In this study, two-dimensional (2D) and three-dimensional (3D) freestanding reduced graphene oxide-supported Cu2O composites (Cu2O-rGO) were synthesized via simple and cost-efficient hydrothermal and ...filtration strategies. The structural characterizations clearly showed that highly porous 3D graphene aerogel-supported Cu2O microcrystals (3D Cu2O-GA) have been successfully synthesized, and the Cu2O microcrystals are uniformly assembled in the 3D GA. Meanwhile, paper-like 2D reduced graphene oxide-supported Cu2O nanocrystals (2D Cu2O-rGO-P) have also been prepared by a filtration process. It was found that the products prepared from different precursors and methods exhibited different sensing performances for H2O2 detection. The electrochemical measurements demonstrated that the 3D Cu2O-GA has high electrocatalytic activity for the H2O2 reduction and excellent sensing performance for the electrochemical detection of H2O2 with a detection limit of 0.37 μM and a linear detection range from 1.0 μM to 1.47 mM. Meanwhile, the 2D Cu2O-rGO-P structure also showed good electrochemical sensing performance toward H2O2 detection with a much wider linear response over the concentration range from 5.0 μM to 10.56 mM. Compared to the previously reported sensing materials, the as-obtained 2D and 3D Cu2O-rGO materials exhibited higher electrochemical sensing properties toward the detection of H2O2 with high sensitivity and selectivity. The 2D and 3D Cu2O-rGO composites also exhibited high sensing performance for the real-time detection of H2O2 in human serum. The present study indicates that 2D and 3D graphene-Cu2O composites have promising applications in the fabrication of nonenzymatic electrochemical sensing devices.
Where Have All the IPOs Gone? Gao, Xiaohui; Ritter, Jay R.; Zhu, Zhongyan
Journal of financial and quantitative analysis,
12/2013, Letnik:
48, Številka:
6
Journal Article
Recenzirano
Odprti dostop
During 1980–2000, an average of 310 companies per year went public in the United States. Since 2000, the average has been only 99 initial public offerings (IPOs) per year, with the drop especially ...precipitous among small firms. Many have blamed the Sarbanes-Oxley Act of 2002 and the 2003 Global Settlement’s effects on analyst coverage for the decline in IPO activity. We find very little support for the conventional wisdom, and we offer an alternative explanation. Our economies of scope hypothesis posits that the advantages of selling out to a larger organization, which can speed a product to market and realize economies of scope, have increased relative to the benefits of operating as an independent firm.
We show that a model featuring an average commodity factor, a carry factor, and a momentum factor is capable of describing the cross-sectional variation of commodity returns. More parsimonious one- ...and two-factor models that feature only the average and/or carry factors are rejected. To provide an economic interpretation, we show that innovations in global equity volatility can price portfolios formed on carry, while innovations in a commodity-based measure of speculative activity can price portfolios formed on momentum. Finally, we characterize the relation between the factors and the investment opportunity set.
Data and the Internet appendix are available at
https://doi.org/10.1287/mnsc.2017.2840
This paper was accepted by Neng Wang, finance.
To obtain stable and ultrafine Pt nanoclusters, a trigonal prismatic coordination cage with the sulfur atoms on the edges was solvothermally synthesized to confine them. In the structure of ...{Ni24(TC4A-SO2)6(TDC)12 (H2O)6} (H4TC4A-SO2 = p-tert-butylsulfonylcalix4arene; H2TDC = 2,5-thiophenedicarboxylic acid), three Ni4-(TC4A-SO2) SBUs are bridged by three TDC ligands into a triangle and two such triangles are pillared by three pairs of TDC ligands to form a trigonal prism. The cage cavity has 12 sulfur atoms on the surface. Because of the porous structure and strong covalent interaction between metal and sulfur, ultrafine Pt nanoclusters composed of less than ∼18 Pt atoms can be facilely confined in the present trigonal prismatic cage (Pt@CIAC-121). The as-synthesized Pt NCs exhibit higher electrocatalytic activity than commercial Pt/C toward hydrogen evolution reaction.
Online Innovation Community (OIC) serves as a virtual space for users to exchange products and services, and share knowledge and information. Previous studies have indicated that community climate is ...an important factor affecting users' value co-creation behavior, however, the influencing process has not been clearly revealed from the perspective of motivation. In this study, we explored the relationship between online innovation community climate (supportive climate and controlling climate), user motivation and value co-creation behavior (user's participation behavior and user's citizenship behavior) based on the SOR model. The study sample included 29,835 pieces of information from 3,315 users in 14 product sections of the OnePlus Community which were analyzed with Mplus8.1. The findings revealed that: (1) The supportive climate had a positive impact on user's citizenship behavior(β = 0.042), while the controlling climate exerted a significant positive impact on user's citizenship behavior (β = 0.078) and user's participation behavior(β = 0.099); (2) The need for achievement played a suppressing effect between community climate and user's participation behavior, the need for power played a suppressing effect between supportive climate and user's value co-creation behavior, and the need for affiliation played a mediating role between supportive climate and user's citizenship behavior (β = 0.010) and user's participation behavior(β = 0.006); (3) Community trust positively moderated the relationship between the need for achievement and user's participation behavior(β = 0.058) as well as between the need for power and user's participation behavior(β = 0.043).
