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Showing papers in "Chemistry: A European Journal in 2013"


Journal ArticleDOI
TL;DR: It is demonstrated that such wholly new CNPs can serve as a very effective fluorescent sensing platform for label-free sensitive and selective detection of Fe(3+) ions and dopamine with a detection limit as low as 0.32 μM and 68 nM, respectively.
Abstract: A facile, economic and green one-step hydrothermal synthesis route using dopamine as source towards photoluminescent carbon nanoparticles (CNPs) is proposed. The as-prepared CNPs have an average size about 3.8nm. The emission spectra of the CNPs are broad, ranging from approximately 380 (purple) to approximately 525nm (green), depending on the excitation wavelengths. Due to the favorable optical properties, the CNPs can readily enter into A549 cells and has been used for multicolor biolabeling and bioimaging. Most importantly, the as-prepared CNPs contain distinctive catechol groups on their surfaces. Due to the special response of catechol groups to Fe3+ ions, we further demonstrate that such wholly new CNPs can serve as a very effective fluorescent sensing platform for label-free sensitive and selective detection of Fe3+ ions and dopamine with a detection limit as low as 0.32M and 68nM, respectively. The new mix-and-detect strategy is simple, green, and exhibits high sensitivity and selectivity. The present method was also applied to the determination of Fe3+ ions in real water samples and dopamine in human urine and serum samples successfully.

611 citations


Journal ArticleDOI
Dengrong Sun1, Yanghe Fu1, Wenjun Liu1, Lin Ye1, Dengke Wang1, Lin Yang1, Xianzhi Fu1, Zhaohui Li1 
TL;DR: This study provides a better understanding of photocatalytic CO2 reduction over MOF-based photocATalysts and also demonstrates the great potential of using MOFs as highly stable, molecularly tunable, and recyclable photoc atalysts inCO2 reduction.
Abstract: Metal-organic framework (MOF) NH2 -Uio-66(Zr) exhibits photocatalytic activity for CO2 reduction in the presence of triethanolamine as sacrificial agent under visible-light irradiation. Photoinduced electron transfer from the excited 2-aminoterephthalate (ATA) to Zr oxo clusters in NH2 -Uio-66(Zr) was for the first time revealed by photoluminescence studies. Generation of Zr(III) and its involvement in photocatalytic CO2 reduction was confirmed by ESR analysis. Moreover, NH2 -Uio-66(Zr) with mixed ATA and 2,5-diaminoterephthalate (DTA) ligands was prepared and shown to exhibit higher performance for photocatalytic CO2 reduction due to its enhanced light adsorption and increased adsorption of CO2 . This study provides a better understanding of photocatalytic CO2 reduction over MOF-based photocatalysts and also demonstrates the great potential of using MOFs as highly stable, molecularly tunable, and recyclable photocatalysts in CO2 reduction.

509 citations


Journal ArticleDOI
TL;DR: This Concept article discusses the potential of oxidative carbene catalysis in synthesis and comprehensively covers pioneering studies as well as recent developments.
Abstract: This Concept article discusses the potential of oxidative carbene catalysis in synthesis and comprehensively covers pioneering studies as well as recent developments. Oxidative carbene catalysis can be conducted by using inorganic and organic oxidants. Applications in cascade processes, in enantioselective catalysis, and also in natural product synthesis are discussed.

392 citations


Journal ArticleDOI
TL;DR: Imaging of HeLa cells and HepG2 cells, a human cervical cancer cell line, was observed with high resolution using N-Cdots as a probe and validates their use in imaging applications and their multicolor property in the living cell system.
Abstract: Carbon dots (Cdots) are an important probe for imaging and sensing applications because of their fluorescence property, good biocompatibility, and low toxicity. However, complex procedures and strong acid treatment are often required and Cdots suffer from low photoluminescence (PL) emission. Herein, a facile and general strategy using carbonization of precursors and then extraction with solvents is proposed for the preparation of nitrogen-doped Cdots (N-Cdots) with 3-(3,4-dihydroxyphenyl)-L-alanine (L-DOPA), L-histidine, and L-arginine as precursor models. After they are heated, the precursors become carbonized. Nitrogen-doped Cdots are subsequently extracted into N,N-dimethylformamide (DMF) from the carbogenic solid. A coreshell structure of Cdots with a carbon core and the oxygen-containing shell was observed. Nitrogen has different forms in N-Cdots and oxidized N-Cdots. The doped nitrogen and low oxidation level in N-Cdots improve their emission significantly. The N-Cdots show an emission with a nitrogen-content-dependent intensity and Cdot-size-dependent emission-peak wavelength. Imaging of HeLa cells, a human cervical cancer cell line, and HepG2 cells, a human hepatocellular liver carcinoma line, was observed with high resolution using N-Cdots as a probe and validates their use in imaging applications and their multicolor property in the living cell system.

