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Optimization of formaldehyde detection performance based on Ni2+ sensitized monodisperse amorphous zinc tin oxide microcubes
摘要： The pure and Ni2+ sensitized monodisperse amorphous zinc tin oxide (a-ZTO) microcubes were synthesized via an in-situ precipitation method and subsequent wet impregnation. XPS results revealed that Ni2+ sensitization increased the relative content of chemisorbed oxygen and oxygen vacancies on the surface of a-ZTO microcubes. Compared to pure a-ZTO microcubes, 0.75 at% Ni2+ sensitized a-ZTO microcubes can significantly improve the gas sensing performance to formaldehyde at 200 °C, which may be attributed to its uniform morphology and modification of Ni2+ on the surface of a-ZTO microcubes. Further, the gas sensing mechanism is briefly discussed.
关键词： Surface sensitization,Zinc tin oxide,Monodisperse,Amorphous material,Sensors
更新于2025-09-23 15:22:29
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Ag nanocrystals with nearly ideal optical quality: synthesis, growth mechanism, and characterizations
摘要： Though Ag nanocrystals are predicted as the best material for localized surface plasmon resonances (LSPR) in the visible light region, realization of their ideal LSPR properties is hindered by the stringent requirement, i.e., simultaneous control of their size, shape, crystallinity, and surface structure. To achieve this goal, a synthetic scheme in non-polar solvent coupled with mild oxidative-etching by H+ ions is established. With a trace amount of Cl- ions as catalysts, H+ ions (in the form of carboxylic acids) become active for selectively etching the nuclei (and small nanocrystals) with imperfect crystal structure, which results in a new growth mechanism for formation of monodisperse nanocrystals, namely “self-focusing of size/crystallinity distribution”. H+ ions, ligands, and other reagents in the scheme are confirmed to possess negligible effects on the surface dielectric properties of Ag nanocrystals. To eliminate radiative damping of LSPR, single-crystalline and monodisperse spherical Ag nanocrystals in the size range between 7 and 20 nm are synthesized using this one-pot scheme. With excellent control of all the structural parameters, the full-width-at-half-maximum of LSPR spectra of single-crystalline Ag nanocrystals match theoretical predictions in the entire size range, and the maximum quality factor (~20) of LSPR predicted by theory is realized. Raman enhancement factor of the single-crystalline Ag nanocrystals for crystal violet (excitation at 514 nm) is 5 times higher than that of the typical multi-twinned ones with the same size.
关键词： localized surface plasmon resonances,oxidative-etching,monodisperse,single-crystalline,Ag nanocrystals,Raman enhancement
更新于2025-09-23 15:21:21
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Manipulation of the Size and Phase Composition of Yttrium Iron Garnet Nanoparticles by Pulsed Laser Post-Processing in Liquid
摘要： Modi?cation of the size and phase composition of magnetic oxide nanomaterials dispersed in liquids by laser synthesis and processing of colloids has high implications for applications in biomedicine, catalysis and for nanoparticle-polymer composites. Controlling these properties for ternary oxides, however, is challenging with typical additives like salts and ligands and can lead to unwanted byproducts and various phases. In our study, we demonstrate how additive-free pulsed laser post-processing (LPP) of colloidal yttrium iron oxide nanoparticles using high repetition rates and power at 355 nm laser wavelength can be used for phase transformation and phase puri?cation of the garnet structure by variation of the laser ?uence as well as the applied energy dose. Furthermore, LPP allows particle size modi?cation between 5 nm (ps laser) and 20 nm (ns laser) and signi?cant increase of the monodispersity. Resulting colloidal nanoparticles are investigated regarding their size, structure and temperature-dependent magnetic properties.
