purity issues associated with its large-scale synthesis. Although different purification methods have been discussed so far, there lacks a scalable solution method in the community. In this work, a simple, high-throughput, and scalable purification of BNNT is reported via modification of an established sorting technique, aqueous polymer two-phase extraction. A complete partition mapping of the boron nitride species is established, which enables the segregation of the highly pure BNNT with a major impurity removal efficiency of > 98%. A successful scaling up of the process is illustrated and provides solid evidence of its diameter sorting behavior. Last, towards its macroscopic assemblies, a liquid crystal of the purified BNNT is demonstrated. The effort toward large-scale solution purification of BNNT is believed to contribute significantly to the macroscopic realization of its exceptional properties in the near future.

Stable water-floating transistor with recyclability.

Electronic wastes from used devices containing environmentally hazardous materials are an immediate concern for the sustainable development of electronic and sensor industries. To address this, a highly controllable and dedicated electronic module should be devised, that allows systematic recollection of as many components from the original device for their reuse. Here, we report the total recycling of an electronic device, exploiting a water-floating system that is based on a water-compatible semiconductor as an active material. To do so, we developed a system for stable electronics on the water surface. The floating semiconductor features a tunable morphology on the water surface, and is constructed into a water-floating gated transistor (WFGT) and water floating sensor (WFS), exhibiting an on-current of 4.2 × 10-5 A and an on/off ratio of ∼103. The device showed high recyclability over 25 cycles, with an efficiency of 99 ± 0.9% within 1 cycle and 92 ± 0.7% within 30 cycles. Furthermore, the device was also found to be stable for over 10 days. Our system has the potential to be an eco-friendly, cost-effective, and scalable device that is fully recyclable, which can be applied in areas once thought of as being beyond the scope of current semiconductor technology.

Mapping Out the Nonconjugated Organic Radical Conductors via Chemical or Physical Pathways.

Stable, nitroxide-based organic radicals have gained tremendous attention in a wide range of research fields, ranging from solid-state electronics to energy storage devices. While the success of these organics has been their designer flexibility and the processability that can fully potentiate the open-shell chemistry, a significant knowledge gap exists on the solid-state electronics of small-molecular radicals. Herein, we examine the structure-property relationship that governs the solid-state electronics of a model nitroxide and its derivatives by seeking the connection to their well-established, electrolyte-based chemistry. Further, we propose a general strategy of enhancing their solid-state conductivity by systematic humidity control. This study demonstrates an open-shell platform of the device operation and underlying principles thereof, which can potentially be applied in a number of future radical-based electronic devices.

Ion-Incorporative, Degradable Nanocellulose Crystal Substrate for Sustainable Carbon-Based Electronics.

Electronic wastes from transient electronics accumulate biologically harmful materials with global concern. Recycling these wastes could prevent the deposition of hazardous chemicals and toxic materials to the environment while saving scarce natural compounds and valuable resources. Here, we report a sustainable electronic device, taking advantage of carbon resources and a biodegradable cellulose composite. The device consists of an ambient-stable carbon nanotube as a semiconductor, graphene as electrodes, and a free-standing cellulose filter paper/nanocellulose composite as a dielectric layer. The dual-functional cellulose composite acting simultaneously as a robust substrate and a dielectric is demonstrated, which is compatible with solution device fabrication processes. An optimized channel dimension of 5 mm × 3 mm with the addition of ions that facilitates a charge transport realized a device with an on-current per width of 9.6 µA mm-1, an on/off ratio >102, a field-effect mobility of 2.03 cm2 V-1 s-1, and long-term stability over 30 days under ambient conditions. Successful separation of the carbonaceous components via an eco-friendly solution sorting protocol allowed the recycled device to display excellent electronic performance, with a recapture efficiency of 90%. This effort demonstrates a processable, low-cost, and sustainable electronic system that can be applied in the current realm of the semiconducting and sensing industry.

Highly Aligned Array of Heterostructured Polyflourene-Isolated Boron Nitride and Carbon Nanotubes.

