Sanjayan Sathasivam

Robust self-cleaning surfaces that function when exposed to either air or oil

A robust paintlike repellent coating Superhydrophobic materials often depend on a particular surface patterning or an applied coating. However, these surfaces can be damaged by wear or fouled by oily materials. Lu et al. devised a suspension of coated titanium dioxide nanoparticles that can be spray-painted or dipcoated onto a range of hard and soft surfaces, including paper, cloth, and glass. The coatings resisted rubbing, scratching, and surface contamination. Science, this issue p. 1132 Robust, coated self-cleaning surfaces function after either abrasion or oil contamination. Superhydrophobic self-cleaning surfaces are based on the surface micro/nanomorphologies; however, such surfaces are mechanically weak and stop functioning when exposed to oil. We have created an ethanolic suspension of perfluorosilane-coated titanium dioxide nanoparticles that forms a paint that can be sprayed, dipped, or extruded onto both hard and soft materials to create a self-cleaning surface that functions even upon emersion in oil. Commercial adhesives were used to bond the paint to various substrates and promote robustness. These surfaces maintained their water repellency after finger-wipe, knife-scratch, and even 40 abrasion cycles with sandpaper. The formulations developed can be used on clothes, paper, glass, and steel for a myriad of self-cleaning applications.

Creating superhydrophobic mild steel surfaces for water proofing and oil-water separation

A simple and inexpensive two-step immersion method is reported to make mild steel superhydrophobic. Micro–nano-scale roughness and surface chemistry modifications were created via immersing mild steel into a salt solution followed by treatment with a low surface-energy polymer. The fabricated mild steel has water contact angles greater than 150° and remarkable water bouncing properties. This method was also used to treat a mild steel mesh for oil–water separation. In this paper, a new, facile and reusable gravity-induced separation system is proposed to collect floating oil, the oil collection rate can reach >96%.

Tungsten Doped TiO2 with Enhanced Photocatalytic and Optoelectrical Properties via Aerosol Assisted Chemical Vapor Deposition.

Tungsten doped titanium dioxide films with both transparent conducting oxide (TCO) and photocatalytic properties were produced via aerosol-assisted chemical vapor deposition of titanium ethoxide and dopant concentrations of tungsten ethoxide at 500 °C from a toluene solution. The films were anatase TiO2, with good n-type electrical conductivities as determined via Hall effect measurements. The film doped with 2.25 at.% W showed the lowest resistivity at 0.034 Ω.cm and respectable charge carrier mobility (14.9 cm3/V.s) and concentration (×1019 cm−3). XPS indicated the presence of both W6+ and W4+ in the TiO2 matrix, with the substitutional doping of W4+ inducing an expansion of the anatase unit cell as determined by XRD. The films also showed good photocatalytic activity under UV-light illumination, with degradation of resazurin redox dye at a higher rate than with undoped TiO2.

Aerosol assisted chemical vapour deposition of hydrophobic TiO2–SnO2 composite film with novel microstructure and enhanced photocatalytic activity

Aerosol assisted chemical vapour deposition (AACVD) was used to synthesise a TiO2–SnO2 composite film onto a glass substrate. For comparison a TiO2 film and a SnO2 film were also prepared. All films were characterised by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and wavelength dispersive X-ray spectroscopy (WDX). XPS and WDX of the composite film revealed a TiO2 rich film with a high level of SnO2 segregation at the surface. Highly structured pyramid-like features gave rise to hydrophobic films with static water contact angles of 134°. Photocatalytic activities were determined by monitoring the degradation of intelligent ink (containing Resazurin redox dye) via UV-visible spectroscopy. Under UVA irradiation, the TiO2 film only began to degrade the dye after being irradiated in excess of 100 minutes, whereas the composite TiO2–SnO2 film required only 6 minutes of irradiation before degradation was observed. The formal quantum efficiency (FQE) for the TiO2–SnO2 composite was determined to be 1.01 × 10−2 molecules per incident photon and the formal quantum yield (FQY) was 1.17 × 10−2 molecules per absorbed photon. This is an order of magnitude superior to Pilkington Activ™ self-cleaning glass a commercial self-cleaning TiO2 coating on glass. This improved photocatalytic activity is attributed to the presence of electron scavenging SnO2 sites that increase charge separation and the increased surface area due to the highly structured morphology.

PbO-Modified TiO2 Thin Films: A Route to Visible Light Photocatalysts

PbO clusters were deposited onto polycrystalline titanium dioxide (anatase) films on glass substrates by aerosol-assisted chemical vapor deposition (AACVD). The as-deposited PbO/TiO2 films were then tested for visible light photocatalysis. This was monitored by the photodegradation of stearic acid under visible light conditions. PbO/TiO2 composite films were able to degrade stearic acid at a rate of 2.28 × 10(15) molecules cm(-2) h(-1), which is 2 orders of magnitude greater than what has previously been reported. The PbO/TiO2 composite film demonstrated UVA degradation of resazurin redox dye, with the formal quantum yield (FQY) and formal quantum efficiency (FQE) exceeding that of a TiO2 film grown under the same conditions and Pilkington Activ, a commercially available self-cleaning glass. This work correlates with computational studies that predicted PbO nanoclusters on TiO2 form active visible light photocatalysts through new electronic states through PbO/TiO2 interfacial bonds resulting in new electronic states above the valence band maximum in TiO2, shifting the valence band upward as well as more efficient electron/hole separation with hole localization on PbO particles and electron on the TiO2 surface.

