posted on 2020-07-22, 14:41authored byJonathan 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).