Photocatalytic conversion of copper (II) ions to metallic copper (0) on TiO₂ nanoparticles

Under the initiative of the United Nations Sustainable Development Goals (SDGs), utilization of clean energy for metallurgy has emerged as a new trend in recent years. Precious metal ions with low chemical reactivity have been readily photoreduced, while active metal such as copper has been rarely reported. In this work, photocatalytic reduction of Cu(II) ions was investigated utilizing TiO₂ nanoparticles as catalyst. By surface charge optimization in different anionic species-based cupric solution, nanoparticle products with Cu₂O as out shell and zero-valent Cu as the core have been photocatalytic prepared. The photocatalysis conditions such as catalyst amount, Cu(II) ions concentration, ethanol addition, and illumination wavelength were optimized, good cycling stability was confirmed. Argon etching results and thermogravimetric analysis confirmed the appearance of zero-valent Cu metal in the core of nanoparticle products. Ex situ photoreaction investigation revealed the consumption pathway of oxidative holes and photoreduction mechanism of Cu(II) ions. This research could provide some insights into the photoreduction method of active metals and the photocatalytic removal of heavy metal ions within the realm of environmental protection.