Mesoporous Co3O4 as an electrocatalyst for water oxidation

Mesoporous Co₃O₄ has been prepared using porous silica as a hard template via a nanocasting route and its electrocatalytic properties were investigated as an oxygen evolution catalyst for the electrolysis of water. The ordered mesostructured Co₃O₄ shows dramatically increased catalytic activity compared to that of bulk Co₃O₄. Enhanced catalytic activity was achieved with high porosity and surface area, and the water oxidation overpotential (η) of the ordered mesoporous Co₃O₄ decreases significantly as the surface area increases. The mesoporous Co₃O₄ also shows excellent structural stability in alkaline media. After 100 min under 0.8 V (versus Ag/AgCl) applied bias, the sample maintains the ordered mesoporous structure with little deactivation of the catalytic properties.      

Ultra-stable silica-coated chiral Au-nanorod assemblies: Core–shell nanostructures with enhanced chiroptical properties

Chiral nano-assemblies with amplified optical activity have attracted particular interest for their potential application in photonics, sensing and catalysis. Yet it still remains a great challenge to realize their real applications because of the instability of these assembled nanostructures. Herein, we demonstrate a facile and efficient method to fabricate ultra-stable chiral nanostructures with strong chiroptical properties. In these novel chiral nanostructures, side-by-side assembly of chiral cysteine-modified gold nanorods serves as the core while mesoporous silica acts as the shell. The chiral core–shell nanostructures exhibit an evident plasmonic circular dichroism (CD) response originating from the chiral core. Impressively, such plasmonic CD signals can be easily manipulated by changing the number as well as the aspect ratio of Au nanorods in the assemblies located at the core. In addition, because of the stabilization effect of silica shells, the chiroptical performance of these core–shell nanostructures is significantly improved in different chemical environments.

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Inhibitory activity of gold and silica nanospheres to vascular endothelial growth factor （VEGF）-mediated angiogenesis is determined by their sizes

Nanoparticles can be involved in biological activities such as apoptosis, angiogenesis, and oxidative stress by themselves. In particular, inorganic nanoparticles such as gold and silica nanoparticles are known to inhibit vascular endothelial growth factor （VEGF）-mediated pathological angiogenesis. In this study, we show that anti-angiogenic effect of inorganic nanospheres is determined by their sizes. We demonstrate that 20 nm size gold and silica nanospheres suppress VEGF-induced activation of VEGF receptor-2, in vitro angiogenesis, and in vivo pathological angiogenesis more efficiently than their 100 nm size counterparts. Our results suggest that modulation of the size of gold and silica nanospheres determines their inhibitory activity to VEGF-mediated angiogenesis.     

Functionalization of high-moment magnetic nanodisks for cell manipulation and separation

Synthetic antiferromagnetic （SAF） nanoparticles are layer-structured particles with high single-particle magnetic moments. In order to covalently bind these nanopartides to cells, they were coated with a silica shell followed by conjugation with streptavidin. The silica coating generates both SAF@SiO2 core-shell nano- particles and silica core-free nanopartides. Using a simple magnetic separation, silica nanoparticles were removed and SAF@SiO2 nanoparticles were purified. After streptavidin conjugation, these particles were used to stain lung cancer cells, making them highly magnetically responsive. The stained cells can rotate in response to an external magnetic field and can be captured when a blood sample containing these cells flows through the sifter.     

Versatile synthesis of yolk/shell hybrid nanocrystals via ion-exchange reactions for novel metal/semiconductor and semiconductor/semiconductor conformations

Yolk/shell (Y–S) hybrid nanoarchitectures, owing to the interior voids created for individualized catalyst applications, have emerged as new candidates for effectively isolating catalytic species. However, the well-defined hollow interiors with flexible core and shell compositions—such as noble-metal cores, metal-oxide cores, and widespread semiconductor shells—and a flexible anisotropic shape are far from the requirements. In particular, the introduction of catalytic noble metals or metal-oxide nanocrystals (NCs) with isotropic or anisotropic shapes into various hollow semiconductor structures with well-defined morphologies has been rarely reported but is urgently needed. Herein, we propose a strategy involving the careful sulfuration of as-prepared cavity-free core/shell NCs or metal-oxide NCs followed by phosphine-initialized cation-exchange reactions for preparing metal@semiconductor and metal oxide@semiconductor (II-VI) Y–S NCs. The geometry, size, and conformations of the core and shell are fully and independently considered. New and unprecendented metal@semiconductor and metal oxide@semiconductor (II-VI) Y–S NCs are prepared via widespread phosphine-initialized cation-exchange reactions.

