Zhongtao Li

Cu–N Dopants Boost Electron Transfer and Photooxidation Reactions of Carbon Dots

The broadband light-absorption ability of carbon dots (CDs) has inspired their application in photocatalysis, however this has been impeded by poor electron transfer inside the CDs. Herein, we report the preparation of Cu-N-doped CDs (Cu-CDs) and investigate both the doping-promoted electron transfer and the performance of the CDs in photooxidation reactions. The Cu-N doping was achieved through a one-step pyrolytic synthesis of CDs with Na2 [Cu(EDTA)] as precursor. As confirmed by ESR, FTIR, and X-ray photoelectron spectroscopies, the Cu species chelates with the carbon matrix through Cu-N complexes. As a result of the Cu-N doping, the electron-accepting and -donating abilities were enhanced 2.5 and 1.5 times, and the electric conductivity was also increased to 171.8 μs cm(-1) . As a result of these enhanced properties, the photocatalytic efficiency of CDs in the photooxidation reaction of 1,4-dihydro-2,6-dimethylpyridine-3,5-dicarboxylate is improved 3.5-fold after CD doping.

Graphene enhanced carbon-coated tin dioxide nanoparticles for lithium-ion secondary batteries

A one-step, scalable method has been developed to prepare SnO2 based carbon materials. Their performances as anodes for lithium-ion batteries can be improved through simultaneous growth of SnO2 nanoparticles, a carbonaceous polymer coating and “doping” of graphene oxide (GO) by thermal treatment. Detailed characterization of the resulting composite materials using transmission electron microscopy and X-ray diffraction suggests that “doping” a certain amount of GO could clearly change the crystallinity and distribution of SnO2 nanoparticles in the mixture. The SnO2 based carbon material exhibits a stable reversible capacity of 720 mA h g−1 after 70 cycles as the anode of lithium-ion batteries, indicating that the composites might have a promising future application in Li-ion batteries.

Synthesis of nanocomposites with carbon–SnO2 dual-shells on TiO2 nanotubes and their application in lithium ion batteries

Through the introduction of well-distributed tin oxide nanocrystals on the surface of pre-prepared TiO2 nanotubes and carbon coating, novel TiO2/SnO2–C double-shell nanotubes have been synthesized. As an anode material of Li-ion batteries (LIBs), DSNTs exhibit excellent long-term cycling stability (256.0 mA h g−1 at 1 A g−1 after 710 cycles) and satisfactory rate capability, which are ascribed to the synergetic effects of a unique combination of material properties in the well-designed conductive matrix: high volume stable titanium dioxide to form a one-dimensional (1D) core section to maintain the structure, large theoretical capacity tin oxide as a functional layer to increase capacity and highly conductive carbon as a buffer layer to accelerate charging rate.

Lamellar Metal Organic Framework-Derived Fe–N–C Non-Noble Electrocatalysts with Bimodal Porosity for Efficient Oxygen Reduction

Developing highly efficient and stable non-Pt electrocatalysts for the oxygen reduction reaction (ORR) to replace the state-of-the-art noble metal is essential for commercialization of fuel cells. Fe-N-C-based electrocatalysts are considered as a promising alternative to commercial Pt/C. An efficient electrocatalyst commonly requires large density of active site, high surface area, and desirable porosity, especially multimodal porosity with both large pores for efficient mass transfer and small pores for exposing as many active sites as possible. Herein, a lamellar metal organic framework (MOF) was developed as a precursor to directly achieve such a highly active Fe-N-C electrocatalyst with high surface area and desirable bimodal porosity. The mesopores arising from the special lamellar morphology of MOF benefits efficient mass transfer, and the nanopores resulting from pyrolysis of the MOF makes the majority of active sites accessible to electrolyte and thus effective for ORR. Uniform distribution of active elements N, C, and Fe at the molecular level in MOF precursor ensures abundant well-dispersed highly active sites in the catalyst. As a result, the catalyst exhibited superior ORR electrocatalytic activity and stability to commercial Pt/C. This strategy, using rarely reported lamellar MOF to prepare ORR catalysts with the merits mentioned, could inspire the exploration of a wide range of electrocatalysts from lamellar MOF precursors for various applications.

Facile hydrothermal synthesis of SnO2/C microspheres and double layered core–shell SnO2 microspheres as anode materials for Li-ion secondary batteries

SnO2/C microspheres and double layered core–shell SnO2 microspheres have been synthesized by a facile hydrothermal method with a post heat-treatment. The soluble starch used as carbon source and the mass ratio of starch to SnCl4·5H2O play key roles in the formation of SnO2/C microspheres, and the hydrothermal synthesis mechanism of SnO2/C microspheres has been proposed. SnO2/C-1.0 microspheres (the mass ratio of soluble starch to SnCl4·5H2O is 1:1) with good spherical shape and 34.91 wt% of SnO2 exhibit superior rate capability and cyclic stability, while double layered core–shell SnO2 microspheres show improved electrochemical performance compared to SnO2 particles. The electrode based on SnO2/C-1.0 microspheres delivers a reversible discharge capacity of 568 mA h g−1 at a constant current density of 100 mA g−1 in the second cycle, and 379 mA h g−1 (67% retention) is retained after the 50th cycle, suggesting SnO2/C microspheres are promising candidates for energy storage.

