529 research outputs found
Hollow Nanostructures
No full textThis special collection on Hollow Nanostructuresis guest edited by Dan Wang, Alexander Eychmuller and Yugang Sun. Read more about the exciting papers in the collection in this editorial
Supplementary_Materials - The Protective Effects of Preconditioning With Dioscin on Myocardial Ischemia/Reperfusion-Induced Ventricular Arrhythmias by Increasing Connexin 43 Expression in Rats
No full textSupplementary_Materials for The Protective Effects of Preconditioning With Dioscin on Myocardial Ischemia/Reperfusion-Induced Ventricular Arrhythmias by Increasing Connexin 43 Expression in Rats by Jin Cheng, Chuang Sun, Jingyu Zhang, Qing Zou, Qimeng Hao, and Yugang Xue in Journal of Cardiovascular Pharmacology and Therapeutics</p
Fabrication and field-emission performance of zinc sulfide nanobelt arrays
No full textLarge-scale, well-aligned, and oriented wurtzite ZnS nanobelt arrays have been synthesized by a simple template-free solvothermal reaction and subsequent heat-treatment process. The ZnS nanobelts grow along the [0001] direction perpendicularly on a zinc substrate, which have a thickness of about 30 nm, widths of several hundreds of narrometers, and uniform length up to 4,mu m. The selection of Zn foil as the substrate is crucial for the formation of ZnS nanostructured arrays. The concentration of Zn ions, the pH value in the initial precursor solution, and the reaction temperature also have an important influence on the morphology of the final arrays. The formation of the nanobelt arrays are attributed to the structural compatibility of the substrate with ZnS and the growth-rate-dependence of morphology. Importantly, such nanostructured arrays show good field-emission properties with low turn-on fields (3.8 V mu m(-1)) and high field-enhancement factors (1839). This is attributed to the top edges and corners of the free-standing and well-aligned nanobelts, suitable number density of emitters, and good electric contact of the nanobelts with the conducting substrate where they grow. This well-aligned ZnS nanobelt array is expected to be the promising candidate for various field-emission applications, such as flat-panel displays and other vacuum microelectronic devices.This work was supported by the National Natural Science Foundation of China (Grant Nos. 50671100 and 50502032), the Major State research program of China
“Fundamental Investigation on Micro-Nano Sensors and Systems based on BNI Fusion” (Grant No. 2006CB300402), and the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KJCX2-SW-W31)
Photocatalytic hot-carrier chemistry
No full textLight absorption in nanoparticles of semiconductors and metals excites electrons from ground states to high-energy levels, generating hot electrons with the addition of kinetic energy, and consequently, complimentary hot holes in the nanoparticles. These hot electrons are capable of injecting themselves into the empty antibonding orbitals of chemical bonds of reactant molecules adsorbed on the surface of the nanoparticles, thereby weakening the chemical bonds to trigger corresponding desirable chemical reactions. Hot-electron chemistry represents a fundamentally different mechanism of solar-to-chemical energy conversion compared to the traditional photochemistry that relies on the direct photo-excitation of electrons in reactant molecules and thermal catalysis. This issue of MRS Bulletin examines the generation and relaxation of hot electrons in typical nanoparticle systems, and the flow of hot electrons across the surfaces of the nanoparticles. The promise of hot-electron chemistry (and the complementary hot-hole chemistry) is supported by its application in many important reactions, including CO2 reduction, water splitting, hydrogenation, and coupling reactions, highlighting its great potential in achieving high energy-conversion efficiency and product selectivity.No Full Tex
Development of polynorbornenes and polypeptides as versatile functional biomaterials
No full textPolymer chemistry is an essential connection between organic chemistry, chemical biology and materials science. This living world has presented us many examples of the usages of polymers, such as delivery vehicle, recognition unit, support materials, information storage,5 and so on. Scientists have been trying to create synthetic polymers that can mimic such functionalities and bring widespread applications in different fields. For all synthetic polymers, their properties and potential applications are all based on their chemical nature. This is especially true for synthetic polymeric materials for bio-related applications, because of the delicate and complicated working environments and mechanisms of such biomaterials. Consequently, more facile and delicate controls over the polymers’ chemical nature are in great demand, and bottom-up strategy for the synthesis of smart polymers have been more common in the recent decades.
