Zhaohui Ren

Facile synthesis of single-crystalline mesoporous α-Fe2O3 and Fe3O4 nanorods as anode materials for lithium-ion batteries

In this work, single-crystalline α-FeOOH nanorods with a length of 400–700 nm and a diameter of 20–80 nm were successfully synthesized via a facile template-free hydrothermal method. Single-crystalline mesoporous α-Fe2O3 and Fe3O4 nanorods could be obtained from these α-FeOOH precursors after calcining at 350 °C in air and 500 °C in nitrogen, respectively. The as-prepared single-crystalline mesoporous α-Fe2O3 and Fe3O4 nanorods exhibited a large specific surface area and porosity, effectively enhancing the electrochemical reaction area and accommodate the strain during the charge–discharge cycling process.

Self‐Templated Synthesis of Single‐Crystal and Single‐Domain Ferroelectric Nanoplates

Low-dimensional nanomaterials, such as nanowires and nanotubes, 3] have received extensive attention because of their fascinating catalysis, optics, and electronics 7] properties, which offer the opportunity to fabricate nanodevices. Much attention has been paid to materials with two-dimensional (2D) nanostructure because of their unique electronic, magnetic, and storage properties. In particular, the recent development of stable graphene has stimulated great interest in studying free-standing 2D nanomaterials. So far, a variety of 2D free-standing materials with nanostructure, such as PbS nanosheets, WO3 nanoplates, [10] CeO2 nanoplates, [11] MoS2 nanoflakes, 13] and TiO2 nanosheets, [4] have been successfully synthesized. Compared to these simple compounds, 2D free-standing, single-crystal multicomponent oxide nanomaterials, such as ferroelectric oxides, have been rarely reported because of the relatively complex crystal structures and rigid crystalline properties of these oxides. Ferroelectric oxide nanomaterials, such as PbTiO3 (PT), Pb(Zr,Ti)O3, and BaTiO3, have versatile properties for various technical applications ranging from nonvolatile ferroelectric random access memories (NFERAMs) to electromechanical applications. 15] Among these nanomaterials, 2D free-standing, single-crystal ferroelectric materials are highly attractive because of their potential performances. For example, ultrathin single crystals of BaTiO3 [16,17] prepared by focused ion beam (FIB) microscopy have been used as single-crystal capacitors with thicknesses down to about 65 nm. These ferroelectric platelets fabricated by FIB have greatly improved our understanding of the fundamental properties of thin films. However, recent theoretical research predicts that ferroelectric nanodiscs could even favor an ultimate NFERAM density of 60 10 bits per square inch as well as a new toroid moment. In contrast to the conventional properties, the surface chemistry of ferroelectric oxides only gradually became an active field of research. In particular, it has been predicted that CO and NO catalysis could be favored on ultrathin Pt(100) films supported on ferroelectric PbTiO3. [22] Various methods have so far been applied to fabricate 0D and 1D ferroelectric nanomaterials, including templated methods, sol-gel processing, 28] soft-chemistry routes, solvothermal/hydrothermal reactions, 31] and electrospinning techniques. 33] Despite much effort, there is still an absence of a simple wet-chemistry method to prepare 2D single-crystal ferroelectric nanomaterials, such as nanoplates and nanodiscs. Here we report, for the first time, that freestanding, single-crystal PT nanoplates can be synthesized by a facile hydrothermal method. The characterization of the microstructure by X-ray diffraction (XRD) and high-resolution transmussion electron microscopy (HRTEM) demonstrates that these PT nanoplates, with side lengths of 600– 1100 nm and heights of about 150 nm, grow along the ab plane of the tetragonal perovskite structure and that {001} facets at the top and bottom surfaces are exposed. The “self-templated” crystal growth has been employed to discuss the mechanism for the formation of PT nanoplates under hydrothermal conditions. Electrostatic force microscopy in the dynamic contact mode (DC-EFM) of operation was also used to study the ferroelectric properties of the PT nonaplates. Furthermore, the catalytic performance of the nanoplates for the oxidation of carbon monoxide (CO) has been evaluated. In brief, tetragonal-phase PT nanoplates were synthesized by a hydrothermal method at 200 8C by using 6m KOH. Figure 1a shows a typical XRD pattern (JCPDS 70-0746) of PT nanoplates prepared by the hydrothermal process at 200 8C for 12 h with 6m KOH, and indicates that the product has a pure tetragonal perovskite PT structure. More importantly, the intensity of the (001) diffraction peak is dramatically higher than that of (100), which is opposite to the case in conventional perovskite PT (JCPDS 70-0746). This observation reveals that {001} crystal planes are prevailent in the sample. Scanning electron microscopy (SEM) and TEM analysis show that the products consist of well-defined structures with a rectangular outline and a side length of 600–1100 nm (Figure 1b,c). The HRTEM image (Figure 1d) of a PT nanoplate shows a clear crystal lattice with uniform interplanar spacings of 0.390 nm and 0.390 nm, which correspond to the tetragonal (100) and (010) planes, respectively, and indicate that the PT nanoplates grow along the ab plane of the perovskite structure. The effect of the KOH concen[*] C. Y. Chao, Dr. Z. H. Ren, Z. Xiao, Z. Y. Liu, Dr. G. Xu, J. Q. Mai, Dr. X. Li, Dr. G. Shen, Dr. G. R. Han State Key Laboratory of Silicon Materials Department of Materials Science and Engineering Cyrus Tang Center for Sensor Materials and Application Zhejiang University, Hangzhou 310027 (P.R. China) E-mail: renzh@zju.edu.cn hgr@zju.edu.cn

