Adapting Aluminum-Doped Zinc Oxide for Electrically Conductive Membranes Fabricated by Atomic Layer Deposition

Abstract

The use of electrically conductive membranes has recently drawn great interest in water treatment as an approach to reduce biofouling. Most conductive membranes are made by binding nanoparticles (carbon nanotubes or graphene) to a polymeric membrane using additional polymers, but this method risks leaching these nanomaterials into the environment. A new approach was developed here based on producing an electrically conductive layer of aluminum-doped zinc oxide (AZO) by atomic layer deposition. The aqueous instability of AZO, which is a critical challenge for water applications, was solved by capping the AZO layer with an ultrathin (∼11 nm) TiO2 layer (AZO/TiO2). The combined film exhibited prolonged stability in water and had a low sheet resistance of 67 Ω/sq with a 120 nm-thick coating, while the noncapped AZO coating quickly deteriorated as shown by a large increase in membrane resistance. The AZO/TiO2 membranes had enhanced resistance to biofouling, with a 72% reduction in bacterial counts in the absence of an applied current due to its higher hydrophilicity than the bare polymeric membrane, and it achieved an additional 50% reduction in bacterial colonization with an applied voltage. The use of TiO2-capped AZO layers provides a new approach for producing conductive membranes using abundant materials, and it avoids the risk of releasing nanoparticles into the environment.

Superhydrophobic, Highly Conductive, and Trilayered Fabric with Connected Carbon Nanotubes for Energy-Efficient Electrical Heating

“…Researchers implemented nanodopants with covalent modification to improve the dispersion of nanodopants and fabricated uniform poly­(vinylidene fluoride)/graphene, silicon carbide/carbon, and polyacrylonitrile/MXene nanofibrous membranes via one-step blend electrospinning. On the other hand, researchers used nanofibrous membranes as substrates and prepared a conductive layer with nanodopants via different surface modifications, including chemical vapor deposition, electrospraying, and in situ deposition. − These conductive nanofibrous materials demonstrated good flexibility, remarkable electrical heating performance, and satisfactory temperature controllability, but these electrical heating textiles showed two flaws, which were involved in heat reflection and water repellence. The first flaw is that these electric-heating fabrics dissipate a significant amount of heat into the environment, while providing warmth to the human body.…”

Harnessing the Potential of Porous ZnO Photoanodes in Dye-Sensitized Solar Cells by Atomic Layer Deposition of Mg-Doped ZnO

“…The ALD process relies on the alternate and sequential exposure of the substrate to two or more vapor-phase precursors that react in self-limiting surface reactions between the functional groups on the substrate and the vapor-phase precursors. Coating of complex inner surfaces, even in porous thin films and nanocomposites, renders ALD superior compared to competing coating methods. , Those advantages have led to widespread applications in photovoltaics where ALD is used for the growth of passivation layers, passivating contacts, transparent conductive oxides in collectors, and protective layers in perovskite solar cells, − tandem solar cells, − and DSSCs − as well as other applications. − One approach for expanding the regular two-step ALD cycle toward advanced materials like ternary oxides consists of the use of supercycles. In this approach, two regular two-step ALD cycles are alternated and repeated to produce multilayered or mixed, multinary thin films.…”

Atomic Layer Deposition for Gradient Surface Modification and Controlled Hydrophilization of Ultrafiltration Polymer Membranes

“…Surface modifications are commonly used practices in membrane fabrication to enhance membrane performance. − Surface modification methods such as polymer or additive incorporation within the membrane matrix, − chemical reactions on the as-cast or prepared membrane, − and grafting or coating with various materials have been shown to improve membrane properties including membrane hydrophilicity, permeability, selectivity, and antifouling. − In the last several years, atomic layer deposition (ALD) has emerged as a powerful technique for membrane surface and pore network modification due to its ability to grow thin inorganic coatings on the walls of the tortuous porous network with sub-nanometer precision of the coating thickness. ,− ALD is based on sequential exposure of two gas-phase precursors, creating thin films, one atomic layer at a time, allowing precise control over the growth process in a wide array of inorganic materials . Conformal coating of metal oxides on the outer and inner pore surfaces by ALD has been demonstrated in microfiltration (MF) and ultrafiltration (UF) membranes and recently in nanofiltration (NF) and reverse osmosis (RO) membranes as well. , With judicious choice of materials and growth conditions, the metal oxide coatings can be harnessed to tune pore structure and pore surface properties, with emphasis on improving surface hydrophilicity and its resistance to fouling.…”