EFFECT OF WET CHEMICAL ETCHING ON IMPURITY REMOVAL AND PHOTOCATALYTIC PERFORMANCE OF METALLURGICAL SILICON POWDER

This study investigates the effect of wet chemical etching on impurity removal and the photocatalytic properties of metallurgical-grade silicon (Si) powder. The Si powder was subjected to a two-stage high-energy ball milling process followed by acid etching using an HF:HCl:HNO3 mixture under controlled conditions. The morphology and composition of the samples were analyzed using transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS). The results revealed particle sizes below 200 nm and a well-defined crystalline structure with an interplanar spacing of ~0.20 nm, corresponding to the Si (220) plane. EDS analysis confirmed the effective removal of metallic impurities (K, Ca, Ni) and carbon, while an increase in oxygen (~8 at.%) and nitrogen (~12.2 at.%) content was observed due to surface oxidation and chemical treatment. The photocatalytic activity of etched (Sip ) and untreated (Sis ) silicon powders was evaluated via the degradation of methylene blue (10 mg/L) under UV irradiation. After 120 minutes, the concentration ratio C_t /C₀ decreased to ~0.18 for Si_p , compared to ~0.9 for Sis . A more than fourfold reduction in the absorption peak at 664 nm was observed for Sip, indicating enhanced dye degradation. Kinetic analysis showed that the degradation process follows a pseudo-first-order model, with higher rate constants for the etched samples. The improved performance is attributed to impurity removal, reduced charge carrier recombination, and increased active surface sites. These results demonstrate that wet chemical etching is an effective and scalable approach to enhance the functional properties of metallurgical silicon for environmental photocatalytic applications.

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