Functionalized Tetrapodal ZnO Membranes Exhibiting Superoleophobic and Superhydrophilic Character for Water/Oil Separation Based on Differential Wettability

Abstract

Achieving the efficacious and rapid separation of mixed water/oil streams has emerged as a fundamental imperative in order to facilitate extraction of fossil fuels by methods such as cyclic steam stimulation as well as to mitigate the potentially calamitous impact of oil spills in natural aquatic environments. Here, we demonstrate functionalized ZnO nanotetrapodal membranes combining the micrometer-scale texturation of underlying stainless steel meshes with the nanoscale texturation of an enmeshed interconnected porous network of ZnO tetrapods, the conformal adhesion afforded by an amorphous silica layer, and the low surface energy of surface-deposited perfluorinated sulfonate layers. The membranes exhibit pronounced differential wettability and selectively permeate water whilst retaining oil. The multivariate design space of the architectures has been evaluated to determine the mesh size and ZnO loading that yield the highest separation efficiencies. Oil content in recovered water is reduced to <300 ppm while maintaining a flux rate of greater than 325 L/(m 2 •h). The functioning of the membranes can be understood in terms of the creation of differential Cassie−Baxter nonwetting and Wenzel wetting regimes for oil and water, respectively.

Three-Dimensional Inverse Opal TiO2 Coatings to Enable the Gliding of Viscous Oils

“…In other formulations, we have seen significant improvement in the stability upon deposition of an amorphous SiO 2 layer (>1 kg in ASTM 2197). 20,21 The coatings are thus suitable for applications in nonabrasive environments.…”

“…For instance, liquid-impregnated coatings show promising performance but are readily damaged and difficult to scale; lithographically patterned architectures provide precise control of re-entrant curvature, but their elaboration to macroscopic scales remains challenging; polymeric coatings, such as block copolymers, enable definition of tailored chemical domains but have inadequate thermal stability and are prone to fouling. In previous work, we have demonstrated the promise of ceramic/metal coatings comprising ZnO tetrapods sprayed onto metal mesh surfaces; surface functionalization of the tetrapods yields hydrophobic/oleophobic, hydrophilic/oleophobic, or hydrophobic/oleophilic , character, enabling applications ranging from gliding of viscous oils to the separation of recalcitrant water/oil emulsions. The ZnO tetrapods serve to amplify the intrinsic wettability of the surface monolayers and yield 3D interconnected plastronic architectures that extend into the pores of the metal meshes, with the meshes additionally providing periodic micron-scale texture.…”

Photopolymerized superhydrophobic hybrid coating enabled by dual-purpose tetrapodal ZnO for liquid/liquid separation

“…We have previously reported the enhanced mechanical resilience of T-ZnO coating materials by incorporating a silica coating layer. [35][36][37] Recently, Yamauchi and coworkers utilized 38 a hybrid of polydimethylsiloxane (PDMS) [38][39][40] and T-ZnO to afford a durable and flexible superhydrophobic surface. Nevertheless, these methods require either continuous high heating that is problematic for large scale production, and/or the addition of catalyst that could lead to significant increase in cost.…”

Asphaltene Microencapsulation of Bitumen as a Means of Solid-Phase Transport

“…15 Efforts to improve bitumen pipeline transportation have focused on optimizing pumping requirements, design of surface coatings that glide viscous oils, 1,5,16 modification of bitumen viscosity through separation of asphaltenes before transportation, solubilization of bitumen in aromatic solvents, and deemulsification to reduce the brine content. 17 While beneficial to promoting flow, these approaches do not address the fundamental issues of spillage and environmental contamination. Modifications to pipelines such as the addition of coatings or innovations in pumping equipment necessitate frequent inspection to ensure preservation of pipeline integrity and are subject to extensive regulation.…”

“…However, pipelines designed for light and medium crude oils are ill-suited for heavy oils such as bitumen given the rheological challenges, high asphaltene content, paraffin deposition, and corrosion issues arising from remnant brine or salts produced during typical extraction processes . Efforts to improve bitumen pipeline transportation have focused on optimizing pumping requirements, design of surface coatings that glide viscous oils, ,, modification of bitumen viscosity through separation of asphaltenes before transportation, solubilization of bitumen in aromatic solvents, and de-emulsification to reduce the brine content . While beneficial to promoting flow, these approaches do not address the fundamental issues of spillage and environmental contamination.…”