Cation-controlled wetting properties of vermiculite membranes and its promise for fouling resistant oil-water separation.

Manipulating the surface energy, and thereby the wetting properties of solids, has promise for various physical, chemical, biological and industrial processes. Typically, this is achieved by either chemical modification or by controlling the hierarchical structures of surfaces. Here we report a phenomenon whereby the wetting properties of vermiculite laminates are controlled by the hydrated cations on the surface and in the interlamellar space. We find that vermiculite laminates can be tuned from superhydrophilic to hydrophobic simply by exchanging the cations; hydrophilicity decreases with increasing cation hydration free energy, except for lithium. The lithium-exchanged vermiculite laminate is found to provide a superhydrophilic surface due to its anomalous hydrated structure at the vermiculite surface. Building on these findings, we demonstrate the potential application of superhydrophilic lithium exchanged vermiculite as a thin coating layer on microfiltration membranes to resist fouling, and thus, we address a major challenge for oil-water separation technology.

Electrically controlled water permeation through graphene oxide membranes.

Controlled transport of water molecules through membranes and capillaries is important in areas as diverse as water purification and healthcare technologies1-7. Previous attempts to control water permeation through membranes (mainly polymeric ones) have concentrated on modulating the structure of the membrane and the physicochemical properties of its surface by varying the pH, temperature or ionic strength3,8. Electrical control over water transport is an attractive alternative; however, theory and simulations9-14 have often yielded conflicting results, from freezing of water molecules to melting of ice14-16 under an applied electric field. Here we report electrically controlled water permeation through micrometre-thick graphene oxide membranes17-21. Such membranes have previously been shown to exhibit ultrafast permeation of water17,22 and molecular sieving properties18,21, with the potential for industrial-scale production. To achieve electrical control over water permeation, we create conductive filaments in the graphene oxide membranes via controllable electrical breakdown. The electric field that concentrates around these current-carrying filaments ionizes water molecules inside graphene capillaries within the graphene oxide membranes, which impedes water transport. We thus demonstrate precise control of water permeation, from ultrafast permeation to complete blocking. Our work opens up an avenue for developing smart membrane technologies for artificial biological systems, tissue engineering and filtration.

Growth kinetics of calcium fluoride at high supersaturation in a fluidized bed reactor.

Crystallization process in a fluidized bed reactor (FBR) has been regarded as an environmentally friendly technology for the removal and recovery of fluoride from industrial wastewater. The growth kinetics of calcium fluoride at high supersaturation was studied for design, control, and operation of an FBR. The main variables, including supersaturation, superficial velocity, pH value, and particle size of seed that influenced the crystal growth were investigated. Then, a growth model was used to predict the linear growth rate of calcium fluoride at a high influent concentration of fluoride. The pressure difference in the FBR was used as a feature to characterize the growth rate of calcium fluoride. The aggregation and adsorption between seeds and fine particles were proven to be a possible mechanism for growth of calcium fluoride.