Ren Cai

Synthesis of cobalt phosphides and their application as anodes for lithium ion batteries

A facile thermal decomposing method has been developed for the fabrication of Co(x)P nanostructures with controlled size, phase, and shape (e.g., Co(2)P rod and spheres, CoP hollow and solid particles). An amorphous carbon layer could be introduced by the carbonization of organic surfactants from the precursors. The electrochemical performance of typical CoP and Co(2)P samples as anode materials has been investigated and the CoP hollow nanoparticle with carbon coating layer depicts good capacity retention and high rate capability (e.g., specific capacity of 630 mA h g(-1) at 0.2 C after 100 cycles, and a reversible capacity of 256 mA h g(-1) can be achieved at a high current rate of 5 C).

Monodispersed Ag nanoparticles loaded on the PVP-assisted synthetic Bi2O2CO3 microspheres with enhanced photocatalytic and supercapacitive performances

Uniform 1 μm-sized Bi2O2CO3 microspheres constructed by nanoplates with a thickness of about 12 nm have been obtained through a facile hydrothermal method. Ag is deposited on the surface of Bi2O2CO3via a subsequent facile photoreduction process. In the synthesis process, polyvinylpyrrolidone (PVP) is used as a reactant that not only provides C and O sources but also serves as a template to induce the nanoplate-assembly to form microspheres. With the addition of KCl in the synthesis, the size of the Bi2O2CO3 microspheres can be reduced from ∼6 μm to ∼1 μm. It is demonstrated that PVP and KCl play key roles in the formation of such hierarchical microspheres. The obtained Bi2O2CO3 and novel Ag/Bi2O2CO3 composites are evaluated for photocatalytic and supercapacitive applications. The test result of the photocatalytic activity demonstrates that 0.6 wt% loading of Ag on the Bi2O2CO3 microspheres exhibits significantly enhanced activity for the photodegradation of methyl orange (MO) dye, compared with Bi2O2CO3. The enhanced photocatalytic activity can be attributed to the Ag deposits acting as electron traps and the high surface area of Bi2O2CO3. Furthermore, the Ag/Bi2O2CO3 composites are primarily evaluated as supercapacitor electrodes, which deliver specific capacities of 620 and 361 F g−1 at current densities of 1 and 5 A g−1, respectively.

Single Nanoparticle to 3D Supercage: Framing for an Artificial Enzyme System

A facile strategy has been developed to fabricate Cu(OH)2 supercages (SCs) as an artificial enzyme system with intrinsic peroxidase-mimic activities (PMA). SCs with high catalytic activity and excellent recyclability were generated via direct conversion of amorphous Cu(OH)2 nanoparticles (NPs) at room temperature. More specifically, the process that takes a single nanoparticle to a 3D supercage involves two basic steps. First, with addition of a copper-ammonia complex, the Cu(2+) ions that are located on the surface of amorphous Cu(OH)2 NPs would evolve into a fine lamellar structure by coordination and migration and eventually convert to 1D nanoribbons around the NPs. Second, accompanied by the migration of Cu(2+), a hollow cavity is generated in the inner NPs, such that a single nanoparticle eventually becomes a nanoribbon-assembled 3D hollow cage. These Cu(OH)2 SCs were then engineered as an artificial enzymatic system with higher efficiency for intrinsic PMA than the peroxidase activity of a natural enzyme, horseradish peroxidase.

Multiwalled carbon nanotubes–V2O5 integrated composite with nanosized architecture as a cathode material for high performance lithium ion batteries

Multiwalled carbon nanotubes (MWCNTs)–V2O5 integrated composite with nanosized architecture has been synthesized through hydrothermal treatment combined with a post-sintering process. During the hydrothermal reaction, protonated hexadecylamine (C16H33NH3+) acts as an intermediator, which links the negatively charged vanadium oxide layer with the mixed-acid pretreated MWCNTs by weak electrostatic forces to form a three-phase hybrid (MWCNTs–C16–VOx). MWCNT–V2O5 composite and V2O5 nanoparticles can be obtained by sintering MWCNTs–C16–VOx at 400 and 550 °C in air, respectively. Among them, MWCNTs–V2O5 possesses better electrochemical performance as a cathode material for lithium ion batteries (LIBs). The unique porous nanoarchitecture of MWCNTs–V2O5 provides a large specific surface area and a good conductive network, which facilitates fast lithium ion diffusion and electron transfer. Additionally, the uniformly dispersed MWCNTs conducting network also behaves as an effective buffer which can relax the strain generated during charge–discharge cycles. Electrochemical tests reveal that MWCNTs–V2O5 could deliver a superior specific capacity (402 mA h g−1 during initial discharge at a current density of 100 mA g−1 between 1.5 and 4 V versus Li/Li+), good cycling stability (222 mA h g−1 after 50 cycles) and high rate capability (194 mA h g−1 at a current density of 800 mA g−1).

