<p>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&#xa0;min⁻¹ and an activation energy (E_<i>a</i>) of 50.06&#xa0;kJ&#xa0;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.</p>