Seed-mediated Growth Process Research Articles

Cu2+-Dominated Chirality Transfer from Chiral Molecules to Concave Chiral Au Nanoparticles.

Foreign ions as additives are of great significance for realizing excellent control over the morphology of noble metal nanostructures in the state-of-the-art seed-mediated growth method; however, they remain largely unexplored in chiral synthesis. Here, we report on a Cu2+-dominated chiral growth strategy that can direct the growth of concave chiral Au nanoparticles with C3-dominant chiral centers. The introduction of trace amounts of Cu2+ ions in the seed-mediated chiral growth process is found to dominate the chirality transfer from chiral molecules to chiral nanoparticles, leading to the formation of chiral nanoparticles with a concave VC geometry. Both experimental and theoretical results further demonstrate the correlation between the nanoparticle structure and optical chirality for the concave chiral nanoparticle. The Cu2+ ion is found to dominate the chiral growth by selectively activating the deposition of Au atoms along the [110] and [111] directions, facilitating the formation of the concave VC. We further demonstrate that the Cu2+-dominated chiral growth strategy can be employed to generate a variety of concave chiral nanoparticles with enriched geometric chirality and desired chiroptical properties. Concave chiral nanoparticles also exhibit appealing catalytic activity and selectivity toward electrocatalytic oxidation of enantiomers in comparison to helicoidal nanoparticles. The ability to tune the geometric chirality in a controlled manner by simply manipulating the Cu2+ ions as additives opens up a promising strategy for creating chiral nanomaterials with increasing architectural diversity for chirality-dependent optical and catalytic applications.

Magnetic anisotropy engineering in onion-structured metal oxide nanoparticles combining dual exchange coupling and proximity effects.

A series of exchange-coupled magnetic nanoparticles combining several magnetic phases in an onion-type structure were synthesized by performing a three-step seed-mediated growth process. Iron and cobalt precursors were alternatively decomposed in high-boiling-temperature solvents (288-310 °C) to successively grow CoO and Fe3-δO4 shells (the latter in three stages) on the surface of Fe3-δO4 seeds. The structure and chemical composition of these nanoparticles were investigated in depth by combining a wide panel of advanced techniques, such as scanning transmission electron microscopy (STEM), electron energy-loss spectroscopy-spectrum imaging (EELS-SI), 57Fe Mössbauer spectrometry, and X-ray circular magnetic dichroism (XMCD) techniques. The size of the nanoparticles increased progressively after each thermal decomposition step, but the crystal structure of core-shell nanoparticles was significantly modified during the growth of the second shell. Indeed, the antiferromagnetic CoO phase was progressively replaced by the CoFe2O4 ferrimagnet due to the concomitant processes of partial solubilization/crystallization and the interfacial cationic diffusion of iron. A much more complex chemical structure than that suggested by a simple size variation of the nanoparticles is thus proposed, namely Fe3-δO4@CoO-CoFe2O4@Fe3-δO4, where an intermediate Co-based layer was shown to progressively become a single, hybrid magnetic phase (attributed to proximity effects) with a reduction in the CoO amount. In turn, the dual exchange-coupling of this hybrid Co-based intermediate layer (with high anisotropy and ordering temperature) with the surrounding ferrite (core and outer shells) stabilized the particle moment well above room temperature. These effects allow for the production of Fe oxide-based magnetic nanoparticles with high effective anisotropy, thus revealing the potential of this strategy to design rare-earth-free permanent nanomagnets at room temperature.

Tuning chiral morphology of gold nanoparticles with reversed chiral signals by adjusting the reaction temperature of the seed-mediated growth process

Reaction temperature was found to reverse the chiral modes of the gold nanoparticles (AuNPs) prepared through the seed-mediated and chiral ligand-directed growth method.