Boron nitride nanotubes (BNNTs) have attracted increasing attention for their exceptional thermal, electronic, and optical properties. However, the progress in BNNTs applications has largely been limited by the low purity of as-synthesized BNNTs and inefficient solution-processing protocols due mainly to the instability of BNNTs in most of the solvents. Therefore, fabrication of highly pure, stable, and fully individualized BNNTs in a rational manner is required. Here, we report a significant improvement in the preparation of well-dispersed BNNTs, utilizing conjugated polymers that interact with BNNTs, allowing selective sorting and individualization of the nanotubes. Evidence of strong interactions between the polymers and BNNTs was observed by optical absorption and photoluminescence spectroscopies, while effective individualization was observed by electron microscopy. The sorted BNNTs were successfully used in a solution-processing protocol called dose-controlled, floating evaporative self-assembly (DFES) previously established for single-walled carbon nanotubes (SWCNT) array fabrication. A device fabricated via DFES from the sorted BNNTs mixed with polymer-wrapped, semiconducting single-walled carbon nanotubes (s-SWCNTs) exhibited an on-state conductance of 253 ± 6 µS µm-1 and an on/off ratio of 106.6±0.4 for a gate voltage of -0.1 V. This breakthrough in BNNT dispersion and isolation is a significant advancement toward the exploitation of BNNTs in future applications.

Making Nonconjugated Small-Molecule Organic Radicals Conduct.

Charge neutral, nonconjugated organic radicals have emerged as extremely useful active materials for solid-state electronic applications. This previous achievement confirmed the potential of radical-based macromolecules in organic electronic devices; however, charge transport in radical molecules has not been studied in great detail from a fundamental perspective. Here we demonstrate the charge transport in a nonconjugated organic small radical, 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (h-TEMPO). The chemical component of this radical molecule allows us to form a single crystal via physical vapor deposition (PVD). While the charge transport of this macroscopic open-shell single crystal is rather low, thermal annealing of the well-defined single crystal enables the molecule to have a rapid charge transfer reaction due to the electronic communication of open-shell sites with each other, which results in electrical conductivities greater than 0.05 S m-1. This effort demonstrates a drastically different model than the commonly accepted conjugated polymers or molecules for the creation of next-generation conductors.

Polymer-Free Electronic-Grade Aligned Semiconducting Carbon Nanotube Array.

Conjugated polymers are used commonly to selectively sort semiconducting carbon nanotubes (S-CNTs) from their metallic counterparts in organic solvents. The polymer-wrapped S-CNTs can be easily processed from organic solvents into arrays of CNTs for scalable device fabrication. Though the conjugated polymers are essential for sorting and device fabrication, it is highly desirable to remove them completely as they limit the electronic properties of the device. Here, we use a commercially available polymer, namely, poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(6,6'-(2,2'-bipyridine))] (PFO-BPy), to sort large-diameter S-CNTs with ultrahigh selectivity and fabricate CNT-array-based field effect transistors (FETs) via a floating evaporative self-assembly (FESA) process. We report quantitative removal of the polymer wrapper from the FESA aligned S-CNT arrays using a metal-chelation-assisted polymer removal (McAPR) process. The implementation of this process on FESA films requires the selective thermal degradation of the polymer into oligomers, combined with optimization of the solvent type and temperature of the metal complexation reaction. Resulting S-CNT array FET devices show that the electronic properties of pristine CNT are preserved through this process. Optical microscopy, UV-vis spectroscopy, and X-ray photoelectron spectroscopy (XPS) were used to characterize the quantitative polymer removal. We quantitatively describe the FET devices to analyze the fundamental characteristics of FETs (mobility (µ), on-conductance (Gon), and contact resistance (2Rc)) by comparing before and after polymer removal. The ability to completely remove the polymer wrapper in aligned CNT arrays without adversely affecting the device properties opens up applications beyond FETs into photovoltaics and biosensing.

Hollow hyaluronic acid particles by competition between adhesive and cohesive properties of catechol for anticancer drug carrier.

The marine mussel-inspired properties of catechol, adhesiveness and cohesiveness, have been applied with pH control to fabricate hollow particles using a silica core and catechol-modified hyaluronic acid (HA-CA) shell for an anticancer drug carrier. The competition between adhesive and cohesive properties of catechol with different pH values leads to various structures, a rough catechol modified HA (HA-CA) shell at pH 5.5, monodisperse spherical silica@HA-CA particles at pH 7.4, and an amorphous HA-CA layer at pH 8.5. The redox transition of catechol with pH is a key factor modulating the behavior of the HA-CA shell on the silica core, which induces strong adhesion of HA-CA to silica at pH 5.5 and structural hardness with cohesive coupling at pH 7.4. In addition, after core removal, the hollow HA-CA particles are followed by loading of anticancer drug, doxorubicin (DOX). DOX loaded HA-CA particles show pH-triggered release behavior and dramatic cytotoxic effect indicating that they are a promising novel anticancer drug carrier.