Insights into the formation of Au@Pt dendritic core-shell nanoparticles with the aid of ultrasonication

Insights into the formation of Au@Pt dendritic core-shell nanoparticles with the aid of ultrasonication | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Insights into the formation of Au@Pt dendritic core-shell nanoparticles with the aid of ultrasonication Hu-Jun LEE, Daisuke HANYU, Anh Thi Ngoc DAO, Kenji KANEKO This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6398480/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 12 Aug, 2025 Read the published version in Scientific Reports → Version 1 posted 17 You are reading this latest preprint version Abstract Bimetallic Au@Pt dendritic core-shell nanoparticles were synthesized via co-reduction with ultrasonication, and their nanostructures were characterized to gain insights into the formation mechanism of the Pt shell on the Au core. Two types of nanoparticles, one with ultrasonication and another without, were prepared and examined by scanning transmission electron microscopy to understand the role of ultrasonication. With or without ultrasonication, a thin layer of Pt shell was present on the Au core. The ultrasonication resulted in the Pt cluster formation from precursors, the Pt cluster dispersion, the Pt granule formation, and the Pt granule collision with the Au core. Consequently, Au@Pt nanoparticles were synthesized with the Pt dendritic shell consisting of Pt granules. These findings highlight the potential of ultrasonication in the controlled synthesis of nanoparticles with unique nanostructures. Physical sciences/Materials science Physical sciences/Nanoscience and technology Core-shell nanoparticle Ultrasonication Noble metal nanoparticle Transmission electron microscopy Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1. Introduction Nanoparticles (NPs) with tailored structures and compositions have attracted significant attention due to their versatile applications in catalysis [ 1 – 4 ], optics [ 5 – 7 ], and biomedical fields [ 8 – 10 ]. Platinum (Pt) NPs are well-known for their exceptional catalytic properties, making them ideal for applications in reduction reactions [ 1 , 2 ], and hydrogen production [ 3 ]. However, the high cost and low durability [ 11 ] of Pt during catalytic processes present challenges for their widespread use. Bimetallization of Pt with another element can reduce the Pt usage undoubtedly, improve durability, and enhance catalytic activity, making them a highly effective approach [ 12 – 17 ]. Among those bimetallic NPs, Au-Pt bimetallic NPs have been designed and synthesized to minimize the amount of Pt but improve the catalytic efficiency [ 18 – 22 ], with various microstructures including core-shell [ 23 – 25 ], solid solution alloys [ 26 ], intermetallic alloys [ 27 , 28 ], phase-segregated structures, [ 29 – 37 ], and others as shown in Fig. 1 . Among these structures, Au@Pt NPs have emerged as promising alternatives to monometallic Pt NPs by combining the unique properties of both Au and Pt. Au with its excellent chemical stability [ 38 ] and tunable plasmon resonance properties [ 39 ] provides a robust core that enhances the durability of the bimetallic Au@Pt NPs. In addition, the plasmonic properties of Au enable enhanced light absorption and localized heating, making Au@Pt NPs suitable for applications in photothermal therapy [ 5 , 7 ] and surface-enhanced Raman scattering (SERS) [ 40 ]. The Pt shell, grown on the Au core, retains its superior catalytic activity, providing high specific surface area and active sites for chemical reactions [ 41 ]. The synergetic effects between Au and Pt not only enhance the catalytic performance but also improve stability and efficiency, making these NPs highly attractive for advanced applications in electrocatalysis [ 4 ], environmental remediation [ 42 ], and biosensing [ 9 ]. Commonly, seed-mediated methods are applied to synthesize Au@Pt NPs, with the controlled morphology and size of the core and shell using two-step synthesis [ 43 , 44 ]. Recently, a more facile one-step synthesis has been applied to synthesize Au@Pt NPs [ 4 ], based on the difference in reduction potentials between PtCl 6 2− and AuCl 4 − [ 4 , 45 , 46 ]. The reduction reactions of these ions and their standard reduction potentials are as shown in the following equations, Eq. (1) to (3) [ 4 ]. $$\:{\text{[Au}{\text{Cl}}_{\text{4}}\text{]}}^{\text{-}}\text{}\text{+}\text{}\text{3}{\text{e}}^{\text{-}}\text{}\text{→}\text{}\text{Au}\text{}\text{+}\text{}\text{4}{\text{Cl}}^{\text{-}}\text{}\text{+}\text{}\text{1.0}\text{}\text{eV}\text{}\text{vs.}\text{}\text{SHE}\text{}\text{Eq}\text{n}\text{.}\text{}\left(\text{1}\right)$$ $$\:{\text{[Pt}{\text{Cl}}_{\text{6}}\text{]}}^{\text{2-}}\text{}\text{+}\text{}\text{2}{\text{e}}^{\text{-}}\text{}\text{→}\text{}{\text{[Pt}{\text{Cl}}_{\text{4}}\text{]}}^{\text{2-}}\text{}\text{+}\text{}\text{2}{\text{Cl}}^{\text{-}}\text{}\text{+}\text{}\text{0.68}\text{}\text{eV}\text{}\text{vs.}\text{}\text{SHE}\text{}\text{Eq}\text{n}\text{.