Xin Yao

Covalent Organic Frameworks Formed with Two Types of Covalent Bonds Based on Orthogonal Reactions

Covalent organic frameworks (COFs) are excellent candidates for various applications. So far, successful methods for the constructions of COFs have been limited to a few condensation reactions based on only one type of covalent bond formation. Thus, the exploration of a new judicious synthetic strategy is a crucial and emergent task for the development of this promising class of porous materials. Here, we report a new orthogonal reaction strategy to construct COFs by reversible formations of two types of covalent bonds. The obtained COFs consisting of multiple components show high surface area and high H2 adsorption capacity. The strategy is a general protocol applicable to construct not only binary COFs but also more complicated systems in which employing regular synthetic methods did not work.

Synergistic Effect of Mesoporous Co3O4 Nanowires Confined by N‐Doped Graphene Aerogel for Enhanced Lithium Storage

A one-step multipurpose strategy is developed to realize a sophisticated design that simultaneously integrates three desirable components of nitrogen dopant, 3D graphene, and 1D mesoporous metal oxide nanowires into one hybrid material. This facile synthetic strategy includes a one-step hydrothermal reaction followed by topotactic calcination. The utilization of urea as the starting reagent enables the precipitation of precursor nanowires and concurrent doping of nitrogen heteroatoms on graphene during hydrothermal reaction, while at the same time the graphene nanosheets are self-assembled to afford a 3D scaffold. Detailed characterizations on the final calcined product are conducted to confirm the phase purity, porosity, nitrogen composition, and morphology. The integration of two building blocks, i.e., flexible graphene nanosheets and Co3 O4 nanowires, enables various intertwining behaviors such as seaming, bridging, hooping, bundling, and sandwiching, of which synergistic effect substantially enhances electrical and electrochemical properties of the resultant hybrid. For lithium ion battery application of the hybrid, a remarkably high capacity more than 1200 mA h g(-1) (at 100 mA g(-1) ) is stabilized over 100 cycles with coulombic efficiency higher than 97%. Even during rapid discharge/charge processes (1000 mA g(-1) ), a reversible charge capacity of 812 mA h g(-1) is still retained after 230 cycles.

In Situ Integration of Anisotropic SnO2 Heterostructures inside Three-Dimensional Graphene Aerogel for Enhanced Lithium Storage

Three-dimensional (3D) graphene aerogel (GA) has emerged as an outstanding support for metal oxides to enhance the overall energy-storage performance of the resulting hybrid materials. In the current stage of the studies, metals/metal oxides inside GA are in uncrafted geometries. Introducing structure-controlled metal oxides into GA may further push electrochemical properties of metal oxide-GA hybrids. Using rutile SnO2 as an example, we demonstrated here a facile hydrothermal strategy combined with a preconditioning technique named vacuum-assisted impregnation for in situ construction of controlled anisotropic SnO2 heterostructures inside GA. The obtained hybrid material was fully characterized in detail, and its formation mechanism was investigated by monitoring the phase-transformation process. Rational integration of the two advanced structures, anisotropic SnO2 and 3D GA, synergistically led to enhanced lithium-storage properties (1176 mAh/g for the first cycle and 872 mAh/g for the 50th cycle at 100 mA/g) as compared with its two counterparts, namely, rough nanoparticles@3D GA and anisotropic SnO2@2D graphene sheets (618 and 751 mAh/g for the 50th cycle at 100 mA/g, respectively). It was also well-demonstrated that this hybrid material was capable of delivering high specific capacity at rapid charge/discharge cycles (1044 mAh/g at 100 mA/g, 847 mAh/g at 200 mA/g, 698 mAh/g at 500 mA/g, and 584 mAh/g at 1000 mA/g). The in situ integration strategy along with vacuum-assisted impregnation technique presented here shows great potential as a versatile tool for accessing a variety of sophisticated smart structures in the form of anisotropic metals/metal oxides within 3D GA toward useful applications.

Fabrication of novel hybrid nanoflowers from boron nitride nanosheets and metal–organic frameworks: a solid acid catalyst with enhanced catalytic performance

A double solvent replacement method was employed for the synthesis of novel hybrid nanoflowers from boron nitride nanosheets (BNNSs) and the metal–organic framework (MOF) MIL-53 in aqueous solutions under hydrothermal treatments. The strong binding ability of aluminum ions onto the surface of BNNSs determines the 3D flowerlike architectures of the BNNSs/MOFs hybrid, and the BNNSs act as a structure-directing template. The BNNSs/MOFs showed an enhanced catalytic activity in the acetalization of benzaldehyde with methanol owing to the facilitated diffusion process in the hierarchical architectures.

