An efficient synthetic strategy for ligand-free upconversion nanoparticles

Chunning Sun,Jan Ron Justin Simke,Michael Gradzielski

doi:10.1039/d0ma00411a

Chunning Sun, Jan Ron Justin Simke + Show 1 more

Open Access

https://doi.org/10.1039/d0ma00411a

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Abstract

An efficient synthetic approach was developed to prepare ligand-free UCNPs using short-chain acids as stripping agents by a simple vortexing method in a short time, allowing the transfer of UCNPs from hydrophobic to hydrophilic media.

Highlights

High-quality upconversion nanoparticles with precisely tuned size, composition, shape, and well-designed architecture are generally synthesized by applying the long-chain oleic acid (OA) as the ligand in the synthetic process.[17,18,19,20,21,22]
The resulting OA-UCNPs can be dispersed in nonpolar solvents owing to the presence of the oleate ligand on their surface
For the ligand removal occurs in biphasic solvent systems, a wide variety of polar solvents including acetonitrile, dimethylformamide, dimethyl sulfoxide, formamide, methanol, and N-methyl-2-pyrrolidone are employed to form liquid–liquid interfaces with cyclohexane, and the reaction is performed by a short contact of the organic dispersion of OA-UCNPs with immiscible polar solvents containing short-chain organic acids on a vortex mixer, leading to the in-solution transfer of upconversion nanoparticles to the polar phase (Fig. S1, Electronic supplementary information (ESI)†)

Summary

Introduction

High-quality upconversion nanoparticles with precisely tuned size, composition, shape, and well-designed architecture are generally synthesized by applying the long-chain oleic acid (OA) as the ligand in the synthetic process.[17,18,19,20,21,22] Sterically stabilized oleate-capped upconversion nanoparticles are prone to disperse in nonpolar and hydrophobic solvents, while most applications of upconversion materials require the particles to be readily dispersed in hydrophilic media. To address this problem, postsynthetic surface modifications are essential for rendering upconversion nanoparticles dispersible in the aqueous solution or polar organic media prior to subsequent practical applications. The resulting ligand-free upconversion nanoparticles can be readily transferred to the aqueous solution and further functionalized by water-soluble capping molecules

Results and discussion

Conclusions

Conflicts of interest