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Formation of CdSe/CdS/ZnS-Au/SiO2 dual-yolk/shell nanostructures through a Trojan-type inside-out etching strategy

In this work we report the development of a rapid and selective etching strategy to synthesize a dual-yolk/shell nanostructure consisting of semiconductor-metal hybrid nanocrystals and hollow SiO₂ for the first time. By utilizing CdSe/CdS/ZnS quantum dot (CSSQD)/SiO₂ core/shell nanoparticles as the template and aurate hydroxyl complexes [Au(OH) ₄ ^? ] as the Trojan-type inside-out etching agent, rapid formation of CSSQD-Au hybrid nanocrystal dual-yolk and SiO₂ hollow shell occur during the reduction of Au(OH) ₄ ^? on CSSQD cores accompanied by localized hydroxyl-liberation from Au(OH) ₄ ^? at the interface between silica and CSSQD. Unlike surface-protected etching strategies, a selective as well as directional etching takes place from the silica internal surface and the thickness of the silica shell can be controlled by varying the etching time. Moreover, the size of attached Au nanoclusters can be tuned by subsequent light exposure. Consequently, the resulting platform offers a number of attractive features: (1) a new, directional, and rapid etching approach toward the formation of hollow silica nanostructures in solution; (2) semiconductor/metal hybrid nanocrystals as yolks within hollow silica nanospheres have been reported for the first time; and (3) the ability, through light exposure, to tune the size of the attached metal nanoclusters on the encapsulated CSSQD within the hollow silica nanospheres. Most importantly, the synthetic method has the capability of introducing additional guest species (e.g. metals) into a primary yolk (e.g. semiconductor) of hollow silica nanoparticles, potentially leading to many promising applications in fuel cells, photocatalysis, bioimaging, and cancer therapy.      

Scalable synthesis of sub-100 nm hollow carbon nanospheres for energy storage applications

Sub-100 nm hollow carbon nanospheres with thin shells are highly desirable anode materials for energy storage applications. However, their synthesis remains a great challenge with conventional strategies. In this work, we demonstrate that hollow carbon nanospheres of unprecedentedly small sizes (down to ～32.5 nm and with thickness of ～3.9 nm) can be produced on a large scale by a templating process in a unique reverse micelle system. Reverse micelles enable a spatially confined Stöber process that produces uniform silica nanospheres with significantly reduced sizes compared with those from a conventional Stöber process, and a subsequent well-controlled sol–gel coating process with a resorcinol–formaldehyde resin on these silica nanospheres as a precursor of the hollow carbon nanospheres. Owing to the short diffusion length resulting from their hollow structure, as well as their small size and microporosity, these hollow carbon nanospheres show excellent capacity and cycling stability when used as anode materials for lithium/sodium-ion batteries.

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Gold nanorods with a hematoporphyrin-loaded silica shell for dual-modality photodynamic and photothermal treatment of tumors in vivo

Nanocomposites （NCs） consisting of a gold nanorod core and a mesoporous silica shell doped with hematoporphyrin （HP） have been fabricated in order to improve the efficiency of cancer treatment by combining photothermal and photodynamic therapies （PDT ＋ PTT） in vivo. In addition to the long-wavelength plasmon resonance near 810-830 nm, the fabricated NCs exhibited a 400-nm absorbance peak corresponding to bound HP, generated singlet oxygen under 633-nm excitation near the 632.5-nm Q-band, and produced heat under a 808-nm near-infrared （NIR） laser irradiation. These modalities were used for a combined PDT ＋ PTT treatment of large （about 3 cm3） solid tumors in vivo with a xenorafted tumor rat model. NCs were directly injected into tumors and irradiated simultaneously with 633-nm and 808-nm lasers to stimulate the combined photodynamic and photothermal activities of NCs. The efficiency of the combined therapy was evaluated by optical coherence tomography, histological analysis, and by measurements of the tumor volume growth during a 21-day period. The NC-mediated PDT led to weak changes in tissue histology and to a moderate 20% decrease in the tumor volume. In contrast, the combined PDT ＋ PTT treatment resulted in the large-area tumor necrosis and led to dramatic decrease in the tumor volume.     

Light-controlled synthesis of uniform platinum nanodendrites with markedly enhanced electrocatalytic activity

We report a fast in situ seeding approach based on zinc（II） porphyrin （ZnP） under white light irradiation, leading to uniform spherical platinum nanodendrites with tunable sizes. The platinum nanodendrites exhibit significantly improved electrocatalytic activities toward oxygen reduction reaction （ORR） and methanol oxidation reaction （MOR） compared with commercial platinum black.     