Aptasensor with Expanded Nucleotide Using DNA Nanotetrahedra for Electrochemical Detection of Cancerous Exosomes

Exosomes are extracellular vesicles (50-100 nm) circulating in biofluids as intercellular signal transmitters. Although the potential of cancerous exosomes as tumor biomarkers is promising, sensitive and rapid detection of exosomes remains challenging. Herein, we combined the strengths of advanced aptamer technology, DNA-based nanostructure, and portable electrochemical devices to develop a nanotetrahedron (NTH)-assisted aptasensor for direct capture and detection of hepatocellular exosomes. The oriented immobilization of aptamers significantly improved the accessibility of an artificial nucleobase-containing aptamer to suspended exosomes, and the NTH-assisted aptasensor could detect exosomes with 100-fold higher sensitivity when compared to the single-stranded aptamer-functionalized aptasensor. The present study provides a proof-of-concept for sensitive and efficient quantification of tumor-derived exosomes. We thus expect the NTH-assisted electrochemical aptasensor to become a powerful tool for comprehensive exosome studies.

Synthesis of Porous Amorphous FePO4 Nanotubes and Their Lithium Storage Properties

The controlled synthesis of functional materials with designed nanostructures has led to many unique applications, including optoelectronic devices, sensors, battery electrodes, and drug delivery. To prepare advanced electrode materials for energy storage devices (for example, lithium ion batteries (LIBs) or supercapacitors), it is desired to develop nanostructures with features such as: 1) a high surface area for the effective interaction between the electrolyte and active materials; 2) a fine feature size to shorten the charge carrier diffusion distance; 3) hollow channels to allow the effective penetration throughout the electrodes; and 4) some void space to buffer mechanical strain that may be generated during the cycling process. For examples, double-shelled nanocapsules of V2O5-based composites has a reversible capacity of 947 mAh g 1 at a rate of 250 mA g 1 and they retain a high capacity of 673 mAh g 1 after 50 cycles as high-performance anode materials for LIBs; Co3O4 porous nanocages show capacities of up to 1465 mAh g 1 that are attained after 50 cycles at a current density of 300 mA g 1 for LIBs. Porous SnO2 nanotubes delivered high specific capacity (540-600 mAh g ) and good cyclability (0.0375 % capacity loss per cycle) in rechargeable LIBs as anode electrode materials. Based on the above discussion, it is attractive to build nanostructures with a hollow interior and porous nature, which has been rarely demonstrated for cathode materials of lithium ion batteries. Herein, we report an oil-phase synthesis of porous aFePO4 nanotubes with a pore size of 2–10 nm. We first prepared Fe2O3 nanotubes and then reacted them in the oil phase with alkyl phosphonic/alkyl phosphinic acids (RP(O)(OH)2/R HP(O)(OH), R and R are alkyl groups ACHTUNGTRENNUNG(CH2)nCH3, n= 5–17), which exist as the impurities in technical-grade trioctylphosphine oxide (TOPO). The second step converted the Fe2O3 into iron alkyl phosphate (Fe2ACHTUNGTRENNUNG(RPO3)3/Fe ACHTUNGTRENNUNG(R1HPO2)3) and simultaneously generated pores in the tubes owing to etchingby the weak acid. After annealing at 350 8C in air, the samples were transferred to a-FePO4 porous nanotubes. Furthermore, the cathode performance of these porous a-FePO4 nanotubes was examined in a LIB half-cell. The results showed that these porous a-FePO4 nanotubes exhibited a reversible specific capacity of 130.4 mAh g 1 during the 35th cycle at a current density of 35.6 mA g 1 (C/5), which was considered better than that of bulk a-FePO4. To prepare the FePO4 samples, we first synthesized Fe2O3 nanotubes according to reported work (Supporting Information, Figures S1,S2). These Fe2O3 nanotubes were dispersed into TOPO (90 %, technical grade) and heating the mixture at about 308 8C under a degassing condition with a rotary pump. After 50 min, the solution was cooled to room temperature and we collected the precipitate by repeated centrifuging and washing with acetone and methanol. We then annealed the precipitates at 350 8C for 60 min in air to further promote the reaction and remove possibly attached surface ligands. The field emission scanning electron microscopy (FESEM) image (Figure 1 a) reveals that the obtained samples are nanotubes, which are highly uniform with length of about 250 nm and width of about 100 nm. The structures of these nanotubes were further studied by means of transmission electron microscopy (TEM) and selectedarea electron diffraction (SAED). The low-magnification TEM image (Figure 1 b) shows that these nanotubes are [a] R. Cai, Dr. Y. Du, W. Zhang, H. Tan, X. Huang, H. Liu, J. Zhu, S. Peng, J. Chen, Prof. Y. Huang, Prof. Q. Zhang, Prof. H. Zhang, Prof. Q. Yan School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore) E-mail : alexyan@ntu.edu.sg [b] C. Chen, Prof. R. Xu School of Chemistry and Biochemistry Engineering Nanyang Technological University 50 Nanyang Avenue, Singapore 639798 (Singapore) [c] Prof. T. M. Lim School of Life Science and Chemical Technology Ngee Ann Polytechnic, Singapore 599489 (Singapore) [d] Prof. Q. Yan Energy research Institute @ NTU, Nanyang Technological University, TUM CREATE Centre for Electromobility@NTU, Singapore 637459(Singapore) [e] T. Zeng, H. Yang, Prof. Y. Zhao, Prof. H. Wu National Center for Nanoscience and Technology of China, Beijing 100190 (P. R. China), Key Laboratory for Biomedical Effects of Nanomaterials & Nanosafety, Institute of High Energy Physics Chinese Academy of Sciences, Beijing 100049 (P. R. China) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201203935.