关键词： laser melting,yttrium iron oxide,monodisperse,laser fragmentation,phase transformation,garnet,perovskite,laser ablation,ferrimagnetic nanoparticles
更新于2025-09-23 15:19:57
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Formation of Size and Density Controlled Nanostructures by Galvanic Displacement
摘要： Gold (Au) and copper (Cu)-based nanostructures are of great interest due to their applicability in various areas including catalysis, sensing and optoelectronics. Nanostructures synthesized by the galvanic displacement method often lead to non-uniform density and poor size distribution. Here, density and size-controlled synthesis of Au and Cu-based nanostructures was made possible by galvanic displacement with limited exposure to hydrofluoric (HF) acid and the use of surfactants like L-cysteine (L-Cys) and cetyltrimethylammonium bromide (CTAB). An approach involving cyclic exposure to HF acid regulated the nanostructure density. Further, the use of surfactants generated monodisperse nanoparticles in the initial stages of the deposition with increased density. The characterization of Au and Cu-based nanostructures was performed by scanning electron microscopy, atomic force microscopy, UV-Visible spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and X-ray diffraction. The surface enhanced Raman spectroscopic measurements demonstrated an increase in the Raman intensity by two to three orders of magnitude for analyte molecules like Rhodamine 6G dye and paraoxon.
关键词： monodisperse,sensing,surfactant,nanostructures,gold
更新于2025-09-23 15:19:57
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Improved electrical performance and transparency of bottom-gate, bottom-contact single-walled carbon nanotube transistors using graphene source/drain electrodes
摘要： We propose a centrifuge-based microfluidic device housed in a standard microtube for generation of monodisperse microdroplets from tens of μl sample volume. Centrifugation drives overpressure of a dispersed phase, thus infuses the dispersed phase into a microchannel. Because of the channel geometry for step emulsification, the infused dispersed phase is pinched off forming droplets. Then, the droplets accumulate on the bottom of the microtube by centrifugal force. We succeeded in generation of monodisperse droplets with a diameter of 130 μm (CV <2%) by operation of centrifuge. Since the device can produce droplets in a microtube without complex experimental setup (e.g. syringe pump), it will be a powerful tool for simple generation of droplets for droplet-based applications.
关键词： centrifuge-based,microfluidic device,monodisperse droplets,step emulsification
更新于2025-09-12 10:27:22
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Gram Scale Synthesis of Isolated Monodisperse Gold Nanorods
摘要： While the gold nanorods (AuNRs) possess a strong potential application in nanotechnology, plasmonics and sensing, the scale-up synthesis of isolated AuNRs in gram quantity remains a challenge. Nearly all previously reported methods produce aqueous solutions of CTAB-coated AuNRs in milligram quantities with the yield of ~20-30 % in terms of Au (I) to Au (0) conversion. In addition, it is difficult to remove CTAB bilayer from the surface of AuNRs and yet make them soluble and functionalized for further processing and chemical modification. This report describes the synthesis of monodisperse functionalized AuNRs (σ~5%) in gram quantities. Our approach is to increase the concentration of HAuCl4.3H20 in the growth solution to produce larger quantities of starting AuNRs and further reduce the remaining Au (I) ions onto the surface of AuNRs. The slow and controlled addition of reducing agent ascorbic acid (AA) continues to Au (0) (via disproportionation reaction) onto the surface of nanorods maintaining their uniform morphology without creating any unwanted impurities of various shapes. In addition, this approach significantly narrows the size distribution due to the continuous growth of partially grown AuNRs during the initial stage of the synthesis. To isolate one-gram quantity of AuNRs and make them functionalized for further chemical reactions, a ligand exchange approach was utilized where surfactant CTAB was replaced with 4-mercaptophenol. The thiol group from 4-mercaptophenol forms a covalent bond to the surface of AuNRs leaving free functional OH groups available for further chemical coupling reactions. For the ligand exchange process, a concentrated solution of 4-mercaptophenol in tetrahydrofuran (THF) solution was introduced into the AuNRs solution. Pure AuNRs, functionalized with 4-mercaptophenol were isolated by dispersion and rinsing with excess of THF, followed by centrifugation.
关键词： Amplification,Surface Functionalization,Gram Scale,Monodisperse,Gold Nanorods
更新于2025-09-10 09:29:36
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Continuous Synthesis of Monodisperse Yolk-Shell Titania Microspheres
摘要： A microfluidic strategy is developed for continuous synthesis of monodisperse yolk-shell titania microspheres. The continuous flow synthesis of titania microparticles is achieved by decoupling the microdroplet formation and interfacial hydrolysis reaction steps by utilizing a polar aprotic solvent as the continuous phase in the microreactor. The decoupling of the precursor microdroplet formation and the hydrolysis reaction allows titania synthesis throughputs an order of magnitude higher than those previously reported in a single-channel flow reactor (~0.1 g/h calcined microparticles), without affecting the microreactor lifetime due to clogging. Flow synthesis and dynamics across a broad range of precursor flow rates are examined, while effects of flow synthesis parameters, including the precursor to continuous phase flow rate ratio, precursor composition, and calcination temperature on the surface morphology, size, and composition of the resulting titania microparticles are explored in detail. Titania microparticle size can be controlled by variation in the precursor to continuous phase flow rate ratio. The surface morphology and porosity of the in-flow synthesized titania microparticles can be varied by adjusting the precursor composition, while crystalline phase can be tuned by varying the calcination temperature.