Light-induced synthesis of silver nanoprisms as a surface-enhanced Raman scattering substrate for N-acetyl procainamide drug quantification

Triangle-shaped silver nanoprisms (AgNPMs) were prepared by a photo-induced method through a seed-mediated growth process and were successfully employed as an ultra-sensitive surface-enhanced Raman scattering (SERS) substrate for the detection of the chemotherapeutic N-acetyl procainamide (NAPA) compound. The transformation of the morphology of the nanoprisms substrate could be noted with a remarkable change in color, possessing an average size of 95 nm. The shape-modified AgNPMs exhibited interesting optical characteristics owing to the truncated dual edges, which led to a pronounced longitudinal localized surface plasmonic resonance (LLSPR) behavior. The nanoprisms-based SERS substrate demonstrated an outstanding sensitivity for NAPA in aqueous solutions with the lowest ever reported detection limit of 0.5 × 10−13 M corresponding to excellent recovery and stability. A steady linear response with a broad dynamic range (10−4–10−12 M) and an R2 of 0.945 was also achieved. The results proved that the NPMs demonstrated excellent efficiency, reproducibility (97%), and stability (30 days) with a superior Raman signal enhancement reaching an ultralow detection limit of 0.5 × 10−13 M compared to the nanosphere particles which could show an LOD of 0.5 × 10−9 M.

Unraveling the Growth Process of Core–Shell Structured Upconversion Nanoparticles: Implications for Color Tuning of Upconversion Luminescence

The core–shell strategy has been routinely employed to improve emissive properties of upconversion nanoparticles (UCNPs). However, the underlying process of forming the core–shell structure still remains largely unexplored. In this work, we have performed a time-course study on the growth process of NaErF4@NaYF4 core–shell UCNPs to track time-dependent variations in size, phase, elemental distribution, and luminescence properties throughout the whole synthesis process. Our results show that the formation of core–shell UCNPs includes three major stages: formation of α-phase shell precursors, transition of the α-phase to β-phase, and seed-mediated growth. Among these stages, the first two mainly occur in the early stage of the growth process, while the last one dominates the subsequent process. During the seed-mediated growth process, the elemental distribution of the core–shell nanostructure is observed to change after a short time of reaching the reaction temperature and it continues throughout the rest of the growth process. Most importantly, the emissive properties also showed time-dependent variations, which were attributed to the activation of different optical pathways due to different shell thicknesses over time. This study is believed to provide fundamental insights into the growth mechanism of core–shell UCNPs, which can also be potentially applied for tuning the luminescence of other core–shell luminescent nanostructures.

The energetic and physical concept of gold nanorod-dependent fluorescence in cancer treatment and development of new photonic compounds|review.

The optical features of gold nanorods (GNR) may be precisely controlled by manipulating their size, shape, and aspect ratio. This review explores the impact of these parameters on the optical tuning of (GNR). By altering the experimental conditions, like the addition of silver ions during the seed-mediated growth process, the aspect ratio of (GNR) may be regulated. The shape is trans from spherical to rod-like structures resulting in noticeable changes in the nanoparticles surface plasmons resonance (SPR) bands. The longitudinal SPR band, associated with electron oscillations along the long axis, exhibits a pronounced red shift into the (NIR) region as the aspect ratio increases. In contrast, the transverse SPR band remains relate unchanged. Using computational methods like the discrete dipole approximation (DDA) allows for analyzing absorption, scattering, and total extinction features of gold (G) nanoparticles. Studies have shown that increasing the aspect ratio enhances the scattering efficiency, indicating a higher scattering quantum yield (QY). These findings highlight the importance of size, shape, and aspect ratio in controlling the optical features of (GNR) providing valuable insights for various uses in nanophotonics and plasmonic-dependent fluorescence in cancer treatment and developing new photonic compound NRs.

Characterization and electrochemical properties of CuO–Cu2O@rGO nanocomposite synthesized by a seed-mediated growth process

