Nano zero-valent iron (nZVI) is often used to get rid of chromium (VI), a heavy metal pollutant, as it has large specific surface area and high reducing activity. However, the effect in removing trace heavy metals appears to be modest and sensitive to environmental pH.
A team led by Prof. Wu Zhengyan and Zhang Jia from Hefei Institutes of Physical Science, Chinese Academy of Sciences offered their solution recently. According to a paper published in Chemical Engineering Journal, they successfully designed iron-based nanocomposite materials that combined galvanic reactions and nanoconfinement effects.
"This is an important progress," said Prof. WU, "this material is good at getting rid of trace Cr(VI) from either acid or oralkali water, which could give us a new way to clean up heavy metal pollution in tricky conditions."
The magic nanomaterial they mentioned above is a Fe-Cu galvanic cell (CnZVI/Cu). It's composed of nZVI with nanocracks and Cu nanoclusters. Using the galvanic reaction to speed up electron transfer and regulate the reaction environment by nanoconfinement effect, they can efficiently remove trace Cr(VI) in acid/alkaline water.
The team further analyzed the prepared CnZVI/Cu composites, and studied their reduction rate and repairing properties for trace Cr(VI) in different pH ranges. The mean pH value in the nanocracks and the spatial heterogeneity of proton limit in alkaline solution were investigated based on theoretical calculation. It was proved that the nanoconfinement effect can help galvanic reactions to repair Cr(VI) efficiently under alkaline condition. In addition, the secondary release of Cr and biosafe experiments show that CnZVI/Cu is both environmentally stable and biosafe.
This innovative nanomaterial shows great promise for efficiently removing chromium (VI) from wastewater with varying pH levels, indicating broad potential for practical applications in heavy metal pollution remediation, according to the team.
Schematic illustration of Cr(VI) removal mechanism by CnZVI/Cu at acidic/alkaline conditions. (Image by LI Sijia)