Polyionic nanoclays as tailorable hybrid organic-inorganic platforms
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We disclose the synthesis, characterization, and application of an imidazolium-based hybrid inorganic-organic layered magnesium phyllo(organo)silicate nanosheets, coined polyionic nanoclays (PINCs), as an emergent class of supported ionic liquids which boast extremely high ionic density (3.8 mmol g⁻¹ for the 1-methyl-3-propylimidazolium chloride PINC, or roughly two-thirds the ion loading in the analogous free-flowing ionic liquid) and exchangeability (i.e., tailorability) of the associated cation and counteranion. The aqueously dispersing imidazolium PINCs are employed as nanocatalyst supports for monometallic gold and silver nanoparticles (PINC@Au- and AgNPs) and their bimetallic intermediates using sodium borohydride as a reducing agent, and the resulting heterogeneous catalysts are applied for the model reduction of 4-nitrophenol to 4-aminophenol to achieve the highest reaction turnover frequency yet reported in the literature (over 33,000 h⁻¹ for nanoparticles comprising a 70:30 molar ratio of Au:Ag). Remarkably, the turnover for PINC@AuNPs is a 4000% increase over the corresponding unsupported borohydride-stabilized AuNPs (600 h⁻¹), indicating an intense synergistic effect imparted by the PINC support. Additionally, aqueous anionic dye sequestration is demonstrated using Congo Red as a model dye system, accomplishing a maximum adsorption capacity of over 2,600 mg dye per g of PINC when maintained at 50 °C. The exceptional performance of these PINCs for the herein applications suggest an auspicious future for PINCs in catalysis, ion exchange, energy storage, separations, (bio)sensing, imaging, and the construction of nanoscale assemblies.
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Ph. D.