}\text{}\left(\text{2}\right)$$ $$\:{\text{[Pt}{\text{Cl}}_{\text{4}}\text{]}}^{\text{2-}}\text{}\text{+}\text{}\text{2}{\text{e}}^{\text{-}}\text{}\text{→}\text{}\text{Pt}\text{}\text{+}\text{}\text{4}{\text{Cl}}^{\text{-}}\text{}\text{+}\text{}\text{0.76}\text{}\text{eV}\text{}\text{vs.}\text{}\text{SHE}\text{}\text{Eq}\text{n}\text{.}\text{}\left(\text{3}\right)$$ Yamauchi et al. have successfully synthesized Au@Pt dendritic core-shell NPs in a one-step synthesis using Pluronic F127 as a capping agent [ 47 , 48 ]. Moreover, Wang et al. reported the successful formation of dendritic Pt granules with high molar concentrations of Pt precursors [ 47 ], suggesting that the degree of Pt supersaturation is an important factor in the formation of dendritic Pt granules. Ataee-Esfahani et al. reported the addition of ultrasonication increased the Pt nucleation rate and caused the granule refinement [ 48 ]. They also suggested that ultrasonication was an effective route to synthesize dendritic Pt shells at low Pt precursor concentrations. Application of ultrasonication to the reaction mixtures can accelerate and promote chemical reactions, including the reduction of Pt ions in solution through ultrasonic cavitation. Cavitation involves the formation and collapse of small bubbles or cavities within a solution [ 49 , 50 ]. The high-pressure and high-temperature conditions generated by bubble collapse facilitate the reduction of Pt ions and the formation of Pt NPs. The sonochemical synthesis of Pt NPs offers several advantages, including high reaction rates, precise control over size and morphology, short reaction periods, low reaction temperatures, high yields, and uniform size distribution [ 51 ]. In this study, Au@Pt dendritic core-shell NPs were synthesized at low Pt precursor concentrations by adding Pluronic F127 as a structural-directing agent and combining co-reduction and ultrasonication. Au@Pt NPs without ultrasonication were also synthesized for comparison. The microstructures of these NPs were characterized by (scanning) transmission electron microscopy ((S)TEM) to investigate the role of ultrasonication and the effect of ultrasonication on the growth mechanism of Pt shells on the Au core. 2. Materials and methods 2.1. Materials Gold (III) chloride trihydrate (HAuCl 4 ·3H 2 O, ≥ 99.9% trace metals basis, Sigma-Aldrich), chloroplatinic acid solution 8 wt% (H 2 PtCl 6 , Sigma-Aldrich), Pluronic F127 (mol. wt. ~12600 g/mol, Sigma-Aldrich), and ʟ(+)-Ascorbic acid (≥ 99.6%, FUJIFILM Wako Pure Chemical Corporation) were purchased and used directly. Deionized water (18.2 MΩ) was used for all reactions. 2.2. Synthesis of Au@Pt nanoparticles Samples were synthesized in aqueous media by a one-pot reaction based on previous reports [ 52 , 53 ] with modifications: aqueous HAuCl 4 (5.0 µmol) and H 2 PtCl 6 (5.0 µmol) solutions were mixed with the ascorbic acid (AA). Pluronic F127 as a structural-directing agent was added, and the mixture was sonicated for 20 minutes, followed by continuous stirring for 2, 4, and 24 hours to study the growth behavior of NPs. The ultrasonication was carried out by Bransonic 2510J-MTH at 42 kHz and 25 ℃. In contrast, the precursor solution after the addition of AA was mixed with a magnetic stirrer without ultrasonication. The samples were also synthesized with a reaction period of 2, 4, and 24 hours. The synthesized NPs were then washed by two cycles of centrifugation (10,000 rpm, 30 min) and redispersed in water. To prepare for (S)TEM observation, the sample was dispersed in an ultrasonic cleaner for 10 minutes, and one drop of the dispersion was placed on a support grid and dried for 24 hours. 2.3. TEM/STEM observation JEM-2100HC at an acceleration voltage of 200 kV was used to study the microstructure of NPs, including size and morphology, at different reaction periods. High-angle annular dark-field (HAADF) images by STEM (JEM-ARM200F, equipped with CEOS Cs-corrector) were obtained at an acceleration voltage of 200 kV to investigate the morphology of NPs. Energy dispersive X-ray spectroscopy (EDS) analysis was also performed to obtain two-dimensional (2D) elemental distribution maps of Au-L edges and Pt-L edges for each element. 2.4. Calculation of the yield of synthesized Au@Pt nanoparticles To evaluate the influence of ultrasonication on the synthesis of Au@Pt NPs, the yields of Au and Pt were calculated at different reaction periods, for both reactions with and without ultrasonication. The yield for each element was determined using the following equation: This approach incorporates the elemental composition obtained from EDS measurements to ensure accurate yield calculations. 