In this thesis paper, multiple bottom-up syntheses of useful polymeric materials are recorded. In the first part of the thesis, a new approach to prepare functional organic nanoparticles (ONPs) from linear polymers is described. The nanoparticles were obtained by consecutive ring-opening metathesis polymerization and ring-closing metathesis. This flexible and mild synthesis allowed preparation of organic- and aqueous-soluble particles with controllable size and narrow molecular weight distributions. The use of functional monomer(s) and/or chain-transfer agents had led to controllable synthesis of nanoparticles containing single, dual, or multiple reactive functional groups. Such non-toxic ONPs with many controllable parameters could be used to study the effect of surface functional groups on the cellular uptake of corresponding nanoparticles. In addition, dye-functionalized ONPs could serve as water-soluble fluorophores with highly enhanced photostability. Moreover, other functional materials such as DNAs could be conjugated onto the ONPs, bringing in new hybrid materials with applications. The ONPs and ONP-DNA conjugates could also serve as templates for the synthesis of metal nanoparticles, providing a direct and facile synthetic route for functional metal nanoparticles.
In the second part of this paper, major focus is set on a polymeric approach to enhance the efficacy of toxic r(CUG)n-binding compounds for potential Myotonic Dystrophy Type I (DM1) treatment. Also using a bottom-up living polymerization strategy, cell-penetrating polymers bearing active r(CUG)n binding ligands are prepared. The synthetic polypeptide binder was shown to have excellent performance in both molecular and cell studies, giving much enhanced binding to the toxic RNA. The ligand-polypeptide conjugates could successfully disperse ribonuclear foci caused by r(CUG)n-MBNL1 complex, and could fully reverse the mis-splicing of Insulin receptor (IR) mRNAs in the model cells. In addition, potentially due to the polymer-mediated catalytic degradation, r(CUG)n level in the model cells could be greatly reduce by low concentration treatment of the ligand-bearing polymeric material.Submission published under a 24 month embargo labeled 'U of I only', the embargo will last until 2017-08-01The student, Yugang Bai, accepted the attached license on 2015-07-08 at 09:49.The student, Yugang Bai, submitted this Dissertation for approval on 2015-07-08 at 10:41.This Dissertation was approved for publication on 2015-07-09 at 16:04.DSpace SAF Submission Ingestion Package generated from Vireo submission #8366 on 2015-09-29 at 14:59:11Made available in DSpace on 2015-09-29T20:49:45Z (GMT). No. of bitstreams: 2
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Plasmonic Particles - Now Tailored to Your Needs
No full textFree electrons in nanosized metal particles can oscillate collectively to generate resonant plasmons on particle surfaces upon illumination of light with energy matching the electron resonance frequency. The resonant plasmons confined in nanoparticles are usually called localized surface plasmon resonances (LSPRs), which are sensitive towards a number of parameters including composition, size, shape, structure, environment, and so forth. The significant advance in colloidal synthesis enables the successful synthesis and investigation of plasmonic nanoparticles with tailorable LSPRs. Due to the LSPRs, metal nanoparticles made of coinage metals such as gold (Au) and silver (Ag) exhibit strong absorption, scattering, and emission, which are tunable by controlling the physical parameters of the nanoparticles. Such distinctive interactions between plasmonic nanoparticles and light endow the nanoparticles with applications ranging from sensing to energy to medicine. For example, plasmonic nanoparticles can drastically concentrate the electric field under resonant excitation, which can be applied in enhanced near-infrared (NIR) absorption spectroscopy, enhanced photoemission spectroscopy and surface-enhanced Raman spectroscopy. Nonradiative Landau damping of LSPRs in plasmonic nanoparticles creates charge carriers with a significant fraction of the plasmon energy being much higher than thermal energy at ambient temperature, i.e., hot electrons above Fermi energy and hot holes below the Fermi energy of the metal. These energetic hot carriers possess very high chemical potentials to drive chemical transformations on (or near) the surfaces of the plasmonic nanoparticles. If the LSPR frequencies are in the NIR spectral region, the light absorbed by the plasmonic nanoparticles can be efficiently converted to heat, thus benefiting the photothermal treatment of cancers and controlled drug delivery. Figure 1 summarizes the major topics in current plasmonic particle research.No Full Tex
