Synthesis and Structural Characterisation of Yttrium-Doped α-Zirconium Phosphate

Gurpreet Singh Suri

doi:10.3390/chemengineering5040083

Abstract

There has been a considerable amount of interest in the ion-exchange properties of layered zirconium phosphates. Potential applications in the remediation of nuclear waste have renewed interest in these inorganic materials, due to their high stability under the acidic conditions typically found in legacy waste pools. It has been well documented that the substitution of metals with different ionic radii into the frameworks of inorganic materials can alter the chemical properties including ion-exchange selectivity. The work presented here focusses on the synthesis and characterisation of yttrium-doped α-zirconium phosphates which are reported for the first time. Two different synthetic methods were used, reflux and hydrothermal syntheses, and the products were characterised by various methods such as powdered X-ray diffraction, MAS-NMR and scanning electron microscopy. It was found that up to 15% of zirconium could be replaced by yttrium before any noticeable impurity phases could be observed. Rietveld refinement from the doping showed that the products did not obey the Vegard’s law. However, the ion-exchange results clearly showed enhanced capacities and selectivity towards Co2+ ions for the substituted materials.

Highlights

Inorganic ion exchangers such as zeolites have higher thermal and radiation stability, compared to their organic counterparts [1]
Two additional peaks can be observed for products with yttrium substitution of 10% and above and 15% and above, which were not attributed to the α-zirconium phosphate
It was demonstrated that yttrium-doped α-zirconium phosphate can be synthesised using both reflux and hydrothermal methods

Summary

Introduction

Inorganic ion exchangers such as zeolites have higher thermal and radiation stability, compared to their organic counterparts [1]. In 1964, Clearfield and Stynes synthesised crystalline α-zirconium phosphate (α-ZrP). Subsequently determined the structure and investigated the ion-exchange mechanism with sodium and caesium ions [5]. It was reported by Clearfield et al, in later studies, that the crystallinity of the product changed with a slight variation in acidity of the phosphoric acid during synthesis [6]. Hodson and Whittaker reported that zirconium phosphates had differing surface areas, even with identical chemical formulae, due to variations in their synthesis methods, which in turn affected their catalytic properties [7].

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