A CuO–Cu2O@rGO nanocomposite (CuO–Cu2O@rGO NCP) has been successfully prepared through a seed-mediated growth process. X-ray diffraction (XRD) analysis results indicated a monoclinic phase of CuO–Cu2O@rGO NCP with space group C2/c. Transmission electron microscopy (TEM) revealed agglomeration of the CuO and Cu2O nanoparticles in the rGO sheet matrix. The interaction of CuO–Cu2O@rGO NPC resulted from the aggregation and overlapping of CuO and Cu2O nanoparticles owing to the influence of a seed-mediated growth process. The electrochemical properties of the CuO–Cu2O@rGO NPC electrode indicate the storage of energy at the surface through a pseudo-capacitive mechanism. The specific capacitance at a current density of 0.5 A g−1 and the average percentage capacity retention after 1000 cycles of a CuO–Cu2O@rGO electrode at a current density of 10 A g−1 were evaluated as 125.54 F g−1 and 89.87 ± 3.30%, respectively. In the CuO–Cu2O@rGO electrode, the incorporated rGO affects the electrical conductivity and the synergistic interactions in charge–discharge processes. Interestingly, these results showed that the material was synthesized through a seed-mediated growth process and reveal the key factors that determine the combination and volume expansion of the reversible redox transition between Cu+ and Cu2+ during charge–discharge processes.

PdAgPt Corner-Satellite Nanocrystals in Well-Controlled Morphologies and the Structure-Related Electrocatalytic Properties.

The functions of heterogeneous metallic nanocrystals (HMNCs) can be undoubtedly tuned by controlling their morphologies and compositions. As a less-studied kind of HMNCs, corner-satellite multi-metallic nanocrystals (CSMNCs) have great research value in structure-related electrocatalytic performance. In this work, PdAgPt corner-satellite nanocrystals with well-controlled morphologies and compositions have been developed by temperature regulation of a seed-mediated growth process. Through the seed-mediated growth, the morphology of PdAgPt products evolves from Pd@Ag cubes to PdAgPt corner-satellite cubes, and eventually to truncated hollow octahedra, as a result of the expansion of {111} facets in AgPt satellites. The growth of AgPt satellites exclusively on the corners of central cubes is realized with the joint help of Ag shell and moderate bromide, and hollow structures form only at higher reaction temperatures on account of galvanic displacement promoted by the Pd core. In view of the different performances of Pd and Pt toward formic acid oxidation (FAO), this structure-sensitive reaction is chosen to measure electrocatalytic properties of PdAgPt HMNCs. It is proven that PdAgPt CSMNCs display greatly improved activity toward FAO in direct oxidation pathway. In addition, with the help of AgPt heterogeneous shells, all PdAgPt HMNCs exhibit better durability than Pd cubes and commercial Pt.

Iridium coated Co nanoparticles embedded into highly porous N-doped carbon nanocubes grafted with carbon nanotubes as a catalytic cathode for high-performance Li–O2 batteries

Ir–Co/HP-NC/CNT was prepared by a seed-mediated growth and Ir-coating process, and further used as a catalytic cathode for Li–O2 batteries. This cell exhibits high discharge capacity, low overpotential and superior cycling life.

Synthesis of Citrate-Coated Penta-twinned Palladium Nanorods and Ultrathin Nanowires with a Tunable Aspect Ratio.

Green and scalable methodologies for the preparation of metal nanoparticles with fine control of shape and size are of high interest in many areas including catalysis, nanomedicine, and nanodiagnostics. In this contribution, we describe a new synthetic method for the production of palladium (Pd) penta-twinned nanowires and nanorods utilizing sodium citrate, formic acid, ascorbic acid, and potassium bromide (KBr) in water, without the use of surfactants or polymers. The synthesis is green, fast, and without the need of complex setups. Interestingly, a microwave-assisted scale-up process has been developed. The combination of a synthetic protocol for seeds and the seed-mediated growth process allows us to synthesize nanorods and nanowires by modulating the concentration of KBr. The synthesized nanomaterials have been physicochemically characterized. High-resolution transmission electron microscopy shows that the nanorods and nanowires have a penta-twinned structure enclosed by {100} lateral facets. Moreover, the absence of sticky molecules or toxic byproducts guarantees the biocompatibility of the nanomaterials, while leaving the surface clean to perform enzymatic activities.