Coordinated buckling of thick multi-walled carbon nanotubes under uniaxial compression

Using a generalized quasi-continuum method, we characterize the post-buckling morphologies and energetics of thick multi-walled carbon nanotubes (MWCNTs) under uniaxial compression. Our simulations identify for the first time evolving post-buckling morphologies, ranging from asymmetric periodic rippling to a helical diamond pattern. We attribute the evolving morphologies to the coordinated buckling of the constituent shells. The post-buckling morphologies result in significantly reduced effective moduli that are strongly dependent on the aspect ratio. Our simulation results provide fundamental principles to guide the future design of high-performance, MWCNT-based nanodevices.      

Ultra-Stable oligonucleotide-gold and -silver nanoparticle conjugates prepared by a facile silica reinforcement method

We report a simple method of enhancing the chemical stability of monothiol-modified oligonucleotide-gold and -silver nanoparticle conjugates by a thin silica reinforcement coating. Conventional conjugates prepared by chemisorption of monothiol-modified oligonucleotides onto nanoparticle surfaces undergo rapid aggregation in the presence of thiol-containing small molecules (e.g., dithiothreitol) due to ligand exchange reactions. When the conjugates are treated with (3-mercaptopropyl)trimethoxysilane, a thin silica layer is formed on the nanoparticle surface, thereby entrapping and reinforcing the thiol-gold/-silver linkage. These silica-modified oligonucleotide-gold and -silver nanoparticle conjugates become much more stable toward dithiothreitol as compared to the unmodified conjugates. Moreover, the silica layer significantly hinders the gold/silver core from oxidative dissolution by sodium cyanide. Importantly, the unique hybridization-induced color change property of the oligonucleotide-gold and -silver nanoparticle conjugates is preserved even under harsh condition (i.e., high concentrations of dithiothreitol). Taken together, these ultra-stable oligonucleotide-nanoparticle conjugates hold promise for new diagnostics and therapeutics.      

Controlled one-pot synthesis of RuCu nanocages and Cu@Ru nanocrystals for the regioselective hydrogenation of quinoline

RuCu nanocages and core–shell Cu@Ru nanocrystals with ultrathin Ru shells were first synthesized by a one-pot modified galvanic replacement reaction. The construction of bimetallic nanocrystals with fully exposed precious atoms and a high surface area effectively realizes the concept of high atom-efficiency. Compared with the monometallic Ru/C catalyst, both the RuCu nanocages and Cu@Ru core–shell catalysts supported on commercial carbon show superior catalytic performance for the regioselective hydrogenation of quinoline toward 1,2,3,4-tetrahydroquinoline. RuCu nanocages exhibit the highest activity, achieving up to 99.6% conversion of quinoline and 100% selectivity toward 1,2,3,4-tetrahydroquinoline.

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A wrinkle to sub-100 nm yolk/shell Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> nanoparticles

Yolk/shell nanoparticles (NPs), which integrate functional cores (likes Fe₃O₄) and an inert SiO₂ shell, are very important for applications in fields such as biomedicine and catalysis. An acidic medium is an excellent etchant to achieve hollow SiO₂ but harmful to most functional cores. Reported here is a method for preparing sub-100 nm yolk/shell Fe₃O₄@SiO₂ NPs by a mild acidic etching strategy. Our results demonstrate that establishment of a dissolution–diffusion equilibrium of silica is essential for achieving yolk/shell Fe₃O₄@SiO₂ NPs. A uniform increase in the silica compactness from the inside to the outside and an appropriate pH value of the etchant are the main factors controlling the thickness and cavity of the SiO₂ shell. Under our “standard etching code”, the acid-sensitive Fe₃O₄ core can be perfectly preserved and the SiO₂ shell can be selectively etched away. The mechanism of regulation of SiO₂ etching and acidic etching was investigated.

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Enhanced π-π interactions between a C60 fullerene and a buckle bend on a double-walled carbon nanotube

In situ low-voltage aberration corrected transmission electron microscopy (TEM) observations of the dynamic entrapment of a C₆₀ molecule in the saddle of a bent double-walled carbon nanotube is presented. The fullerene interaction is non-covalent, suggesting that enhanced π-π interactions (van der Waals forces) are responsible. Classical molecular dynamics calculations confirm that the increased interaction area associated with a buckle is sufficient to trap a fullerene. Moreover, they show hopping behavior in agreement with our experimental observations. Our findings further our understanding of carbon nanostructure interactions, which are important in the rapidly developing field of low-voltage aberration corrected TEM and nano-carbon device fabrication.      

