Scaling-Up Seeded Hydrothermal Nanowire Synthesis on Non-planar Surfaces Using a Flow Reactor

Abstract

While many nanomaterial synthesis processes have been demonstrated at the laboratory scale, grand challenges remain at the nanomanufacturing frontier, where it is necessary to maintain tunable material structure and properties at large length scales using high-throughput, low-cost, and sustainable processes. Seeded hydrothermal synthesis is widely used to generate tunable nanostructures with controlled geometric parameters. In this study, we used atomic layer deposition to deposit precise and conformal seed layers which were subsequently processed using a customized hydrothermal flow reactor. The reactor design allows for control of the solution temperature profile in space and time, as well as the solution flow profile. Recirculation of the hydrothermal growth solution enables reduction of the chemical waste by 77–92% compared to a single pass flow reactor. This “surface-directed assembly” process allows for the growth of vertically aligned zinc oxide (ZnO) nanowires (NWs) directly onto macroscopic (cm-scale) non-planar surfaces. We quantify the uniformity of the NW morphology using scanning electron microscopy and UV absorption measurements. The NWs were further functionalized to form superhydrophobic and optically transparent surface coatings along a curved glass dome substrate. The surface coatings were shown to significantly reduce the rate of biofouling from marine algae by ∼75%. This demonstrates a pathway for the scale-up of hydrothermal synthesis processes with a variety of applications in the biological and environmental fields, including medical devices and optical and oceanographic sensors.