Yihan Zhu

Sub-10 nm Fe3O4@Cu2–xS Core–Shell Nanoparticles for Dual-Modal Imaging and Photothermal Therapy

Photothermal nanomaterials have recently attracted significant research interest due to their potential applications in biological imaging and therapeutics. However, the development of small-sized photothermal nanomaterials with high thermal stability remains a formidable challenge. Here, we report the rational design and synthesis of ultrasmall (<10 nm) Fe3O4@Cu2-xS core-shell nanoparticles, which offer both high photothermal stability and superparamagnetic properties. Specifically, these core-shell nanoparticles have proven effective as probes for T2-weighted magnetic resonance imaging and infrared thermal imaging because of their strong absorption at the near-infrared region centered around 960 nm. Importantly, the photothermal effect of the nanoparticles can be precisely controlled by varying the Cu content in the core-shell structure. Furthermore, we demonstrate in vitro and in vivo photothermal ablation of cancer cells using these multifunctional nanoparticles. The results should provide improved understanding of synergistic effect resulting from the integration of magnetism with photothermal phenomenon, important for developing multimode nanoparticle probes for biomedical applications.

Enhanced Binding Affinity, Remarkable Selectivity, and High Capacity of CO2 by Dual Functionalization of a rht‐Type Metal–Organic Framework

This work was supported by the Foundation of the National Natural Science Foundation of China (grant numbers 20971054 and 90922034) and the Key Project of the Chinese Ministry of Education. The RU and UTD teams would like to acknowledge support from DOE (grant number DE-FG02-08ER46491). We thank Prof. Xianhe Bu and Dr. Ze Chang (Nankai University, China) and Dr. Ruiping Chen (Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences) for part of the gas adsorption measurements.

Lanthanide-doped NaxScF3+ x nanocrystals : crystal structure evolution and multicolor tuning

Rare-earth-based nanomaterials have recently drawn considerable attention because of their unique energy upconversion (UC) capabilities. However, studies of Sc(3+)-based nanomaterials are still absent. Herein we report the synthesis and fine control of Na(x)ScF(3+x) nanocrystals by tuning of the ratio of oleic acid (OA, polar surfactant) to 1-octadecene (OD, nonpolar solvent). When the OA:OD ratio was increased from low (3:17) to high (3:7), the nanocrystals changed from pure monoclinic phase (Na(3)ScF(6)) to pure hexagonal phase (NaScF(4)) via a transition stage at an intermediate OA:OD ratio (3:9) where a mixture of nanocrystals in monoclinic and hexagonal phases was obtained and the coexistence of the two phases inside individual nanocrystals was also observed. More significantly, because of the small radius of Sc(3+), Na(x)ScF(3+x):Yb/Er nanocrystals show different UC emission from that of NaYF(4):Yb/Er nanocrystals, which broadens the applications of rare-earth-based nanomaterials ranging from optical communications to disease diagnosis.

Monolayer MoSe2 Grown by Chemical Vapor Deposition for Fast Photodetection

Monolayer molybdenum disulfide (MoS2) has become a promising building block in optoelectronics for its high photosensitivity. However, sulfur vacancies and other defects significantly affect the electrical and optoelectronic properties of monolayer MoS2 devices. Here, highly crystalline molybdenum diselenide (MoSe2) monolayers have been successfully synthesized by the chemical vapor deposition (CVD) method. Low-temperature photoluminescence comparison for MoS2 and MoSe2 monolayers reveals that the MoSe2 monolayer shows a much weaker bound exciton peak; hence, the phototransistor based on MoSe2 presents a much faster response time (<25 ms) than the corresponding 30 s for the CVD MoS2 monolayer at room temperature in ambient conditions. The images obtained from transmission electron microscopy indicate that the MoSe exhibits fewer defects than MoS2. This work provides the fundamental understanding for the differences in optoelectronic behaviors between MoSe2 and MoS2 and is useful for guiding future designs in 2D material-based optoelectronic devices.