Room-temperature synthesis of bimetallic Co–Zn based zeolitic imidazolate frameworks in water for enhanced CO2 and H2 uptakes

A simple methodology was explored to access highly robust bimetallic Co–Zn based zeolitic imidazolate frameworks at room temperature. By tuning the content of Co and Zn precursors, CoZn-ZIF-8 frameworks with varying Co : Zn (25–90% of Co2+ as confirmed by ICP-AES results) were synthesized. Electron micrographs and powder X-ray diffraction (PXRD) patterns confirmed the formation of bimetallic CoZn-ZIF-8 frameworks of 150–300 nm size, where Zn atoms were partially replaced by Co atoms. The as-synthesized CoZn-ZIF-8 frameworks displayed a tuned pore size, pore volume and surface area, with the highest surface area (enhanced by ∼40% compared to Zn-ZIF-8) and pore volume (enhanced by ∼33% compared to Zn-ZIF-8) for Co75Zn25-ZIF-8. The as-synthesized CoZn-ZIF-8 frameworks also displayed enhanced CO2 and H2 uptakes at 298 K and 77 K, respectively, at 1 bar. Noteworthy enhancement of ∼30% in the CO2 and ∼23% in the H2 uptake was displayed by Co75Zn25-ZIF-8 frameworks as compared to Zn-ZIF-8 under analogous conditions.

Fast-Clearable Nanocarriers Conducting Chemo/Photothermal Combination Therapy to Inhibit Recurrence of Malignant Tumors

Inhomogeneous heating by photothermal therapy (PTT) during cancer treatment often results in the recurrence of tumors. Thus, integrating PTT with chemotherapy (CHT) may provide a complementary treatment for enhanced therapeutic efficiency. Herein, this study develops a hollow structured polymer-silica nanohybrid (HPSN) as a nanocarrier to simultaneously deliver the anticancer drug paclitaxel and photothermal agent palladium phthalocyanine to tumors through enhanced permeation and the retention effect. A combinational CHT/PTT therapy on mice bearing aggressive tumor grafts is conducted. The highly malignant tumor model, which recurs after sole treatment of PTT, can be eradicated by the combined CHT/PTT treatment. In addition, most of the off-targeted HPSN nanocarriers can be excreted through a hepatobiliary pathway in about 10 d. Serology results show that the fast-clearable HPSN can significantly reduce the side effect of the loaded paclitaxel drug. The present work provides an alternative approach for combinational cancer treatment with high therapeutic efficiency.

A theoretical study on the surface and interfacial properties of Ni3P for the hydrogen evolution reaction

We report a comprehensive density functional theory (DFT) study on the stability, geometric structure, electronic characteristics, and catalytic activity for the hydrogen evolution reaction (HER) on low-index Ni3P crystal surfaces, namely, the (001), (100), (110), (101) and (111) planes with different surface terminations. The results indicate that P-rich and some stoichiometric surfaces are thermodynamically stable. Eight stable surfaces were selected to investigate the electronic characteristics and catalytic activity. The (110)B facet of Ni3P is indispensable for the HER, because it not only displays improved electrocatalytic activity, but also possesses suitable potential and high stability. Increasing the active sites through doping or enlarging the surface area could be a useful strategy to improve the HER activity further. Furthermore, it was found that Ni3P requires higher energies for decomposition in the absence of O2, although it is thermodynamically unstable in aqueous solutions with most pH values and potentials. This study provides important insights into the surface properties of Ni3P for water splitting and opens up an exciting opportunity to optimize the performance of solar energy conversion devices by synthesizing preferentially exposed catalyst facets.

Scalable Synthesis of Honeycomblike V2O5/Carbon Nanotube Networks as Enhanced Cathodes for Lithium-Ion Batteries

A green and scalable route to form a honeycomblike macroporous network by homogeneously weaving V2O5 nanowires and carbon nanotubes (CNTs) was developed. The intertwinement between V2O5 nanowires and CNTs not only integrates nanopores into the macroporous system but also elevates the collection and transfer of charges through the conductive network. The unique combination of V2O5 nanowires and CNTs renders the composite monolith with synergic properties for substantially enhancing electrochemical kinetics of lithiation/delithiation when used as a lithium-ion battery (LIB) cathode. This work presents a useful approach for a large-scale production of cellular monoliths as high-performance LIB cathodes.

Using elastin protein to develop highly efficient air cathodes for lithium-O2 batteries

Transition metal-nitrogen/carbon (M-N/C, M = Fe, Co) catalysts are synthesized using environmentally friendly histidine-tag-rich elastin protein beads, metal sulfate and water soluble carbon nanotubes followed by post-annealing and acid leaching processes. The obtained catalysts are used as cathode materials in lithium-O2 batteries. It has been discovered that during discharge, Li2O2 nanoparticles first nucleate and grow around the bead-decorated CNT regions (M-N/C centres) and coat on the catalysts at a high degree of discharge. The Fe-N/C catalyst-based cathodes deliver a capacity of 12,441 mAh g(-1) at a current density of 100 mA g(-1). When they were cycled at a limited capacity of 800 mAh g(-1) at current densities of 200 or 400 mA g(-1), these cathodes showed stable charge voltages of ∼3.65 or 3.90 V, corresponding to energy efficiencies of ∼71.2 or 65.1%, respectively. These results are considerably superior to those of the cathodes based on bare annealed CNTs, which prove that the Fe-N/C catalysts developed here are promising for use in non-aqueous lithium-O2 battery cathodes.