3. Results and discussion 3.1. Nanostructure analyses of NPs obtained without ultrasonication Bright-field (BF) TEM images of Au@Pt NPs synthesized without ultrasonication are shown in Figs. 2 (a)-(c), revealing a variety of sizes and morphologies of NPs, such as plate (triangle and trapezoid) and polyhedron, at all reaction periods. The average particle sizes are found almost the same for the different reaction periods, as shown in Fig. 2 (d). Without ultrasonication, Pt atoms tend to grow as continuous layers on the Au core, forming a smooth Pt layer. In addition, the small NPs observed on the TEM grid are residual Pt NPs that did not integrate into the shell structure, likely due to incomplete attachment or insufficient surface diffusion of Pt atoms. These residual Pt NPs indicate that, in the absence of ultrasonication, the reduction and deposition of Pt occur in a relatively controlled manner, leading to the formation of a uniform shell rather than dendritic structures. Figure 3 (a) shows a high-resolution HAADF-STEM image of the representative NPs synthesized in the shortest reaction period of 2 hours. The atomic numbers of the neighboring elements, Pt and Au, are close enough not to be distinguishable through the contrast in the HAADF-STEM image, known as the atomic number contrast. The surface of NPs reflects the polyhedral nature of the Au core synthesized by Au(III) reduction [ 54 ]. Elemental distribution maps of Au and Pt were obtained by STEM-EDS, as shown in Figs. 3 (b) and 3(c), respectively. Their overlay images also shown in Fig. 3 (d) represent the Au core and Pt (ca. 1 nm) shell, resulting in the formation of Au@Pt NPs. 3.2. Nanostructure analyses of NPs synthesized with ultrasonication Figures 4 (a)-(c) show BF-TEM images of NPs synthesized with ultrasonication at different reaction periods. Compared to the case without ultrasonication, these NPs consist of one core NP and are covered with numerous fine granules. The morphology and size of the ultrasonically treated core NPs were similar to those of the non-ultrasonically treated core NPs shown in Fig. 2 , with plate-like (triangular, trapezoidal) and polyhedral shapes formed in all reaction periods. This fact suggests that ultrasonication affected only the shell part of Au@Pt, composed of fine Pt granules. The sizes of NPs and those of Au cores synthesized in each reaction period are summarized in Fig. 4 (d). Although the average size of the Au core was maintained at about 15 nm, the average size of Au@Pt NPs was found to increase with the reaction period, namely the thickness of the shells was found to increase with the reaction period, from 2 nm at 2 hours to 4 nm at 24 hours, respectively. It strongly suggests that the number of granules on the core increased with the reaction period and resulted in a dendritic Pt shell. Figure 5 shows HAADF-STEM and STEM-EDS images of the representative Au@Pt NPs at a reaction period of 2 hours with ultrasonication. The high-resolution HAADF-STEM image confirmed the presence of both rough and smooth surfaces on the core. Au-L and Pt-L elemental distribution maps of this NP are shown in Figs. 5 (b) and 5(c), respectively. As in the case of the Au@Pt NPs without ultrasonication, a Pt shell layer was found on the Au core. Furthermore, the rough surface region, i.e., the fine granules, was also found to be composed of Pt. The overlay image confirms the formation of Au@Pt dendritic core-shell NPs. Furthermore, the presence of a thin Pt layer was present on the surface of the Au core and seen at the interface between the Pt granules and the Au core. Figure 6 shows high-resolution TEM images of the interface between the Pt granules located on the Au core of NPs with a reaction period of 2 hours. Figures 6 (b) to 6(d) confirm the presence of epitaxial growth between the core and shell, as the continuous atomic arrangement between the {111} lattices from the Au core to the Pt shell and then to the Pt granules. 3.3. Growth mechanism of Au@Pt dendritic core-shell NPs In general, the growth model of core-shell NPs is strongly influenced by a complex combination of factors, including the lattice mismatch between core and shell, the ratio of reducing agents per capping agents, and the molar ratio of metal ions [ 43 ]. There are three representative models when a substance is deposited on a substrate, as shown in Fig. 7 schematically illustrating four different growth models for the epitaxial deposition of two different elements. Figure 7 (a) to (c) illustrates the heteroepitaxial layered growth known as F-M mode (Frank-van der Merwe) [ 55 ], the island-like growth known as V-W mode (Volmer-Weber) [ 56 ], and the intermediary process by both F-M and V-W mode known as S-K mode (Stranski-Krastanov) [ 57 ]. In the case of Au@Pt NPs synthesis without ultrasonication, as seen in Fig. 8 (a), a thin layer of Pt was observed on the Au core, which suggested that the Pt layer was grown in the F-M mode. In the case of Au@Pt NPs synthesis with ultrasonication, as seen in Fig. 8 (b), fine Pt granules were observed on the thin Pt layer covering the Au core. This fact suggested that the Pt granules grew in a form similar to the S-K mode. The Pt atoms have grown in the form of fine granules as shown in Fig. 7 (d), not in the case of typical islandic growth forms of the V-W or S-K modes. Although these models were originally developed for the thin film growth, they are beneficial for understanding the Pt deposition behavior on the Au core. There is a possibility that dendritic structures are formed by the deposition of homogeneously synthesized