Nanoscale, Electrified Liquid Jets for High-Resolution Printing of Charge
No full textNearly all research in micro- and nanofabrication focuses on the formation of solid structures of materials that perform some mechanical, electrical, optical, or related function. Fabricating patterns of charges, by contrast, is a much less well explored area that is of separate and growing Interesting because the associated electric fields can be exploited to control the behavior of nanoscale electronic and mechanical devices, guide the assembly of nanomaterials. or modulate the properties of biological systems. This paper describes a versatile technique that uses fine, electrified liquid jets formed by electrohydrodynamics at micro- and nanoscale nozzles to print complex patterns of both positive and negative charges, with resolution that can extend into the submicrometer and nanometer regime. The reported results establish the basic aspects of this process and demonstrate the capabilities through printed patterns with diverse geometries and charge configurations in a variety of liquid inks, including suspensions of nanoparticles and nanowires. The use of printed charge to control the properties of silicon nanomembrane transistors provides an application example.close464
Reprint of “Post-buckling analysis for the precisely controlled buckling of thin film encapsulated by elastomeric substrates” [In. J. Solids Struct. 45 (2008) 2014–2023]
No full textAbstractThe precisely controlled buckling of stiff thin films (e.g., Si or GaAs nano ribbons) on the patterned surface of elastomeric substrate (e.g., poly(dimethylsiloxane) (PDMS)) with periodic inactivated and activated regions was designed by Sun et al. [Sun, Y., Choi, W.M., Jiang, H., Huang, Y.Y., Rogers, J.A., 2006. Controlled buckling of semiconductor nanoribbons for stretchable electronics. Nature Nanotechnology 1, 201–207] for important applications of stretchable electronics. We have developed a post-buckling model based on the energy method for the precisely controlled buckling to study the system stretchability. The results agree with Sun et al.’s (2006) experiments without any parameter fitting, and the system can reach 120% stretchability
PHOTOCATALYSIS ON DIELECTRIC ANTENNA SUPPORTED-RHODIUM NANOPARTICLES
No full textLight absorption in metal catalyst nanoparticles can excite charge carriers to generate hot electron (and complimentary hot holes) with energy higher than the Fermi level. When hot electrons possess energy high enough, they exhibit a high tendency to inject into antibonding orbitals of adsorbates on the photoexcited metal nanoparticles, weakening the corresponding chemical bonds to promote chemical reactions with accelerated reaction kinetics and improved selectivity. Such hot-carrier chemistry has been reported on plasmonic metal nanoparticles, such as silver and gold, which exhibit strong surface plasmon resonances (SPRs) and strong light absorption. However, these metal nanoparticles are not suitable catalysts because their affinity toward interesting molecules is limited. In contrast, most transition metals, such as platinum-group metals and early transition metals, are industrially essential catalysts, but light absorption power in metal nanoparticles is low due to the absence of SPRs in the visible spectral range. Therefore, it is intriguing to explore the potential of hot-carrier catalytic chemistry on photoexcited non-plasmonic metal nanoparticles. Upon the absorption of the same optical power, metal nanoparticles with a small size usually exhibit a high probability of hot electron production and high efficiency of injecting hot electrons into adsorbates. It is challenging to have strong light absorption power and operation stability of the catalyst metal nanoparticles with small sizes. In this thesis, dielectric light antenna, i.e., spherical silica nanoparticles with strong surface scattering resonances near their surfaces, is introduced to support the metal catalyst nanoparticles, enabling improved light absorption power in the metal nanoparticles and operation stability. This thesis focuses on ultrafine rhodium (Rh) nanoparticles (with sizes ranging from 1.7 nm to 4.2 nm) that are widely used as thermal catalysts in many important industry reactions, especially for oxygen-containing species conversion, an oxyphilic feature of Rh nanoparticles.
