# Flexible Cation Exchange Environment via Ligand-Free Metal Chalcogenide Thin Films

## TL;DR

Researchers developed a new method for cation exchange in nanocrystals using ligand-free metal chalcogenide thin films, enabling flexible and diverse chemical transformations.

## Contribution

The study introduces a ligand-free approach to cation exchange using metal chalcogenide thin films, enabling sequential or simultaneous cation incorporation.

## Key findings

- Cation exchange reactions were successfully performed using ligand-free CdS and CuxSey thin films with various guest cations.
- The method allows for sequential or simultaneous exchange, producing compositionally diverse products confirmed by SEM-EDS, XPS, and ICP-MS.
- The approach is generalizable to selenide and sulfide films and operates under milder conditions than traditional nanocrystal reactions.

## Abstract

Cation exchange (CE) has emerged as a premier postsynthetic
method
to carefully tune the chemical composition and properties of nanocrystals
with excellent morphology retention. However, reaction conditions
are typically dictated by the ubiquitous ligands bound to their surface,
limiting their solubility and influencing the thermodynamics/kinetics
of the reaction. To bypass these challenges, we report on CE reactions
with Cu+, Ag+, Cu2+, Cd2+, Zn2+, and Mn2+ utilizing ligand-free CdS
and CuxSey thin films as host templates. The exchange reactions could be performed
sequentially or simultaneously (i.e., two guest cations) to access
compositionally diverse products. The incorporation of cations on
the host films was confirmed using SEM-EDS, XPS, and ICP-MS analyses,
as well as tracking wavelength shifts in the UV–vis absorption
spectra. The flexibility of this approach was demonstrated as reactions
were carried out using an array of different guest precursor salts
and solvents with a range of polarities. Moreover, the reactions were
generalizable among selenide and sulfide films and proceeded under
milder conditions in comparison with reported nanocrystal reactions.
A ligand-free environment with flexible reaction conditions, as the
work herein, could aid in deconvoluting the different factors involved
in CE reactions and further expand its use for fundamental research
and applications like photovoltaics, optoelectronics, and catalysis.