A major outstanding challenge in the field of intercalation chemistry has been the insertion of heavy metals into a 2D layered material. Heavy metal intercalation is a promising route towards access of chemically tailored materials or enhancement of novel physics. We present a new series of wet chemical strategies to intercalate atomic heavy metal and semimetal species (Bi, Cr, Ge, Mn, Mo, Ni, Os, Pb, Pd, Pt, Rh, Ru, Sb, and W) into layered chalcogenides. Bismuth selenide, Bi2Se3, and niobium diselenide, NbSe2, are used to demonstrate this chemistry. Atomic intercalation is performed in solution using decomposition of zero-valent coordination compounds at low temperatures (∼50 °C–170 °C) or reduction with tin chloride. This host of chemical routes is non-destructive, general for chalcogens, and can be used to intercalate some lighter elements as well. These intercalation reactions more than double the current number of atomic intercalants and give access to unique physical properties including heterostructures, charge density waves, and polytypic superlattice structures.

Silicon telluride (SiTe) is a two-dimensional, layered, p-type semiconductor that shows broad near-infrared photoluminescence. We show how, through various means of chemical modification, SiTe can have its optoelectronic properties modified in several independent ways without fundamentally altering the host crystalline lattice. Substitutional doping with Ge strongly red-shifts the photoluminescence while substantially lowering the direct and indirect band gaps and altering the optical phonon modes. Intercalation with Ge introduces a sharp 4.3 eV ultraviolet resonance and shifts the bulk plasmon even while leaving the infrared response and band gaps virtually unchanged. Intercalation with copper strengthens the photoluminescence without altering its spectral shape. Thus, silicon telluride is shown to be a chemically tunable platform of full spectrum optical properties promising for optoelectronic applications.

Hydrogenation of aromatic molecules in fossil- and bio-derived fuels is essential for decreasing emissions of harmful combustion products and addressing growing concerns around urban air pollution. In this work, we used atomic layer deposition to significantly enhance the hydrogenation performance of a conventional supported Pd catalyst by applying an ultrathin coating of TiO2 in a scalable powder coating process. The TiO2-coated catalyst showed substantial gains in the conversion of multiple aromatic molecules, including a 5-fold improvement in turnover frequency versus the uncoated catalyst in the hydrogenation of naphthalene. This activity enhancement was maintained upon scaling the coating synthesis process from 3 to 100 g. Based on the results from X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and computational modeling, the activity enhancement was attributed to ensemble effects resulting from partial TiO2 coverage of the Pd surface rather than fundamental changes to the Pd electronic structure. Additional durability testing confirmed that the TiO2 coating improved the thermal and hydrothermal stability of the catalyst as well as tolerance toward sulfur impurities in the reactant stream. Using an economic model of an industrial deep hydrogenation process, we found that an increase in catalyst activity or lifetime of 2× would justify even a relatively high estimate for the cost of TiO2 atomic layer deposition coatings at scale.

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