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

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 (similar to 11 nm) TiO2 layer (AZO/TiO2). The combined film exhibited prolonged stability in water and had a low sheet resistance of 67 Omega/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.