Tailored
Synthesis of Photoactive TiO<sub>2</sub> Nanofibers
and Au/TiO<sub>2</sub> Nanofiber Composites: Structure and Reactivity
Optimization for Water Treatment Applications
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Abstract
Titanium
dioxide (TiO<sub>2</sub>) nanofibers with tailored structure
and composition were synthesized by electrospinning to optimize photocatalytic
treatment efficiency. Nanofibers of controlled diameter (30–210
nm), crystal structure (anatase, rutile, mixed phases), and grain
size (20–50 nm) were developed along with composite nanofibers
with either surface-deposited or bulk-integrated Au nanoparticle cocatalysts.
Their reactivity was then examined in batch suspensions toward model
(phenol) and emerging (pharmaceuticals, personal care products) pollutants
across various water qualities. Optimized TiO<sub>2</sub> nanofibers
meet or exceed the performance of traditional nanoparticulate photocatalysts
(e.g., Aeroxide P25) with the greatest reactivity enhancements arising
from (i) decreasing diameter (i.e., increasing surface area), (ii)
mixed phase composition [74/26 (±0.5) % anatase/rutile], and
(iii) small amounts (1.5 wt %) of surface-deposited, more so than
bulk-integrated, Au nanoparticles. Surface Au deposition consistently
enhanced photoactivity by 5- to 10-fold across our micropollutant
suite independent of their solution concentration, behavior that we
attribute to higher photocatalytic efficiency from improved charge
separation. However, the practical value of Au/TiO<sub>2</sub> nanofibers
was limited by their greater degree of inhibition by solution-phase
radical scavengers and higher rate of reactivity loss from surface
fouling in nonidealized matrixes (e.g., partially treated surface
water). Ultimately, unmodified TiO<sub>2</sub> nanofibers appear most
promising for use as reactive filtration materials because their performance
was less influenced by water quality, although future efforts must
increase the strength of TiO<sub>2</sub> nanofiber mats to realize
such applications