Layered double hydroxides (LDH), also known as hydrotalcite-like compounds (HTLc), are inorganic compounds composed of a mixture of divalent and trivalent metal hydroxide layers that form sheet-like crystal structures. Excess positive charges created by the trivalent cations within the hydroxide layers are balanced by hydrated interlayer domains that contain interchangeable anionic species. In this work we demonstrate a rapid (&lt;5 minutes), room-temperature synthesis of dense, uniform, and highly oriented Zn2+/Cr3+ LDH thin films from aluminum-doped zinc oxide (AZO) templates. The LDH crystals are formed on the template with preferred orientation such that the ab plane is perpendicular to the substrate. The LDH films were characterized with scanning electron microscopy (SEM), X-ray diffraction (XRD), UV/Vis spectroscopy, and contact angle measurements. Like bulk LDH powder, these LDH films can undergo anion exchange by immersing the film in different aqueous salt solutions. ZnCr LDH films were immersed in perfluorooctanoic acid (PFOA) solution to exchange the as-synthesized interlayer nitrate ions with PFOA ions. ZnCr-PFOA LDH thin films displayed a ~2.6-fold interlayer distance increase and ultra-hydrophobicity as compared to ZnCr-NO3 LDH films. Additionally, ZnCr-PFOA LDH thin films demonstrated adsolubilization of large organic molecule guests within their interlayer domains. This synthetic method can adjust the thickness of the LDH layer by controlling reaction time and preliminary AZO thickness; additionally, it can be adapted toward a variety of substrate surfaces. For example, ZnCr LDH thin films were grown on the surface of optical fibers and applied as chemical sensors. The sensors displayed sensitivity toward dry CO2 and humidity. In conclusion, we have developed a new room-temperature synthetic method to rapidly achieve high-quality ZnCr LDH thin films that demonstrate the same anion exchange properties as bulk LDH powder. The templated approach of this synthesis can be adapted to various substrates, thus opening new avenues of application for LDH.

Rapid, room-temperature synthesis of oriented zinc-chromium layered double hydroxide thin films via aluminum-doped zinc oxide templates

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.