PbTiO3 nanofibers with edge-shared TiO6 octahedra.

A new tetragonal phase of PbTiO(3) was discovered, in which each TiO(6) octahedron pair shares an edge and stacks over following pairs in an interlaced manner to form a one-dimensional (1D) columned structure along the c-axis. This new tetragonal phase of PbTiO(3) transforms into a normal perovskite phase in air at elevated temperature.

Mesoporous silica nanoparticles with manipulated microstructures for drug delivery.

A range of mesoporous silica nanoparticles (MSNs) with controlled microstructural characteristics were successfully prepared via the binary surfactant templated synthesis approach with varied concentration of triblock copolymer Pluronic F127. The relationship between the MSNs structural evolution and the surfactant concentration was extensively discussed. Ibuprofen (IBU) was loaded as drug model to uncover the in vitro drug releasing kinetics. It was found that the quantity of the drug loaded mainly depended on the specific surface area, while the drug releasing rate was dominantly determined by the length and curvature of the mesopores. This study has uncovered the core influential factors of MSNs system on its drug releasing properties, and thus demonstrated a facile approach to prepare MSNs with manipulated structural characteristics for drug delivery applications.

A Fibrous Localized Drug Delivery Platform with NIR-Triggered and Optically Monitored Drug Release

Implantable localized drug delivery systems (LDDSs) with intelligent functionalities have emerged as a powerful chemotherapeutic platform in curing cancer. Developing LDDSs with rationally controlled drug release and real-time monitoring functionalities holds promise for personalized therapeutic protocols but suffers daunting challenges. To overcome such challenges, a series of porous Yb(3+)/Er(3+) codoped CaTiO3 (CTO:Yb,Er) nanofibers, with specifically designed surface functionalization, were synthesized for doxorubicin (DOX) delivery. The content of DOX released could be optically monitored by increase in the intensity ratio of green to red emission (I550/I660) of upconversion photoluminescent nanofibers under 980 nm near-infrared (NIR) excitation owing to the fluorescence resonance energy transfer (FRET) effect between DOX molecules and the nanofibers. More importantly, the 808 nm NIR irradiation enabled markedly accelerated DOX release, confirming representative NIR-triggered drug release properties. In consequence, such CTO:Yb,Er nanofibers presented significantly enhanced in vitro anticancer efficacy under NIR irradiation. This study has thus inspired another promising fibrous LDDS platform with NIR-triggered and optics-monitored DOX releasing for personalized tumor chemotherapy.

Size-Controlled Single-Crystal Perovskite PbTiO3 Nanofibers from Edge-Shared TiO6 Octahedron Columns

With the minimization of device sizes, great efforts have been devoted to the synthesis and understanding of ferroelectrics at the nanoscale. [ 3 , 4 ] In particular, one-dimensional (1D) perovskite nanostructures have been the focus of numerous research projects for their potential applications in high-density ferroelectric random access memory, piezoelectricity nanogenerators, and nonlinear optics. [ 5–9 ] As a prototypical perovskite-type ferroelectric, lead titanate (PbTiO 3 ) is a desired system to understand ferroelectricity and ferroelectric phase transformation at the nanoscale because of its simple structure and very large spontaneous polarization. [ 10 , 11 ] Recent experimental results indicate that ferroelectricity could be sustainable in a three unit cell (1.2 nm) thick fi lm of PbTiO 3 at room temperature. [ 4 ] For PbTiO 3 nanowires, an unknown phase transition between the vortex polarization and conventional one mediated by strain and surface terminations has been revealed theoretically. [ 12 , 13 ] It also suggests that ferroelectricity could be enhanced within PbO-terminated PbTiO 3 nanowires, thus leading to a critical size of the nanowire down to only one unit cell. As a comparison, the size effect of single-crystal ferroelectric nanowires has rarely been investigated experimentally. Different methods have been exploited in the last decade to synthesize 1D perovskite oxide nanostructures, such as template preparation, [ 14–18 ] hydrothermal methods, [ 19 , 20 ]

