Facile conversion of kaolinite into clay nanotubes (KNTs) of enhanced adsorption properties for toxic heavy metals (Zn²⁺, Cd²⁺, Pb²⁺, and Cr⁶⁺) from water

Kaolinite nanotubes (KNTs) were synthesized from kaolinite by ultrasonic scrolling and characterized using X-ray diffractometer, scanning and transmission electron microscopes; and FTIR-FT Raman spectrometer. The synthetic KNTs appear as multi-walled scrolls of 12 nm average pore diameter and 50–600 nm particle length; and exhibit surface area of 105 m2/g. KNTs were used as adsorbents for Zn2+, Cd2+, Pb2+, and Cr6+ with uptake capacities of 103 mg/g, 116 mg/g, 89 mg/g, and 91 mg/g, respectively. The equilibration time of Cd2+ and Pb2+ adsorption is 360 min and for Cr6+ and Zn2+ area 120 min and 240 min, respectively. KNTs adsorption systems can be described mainly by Lagergren-second order and Freundlich models (R2> 0.95) as kinetic and isotherm models. This reflected multilayer adsorption forms with chemical sharing or ion exchange processes. KNTs exhibits high reusability and used for five cycles in the removal of the studied metals (100 mg/L). The removal percentages declined by 20.5%, 15.12%, 22.8% and 23.16% with repeating the reused cycles from cycle 1 to cycle 5 for Zn2+, Cd2+, Pb2+, and Cr6+, respectively. KNTs were applied successfully in realistic purification of tap water, groundwater, and sewage water from the inspected metals.