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In-Situ Observation of Coulomb Fission of Individual Plasmonic Nanoparticles
摘要： Reshaping plasmonic nanoparticles with laser pulses has been extensively researched as a tool for tuning their properties. However, in the absence of direct observations of the processes involved, important mechanistic details have remained elusive. Here, we present an in-situ electron microscopy study of one such process that involves Coulomb fission of plasmonic nanoparticles under femtosecond laser irradiation. We observe that gold nanoparticles encapsulated in a silica shell fission by emitting progeny droplets comprised of about 10-500 atoms, with ejection preferentially occurring along the laser polarization direction. Under continued irradiation, the emitted droplets coalesce into a second core within the silica shell, and the system evolves into a dual-core particle. Our findings are consistent with a mechanism in which electrons are preferentially emitted from the gold core along the laser polarization direction. The resulting anisotropic charge distribution in the silica shell then determines the direction in which progeny droplets are ejected. In addition to yielding insights into the mechanism of Coulomb fission in plasmonic nanoparticles, our experiments point towards a facile method for forming surfaces decorated with aligned dual-gold-core silica shell particles.
关键词： single-particle observation,gold-core silica shell particles,plasmonic nanoparticles,in-situ,nanoparticle reshaping,Coulomb fission,transmission electron microscopy
更新于2025-09-11 14:15:04
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Phase Transition of SiO <sub/>2</sub> Nanoparticles Prepared from Natural Sand: The Calcination Temperature Effect
摘要： In this paper, we systematically report the synthesis of nano silica powder from natural silica sand by a continuous process. Extraction of sodium silicate from silica sand was through a hydrothermal process, then sodium silicate was ready to be used as a precursor in the form of silicate slurry by coprecipitation process. The silicate slurry of SiO2.XH2O was then dried in a furnace at 150 °C for 4 hours until obtaining a pure white SiO2 powder. At a calcination temperature of 900 °C, the sample was then tested by XRD to analyze the transformation of the crystal phase of SiO2 nanoparticles. Identification of functional group absorption was undertaken by FTIR test, and the particle grain microstructure was analyzed by SEM. At calcination temperature of 900 °C, the SiO2 silica nanoparticles experienced a change of phase from amorphous to crystal or amorphous-cristobalite phase; a shift in stiffness for positions of functional group absorption of Si-O stretching or LO functional groups, Si-O stretching or TO, Si-O-Si bending and Si-O-Si rocking and OH-functional groups occurred; the growth of particle grains happened with a spherical and oval trend, with a larger size. SiO2 nanoparticles were successfully synthesized by a continuous method and 900 °C calcination temperature had a significant effect on structural phase changes, the formation of siloxane functional groups, silanol, and grain growth on SiO2 nanoparticles.
关键词： calcination,nanoparticle,amorphous,cristobalite,natural sand,Silica
更新于2025-09-11 14:15:04
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Chemically modified silica-based sensors: effect of the nature of organosilane
摘要： The use of organosilanes to produce hybrid materials, also known as ORMOSILs (organically modified silicas) can be a good strategy to tune a material’s properties, enabling, for example, the optimization of important features of chemical sensors such as specificity, sensitivity and response time. Thus, different hybrid silicas were prepared by the sol-gel method to be employed as a colorimetric sensor. The investigated organic groups for producing hybrid materials included methyl, octyl, octadecyl, vinyl, phenyl, aminopropyl, isocyanatopropyl, mercaptopropyl, chloropropyl, iodopropyl and glycidoxypropyl groups, and the pH indicator alizarin red was used as the encapsulated receptor element. The sensors were characterized using a set of complementary techniques such as UV-vis spectroscopy, cyclic and differential pulse voltammetry, nuclear magnetic resonance, nitrogen porosimetry, small-angle X-ray scattering and transmission electronic microscopy. The performance was evaluated according to the color change (ΔE* ab) by conducting a colorimetric analysis and measuring the response time after ammonia exposure, with results varying from 48 to 95 s. Additionally, other characteristics of the hybrid materials, such as their surface area, reticulation degree, texture and morphologic properties, were altered depending on the organic modification present in the silica network. The potentiality for material optimization, to achieve better sensor performance, depends on the employed organosilane.