Pt granules, a process that deviates from the classical model. This deviation reflects the complex growth environment caused by ultrasonication, which probably promoted non-classical nucleation and aggregation mechanisms. Three classical models, Fig. 7 (a) to 7(c) are shown for the comparison, the current models can also be acknowledged as the unique nature of dendritic formation. A key difference between the classical S-K mode (Fig. 7 (c)) and the proposed model (Fig. 7 (d)) lies in the nature of the deposited Pt atoms. In the S-K mode, a layer first forms on the substrate, followed by the nucleation of discrete islands due to accumulated strain energy [ 57 ]. In contrast, in the proposed model (Fig. 7 (d)), ultrasonication appears to modify the nucleation and growth behavior, leading to the formation of uniformly distributed Pt granules rather than islands. This suggests that ultrasonication enhances the nucleation rate while simultaneously preventing excessive aggregation, resulting in a dendritic morphology rather than discrete islands. 4. Discussions Nanostructural characterizations by (S)TEM revealed the growth behavior of the thin Pt layer on the Au core during the synthesis without ultrasonication, while Pt granules were found present on the Pt layer with ultrasonication. High-resolution STEM analysis revealed that the surface of NPs was covered entirely by epitaxially grown Pt layer on the Au core, while misfit dislocations were occasionally observed. Moreover, the epitaxial growth of Pt granules on top of the Pt layer was confirmed by HRTEM, where the number of Pt granules was found to be increased with the reaction period. The Pt granules were linked further to form a dendritic Pt shell. Although the synthesis of Au@Pt dendritic core-shell NPs was previously reported by Ataee-Esfahani et al. [ 4 , 48 ], the dendritic Pt shells were hardly observed in the sample without ultrasonication, probably due to the low molar ratio of Pt precursor. The formation of dendritic Pt shells through ultrasonication, even at the low molar ratio of the Pt precursor in this study, suggests an increase in the effective molar ratio of the Pt precursor. The yields of Au and Pt were measured for samples with and without ultrasonication at various reaction periods, as shown in Fig. 9 . In the case of NPs synthesized without ultrasonication, the reduction yields remained constant regardless of the reaction periods, with Au at 55% and Pt at 31%, suggesting that the Au@Pt NPs formation was completed within 2 hours. In the case of NPs with ultrasonication, the yield of Au maintained consistently at 55%, while the Pt yield increased with the reaction period, reaching 38%, 45%, and 67% at 2, 4, and 24 hours, respectively. This indicates that ultrasonication promotes the formation of dendritic Pt shells. Two mechanisms have been proposed for the growth mechanism of metal@Pt dendritic core-shell NPs in the past. One is the growth of Pt granules on the metal core by heterogeneous nucleation [ 44 , 48 ], and another one is the growth of Pt clusters nucleated homogeneously by attachment [ 58 – 60 ]. Through the current study, Pt granules were commonly observed on the Au@Pt NPs, which support the latter mechanism strongly. The area where Pt could heterogeneously nucleate on the Au core was insufficient when the Pt precursor was reduced. It is known that ultrasonication has mechanical effects during the synthesis of NPs driven by shock waves from bubble collapse [ 61 ], as shown in Fig. 10 , which disrupts the formation of small clusters and facilitates particle collisions, lead to a controlled agglomeration on the primary core particles [ 49 , 50 ]. As a result, the Au core was formed firstly due to its lower reduction potential, then formed Pt layers on the previously formed Au core with the aid of a reducing agent and a surfactant, as schematically shown in Fig. 11. In the case of the sample without ultrasonication, the smooth Pt layer grew via the F-M mode, while in the sample with ultrasonication, the dendritic Pt shell grew similarly to the S-K mode due to the mechanical effects. 5. Conclusion Au@Pt NPs with/without ultrasonication were synthesized by co-reduction and their nanostructures were characterized by (S)TEM and HRTEM. For the case of NPs without ultrasonication, smooth thin Pt layers were formed on the Au core, while Pt granules are present on the Pt layers for the case of NPs with ultrasonication. The successful synthesis of Au@Pt NPs with dendritic Pt shells was confirmed from the NPs with ultrasonication. Moreover, HR-TEM characterization confirmed the epitaxial growth of Pt granules on thin Pt layer under ultrasonication, which resulted in the formation of the dendritic Pt shell. This study opens a new possibility for the controlled synthesis of NPs with complex nanostructures through facile and ultrasonication. In addition, understanding the precise role of ultrasonication in NP synthesis could lead to innovative approaches in nanotechnology, materials science, catalysis, electronics, and medicine. Declarations Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Author Contribution Hu-Jun LEE: Investigation, Data curation, Formal analysis, Writing - original draft.Daisuke HANYU: Investigation, Data curation, Formal analysis, Writing - review and editing. Anh Thi Ngoc DAO and Kenji KANEKO: Conceptualization, Methodology, Data curation, Formal analysis, Resources, Funding acquisition, Writing - review and editing, Supervision. Acknowledgements This work was partially supported by JSPS KAKENHI (Grant Numbers JP 22K14742 to A.T.N.D.). 