The acid–base properties of supports have an enormous impact on catalytic reactions to regulate the selectivity and activity of supported catalysts. Herein, a train of Pd‐X‐UiO‐66 (X = NO2, NH2, ...and CH3) catalysts with different acidity/alkalinity functional groups and encapsulated Pd(II) species is first developed, whose activities in dimethyl carbonate (DMC) catalysis are then investigated in details. Thereinto, the Pd‐NO2‐UiO‐66 catalyst with acidity functionalization exhibits the best catalytic behavior: the DMC selectivity stemmed from methyl nitrite (MN) is up to 68%, the conversion of CO is 73.4%. The obtained experimental results demonstrate that the NO2 group not only affected the interaction between X‐UiO‐66 and Pd(II) active sites but also play an indispensable role in the adsorption and activation of MN and CO, which remarkably promote the formation of the COOCH3* intermediate and DMC product.
Acidity/alkalinity functionalized MOFs into dimethyl carbonate catalysis are first introduced, and the Lewis acidic Pd‐NO2‐UiO‐66 exhibits excellent catalytic performance. In addition to affecting the interaction of Pd(II) and support, the NO2 group has a dominant role in the chemisorption of MN and CO for generating the intermediates COOCH3*, leading to higher catalytic performance.
ZnO nanowires (ZnO-NWs) were adhesively grown on multiwalled carbon nanotubes (MWCNTs) arrays by a hydrothermal process. Electrochemical properties of the electrode based on the ZnO-NWs/MWCNTs ...nanocomposite were investigated by electrochemical impedance spectroscopy and cyclic voltammetry. The photoelectrochemical responses of the ZnO-NWs/MWCNTs nanocomposite electrode were further studied by linear sweep voltammetry and amperometry under sunlight or UV light irradiation. Compared with pure ZnO-NWs on tantalum substrate, the charge transfer rate of the ZnO-NWs/MWCNTs nanocomposite was remarkably increased because of the MWCNTs. A Mott−Schottky plot displayed a high donor density of 3.9 × 1019 cm−3, a flat band potential of −0.8 V, and a space charge layer of 7 nm. In addition, the ZnO-NWs/MWCNTs nanocomposite yielded higher photocurrent than pure ZnO-NWs. The decay constant of the ZnO-NWs/MWCNTs nanocomposite was also lower than that of its pure counterpart. The recombination of photoinduced electron−hole pairs in the ZnO-NWs/MWCNTs heterojunction was hindered, thus enhancing the photoelectrical conversion efficiency. The heterojunction of ZnO-NWs/MWCNTs provides potential applications in the field of photocatalysis and photoelectrical devices.
Abstract
An electrochemical synthesis of benzazoles directly from alcohols and
o
‐substituted anilines has been developed. The reaction conditions have been optimized by varying the composition of ...the electrolyte and the metal salt used as catalyst. The cyclization proceeds smoothly with a catalytic amount of a cobalt salt under air at room temperature to afford 2‐substituted benzimidazoles, benzothiazoles, and benzoxazoles in good to excellent yields with a wide substrate scope.
An electrochemical synthesis of benzazoles directly from alcohols and o-substituted anilines has been developed. The reaction conditions have been optimized by varying the composition of the ...electrolyte and the metal salt used as catalyst. The cyclization proceeds smoothly with a catalytic amount of a cobalt salt under air at room temperature to afford 2-substituted benzimidazoles, benzothiazoles, and benzoxazoles in good to excellent yields with a wide substrate scope.
An efficient and selective electrosynthesis of phenols and anilines from arylboronic acids in aqueous ammonia is achieved in an undivided cell. By simply changing the concentration of aqueous ammonia ...and the anode potential, good yields of phenols and anilines can be obtained chemoselectively with high reaction rates. We propose that anodic oxidation could have played an important role in these transformations.
Over‐harvesting, habitat loss and fragmentation, and biological invasions have led to a sharp decline in wild medicinal plants population in China, where they are an essential component of ...traditional medicine and used widely. The current national list of protected medicinal materials, the State Key‐protected Wild Medicinal Species List (SKPWMSL), which has not been revised for 30 years, is in urgent need of an update. This study proposes a new scoring system with seven indicators that set the conservation priorities of threatened medicinal plants. The advantages of our approach include: (i) quantitative methods with high repeatability and comparability; and (ii) consideration of the evolutionary history of medicinal species. After assessing 911 threatened medicinal angiosperms in China, we identified 112 species as key medicinal plants for conservation priority (KMPCP). We suggest promoting the SKPWMSL with KMPCP as a supplement and update. Meanwhile, our scoring system will improve the future setting of conservation priority and can be extended to other countries or regions.
