Highly efficient and recyclable triple-shelled Ag@Fe3O4@SiO2@TiO2 photocatalysts for degradation of organic pollutants and reduction of hexavalent chromium ions

Abstract

Herein, we demonstrate the design and fabrication of the well-defined triple-shelled Ag@Fe₃O₄@SiO₂@TiO₂ nanospheres with burr-shaped hierarchical structures, in which the multiple distinct functional components are integrated wonderfully into a single nanostructure. In comparison with commercial TiO₂ (P25), pure TiO₂ microspheres, Fe₃O₄@SiO₂@TiO₂ and annealed Ag@Fe₃O₄@SiO₂@TiO₂ nanocomposites, the as-obtained amorphous triple-shelled Ag@Fe₃O₄@SiO₂@TiO₂ hierarchical nanospheres exhibit a markedly enhanced visible light or sunlight photocatalytic activity towards the photodegradation of methylene blue and photoreduction of hexavalent chromium ions in wastewater. The outstanding photocatalytic activities of the plasmonic photocatalyst are mainly due to the enhanced light harvesting, reduced transport paths for both mass and charge transport, reduced recombination probability of photogenerated electrons/holes, near field electromagnetic enhancement and efficient scattering from the plasmonic nanostructure, increased surface-to-volume ratio and active sites in three dimensional (3D) hierarchical porous nanostructures, and improved photo/chemical stability. More importantly, the hierarchical nanostructured Ag@Fe₃O₄@SiO₂@TiO₂ photocatalysts could be easily collected and separated by applying an external magnetic field and reused at least five times without any appreciable reduction in photocatalytic efficiency. The enhanced photocatalytic activity and excellent chemical stability, in combination with the magnetic recyclability, make these multifunctional nanostructures promising candidates to remediate aquatic contaminants and meet the demands of future environmental issues.