High Performance in the Piezocatalytic Reduction of p -Nitrophenol to p -Aminophenol Using Li1– x Cu x NbO3 Synthesized by the Modified Pechini Method

Abstract The development of efficient catalysts for environmental remediation and the conversion of chemical compounds into value-added products remains an important challenge in materials science. Herein, Cu-doped lithium niobate (Li1–xCuxNbO3; 0 ≤ x ≤ 0.025) was synthesized by a modified sol–gel method followed by heat treatment at 500 °C for 2 h. X-ray diffraction and Raman spectroscopy confirmed the predominant formation of trigonal LiNbO3 (R–3c), together with less than 5% monoclinic CuNb2O6 (P21/c) as a secondary phase in the doped samples. Cu incorporation enhanced visible-light absorption and decreased the optical bandgap from 3.95 eV for pure LiNbO3 to 2.96 eV for the x = 0.025 composition, likely owing to the introduction of intermediate electronic states. X-ray photoelectron spectroscopy confirmed the expected Li, Nb, O, and Cu surface chemical states. The materials were evaluated as piezocatalysts for the reduction of p-nitrophenol (PNP), mainly to p-aminophenol (PAP), which was supported by UV–vis and 1H NMR analyses. Cu-doped samples achieved PNP reduction above 93% within 5 min and retained this performance after four reuse cycles, whereas pure LiNbO3 exhibited conversion below 20%. Scavenger experiments indicated that electrons were the primary charge carriers involved in the reaction. These findings demonstrate that Cu-doped LiNbO3 is a promising reusable piezocatalyst for the rapid conversion of PNP under ambient conditions.