We propose a new robust and highly repeatable scoring system that includes seven indicators (i.e., threatened and conservation status, evolutionary distinctiveness, harvesting parts, medicinal usage, ecological value, and number of uses) to set the conservation priorities of threatened medicinal plants. To our knowledge, this is the first time that the evolutionary distinctiveness is considered for setting conservation priorities of medicinal plants.
Electrodeposition of Pt–Pb nanoparticles (PtPbNPs) to multi-walled carbon nanotubes (MWCNTs) resulted in a stable PtPbNP/MWCNT nanocomposite with high electrocatalytic activity to glucose oxidation ...in either neutral or alkaline medium. More importantly, the nanocomposite electrode with a slight modification exhibited high sensitivity, high selectivity, and low detection limit in amperometric glucose sensing at physiological neutral pH (poised at a negative potential). At +0.30
V in neutral solution, the nanocomposite electrode exhibited linearity up to 11
mM of glucose with a sensitivity of 17.8
μA
cm
−2
mM
−1 and a detection limit of 1.8
μM (S/N
=
3). Electroactive ascorbic acid (0.1
mM), uric acid (0.1
mM) and fructose (0.3
mM) invoked only 23%, 14% and 9%, respectively, of the current response obtained for 3
mM glucose. At −0.15
V in neutral solution, the electrode responded linearly to glucose up to 5
mM with a detection limit of 0.16
mM (S/N
=
3) and detection sensitivity of ∼18
μA
cm
−2
mM
−1. At this negative potential, ascorbic acid, uric acid, and fructose were not electroactive, therefore, not interfering with glucose sensing. Modification of the nanocomposite electrode with Nafion coating followed by electrodeposition of a second layer of PtPbNPs on the Nafion coated PtPbNP/MWCNT nanocomposite produced a glucose sensor (poised at −0.15
V) with a lower detection limit (7.0
μM at S/N
=
3) and comparable sensitivity, selectivity and linearity compared to the PtPbNP/MWCNT nanocomposite. The Nafion coating lowered the detection limit by reducing the background noise, while the second layer of PtPbNPs restored the sensitivity to the level before Nafion coating.
The development of effective transition metal oxygen reduction reaction (ORR) catalysts performing well in alkaline environments remains challenging. In this study, ordered macroporous ZIF-8 @C ...supports were prepared via carbonization using polystyrene microspheres as templates, and transition metal oxygen reduction catalysts (M-Nx/OMC; M = Fe, Co, and Mn) were prepared by loading metalloporphyrins and carbonization. Among the catalysts prepared, Fe-Nx/OMC exhibited excellent electrocatalytic activity under alkaline conditions, the half-wave (0.911 V) and initial (0.960 V) potentials are 80 and 60 mV higher than that of Pt/C respectively. In addition, the specific capacity of the zinc–air battery (ZAB) catalyzed by Fe-Nx/OMC reached 751 mAh g−1, which is 84 mAh g−1 higher than that of the ZAB catalyzed by Pt/C. The superior catalytic ORR activity is attributed to the hierarchical porous structure, which may have more exposed active centers in the carbon materials and improved mass-transfer efficiency. This study offers a new method for preparing high-performance carbon-based metal–organic framework electrocatalysts.
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•Macropore ZIF-8 frameworks were prepared using polystyrene sphere template.•Ordered macroporous structure provides rapid mass transport.•Fe-Nx-OMC exhibits remarkable ORR performances in alkaline media.•Zn-air battery assembled using Fe-Nx-OMC exhibits excellent performance.
This work has manufactured a series of M-NX/C (M = Fe, Cu, Ni) ORR catalysts by the pyrolysis of metal tetraphenylporphyrin (MTPP) adsorbed onto N-doped porous carbon polyhedrons (NPCP) derived from ...ZIF-8. The comprehensive characterization data shows that the prepared M-NX/C catalysts have hierarchical porous structure with high specific surface area and abundant M-NX moieties. All prepared M-NX/C catalysts exhibit good ORR performance. The ORR half-wave potentials E1/2 of Fe-NX/C, Cu-NX/C and Ni-NX/C catalyst are 0.885, 0.801 and 0.755 V respectively. The rotating ring-disk electrode (RRDE) test reveals that the ORR of Fe-NX/C is a four electron process. While a two and four electron mixing ORR process are observed for Cu-NX/C and Ni-NX/C. In an alkaline medium, E1/2 of Fe-NX/C is observed 44 mV higher than that of commercial Pt/C. Also, Fe-NX/C catalyst has outstanding long-term durability and good methanol resistance.
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•Porous carbon polyhedron catalysts containing dispersed metal-Nx are prepared.•The catalysts have excellent performance in oxygen reduction reaction.•Fe-Nx/C catalyst had methanol resistant and long-term durability.
