Synergistic effects of lanthanide surface adhesion and photon-upconversion for enhanced near-infrared responsive photodegradation of organic contaminants in wastewater

Suspended matter and organic contaminants would prevent short-wavelength UV/visible light from penetrating deeper into real wastewater. This has hindered the practical use of photocatalysts in wastewater remediation. Construction of near-infrared light responsive photocatalysts can partially overcome this issue, due to the larger penetration depth of near-infrared light into the waste media. However, the development of near-infrared responsive photocatalysts is constrained by low photoconversion efficiency. In this work, we developed an approach to enhance the performance of NIRresponsive photocatalysis of a lanthanide-doped upconversion nanoparticle-TiO2 hybrid system through coupling the surface adhesion capability of heavy lanthanides with a NIR to UV/vis light upconversion process. We demonstrated that a Gd3+-rich nanoparticle surface can enhance the adhesion of organic compounds on the heterogeneous catalysts, resulting in more complete cycloreversion of organic chromophores. We systematically investigated the photooxidation pathways of the upconversion nanoparticle-TiO2 hybrid catalysts in degradation of rhodamine B through liquid chromatography-mass spectrometry analysis. The results reveal that Gd3+ ions on the catalyst surface could facilitate the complete mineralization of the organic molecules to achieve a total organic carbon removal efficiency of around 70%, which is three times higher than that of the conventional upconversion nanoparticle-TiO2 systems. The results offer new opportunities for near-infrared light driven photocatalysis in water remediation, which is potentially applicable for large quantity deep wastewater treatment.