379 citations


Journal ArticleDOI
TL;DR: A 2D mesoporous covalent organic framework featuring expanded pyrene cores and linked by imine linkages has a high surface area and exhibits significant gas storage capacities under high pressure, which make this class of material very promising for gas storage applications.
Abstract: Hole-some mixture: A 2D mesoporous covalent organic framework (see figure) featuring expanded pyrene cores and linked by imine linkages has a high surface area (SA(BET) = 2723 m(2) g(-1)) and exhibits significant gas storage capacities under high pressure, which make this class of material very promising for gas storage applications.

355 citations


Journal ArticleDOI
TL;DR: The facile synthesis of microporous carbon polyhedrons (MPCPs) using unique MOFpolyhedrons as both the template and precursor, and their use as carbon host to incorporate sulfur for Li–S batteries is reported.
Abstract: As a promising rechargeable battery system, lithium– sulfur (Li–S) batteries can deliver an exceptionally high theoretical specific capacity of 1672 mAhg 1 and an energy density of 2500 Whkg 1 with the low-cost and environmentfriendly sulfur as the cathode material. Although the potential use of sulfur as a cathode material has long been discovered, several severe drawbacks have hindered the realization of Li–S batteries. One limitation is the insulating nature of sulfur with a very low conductivity of 5 10 30 Scm , which results in low utilization of sulfur. Another well-known problem is associated with the easy dissolution of polysulfides, the intermediate products formed during the electrochemical reaction, in organic electrolytes. The dissolved polysulfides “shuttle” between the electrodes, leading to the low Coulombic efficiency and deposition of a highly resistive layer on the surface of electrodes. These detrimental issues result in unsatisfactory electrochemical performance with rapid fading of capacity. Several approaches have been proposed to overcome the above-mentioned challenges in Li–S batteries, such as developing novel electrolytes and electrode materials. Among these efforts, using sulfur-containing composites instead of pure sulfur as the cathode materials has been demonstrated as an effective way towards high-performance Li–S batteries. Polymers and porous carbons are the common candidates to form composites with sulfur, which immobilize the loaded sulfur, and probably also the derived polysulfides via physical and/or chemical interactions. In addition, the electrical conductivity of composite materials is also better than that obtained with pristine sulfur. In particular, porous carbon materials have attracted intensive attention due to their good compatibility with sulfur, easy accessibility, and the abundance of candidates with diverse porosity and structures. Mesoporous carbon materials have been widely studied as the host materials to confine sulfur. For example, nanocomposites consisting of sulfur and ordered mesoporous carbon or mesoporous hollow carbon spheres have shown improved sulfur utilization and cycling stability. Nonetheless, continuous capacity fading upon prolonged cycling is still commonly observed, and the use of optimized ether-based electrolytes seems to be indispensable. Recent reports on carbon materials with rich micropores have revealed distinct characteristics. 25] Sulfur embedded in microporous carbon shows a pronounced discharge plateau at a lower potential of about 1.8 V versus Li/Li, which is different from the two plateaus of a typical sulfur cathode. More importantly, these microporous carbon/sulfur nanocomposites generally show outstanding capacity retention upon cycling and good compatibility with conventional carbonate-based electrolytes. However, the origins of the unusual characteristics of microporous carbon are not fully understood yet. In recently years, syntheses of porous carbon materials from metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) have attracted growing attention due to the facile preparation procedures, high carbon yield, and unique porous structures. For example, carbonization of MOF-5 with furfuryl alcohol results in nanoporous carbon, which shows excellent supercapacitive performance. The carbon materials with fiber-like morphology prepared from Al-based PCPs exhibit remarkably high porosity. In particular, MOFs and PCPs are very attractive as both the template and the precursor for the fabrication of microporous carbon. Compared with many other highly porous carbon materials, such as those prepared by post-activation processes, the porous carbon derived from MOFs and PCPs exhibits highly uniform porosity, largely originating from the ordered crystalline structures of the MOFs and PCPs. However, the interesting application of these carbon materials derived from MOFs and PCPs for Li–S batteries needs to be further explored. Herein, we report the facile synthesis of microporous carbon polyhedrons (MPCPs) using unique MOF polyhedrons as both the template and precursor, and their use as carbon host to incorporate sulfur for Li–S batteries. The asprepared MPCPs with abundant and uniform micropores serve as an ideal model system for investigating the electrochemical behaviors of sulfur embedded in microporous [a] H. B. Wu, S. Wei, Dr. L. Zhang, Prof. R. Xu, Prof. X. W. Lou School of Chemical and Biomedical Engineering Nanyang Technological University 62 Nanyang Drive, Singapore 637459 (Singapore) E-mail : rxu@ntu.edu.sg xwlou@ntu.edu.sg Homepage: http://www.ntu.edu.sg/home/xwlou [b] H. B. Wu, Prof. H. H. Hng School of Materials Science and Engineering Nanyang Technological University 50 Nanyang Avenue, Singapore 639798 (Singapore) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201301689.