Hydrothermal synthesis, characterization and growth mechanism of single crystal lead titanate pyrochlore dendrites

Lead titanate pyrochlore (Pb2Ti2O6) dendrites have been synthesized via hydrothermal treatment of the mixture of lead and titanium hydroxides with the use of ammonia. The products were characterized by XRD, FESEM, TEM, HRTEM, SAED and EDX, respectively. TEM and FESEM show that an individual Pb2Ti2O6 pyrochlore dendrite is composed of a long central trunk and more than three rows of secondary branches. Furthermore, the secondary branches cross the long central trunk exhibiting a cross-like morphology. The SAED patterns reveal the dendrites are single crystalline in nature. And the HRTEM images further demonstrate that both the trunk and the branches all grow along directions. Based on the time-dependent experiments, the analyses of the effects of ammonia and the configuration of cubic pyrochlore structure, the growth mechanism of the single crystal Pb2Ti2O6 pyrochlore dendrites was discussed.

The hydrothermal synthesis and formation mechanism of single-crystalline perovskite BiFeO3 microplates with dominant (012) facets

A facile hydrothermal method has been developed to prepare single-crystal BiFeO3 (BFO) microplates, where the raw material (C6H10BiNO8) was used both as a reactant and a surface modifier. The as-synthesised BFO microplates were dominated by (012) facets with the lateral length of 8 μm and thickness of 510–550 μm. The results of XRD, SEM, TEM, HRTEM and FT-IR indicate that the adsorption behaviour of the organic ligands could play a key role in the formation of the BFO microplates. Moreover, the dielectric constant of the BFO–PVDF film is much higher than the pure BFO at room temperature. The specially chosen raw material (C6H10BiNO8) and the proposed formation mechanism of the BFO microplates could be extended to tailor the crystal growth of the 2D structures of other perovskite oxides.

Crystallization and concentration modulated tunable upconversion luminescence of Er3+ doped PZT nanofibers

Ferroelectric oxides with excellent electrical, mechanical and optical multifunctions play a vital role in future microdevices with diverse applications in energy, sensors and actuators. A series of Er doped PbZr0.52Ti0.48O3 (PZT:Er3+) nanofibers with tunable upconversion photoluminescence (PL) properties were successfully synthesized via a sol–gel based electrospinning process. By controlled crystallization, PZT:Er3+ nanofibers evolve from a polycrystalline to a single-crystalline-like structure, resulting in a remarkable increase in the visible upconversion emission intensity. It was uncovered that Er3+ doping site in PZT shifts from B site to A site with increase in crystallinity and crystal size. In addition, remarkable enhancement in red emission is observed with increased Er3+ doping concentration, which facilitates the modulation of emission colour from green to orange. Combined with the excellent ferroelectric properties of PZT, such spectral tunable PZT:Er3+ nanofibers are considered as a promising multifunctional candidate for integrated electro-mechano-optical devices.

Near-infrared luminescent CaTiO3:Nd3+ nanofibers with tunable and trackable drug release kinetics

750-850 nm (NIR I) and 1000-1400 nm (NIR II) in the near infrared (NIR) spectra are two windows of optical transparency for biological tissues with the latter capable of penetrating tissue deeper. Monitoring drug release from the drug carrier is still a daunting challenge in the field of nanomedicine. To overcome such a challenge, we propose to use porous Nd3+-doped CaTiO3 nanofibers, which can be excited by NIR I to emit NIR II light, to carry drugs to test the concept of monitoring drug release from the nanofibers by detecting the NIR II emission intensity. Towards this end, we first used electrospinning to prepare porous Nd3+-doped CaTiO3 nanofibers by adding micelle-forming surfactant Pluronic F127, followed by annealing to remove the organic component. After a model drug, ibuprofen, was loaded into the porous nanofibers, the drug release from the nanofibers into the phosphate buffered saline (PBS) solution was monitored by detecting the NIR II emission from the nanofibers. We found that the release of the drug molecules from the nanofibers into the PBS solution triggers the quenching of NIR II emission by the hydroxyl groups in the surrounding media. Consequently, more drug release corresponded to more reduction in the intensity of the NIR II emission, allowing us to monitor the drug release by simply detecting the intensity of NIR II from the nanofibers. In addition, we demonstrated that tuning the amount of micelle-forming surfactant Pluronic F127 enabled us to tune the porosity of the nanofibers and thus the drug release kinetics. This study suggests that Nd3+ doped CaTiO3 nanostructures can serve as a promising drug delivery platform with the potential to monitor drug release kinetics by detecting the tissue-penetrating NIR emission.