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. 2018 Oct 10;8(10):816.
doi: 10.3390/nano8100816.

A Solvothermal Synthesis of TiO₂ Nanoparticles in a Non-Polar Medium to Prepare Highly Stable Nanofluids with Improved Thermal Properties

Teresa Aguilar  1 , Ivan Carrillo-Berdugo  2 , Roberto Gómez-Villarejo  3 , Juan Jesús Gallardo  4 , Paloma Martínez-Merino  5 , José Carlos Piñero  6 , Rodrigo Alcántara  7 , Concha Fernández-Lorenzo  8 , Javier Navas  9
Affiliations

A Solvothermal Synthesis of TiO₂ Nanoparticles in a Non-Polar Medium to Prepare Highly Stable Nanofluids with Improved Thermal Properties

Teresa Aguilar et al. Nanomaterials (Basel). .

Abstract

Nanofluids are systems with several interesting heat transfer applications, but it can be a challenge to obtain highly stable suspensions. One way to overcome this challenge is to create the appropriate conditions to disperse the nanomaterial in the fluid. However, when the heat transfer fluid used is a non-polar organic oil, there are complications due to the low polarity of this solvent. Therefore, this study introduces a method to synthesize TiO₂ nanoparticles inside a non-polar fluid typically used in heat transfer applications. Nanoparticles produced were characterized for their structural and chemical properties using techniques such as X-ray Diffraction (XRD), Raman spectroscopy, Transmission Electron Microscopy (TEM), Fourier Transform Infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The nanofluid showed a high stability, which was analyzed by means of UV-vis spectroscopy and by measuring its particle size and ζ potential. So, this nanofluid will have many possible applications. In this work, the use as heat transfer fluid was tested. In this sense, nanofluid also presented enhanced isobaric specific heat and thermal conductivity values with regard to the base fluid, which led to the heat transfer coefficient increasing by 14.4%. Thus, the nanofluid prepared could be a promising alternative to typical HTFs thanks to its improved thermal properties and high stability resulting from the synthesis procedure.

Keywords: concentrating solar power; heat transfer process; nanofluids; nanoparticles; thermal properties.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
X-ray Diffraction (XRD) patterns for TiO2 synthesized and commercial TiO2 nanoparticles used as a reference.
Figure 2
Figure 2
Raman spectroscopy of TiO2 synthesized (a) and the reference of TiO2 anatase structure (b).
Figure 3
Figure 3
(a) Transmission Electron Microscopy (TEM) bright field overview of a single nanoparticle; dark contrast indicates the TiO2 core, while the weaker dark contrast surrounding the nuclei reveals an outer carbon-made shell. (b) Selected area electron diffraction patterns (SAED) obtained in the nanoparticle. Superlattice spots are evidenced. (c) Indexed diffraction pattern, contrast inverted. (d) Definition of the L and M axis, used to calculate the zone axis. (e) Definition of the angles α and 𝛽, used to calculate the zone axis.
Figure 4
Figure 4
Energy-dispersive X-ray (EDX) spectra acquired right in the core of the nanoparticle.
Figure 5
Figure 5
Fourier Transform Infrared (FTIR) spectra of TiO2 sample extracted from the nanofluid (a), base fluid (b), and reference TiO2 anatase (c).
Figure 6
Figure 6
General X-ray photoelectron spectroscopy (XPS) spectrum for TiO2 nanoparticles synthesized (a), signals for Ti 2p (b), and O 1s (c) obtained from XPS measurements.
Figure 7
Figure 7
UV-vis spectrum of the TiO2-based nanofluid just after preparation.
Figure 8
Figure 8
Stability of TiO2-nanofluid measured for 30 days: (a) extinction coefficient at λ = 550 nm, (b) particle size, and (c) ζ potential.
Figure 9
Figure 9
Results of particle size and size distribution from dynamic light scattering (DLS) technique.
Figure 10
Figure 10
(a) Isobaric specific heat, (b) thermal conductivity, and (c) ratio of the heat transfer coefficient between TiO2-nanofluid and the base fluid.
Figure 11
Figure 11
Outlet temperature in the solar collectors if nanofluids are incorporated.
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