A spherical MoO<inf>3</inf>–SnO<inf>2</inf> nanocomposite was synthesized via a precipitation–sonication approach and thoroughly characterized to evaluate its structural, optical, and catalytic properties. XRD, SEM-EDX, and HR-TEM analyses confirmed the formation of a crystalline spherical nanostructure with uniform particle distribution. DRS spectra indicated a reduced band gap of 3.25 eV compared to 3.5 eV for pure SnO<inf>2</inf>, while photoluminescence studies revealed suppressed electron–hole recombination, confirming improved charge separation. The nanocomposite demonstrated remarkable photocatalytic performance toward the degradation of Naphthol Blue Black (NBB) dye under UV light, achieving 84% degradation within 45 min at neutral pH, significantly higher than the 59% achieved with SnO<inf>2</inf>. The material retained 90% of its activity after four reuse cycles, highlighting excellent stability and reusability. COD analysis confirmed efficient dye mineralization with evidence of CO<inf>2</inf> capture. Additionally, electrochemical studies revealed enhanced anodic current and superior electrocatalytic activity in dye-sensitized solar cells, attaining an efficiency of 1.7%. Overall, the synergistic interaction between MoO<inf>3</inf> and SnO<inf>2</inf> enhances charge transfer, optical absorption, and catalytic efficiency, making this nanocomposite a versatile material for environmental remediation, green synthesis, and renewable energy applications. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2025.