Understanding the Origin of Formation and Active Sites for Thiomolybdate [Mo₃S₁₃]^2– Clusters as Hydrogen Evolution Catalyst through the Selective Control of Sulfur Atoms

[Mo₃S₁₃]^2– clusters have become known as one of the most efficient catalysts for the hydrogen evolution reaction (HER) because most of the sulfur (S) atoms in the cluster are exposed, resulting in many active sites. However, the origin of the cluster formation and active S sites in the cluster is unknown, hindering the development of efficient catalysts. Herein, the mechanism of the transition from amorphous MoS₃ to [Mo₃S₁₃]^2– clusters is systematically investigated. In addition, the active S sites have been identified by the selective removal of S atoms via low-temperature heat treatment. In summary, we believe that the clusters grow from amorphous MoS₃ with apical S atoms, and bridging S atoms are the active HER sites in the [Mo₃S₁₃]^2– clusters. The clusters deposited on carbon nanotubes exhibited good electrochemical HER activity with a low onset potential of −96 mV, a Tafel slope of 40 mV/decade, and stability for 1000 cycles

Exposed Edge Planes of Cup-Stacked Carbon Nanotubes for an Electrochemical Capacitor

The end sites of graphitic planes and their catalytic, chemical, physical, and electrochemical roles have been a longstanding issue in the surface chemistry of carbon science. In this study, complete exposure of the active edge sites on the outer surface of catalytically grown cup-stacked carbon nanotubes is accomplished using a conventional exfoliation method, and its intrinsic contribution to the improvement of the electrochemical behavior in an electrochemical capacitor is demonstrated. The significant enhancement in the capacitance of the nanotubes after exfoliation, occurring without a distinctive change in pore structure, was confirmed with the exposure of the electrochemically active edge sites thus being able to accumulate more charge. Such active sites make nanotubes useful in the fabrication of high-performance electrochemical capacitors, catalysts, supporting materials for catalysts, and photocurrent generators in photochemical cells

Enhancement of Adsorption Performance for Organic Molecules by Combined Effect of Intermolecular Interaction and Morphology in Porous rGO-Incorporated Hydrogels

In this study, we developed reduced graphene oxide (rGO)-incorporated porous agarose (Ar-rGO) composites that were prepared via a “one-pot” sol–gel method involving a mixing and vacuum freeze-drying process. These composites represent an easy-to-use adsorbent for organic contaminant removal. Ar-rGOs can efficiently adsorb organic molecules, especially aromatic organic compounds from wastewater, because of the synergistic effect between the agarose bundles, which function as a water absorption site, and the rGO sheets, which function as active sites for pollutant binding. The pore structures and morphology of the Ar-rGO composites varied according to the added rGO, resulting in effective water infiltration into the composites. The main adsorption mechanism of the aromatic organic compounds onto Ar-rGOs involved π–π interactions with the rGO sheets. The surface interaction was more effective for adsorbing/desorbing the aromatic pollutants than the electrostatic interaction via the O-containing functional groups. In addition, we confirmed that Ar-rGO is highly stable over the entire pH range (1–13) because of the presence of the rGO sheets

Encapsulation and Enhanced Delivery of Topoisomerase I Inhibitors in Functionalized Carbon Nanotubes

The topoisomerase I inhibitors SN-38 and camptothecin (CPT) have shown potent anticancer activity, but water insolubility and metabolic instability limits their clinical application. Utilizing carbon nanotubes as a protective shell for water-insoluble SN-38 and CPT while maintaining compatibility with aqueous media via a carboxylic acid-functionalized surface can thus be a strategy to overcome this limitation. Through hydrophobic–hydrophobic interactions, SN-38 and CPT were successfully encapsulated in carboxylic acid functionalized single-walled carbon nanotubes and dispersed in water. The resulting cell proliferation inhibition and drug distribution profile inside the cells suggest that these drug-encapsulated carbon nanotubes can serve as a promising delivery strategy for water-insoluble anticancer drugs

Solid-Phase Synthesis of Peptide-Conjugated Perylene Diimide Bolaamphiphile and Its Application in Photodynamic Therapy

Here, we describe a rapid and efficient synthetic method of peptide-conjugated perylene diimide (P-PDI) using solid-phase peptide synthesis (SPPS). Due to severe insolubility of perylene dianhydride (PDA) as a starting material of perylene diimide (PDI), PDA was initially conjugated with amino acids to obtain soluble PDI derivatives. Target peptides were synthesized on a 2-chlorotrityl chloride resin using the SPPS method and then conjugated with the amino acid-appended PDI. Various conditions such as loading levels, reaction times and solvents were optimized for introducing the peptides to both sides of the amino acid-appended PDI. The final P-PDI was obtained with a maximum yield of 80% in 12 h. Its singlet oxygen-derived phototoxicity on cells was confirmed, which could be applicable to photodynamic therapy

Defect-Assisted Heavily and Substitutionally Boron-Doped Thin Multiwalled Carbon Nanotubes Using High-Temperature Thermal Diffusion

Carbon nanotubes have shown great potential as conductive fillers in various composites, macro-assembled fibers, and transparent conductive films due to their superior electrical conductivity. Here, we present an effective defect engineering strategy for improving the intrinsic electrical conductivity of nanotube assemblies by thermally incorporating a large number of boron atoms into substitutional positions within the hexagonal framework of the tubes. It was confirmed that the defects introduced after vacuum ultraviolet and nitrogen plasma treatments facilitate the incorporation of a large number of boron atoms (ca. 0.496 atomic %) occupying the trigonal sites on the tube sidewalls during the boron doping process, thus eventually increasing the electrical conductivity of the carbon nanotube film. Our approach provides a potential solution for the industrial use of macro-structured nanotube assemblies, where properties, such as high electrical conductance, high transparency, and lightweight, are extremely important