Conversion of Bulk Metallurgical Silicon into Photocatalytic Nanoparticles by Copper-Assisted Chemical Etching

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 car...