Tailored Synthesis of Photoactive TiO₂ Nanofibers and Au/TiO₂ Nanofiber Composites: Structure and Reactivity Optimization for Water Treatment Applications

Abstract

Titanium dioxide (TiO2) 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 TiO2 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/TiO2 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 TiO2 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 TiO2 nanofiber mats to realize such applications.

Synthesis and optimization of Ag–TiO2 composite nanofibers for photocatalytic treatment of impaired water sources

“…The motivation for such phase tuning is Aeroxide® P25, a mixed phase TiO 2 photocatalyst with a anatase to rutile ratio of 70-80%-to-20-30% [1,26] that outperforms both pure phases in reactivity studies [27]. Additionally, this finding had also been observed in our previous work with unmodified TiO 2 nanofibers [24]. After annealing, typically 20-25 mg of nanofibers were produced and combined with a designated amount of DI water to create a 1 g/L TiO 2 stock and sonicated in a Branson sonicator to disperse the nanofibers into a homogenous suspension.…”

“…Through electrospinning, nanofibers mats can be immobilized on membrane substrates in order to utilized this highly reactive nanotechnology safely without the risk of incident material release into the aquatic environment [21]. Ultimately, these findings, in addition to other work, would be the first step toward developing of nanofiber-enabled treatment technologies, which include single or multi-component nanofiber mats immobilized on ceramic membranes with the potential for multi-functional chemical (e.g., oxidation) and physical (e.g., filtration) treatment of impaired water supplies [24]. By taking advantage of these nanofiber mats as a collective filtration membrane for either full scale or pointof-use purposes, there is the possibility of increased contact time, and consequently increased pollutant removal during influent movement, as well as other synergistic performance enhancements.…”

“…Although there is much work on electrospun TiO 2 nanofibers, relatively little work has been conducted to optimize structure, morphology, and composition toward improving photocatalytic reactivity [24]. Additionally, further work is necessary to understand the effects of noble metal additives in composite nanofibers towards TiO 2 structure and morphology, as well as photocatalytic performance.…”

Synthesis and optimization of Fe2O3 nanofibers for chromate adsorption from contaminated water sources

“…S4. Interestingly, the average grain size was equal to or greater than some of the smaller nanofiber sizes, indicating the absence of dimensional confinement and possible ellipsoid grains (Lee et al, 2010;Nalbandian et al, 2015;Park and Kim, 2009). Additionally, texture coefficient calculations verified that the synthesis yielded random crystal orientation (Table S1).…”

Synthesis of Cu-doped nano-TiO2 by detonation method

“…However, UV light only accounts for 4% of sunlight, so the utilization rate of sunlight is very low. To fully make use of solar energy and develop new photocatalysts that can react in visible light with stable structure and performance, studies have focused on the modification of TiO 2 , such as noble metal deposition [13,14], metal ion doping [15][16][17], nonmetal doping [18,19], and coupled semiconductor [20,21]. The band gap of TiO 2 is reduced and its catalytic property is improved after modification.…”