Firstly, this dissertation conducted a comparative study to investigate the influence of silica geometry, nanospheres, and rodlike nanoparticles on the light absorption of Rh nanoparticles. Both silica substrates enhanced the light absorption of loaded Rh nanoparticles due to elongated light scattering paths (random scattering) and enhanced electromagnetic field intensity (resonant scattering). However, silica nanospheres support both resonant scattering and random light scattering modes, exhibiting a higher Rh absorption than the usage of rodlike silica nanoparticles. The light resonant scattering modes on highly symmetrical silica nanospheres enable producing "hot spots" with a much higher electromagnetic field intensity than incident light intensity. This study then investigated the effect of silica geometries on photocatalytic performance. The CO2 hydrogenation was studied as a model reaction. The Rh/silica nanosphere system exhibited a faster photocatalytic kinetic than the case of rodlike silica nanoparticles. It is possibly due to the enhanced light power density around the silica nanospheres. The results give a promise of expanding Rh nanoparticles from thermo-catalysis to photocatalysis.
Secondly, this dissertation moves onto accelerating aerobic oxidation of primary alcohols to aldehydes, which was benefited from activated oxygen molecules by hot electron injection. This study found that photoexcited Rh nanoparticles enabled accelerating the alcohol oxidation kinetics by four times at a light power intensity of 0.4 W cm-2, accompanied by a reduced activation energy of 21 kJ mol-1. The derived Langmuir-Hinshelwood rate equation was used to fit the oxygen partial pressure results. Photo-illumination promotes the cleavage of associatively adsorbed oxygen molecules into adsorbed oxygen atoms, reducing the energy barrier. Besides, the silica-supported Rh nanoparticles exhibited a higher photocatalytic performance because of the good colloidal stability and enhanced light absorption of small-sized Rh particles. This part of the dissertation shows the possibility of hot-electron mediated reaction pathways towards a desirable kinetic of alcohol oxidation.
Thirdly, it will be meaningful to use the abstracted protons from cheap alcohol sources to reduce other organic molecules rather than dangerous hydrogen gas. This dissertation then investigated the possibility of using an isopropanol solvent as a hydrogen source to reduce nitrobenzene and the feasibility of enhancing the selectivity of the reaction with the light illumination. The results showed that the isopropanol was spontaneously oxidized, producing acetone. Light illumination onto Rh particles selectively enhanced the coupling of reduced nitrobenzene intermediates to produce azoxybenzene. The selectivity of nitrobenzene and production rates gradually increased with a higher number of light photons. Photo-illumination promotes both aniline and azoxybenzene production rates. Hot electrons on Rh particles possibly enabled activating nitrobenzene molecules and increasing concentrations of reduced nitrobenzene intermediates. It resulted in a higher possibility of condensation product and azoxybenzene selectivity, which could not be obtained by elevating temperature without light illumination. This part of the work demonstrated the feasibility of hot electrons from Rh nanoparticles to tune the reaction selectivity in a liquid phase.
Lastly, it is challenging to modulate the selectivity of CH4 from CO2 hydrogenation because of the competitive CO production. This dissertation moves towards enhancing both kinetic rates and selectivity of CH4 for gaseous CO2 hydrogenation by photoexcited Rh nanoparticles. Light illumination onto Rh/silica nanosphere particles resulted in the selectivity of CH4 over 99% in contrast to ~70% under dark conditions at 330 oC and with an absorbed light power intensity of 1.5 W cm-2. The activation energy of CH4 production and CO2 consumption gradually decreased with higher light power intensity because of the transient injection of hot electrons into adsorbates to activate intermediates. Increasing operating temperature and light power intensity synergistically enhanced the reaction kinetics.