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KANEKO","email":"data:image/png;base64,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","orcid":"","institution":"Kyushu University","correspondingAuthor":true,"prefix":"","firstName":"Kenji","middleName":"","lastName":"KANEKO","suffix":""}],"badges":[],"createdAt":"2025-04-08 02:53:09","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6398480/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6398480/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-09572-0","type":"published","date":"2025-08-12T15:57:23+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":81964821,"identity":"1bb288b4-9eba-40f0-939d-03d9d0e827e3","added_by":"auto","created_at":"2025-05-05 11:27:34","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":258289,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagrams of (a) monometallic NP, and bimetallic NPs in various structures: (b) alloy, (c) core-thin shell, (d) core-thick shell NP, (e) ordered (layered), (f) Janus, and (g) disordered (segregated).\u003c/p\u003e","description":"","filename":"Slide1.png","url":"https://assets-eu.researchsquare.com/files/rs-6398480/v1/b836daf9034cea07d9179646.png"},{"id":81967748,"identity":"44d4a01f-ec69-490e-8e43-aeccafced229","added_by":"auto","created_at":"2025-05-05 11:43:34","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":240694,"visible":true,"origin":"","legend":"\u003cp\u003eBF-TEM images of Au@Pt core-shell NPs synthesized without ultrasonication for (a) 2, (b) 4, (c) 24 hours, respectively, and (d) correlation between the size and reaction periods.\u003c/p\u003e","description":"","filename":"Slide2.png","url":"https://assets-eu.researchsquare.com/files/rs-6398480/v1/e70a9fbb888123254d4d60c1.png"},{"id":81966247,"identity":"4b334b73-245e-4d32-819b-d7e890e6b866","added_by":"auto","created_at":"2025-05-05 11:35:34","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":375340,"visible":true,"origin":"","legend":"\u003cp\u003e(a) High-resolution HAADF-STEM image, elemental distribution maps of (b) Au and (c) Pt, and (d) overlay image, of Au@Pt NPs synthesized with a reaction period of 2 hours without ultrasonication.\u003c/p\u003e","description":"","filename":"Slide3.png","url":"https://assets-eu.researchsquare.com/files/rs-6398480/v1/da79e3d72057907c4235c45a.png"},{"id":81966244,"identity":"465e92e1-1047-4b2b-9a74-90bed7bbdaff","added_by":"auto","created_at":"2025-05-05 11:35:34","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":244500,"visible":true,"origin":"","legend":"\u003cp\u003eBF-TEM images of Au@Pt core-shell NPs synthesized with ultrasonication for (a) 2, (b) 4, (c) 24 hours, respectively, and (d) correlation between the size and reaction times.\u003c/p\u003e","description":"","filename":"Slide4.png","url":"https://assets-eu.researchsquare.com/files/rs-6398480/v1/d54ec80cabfdb3060c56111c.png"},{"id":81968145,"identity":"a132e506-8d97-4ea2-9695-ed190d4f1048","added_by":"auto","created_at":"2025-05-05 11:51:34","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":249076,"visible":true,"origin":"","legend":"\u003cp\u003e(a) HAADF-STEM image, (b) Au-L map, (c) Pt-L map, and (d) an overlay image of Au@Pt NPs with a reaction period of 2 hours.\u003c/p\u003e","description":"","filename":"Slide5.png","url":"https://assets-eu.researchsquare.com/files/rs-6398480/v1/ef0eba7c9b6a2f22f5754d7b.png"},{"id":81964828,"identity":"110e8bfe-6b16-4410-9239-f573ca563484","added_by":"auto","created_at":"2025-05-05 11:27:34","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":387007,"visible":true,"origin":"","legend":"\u003cp\u003e(a) high-resolution TEM images of NPs after a reaction period of 2 hours, and (b) to (d) show slightly magnified images of the interfacial regions between the Pt granules and the Au core.\u003c/p\u003e","description":"","filename":"Slide6.png","url":"https://assets-eu.researchsquare.com/files/rs-6398480/v1/fbc3f62c2840f9f0e3f28aa0.png"},{"id":81966248,"identity":"92f2220e-b336-417f-8f12-0e35a609796f","added_by":"auto","created_at":"2025-05-05 11:35:34","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":149334,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagrams of the representative growth models, (a) heteroepitaxial layered growth F-M model, (b) the island-like growth model V-W model, (c) the intermediary process by both F-M and V-W model, and (d) current study.