Electrochemical synthesis of hollow and solid carbon nano onions from simple aromatic compounds in acetonitrile on a platinum plate electrode by a multi-potential steps method.
Detection of inorganic phosphate is very important in environmental and health care applications. In this work, we found that phenomenon similar to “catalytic hydrogen wave” occurred on a molybdenum phosphide (MoP) modified electrode in the presence of phosphate, that is, a new wave of catalytic hydrogen evolution appeared before the normal hydrogen evolution reaction. The catalytic hydrogen wave arose from a structure similar to phosphomolybdic acid (noted as MoPO), which was formed by the interaction between phosphate and molybdenum oxides on the surface of the MoP modified electrode, resulting in the altered surface structure and adjusted interface catalytic activity. A novel phosphate electrochemical sensor was constructed based on this phenomenon with a linear range from 0.10 to 20.0 mmol·L–1, an actually determined minimum concentration of 0.030 mmol·L–1, and recoveries of 94%–107%, and this sensor was successfully applied to the detection of phosphate in human blood. Furthermore, this work proposes a new sensing method based on catalytic hydrogen waves on the modified electrodes.
Presented here are two open-framework zinc phosphites, namely, Zn(dabco)0.5(HPO3) (SCU-18) and Zn4(Hdabco)2(CH3COO)2(HPO3)4 (SCU-20), where dabco = 1,4-diazabicyclo[2.2.2]octane. SCU-18 features a rare 3-connected inorganic skeleton with a chiral qtz-h topology. It contains 18-membered-ring (18 MR) channels displaying porosity and second-harmonic-generation response. SCU-20 has a bnn topology containing large 20 MR channels that shows a strong blue emission as a result of excitation at 375 nm.
A series of new metal phosphate-oxalates were synthesized under solvent-free conditions. These compounds display interesting open-framework structures with mmt, ins, fsd, and hcb topologies, respectively. The extra-large 20-ring channel, nanobelt-like inorganic skeleton, and the use of cadmium ions as framework cations are unprecedented in metal phosphate-oxalate structures.
Molybdenum disulfide nanomaterials nowadays are very popular in electrocatalysis field due to their outstanding catalytic performance toward many electrochemical reactions. However, the electrochemical oxidation reaction of molybdenum disulfide nanomaterials in the range of positive potential has not been studied thoroughly. Herein, we have investigated electro-oxidation of molybdenum disulfide nanomaterials and put forward a new reaction mechanism: molybdenum disulfide nanomaterials are electro-oxidized with water to form molybdenum oxysulfide (MoOS2) and hydrogen ions, leading to the release of hydrogen on the counter electrode. Various characterization methods such as contact angle measurement, scanning electron microscope (SEM), transmission electron microscope (TEM) with energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) spectroscopy, time-of-flight secondary ion mass spectrometry (ToF-SIMS), and gas chromatography (GC) were applied to attest the doping of oxygen and the generation of hydrogen. Based on this reaction, we constructed a novel ultrasensitive electrochemical sensor for detecting trace water with the minimum detectable content of 0.0010% (v/v) in various organic solvents and ionic liquids, which is comparable to the Karl Fischer titration, but with much simpler reagent.
Charge (ion and electron)-transfer reactions at a liquid/ liquid interface are critical processes in many important biological and chemical systems. An ion-transfer (IT) process is usually very fast, making it difficult to accurately measure its kinetic parameters. Nanoliquid/liquid interfaces supported at nanopipettes are advantageous approaches to study the kinetics of such ultrafast IT processes due to their high mass transport rate. However, correct measurements of IT kinetic parameters at nanointerfaces supported at nanopipettes are inhibited by a lack of knowledge of the nanometer-sized interface geometry, influence of the electric double layer, wall charge polarity, etc. Herein, we propose a new electrochemical characterization equation for nanopipettes and make a suggestion on the shape of a nano-water/1,2-dichloroethane (nano-W/DCE) interface based on the characterization and calculation results. A theoretical model based on the Poisson−Nernst−Planck equation was applied to systematically study how the electric double layer influences the IT process of cations (TMA + , TEA + , TPrA + , ACh + ) and anions (ClO 4 − , SCN − , PF 6 − , BF 4 − ) at the nano-W/DCE interface. The relationships between the wall charge conditions and distribution of concentration and potential inside the nanopipette revealed that the measured standard rate constant (k 0 ) was enhanced when the polarity of the ionic species was opposite to the pipette wall charge and reduced when the same. This work lays the right foundation to obtain the kinetics at the nano-liquid/liquid interfaces.