Besides, a middle-sized Rh nanoparticle showed a better photocatalytic performance than that of the largest-sized Rh nanoparticles because of the balance in hot-electron production efficiency and intrinsic catalytic performance. Partial pressure dependence and in situ infrared characterizations showed that the critical stable intermediates for CH4 production should be hydrogenated CO2 species (HCOO* COOH*) and hydrogenated CO* species (carbonyl hydride or HxCO*). The light illumination exclusively enhanced the dissociation of CO2 and CO* without apparent influence on CO* desorption. Under high reaction temperature, light illumination preferred a faster CO* conversion than CO2 dissociation, leading to high CH4 selectivity. This result was also supported by higher methanation rates of CO gas under light illumination. The infrared result showed a reduced stretching frequency of CO*, which supported the possibility of the electron from Rh back-donating into antibonding orbitals of strongly adsorbed CO* species. However, hot electrons from silver nanoparticles with a weak COOH* or CO* adsorption could not efficiently activate carbon-species and could not promote CO2 hydrogenation kinetics.
This dissertation offers an avenue of enhancing light absorption of small-sized Rh nanoparticles and expanding its usage from thermal catalysis to photocatalysis for driving oxidation and reduction reactions. The reactants share a common feature containing oxygen elements, a strong affinity with rhodium metal for efficient hot electron injection. We studied the light power intensity and temperature-dependence, showing the accelerated reaction kinetics by hot electron-driven pathways. Photo-excited rhodium nanoparticles were believed to promote the cleavage of chemical bonds O-O, N-O, and C-O to drive chemical transformations. The findings offer insights into developing the scope of non-plasmonic metal nanoparticles in photocatalytic reactions for industrial applications.Chemistr
SYNTHESIS AND OPTICAL PROPERTIES OF ULTRAFINE METAL NANOPARTICLES ON DIELECTRIC ANTENNA PARTICLES
No full textEffective light energy conversion into other forms of energy in metal and metal compound nanoparticles has been of great interest in past decades. Being illuminated by incident light, electrons in the nanoparticles can be excited to higher energy states followed by deposition of energy into other molecules around their surface and the lattices in the following relaxation process. Ultrafine nanoparticles are thus preferred in these processes due to their high specific surface areas. Moreover, the portion of excited electrons with higher energies is higher in smaller nanoparticles than in larger ones. However, the overall light power absorbed by nanoparticles is proportional to the square of particle size, which causes the ultrafine nanoparticles not to efficiently absorb the incident light, or to drive further chemical or physical processes.Light antennae materials are usually employed to enhance the light absorption of these ultrafine nanoparticles. Plasmonic nanoparticles, e.g., Ag, Au, Cu, and Al nanoparticles, enhance the light absorption of loaded nanoparticles mainly through strong electromagnetic fields generated near their surfaces and have been proven to be effective light antennae to benefit the light energy conversion of ultrafine nanoparticles. On the other hand, spherical dielectric particles, e.g., silicon dioxide nanospheres, represent a different type of light antennae with the advantages of low cost, simple synthesis, and negligible Ohmic loss when being illuminated. When the sizes of high geometric symmetry dielectric nanospheres are comparable with the wavelength of the incident light, Mie scattering can happen based on the difference in refractive index between the sphere and the surrounding medium, generating size-dependent scattering resonances at various wavelengths. At these wavelengths, strong electric fields can be created on the surface of dielectric spheres to enhance the light absorption of the nanoparticles loaded on the surface. Previous works have shown that silica nanospheres with a diameter of several hundreds of nanometers can effectively enhance the light absorption of ultrafine Pt nanoparticles and benefit photocatalytic reactions, e.g., selective oxidation of benzyl alcohol. Over the past few years, this concept has been broadened to other ultrafine nanoparticles to study their novel photo-to-chemical/physical properties. However, the availability and comprehensive understanding of the optical properties of this class of composite particles still need to be improved. These challenges limit the further development of these composite materials in new light energy conversion processes. This dissertation aims at studying this class of novel ultrafine nanoparticles/dielectric sphere composite particles synthesis and optical properties.
