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Hierarchical TiO2 Nanoflower Photocatalysts with Remarkable Activity for Aqueous Methylene Blue Photo-Oxidation

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posted on 2020-07-22, 14:41 authored by Jonathan Harris, Ryan Silk, Mark Smith, Yusong Dong, Wan-Ting Chen, Geoffrey I. N. Waterhouse
This study systematically evaluates the performance of a series of TiO2 nanoflower (TNF) photocatalysts for aqueous methylene blue photo-oxidation under UV irradiation. TNF nanoflowers were synthesized from Ti­(IV) butoxide by a hydrothermal method and then calcined at different temperatures (T = 400–800 °C) for specific periods of time (t = 1–5 h). By varying the calcination conditions, TNF-T-t photocatalysts with diverse physicochemical properties and anatase/rutile ratios were obtained. Many of the TNF-T-1 photocatalysts demonstrated remarkable activity for aqueous methylene blue photo-oxidation at pH 6 under UV excitation (365 nm), with activities following the order TNF-700-1 > TNF-600-1 > TNF-500-1 > TNF-400-1 ∼ P25 TiO2 ≫ TNF-800-1. The activity of the TNF-700-1 photocatalyst (99% anatase, 1% rutile) was 2.3 times that of P25 TiO2 at pH 6 and 14.4 times that of P25 TiO2 at pH 4. Prolonged calcination of the TNFs at 700 °C proved detrimental to dye degradation performance due to excessive rutile formation, which reduced the photocatalyst surface area and suppressed OH generation. The outstanding activities of TNF-700-1 and TNF-600-1 are attributed to their hierarchical nanoflower morphology which benefitted UV absorption, a near-ideal anatase crystallite size for efficient charge separation, and their unusually low isoelectric point (IEP = 4.3–4.5).

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