\u003c/p\u003e","description":"","filename":"Slide7.png","url":"https://assets-eu.researchsquare.com/files/rs-6398480/v1/1821cf74dd4d4f0dae7035bb.png"},{"id":81967751,"identity":"d82ab34e-0db2-4af9-b4df-140c61732e58","added_by":"auto","created_at":"2025-05-05 11:43:34","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":128565,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagrams of Au@Pt NPs: (a) without and (b) with ultrasonication.\u003c/p\u003e","description":"","filename":"Slide8.png","url":"https://assets-eu.researchsquare.com/files/rs-6398480/v1/8dd135a5f89aa77310bd7c7a.png"},{"id":81964830,"identity":"8abd7f70-6ec3-413c-bc2d-97463f8149ce","added_by":"auto","created_at":"2025-05-05 11:27:34","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":92522,"visible":true,"origin":"","legend":"\u003cp\u003eYields of Au and Pt formation on Au@Pt NPs (a) without and (b) with ultrasonication.\u003c/p\u003e","description":"","filename":"Slide9.png","url":"https://assets-eu.researchsquare.com/files/rs-6398480/v1/ef1d28629418b187637d7e72.png"},{"id":81964837,"identity":"faba01dc-5cbe-4368-b6a6-76fb1c1c97f0","added_by":"auto","created_at":"2025-05-05 11:27:34","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":141219,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagrams of mechanical effects during synthesis of Au@Pt NP.\u003c/p\u003e","description":"","filename":"Slide10.png","url":"https://assets-eu.researchsquare.com/files/rs-6398480/v1/93723113a0c9557bd69c0110.png"},{"id":81966251,"identity":"310172e8-04ee-46d0-889d-e9d7ef28afe1","added_by":"auto","created_at":"2025-05-05 11:35:34","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":104685,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagrams of proposed growth modes of Au@Pt with and without the ultrasonication.\u003c/p\u003e","description":"","filename":"Slide11.png","url":"https://assets-eu.researchsquare.com/files/rs-6398480/v1/b3342753e91ef44613f133d6.png"},{"id":89311259,"identity":"7269f88d-2fcb-4630-9ba0-6029445139b1","added_by":"auto","created_at":"2025-08-18 16:10:33","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3009990,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6398480/v1/3d3a2737-06b5-431e-a3d4-02ce7c6ff070.pdf"},{"id":81964820,"identity":"26f73215-6157-417a-b79b-bfdfbfdf4463","added_by":"auto","created_at":"2025-05-05 11:27:34","extension":"xlsx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":33777,"visible":true,"origin":"","legend":"","description":"","filename":"Data.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-6398480/v1/4b2ca753c3119a4210c2dbd9.xlsx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Insights into the formation of Au@Pt dendritic core-shell nanoparticles with the aid of ultrasonication","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eNanoparticles (NPs) with tailored structures and compositions have attracted significant attention due to their versatile applications in catalysis [\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], optics [\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], and biomedical fields [\u003cspan additionalcitationids=\"CR9\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Platinum (Pt) NPs are well-known for their exceptional catalytic properties, making them ideal for applications in reduction reactions [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], and hydrogen production [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. However, the high cost and low durability [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] of Pt during catalytic processes present challenges for their widespread use. Bimetallization of Pt with another element can reduce the Pt usage undoubtedly, improve durability, and enhance catalytic activity, making them a highly effective approach [\u003cspan additionalcitationids=\"CR13 CR14 CR15 CR16\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Among those bimetallic NPs, Au-Pt bimetallic NPs have been designed and synthesized to minimize the amount of Pt but improve the catalytic efficiency [\u003cspan additionalcitationids=\"CR19 CR20 CR21\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e], with various microstructures including core-shell [\u003cspan additionalcitationids=\"CR24\" citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], solid solution alloys [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e], intermetallic alloys [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], phase-segregated structures, [\u003cspan additionalcitationids=\"CR30 CR31 CR32 CR33 CR34 CR35 CR36\" citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e], and others as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAmong these structures, Au@Pt NPs have emerged as promising alternatives to monometallic Pt NPs by combining the unique properties of both Au and Pt. Au with its excellent chemical stability [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e] and tunable plasmon resonance properties [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e] provides a robust core that enhances the durability of the bimetallic Au@Pt NPs. In addition, the plasmonic properties of Au enable enhanced light absorption and localized heating, making Au@Pt NPs suitable for applications in photothermal therapy [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] and surface-enhanced Raman scattering (SERS) [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. The Pt shell, grown on the Au core, retains its superior catalytic activity, providing high specific surface area and active sites for chemical reactions [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. The synergetic effects between Au and Pt not only enhance the catalytic performance but also improve stability and efficiency, making these NPs highly attractive for advanced applications in electrocatalysis [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], environmental remediation [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e], and biosensing [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eCommonly, seed-mediated methods are applied to synthesize Au@Pt NPs, with the controlled morphology and size of the core and shell using two-step synthesis [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. Recently, a more facile one-step synthesis has been applied to synthesize Au@Pt NPs [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], based on the difference in reduction potentials between PtCl\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e and AuCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. The reduction reactions of these ions and their standard reduction potentials are as shown in the following equations, Eq.\u0026nbsp;(1) to (3) [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:{\\text{[Au}{\\text{Cl}}_{\\text{4}}\\text{]}}^{\\text{-}}\\text{}\\text{+}\\text{}\\text{3}{\\text{e}}^{\\text{-}}\\text{}\\text{\u0026rarr;}\\text{}\\text{Au}\\text{}\\text{+}\\text{}\\text{4}{\\text{Cl}}^{\\text{-}}\\text{}\\text{+}\\text{}\\text{1.0}\\text{}\\text{eV}\\text{}\\text{vs.}\\text{}\\text{SHE}\\text{}\\text{Eq}\\text{n}\\text{.}\\text{}\\left(\\text{1}\\right)$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:{\\text{[Pt}{\\text{Cl}}_{\\text{6}}\\text{]}}^{\\text{2-}}\\text{}\\text{+}\\text{}\\text{2}{\\text{e}}^{\\text{-}}\\text{}\\text{\u0026rarr;}\\text{}{\\text{[Pt}{\\text{Cl}}_{\\text{4}}\\text{]}}^{\\text{2-}}\\text{}\\text{+}\\text{}\\text{2}{\\text{Cl}}^{\\text{-}}\\text{}\\text{+}\\text{}\\text{0.68}\\text{}\\text{eV}\\text{}\\text{vs.}\\text{}\\text{SHE}\\text{}\\text{Eq}\\text{n}\\text{.}\\text{}\\left(\\text{2}\\right)$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$$\\:{\\text{[Pt}{\\text{Cl}}_{\\text{4}}\\text{]}}^{\\text{2-}}\\text{}\\text{+}\\text{}\\text{2}{\\text{e}}^{\\text{-}}\\text{}\\text{\u0026rarr;}\\text{}\\text{Pt}\\text{}\\text{+}\\text{}\\text{4}{\\text{Cl}}^{\\text{-}}\\text{}\\text{+}\\text{}\\text{0.76}\\text{}\\text{eV}\\text{}\\text{vs.}\\text{}\\text{SHE}\\text{}\\text{Eq}\\text{n}\\text{.}\\text{}\\left(\\text{3}\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eYamauchi et al. have successfully synthesized Au@Pt dendritic core-shell NPs in a one-step synthesis using Pluronic F127 as a capping agent [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. Moreover, Wang et al. reported the successful formation of dendritic Pt granules with high molar concentrations of Pt precursors [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e], suggesting that the degree of Pt supersaturation is an important factor in the formation of dendritic Pt granules. Ataee-Esfahani et al. reported the addition of ultrasonication increased the Pt nucleation rate and caused the granule refinement [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. They also suggested that ultrasonication was an effective route to synthesize dendritic Pt shells at low Pt precursor concentrations. Application of ultrasonication to the reaction mixtures can accelerate and promote chemical reactions, including the reduction of Pt ions in solution through ultrasonic cavitation. Cavitation involves the formation and collapse of small bubbles or cavities within a solution [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]. The high-pressure and high-temperature conditions generated by bubble collapse facilitate the reduction of Pt ions and the formation of Pt NPs. The sonochemical synthesis of Pt NPs offers several advantages, including high reaction rates, precise control over size and morphology, short reaction periods, low reaction temperatures, high yields, and uniform size distribution [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn this study, Au@Pt dendritic core-shell NPs were synthesized at low Pt precursor concentrations by adding Pluronic F127 as a structural-directing agent and combining co-reduction and ultrasonication. Au@Pt NPs without ultrasonication were also synthesized for comparison. The microstructures of these NPs were characterized by (scanning) transmission electron microscopy ((S)TEM) to investigate the role of ultrasonication and the effect of ultrasonication on the growth mechanism of Pt shells on the Au core.