Single-walled carbon nanotubes (SWCNTs) are a class of one-dimensional nanomaterials that exhibit extraordinary electrical and optical properties. However, many of the fundamental studies and practical applications are stymied by sample polydispersity. SWCNTs are synthesized in bulk with broad structural (chirality) and geometrical (length and diameter) distributions; problematically, all known post-synthetic sorting methods rely on ultrasonication, which cuts SWCNTs into short segments (typically <1 μm). Here we demonstrate that ultralong (>10 μm) SWCNTs can be efficiently separated from the shorter ones through a solution-phase "self-sorting". We show that thin film transistors fabricated from long semiconducting SWCNTs exhibit a carrier mobility as high as ~90 cm 2 •V -1 •s -1 , which is ~10 times higher than the shorter counterparts and well exceeding other known materials such as organic semiconducting polymers (<1 cm 2 •V -1 •s -1 ), amorphous silicon (~1 cm 2 •V -1 •s -1 ) and nanocrystalline silicon (~50 cm 2 •V -1 •s -1 ). Mechanistic studies suggest that This article is protected by copyright. All rights reserved.2 this self-sorting relies on the equilibrium between isotropic and liquid crystalline SWCNT phases, which is driven by the solution phase behavior above the cloud point of the isotropic phase, and inversely scales with the SWCNT length. This length-dependent self-sorting technique opens a path to attain the long-sought ultralong, electronically pure carbon nanotube materials through scalable solution processing.
For thousands of years, carbon ink has been used as a black color pigment for writing and painting purposes. However, recent discoveries of nanocarbon materials, including fullerenes, carbon nanotubes, graphene, and their various derivative forms, together with the advances in large‐scale synthesis, are enabling a whole new generation of carbon inks that can serve as an intrinsically programmable materials platform for developing advanced functionalities far beyond color. The marriage between these multifunctional nanocarbon inks with modern printing technologies is facilitating and even transforming many applications, including flexible electronics, wearable and implantable sensors, actuators, and autonomous robotics. This review examines recent progress in the reborn field of carbon inks, highlighting their programmability and multifunctionality for applications in flexible electronics and stimuli‐responsive devices. Current challenges and opportunities will also be discussed from a materials science perspective towards the advancement of carbon ink for new applications beyond color.
Surfactants, molecular surface-active agents, are widely used to stabilize single-walled carbon nanotubes (SWCNTs) and many other nanomaterials in water to facilitate solution processing and device integration. However, it is notoriously difficult to cleanly remove surfactants when they are no longer needed. Even high-temperature thermal annealing leaves residues that can degrade the otherwise remarkable electrical and optical properties of SWCNTs. Moreover, thermal annealing damages smaller-diameter nanotubes (<1 nm) due to aggressive oxidation at elevated temperatures. To address this challenge, we report the synthesis of ammonium deoxycholate (ADC) that can be cleanly removed at a relatively low temperature that preserves the SWCNT structure. We find that ADC is as efficient as sodium deoxycholate (a commonly used surfactant featuring the same anion) at individually dispersing SWCNTs in water. However, replacing the metal cation (Na+) of sodium deoxycholate with ammonium (NH4 +) to form ADC reduces the peak thermal decomposition temperature by nearly 70 °C. Furthermore, unlike sodium deoxycholate, thermal annealing of ADC in Ar leaves behind only a small amount of carbonized residue that can be cleanly decomposed in the presence of 5% O2 at 400 °C, a condition that preserves SWCNTs even with a small diameter of just 0.76 nm. This work uncovers the chemical origin of residues from the thermal annealing of surfactant-processed carbon nanomaterials and provides an unexpectedly simple solution to this persistent challenge.
The nature of copper phosphate minerals in drinking water distribution systems has remained largely unsolved despite being an important link to reducing cuprosolvency. Chemical equilibrium modeling has also largely failed to accurately predict soluble copper in the presence of orthophosphate. The objective of this work was to develop and validate an empirical copper solubility model that considered pH, dissolved inorganic carbon (DIC), and orthophosphate from a series of bench-scale copper precipitation experiments. An empirical model was constructed that allows for the determination of copper levels in a system given pH, DIC, and orthophosphate data. The predictive reliability of this model was assessed by evaluating a collection of cuprosolvency data from two decades of research and field observations and water treatment reports. The tests yielded a firm correlation between predicted and observed copper levels attested by a regression coefficient of 0.86 for a total of 851 observations.
The discovery of resistance switching memristors marks a paradigm shift in the search for alternative non-volatile memory components in the semiconductor industry. Normally a dielectric in these bistable memory cells changes its resistance with an applied electric field or current, albeit retaining the resistive state based on the history of the applied field. Despite showing immense potential, sustainable growth of this new memory technology is bogged down by several factors including cost, intricacies of design, lack of efficient tunability, and issues with scalability and eco-friendliness. Here, we demonstrate a simple arrangement wherein an ethanol-adsorbed ZnO thin film exhibits orders of magnitude change in resistance when activated by visible light. We show that there exists two stable ohmic states, one in the dark and the other in the illuminated regime, as well as a significant delay in the transition between these saturated states. We also demonstrate that visible light acts as a non-invasive tuning parameter for the bistable resistive states. Furthermore, a pinched hysteresis I-V response observed in these devices indicate what seems to be a new type of memristive behaviour.
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