Molecule-level g-C3N4 coordinated transition metals as a new class of electrocatalysts for oxygen electrode reactions

Organometallic complexes with metal-nitrogen/carbon (M-N/C) coordination are the most important alternatives to precious metal catalysts for oxygen reduction and evolution reactions (ORR and OER) in energy conversion devices. Here, we designed and developed a range of molecule-level graphitic carbon nitride (g-C3N4) coordinated transition metals (M-C3N4) as a new generation of M-N/C catalysts for these oxygen electrode reactions. As a proof-of-concept example, we conducted theoretical evaluation and experimental validation on a cobalt-C3N4 catalyst with a desired molecular configuration, which possesses comparable electrocatalytic activity to that of precious metal benchmarks for the ORR and OER in alkaline media. The correlation of experimental and computational results confirms that this high activity originates from the precise M-N2 coordination in the g-C3N4 matrix. Moreover, the reversible ORR/OER activity trend for a wide variety of M-C3N4 complexes has been constructed to provide guidance for the molecular design of this promising class of catalysts.

Site-specific growth of Au-Pd alloy horns on Au nanorods: a platform for highly sensitive monitoring of catalytic reactions by surface enhancement Raman spectroscopy.

Surface-enhanced Raman scattering (SERS) is a highly sensitive probe for molecular detection. The aim of this study was to develop an efficient platform for investigating the kinetics of catalytic reactions with SERS. To achieve this, we synthesized a novel Au-Pd bimetallic nanostructure (HIF-AuNR@AuPd) through site-specific epitaxial growth of Au-Pd alloy horns as catalytic sites at the ends of Au nanorods. Using high-resolution electron microscopy and tomography, we successfully reconstructed the complex three-dimensional morphology of HIF-AuNR@AuPd and identified that the horns are bound with high-index {11l} (0.25 < l < 0.43) facets. With an electron beam probe, we visualized the distribution of surface plasmon over the HIF-AuNR@AuPd nanorods, finding that strong longitudinal surface plasmon resonance concentrated at the rod ends. This unique crystal morphology led to the coupling of high catalytic activity with a strong SERS effect at the rod ends, making HIF-AuNR@AuPd an excellent bifunctional platform for in situ monitoring of surface catalytic reactions. Using the hydrogenation of 4-nitrothiophenol as a model reaction, we demonstrated that its first-order reaction kinetics could be accurately determined from this platform. Moreover, we clearly identified the superior catalytic activity of the rod ends relative to that of the rod bodies, owing to the different SERS activities at the two positions. In comparison with other reported Au-Pd bimetallic nanostructures, HIF-AuNR@AuPd offered both higher catalytic activity and greater detection sensitivity.

Highly Mesoporous Single-Crystalline Zeolite Beta Synthesized Using a Nonsurfactant Cationic Polymer as a Dual-Function Template

Mesoporous zeolites are useful solid catalysts for conversion of bulky molecules because they offer fast mass transfer along with size and shape selectivity. We report here the successful synthesis of mesoporous aluminosilicate zeolite Beta from a commercial cationic polymer that acts as a dual-function template to generate zeolitic micropores and mesopores simultaneously. This is the first demonstration of a single nonsurfactant polymer acting as such a template. Using high-resolution electron microscopy and tomography, we discovered that the resulting material (Beta-MS) has abundant and highly interconnected mesopores. More importantly, we demonstrated using a three-dimensional electron diffraction technique that each Beta-MS particle is a single crystal, whereas most previously reported mesoporous zeolites are comprised of nanosized zeolitic grains with random orientations. The use of nonsurfactant templates is essential to gaining single-crystalline mesoporous zeolites. The single-crystalline nature endows Beta-MS with better hydrothermal stability compared with surfactant-derived mesoporous zeolite Beta. Beta-MS also exhibited remarkably higher catalytic activity than did conventional zeolite Beta in acid-catalyzed reactions involving large molecules.

Highly Selective and Complete Conversion of Cellobiose to Gluconic Acid over Au/Cs2HPW12O40 Nanocomposite Catalyst

