<p>This study reports the synthesis of chromium oxide nanoparticles (Cr₂O₃ NPs) through two distinct approaches: a green synthesis method employing <i>Saraca asoca</i> extract and a chemical sol–gel method using methanol as a capping agent. The nanoparticles were characterized by XRD, FTIR, SEM, zeta potential, and particle size analyses to evaluate their structural, morphological, and surface properties. The green-synthesized Cr₂O₃ nanoparticles (Cr₂O₃-G) exhibited a smaller crystallite size and a slightly wider band gap, which enhanced light absorption and charge carrier mobility, thereby improving photocatalytic efficiency. Additionally, its higher colloidal stability and larger specific surface area facilitated better dispersion and greater active site availability. In contrast, the chemically synthesized Cr₂O₃ nanoparticles (Cr₂O₃-C) showed larger crystallites, a narrower band gap, and reduced surface stability, resulting in comparatively lower photocatalytic activity. During methylene blue degradation under visible light, Cr₂O₃-G achieved faster and more complete degradation than Cr₂O₃-C, highlighting the synergistic effect of its refined structural and surface characteristics. This study demonstrates that the green synthesis route offers an environmentally sustainable and efficient approach to producing Cr₂O₃ nanoparticles with optimized crystallite size, band gap, and colloidal stability, making them highly suitable for photocatalytic and environmental remediation applications.</p>