A perspective on functionalizing colloidal quantum dots with DNA

This perspective provides an overview of the techniques that have been developed for the conjugation of DNA to colloidal quantum dots (QDs), or semiconductor nanocrystals. Methods described include: ligand exchange at the QD surface, covalent conjugation of DNA to the QD surface ligands, and one-step DNA functionalization on core QDs or during core/shell QD synthesis in aqueous solution, with an emphasis on the most recent progress in our lab. We will also discuss emerging trends in DNA-functionalized QDs for potential applications.      

Closely packed nanoparticle monolayer as a strain gauge fabricated by convective assembly at a confined angle

The reliability and sensitivity of a strain gauge made from a nanoparticle monolayer intrinsically depend on electron tunneling between the adjacent nanoparticles, so that creating nanoscale interstitials with uniform distribution and tuning the interparticle separation reversibly during cyclic mechanical stress are two vital issues for performance enhancement. In this work, one assembly technique is initialized to fabricate parallel nanoparticle strips by precisely tailoring the contact angle of a gold colloid on a substrate. The assembly of a nanoparticle monolayer with a close-packed pattern can be simultaneously switched on and off by independently varying the contact angle across a threshold value of 4.2~. This nanoparticle strip shows a reversible and reliable electrical response even if a mechanical strain as small as 0.027% is periodically supplied, implying well-controlled electron tunneling between the adjacent nanoparticles.     

Hydroformylation of alkenes over rhodium supported on the metal-organic framework ZIF-8

A highly porous and crystalline metal-organic framework （MOF） ZIF-8 has been synthesized and used for the preparation of a supported rhodium nanoparticle catalyst （Rh@ZIF-8）. The material has been characterized by PXRD, TEM, EDX, ICP-AES and nitrogen adsorption. The catalytic properties of Rh@ZIF-8 have been investigated in the hydroformylation of alkenes, with different chain length and structure, to give the corresponding aldehydes, and showed high activity. Furthermore, after the reaction was complete, the catalyst could be easily separated from the products by simple decantation and reused five times without a significant decrease in the activity under the investigated conditions.     

Superior electrocatalytic activity of mesoporous Au film templated from diblock copolymer micelles

Mesoporous Au films consisting of a network of interconnected Au ligaments around ultra-large pores were found to exhibit a promising electrocatalytic activity towards sluggish reactions. Mesoporous Au films with pore sizes up to 25 nm were successfully fabricated using a polymeric micelle approach. A superior catalytic activity of the mesoporous Au films towards methanol oxidation was confirmed, which was thoroughly analyzed and compared with that of other Au materials. An intrinsic investigation on the high catalytic activity revealed that the superior performance of the as-prepared mesoporous Au film was related to its unique atomic structures around the mesopores with well-crystallized facets and several step/kink sites on the Au surfaces. These findings showcase a strategic and feasible design for preparing highly active Au-based catalysts that could be used as promising candidates in electrocatalytic applications.

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Construction of Pd-M (M = Ni,Ag, Cu) alloy surfaces for catalytic applications

The fabrication of ultrathin alloy shells as heterogeneous catalysts to increase the utilization efficiency and enhance the catalytic activity of metal atoms has been recognized as an effective method for the construction of efficient metal nanocatalysts, particularly noble-metal nanocatalysts. In this study, we demonstrate the successful formation of Pd-M (M = Ni, Ag, Cu) alloy shells with a tunable thickness on preformed nanoscale Pd seeds. The success of this synthesis mainly relies on the combination of the slow reduction of “M” ions and the subsequent diffusion of M ad-atoms into the surface lattice of Pd seeds. The composition of the Pd-M alloy shell is easily tuned by changing the type and amount of the added precursor, and the shell thickness is manipulated according to the reaction time. More significantly, the surface structure of these alloy shells is maintained after the reaction, implying that any desired surface structure of Pd-M alloy shells can be prepared by using the appropriate starting materials. Further catalytic evaluation of the hydrogenation of chloronitrobenzenes shows that these alloy surfaces exhibit significantly improved selectivity compared to the Pd seeds. The Pd-Ni alloy surfaces exhibit much better catalytic selectivity (as high as > 99%) than Pd catalysts.

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Growth of silicon nanowires in aqueous solution under atmospheric pressure

A new method for growing silicon nanowires is presented. They were grown in an aqueous solution at a temperature of 85℃ under atmospheric pressure by using sodium methylsiliconate as a water-soluble silicon precursor. The structure, morphology, and composition of the as-grown nanowires were characterized by scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectrometry. It was also confirmed by X-ray powder diffraction and Raman spectroscopy that the silicon nanowire has a hexagonal structure. It was possible to grow the crystalline silicon nanowires at low temperature under atmospheric pressure because potassium iodide, which was used as a gold etchant, sufficiently increased the surface energy and reactivity of gold as a metal catalyst for the reaction of the Si precursor even at low temperature.