Gold nanobipyramids integrated ultrasensitive optical and electrochemical biosensor for Aflatoxin B1 detection

This work reports the development of an electrical and optical biosensing for label-free detection of Aflatoxin B1 (AFB1) using gold (Au) nanobipyramids (NBPs). AuNBPs were synthesized through a two-step seed-mediated growth process followed by an exchange of capping agent from surfactant to lipoic acid. Pure and monodispersed AuNBPs of 70 nm base length were obtained and deposited on indium tin oxide (ITO)-coated glass substrate modified with self-assembled (3-Aminopropyl) triethoxysilane (APTES) film. The characterization of the obtained surfaces using spectroscopy, microscopy and diffractometry confirms the formation of AuNBPs, the conjugation to ITO electrode substrate and the immobilization of anti-AFB1 antibodies. AuNBPs modified ITO substrates were used for both electrochemical and Surface Plasmon Resonance biosensing studies. Localized Surface Plasmon Resonance (LSPR) local field enhancement was demonstrated. SPR based AFB1 detection was found to be linear in the 0.1–500 nM range with a limit of detection of 0.4 nM, whereas, impedimetric AFB1 detection was shown to be linear in the 0.1–25 nM range with a limit of detection of 0.1 nM. The practical utility of the impedimetric sensor was tested in spiked maize samples and 95–100% recovery percentage was found together with low relative standard deviation, proof of the robustness of this AFB1 sensor.

Electro-oxidation of glycerol by tetrametallic platinum-gold–palladium-silver nanoparticles

In this work, the electrochemical conversion of glycerol was studied on tetrametallic PtAuPdAg catalyst. The PtAuPdAg nanoparticles were synthesized via a seed-mediated growth process. The structure of the as-prepared PtAuPdAg nanoparticles was characterized by transmission electron microscopy, electron energy loss spectroscopy and UV–vis absorption spectroscopy. Electrochemical results indicate that the PtAuPdAg catalyst exhibits superior activity towards glycerol oxidation when compared with the Pt/C catalyst. In alkaline solutions, the PtAuPdAg catalyst possesses a current density of 8.90 mA cm−2, which is 18.2 times that of the Pt/C. Moreover, this result is higher than that of most previously reported catalysts. Additionally, the products of glycerol oxidation over the catalyst at potentials of 0.5, 0.7, 0.9, 1.1 and 1.3 V were analyzed by high performance liquid chromatography (HPLC). HPLC results show that the PtAuPdAg catalyst yields a remarkable dihydroxyacetone selectivity of 79.6%, and that the operating conditions have limited effects on the product distribution.

Structural transformation of Au seeds: the influence of temperature and surfactants

In the seed-mediated growth process of Au nanostructures, the uniformity and structures of the ultrafine seeds determine the purity and structures of the final Au products. Based on the highly shape-dependent surface plasmon resonance properties of Au nanostructures, we present the structures and structural transformation of Au seeds that have overgrown into Au nanostructures. The optical spectra and transmission electron microscopy images of the final product reflected that structures of the ultrafine seed are sensitive to the temperature and surfactants. It is found that the single-twinned Au seeds obtained at 30°C will transform into fivefold-twinned crystals at 90°C, which subsequently grow into Au nanobipyramids with a high surface plasmon resonance quality factor. The introduction of sodium citrate is beneficial for the formation of twinned crystal seeds. Hexadecyltrimethylammonium chloride can be used to keep the size of seeds small enough to allow Ostwald ripening at the initial heat treatment stage.

Optimizing the activity and selectivity of glycerol oxidation over core-shell electrocatalysts

High-performance electrocatalysts with excellent activity and selectivity hold the key to the electrochemical conversion of glycerol. Herein, well-defined bimetallic Au@Ag and trimetallic PdAu@Ag core-shelled nanoparticles were fabricated using a seed-mediated growth process and further examined as electrocatalysts for glycerol oxidation in both alkaline and acidic solutions. The activity of the catalysts was evaluated via cyclic voltammetry, linear sweep voltammetry and chronoamperometric measurements. The Au@Ag and PdAu@Ag nanoparticles are highly active in alkaline solutions, but inactive in acidic solutions. In alkaline solutions, the PdAu@Ag and Au@Ag nanoparticles show current densities of 3.94 and 2.57 mA cm−2, which are 4.3 and 25.7 times those of the commercial Pd/C and Au/C catalysts, respectively. The products of glycerol electro-oxidation were analyzed by high performance liquid chromatography (HPLC). Three major products, namely dihydroxyacetone (DHA), glyceric acid, glyceraldehyde and five minor products including oxalate acid, tartronic acid, formic acid, glycolic acid (GA) and glyoxylic acid were detected. Notably, a remarkable DHA selectivity of 70.1% was obtained from the PdAu@Ag catalyst at 0.9 V. The Au@Ag yields the largest GA selectivity of 31.6% at 1.1 V. The PdAu@Ag tends to yield more C3 products at high applied potentials.

