Citric acid-assisted ultrasmall CeO2 nanoparticles for efficient photocatalytic degradation of glyphosate

Degradation of glyphosate has attracted much attention all over the world, since glyphosate has been demonstrated to affect the human health through the accumulation in food chain. Herein, we use citric acid as capping agent to synthesize highly-stable aqueous dispersions of monodispersed CeO2 nanoparticles (NPs) with ultrasmall controllable size of 2.1–4.8 nm, high surface areas and rich oxygen defects, which were firstly used as photocatalyst for efficient degradation of glyphosate. The obtained CeO2 NPs display a significantly size-dependent catalytic activity and a good stability performance. Ultrasmall 2.1 nm CeO2 NPs have 6 times (UV) and 20 times (visible light) degradation rates of 4.8 nm counterpart, which can rapidly remove glyphosate from water at pH = 4 in 5 min (UV) and 20 min (visible light). And the related degradation kinetics data at pH = 4 are well related to the pseudo-first-order kinetic model. In this highly-efficient photocatalytic degradation process, the grafted citric acid can initiate the electron transfer to accelerate the regeneration of Ce3+ sites as electron donors and enhance photocatalytic performance via ligand-to-metal charge transfer. This work provides a new method to prepare high-performance CeO2 photo-nanocatalysts for the removal of glyphosate and emphasizes the important role of modifier, oxygen defects and particle size in seeking efficient photocatalytic materials.