Nitrate-assisted photocatalytic efficiency of defective Eu-doped Pr(OH)₃ nanostructures

Pr(OH)₃ one-dimensional nanostructures are a less studied member of lanthanide hydroxide nanostructures, which recently demonstrated an excellent adsorption capacity for organic pollutant removal from wastewater. In this study, Pr_1-xEu_x(OH)₃ (x = 0, 0.01, 0.03, and 0.05) defective nanostructures were synthesized by a facile and scalable microwave-assisted hydrothermal method using KOH as an alkaline metal precursor. The phase and surface composition, morphology, vibrational, electronic and optical properties of the as-prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma optical emission spectrometry (ICP-OES), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), Raman, infrared (IR), photoluminescence (PL), and diffuse reflectance spectroscopy (DRS). It was deduced that the incorporation of Eu³⁺ ions promoted the formation of oxygen vacancies in the already defective Pr(OH)₃, subsequently changing the Pr(OH)₃ nanorod morphology. The presence of KNO₃ phase was registered in the Eu-doped samples. The oxygen-deficient Eu-doped Pr(OH)₃ nanostructures displayed an improved photocatalytic activity in the removal of reactive orange (RO16) dye under UV-vis light irradiation. An enhanced photocatalytic activity of the Eu-doped Pr(OH)₃ nanostructures was caused by the synergetic effect of oxygen vacancies and Eu³⁺ (NO₃^-) ions present on the Pr(OH)₃ surface, the charge separation efficiency and the formation of the reactive radicals. In addition, the 3% Eu-doped sample exhibited very good adsorptive properties due to different morphology and higher electrostatic attraction with the anionic dye. Pr_1-xEu_x(OH)₃ nanostructures with the possibility of tuning their adsorption/photocatalytic properties present a great potential for wastewater treatment.