ABSTRACT
Control over the morphology of nanomaterials to have a 2D structure and manipulating the surface strain of nanostructures through defect control have proved to be promising for developing efficient catalysts for sustainable chemical and energy conversion. Here a one-pot aqueous synthesis route of freestanding Pd nanosheets with a penta-twinned structure (PdPT NSs) is presented. The generation of the penta-twinned nanosheet structure can be succeeded by directing the anisotropic growth of Pd under the controlled reduction kinetics of Pd precursors. Experimental and computational investigations showed that the surface atoms of the PdPT NSs are effectively under a compressive environment due to the strain imposed by their twin boundary defects. Due to the twin boundary-induced surface strain as well as the 2D structure of the PdPT NSs, they exhibited highly enhanced electrocatalytic activity for oxygen reduction reaction compared to Pd nanosheets without a twin boundary, 3D Pd nanocrystals, and commercial Pd/C and Pt/C catalysts.
ABSTRACT
2D nanostructures of noble metals hold great potential for developing efficient electrocatalysts due to their high atom efficiency associated with their large specific surface area and abundant active sites. Here, we introduce a one-pot solvothermal synthesis method that can enable the fabrication of freestanding atomically thin Ir nanosheets. The thermal decomposition of a complex of Ir and a long-chain amine, which could readily be formed with the assistance of a strong base, under CO flow conditions successfully yielded Ir nanosheets consisting of 2-4 atomic layers. The prepared Ir nanosheets showed prominent activity and stability toward oxygen evolution electrocatalysis in acidic conditions, which can be attributed to their ultrathin 2D structure.
ABSTRACT
Exploring the atomic or molecular transport properties of two-dimensional materials is vital to understand their inherent functions and, thus, to expedite their use in various applications. Herein, a surface-enhanced Raman spectroscopy (SERS)-based in situ analytical tool for the sensitive and rapid monitoring of hydrogen transport through graphene is reported. In this method, a reducing agent, which can provide hydrogen species, and a Raman dye self-assembled on a SERS platform are separated by a graphene membrane, and the reduction of the Raman dye by hydrogen species transferred through graphene is monitored with SERS. For validating the efficacy of our method, the catalytic reduction of surface-bound 4-nitrothiophenol by sodium borohydride was chosen in this study. The experimental results distinctly demonstrate that the high sensitivity and rapid detection ability of SERS can allow the effective analysis of the hydrogen transport properties of graphene.
ABSTRACT
The existence of various surface active sites within a nanocrystal (NC) catalyst complicates understanding their respective catalytic properties and designing an optimal catalyst structure for a desired catalytic reaction. Here, we developed a novel approach that allows unequivocal investigation on the intrinsic catalytic reactivity of the edge and terrace atoms of NCs. Through the comparison of the catalytic behaviors of edge-covered Pd NCs, which were prepared by the selective deposition of catalytically inactive Au atoms onto the edge sites of rhombic dodecahedral (RD) Pd NCs, with those of the pristine RD Pd NCs toward alkyne hydrogenation and Suzuki-Miyaura coupling reactions, we could decouple the activity of the edge and {110}-plane atoms of the Pd NCs without uncertainties. We expect that this study will provide an opportunity to scrutinize the surface properties of various NC catalysts to a more precise level and devise ideal catalysts for intended catalytic reactions.
ABSTRACT
OBJECTIVES: To evaluate the diagnostic performance and image quality of an iterative model-based reconstruction (IMR) using a 100-kVp protocol for the assessment of heavily calcified coronary vessels, compared to those of filtered back projection (FBP) and hybrid iterative technique (iDose4), and also compared to those of IMR with standard 120 kVp protocol. METHODS: Among patients with Agatston scores ≥ 400 who had undergone both coronary CT angiography (CCTA) and invasive coronary angiography (ICA), age- and sex-matched patients with body mass index < 30 were retrospectively enrolled from CCTA with low-kVp protocol (100 kVp, n = 30) and with standard-kVp protocol (120 kVp, n = 30). Image data were all reconstructed with FBP, iDose4, and IMR. In each dataset, the objective and subjective image quality, and diagnostic accuracy (> 50% in luminal reduction as compared with ICA) were assessed. RESULTS: IMR showed better objective and subjective image quality than FBP and iDose4 in both 100 kVp and 120 kVp groups (all p < 0.05). IMR showed a significantly improved all diagnostic performance compared with FBP (p < 0.05). Compared with iDose4, IMR significantly improved positive predictive value (85.0% vs. 80.5%; p < 0.05). There was no significant difference in image quality and diagnostic performance using IMR between the 100 kVp and 120 kVp groups. CONCLUSIONS: 100 kVp IMR may be useful for the assessment of heavily calcified coronary vessels, providing better diagnostic performance than FBP or iDose4 at the same dose, while maintaining similar diagnostic accuracy to 120 kVp IMR.