关键词： colorimetric sensor,sol-gel,ammonia,ORMOSIL,organosilanes,hybrid silica
更新于2025-09-11 14:15:04
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Pentacene Crystal Growth on Silica and Layer-Dependent Step-Edge Barrier From Atomistic Simulations
摘要： Understanding and controlling the growth of organic crystals deposited from the vapor phase is important for fundamental materials science and necessary for its application in pharmaceutical and organic electronics industries. Here this process is studied for the paradigmatic case of pentacene on silica by means of a specifically tailored computational approach inspired by the experimental vapor deposition process. This scheme is able to reproduce the early stages of the thin film formation, characterized by a quasi layer-by-layer growth, thus showcasing its potential as a tool complementary to experimental techniques for investigating organic crystals. Crystalline islands of standing molecules are formed at a critical coverage, as a result of a collective reorientation of disordered aggregates of flat-lying molecules. The growth then proceeds by sequential attachment of molecules at the cluster and then terrace edges. Free energy calculations allowed us to characterize the step edge barrier for descending the terraces, a fundamental parameter for growth models for which only indirect experimental measurements are available. The barrier is found to be layer dependent (approximately 1 kcal/mol for the first monolayer on silica, 2 kcal/mol for the second monolayer) and to extend over a distance comparable with the molecular length.
关键词： pentacene,atomistic simulations,silica,step-edge barrier,crystal growth
更新于2025-09-11 14:15:04
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Synthesis of Hollow Silica Nanocubes with Tuneable Size and Shape, Suitable for Light Scattering Studies
摘要： We present a preparation method for hollow silica nanocubes with tuneable size and shape in the range required for light scattering studies. Cuprous oxide nanocubes are prepared by a water-assisted polyol method. By adjusting the water content, the size of the nanocubes can be tuned in the range of 40–120 nm. These cubes function as a shape template in the subsequent coating with St?ber silica, resulting in core-shell nanocubes. Dissolving the core with nitric acid results in hollow silica nanocubes with sizes ranging from 80–120 nm and cubicity shape parameters between 3 and 6.5.
关键词： colloids,nanocubes,microscopy,silica,superballs,synthesis
更新于2025-09-10 09:29:36
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Studies of the characteristic and reaction mechanism of silica xerogel by sol–gel method catalyzed by alkylbiguanide as a strong organic base
摘要： Treatment of tetraethyl orthosilicate with 1,2-diisopropyl-4,4,5,5-tetra-methyl biguanide (A) as a highly strong base immediately gave silica gel by means of hydrolysis and condensation reaction at room temperature. The resulting wet gel was transparent and showed high density after dryness. From the results of gas adsorption and BET analysis, silica gel obtained by the treatment of strong base A had larger specific surface area and pore volume than silica gel that was prepared by a regular or less strong base such as tetramethylammonium hydroxide (TMAH). FTIR analysis revealed that the peak strength of Si-OH bond at 960 cm?1 of silica gel prepared by highly strong base A was smaller than that of TMAH. To understand the mechanism behind such difference, a mixture of diphenylsilandiol and dimethoxydiphenylsilane were reacted with highly strong base A, and the resulting products comprised linear-chain siloxane oligomer and octaphenylcyclotetrasiloxane. Our results indicate that silanol generated by hydrolysis of TEOS is activated by A and the activated silanol undergoes subsequent direct reaction with unhydrolyzed alkoxy silane to give condensation products in ethanol. Such a direct polycondensation between silanol and alkoxy silane brought by highly strong base A led to three-dimensional crosslinking having a higher bulk density of silica gel.
关键词： Biguanide,Silica xerogel,Sol–gel processes,Strong organic base
更新于2025-09-10 09:29:36
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Confined electrochemiluminescence in vertically ordered silica mesochannels for the imaging of hydrogen peroxide released from single cells
摘要： Here, the confined electrochemiluminescence (ECL) of luminol and hydrogen peroxide is achieved in vertically ordered silica mesochannels (SMCs) and applied to map the efflux of hydrogen peroxide from single living cells. The vertical alignment of SMCs on indium tin oxide (ITO) slides restricts the lateral diffusion of species generated in the ECL process. Accordingly, the cross-talk of luminescence intensity from nearby microregions is minimized for higher-spatial-resolution ECL imaging. The characterization of luminol ECL on these SMC-coated slides yields a detection range of hydrogen peroxide between 5 μM and 1 mM, providing high sensitivity in imaging the efflux of hydrogen peroxide from cells. Compared with the luminescence from individual cells on bare ITO slides, ~ 4-fold intensity is observed for SMC-coated ITO, suggesting a better electrode surface for single-cell ECL imaging.