Highly sensitive and selective visual detection of Cr(VI) ions based on etching of silver-coated gold nanorods

We report a visual detection of Cr(VI) ions using silver-coated gold nanorods (AuNR@Ag) as sensing probes. Au NRs were prepared by a seed-mediated growth process and AuNR@Ag nanostructures were synthesized by growing Ag nanoshells on Au NRs. Successful coating of Ag nanoshells on the surface of Au NRs was demonstrated with TEM, EDS, and UV–vis spectrometer. By increasing the overall amount of the deposited Ag on Au NRs, the localized surface plasmon resonance (LSPR) band was significantly blue-shifted, which allowed tuning across the visible spectrum. The sensing mechanism relies on the redox reaction between Cr(VI) ions and Ag nanoshells on Au NRs. As the concentration of Cr(VI) ions increased, more significant red-shift of the longitudinal peak and intensity decrease of the transverse peak could be observed using UV–vis spectrometer. Several parameters such as concentration of CTAB, thickness of the Ag nanoshells and pH of the sample were carefully optimized to determine Cr(VI) ions. Under optimized condition, this method showed a low detection limit of 0.4 μM and high selectivity towards Cr(VI) over other metal ions, and the detection range of Cr(VI) was tuned by controlling thickness of the Ag nanoshells. From multiple evaluations in real sample, it is clear that this method is a promising Cr(VI) ion colorimetric sensor with rapid, sensitive, and selective sensing ability.

Beyond the Concentration Limitation in the Synthesis of Nanobipyramids and Other Pentatwinned Gold Nanostructures.

Gold nanoparticles offer unique optoelectronic properties relevant for a wide range of processes and products, in biology and medicine (therapeutic agents, diagnostic, drug delivery), as well as in electronics, photovoltaics, and catalysis. So far, various synthesis methods proposed have led to rather limited concentration and purity of the colloidal suspensions, severely hindering their use. Here, we present a simple and versatile procedure for the synthesis of gold pentatwinned nanostructures, including nanobipyramids based on a seed-mediated growth process that overcomes the concentration limitations of current methods by 2 orders of magnitude. Moreover, our novel process offers quantitative yields while easily allowing a fine control of the particles' shape, size (with a high monodispersity), and plasmonic properties. Finally, we demonstrate that our method can be easily upscaled to produce large amounts of nanostructures, up to the gram scale, with minimal waste and postprocessing, thus facilitating their use for further applications and industrial developments.

Flow synthesis of silver nanoshells using a microreactor

Silver nanoshells have wide-ranging applications spanning from catalysis to bio-sensing because of their unique optical and chemical properties. They are synthesized through a seed-mediated growth process, in which surfaces of the core particle are decorated with metal seeds followed by the growth of silver. However, a typical synthesis is a time-consuming batch-process which creates inhomogeneity in the shell structures. Hence, it is required to establish a quick, simple, and robust synthetic method. Using a central collision type microreactor instead of a batch reactor is advantageous because of its large surface to volume ratio and rapid mixing. In this study, we synthesize silver nanoshells by using such a microreactor and investigate the effects of the molar ratio of ammonia to silver ion, the types of reducing agents, and the addition of polyvinylpyrrolidone (PVP) on the complete nanoshell formation. Our experiments demonstrate that a large molar ratio of ammonia to silver ion is required to form silver-ammonia complexes and regulate the reducing power of reductants to cover the core particles with silver. Formaldehyde, due to its weaker reducing power, is found to be a more suitable reducing agent than ascorbic acid. PVP molecules serve not only as a stabilizer but also as a facilitator to help smooth shell growth. Most importantly, the use of the microreactor is critical to the formation of complete silver nanoshells.

