Abstract
Nanoparticles have been used in thermal applications to increase the specific heat of the molten salts used in Concentrated Solar Power plants for thermal energy storage. Although several mechanisms for abnormal enhancement have been proposed, they are still being investigated and more research is necessary. However, this nanoparticle-salt interaction can also be found in chemical applications in which nanoparticles have proved suitable to be used as an adsorbent for nitrate removal given their high specific surface, reactivity and ionic exchange capacity. In this work, the ionic exchange capacity mechanism for the nanoparticles functionalization phenomenon was evaluated. The ionic exchange capacity of silica and alumina nanoparticles dispersed in lithium, sodium and potassium nitrates was measured. Fourier-transform infrared spectroscopy tests confirmed the adsorption of nitrate ions on the nanoparticle surface. A relationship between the ionic exchange capacity of nanoparticles and the specific heat enhancement of doped molten salts was proposed for the first time.
Highlights
The development of nanotechnology in recent decades has allowed nanoparticles to be used in different applications, such as thermal, optical, water treatment, pharmacology, development of new materials, etc. to improve the properties and efficiency of the involved processes
Since the first works reported by Shin and Banerjee in 20115,6, in which abnormal specific heat enhancement was achieved when titania and silica nanoparticles were added to mixtures of carbonate and chloride salts, several authors have focused on the specific heat enhancement of molten salts by adding nanoparticles[7,8,9,10,11,12,13,14,15,16,17,18,19,20]
Both nanoparticles agglomerate and bigger sized clusters than the primary particles are present. These clusters were those that interacted with the surrounding media and, with the involved phenomena,and the final properties depended on their size
Summary
The development of nanotechnology in recent decades has allowed nanoparticles to be used in different applications, such as thermal, optical, water treatment, pharmacology, development of new materials, etc. to improve the properties and efficiency of the involved processes. Interest in the effect of nanoparticles on the specific heat of HTF and TES fluids appeared given the benefits reported in HTF when nanoparticles are added to increase thermal conductivity and the heat transfer coefficient[2,3] In this case, according to the mixture rule, the specific heat of the nanofluid should decrease if nanoparticles with a lower specific heat than the base fluid are added. This theory agrees with the results obtained for molecular liquids, such as water, ethylene glycol, alcohols and thermal oils[4]. The exact mechanisms and theories for the enhanced thermo-physical properties of doped molten salts are not yet completely understood and are still being investigated[21]
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