关键词： single-cell imaging,hydrogen peroxide,silica mesochannels,confined electrochemiluminescence,luminol
更新于2025-09-10 09:29:36
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Reaction-probe infrared investigation on drastic change in reactivity of mesoporous silica for acetalization of cyclohexanone with methanol; pore-size dependence
摘要： Small-pored (< 2.5 nm) mesoporous silica showed remarkably higher catalytic activity for cyclohexanone acetalization with methanol than large-pored ones (≥2.5 nm). For the clari?cation of the pore-size e?ect of mesoporous silicas (MCM-41 and SBA-15) on the reactivity, the reaction probe infrared (IR) method was applied. No evident di?erences were observed by conventional IR characterization methods using CO, pyridine and acetonitrile adsorption. IR spectra of methanol, one of the reactants, on small-pored (MCM-41) and large-pored (SBA-15) samples appeared the same. On the other hand, adsorption of cyclohexanone resulted in di?erent IR spectra: a C]O stretching band appeared at lower frequency side on MCM-41 at a small amount of adsorption in addition to that observed on SBA-15. This result indicates the presence of the stronger interaction of cyclohexanone with MCM-41 than that with SBA-15. When the time course of the reaction was observed by in-situ IR observation, the consumption of activated carbonyl groups and the generation of 1,1-dimethoxycyclohexane, the reaction product, were con?rmed. The presence of the activated cyclohexanone was most probably due to the adsorption on two (or more) OH groups in vicinity, while a non-activated species occupied a single OH group. The reaction probe IR method is thus, a direct and e?ective approach to extract the small di?erences in catalysis.
关键词： Pore-size dependence,Acetalization,Infrared spectroscopy,Reaction-probe,Mesoporous silica
更新于2025-09-10 09:29:36
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Influence of the parameters in the preparation of silica nanoparticles from biomass and chemical silica precursors towards bioimaging application
摘要： Silica nanoparticles (SNP’s) occupy a prominent role in scientific research due to their easy preparation methodology and its wide uses in various applications. In this work, SNP’s were prepared from biomass (rice husk) and chemical precursor, tetraethoxysilane (TEOS) with the particle sizes of 50 nm and 200 nm respectively. The influence of particle size on varying the concentration of ethanol and water in Stober method of synthesis were also analysed. Since, porphyrin has the good electro and photo catalytic property, in this study, porphyrin NP’s was functionalized on the surface of the SNP’s. The functional groups were confirmed from FTIR spectra. From SEM analysis, it was observed that, the size of the SNP’s increased with increase in the concentration of ethanol. The optical dynamic properties of SNP’s functionalized with porphyrin NP’s were analysed from UV-Vis spectroscopy and Fluorolog. Further, the functionalization of SNP’s and their binding affinity were calculated by UV absorption spectra.
关键词： Porphyrin,Rice husk,photoluminescence,Silica nanoparticle
更新于2025-09-10 09:29:36
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[Springer Series on Polymer and Composite Materials] Polymer/POSS Nanocomposites and Hybrid Materials (Preparation, Properties, Applications) || Organic–Inorganic Hybrid Materials with POSS for Coatings
摘要： Surface coatings are important in terms of aesthetic and protection against the environmental and harsh conditions such as corrosion, erosion, abrasion, mechanical forces. Importance of coating is due to this fact that by use of a sub-micrometer film special substrates can be protected and find an appropriate role in the application sought. However, improvement in properties of coating is so important and one of the best methods to improve their properties is using nanotechnology. Polyhedral oligomeric silsesquioxane (POSS) is a special type of silica family with the imperial structure of RSiO1.5. This is a cage-like molecule that has been able to take on a special space in coating industry. It can affect mechanical properties (modulus, elongation at break, yield strength, impact resistance), surface properties (hydrophilicity, hydrophobicity, surface friction, and surface roughness), thermochemical properties (curing time and curing behavior), rheological properties, chemical resistance, and permeability. In this chapter, the effect of POSS addition on the mechanical properties, surface properties, flame retardant effect, and corrosion resistance has been studied.
关键词： POSS,Nano,Coating,Silica,Hybrid
更新于2025-09-10 09:29:36