Carbon nano-onions (CNOs) as one of the carbon allotropes, possessing peculiar structure, are composed of multilayered concentric graphitic shells. CNOs can be classified into two types, including hollow polyhedral CNOs and core–shell structured CNOs. CNOs have attracted a great deal of attention because of their unique chemical and physical properties. Dependent on these properties they show potential applications in many areas such as solid lubricants, electrode materials in capacitors, as anode materials in lithium-ion batteries, and as catalyst support in fuel cells as well as biomedical field as pharmaceutical delivery platforms 1. However, to produce CNOs in quantity would be extremely challenging, especially hollow polyhedral carbon onions. At present, the preparation methods of CNOs reported included annealing of nanodiamonds at high temperature 2, thermal treatment of laser pyrolysis carbon blacks and co-sputtering 3, chemical vapour deposition 4 and so on. The common characteristic of these methods was the need for high temperature. Due to lack of controllable preparation methods, little research on hollow polyhedral CNOs has been reported. Here, we describe a simple electrochemical method to prepare high quality hollow polyhedral CNOs without the use of high temperature equipment. Electrochemical synthesis was carried out in a mixed solution of acetonitrile and toluene containing 0.10 M tetra-n-butylammonium perchlorate by using a three-electrode electrochemical system with a platinum plate electrode as the working electrode, a platinum plate electrode as the counter electrode and a Ag rod as the quasi reference electrode in a glove box, as shown in Figure 1a. Multi-potential steps electrolysis were employed. The obtained solid products after electrolysis for a few hours were dispersed in N-cyclohexylpyrrolidone by ultrasonication, and then the solid spherical CNOs and the hollow polyhedral CNOs were separated by gradient centrifugation, as shown in Figures 1b and 1c by high resolution transmission electron microscope characterization. Figure 1d displays TEM oblique image of a hollow polyhedral CNO. A series of images obtained from different tilt angles proved that CNOs were polyhedral hollow structures. Hollow carbon nano onions have an average diameter of 20 nm. The synthetic method is economical and environmentally friendly. Because the CNOs obtained by different methods owned different structures and properties, the properties and applications of the hollow polyhedral CNOs are under way. ACKNOWLEDGEMENT This work was supported by the National Natural Science Foundation of China (No 21675003 and 21974003). REFERENCES 1. Mykhailiv, O.; Zubyk, H.; Plonska-Brzezinska, M. E., Carbon nano-onions: Unique carbon nanostructures with fascinating properties and their potential applications. Inorganica Chimica Acta 2017, 468, 49-66. 2. Kuznetsov, V. L.; Chuvilin, A. L.; Butenko, Y. V.; Mal'kov, I. Y.; Titov, V. M., Onion-like carbon from ultra-disperse diamond. Chemical Physics Letters 1994, 222, 343-348. 3. Sano, N.; Wang, H.; Alexandrou, I.; Chhowalla, M.; Teo, K. B. K.; Amaratunga, G. A. J.; Iimura, K., Properties of carbon onions produced by an arc discharge in water. Journal of Applied Physics 2002, 92, 2783-2788. 4. Zhang, C.; Li, J.; Liu, E.; He, C.; Shi, C.; Du, X.; Hauge, R. H.; Zhao, N., Synthesis of hollow carbon nano-onions and their use for electrochemical hydrogen storage. Carbon 2012, 50, 3513-3521.
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