354 citations


Journal ArticleDOI
Lunhong Ai1, Lili Li1, Caihong Zhang1, Jian Fu1, Jing Jiang1 
TL;DR: This work reports that MIL-53 iron ACHTUNGTRENNUNG(III) terephthalate (MIL-53(Fe), a typical iron-based metal–organic framework (MOF) with formula Fe(OH), possesses intrinsic peroxidase-like activity, catalyzing the oxidation of 3,3’,5,5’-tetramethylbenzidine (TMB), o-phenylenediamine (OPD
Abstract: Owing to both the enhanced instrumental transduction and the potential for direct visual readout, colorimetric biosensing has drawn intense attention in biological science and analytical chemistry. It offers the advantages of simplicity, rapidity, and cheapness as well as the fact that there is no requirement for any sophisticated instrumentation. As a basis for this technique, colorimetric sensors that signal analyte interaction through a change in color are undoubtedly crucial for its successful implementation. To this end, biosensors based on enzyme-mimetic inorganic materials have emerged as a new class of ideal and important colorimetric detection tools for biosensing, owing to their high stability, easy preparation, controllable structure and composition, and tunable catalytic activity. So far, a number of inorganic materials with peroxidase-like activity, including oxides, metals, sulfides, carbon, and polyoxometalates have been successfully exploited. Metal–organic frameworks (MOFs) are an intriguing class of porous crystalline inorganic– organic hybrid materials built from metal ions and polyfunctional organic ligands and have attracted increasing attention in recent years, owing to both fundamental scientific interest and attractive applications. Particularly, the fascinating features, which include structural diversity, flexibility and alterability, intrinsic porosity, and desired chemical functionality, endow them with great promise in a variety of fields such as gas storage, separation, drug delivery, bioimaging, and catalysis. Very recently, great effort has been made to provide new insights into the application of MOFs in sensing. Herein, we report that MIL-53 iron ACHTUNGTRENNUNG(III) terephthalate (MIL-53(Fe)), a typical iron-based metal–organic framework (MOF) with formula Fe(OH)(O2C C6H4 CO2)·H2O (Scheme S1 in the Supporting Information), possesses intrinsic peroxidase-like activity, catalyzing the oxidation of 3,3’,5,5’-tetramethylbenzidine (TMB), o-phenylenediamine (OPD), and 1,2,3-trihydroxybenzene (THB) in the presence of H2O2. MIL-53(Fe) as a peroxidase mimic provided a colorimetric assay for H2O2 (Scheme 1A). Moreover, an inhibition effect was induced by ascorbic acid (AA) on the oxidation of OPD cata-

338 citations


Journal ArticleDOI
TL;DR: Heteroleptic complexes that contain electron-donor moieties on one of the two Pc ligands show higher effective barriers and blocking temperatures than their homoleptic derivatives, and heteroleptic [Tb(III) (Pc)(Pc')] complex 4, which contains one octa(tert-butylphenoxy)-substituted PC ring and one bare Pc ring, exhibits the highest effective barrier and blocking temperature for a single-mole
Abstract: A series of homoleptic ([Tb(III)(Pc)(2) ]) and heteroleptic ([Tb(III)(Pc)(Pc')]) Tb(III) bis(phthalocyaninate) complexes that contain different peripheral substitution patterns (i.e., tert-butyl or tert-butylphenoxy groups) have been synthesized in their neutral radical forms and then reduced into their corresponding anionic forms as stable tetramethylammonium/tetrabutylammonium salts. All of these compounds were spectroscopically characterized and their magnetic susceptibility properties were investigated. As a general trend, the radical forms exhibited larger energy barriers for spin reversal than their corresponding reduced compounds. Remarkably, heteroleptic complexes that contain electron-donor moieties on one of the two Pc ligands show higher effective barriers and blocking temperatures than their homoleptic derivatives. This result is assigned to the elongation of the N-Tb distances in the substituted macrocycle, which brings the terbium(III) ion closer to the unsubstituted Pc, thus enhancing the ligand-field effect. In particular, heteroleptic [Tb(III) (Pc)(Pc')] complex 4, which contains one octa(tert-butylphenoxy)-substituted Pc ring and one bare Pc ring, exhibits the highest effective barrier and blocking temperature for a single-molecule magnet reported to date.

303 citations


Journal ArticleDOI
TL;DR: Separating the electron acceptor from the anchoring unit in the donor-acceptor-type organic dye would be a promising strategy to reduce recombination and improve photocurrent generation.
Abstract: All-organic dyes have shown promising potential as an effective sensitizer in dye-sensitized solar cells (DSSCs). The design concept of all-organic dyes to improve light-to-electric-energy conversion is discussed based on the absorption, electron injection, dye regeneration, and recombination. How the electron-donor-acceptor-type framework can provide better light harvesting through bandgap-tuning and why proper arrangement of acceptor/anchoring groups within a conjugated dye frame is important in suppressing improper charge recombination in DSSCs are discussed. Separating the electron acceptor from the anchoring unit in the donor-acceptor-type organic dye would be a promising strategy to reduce recombination and improve photocurrent generation.

