Giant zirconium-bisphosphonate nano-ribbons and their liquid crystalline phase behaviour in water.

Dirk Schmelter,Edmund Welter,Rodolphe Nekui Tagné,Jörn Schmedt Auf Der Günne,Hector Cortes-Sanchez,Horst Hintze-Bruening

doi:10.1039/d1dt00736j

Abstract

In decimolar aqueous solutions, zirconium oxychloride octahydrate forms several micrometer long and approximately 15 nm wide thin ribbons through the reaction with excess amounts of the sodium salt of 1-hydroxyethane-1,1-diphosphonic acid (HEDP, known as etidronic acid). Primarily deduced from SAXS, TEM, EXAFS and solid-state NMR analyses, a consistent structural model enables congruous explanations for the colloidal behaviour of the purified ribbons as well as of their reaction products with ammonia and amines, respectively. Properties of the lyotropic, liquid crystalline phases are discussed in the light of potential applications in aqueous coatings.

Highlights

In the domain of metal phosphonates, zirconium monophosphonates are known to form low dimensional frameworks derived from the zirconium phosphates while the incorporation of bisphosphonates can be used to fabricate porous 3D materials.[1]The overwhelming part of the zirconium bibliography related to 1-hydroxyethane-1,1-diphosphonic acid (= HEDP or etidronic acid) which has been used in our group in the context of exfoliated α-zirconium phosphate (α-ZrP) platelets is covered by patents which represent 90% of 301 SciFinder references in February 2021
We note that variants of Na-2-ht with added fluoride or synthesized at higher temperature (200 °C, denoted as Na-2-ht-473) yielded either amorphous powder or zirconium phosphate crystals according to polarized optical microscopy and X-ray diffraction (XRD), respectively (shown for NaZr2(PO4)3·H2O, Fig. SI 2†)
The present work somehow revives early experiments which monitored the evolution of pH values and 31P nuclear magnetic resonance (NMR) signals during the titration of mixed ZrOCl2/HEDP solutions with potassium hydroxide.[10,11]

Summary

Introduction

In the domain of metal phosphonates, zirconium monophosphonates are known to form low dimensional frameworks derived from the zirconium phosphates while the incorporation of bisphosphonates can be used to fabricate porous 3D materials.[1]The overwhelming part of the zirconium bibliography related to 1-hydroxyethane-1,1-diphosphonic acid (= HEDP or etidronic acid) which has been used in our group in the context of exfoliated α-zirconium phosphate (α-ZrP) platelets is covered by patents which represent 90% of 301 SciFinder references in February 2021. The lack of a long-range order of the nano-ribbons, as suggested by SAD (vide supra), is confirmed by powder XRD (Fig. SI 8†).

Results

Conclusion