Bismuth oxychloride anchored on waste stainless-steel slag: preliminary assessment of its potential as an active photocatalytic support.

Environmental pollution remains a critical barrier to sustainable societal development. In this context, the present work explores a sustainable approach to environmental remediation through the mechanochemical synthesis of bismuth oxychloride (BiOClm) immobilized on waste stainless-steel slags (SSS) at varying proportions. This strategy exemplifies the principles of circular economy by transforming industrial waste into a high-value, photocatalytically functionalized material. The composites were thoroughly characterized in terms of their physicochemical and optical properties, and their photocatalytic activity was evaluated through nitrogen oxide (NOx) abatement under UV and visible light. Although the absolute photocatalytic activity of the composites was lower than that of pure BiOClm, their efficiency per unit of BiOClm was higher, indicating improved utilization of the active phase. This enhancement is attributed to a slight semiconductor behavior of SSS metallic constituents, as confirmed by photocurrent measurements. The coupling between BiOCl and the metal-rich support results in an upward shift of the band energy positions, thereby encompassing the energy of oxygen conversion to superoxide. Thus, the superior photocatalytic activity (normalizes to the photocatalyst mass) of BiOCl_m supported on SSS is attributed to the BiOCl-metal-support interactions, which facilitate charge separation and enhance redox performance. The results indicate that BiOCl/SSS composites with BiOCl contents between 20 and 40% exhibit the most effective photocatalytic performance, achieving a maximum NOx removal efficiency of 1.49% per gram, compared to 0.8% for pure BiOCl. According to the results, a proportion of SSS in the range 60-80% would be the optimum to be used as an active support for BiOCl_m. Overall, this work offers a promising route for the valorization of industrial waste into functional materials for air pollution control.