关键词： continuous synthesis,titania,microfluidic,yolk-shell,monodisperse
更新于2025-09-09 09:28:46
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Controllable synthesis of transparent dispersions of monodisperse anatase-TiO2 nanoparticles and nanorods
摘要： Controllable synthesis of monodisperse nanocrystals is still a great challenge. In this study, the control strategy of alcohol medium was developed to conveniently synthesize monodisperse anatase-TiO2 nanocrystals with controllable size and shape by sol-gel method combined with solvothermal treatment. The effects of the amount of stearic acid and water, and molecular structure of alcohol on the size, the shape and the dispersity of TiO2 nanocrystals were explored. The optimum synthesis conditions were achieved. Monodisperse TiO2 nanoparticles and nanorods were obtained by using linear and branched alcohols, respectively. The size of nanoparticles decreased from 12 to 5 nm with increasing carbon number of linear alcohol. The aspect ratio of nanorods was adjusted from 1 to 5 by selecting alcohols with different locations of branched methyl group. The as-prepared monodisperse TiO2 nanocrystals could be readily dispersed in some commonly-used solvents to form transparent nanodispersions. Furthermore, a possible formation mechanism was also investigated.
关键词： Monodisperse TiO2 nanocrystals,transparent dispersion,nanoparticles,nanorods,tunable preparation
更新于2025-09-04 15:30:14
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Sequential Growth of High Quality Sub-10 nm Core-Shell Nanocrystals: Understanding the Nucleation and Growth Process Using Dynamic Light Scattering
摘要： Monodisperse sub-10 nm core-shell nanocrystals have been extensively studied owing to their important applications in catalysis, bioimaging, nanomedicine and so on. In this work, an amorphous shell component-crystallization strategy has been proposed to prepare high quality sub-10 nm NaYF4:Yb/Er@NaGdF4 core-shell nanocrystals successfully via a sequential growth process. Dynamic light scattering technique has been used to investigate the secondary nucleation and growth process of forming the core-shell nanocrystals. The size and morphologies evolution of the core-shell nanocrystals reveal that the secondary nucleation of the shell component is unavoidable after hot-injecting of the shell precursor at high temperature, which followed by dissolution and re-crystallization process (an Ostwald Ripening process) to partially produce the core-shell nanocrystals. The present study demonstrates that the size of seed nanocrystals and the injection temperature of the shell component precursor play a vital role in formation of core-shell nanostructures completely. This work will provide an alternative strategy for precisely controllable fabrication of sub-10nm core-shell nanostructures for various applications.
关键词： Seed-mediated growth,Monodisperse,Core-shell nanoparticles,Dynamic light scattering
更新于2025-09-04 15:30:14
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Sequence-definition in stiff conjugated oligomers
摘要： The concept of sequence-definition in the sense of polymer chemistry is introduced to conjugated, rod-like oligo(phenylene ethynylene)s via an iterative synthesis procedure. Specifically, monodisperse sequence-defined trimers and pentamers were prepared via iterative Sonogashira cross-coupling and deprotection. The reaction procedure was extended to tetra- and pentamers for the first time yielding a monodisperse pentamer with 18% and a sequence-defined pentamer with 3.2% overall yield. Furthermore, three novel trimers with a 9H-fluorene building block at predefined positions within the phenylene ethynylene chain were synthesised in 23–52% overall yields. Hence, it was confirmed that a functionality of interest can be incorporated selectively at a pre-defined position of these monodisperse oligomers. All respective intermediate structures were fully characterised by proton and carbon NMR, mass spectrometry, size-exclusion chromatography, and IR spectroscopy. Additionally, thermal and optical transitions are reported for the different oligomers.
关键词： fluorene,monodisperse,Sonogashira cross-coupling,sequence-definition,conjugated oligomers
更新于2025-09-04 15:30:14