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Abstract
In this article, we report on an efficient post-treatment protocol for the manufacturing of pristine single-walled carbon nanotube (SWCNT) films. To produce an ink for the deposition, the SWCNTs are dispersed in an aqueous solution with the aid of a carboxymethyl cellulose (CMC) derivative as the dispersing agent. On the basis of this SWCNT-ink, ultra-thin and uniform films are then fabricated by spray-deposition using a commercial and fully automated robot. By means of X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), we show that the CMC matrix covering the CNTs can be fully removed by an immersion treatment in HNO3 followed by thermal annealing at a moderate temperature of 100 °C, in the ambient air. We propose that the presented protocols for the ink preparation and the post-deposition treatments can in future serve as a facile and efficient platform for the fabrication of high-quality and residual-free SWCNT films. The purity of SWCNT films is of particular importance for sensing applications, where residual-induced doping and dedoping processes distort the contributions from the sensing specimen. To study the usability of the presented films for practical applications, gas sensors are fabricated and characterized with the CNT-films as the sensing material, screen printed silver-based films for the interdigitated electrode (IDE) structure, and polyimide as a flexible and robust substrate. The sensors show a high and stable response of 11% to an ammonia (NH3) test gas, at a concentration of 10 ppm.
Highlights
Carbon nanotubes (CNTs) have sparked the interest of many researchers in the last two decades because of their outstanding mechanical and electrical properties, which have been comprehensively summarized in previous review papers [1,2,3]
single-walled carbon nanotube (SWCNT) promise a higher sensitivity compared with MWCNTs, which can be ascribed to their increased surface-to-volume ratio, and an increased number of unsaturated bonds that can act as reaction sites for the sensing specimen [16]
The effect of the immersion treatment in HNO3 solution was studied by means of X-ray photoelectron spectroscopy (XPS) to resolve the chemical alterations and by means of scanning electron microscopy (SEM) to observe the change in morphology
Summary
Carbon nanotubes (CNTs) have sparked the interest of many researchers in the last two decades because of their outstanding mechanical and electrical properties, which have been comprehensively summarized in previous review papers [1,2,3]. Non-destructive, and scalable purification procedure based on a carboxy methyl cellulose (CMC) dispersing agent for SWCNTs [33,34,35,36] at a markedly high purity of >95 wt% has recently been reported [19,37] In these works, the following fabrication procedure was reported: (i) annealing of the raw (as-purchased) SWCNTs in air at a temperature of 350 ◦C for a duration of 60 min, (ii) dispersion of the SWCNTs in an aqueous solution of CMC followed by sonication, and iii) removal of the CMC and metal catalysts using concentrated hydrochloric acid (HCl). These studies employ an aggressive halide-containing acid and a high annealing temperature that prohibits the use of most polymer substrates, except for some heat-resistant polyimides
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