Facile defluoridation of drinking water by forming shell@fluorapatite nanoarray during boiling egg shell

High fluoride water is one of the major problems against drinking water and are affecting millions of people all over the world. Refined adsorbents and water treatment plants aim at massive water supply but can't meet scattered household requirements, especially in the developing areas. Here, we developed a facile defluoridation method in which F⁻ can be removed by boiling eggs or shell assisted by phosphate. 0.4 L of high fluoride water (10 mg/L) can be transformed to safe drinking water with F⁻ concentration lower than 1.5 mg/L by boiling one egg at 80 °C for 10 min with the addition of 0.3 g/L of NaH₂PO₄ and 0.05 v% acetic acid. The mechanism study shows that F⁻ is adsorbed onto the egg shell outer surface forming nanorod arrays of fluorapatite and/or F⁻ substituted hydroxyapatite. Higher F⁻ adsorption capacity can be obtained (Langmuir adsorption capacity, 47.9 mg/g) if using egg shell powder instead of whole eggs. Pilot scale defluoridation (2.5 L, 10 times) was successfully realized by boiling egg shell in the presence of phosphate and acetic acid. The boiling shell defluoridation technology has potential household applications by common people with little professional backgrounds.