Cation modulating electrocatalyst derived from bimetallic metal–organic frameworks for overall water splitting

Metal carbides with unique electrical properties and high catalytic efficiency have attracted tremendous interest for applications involving water electrolysis. In this paper the design of a novel cation modulating electrocatalyst Ni3ZnC0.7 using homogeneous bimetallic metal–organic frameworks (NiZn-MOFs) as precursor is reported. The synergistic effect between the unique chemical properties and nanostructure endows Ni3ZnC0.7 with a remarkable electrocatalytic performance. The balance of Ni(0) and Ni(II) achieved by Zn modulation is beneficial to both the hydrogen evolution reaction and the oxygen evolution reaction under alkaline conditions. The bifunctional catalyst, Ni3ZnC0.7, can drive overall water splitting through a symmetrical double electrode at a current density of 10 mA cm−2 with only 1.65 mV, and also shows excellent stability without obvious degradation after 24 h of operation, which makes it a promising noble metal free electrocatalyst. This easy preparation method for Ni3ZnC0.7 makes it a promising candidate for a practical answer to water splitting. Furthermore, this cation modulating strategy provides an ingenious way to realize the precise control of the catalysts and can be extended to the synthesis of various novel nanomaterials.

BODIPY-based photosensitizers with intense visible light harvesting ability and high 1O2 quantum yield in aqueous solution

A novel method to enhance the singlet oxygen quantum yield of photosensitizers in aqueous solution has been developed by introducing an electron-withdrawing group into BODIPY. B-2 was prepared based on this method and shows intense light harvesting ability (e = 6.8 × 104 M−1 cm−1 at 643 nm) and high 1O2 quantum yield in aqueous solution (Φ = 0.21). B-2 has been successfully used as an 1O2 sensitizer for the photo-oxidation of 1,5-dihydroxynaphthalene. This method substantially improves the photooxidation capability and photostability of 1O2 sensitizers in aqueous solution.

Metal–Organic Frameworks Mediated Synthesis of One-Dimensional Molybdenum-Based/Carbon Composites for Enhanced Lithium Storage

Molybdenum (Mo)-based compounds with properly engineered nanostructures usually possess improved reversible lithium storage capabilities, which offer great promise to boost the performance of lithium-ion batteries (LIBs). Nevertheless, a lack of efficient and high-yield methods for constructing rational nanostructures has largely restricted the application of these potentially important materials. Herein we demonstrate a metal-organic frameworks (MOFs) mediated strategy to successfully synthesize a series of one-dimensional Mo-based/carbon composites with distinct nanostructures. In this process, starting from well-designed MoO3 nanorods, the crystal control growth is first proposed that a layer of MOFs is achieved to be controllably grown on surfaces of MoO3, forming an obvious core-shell structure, and then the adopted precursor can be in situ transformed into MoO2 or Mo2C which are both well confined in conductive porous carbons through direct carbonization at different temperatures, where the MOFs shell serve as both carbon sources and the reactant to react with MoO3 simultaneously. Benefiting from this design, all optimized products exhibit enhanced electrochemical performances when evaluated as anode materials for LIBs, especially the hollow MoO2/C and core-shell Mo2C/C electrodes, show best reversible capacities up to 810 and 530 mAh g-1 even after 600 cycles at a current density of 1 A g-1, respectively. So this work may broaden the application of MOFs as a kind of coating materials and elucidates the attractive lithium storage performances of molybdenum-based compounds.

Controllable growth of MnOx dual-nanocrystals on N-doped graphene as lithium-ion battery anode

Nanocomposites containing Mn3O4 and MnOOH dual-nanocrystals on N-doped graphene sheets were prepared using a solvothermal method. Nanostructure and rate of dual-nanocrystals in the composites can be adjusted, having effects on their electrochemical performance. The nanohybrid NG-36 is composed of 1D MnOOH nanowires, Mn3O4 nanotetragonals and electroconductive N-doped graphene matrix. Experimental data for NG-36 reveals a high rechargeable specific capacity of 341.5 mA h g−1 at a current density 3 A g−1 after 500 cycles, resulting from synergetic effects among the components.

Synergistic Effects between Doped Nitrogen and Phosphorus in Metal-Free Cathode for Zinc-Air Battery from Covalent Organic Frameworks Coated CNT

A covalent organic framework that is composed of hexachlorocyclotriphosphazene and dicyanamide has been coated on CNT to prepare metal-free oxygen reduction reaction catalyst through thermal polymerization of the Zn-air battery cathode. The N,P-codoped nanohybrids have highly porous structure and active synergistic effect between graphitic-N and -P, which promoted the electrocatalytic performance. The electrocatalysts exhibits remarkable half-wave potential (-0.162 V), high current density (6.1 mA/cm-2), good stability (83%), and excellent methanol tolerance for ORR in alkaline solution. Furthermore, the N,P-codoped nanohybrids were used as an air electrode for fabrication of a high performance Zn-air battery. The battery achieves a high open-circuit potential (1.53 V) and peak power density (0.255 W cm-2). Moreover, the effect of N,P codoping on the conjugate carbon system and the synergistic effect between graphitic-N and P have been calculated through density functional theory calculations, which are essentially in agreement with experimental data.