<p>The development of multifunctional nanomaterials capable of both pollutant degradation and chemical sensing has attracted considerable attention for environmental monitoring applications. In the present work, a Mn₂O₃–Co₃O₄ nanocomposite was successfully synthesized via a facile and cost-effective sol–gel method and explored for dual applications in photocatalytic degradation and electrochemical detection of the antibiotic trimethoprim (TMP). Structural and morphological analyses confirmed the formation of a porous heterostructured composite with enhanced surface properties. Optical studies revealed a narrow band gap of 2.1&#xa0;eV, enabling efficient visible-light absorption. The photocatalytic performance of the Mn₂O₃–Co₃O₄ nanocomposite was evaluated under sunlight irradiation, where a maximum degradation efficiency of 95% was achieved within 50&#xa0;min under optimized conditions (pH 5, temperature 35&#xa0;°C, and initial TMP concentration of 20 ppm). Kinetic studies indicated that the degradation process follows pseudo-first-order reaction kinetics. In addition to photocatalysis, the synthesized nanocomposite exhibited excellent electrocatalytic activity toward TMP sensing. The electrochemical sensor demonstrated a wide linear detection range of 0.05–25 µM, a limit of detection (LOD) of 0.5 µM, and a high sensitivity of 10 µA µM⁻¹ cm⁻². The improved performance is attributed to the synergistic interaction between Mn₂O₃ and Co₃O₄, which facilitates efficient charge separation and enhances electron transfer. These findings highlight the Mn₂O₃–Co₃O₄ nanocomposite as a promising dual-functional material for environmental remediation and antibiotic monitoring.</p> Graphical Abstract <p></p>