278 citations


Journal ArticleDOI
TL;DR: Structural investigation is reported of polymorphs of Ga(2)O(3) that, despite much interest in their properties, have hitherto remained uncharacterised due to structural disorder, and thermodiffraction provides no evidence for the existence of the speculated bixbyite structured δ-Ga(2).
Abstract: A structural investigation is reported of polymorphs of Ga2O3 that, despite much interest in their properties, have hitherto remained uncharacterised due to structural disorder. The most crystalline sample yet reported of γ-Ga2O3 was prepared by solvothermal oxidation of gallium metal in ethanolamine. Structure refinement using the Rietveld method reveals γ-Ga2O3 has a defect Fdequation imagem spinel structure, while pair distribution function analysis shows that the short-range structure is better modelled with local Fequation image3m symmetry. In further solvothermal oxidation reactions a novel gallium oxyhydroxide, Ga5O7(OH), is formed, the thermal decomposition of which reveals a new, transient gallium oxide polymorph, κ-Ga2O3, before transformation into β-Ga2O3. In contrast, the thermal decomposition of Ga(NO3)3⋅9 H2O first forms e-Ga2O3 and then β-Ga2O3. Examination of in situ thermodiffraction data shows that e-Ga2O3 is always contaminated with β-Ga2O3 and with this knowledge a model for its structure was deduced and refined—space group P63mc with a ratio of tetrahedral/octahedral gallium of 2.2:1 in close-packed oxide layers. Importantly, thermodiffraction provides no evidence for the existence of the speculated bixbyite structured δ-Ga2O3; at the early stages of thermal decomposition of Ga(NO3)3⋅9 H2O the first distinct phase formed is merely small particles of e-Ga2O3.

276 citations


Journal ArticleDOI
TL;DR: The reaction mechanism for the Zn(salphen)/NBu4X (X = Br, I) mediated cycloaddition of CO2 to a series of epoxides, affording five-membered cyclic carbonate products has been investigated in detail by using DFT methods and should allow the design and application of more efficient catalysts for organic carbonate formation.
Abstract: The reaction mechanism for the Zn(salphen)/NBu4X (X=Br, I) mediated cycloaddition of CO2 to a series of epoxides, affording five-membered cyclic carbonate products has been investigated in detail by using DFT methods. The ring-opening step of the process was examined and the preference for opening at the methylene (Cβ) or methine carbon (Cα) was established. Furthermore, calculations were performed to clarify the reasons for the lethargic behavior of internal epoxides in the presence of the binary catalyst. Also, the CO2 insertion and the ring-closing steps have been explored for six differently substituted epoxides and proved to be significantly more challenging compared with the ring-opening step. The computational findings should allow the design and application of more efficient catalysts for organic carbonate formation.

Journal ArticleDOI
TL;DR: This Minireview attempts to classify recent advances in this area including the transition to non-activated sp(3) C-H bonds and asymmetric hydride transfers.
Abstract: The direct functionalization of C-H bonds is an attractive strategy in organic synthesis. Although several advances have been made in this area, the selective activation of inert sp(3) C-H bonds remains a daunting challenge. Recently, a new type of sp(3) C-H activation mode through internal hydride transfer has demonstrated the potential to activate remote sp(3) C-H linkages in an atom-economic manner. This Minireview attempts to classify recent advances in this area including the transition to non-activated sp(3) C-H bonds and asymmetric hydride transfers.

Journal ArticleDOI
TL;DR: The desirable enhanced capacitive performance of NCO-NTs can be attributed to the relatively large specific surface area of these porous and hollow one-dimensional nanostructures.
Abstract: Novel, porous NiCo2O4 nanotubes (NCO-NTs) are prepared by a single-spinneret electrospinning technique followed by calcination in air. The obtained NCO-NTs display a one-dimensional architecture with a porous structure and hollow interiors. The effect of precursor concentration on the morphologies of the products is investigated. Due to their unique structure, the prepared NCO-NT electrode exhibits a high specific capacitance (1647 F g(-1) at 1 A g(-1)), excellent rate capability (77.3 % capacity retention at 25 A g(-1)), and outstanding cycling stability (6.4 % loss after 3000 cycles), which indicates it has great potential for high-performance electrochemical capacitors. The desirable enhanced capacitive performance of NCO-NTs can be attributed to the relatively large specific surface area of these porous and hollow one-dimensional nanostructures.

