2.4.1. Synthesis of La(OH)3@MWCNT Nanocomposite

La(OH)**3**@MWCNT powder was prepared by means of the method reported in the literature [51], after some modifications. At the very beginning, a 1 M solution of LaCl**<sup>3</sup>** was prepared by dissolving the proper amount of corresponding salt in ultra-pure water. A volume (5 mL) of the starting solution was treated with vigorous and constant stirring. Then, the same volume of 2 M K**2**CO**<sup>3</sup>** solution (5 mL) was rapidly introduced into this

mixture, with the addition of a few drops of 1 M NaOH solution to initiate precipitation. After the precipitation was complete, the precipitate was filtered and washed with distilled water several times until the washed water became neutral (pH = 7). Furthermore, the obtained product was washed three times with ethanol and then dried at 100 ◦C for 6 h.