Carbon buffered-transition metal oxidenanoparticle- graphene hybrid nanosheets as high-performance anode materials for lithium ion batteries

In this article, we report a simple and general method for the synthesis of carbon buffered-metal oxidenanoparticle (NP)–graphene hybrid 2D nanosheets, which include C-SnO2–rGO and C-Fe2O3–rGO nanosheets. For the preparation of these anodes, tannic acid (TA), a kind of polyphenol extracted from plants, was used as a dispersing agent to introduce a metal precursor on the surface of rGO, and the metal precursor was subsequently converted to the corresponding metal oxide NPs by thermal annealing in a vacuum. During the thermal annealing process, TA was decomposed to form carbon materials, which acted as a buffering matrix to effectively suppress the aggregation and pulverization of the active NPs during the electrochemical performances. It is found that the as-prepared C-SnO2–rGO and C-Fe2O3–rGO nanosheets both exhibited high reversible capacity and rate capability. After 100 discharge/charge cycles, the C-SnO2–rGO nanosheet delivered the reversible capacity of 633.2 mA h g−1 at a current density of 200 mA g−1 with extremely low capacity fading (0.32 mA h g−1 per cycle), and it can deliver discharge capacities of 641.3, 526.5, 452.7, 408.1 and 379.5 mA h g−1 in the 10th cycle at current densities of 200, 400, 800, 1200 and 1600 mA g−1, respectively. Upon return to a cycling rate of 200 mA g−1, the C-SnO2–rGO can maintain a specific capacity of 607.0 mA h g−1 even after 35 cycles. As for the C-Fe2O3–rGO nanosheet, it can deliver 504.1 mA h g−1 at a current density of 500 mA g−1 after 100 cycles, and the corresponding discharge capacities in the 10th cycle at current densities of 1000, 1500 and 2000 mA g−1 are 365.9, 319.0 and 288.6 mA h g−1, respectively.

Controlled Synthesis of Double-Wall a-FePO4 Nanotubes and their LIB Cathode Properties

Double-wall amorphous FePO4 nanotubes are prepared by an oil-phase chemical route. The inward diffusion of vacancies and outward diffusion of ions through passivation layers result in double-wall nanotubes with thin walls. Such a process can be extended to prepare hollow polydedral nanocrystals and hollow ellipsoids. The double-wall FePO4 nanotubes show interesting cathode performance in Li ion batteries.

Synthesis of Porous, Hollow Metal MCO3 (M=Mn, Co, Ca) Microstructures and Adsorption Properties Thereof

Porous, hollow metal carbonate microstructures show many unique properties, and are attractive for various applications. Herein, we report the first demonstration of a general strategy to synthesize hollow metal carbonate structures, including porous MnCO3 hollow cubics, porous CoCO3 hollow rhombuses and porous CaCO3 hollow capsules. For example, the porous, hollow MnCO3 microcubes show larger Brunauer-Emmett-Teller (BET) surface areas of 359.5 m(2)  g(-1) , which is much larger than that of solid MnCO3 microcubics (i.e., 12.03 m(2)  g(-1) ). As a proof of concept, these porous MnCO3 hollow microcubes were applied to water treatment and exhibited an excellent ability to remove organic pollutants in waste water owing to their hollow structure and large specific surface area.

Solvothermal-induced conversion of one-dimensional multilayer nanotubes to two-dimensional hydrophilic VOx nanosheets: Synthesis and water treatment application

Ultrathin 2D nanostructures have shown many unique properties and are attractive for various potential applications. Here, we demonstrated a strategy to synthesize ultrathin VOx nanosheets. The as-obtained ultrathin VOx nanosheets showed a large Brunauer-Emmett-Teller (BET) surface area of 136.3 m2 g(-1), which is much larger than that of 1D multilayer VOx nanotubes. As a proof of concept, these hydrophilic ultrathin nanosheets were applied in water treatment and exhibited excellent absorption capability to remove Rhodamine B (RhB) in wastewater owing to their large specific surface area, good hydrophilic property, and more negative zeta potential. In addition, this method could be generalized to prepare other 2D nanostructures with great potential for various attractive applications.