Electrochemical Synthesis\nof Zeolite Coatings with\nControlled Crystal Polymorphism and Self-Regulating Growth

Zeolite coatings are studied as molecular sieves for\nmembrane separation,\nmembrane reactors, and chemical sensor applications. They are also\nstudied as anticorrosive films for metals and alloys, antimicrobial\nand hydrophobic films for heating, ventilation, and air conditioning,\nand dielectrics for semiconductor applications. Zeolite coatings are\nsynthesized by hydrothermal, ionothermal, and dry-gel conversion approaches,\nwhich require high process temperatures and lengthy times (ranging\nfrom hours to days). Here, we report the first zeolite coatings synthesized\nvia electrochemical deposition on a cathodic electrode, with controlled\ncrystal polymorphism achieved within subhourly duration. We demonstrate\nthis approach by developing sodium zeolite (e.g., sodalite (SOD),\nNaA (LTA), and Linde Type N (LTN)) coatings on a titanium electrode\nand extending the synthesis method to porous stainless steel. The\ncoating morphology and crystallinity depend on the temperature, time,\nand applied current. The coating thickness is independent of the applied\ncurrent, showing the presence of a self-regulating mechanism to ensure\na uniform coating thickness across the metal surface. The electrochemical\nzeolite growth mechanism was elucidated with high-resolution transmission\nelectron microscopy, and applications of the resultant zeolite coatings\nfor oil/water separation and ethanol/water pervaporation were exploited.\nElectrochemical synthesis represents a novel, simple, fast, and environmentally\nfriendly approach to preparing zeolite coatings. It can potentially\nbe generalized for developing zeolite materials with diverse framework\nstructures, morphologies, and orientations for substrates with complicated\ngeometries.