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

Abstract

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 roomtemperature one-step Cu-assisted chemical etching (CuACE) process, which successfully purifies MG-Si into active photocatalysts. We discover that the use of reducing agent (H 3 PO 3 ) instead of commonly employed oxidant (H 2 O 2 ) 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.

Synthesis of Si /rgo Nano-composites as Anode Electrode for Lithium-ion Battery by Ctab and Citrate Methods: Physical Properties and Voltage-capacity Cyclic Characterizations.

“…This acid reacts with GO functional groups due to carboxyl and hydroxyl functional groups and therefore causes Si nanoparticles to adhere to graphene plates [50]. Also, the presence of this acid and the CTAB prevented the nanoparticles from bonding to each other and caused the nanoparticles to spread on all rGO surfaces.As previously mentioned, in the synthesis 3, ultrasonic was used for the initial combination of Si and GO powder.…”

Nanometallurgical Silicon for Energy Application

“…There are two types, including acid etching and metal-assisted chemical etching (MACE). [6][7][8][9] For the acid etching, the metal removal efficiency increases proportionally with the surface area of MG-Si particles. Zong and co-workers obtained nano-Si of 99.999% (5N) purity from low-grade ferro silicon (84%) using an acidic etchant consisting of HF, HNO 3 , and HCl.…”

“…By contrast, MACE can process coarse MG-Si particles since it is a self-catalyzing porosification process. [7][8][9] The MG-Si particle size can be tens of micrometers without compromising purification effect as the metal nanoparticles can drill deep into the silicon particles and expose new surfaces. Our group achieved MG-Si purification from 99.74% to 99.9884% via Ag-based MACE.…”

“…8 Recently, we observed chemical cracking effect induced by Cu-based MACE. 9 Coarse MG-Si particles can be disintegrated into fine nanoparticles. Therefore, this method may replace the ball milling process.…”

New Insights into Silicon Purification by Alloying–Leaching Refining: A Comparative Study of Mg–Si, Ca–Si, and Ca–Mg–Si Systems

“…By exposing the solidified silicon to the acid solution, impurities located at grain boundaries of precipitates between the primary silicon grains can be carried away, and pure Si can be obtained. Considerable research has been performed to study the impurity extraction from MG-Si by acid leaching. − It has been found that most of the metallic impurities can be effectively extracted by adjusting a variety of processing parameters like leaching temperature, time, acid combination, and particle size, but the effective P extraction by direct leaching of MG-Si still remains a challenge. Even though it has been theoretically and experimentally confirmed that P tends to segregate along Si grain boundaries, its segregation coefficient ( k p = 0.35) is still relatively high compared to metallic impurities, which is usually less than 10 –3 .…”