Vepa Rozyyev^1,2, Feng Gao¹, Yining Liu^1,2, Rahul Shevate¹, Rajesh Pathak¹, Anil U. Mane¹, Seth B. Darling^1,2, Jeffrey W. Elam^1
1Argonne National Laboratory, Lemont, IL
²University of Chicago, Chicago, IL
Atomic layer deposition (ALD) and vapor-phase grafting are surface engineering techniques that offer highly conformal and uniform coatings essential for the next generation water treatment technologies. The atomic-level control achieved by ALD over film thickness and composition, combined with the ability of vapor-phase grafting to tailor surface chemistry, provides a powerful toolkit for enhancing the efficacy of membrane filtration and adsorption processes. This work explores the application of these techniques to enhance the adsorption performance of porous silica. Our approach involves first applying a thin (~0.5 nm) ALD Al₂O₃ coating to porous silica, followed by modification with thiol-functional silane through vapor-phase grafting. This treatment significantly enhances the selectivity for capturing hazardous heavy metal ions, Cd(II), As(V), Pb(II), Hg(II), and Cu(II), particularly in acidic conditions (pH=4), in mixed ion solutions over common benign metals (e.g., Na, K, Ca, and Mg). Langmuir adsorption isotherms and breakthrough adsorption studies revealed a distinct affinity sequence: Cd(II) < Pb(II) < Cu(II) < As(V) < Hg(II), demonstrating a significantly higher affinity towards As(V) and Hg(II) ions. Time-dependent uptake studies highlighted the rapid removal of heavy metals from water, with Hg(II) ions exhibiting fastest adsorption kinetics. The findings presented herein not only contribute to the advancement of water treatment technologies but also underscore the significance of ALD and vapor-phase grafting as key surface engineering techniques with potential applications beyond water purification.