Synthesis of hierarchical flower-like particles and its application as super-hydrophobic coating

Surface Engineering of Ceramic Nanomaterials for Separation of Oil/Water Mixtures

Oil/water mixtures are a potentially major source of environmental pollution if efficient separation technology is not employed during processing. A large volume of oil/water mixtures is produced via many manufacturing operations in food, petrochemical, mining, and metal industries and can be exposed to water sources on a regular basis. To date, several techniques are used in practice to deal with industrial oil/water mixtures and oil spills such as in situ burning of oil, bioremediation, and solidifiers, which change the physical shape of oil as a result of chemical interaction. Physical separation of oil/water mixtures is in industrial practice; however, the existing technologies to do so often require either dissipation of large amounts of energy (such as in cyclones and hydrocyclones) or large residence times or inventories of fluids (such as in decanters). Recently, materials with selective wettability have gained attention for application in separation of oil/water mixtures and surfactant stabilized emulsions. For example, a superhydrophobic material is selectively wettable toward oil while having a poor affinity for the aqueous phase; therefore, a superhydrophobic porous material can easily adsorb the oil while completely rejecting the water from an oil/water mixture, thus physically separating the two components. The ease of separation, low cost, and low-energy requirements are some of the other advantages offered by these materials over existing practices of oil/water separation. The present review aims to focus on the surface engineering aspects to achieve selectively wettability in materials and its their relationship with the separation of oil/water mixtures with particular focus on emulsions, on factors contributing to their stability, and on how wettability can be helpful in their separation. Finally, the challenges in application of superwettable materials will be highlighted, and potential solutions to improve the application of these materials will be put forward.

Complex ZnO-TiO2 Core-Shell Flower-Like Architectures with Enhanced Photocatalytic Performance and Superhydrophilicity without UV Irradiation

ZnO-TiO₂ core-shell photocatalysts of a complex flower-like architecture were synthesized, using a well-controlled sol-gel coating reaction of presynthesized ZnO flower-like structures. The samples were characterized by X-ray diffraction, field emission scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, diffuse reflectance UV-vis and attenuated total reflectance-Fourier transform infrared spectroscopy, nitrogen adsorption-desorption measurements, and photoluminescence measurements. Well-defined, core-shell flowers with a wurtzite ZnO core and anatase TiO₂ shells, with variable shell thickness, were acquired by appropriately adjusting the ZnO/Ti precursor mass feed ratio in the reaction. Moreover, hollow TiO₂ flowers were obtained, and they retained their morphology following the etching of the ZnO core in an acidic solution. The photocatalytic performance of the core-shell and hollow semiconductors was evaluated via the decoloration of a methylene blue dye solution under UV-vis irradiation. The core-shell flowers exhibited a higher decoloration rate, when compared with bare ZnO flowers, TiO₂ particles, and hollow TiO₂ flowers, and the photoactivity was dependent on the TiO₂ shell thickness. This was attributed to the efficient separation of the photogenerated holes and electrons at the ZnO-TiO₂ interface. Moreover, the most photoactive core-shell catalyst exhibited excellent reusability and stability for at least three photocatalytic cycles and excellent superhydrophilicity without UV irradiation, which is due to the increased roughness of the flower-like structures.