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•N-acetyl-l-cysteine-stabilized Ag nanoparticles are synthesized by a chemical reduction method.•The surface plasmon resonance intensity of the silver nanoparticles decreases with ...Fe3+ concentration.•The silver nanoparticles can be used for sensitive and selective detection of Fe3+ ions in water.•A new detection mechanism of oxidation–reduction reaction between Ag NPs and Fe3+ ions is proposed.
We report here a facile colorimetric sensor based on the N-acetyl-l-cysteine (NALC)-stabilized Ag nanoparticles (NALC–Ag NPs) for detection of Fe3+ ions in aqueous solution. The Ag NPs with an average diameter of 6.55±1.0nm are successfully synthesized through a simple method using sodium borohydride as reducing agent and N-acetyl-l-cysteine as protecting ligand. The synthesized silver nanoparticles show a strong surface plasmon resonance (SPR) around 400nm and the SPR intensity decreases with the increasing of Fe3+ concentration in aqueous solution. Based on the linear relationship between SPR intensity and concentration of Fe3+ ions, the as-synthesized water-soluble silver nanoparticles can be used for the sensitive and selective detection of Fe3+ ions in water with a linear range from 80nM to 80μM and a detection limit of 80nM. On the basis of the experimental results, a new detection mechanism of oxidation–reduction reaction between Ag NPs and Fe3+ ions is proposed, which is different from previously reported mechanisms. Moreover, the NALC–Ag NPs could be applied to the detection of Fe3+ ions in real environmental water samples.
Electrolysis of water is regarded as an attractive and feasible way for producing hydrogen. So far, various non‐noble metal nanomaterials have been reported as excellent electrocatalysts for hydrogen ...evolution reaction. Especially, due to the low cost, earth‐abundance and tunable properties, transition metal selenides with different compositions, sizes and structures have been explored broadly as efficient catalysts with the relatively high activities, high stabilities and high efficiencies in full pH range of electrolyte for electrochemical hydrogen evolution reaction. Thus, in this Minireview, after introducing several commonly used electrochemical terms about hydrogen evolution reaction, we mainly focus on various kinds of the transition metal selenides that have been documented as electrocatalysts for hydrogen evolution reaction. Particularly, the merits and demerits of transition metal selenides for hydrogen evolution reaction are systematically discussed. Moreover, we also analyze the encountered challenges and present an outlook for the rapid development of transition metal selenides. We hope this Minireview can bring some fundamental understanding for the readers interested in the transition metal selenides and hydrogen evolution reaction.
Abundant and efficient: Thanks to low cost, earth‐abundance, and tuneable properties, transition metal selenides (TMSs) have been explored as efficient catalysts for electrochemical hydrogen evolution reaction. The advances of the synthesis methods, physical and chemical properties of TMSs for electrocatalysis in hydrogen production has been summarized in this Minireview. Moreover, the application and perspective for TMSs in electrocatalytic hydrogen evolution reaction, including single‐metal selenides and multi‐metal selenides, have been discussed systematically.
Biomaterials in nature often exhibit hierarchical chiral structures with an intriguing mechanism involving hierarchical chirality transfer from molecular to supramolecular and the nano- or microscale ...level. To mimic the cross-level chirality transfer, we present here one kind of host–guest complex system built of β-cyclodextrin (β-CD), sodium dodecyl sulfate (SDS), and fluorescent dyes, which show multilevel chirality, including molecular chirality of β-CD, induced supramolecular chirality of β-CD/SDS host–guest complexes, a chiral lattice self-assembled nanosheet, mesoscopic chirality of an assembled helical tube, induced chirality of a dye-doped chiral tube. The hierarchical chirality involved a chiral lattice self-assembly process, which can be identified by small-angle X-ray scattering, optical studies, circular dichroism, and circularly polarized luminescence spectral measurements. Benefiting from the chiral lattice self-assembly, intense circularly polarized luminescence was observed from the achiral dye-doped complexes with a large dissymmetry factor up to +0.1. This work thus provides a feasible insight for developing hierarchical chiroptical materials based on the lattice self-assembly.
Due to the wide use of iron in all kinds of areas, the design and construction of direct, fast, and highly sensitive sensor for Fe
3+
are highly desirable and important. In the present work, a kind ...of fluorescent MXene quantum dots (MQDs) was synthesized via an intermittent ultrasound process using
N,N
-dimethyl formamide as solvent. The prepared MQDs were characterized via a combination of UV–Vis absorption, fluorescence spectra, X-ray photoelectron energy spectra, and Fourier-transform infrared spectroscopy. Based on the electrostatic-induced aggregation quenching mechanism, the fluorescent MQDs probes exhibited excellent sensing performance for the detection of Fe
3+
, with a sensitivity of 0.6377 mM
−1
and the detection limit of 1.4 μM, superior to those reported in studies. The present MQDs-based probes demonstrate the potential promising applications as the sensing device of Fe
3+
.
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