Journal ArticleDOI
TL;DR: The striking influence of coordinating NHSi's to transition-metal complex fragments affording different reactivities to the "free" NHSi is a connecting theme ("leitmotif") throughout the review, and highlights the potential of these compounds which lie at the interface of contemporary main-group and classical organometallic chemistry towards new molecular catalysts for small-molecule activation.
Abstract: This account is a review on the synthesis and transition-metal coordination chemistry of N-heterocyclic silylenes (NHSi’s) over the last 20 years till the present time (2012). Recently, fascinating and novel synthetic methods have been developed to access transition-metal–NHSi complexes as an emerging class of compounds with a wealth of intriguing reactivity patterns. The striking influence of coordinating NHSi’s to transition-metal complex fragments affording different reactivities to the “free” NHSi is a connecting theme (“leitmotif”) throughout the review, and highlights the potential of these compounds which lie at the interface of contemporary main-group and classical organometallic chemistry towards new molecular catalysts for small-molecule activation.

Journal ArticleDOI
TL;DR: The exposed abundant Mo edges of the MoS2 nanoparticles were proven to be responsible for the high ORR catalytic activity, whereas the origin of the improved HER activity of the nanoparticles was attributed to the plentiful exposed S edges.
Abstract: MoS2 particles with different size distributions were prepared by simple ultrasonication of bulk MoS2 followed by gradient centrifugation. Relative to the inert microscale MoS2, nanoscale MoS2 showed significantly improved catalytic activity toward the oxygen-reduction reaction (ORR) and hydrogen-evolution reaction (HER). The decrease in particle size was accompanied by an increase in catalytic activity. Particles with a size of around 2 nm exhibited the best dual ORR and HER performance with a four-electron ORR process and an HER onset potential of −0.16 V versus the standard hydrogen electrode (SHE). This is the first investigation on the size-dependent effect of the ORR activity of MoS2, and a four-electron transfer route was found. The exposed abundant Mo edges of the MoS2 nanoparticles were proven to be responsible for the high ORR catalytic activity, whereas the origin of the improved HER activity of the nanoparticles was attributed to the plentiful exposed S edges. This newly discovered process provides a simple protocol to produce inexpensive highly active MoS2 catalysts that could easily be scaled up. Hence, it opens up possibilities for wide applications of MoS2 nanoparticles in the fields of energy conversion and storage.

Journal ArticleDOI
TL;DR: This reaction serves as a powerful and ecofriendly synthetic method for the preparation of a variety of CF3 -containing oxindoles bearing a quaternary carbon center.
Abstract: Trifluoromethylation/arylation: N-aryl acrylamides undergo visible-light-induced tandem trifluoromethylation/arylation in the presence of a ruthenium photocatalyst with Togni's reagent as the CF3 source. This reaction serves as a powerful and ecofriendly synthetic method for the preparation of a variety of CF3 -containing oxindoles bearing a quaternary carbon center.

Journal ArticleDOI
TL;DR: Results show that nanostructured carbon with hierarchical pore distribution could be a promising scaffold for encapsulating sulfur to approach high specific capacity and energy density with long cycling performance.
Abstract: A three-dimensional (3D) hierarchical carbon-sulfur nanocomposite that is useful as a high-performance cathode for rechargeable lithium-sulfur batteries is reported. The 3D hierarchically ordered porous carbon (HOPC) with mesoporous walls and interconnected macropores was prepared by in situ self-assembly of colloidal polymer and silica spheres with sucrose as the carbon source. The obtained porous carbon possesses a large specific surface area and pore volume with narrow mesopore size distribution, and acts as a host and conducting framework to contain highly dispersed elemental sulfur. Electrochemical tests reveal that the HOPC/S nanocomposite with well-defined nanostructure delivers a high initial specific capacity up to 1193 mAh g(-1) and a stable capacity of 884 mAh g(-1) after 50 cycles at 0.1 C. In addition, the HOPC/S nanocomposite exhibits high reversible capacity at high rates. The excellent electrochemical performance is attributed exclusively to the beneficial integration of the mesopores for the electrochemical reaction and macropores for ion transport. The mesoporous walls of the HOPC act as solvent-restricted reactors for the redox reaction of sulfur and aid in suppressing the diffusion of polysulfide species into the electrolyte. The "open" ordered interconnected macropores and windows facilitate transportation of electrolyte and solvated lithium ions during the charge/discharge process. These results show that nanostructured carbon with hierarchical pore distribution could be a promising scaffold for encapsulating sulfur to approach high specific capacity and energy density with long cycling performance.

