Preparation of stable ultrahydrophobic and superoleophobic silica-based coating

Silica-Based coatings having excellent water- and oil-repellent properties and good weathering stability have been deposited onto glass surface by a simple one-step dip coating technique. To achieve ultra water repellency and super oil repellency, the chemical composition of SiO2 nanoparticle employed as surface roughness enhancer and trichloro(1H,1H,2H,2H-perfluorooctyl)silane employed as surface-energy reducing substance was varied. At the optimum synthesis condition, the coating exhibited very high contact angles of 173.2, 146.7 and 147.6 degrees for water, ethylene glycol and seed oil, respectively. The achievement of excellent water- and oil-repellency is also described based on the presence of air trapped in micropore of the coating in addition to its high surface roughness and low surface free energy. The coatings have good weathering stability based on natural and accelerated weathering tests indicating feasibility for practical use.     

Hydrothermal synthesis and photocatalytic activity of anatase TiO2 nanofiber

TiO2 nanofiber consisting of 15 +/- 5 nm anatase grains was synthesized by hydrothermal treatment of fibrous hydrogen titanate precursor at 180 degrees C for 20 h. The hydrogen titanate precursor was synthesized by hydrothermal treatment of commercial P25 TiO2 powder in 10 M NaOH at 200 degrees C for 20 h followed by soaking in 0.1 M HNO3 to perform ion exchange between the as-synthesized Na titanate and H. By controlling pH of the solution during hydrothermal treatment of the hydrogen titanate precursor, pure anatase TiO2 nanofiber was obtained. Its band-gap energy determined from the onset of diffused reflectance spectrum was 3.19 eV which is equal to that of anatase TiO2 powder. The TiO2 nanofiber showed higher photodecomposition efficiency than the Cotiox KA-100 TiO2 but lower than the P25 TiO2. Photodegradation is the predominant process for 'Reactive blue 171' removal.     

Preparation and photocatalytic activity of iron oxide-loaded potassium titanate layered compounds

Iron oxide-loaded hydrous potassium tetratitanate (K0.3Ti4O7.3(OH)1.7) compounds consisting of 1.48 wt% (sample 'B'), 1.87 wt% (sample 'C') and 5.60 wt% (sample 'D') of iron oxide were synthesized by suspending the K0.3Ti4O7.3(OH)1.7 (sample 'A') in Fe2(SO4)3 solution for 24 h, followed by washing several times with deionized water and then dried at 120 degrees C for 24 h. The K0.3Ti4O7.3(OH)1.7 was synthesized by refluxing the K2Ti4O9 x 2H2O in 1 M HNO3 solution. Band-gap energies of the K0.3Ti4O7.3(OH)1.7 and the iron oxide-loaded samples are 3.12 +/- 0.6 eV and 2.23 +/- 0.09 eV, respectively. Photooxidation activity towards methylene blue decomposition under fluorescence irradiation was found to decrease as follow: sample 'B' > sample 'C' > Sample 'A' > sample 'D' > commercial Fe2O3-Blank. The photoactivity under sunlight irradiation was found to decrease as follow: sample 'B' > sample 'A' > Sample 'C' > sample 'D' > commercial Fe2O3-Blank.     

Preparation and photocatalytic study of fibrous K0.3Ti4O7.3(OH)1.7–anatase TiO2 nanocomposite photocatalyst

Nanocomposite of K_0.3Ti₄O_7.3(OH)_1.7 fiber and anatase TiO₂ nanoparticle was prepared by hydrothermal treatment of the K_0.3Ti₄O_7.3(OH)_1.7 which was synthesized by calcination of K₂CO₃ and TiO₂ at 1250 °C followed by refluxing in nitric acid. Effects of hydrothermal treatment conditions such as temperature and time on morphology, phase composition and crystal structure of the nanocomposites were extensively studied. Photocatalytic activities of the catalysts prepared at various hydrothermal conditions were evaluated by means of methylene blue decomposition under blacklight irradiation.     

Nanocrystalline Tin Oxide Thin Films via Liquid Flow Deposition

Nanocrystalline films of SnO₂ were deposited by liquid flow deposition (LFD), i.e., by flowing aqueous solutions of SnCl₄·5H₂O and HCl over single-crystalline silicon substrates at 80°C. The substrates were either oxidized and fully hydrolyzed (bare silicon) or oxidized, hydrolyzed, and then coated with siloxy-anchored organic self-assembled monolayers (SAMs). Continuous, adherent films formed on sulfonate- and thioacetate-functionalized SAMs; adherent but sometimes discontinuous films formed on bare silicon and methyl-functionalized SAMs. The films contained equiaxed cassiterite crystals, ∼4–10 nm in size. The film thickness increased linearly with deposition time. The maximum growth rate observed was 85 nm·h⁻¹ on sulfonate SAM, and the maximum film thickness obtained was 1 μm. A new dimensionless parameter, the normalized residence time, τ, was introduced for the purpose of interpreting the influence of solution conditions (i.e., degree of supersaturation, as controlled via pH, and tin concentration) and flow characteristics (flow rate and the configuration of the deposition chamber) on the growth rate in LFD processes. The results were consistent with a particle attachment mechanism for film growth and inconsistent with heterogeneous nucleation on the substrate.     

