AbstractThis study aims to explore how altering solvothermal duration influences the characteristics of the resulting products, spanning crystal structure, band gap energy, morphology, and photocatalytic performance. Bismuth‐rich oxyiodide was synthesized via the solvothermal method by dissolving Bi(NO3)3 ⋅ 5H2O and KI in ethylene glycol. The mixture underwent heating in a Teflon autoclave stainless steel at 120 °C for durations of 6, 12, 24, and 48 hours. Analysis using FTIR revealed the presence of Bi−O and I−O bonds. Diffractograms indicated that all products exhibited traits of Bi4O5I2, with slight traces of Bi5O7I. Distinct band gap energies were observed across the solvothermal durations: 2 eV for 6 hours, 2.08 eV for 12 hours, and 1.89 eV for both 24 and 48 hours, delineating temporal nuances in product properties. Noteworthy, the morphology of the 12 hour variant revealed surface pores, indicative of intricate structural features. Notably, the 12 hour product exhibited the pinnacle of photocatalytic efficacy in methyl orange decolorization under UV light. Furthermore, investigations into photocatalyst mass variations and the inclusion of additional dyes, such as rhemazol black B, further elucidated the robust photocatalytic potential inherent in the B12 variant.