Self‐Aligned Anisotropic Plasmonic Nanostructures

Great opportunities emerge not only in the generation of anisotropic plasmonic nanostructures but also in controlling their orientation relative to incident light. Herein, a stepwise seeded growth method is reported for the synthesis of rod-shaped plasmon nanostructures which are vertically self-aligned with respect to the surface of colloidal substrates. Anisotropic growth of metal nanostructure is achieved by depositing metal seeds onto the surface of colloidal substrates and then selectively passivating the seed surface to induce symmetry breaking in the subsequent seed-mediated growth process. The versatility of this method is demonstrated by producing nanoparticle dimers and linear trimers of Au, Au-Ag, Au-Pd, and Au-Cu2 O. Further, this unique method enables the automatic vertical alignment of the resulting plasmonic nanostructures to the surface of the colloidal substrate, thereby making it possible to design magnetic/plasmonic nanocomposites that allow the dynamic tuning of the plasmon excitation by controlling their orientation using an external magnetic field. The controlled anisotropic growth of colloidal plasmonic nanostructures and their dynamic modulation of plasmon excitation further allow them to be conveniently fixed in a thin polymer film with a well-controlled orientation to display polarization-dependent patterns that may find important applications in information encryption.

Seed-mediated synthesis of PtxAuy@Ag electrocatalysts for the selective oxidation of glycerol

Trimetallic PtxAuy@Ag nanoparticles with varying Pt/Au ratios were prepared via a seed-mediated growth process, in which Ag nanoparticles were employed as sacrificial seeds, and further evaluated as electrocatalysts for the selective oxidation of glycerol. The structures of the as-prepared PtxAuy@Ag nanoparticles were characterized by transmission electron microscopy, electron energy loss spectroscopy and UV–vis absorption spectroscopy. The electrocatalytic activity of the PtxAuy@Ag nanoparticles was extensively evaluated by various electrochemical methods including cyclic voltammetry, linear sweep voltammetry, and chronoamperometric measurements. The PtxAuy@Ag catalysts exhibit superior activity in alkaline solutions relative to acidic solutions. In acidic solutions, the Pt6Au4@Ag catalyst shows the highest current density of 0.67 mA cm−2, which is 2.6 times that of the Pt/C catalyst. In alkaline solutions, the Pt4Au6@Ag has the highest current density of 3.1 mA cm−2, which is 4.7 times that of the Pt/C catalyst. The products of glycerol oxidation over the catalysts at potentials of 0.5, 0.7, 0.9, 1.1 and 1.3 V were analyzed by high performance liquid chromatography (HPLC). Nine products including oxalate acid, tartronic acid, glyoxylic acid, glyceric acid, glyceraldehyde, glycolic acid, lactic acid, dihydroxyacetone (DHA), and formic acid were detected. HPLC results show that the PtxAuy@Ag catalysts tend to yield more C3 products. Notably, among the catalysts, the Pt4Au6@Ag yields the largest DHA selectivity of 77.1% at a potential of 1.1 V. The remarkable selectivity of the C3 products can be ascribed to the dominant Pt (111) facets in the PtxAuy@Ag catalysts and the synergistic effects of Pt and Au/Ag atoms.

Preparation of Ordered Mesoporous Au using Double Gyroid Mesoporous Silica KIT-6 via a Seed-Mediated Growth Process.

Ordered mesoporous Au was prepared using double gyroid (cubic Ia-3d) mesoporous silica KIT-6 as a template. The Au frameworks were formed within the template via a seed-mediated growth process. Au nanoparticles were initially prepared as seeds within the mesopores, and subsequently, they were grown under mild and controlled reducing conditions. The transmission electron micrographs and scanning electron micrographs of mesoporous Au after the removal of the template revealed the formation of mesoporous Au replicas. The small-angle X-ray scattering pattern of mesoporous Au reveals that the obtained mesoporous Au has a cubic I41 32 mesostructure, which is different from that of the original template, implying that Au was deposited within only one mesochannel of the two interconnected ones. The seed-mediated growth process is a key factor in the successful formation of ordered mesoporous Au using a mesoporous silica template. Our preparative method can serve as a guide for further development of synthetic and materials chemistry of mesoporous Au.