A high specific surface 1-(2-pyridylazo) 2-naphthol (PAN)-modified carbon-based silicon film with cellulose nanocrystalline structure for the efficient adsorption of rare-earth elements

The recycling of rare-earth elements from wastewater has important economic and environmental benefits. In this study, cellulose nanocrystals used as a liquid crystal template and tetraethyl orthosilicate (TEOS) used as a silicon-source precursor drive were self-assembled into thin-film materials via a sol–gel method, and then calcined into carbon-based materials at high temperatures in a nitrogen atmosphere to improve the mechanical properties of the films and increase surface areas. The 3-aminopropyl triethoxysilane and 1-(2-pyridylazo)-2-naphthol were introduced into the surface of carbon-based thin-film materials by chemical grafting to improve the adsorption properties of rare-earth elements. For heavy rare-earth ions, the adsorption performance of the carbon-based silicon membrane was better as compared to the light rare-earth ions. At pH = 7, the maximum adsorption capacity of the carbon-based silicon membrane and the adsorption efficiency can reach more than 90%. The regeneration performance test indicated that the carbon-based silicon membrane can be reused many times. In general, it is an environmentally friendly, efficient, and non-toxic new adsorption material for heavy rare-earth ion adsorption.