Ultrafine Cu2O nanoparticles supported on MIL-125-NH2 as an efficient and stable 4‑nitrophenol reduction catalyst

Abstract

To resolve these dire environmental issues of today, it is imperative to develop highly effective and stable catalysts for the catalytic reduction of poisonous 4-nitrophenol (4-NP) to more useful and readily biodegradable 4-aminophenol (4-AP). Herein, we present a Cu₂O nanoparticle-immobilized Ti-based metal–organic framework MIL-125-NH₂ composite catalyst (Cu₂O/NM), which was synthesized by facile coordination combined with an in situ reduction process. The Cu₂O/NM catalyst has exhibited good catalytic performances in the reduction of 4-NP, with a rate constant of 3.524 min⁻¹ and an activation energy (E_a) of 50.06 kJ mol⁻¹, comparable to other reported Cu-based catalysts and even noble metal-based catalysts. The higher catalytic performance of Cu₂O/NM can be ascribed to the high adsorption ability of NM and high effective electron transfer due to the Cu²⁺/Cu⁺ and Ti⁴⁺/Ti³⁺ redox couples (part of the Ti⁴⁺ in the NM was reduced to Ti³⁺ by NaBH₄). Furthermore, it demonstrates exceptional recyclability and structural stability, highlighting its potential as an effective and durable catalyst for practical applications. Based on the composition, structure, and catalytic performance of Cu₂O/NM, a plausible reaction mechanism is proposed. Therefore, this study presents a new paradigm for the fabrication of MOF-based composite catalysts with high catalytic activity and stability for the treatment of 4-NP-containing wastewater.