Mechanochemical One-Pot Transformation of Indium from ITO into Functional Materials: A Coordination-Based Approach to
Chiaki Hotta1, Masayuki Gon1,2, Kazuo Tanaka1,2
1Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto, Japan.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|July 31, 2026
Summary
This study introduces a novel mechanochemical method for selectively recycling rare metals like indium. The process efficiently complexes indium using an azobenzene ligand, enabling selective recovery from mixed metal oxides with reduced environmental impact.
Area of Science:
- Materials Science
- Green Chemistry
- Inorganic Chemistry
Background:
- Growing demand for sustainable rare metal recycling.
- Need for environmentally friendly methods to reduce the burden of metal extraction.
- Limitations of current methods in selectively recovering metals from complex mixtures.
Purpose of the Study:
- To develop a selective and efficient method for rare metal complexation and recycling.
- To utilize mechanochemical reactions for metal recovery.
- To achieve high selectivity for indium from mixed metal oxides.
Main Methods:
- A one-pot grinding method involving acid-mediated chlorination of indium oxide (In2O3) to indium trichloride (InCl3).
- Mechanochemical complexation of InCl3 with an azobenzene ligand to form a luminescent azobenzene-indium complex (AzInCl).
- Exploiting reactivity differences between indium and tin oxides and their complexes for selective separation.
Main Results:
- Quantitative complexation (>99%) of indium achieved using stoichiometric hydrochloric acid (HCl) and facilitated by H2O/pyridine.
- High selectivity for indium recovery from a mixture of indium oxide and tin (IV) oxide (SnO2).
- Selective isolation of AzInCl from an indium tin oxide (ITO) substrate with a 79% indium reaction rate, even with other metals present.
Conclusions:
- The developed mechanochemical approach offers a foundational technology for selective metal recycling and upcycling.
- This method minimizes solvent use, aligning with green chemistry principles.
- The azobenzene ligand's selective complexation capability is key to efficient rare metal recovery.
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