Metal oxide nanoparticles, specifically rare earth-transition metal oxide-supported nanocomposites, are gaining popularity due to their unique properties and applications in various fields. In this work, the Sm2O3/MXene/g-C3N4 (SMG) nanocomposite was prepared using a facile and low-cost technique through the co-precipitation method. The prepared SMG photocatalyst was characterized by various analytical techniques. The photocatalytic ability was examined by the photocatalytic degradation of frequently used organic dye (Orange G) under visible light irradiation. The optimization studies were also examined to determine the suitable conditions for photocatalytic degradation such as variations in catalyst dosage, pH, dye concentration, and electrolytes effects. Kinetic studies were conducted for various dye concentrations (5, 10, 15, and 20 ppm), and 10 ppm showed 99.50% degradation at 300 min following a pseudo-first-order reaction. This technique revolutionizes wastewater treatment by introducing a Sm2O3/MXene/g-C3N4 nanocomposite that can efficiently remove environmental pollutants in real time under visible light irradiation. © 2025 Elsevier B.V., All rights reserved.