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a) Contact angles of a sessile water droplet (V = 3 µL) under an oil environment on a LBL TiO 2 surface (30 bilayers) after various time intervals of immersion under oil for contamination. The inset shows the procedure for contamination and subsequent contact angle goniometry using sessile droplets; b) Time-resolved changes in under-oil water contact angles on precontaminated (t c = 18 h) TiO 2 surfaces upon UV light illumination. Here three different UV light intensities are shown (I = 40, 120, and 200 mW cm-2 ). The inset shows a drop of water spreading on a nanostructured TiO 2 surface immersed in dodecane under UV irradiation at I = 120 mW cm-2 (scale bar = 1 mm).
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Titanium dioxide (titania or TiO2) is well known for its photocatalytic properties and its ability to remove organic contaminants under UV light illumination. It is also known to switch its surface wetting characteristics from being hydrophilic to superhydrophilic under exposure to UV light in air. However, less is known about the switching of the...
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... 2017, 1700462 In order to study the time-dependent evolution in the surface energy of contaminated TiO 2 surfaces, we conducted under- oil water contact angle ( ) w,o * θ measurements on TiO 2 surfaces for a range of times of contamination. In Figure 3a, we show the evolution of w,o * θ as a function of contamination time (t c ) ranging from 0 to 30 h. The nanotextured TiO 2 surfaces exhibit a gradual increase in w,o * θ with increasing time of contamina- tion. ...
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... con- ducted in situ contact angle measurements for sessile water droplets on the precontaminated (t c = 18 h) LBL-assembled TiO 2 surfaces submerged in oil while illuminating them with UV light. In Figure 3b, we show a plot of w,o * θ as a function of UV light illumination time (t uv ) for three different intensi- ties (I = 40, 120, and 200 mW cm -2 ) on the precontaminated nanostructured TiO 2 surfaces. Before UV light illumination, the precontaminated TiO 2 surface is hydrophobic, displaying 120 Figure 3b). ...
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... Figure 3b, we show a plot of w,o * θ as a function of UV light illumination time (t uv ) for three different intensi- ties (I = 40, 120, and 200 mW cm -2 ) on the precontaminated nanostructured TiO 2 surfaces. Before UV light illumination, the precontaminated TiO 2 surface is hydrophobic, displaying 120 Figure 3b). After the onset of illumina- tion, a droplet of water starts to spread on the surface (insets (ii) and (iii) in Figure 3b), and eventually the surface reverts back to its original under-oil superhydrophilic state character- ized by 10 Figure 3b). ...
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... UV light illumination, the precontaminated TiO 2 surface is hydrophobic, displaying 120 Figure 3b). After the onset of illumina- tion, a droplet of water starts to spread on the surface (insets (ii) and (iii) in Figure 3b), and eventually the surface reverts back to its original under-oil superhydrophilic state character- ized by 10 Figure 3b). Movie S1 (Supporting Information) demonstrates the UV light-induced spreading of a droplet of water on a precontaminated TiO 2 surface submerged in oil. ...
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... UV light illumination, the precontaminated TiO 2 surface is hydrophobic, displaying 120 Figure 3b). After the onset of illumina- tion, a droplet of water starts to spread on the surface (insets (ii) and (iii) in Figure 3b), and eventually the surface reverts back to its original under-oil superhydrophilic state character- ized by 10 Figure 3b). Movie S1 (Supporting Information) demonstrates the UV light-induced spreading of a droplet of water on a precontaminated TiO 2 surface submerged in oil. ...
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... order to obtain the rate constants for adsorption (k c ) and des- orption (k -c ) of oil on the nanotextured TiO 2 surfaces, we first apply the LuCY model to the data obtained during our contami- nation study. Figure 3a. Fitting our LuCY model to the experimental data gives the adsorption and desorption rate constants as k c = 3.54 × 10 -5 s -1 and k -c = 3.58 × 10 -7 s -1 , respectively. ...
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... these values of the rate constants of adsorption and desorption, we estimated the rate constant for photocata- lytic destruction (k p ) of adsorbed oil on TiO 2 surfaces using the data from experiments conducted under UV light illumina- tion. Figure 5b shows a plot of cos w,o * θ as a function of UV illu- mination time, constructed using the values of w,o * θ shown in Figure 3 b. The LuCY model was fitted to the experimental data to obtain the photocatalytic rate constants, k p = 7.1 × 10 -3 s -1 , k p = 14.5 × 10 -3 s -1 , and k p = 49.5 × 10 -3 s -1 for the intensities of I = 40, 120, and 200 mW cm -2 , respectively. ...
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... Panchanathan et al., [163] in their work showed that the three reactions above obey the first order kinetics. Now for F-SiO 2 not photocatalytic [164], and N-TiO 2 photocatalytic [165], the following differential equation can be obtained describing a time-dependent photocatalysis-driven evolution of the area fraction of the surface of the membrane contaminated with oil (f c (t i )): ...
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Surface hydrophobicity/hydrophilicity of titania (TiO2) films, spin-coated on silicon wafers, were
tuned by introducing surface mesopores with various morphologies using a triblock copolymer F38 as
the template agent of different weight ratios via a sol-gel method. It is found that both the porosity
(2.92 ∼ 33.03%) and the surface roughness(0.22 ∼ 0.43 nm for arithmetic mean roughness and
0.28 ∼ 0.58 nm for root mean square roughness) of the films increase monotonically as increasing
F38 ratio from 5 to 25 wt%, accompanied by distinct changes of pore morphology from isolated
mesopores with pore sizes of 5 ∼ 7 nm to longer worm-like pores(30 ∼ 100 nm in length). The
apparent static contact angle (θ*) of the films with isolated mesopores is enhanced from ca. 90.6°to
100.1° as indicated by an increase of the roughness factor with incresing F38 from 5 to 15 wt%, which
is in qualitative agreement with the Wenzel’s equation. Interestingly, the films with interconnected
worm-like pores show obvious hydrophilicity (θ* = 80.7°)with further increasing F38 ratio higher
than 20 wt%. The reversed surface wettability show that not only surface roughness but also pore
morphology could significantly affect the wettability of the mesoporous TiO2 films.
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