Novel sol-gel synthesis of bismuth molybdate decorated with Au nanoparticles for solar CO2 photoreduction

Abstract

Bismuth molybdate photocatalyst powders were synthesized via a novel sol-gel process using citric acid and PEG 200. The powders were sintered for 2 h at 450 °C and 500 °C, then decorated with different concentrations of gold nanoparticles (Au NPs) to enhance the photoreduction of CO₂ to methanol under sunlight. Au NPs were incorporated onto the powder surface using the photodeposition method. X-ray diffraction, Raman spectroscopy, UV-Vis diffuse reflectance spectroscopy, and scanning electron microscopy were performed to characterize the textural, structural, and compositional properties of the materials. The photocatalytic activity was assessed through methylene blue degradation and CO₂ photoreduction, using sunlight as the energy source. The pristine material exhibited a band gap of approximately 3.0 eV and contained a mixture of two phases: Bi₂MoO₆ and Bi₆Mo₂O₁₅. After decoration with Au NPs, the band gap narrowed to 2.9 eV, and a surface plasmonic effect was observed above 520 nm. The sample exhibiting the best performance in dye photodegradation and CO₂ photoreduction was sintered at 500 °C with 0.05 mM of Au NPs, achieving 82.89% methylene blue degradation after 3 h, and a peak methanol production of 15.87 µmol•g⁻¹ after 4 h of reaction under sunlight. The methanol yield was comparable to that obtained with materials synthesized using other methods.

Graphical Abstract