Boosting defects through divalent ion substitution to tailor the optical, textural, catalytic, and photocatalytic properties of Th4+-stabilized δ-Bi2O3

Abstract

The current article reports a facile solution combustion synthesis of lead and cadmium doped Th4+ modified bismite and its application as a heterogeneous catalyst in Knoevenagel condensation reaction and visible light assisted disintegration of Eosin Yellow dye from aqueous solutions. The samples were extensively characterized by various physicochemical techniques such as powder X-ray diffraction, electron microscopy measurements, Raman, diffuse reflectance, and photoluminescence spectroscopy measurements, along with Brunauer-Emmett-Teller analysis. The oxides' catalytic activity was probed in the Knoevenagel condensation reaction of various substituted aldehydes coupled with malononitrile, resulting in excellent yields (˃ 99%) after optimization of various reaction parameters such as temperature, catalyst dosage, amount of aldehyde, and malononitrile. 1H and 13C NMR spectra confirmed selectivities (˃ 99%). A probable mechanism was deduced after combining these results with GC-MS analysis. The oxides' high surface area was also exploited for photocatalytic disintegration of Eosin Yellow (toxic xanthene dye). The presence of oxygen vacancies and the generated superoxide radicals played a dominant role in enhancing photocatalytic activity. The electrical efficiency for practical utility, electrical energy per order (EEO) was assessed for all the samples. The divalent doped oxides’ catalytic and photocatalytic efficiencies were higher than the tetravalent stabilized δ-Bi2O3 elucidating the synergistic effect of oxygen vacancies and Lewis acid-base interaction in enhancing the catalytic activity and in suppressing the recombination of photogenerated holes and electrons. Excellent recycling efficiency and stability exhibited by an optimally doped δ-Bi2O3 demonstrated it to be a promising bifunctional catalyst.