Tandem Catalysis of Amines Using Porous Graphene Oxide

Porous graphene oxide can be used as a metal-free catalyst in the presence of air for oxidative coupling of primary amines. Herein, we explore a GO-catalyzed carbon–carbon or/and carbon–heteroatom bond formation strategy to functionalize primary amines in tandem to produce a series of valuable products, i.e., α-aminophosphonates, α-aminonitriles, and polycyclic heterocompounds. Furthermore, when decorated with nano-Pd, the Pd-coated porous graphene oxide can be used as a bifunctional catalyst for tandem oxidation and hydrogenation reactions in the <i>N</i>-alkylation of primary amines, achieving good to excellent yields under mild conditions

Phase Restructuring in Transition Metal Dichalcogenides for Highly Stable Energy Storage

Achieving homogeneous phase transition and uniform charge distribution is essential for good cycle stability and high capacity when phase conversion materials are used as electrodes. Herein, we show that chemical lithiation of bulk 2H-MoS₂ distorts its crystalline domains in three primary directions to produce mosaic-like 1T′ nanocrystalline domains, which improve phase and charge uniformity during subsequent electrochemical phase conversion. 1T′-Li_<i>x</i>MoS₂, a macroscopic dense material with interconnected nanoscale grains, shows excellent cycle stability and rate capability in a lithium rechargeable battery compared to bulk or exfoliated-restacked MoS₂. Transmission electron microscopy studies reveal that the interconnected MoS₂ nanocrystals created during the phase change process are reformable even after multiple cycles of galvanostatic charging/discharging, which allows them to play important roles in the long term cycling performance of the chemically intercalated TMD materials. These studies shed light on how bulk TMDs can be processed into quasi-2D nanophase material for stable energy storage

Substoichiometric Molybdenum Sulfide Phases with Catalytically Active Basal Planes

Molybdenum sulfide (MoS₂) is widely recognized for its catalytic activities where the edges of the crystals turn over reactions. Generating sulfur defects on the basal plane of MoS₂ can improve its catalytic activity, but generally, there is a lack of model systems for understanding metal-centered catalysis on the basal planes. Here, we synthesized a new phase of substoichiometric molybdenum sulfide (s-MoS_<i>x</i>) on a sulfur-enriched copper substrate. The basal plane of s-MoS_<i>x</i> contains chemically reactive Mo-rich sites that can undergo dynamic dissociative adsorption/desorption processes with molecular hydrogen, thus demonstrating its usefulness for hydrogen-transfer catalysis. In addition, scanning tunneling microscopy was used to monitor surface-directed Ullmann coupling of 2,8-dibromo-dibenzothiophene molecules on s-MoS_<i>x</i> nanosheets, where the 4-fold symmetric surface sites on s-MoS_<i>x</i> direct C–C coupling to form cyclic tetramers with high selectivity