Photocatalytic Degradation of Diclofenac Using Al₂O₃-Nd₂O₃ Binary Oxides Prepared by the Sol-Gel Method

This paper reports the sol-gel synthesis of Al₂O₃-Nd₂O₃ (Al-Nd-x; x = 5%, 10%, 15% and 25% of Nd₂O₃) binary oxides and the photodegradation of diclofenac activated by UV light. Al-Nd-based catalysts were analyzed by N₂ physisorption, XRD, TEM, SEM, UV-Vis and PL spectroscopies. The inclusion of Nd₂O₃ in the aluminum oxide matrix in the 10-25% range reduced the band gap energies from 3.35 eV for the γ-Al₂O₃ to values as low as 3.13-3.20 eV, which are typical of semiconductor materials absorbing in the UV region. γ-Al₂O₃ and Al-Nd-x binary oxides reached more than 92.0% of photoconverted diclofenac after 40 min of reaction. However, the photocatalytic activity in the diclofenac degradation using Al-Nd-x with Nd₂O₃ contents in the range 10-25% was improved with respect to that of γ-Al₂O₃ at short reaction times. The diclofenac photoconversion using γ-Al₂O₃ was 63.0% at 10 min of UV light exposure, whereas Al-Nd-15 binary oxide reached 82.0% at this reaction time. The rate constants determined from the kinetic experiments revealed that the highest activities in the aqueous medium were reached with the catalysts with 15% and 25% of Nd₂O_3, and these compounds presented the lowest band gap energies. The experimental results also demonstrated that Nd₂O₃ acts as a separator of charges favoring the decrease in the recombination rate of electron-hole pairs.