Journal ArticleDOI
Nasir Mahmood1, Chenzhen Zhang1, Jie Jiang1, Fei Liu1, Yanglong Hou1 
TL;DR: Electrochemical measurements indicated that the as-synthesized Co3S4/G composites exhibit good cyclic stability and a high discharge capacity, and stability of the composites is much higher than that of Pt/C, and exhibit high methanol tolerance, which endorse Co3 S4 /G Composites as auspicious candidates for both LIBs and ORR.
Abstract: Cobalt sulfide is a good candidate for both lithium ion batteries (LIBs) and cathodic oxygen reduction reaction (ORR), but low conductivity, poor cyclability, capacity fading, and structural changes hinder its applications. The incorporation of graphene into CO 3 S 4 makes it a promising electrode by providing better electrochemical coupling, enhanced conductivity, fast mobility of ions and electrons, and a stabilized structure due to its elastic nature. With the objective of achieving high-performance composites, herein we report a facile hydrothermal process for growing CO 3 S 4 nanotubes (NTs) on graphene (G) sheets. Electrochemical impedance spectroscopy (EIS) verified that graphene dramatically increases the conductivity of the composites to almost twice that of pristine CO 3 S 4 . Electrochemical measurements indicated that the as-synthesized CO 3 S 4 / G composites exhibit good cyclic stability and a high discharge capacity of 720 mAhg1 up to 100 cycles with 99.9% coulombic efficiency. Furthermore, the composites react with dissolved oxygen in the ORR by fourand two-electron mechanisms in both acidic and basic media with an onset potential close to that of commercial Pt/C. The stability of the composites is much higher than that of Pt/C, and exhibit high methanol tolerance. Thus, these properties endorse CO 3 S 4 /G composites as auspicious candidates for both LIBs and ORR.

Journal ArticleDOI
Hanjun Sun1, Nan Gao1, Li Wu1, Jinsong Ren1, Weili Wei1, Xiaogang Qu1 
TL;DR: A new kind of highly fluorescent probe for Cu(2+) sensing generated by hydrothermal treatment of graphene quantum dots (GQDs) that offers a "mix-and-detect" protocol without dye-modified oligonucleotides or complex chemical modification.
Abstract: Herein, we report a new kind of highly fluorescent probe for Cu2+ sensing generated by hydrothermal treatment of graphene quantum dots (GQDs). After hydrothermal treatment in ammonia, the greenish-yellow fluorescent GQDs (gGQDs) with a low quantum yield (QY, 2.5%) are converted to amino-functionalized GQDs (afGQDs) with a high QY (16.4%). Due to the fact that Cu2+ ions have a higher binding affinity and faster chelating kinetics with N and O on the surface of afGQDs than other transition-metal ions, the selectivity of afGQDs for Cu2+ is much higher than that of gGQDs. Furthermore, afGQDs are biocompatible and eco-friendly, and the afGQDs with a positive charge can be easily taken up by cells, which makes it possible to sense Cu2+ in living cells. The strategy presented here is simple in design, economical, and offers a mix-and-detect protocol without dye-modified oligonucleotides or complex chemical modification.

Journal ArticleDOI
TL;DR: Helical microrobots have the potential to be used in a variety of application areas, such as in medical procedures, cell biology, or lab-on-a-chip, using powered and steered wirelessly using low-strength rotating magnetic fields.
Abstract: Helical microrobots have the potential to be used in a variety of application areas, such as in medical procedures, cell biology, or lab-on-a-chip. They are powered and steered wirelessly using low-strength rotating magnetic fields. The helical shape of the device allows propulsion through numerous types of materials and fluids, from tissue to different types of bodily fluids. Helical propulsion is suitable for pipe flow conditions or for 3D swimming in open fluidic environments.

Journal ArticleDOI
TL;DR: In situ IR spectroscopy unequivocally shows the presence of adsorbed ketene on the surface of ZrO2 during the reaction with palmitic acid at 260 °C in the presence or absence of H2, which indicates rate-determining reduction of the carboxylic group of palMITic acid to give hexadecanal.
Abstract: The mechanism of the catalytic reduction of palmitic acid to n-pentadecane at 260 degrees C in the presence of hydrogen over catalysts combining multiple functions has been explored. The reaction involves rate-determining reduction of the carboxylic group of palmitic acid to give hexadecanal, which is catalyzed either solely by Ni or synergistically by Ni and the ZrO2 support. The latter route involves adsorption of the carboxylic acid group at an oxygen vacancy of ZrO2 and abstraction of the alpha-H with elimination of O to produce the ketene, which is in turn hydrogenated to the aldehyde over Ni sites. The aldehyde is subsequently decarbonylated to n-pentadecane on Ni. The rate of deoxygenation of palmitic acid is higher on Ni/ZrO2 than that on Ni/SiO2 or Ni/Al2O3, but is slower than that on H-zeolite-supported Ni. As the partial pressure of H-2 is decreased, the overall deoxygenation rate decreases. In the absence of H-2, ketonization catalyzed by ZrO2 is the dominant reaction. Pd/C favors direct decarboxylation (-CO2), while Pt/C and Raney Ni catalyze the direct decarbonylation pathway (-CO). The rate of deoxygenation of palmitic acid (in units of mmol mol(total metal)(-1) h(-1)) decreases in the sequence r((Pt black)) approximate to r((Pd black)) > r((Raney Ni)) in the absence of H-2. In situ IR spectroscopy unequivocally shows the presence of adsorbed ketene (C=C=O) on the surface of ZrO2 during the reaction with palmitic acid at 260 degrees C in the presence or absence of H-2.

