Shiguang Mo

Photochemical route for synthesizing atomically dispersed palladium catalysts

Lightly dispersed palladium Catalysts made from atomically dispersed metal atoms on oxide supports can exhibit very high per atom activity. However, the low loadings needed to prevent metal particle formation can limit overall performance. Liu et al. stably decorated titanium oxide nanosheets with relatively high loadings of single palladium atoms by reducing the ions with ultraviolet light and ethylene glycol. These catalysts cleaved H2 into atoms and were highly effective for hydrogenating alkenes and aldehydes. Science, this issue p. 797 Ultraviolet light and ethylene glycol enable decoration of titanium oxide nanosheets with high loading of palladium atoms. Atomically dispersed noble metal catalysts often exhibit high catalytic performances, but the metal loading density must be kept low (usually below 0.5%) to avoid the formation of metal nanoparticles through sintering. We report a photochemical strategy to fabricate a stable atomically dispersed palladium–titanium oxide catalyst (Pd1/TiO2) on ethylene glycolate (EG)–stabilized ultrathin TiO2 nanosheets containing Pd up to 1.5%. The Pd1/TiO2 catalyst exhibited high catalytic activity in hydrogenation of C=C bonds, exceeding that of surface Pd atoms on commercial Pd catalysts by a factor of 9. No decay in the activity was observed for 20 cycles. More important, the Pd1/TiO2-EG system could activate H2 in a heterolytic pathway, leading to a catalytic enhancement in hydrogenation of aldehydes by a factor of more than 55.

Core–Shell Pd@Au Nanoplates as Theranostic Agents for In-Vivo Photoacoustic Imaging, CT Imaging, and Photothermal Therapy

Uniform plasmonic Pd@Au core-shell bimetallic nanoplates are synthesized by seeded growth strategy. Surface modified with SH-PEG makes it good biocompatibility, prolonged blood circulation, and relatively high tumor accumulation. Enhanced tumor contrast effects can be obtained for in vivo photoacoustic/CT imaging after intravenous injection of Pd@Au-PEG. Moreover, efficient photothermal tumor ablation is achieved, guided by the imaging techniques. This work promises further exploration of the superiority of 2D nanostructures for in vivo biomedical applications.

Self-supporting sulfur cathodes enabled by two-dimensional carbon yolk-shell nanosheets for high-energy-density lithium-sulfur batteries

How to exert the energy density advantage is a key link in the development of lithium–sulfur batteries. Therefore, the performance degradation of high-sulfur-loading cathodes becomes an urgent problem to be solved at present. In addition, the volumetric capacities of high-sulfur-loading cathodes are still at a low level compared with their areal capacities. Aiming at these issues, two-dimensional carbon yolk-shell nanosheet is developed herein to construct a novel self-supporting sulfur cathode. The cathode with high-sulfur loading of 5 mg cm−2 and sulfur content of 73 wt% not only delivers an excellent rate performance and cycling stability, but also provides a favorable balance between the areal (5.7 mAh cm–2) and volumetric (1330 mAh cm–3) capacities. Remarkably, an areal capacity of 11.4 mAh cm–2 can be further achieved by increasing the sulfur loading from 5 to 10 mg cm–2. This work provides a promising direction for high-energy-density lithium–sulfur batteries.One of the challenges facing lithium-sulfur batteries is to develop cathodes with high mass and high volume loading. Here the authors show that two-dimensional carbon yolk-shell nanosheets are promising sulfur host materials, enabling stable battery cells with high energy density.

Carbon Monoxide-Assisted Synthesis of Ultrathin PtCu3 Alloy Wavy Nanowires and Their Enhanced Electrocatalysis.

Glucose sensing that is not influenced by the presence of chloride, uric acid, ascorbic acid and dopamine is achieved on ultrathin PtCu3 alloy wavy nanowires (WNWs). These WNWs are synthesized by a facile, one-pot, templateless hydrothermal method in an atmosphere of CO, which is critical to the formation process. Their structural properties, including the abundance of twinning defects, make the as-prepared PtCu3 WNWs excellent electrocatalysts for methanol oxidation as well as great sensors for glucose.

Safety profile of two-dimensional Pd nanosheets for photothermal therapy and photoacoustic imaging

Two-dimensional (2D) nanosheets have emerged as an important class of nanomaterial with great potential in the field of biomedicines, particularly in cancer theranostics. However, owing to the lack of effective methods that synthesize uniform 2D nanomaterials with controlled size, systematic evaluation of size-dependent bio-behaviors of 2D nanomaterials is rarely reported. To the best of our knowledge, we are the first to report a systematic evaluation of the influence of size of 2D nanomaterials on their bio-behaviors. 2D Pd nanosheets with diameters ranging from 5 to 80 nm were synthesized and tested in cell and animal models to assess their size-dependent bioapplication, biodistribution, elimination, toxicity, and genomic gene expression profiles. Our results showed size significantly influences the biological behaviors of Pd nanosheets, including their photothermal and photoacoustic effects, pharmacokinetics, and toxicity. Compared to larger-sized Pd nanosheets, smaller-sized Pd nanosheets exhibited more advanced photoacoustic imaging and photothermal effects upon ultralow laser irradiation. Moreover, in vivo results indicated that 5-nm Pd nanosheets escape from the reticuloendothelial system with a longer blood half-life and can be cleared by renal excretion, while Pd nanosheets with larger sizes mainly accumulate in the liver and spleen. The 30-nm Pd nanosheets exhibited the highest tumor accumulation. Although Pd nanosheets did not cause any appreciable toxicity at the cellular level, we observed slight lipid accumulation in the liver and inflammation in the spleen. Genomic gene expression analysis showed that 80-nm Pd nanosheets interacted with more cellular components and affected more biological processes in the liver, as compared to 5-nm Pd nanosheets. We believe this work will provide valuable information and insights into the clinical application of 2D Pd nanosheets as nanomedicines.

