Nanoparticle Size Effect on Water Vapour Adsorption by Hydroxyapatite.

Urszula Szałaj,Stanisław Gierlotka,Agnieszka Chodara,Witold Łojkowski,Anna Świderska-Środa

doi:10.3390/nano9071005

Abstract

Handling and properties of nanoparticles strongly depend on processes that take place on their surface. Specific surface area and adsorption capacity strongly increase as the nanoparticle size decreases. A crucial factor is adsorption of water from ambient atmosphere. Considering the ever-growing number of hydroxyapatite nanoparticles applications, we decided to investigate how the size of nanoparticles and the changes in relative air humidity affect adsorption of water on their surface. Hydroxyapatite nanoparticles of two sizes: 10 and 40 nm, were tested. It was found that the nanoparticle size has a strong effect on the kinetics and efficiency of water adsorption. For the same value of water activity, the quantity of water adsorbed on the surface of 10 nm nano-hydroxyapatite was five times greater than that adsorbed on the 40 nm. Based on the adsorption isotherm fitting method, it was found that a multilayer physical adsorption mechanism was active. The number of adsorbed water layers at constant humidity strongly depends on particles size and reaches even 23 layers for the 10 nm particles. The amount of water adsorbed on these particles was surprisingly high, comparable to the amount of water absorbed by the commonly used moisture-sorbent silica gel.

Highlights

Exploitation of the specific properties of nanomaterials, which are not observed in their microcrystalline counterparts, is a fundamental basis of nanotechnology [1]
Water adsorption and desorption by hydroxyapatite were tested as a function of nanoparticle size and the ambient relative air humidity
Nanoparticle size has a strong effect on the kinetics and efficiency of water adsorption

Summary

Introduction

Exploitation of the specific properties of nanomaterials, which are not observed in their microcrystalline counterparts, is a fundamental basis of nanotechnology [1] Due to these properties, nanoparticles are increasingly applied as additives, modifiers of composite materials, reaction catalysts [2,3], nano-solders [4,5], sensors [6,7,8], coatings [9,10] and materials for medical applications [11,12,13,14,15,16]. The large specific surface area of nanomaterials leads to sorption processes on their surfaces As a result, these materials can bind water contained in the air even during production processes. Depending on the application of a given nanomaterial, the water adsorbed on the nanoparticle surface may be either beneficial or unfavourable [19]

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