Journal ArticleDOI
TL;DR: The most recent and original progresses inymmetric hydroamination are pointed out, offering nearby developments, and addressing the next challenges are addressed.
Abstract: Asymmetric hydroamination allows the direct and selective formation of a new CN bond as a simple procedure towards valuable scalemic synthons. Huge efforts have recently been made to overcome the challenges associated with this transformation. This non-comprehensive Concept article aims at pointing out the most recent and original progresses, offering nearby developments, and addressing the next challenges.

Journal ArticleDOI
TL;DR: Results are expected to facilitate the design of chiral diaryliodonium salts and the development of catalytic arylation reactions that are based on these sustainable and metal-free reagents.
Abstract: Phenols, anilines, and malonates have been arylated under metal-free conditions with twelve aryl(phenyl)iodonium salts in a systematic chemoselectivity study. A new “anti-ortho effect” has been identified in the arylation of malonates. Several “dummy groups” have been found that give complete chemoselectivity in the transfer of the phenyl moiety, irrespective of the nucleophile. An aryl exchange in the diaryliodonium salts has been observed under certain arylation conditions. DFT calculations have been performed to investigate the reaction mechanism and to elucidate the origins of the observed selectivities. These results are expected to facilitate the design of chiral diaryliodonium salts and the development of catalytic arylation reactions that are based on these sustainable and metal-free reagents.

Journal ArticleDOI
TL;DR: The driving forces for the formation of the pillararene-based assemblies are discussed first, and the host-guest interactions are deemed as not only general strategy for constructing assemblies but also essential components for preventing the assemblies from the dissociation.
Abstract: In this review, we highlight recent advancements on pillararene-based assemblies. The driving forces for the formation of the pillararene-based assemblies are discussed first. The host-guest interactions are deemed as not only general strategy for constructing assemblies but also essential components for preventing the assemblies from the dissociation. Solvent effect is also important in the assembling process, since it could influence the host-guest interactions and provide solvophobic effect on pillararenes for the assembly. Then, several pillararene-based assembly architectures are introduced, including pillararene-based interlocked structures, such as (poly)pseudorotaxanes, (poly)rotaxanes, and daisy chains, classified by their topological structures and synthetic strategy. The morphologies of the supramolecular assemblies are divided into several types, for example, nanospheres, nanotubes and supramolecular polymers. Furthermore, the functions and potential applications are summarized accompanied with related assembly structures. The review not only provides fundamental findings, but also foresights future research directions in the research area of pillararene-based assemblies.

Journal ArticleDOI
TL;DR: Owing to the imino triazine backbone and carboxyl groups of the hexatopic ligand, which provide important host-guest interactions, rare solvatochromic phenomena of 1 and 2 are observed on incorporating acetone and ethanol guests.
Abstract: Two anionic metal-organic frameworks (MOFs) with 1D mesoporous tubes (1) and chiral mesoporous cages (2) have been rationally constructed by means of a predesigned size-extended hexatopic ligand, namely, 5,5',5''-(1,3,5-triazine-2,4,6-triyl)tris- (azanediyl)triisophthalate (TATAT). Charge neutrality is achieved by protonated dimethylamine cations. Notably, the two MOFs can be used to separate large molecules based on ionic selectivity rather than the size-exclusion effect so far reported in the literature. Owing to the imino triazine backbone and carboxyl groups of the hexatopic ligand, which provide important host-guest interactions, rare solvatochromic phenomena of 1 and 2 are observed on incorporating acetone and ethanol guests. Furthermore, guest-dependent luminescence properties of compound 2 were investigated, and the results show that luminescence intensity is significantly enhanced in toluene and benzene, while quenching effects are observed in acetone and ethanol. Thus, compound 2 may be a potential material for luminescent probes.

Journal ArticleDOI
TL;DR: The efficient and selective hydrogen liberation from formic acid is catalyzed by an iron pincer complex in the presence of trialkylamine and turnover numbers up to 100,000 were achieved at 40 °C.
Abstract: Hydrogen liberation: An attractive approach to reversible hydrogen storage applications is based on the decomposition of formic acid. The efficient and selective hydrogen liberation from formic acid is catalyzed by an iron pincer complex in the presence of trialkylamine. Turnover frequencies up to 836 h⁻¹ and turnover numbers up to 100,000 were achieved at 40 °C. A mechanism including well-defined intermediates is suggested on the basis of experimental and computational data.

