Active Sites and Their Individual Turnover Frequencies for Ethylene Hydrogenation on Reduced Graphene Aerogel.

Graphene aerogel (GA) was reduced at various temperatures to prepare a series of reduced graphene aerogels (rGAs) with different surface characteristics. Detailed characterization demonstrated that an increase in the thermal reduction temperature leads to an increase in surface area accompanied by an increase in surface density of defect sites formed by the removal of the oxygen-containing functional groups. rGA samples were then tested for ethylene hydrogenation under identical conditions. A comparison of catalytic performances of each catalyst demonstrated that the rGA sample prepared by reduction in Ar at 900 °C (rGA-900) provides the highest performance compared with others prepared at lower temperatures. Next, we analyzed the per-gram activity of each catalyst as a sum of individual contributions from different defect sites quantified by Raman spectroscopy and CHNS-O analysis to determine the individual turnover frequencies (TOFs) of each active site. This analysis identified polyene-like structures and interstitial defects associated with amorphous sp2 bonded carbon atoms as the dominant active sites responsible for hydrogenation. A comparison of their TOFs further indicated that the polyene-like structures provide approximately ten times higher TOF compared to those associated with the amorphous carbon defects. These results, identifying the dominant active centers and quantifying their corresponding TOFs, provide opportunities toward the rational design of GA-based carbocatalysts.

First-Row Transition-Metal Cations (Co2+ , Ni2+ , Mn2+ , Fe2+ ) and Graphene (Oxide) Composites: From Structural Properties to Electrochemical Applications.

Composites of graphene (oxide) (GO) and first-row transition-metal cations (Co2+ , Ni2+ , Mn2+ , Fe2+ ) are prepared by mixing GO and aqueous metal salt solutions. The amount of metal cation bound to GO nanosheets is calculated by using inductively coupled plasma mass spectrometry (ICP-MS) and the possible binding sites of the metals are investigated by means of attenuated total reflectance infrared (ATR-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) measurements. Electrodes loaded with the metal/GO composites are prepared by a simple drop-casting technique without any binders or conductive additives. The effect of electrochemical reduction on the structure of the composite electrodes is investigated by Raman spectroscopy, XPS, X-ray diffraction (XRD) analysis, and field emission scanning electron microscopy (FESEM). A detailed electrochemical characterization is performed for the utilization of the composite electrodes for electrochemical capacitors and possible oxygen reduction reaction electrocatalysts by cyclic voltammetry (CV) and rotating disk electrode measurements. The highest areal capacitance is achieved with the as-deposited Fe/GO composite (38.7 mF cm-2 at 20 mV s-1 ). In the cyclic stability measurements, rCo/GO, rNi/GO, rMn/GO, and rFe/GO exhibit a capacitance retention of 44, 1.1, 73, and 87 % after 3000 cycles of CV at 100 mV s-1 , respectively.

Intensive pulmonary care after liver surgery: a retrospective survey from a single center.

BACKGROUND: Prevention from postoperative pulmonary complications (PPCs) has been an important topic. The aims of this study were to determine the risk factors for PPC after liver surgery and to analyze the efficacy of postoperative pulmonary care on PPC prevention. MATERIALS AND METHODS: We retrospectively analyzed variables of 81 patients who underwent hepatectomy and 4 transplantations between January 2007 and March 2012. RESULTS: Nineteen patients suffered PPCs (22.4%). Bivariate analysis identified four risk factors: preoperative anemia (odds ratio [OR] = 5.69), the American Society of Anesthesiologists (ASA) score of 3 or 4 (OR = 5.36), blood transfusion (OR = 2.81), and prolonged operative time (OR = 1.01). Upon multivariate analysis, only prolonged operative time was an independent risk factor for PPC (OR = 1.01). Pulmonary function test (PFT) was performed for 22 of 41 patients with an ASA score ≥ 2 (53.7%); there was no significant relationship between abnormal PFTs (n = 13) and the development of PPCs (P = .12). CONCLUSIONS: The elimination of risk factors may reduce the incidence of PPCs. Postoperative intensive pulmonary care should be given to all patients after liver surgery but particularly to patients with high ASA scores and those with abnormal PFTs irrespective of age.