Preparation of mesoporous ThO2 nanoparticles: Influence of calcination on morphology and visible-light-driven photocatalytic degradation of indigo carmine and methylene blue.
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The present article reports the synthesis of thoria nanoparticles (ThO2 NPs) via sol-gel process and examines the effect of calcination temperature of ThO2 on the morphology and photocatalytic degradation of indigo carmine (IC) and methylene blue (MB) under visible-light. As-synthesized white crystals of ThO2 were subjected to calcination at different temperatures, viz. 700C (TH-700), 800C (TH-800), and 900C (TH-900). The effect of calcination temperature on the structural, morphological, thermal, surface area-porosity, and optical properties of ThO2 NPs were investigated by diverse analytical techniques. XRD patterns show the cubic-space group Fm-3m (225) with parameter a=5.597 and reveals crystallite sizes increased with calcination temperature. The bandgap energy was found to be 1.85eV, 2.33eV, and 2.71eV for TH-700, TH-800, and TH-900 NPs, respectively, calculated by Kubelka-Munk (KM) plot. SEM and TEM unveil that the sample TH-700 calcined at a low temperature of 700C yields assembled nanosheets, while at higher temperatures, i.e., 800C (TH-800) and 900C (TH-900), produces agglomerated nanomaterials. Further, TH-700 sample exhibits enhanced photocatalytic degradation within 120min for both IC and MB dye than TH-800 and TH-900 counterparts. Among the dyes, IC shows improved photocatalytic efficiency than MB for TH-700, owing to the increased optical absorption and improved separation of photogenerated charge carriers. The reusability study of TH-700 reveals that the catalysts were stable up to four successive cycles with no drastic changes in photocatalytic efficiency. Also, systematic photodisintegration of IC was investigated by Liquid chromatography-mass spectrometry (LC-MS).
