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. 2022 Aug 6;12(15):2705.
doi: 10.3390/nano12152705.

Hybrid Plasma-Liquid Functionalisation for the Enhanced Stability of CNT Nanofluids for Application in Solar Energy Conversion

Ruairi J McGlynn  1 , Hussein S Moghaieb  1 , Paul Brunet  1 , Supriya Chakrabarti  1 , Paul Maguire  1 , Davide Mariotti  1
Affiliations

Hybrid Plasma-Liquid Functionalisation for the Enhanced Stability of CNT Nanofluids for Application in Solar Energy Conversion

Ruairi J McGlynn et al. Nanomaterials (Basel). .

Abstract

Macroscopic ribbon-like assemblies of carbon nanotubes (CNTs) are functionalised using a simple direct-current-based plasma-liquid system, with oxygen and nitrogen functional groups being added. These modifications have been shown to reduce the contact angle of the ribbons, with the greatest reduction being from 84° to 35°. The ability to improve the wettability of the CNTs is of paramount importance for producing nanofluids, with relevance for a number of applications. Here, in particular, we investigate the efficacy of these samples as nanofluid additives for solar-thermal harvesting. Surface treatments by plasma-induced non-equilibrium electrochemistry are shown to enhance the stability of the nanofluids, allowing for full redispersion under simulated operating conditions. Furthermore, the enhanced dispersibility results in both a larger absorption coefficient and an improved thermal profile under solar simulation.

Keywords: carbon nanotubes; plasma functionalisation; solar–thermal.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) The configuration of the plasma-induced non-equilibrium electrochemistry system used to treat the ribbons, and (b) a photograph illustrating the PTFE holder used to secure the carbon nanotubes.
Figure 2
Figure 2
Schematic of the experimental solar–thermal conversion setup used to measure the time-dependent temperature variation of nanofluids exposed to simulated solar irradiation.
Figure 3
Figure 3
X-ray photoelectron spectroscopy summary of atomic percentages by element for oxygen and nitrogen. The remaining percentage is composed of carbon.
Figure 4
Figure 4
High-resolution X-ray photoelectron spectra of (a) oxygen and (b) nitrogen for pristine and pre-annealed carbon nanotube ribbons.
Figure 5
Figure 5
Summary of the G-band to D-band area ratios determined by Raman spectroscopy.
Figure 6
Figure 6
Summary of the contact angle measurement results for the 6 different carbon nanotube treatments.
Figure 7
Figure 7
Photographs of the nanofluids after 809 days of storage before shaking, and after 2 vigorous shakes by hand. Note that the photographs have been modified to enhance the contrast and brightness to highlight flocculation.
Figure 8
Figure 8
The values of absorption and scattering coefficients obtained from ultraviolet–visible spectroscopy via the transmittance port and an integrating sphere (a–d). The percentage of incident power absorbed for each carbon-nanotube-based nanofluid over 120 days (e).
Figure 8
Figure 8
The values of absorption and scattering coefficients obtained from ultraviolet–visible spectroscopy via the transmittance port and an integrating sphere (a–d). The percentage of incident power absorbed for each carbon-nanotube-based nanofluid over 120 days (e).
Figure 9
Figure 9
(a) Variation in temperature of the nanofluids and ethylene glycol over 20 min of exposure to simulated solar radiation, and (b) their resulting solar–thermal conversion efficiency after accounting for heat lost.
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