An effect of silicon micro-nano-patterning arrays on superhydrophobic surface

Superhydrophobic surface can be fabricated by creating a rough surface at very fine scale and modify it with low-surface energy material. To obtain the optimum superhydrophobicity, the surface roughness must be maximized. To avoid the limitation of scaling down the pattern size by using an expensive lithography tools, the surface roughness factor (r) was increased by means of changing an asperity shape so as to increase its overall surface area. In this paper, the patterns of the asperities under studied were wave stripes, line stripes, cylindrical pillars, square pillars, pentagonal pillars, hexagonal pillars, and octagonal pillars. All pillar shapes were arranged in square arrays, hexagonal arrays, and continuous stripes. The asperities sizes and the pitches were varied from 1 to 5 microm with 10 microm of asperity height. Then the patterned surfaces were coated with polydimethylsiloxane mixed with 10 wt% dicumylperoxide. It was found that the stripe asperities can generate only hydrophobic surface with water contact angle (WCA) of 135 degrees to 145 degrees. The pillars with square and hexagonal arrays had the WCA of 149 degrees to 158 degrees. The pentagonal pillars with square and hexagonal arrays achieved the highest WCA with an average WCA of 156 degrees. It was evident that the pillar shape had significant effect on the superhydrophobicity.     

Increasing active surface area to fabricate ultra-hydrophobic surface by using "Black silicon" with bosch etching process

Needle-shaped pillars so-called "Black silicon" (B-Si) were fabricated by etching cleaned silicon wafer with fluorine-based deep reactive ion etching plasma. The B-Si pillar with the pillar size (a) and spacing (b) of 250 nm, and height (h) of 6.47 microm, coated with SiOxFy film had water contact angle (WCA) and ethylene glycol contact angle (ECA) of 159.8 degrees and 135.5 degrees, respectively. After coating the pillar with trichloro(1H,1H, 2H,2H-perfluorooctyl)silane (TPFS), the WCA and ECA increased to 166.2 degrees and 161.8 degrees, respectively. At the optimum etching condition, the B-Si pillar with the size a = 376 nm, b = 576 nm, h = 6.47microm, and the aspect ratio of 14.80 showed the WCA and ECA of 4.25 degrees and 14.77 degrees, respectively. After coating with the TPFS, liquid droplets ran across the sample's surface rapidly and the WCA and ECA could not be measured. Moreover, when the pillar height was increased twice, the WCA and ECA of the B-Si with and without the TPFS coating were greater than 170 degrees, indicating excellent water-and-oil repellency and can be applied for Micro-Electro-Mechanical Systems (MEMS).     

Fabrication of silica-based multilayer films with self-cleaning and antireflective properties

The silica-based multilayer films exhibiting both self-cleaning property and antireflection in the visible and near infrared regions have been deposited onto glass substrate by layer-by-layer deposition of PAH/PAA polyelectrolyte bilayers, followed by sequential deposition of PAH/SiO2 nanocomposite layers to create the nanoporous structure in the film, and finally treating with fluorosilane. To obtain the appropriate porosity and surface roughness so as to satisfy both antireflection and self-cleaning properties, the deposition of PAH/SiO2 nanocomposite layers was varied from 2 to 8 layers. Scanning electron microscopy and atomic force microscopy analysis revealed that a highly nanoporous structure was obtained from the more deposition of loosely agglomerated SiO2 nanoparticles which increased with the increased cycle of PAH/SiO2 deposition. The film consisting of 6 and 8 PAH/SiO2 layers exhibited a very low reflection of only 1-2% in the visible region and approximately 2-4% in the near infrared region, a maximum transmittance of approximately 93% in the visible region and approximately 94% in the near infrared region, and a high advancing contact angle of approximaetly 150 degrees. It is anticipated that the film which exhibited both self-cleaning and antireflection properties enables the application of the antireflection coatings under humid environments.     

Effect of synthesis condition on morphology and yield of hydrothermally grown SnO2 nanorod clusters

In this present work, we report the synthesis of SnO₂ nanorod clusters by means of hydrothermal treatment of colloidal hydrous tin oxide at 200 °C. Effect of synthesis parameters including concentrations of Na₂SnO₃·3H₂O and NaOH, and hydrothermal time on morphology and yield of the products is investigated. At optimum synthesis condition, nanorod clusters consisting of single crystalline, tetragonal-shaped rutile SnO₂ nanorod with uniform shape and size of 190 ± 6 nm in diameter and 1.4 ± 0.2 μm in length were obtained. The influence of precursor concentration on yield and morphology development was discussed. Grown mechanism is described based on aggregation of nanocrystals and their subsequent growth homocentrically.