Ultrastable atomic copper nanosheets for selective electrochemical reduction of carbon dioxide

Air-stable atomically thick copper nanosheets are prepared and used for selective electrochemical reduction of CO2 into CO. The electrochemical conversion of CO2 and H2O into syngas using renewably generated electricity is an attractive approach to simultaneously achieve chemical fixation of CO2 and storage of renewable energy. Developing cost-effective catalysts for selective electroreduction of CO2 into CO is essential to the practical applications of the approach. We report a simple synthetic strategy for the preparation of ultrathin Cu/Ni(OH)2 nanosheets as an excellent cost-effective catalyst for the electrochemical conversion of CO2 and H2O into tunable syngas under low overpotentials. These hybrid nanosheets with Cu(0)-enriched surface behave like noble metal nanocatalysts in both air stability and catalysis. Uniquely, Cu(0) within the nanosheets is stable against air oxidation for months because of the presence of formate on their surface. With the presence of atomically thick ultrastable Cu nanosheets, the hybrid Cu/Ni(OH)2 nanosheets display both excellent activity and selectivity in the electroreduction of CO2 to CO. At a low overpotential of 0.39 V, the nanosheets provide a current density of 4.3 mA/cm2 with a CO faradaic efficiency of 92%. No decay in the current is observed for more than 22 hours. The catalysts developed in this work are promising for building low-cost CO2 electrolyzers to produce CO.

Two-dimensional antibacterial Pd@Ag nanosheets with a synergetic effect of plasmonic heating and Ag+ release

In this work, a novel bactericidal agent based on two-dimensional Pd@Ag nanosheets (Pd@Ag NSs) that is responsive to near-infrared (NIR) light has been developed. These Pd@Ag NSs were prepared by reducing silver ions on the surface of Pd nanosheets (Pd NSs) seeds by formaldehyde, and displayed excellent NIR absorption and photothermal conversion properties. In addition, the NIR irradiation triggers the release of more Ag+ from the Pd@Ag NSs. Upon exposure to a NIR laser at a low power density (0.5 W cm-2), Pd@Ag NSs kill both Gram-negative (Escherichia coli, E. coli) and Gram-positive (Staphylococcus aureus, S. aureus) bacteria effectively by the synergistic effect of plasmonic heating and Ag+ release, which is much higher than either plasmonic heating or Ag+ alone. Such a novel nanomaterial is promising as an adjuvant therapeutic method for the treatment of patients suffering from severe bacterial infections.

Electrochemical Partial Reforming of Ethanol into Ethyl Acetate Using Ultrathin Co3O4 Nanosheets as a Highly Selective Anode Catalyst

Electrochemical partial reforming of organics provides an alternative strategy to produce valuable organic compounds while generating H2 under mild conditions. In this work, highly selective electrochemical reforming of ethanol into ethyl acetate is successfully achieved by using ultrathin Co3O4 nanosheets with exposed (111) facets as an anode catalyst. Those nanosheets were synthesized by a one-pot, templateless hydrothermal method with the use of ammonia. NH3 was demonstrated critical to the overall formation of ultrathin Co3O4 nanosheets. With abundant active sites on Co3O4 (111), the as-synthesized ultrathin Co3O4 nanosheets exhibited enhanced electrocatalytic activities toward water and ethanol oxidations in alkaline media. More importantly, over the Co3O4 nanosheets, the electrooxidation from ethanol to ethyl acetate was so selective that no other oxidation products were yielded. With such a high selectivity, an electrolyzer cell using Co3O4 nanosheets as the anode electrocatalyst and Ni–Mo nanopowders as the cathode electrocatalyst has been successfully built for ethanol reforming. The electrolyzer cell was readily driven by a 1.5 V battery to achieve the effective production of both H2 and ethyl acetate. After the bulk electrolysis, about 95% of ethanol was electrochemically reformed into ethyl acetate. This work opens up new opportunities in designing a material system for building unique devices to generate both hydrogen and high-value organics at room temperature by utilizing electric energy from renewable sources.

Effect of glutathione on in vivo biodistribution and clearance of surface-modified small Pd nanosheets

Plasmonic Pd nanosheets have been emerging as promising materials for applying in near-infrared (NIR) photothermal therapy (PTT) of cancer. However, animal in mice studies indicated that the original synthesized poly(vinylpyrrolidone) (PVP)-protected small Pd nanosheets (Pd-PVP) and some further surface-modified small Pd nanosheets such as Pd-PEG(SH) easily accumulated in reticuloendothelial system (RES) organs (liver, spleen, etc.) and were difficult to be cleared from these organs quickly. In the work, we surprisingly found that glutathione (GSH) could promote the clearance of surface-modified small Pd nanosheets (e.g. Pd-PVP, Pd-PEG(SH) and Pd-GSH) from the RES organs efficiently. The effects of GSH on the biodistribution and clearance of different surface-modified Pd nanosheets were investigated. Our results indicated that these surface-modified Pd nanosheets with or without GSH added caused no morbidity at target primary organs, and GSH can promote the clearance of different surface-modified Pd nanosheets in the order of Pd-PVP≈Pd-PEG(SH)>Pd-GSH. This study suggests that glutathione could be an attractive reagent for promoting nanomaterials eliminated from the reticuloendothelial systems (RES).