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TL;DR: All four compounds are capable of detecting these molecules in the vapor phase through fluorescence quenching or enhancement and Interestingly, compound 3 also shows an emission frequency shift when exposed to benzene, chlorobenzene, and toluene, which provides an additional variable for the identification of different analytes in the same category.
Abstract: A systematic study is conducted on four microporous metal-organic framework compounds built on similar ligands but different structures, namely [Zn3(bpdc)3(bpy)]·4DMF·H2O (1), [Zn3(bpdc)3(2,2'dmbpy)]·4DMF·H2O (2), [Zn2(bpdc)2(bpe)]·2DMF (3), and [Zn(bpdc)(bpe)]·DMF (4) (bpdc=4,4'-biphenyldicarboxylate; bpy=4,4'-bipyridine; 2,2'dmbpy=2,2'-dimethyl-4,4'bipyridine; bpe=1,2-bis(4-pyridyl)ethane; DMF=N,N'-dimethylformamide) to investigate their photoluminescence properties and sensing/detection behavior upon exposure to vapors of various aromatic molecules (analytes) including nitroaromatic explosives. The results show that all four compounds are capable of detecting these molecules in the vapor phase through fluorescence quenching or enhancement. Both electrochemical measurements and theoretical calculations are performed to analyze the analyte-MOF interactions, to explain the difference in signal response by different analytes, and to understand the mechanism of fluorescence quenching or enhancement observed in these systems. Interestingly, compound 3 also shows an emission frequency shift when exposed to benzene (BZ), chlorobenzene (ClBZ), and toluene (TO), which provides an additional variable for the identification of different analytes in the same category.

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Jiwei Liu1, Junjie Xu1, Renchao Che1, Huajun Chen1, Mengmei Liu1, Zhengwang Liu1 
TL;DR: The electromagnetic data demonstrate that the as-synthesized Fe3O4@TiO2 yolk-shell microspheres exhibit significantly enhanced microwave absorption properties compared with pure Fe 3O4 and the authors' previously reported Fe3 O4@ TiO2 core-shellmicrospheres, which may result from the unique yolk -shell structure with a large surface area and high porosity.
Abstract: A facile and efficient strategy for the synthesis of hierarchical yolk-shell microspheres with magnetic Fe3O4 cores and dielectric TiO2 shells has been developed. Various Fe3O4@TiO2 yolk-shell microspheres with different core sizes, interstitial void volumes, and shell thicknesses have been successfully synthesized by controlling the synthetic parameters. Moreover, the microwave absorption properties of these yolk-shell microspheres, such as the complex permittivity and permeability, were investigated. The electromagnetic data demonstrate that the as-synthesized Fe3O4@TiO2 yolk-shell microspheres exhibit significantly enhanced microwave absorption properties compared with pure Fe3O4 and our previously reported Fe3O4@TiO2 core-shell microspheres, which may result from the unique yolk-shell structure with a large surface area and high porosity, as well as synergistic effects between the functional Fe3O4 cores and TiO2 shells.

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TL;DR: Through a combination of structural chemistry, vibrational spectroscopy, and theory, the relative structure-directing importance of a series of ditopic halogen-bond (XB) donors is examined and the results offer practical guidelines for synthetic crystal engineering driven by robust and directional halogen bonds.
Abstract: Through a combination of structural chemistry, vibrational spectroscopy, and theory, we have systematically examined the relative structure-directing importance of a series of ditopic halogen-bond (XB) donors. The molecular electrostatic potential surfaces of six XB donors were evaluated, which allowed for a charge-based ranking. Each molecule was then co-crystallized with 21 XB acceptors and the results have made it possible to map out the supramolecular landscape describing the competition between I/Br-ethynyl donors, perfluorinated I/Br donors, and I/Br-phenyl based donors. The results offer practical guidelines for synthetic crystal engineering driven by robust and directional halogen bonds.

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TL;DR: The identification of organosulfate groups beneath epoxy groups makes new molecular architectures feasible and can be used to explain the properties of GO in various applications and to exclude the possibility that sulfonic groups are present in GO as major species after aqueous work up.
Abstract: The structure of graphene oxide (GO) is of crucial importance for its chemical functionalization. However, the sulfur content present in GO prepared by Hummers' method has only been addressed by a few authors so far. It has been reported that hydrolysis of sulfur species takes place and that stable sulfonic groups are present in graphite oxide. In this manuscript, in contrast to earlier reports, sulfate species are identified that are covalently bound to GO and still present after extensive aqueous work-up. Additionally, we exclude the possibility that sulfonic groups are present in GO as major species after aqueous work up. Our results are based on bulk characterization of graphene oxide by thermogravimetry and subsequent analysis of the decomposition products using mass spectroscopy and infrared spectroscopy. Up to now, the combustion temperature between 200 and 300 °C remained almost unaddressed. In a temperature dependant experiment we reveal two main decomposition steps that differ in temperature and that are closely related to the sulfur species in GO. While the decomposition, between 200 and 300 °C, is related to the degradation of organosulfate, the other one, between 700 and 800 °C, is assigned to the pyrolysis of inorganic sulfate. Furthermore, organosulfate is to some extent responsible for the reactivity of GO. Therefore, the structural model of GO was extended by adding organosulfate in addition to epoxy and hydroxyl groups, which are predominantly covalently bound above and below the carbon skeleton. Furthermore, the identification of organosulfate groups beneath epoxy groups makes new molecular architectures feasible and can be used to explain the properties of GO in various applications.