In Chapter 2, a synthesis protocol of ultrafine ruthenium oxyhydroxide nanoparticles on the surface of silica nanospheres’ surfaces is introduced. Unlike the traditional synthesis of nanoparticles in solution followed by a loading process, the method developed in this chapter only requires the injection of aqueous ruthenium salt solution into a silica nanosphere dispersion. The obtained ultrafine nanoparticles with sizes of 2-3 nm are characterized to be ruthenium oxyhydroxide (RuOOH) nanoparticles. The silica nanospheres are crucial in stabilizing these ultrafine RuOOH nanoparticles and enhancing their light absorption. Due to the presence of ruthenium-oxygen bonds in the nanoparticles, the absorbed photons are converted to heat and transferred to the surrounding media with a photo-to-thermal conversion efficiency close to the unity. Experimental results have shown that heat can be effectively used in accelerating the reaction rate of selective oxidation of benzyl alcohol by molecular oxygen. Kinetics data also have shown that these ultrafine RuOOH nanoparticles are able to activate molecular oxygen adsorbed on their surfaces, which represents a novel property of these ultrafine RuOOH nanoparticles that is not observed in other traditional ruthenium catalysts.
In Chapter 3, a more general synthesis method of ultrafine metal and metal oxyhydroxide nanoparticles on silica nanospheres is developed, inspired by the synthetic route in Chapter 2. Instead of functionalizing silica surfaces with silane agents with amino groups, the silica surfaces are selectively etched by an aqueous base to create a high density of surface hydroxyl groups. These hydroxyl groups can provide basic sites to stabilize metal ions in aqueous dispersion, which are nuclei for the further growth of larger metal oxyhydroxide nanoparticles. In this chapter, more than ten kinds of metal ions are loaded onto silica spheres, forming oxyhydroxide nanoparticles with average sizes below 5 nm. Some oxyhydroxide nanoparticles can be reduced by 5% H2/N2 to form metal nanoparticles with their ultrafine sizes maintained. The synthesis protocol is promising in preparation of bimetallic samples. The composition and optical absorption of all obtained composite particles are analyzed, demonstrating the practicability of utilizing the reported method to prepare high-quality light-absorbing composite particles.
In Chapter 4, the optical absorption property of the composite particle is systematically studied. Using ultrafine Pt nanoparticles as the light absorbing material, the light absorptions of composite particles consisting of silica spheres with diameters from 100 to 1100 nm loaded with these Pt nanoparticles are studied. Through the combination of theoretical calculation based on Mie theory and the measured optical absorption spectra, the scattering resonance peaks are successfully located in each sample. It is also found that the photonic crystal effect and the general absorption of Pt nanoparticles can contribute to the light absorption spectra, especially at higher wavelengths. The relationship between the general absorption of Pt nanoparticles and the packing density of the powder is further studied. The successful deconvolution of several components in the absorption spectra can guide the further rational design of composite particles in optical-related applications.
In Chapter 5, the composite particle system is further broadened to using high refractive index zinc sulfide nanospheres as a light antenna. The use of a higher refractive index light antenna is promising for obtaining higher light absorption enhancement in loaded ultrafine nanoparticles, even though the sample is dispersed in organic media with a high refractive index as well. After the successful loading of Pt nanoparticles to the surface of silica-coated zinc sulfide nanospheres, a protocol for analyzing their light absorption spectra in organic media is proposed. Size-dependent scattering resonance peaks are observed in bare zinc sulfide nanospheres and can be utilized to enhance the light absorption of Pt nanoparticles, even when the sample is sealed in high refractive index polymeric matrices. The composite particles are further employed in photothermal tests, the results prove that the better light absorption enhancement using zinc sulfide than silica nanospheres.
The results introduced in this dissertation represent the first systematic and comprehensive study of ultrafine metal and metal oxyhydroxide nanoparticles loaded on the surface of dielectric light antenna particles. The conclusions open an avenue to further rational design of high-performance light-absorbing composite particles to be used in photo-to-thermal/chemical processes.Chemistr
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