Cellulose is the most abundant source of biomass and holds potential as an alternative to the currently dominant, but nonsustainable, fossil feedstocks. Cellulose is a polysaccharide that consists of a linear chain of d-glucose connected by a b1,4-glycosidic linkage, normally in a robust crystalline form. Although some success has been achieved in catalytic conversion of cellulose to alcohols, the effective and environment-friendly utilization of cellulose is still a challenge, mainly because cellulose is highly stable and insoluble in most solvents. Cellobiose is a glucose dimer connected by a b-1,4-glycosidic bond and represents the basic repeating structural unit as well as the major decomposition product of cellulose. Therefore, cellobiose is a good model compound for the studies of cellulose conversion. Gluconic acid is a widely used food additive and also an important intermediate for the synthesis of fine chemicals and pharmaceuticals; it is conventionally produced by the fermentation of glucose. Transitionmetal particles were used to catalyze the oxidation of glucose to gluconic acid, but the direct conversion of cellobiose to gluconic acid has been seldom reported. Hence, the selective oxidation of cellobiose to gluconic acid should attract both scientific and commercial interest, and an insight into the mechanism of this catalytic reaction would be helpful for designing new strategies for the direct conversion of cellulose. The conversion of cellobiose to gluconic acid basically requires two successive steps: the hydrolysis of cellobiose and the oxidation of the produced glucose. The desired catalyst should therefore be an acidic/oxidative bifunctional that can provide both acid sites for hydrolyzing the b-1,4-glycosidic bond and redox sites for activating oxygen to oxidize the aldehyde group to the carboxyl group (see the Supporting Information, Scheme S1). Moreover, eco-benign reactions with heterogeneous catalysts in water media are preferred. To this end, one would consider the use of a solid acid supported transition metal catalyst. Gold nanoparticles (NPs) have been extensively employed as catalysts for various mild aerobic oxidation reactions. Herein we report a novel heterogeneous cesium hydrogen phosphotungstate-supported Au catalyst (Au/ Cs2HPW12O40) for the oxidation of cellobiose to gluconic acid. Cs2HPW12O40 is selected as the catalyst support for its strong acidity and solid form. More important, as discovered in this work, it possesses a special ability to modulate the oxidative activity of Au NPs, which leads to a specifically high selectivity toward gluconic acid. Density functional theory (DFT) calculations indicate that the strong metal–support interfacial interaction accounts for the catalytic activity modulation. A series of Au catalysts were prepared by loading AuCl3 on different support materials, followed by reduction with hydrogen at 300 8C. The Au loading amount was controlled to be 1 wt % for all the catalysts. The transmission electron microscopy (TEM) image shows that the Au/Cs2HPW12O40 catalyst consists of irregular particles with overall sizes ranging from 15 to 40 nm (Figure 1 a). The Au NPs deposited on the support are not clearly discernible in the TEM image because of their ultrasmall sizes, as well as the fact that tungsten and gold have little difference in atomic number, which results in a low-contrast image. Scanning transmission electron microscopy (STEM) was, therefore, employed to identify the Au particles on the support because in STEM the electron beam is focused into a

Surface modification-induced phase transformation of hexagonal close-packed gold square sheets

Conventionally, the phase transformation of inorganic nanocrystals is realized under extreme conditions (for example, high temperature or high pressure). Here we report the complete phase transformation of Au square sheets (AuSSs) from hexagonal close-packed (hcp) to face-centered cubic (fcc) structures at ambient conditions via surface ligand exchange, resulting in the formation of (100)f-oriented fcc AuSSs. Importantly, the phase transformation can also be realized through the coating of a thin metal film (for example, Ag) on hcp AuSSs. Depending on the surfactants used during the metal coating process, two transformation pathways are observed, leading to the formation of (100)f-oriented fcc Au@Ag core-shell square sheets and (110)h/(101)f-oriented hcp/fcc mixed Au@Ag nanosheets. Furthermore, monochromated electron energy loss spectroscopy reveals the strong surface plasmon resonance absorption of fcc AuSS and Au@Ag square sheet in the infrared region. Our findings may offer a new route for the crystal-phase and shape-controlled synthesis of inorganic nanocrystals.

Synthesis of Ultrathin Face-Centered-Cubic Au@Pt and Au@Pd Core–Shell Nanoplates from Hexagonal-Close-Packed Au Square Sheets†

The synthesis of ultrathin face-centered-cubic (fcc) Au@Pt rhombic nanoplates is reported through the epitaxial growth of Pt on hexagonal-close-packed (hcp) Au square sheets (AuSSs). The Pt-layer growth results in a hcp-to-fcc phase transformation of the AuSSs under ambient conditions. Interestingly, the obtained fcc Au@Pt rhombic nanoplates demonstrate a unique (101)f orientation with the same atomic arrangement extending from the Au core to the Pt shell. Importantly, this method can be extended to the epitaxial growth of Pd on hcp AuSSs, resulting in the unprecedented formation of fcc Au@Pd rhombic nanoplates with (101)f orientation. Additionally, a small amount of fcc (100)f -oriented Au@Pt and Au@Pd square nanoplates are obtained with the Au@Pt and Au@Pd rhombic nanoplates, respectively. We believe that these findings will shed new light on the synthesis of novel noble bimetallic nanostructures.