Large-scale fabrication of translucent and repairable superhydrophobic spray coatings with remarkable mechanical, chemical durability and UV resistance

In this work, we present a simple and effective silica–polymer-based spray coating to create a translucent, mechanically durable, chemically stable, healable and environmentally friendly superhydrophobic coating with UV resistance. The coatings retained superhydrophobicity after UV radiation for at least 175 hours, heating up to 150 °C, exposure to strong acids and bases, and various mechanical durability tests such as knife scraping, hand kneading, and multiple cycles of tape peeling 100 times. In addition, the coating treated sponge was used for continuous oil–water separation through connection with a vacuum system, the separation efficiency was greater than 95% for various liquid hydrocarbons. This substrate-independent spray coating is believed to be useful for large-scale application for both outdoor and indoor applications.

Water droplets bouncing on superhydrophobic soft porous materials

Creating superhydrophobic soft porous materials, such as cotton and cloths is an important area of research as these materials have important practical applications such as water repellent clothing. In this paper, a generic method is reported to fabricate superhydrophobic surfaces on soft porous substrates, which were treated with crystalline copper chloride-hydroxide, followed by a fluorinated polymer. Water droplets can be supported as a perfect sphere and even bounce on the prepared surfaces, which demonstrate superior superhydrophobicity. For many soft porous materials, it is difficult to identify superhydrophobicity using water droplet contact angles. This is because water droplets may be trapped in the concave structures, making the necessary contact line to define the contact angle unobtainable. To solve this problem, water bouncing was used as a sufficient and necessary identification for superhydrophobic soft porous materials, and a model was also made to discuss how a water droplet can bounce on soft materials.

Transparent conductive aluminium and fluorine co-doped zinc oxide films via aerosol assisted chemical vapour deposition

Aerosol assisted chemical vapour deposition (AACVD) was employed to synthesise highly transparent and conductive ZnO, fluorine or aluminium doped and aluminium–fluorine co-doped ZnO thin films on glass substrates at 450 °C. All films were characterised by X-ray diffraction (XRD), wavelength dispersive X-ray spectroscopy (WDX), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and UV/Vis/Near IR spectroscopy. The films were 300–350 nm thick, crystalline and displayed high transparency at 550 nm (80–90%). The co-doped film consisted of 1 at.% fluorine and 2 at.% aluminium, exhibiting a charge carrier concentration and a charge carrier mobility of 3.47 × 1020 cm−3 and 9.7 cm2 V−1 s−1, respectively. The band gap of the co-doped film was found to be 3.7 eV and the plasma edge crossover was ca. 1800 nm. This film had a highly structured morphology in comparison to the un-doped and single doped ZnO films for transparent conducting oxide applications.

Aerosol assisted chemical vapor deposition of conductive and photocatalytically active tantalum doped titanium dioxide films

This paper shows the aerosol assisted chemical vapour deposition of transparent, blue coloured and conductive tantalum doped titanium dioxide films from the CVD reaction of Ti(OEt)4 and Ta(OEt)5. Hall effect measurements showed the doped films to have excellent n-type electrical conductivity showing, to the best of our knowledge, the lowest reported sheet resistance ever recorded for Ta-doped TiO2 of 14 Ω sq−1. The Ta 6 atom% doped TiO2 film also showed the best electrical results with a charge carrier concentration of 1.60 × 1021 cm−3 and mobility of 1.44 cm2 V−1 s−1 making it a suitable electrode in photovoltaic devices. The doped films were multifunctional, showing good photocatalytic activity under UV-light illumination. XPS and XRD studies gave strong evidence that the Ta was entering the TiO2 lattice as Ta5+ and that a reduction of some Ti4+ to Ti3+ was observed.

Combinatorial aerosol assisted chemical vapour deposition of a photocatalytic mixed SnO2/TiO2 thin film

Combinatorial Aerosol Assisted Chemical Vapour Deposition (cAACVD) was used to grow a thin film that graduated across its width from tin dioxide to titanium dioxide. This is a relatively new technique that can be used to create a variety of mixed phase and composition thin films on a single substrate. Here cAACVD was used to deposit a mixed phase TiO2 and SnO2 film and composition was related to UV photocatalysis, hydrophobicity and microstructure not inherent to anatase TiO2 or cassiterite SnO2. Characterisation was achieved using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and UV-Vis spectroscopy. Functional testing to elucidate the differences in functional properties across the film was undertaken by the photo-induced degradation of a resazurin ‘intelligent’ ink, a photo-induced wettability study and two-point resistivity measurements. Functional properties showed enhanced photocatalysis in comparison to Pilkington Activ™ with similar formal quantum yield (molecules destroyed per absorbed photon) and formal quantum efficiency (molecules destroyed per incident photon) values.