GO-CeO₂ nanohybrid for ultra-rapid fluoride removal from drinking water.

The presence of excess fluoride (F- > 1.5 mg/L) in drinking water affects more than 260 million people globally and leads to dental and skeletal fluorosis among other health problems. This study investigated fluoride removal by graphene oxide-ceria nanohybrid (GO-CeO2) and elucidated the mechanisms involved. The nanohybrid exhibited ultra-rapid kinetics for fluoride removal and the equilibrium (85% removal, 10 mg F-/L initial concentration) was achieved within 1 min which is one of the fastest kinetics for fluoride removal reported so far. Fluoride removal by the nanohybrid followed Langmuir isotherm with a maximum adsorption capacity of 8.61 mg/g at pH 6.5 and that increased to 16.07 mg/g when the pH was lowered to 4.0. Based on the experimental results and characterization data, we have postulated that both electrostatic interaction and surface complexation participated in the fluoride removal process. The O2- ions present in the CeO2 lattice were replaced by F- ions to make a coordination compound (complex). While both Ce4+ and Ce3+ were present in ceria nanoparticles (CeO2 NPs), Ce3+ participated in fluoride complexation. During fluoride removal by GO-CeO2, the GO sheets acted as electron mediators and help to reduce Ce4+ to Ce3+ at the CeO2 NPs-GO interface, and the additional Ce3+ enhanced fluoride removal by the nanohybrid.