Tryptophan-assisted hydrothermal synthesis and sodium hydroxide-induced phase transformation of zirconia nanocrystals with excellent adsorption performance

다국어 초록 (Multilingual Abstract)

A serial of zirconia (ZrO 2) nanocrystals was hydrothermally synthesized without or with the addition of a certain amount of sodium hydroxide (NaOH) solution using a new water-soluble zirconium precursor solution obtained by mixing zirconium oxychloride octahydrate with nonpolar amino acid tryptophan (Trp) in water. The morphology and crystal structure of the resulting ZrO 2 nanocrystals were characterized by powder X-ray diffraction, transmission electron microscopy, field-emission scanning electron microscopy, and Fourier transform infrared spectroscopy. The results showed that when using Trp as the sole additive without any addition of NaOH solution, pure monoclinic-phase Trp-coated ZrO 2 nanorods with the average diameter and length of about 5 and 27 nm were formed and further assembled anisotropically into 40–70 nm tetragonal star- like nanostructures. The addition of the increasing NaOH solution in the Trp-assisted hydrothermal reaction induced gradual transformation of both crystal structure and morphology of the resulting ZrO 2 products, which fi nally evolved into sheet-like aggregates of pure tetragonal-phase 5–7 nm ZrO 2 nanospheres simultaneously coated by both Trp and –OH groups/OH − ions. These ZrO 2 products synthesized in the presence of both Trp and NaOH solution compared with those synthesized with the addition of either only Trp or NaOH solution showed more excellent adsorption abilities towards cationic dye rhodamine B, with high adsorption efficiencies of up to 80% within 30 min, and can be potentially applied as absorbents for chemical wastewater treatment.