Recyclable photo-thermal conversion and purification systems via Fe₃O₄@TiO₂ nanoparticles

In recent years, nanoscale particles have been applied in the utilisation of solar energy due to their excellent properties. In light of the multiple functions of composite nanoparticles, some solar-assisted systems have been developed and exhibited comprehensive photoelectric and photo-thermal transformation effects. However, the presence of nanoparticles in these systems can cause secondary pollution and severely limit large-scale application of the solar technology. Herein we developed a recyclable photo-thermal conversion and purification system based on Fe₃O₄ nanoparticles decorated with TiO₂ nanoparticles, which could be separated from water under the action of a magnetic force. Under the solar illumination power of 1 sun (1 sun = 1000 W·m⁻²), thermal receiver efficiency of 76.4% and Rhodamine B degradation efficiency of 85% were obtained with a 0.1 g/L Fe₃O₄@TiO₂ nanofluid. With the increase of the solar illumination power, the degradation efficiency has been increased to 94%. The recovery rate and efficiency could be controlled by adjusting the magnetic field strength and the magnetic property of Fe₃O₄@TiO₂ nanoparticles. This study provides an approach to not only significantly reduce material consumption in the design of solar devices, but also to realise broad solar energy applications for water purification and photo-thermal conversion.