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Conversion of bulk metallurgical silicon into photocatalytic nanoparticles by copper-assisted chemical etching

: Guan, B.; Sun, Y.; Li, X.; Wang, J.; Chen, S.; Schweizer, S.; Wang, Y.; Wehrspohn, R.B.


ACS sustainable chemistry & engineering 4 (2016), Nr.12, S.6590-6599
ISSN: 2168-0485
Fraunhofer IMWS ()

Low-grade metallurgical silicon (MG-Si, purity ∼98%–99%, $1/kg) with annual production over six million tons is an attractive feedstock to produce active photocatalysts. However, MG-Si is known as an electronically dead material due to serious charge recombination associated with high metal impurity levels. Upgrading MG-Si close to solar grade is essential to achieve desired performance; nevertheless, the traditional silicon refinement process is cost ineffective, has high energy consumption, and causes environmental pollution. Here, we address this critical issue by employing a room-temperature one-step Cu-assisted chemical etching (CuACE) process, which successfully purifies MG-Si into active photocatalysts. We discover that the use of reducing agent (H3PO3) instead of commonly employed oxidant (H2O2) in the etchant system induces a novel phenomenon called “chemical cracking effect”. This effect significantly decreases the granularity of bulk MG-Si particles and simultaneously exposes fresh surfaces carrying impurities to the acids. This induces CuACE with promising purification rates, where major removal efficiencies of metal impurity reach 98.2% for Fe, 62.6% for Ca, and 61.0% for Al. Also, purified MG-Si exhibits excellent photocatalytic activity toward methyl orange (MO) degradation. Our approach provides new insights into metal-assisted chemical etching (MACE) of dirty silicon and opens a path for utilization of MG-Si in heterogeneous photocatalysis.