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003e2.1. Materials\u003c/h2\u003e\n \u003cp\u003eGold (III) chloride trihydrate (HAuCl\u003csub\u003e4\u003c/sub\u003e\u0026middot;3H\u003csub\u003e2\u003c/sub\u003eO, \u0026ge;\u0026thinsp;99.9% trace metals basis, Sigma-Aldrich), chloroplatinic acid solution 8 wt% (H\u003csub\u003e2\u003c/sub\u003ePtCl\u003csub\u003e6\u003c/sub\u003e, Sigma-Aldrich), Pluronic F127 (mol. wt. ~12600 g/mol, Sigma-Aldrich), and ʟ(+)-Ascorbic acid (\u0026ge;\u0026thinsp;99.6%, FUJIFILM Wako Pure Chemical Corporation) were purchased and used directly. Deionized water (18.2 MΩ) was used for all reactions.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003e2.2. Synthesis of Au@Pt nanoparticles\u003c/h2\u003e\n \u003cp\u003eSamples were synthesized in aqueous media by a one-pot reaction based on previous reports [\u003cspan class=\"CitationRef\"\u003e52\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e53\u003c/span\u003e] with modifications: aqueous HAuCl\u003csub\u003e4\u003c/sub\u003e (5.0 \u0026micro;mol) and H\u003csub\u003e2\u003c/sub\u003ePtCl\u003csub\u003e6\u003c/sub\u003e (5.0 \u0026micro;mol) solutions were mixed with the ascorbic acid (AA). Pluronic F127 as a structural-directing agent was added, and the mixture was sonicated for 20 minutes, followed by continuous stirring for 2, 4, and 24 hours to study the growth behavior of NPs. The ultrasonication was carried out by Bransonic 2510J-MTH at 42 kHz and 25 ℃.\u003c/p\u003e\n \u003cp\u003eIn contrast, the precursor solution after the addition of AA was mixed with a magnetic stirrer without ultrasonication. The samples were also synthesized with a reaction period of 2, 4, and 24 hours.\u003c/p\u003e\n \u003cp\u003eThe synthesized NPs were then washed by two cycles of centrifugation (10,000 rpm, 30 min) and redispersed in water. To prepare for (S)TEM observation, the sample was dispersed in an ultrasonic cleaner for 10 minutes, and one drop of the dispersion was placed on a support grid and dried for 24 hours.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n \u003ch2\u003e2.3. TEM/STEM observation\u003c/h2\u003e\n \u003cp\u003eJEM-2100HC at an acceleration voltage of 200 kV was used to study the microstructure of NPs, including size and morphology, at different reaction periods. High-angle annular dark-field (HAADF) images by STEM (JEM-ARM200F, equipped with CEOS Cs-corrector) were obtained at an acceleration voltage of 200 kV to investigate the morphology of NPs. Energy dispersive X-ray spectroscopy (EDS) analysis was also performed to obtain two-dimensional (2D) elemental distribution maps of Au-L edges and Pt-L edges for each element.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n \u003ch2\u003e2.4. Calculation of the yield of synthesized Au@Pt nanoparticles\u003c/h2\u003e\n \u003cp\u003eTo evaluate the influence of ultrasonication on the synthesis of Au@Pt NPs, the yields of Au and Pt were calculated at different reaction periods, for both reactions with and without ultrasonication. The yield for each element was determined using the following equation:\u003c/p\u003e\n \u003cdiv id=\"Equd\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equd\" name=\"EquationSource\"\u003e\u003cimg 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\" height=\"152\" width=\"615\"\u003e\u003c/div\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Equf\" class=\"Equation\"\u003e\u003cbr\u003e\u003c/div\u003e\n \u003cp\u003eThis approach incorporates the elemental composition obtained from EDS measurements to ensure accurate yield calculations.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1. Nanostructure analyses of NPs obtained without ultrasonication\u003c/h2\u003e\n \u003cp\u003eBright-field (BF) TEM images of Au@Pt NPs synthesized without ultrasonication are shown in Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(a)-(c), revealing a variety of sizes and morphologies of NPs, such as plate (triangle and trapezoid) and polyhedron, at all reaction periods. The average particle sizes are found almost the same for the different reaction periods, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(d). Without ultrasonication, Pt atoms tend to grow as continuous layers on the Au core, forming a smooth Pt layer. In addition, the small NPs observed on the TEM grid are residual Pt NPs that did not integrate into the shell structure, likely due to incomplete attachment or insufficient surface diffusion of Pt atoms. These residual Pt NPs indicate that, in the absence of ultrasonication, the reduction and deposition of Pt occur in a relatively controlled manner, leading to the formation of a uniform shell rather than dendritic structures.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e(a) shows a high-resolution HAADF-STEM image of the representative NPs synthesized in the shortest reaction period of 2 hours. The atomic numbers of the neighboring elements, Pt and Au, are close enough not to be distinguishable through the contrast in the HAADF-STEM image, known as the atomic number contrast. The surface of NPs reflects the polyhedral nature of the Au core synthesized by Au(III) reduction [\u003cspan class=\"CitationRef\"\u003e54\u003c/span\u003e]. Elemental distribution maps of Au and Pt were obtained by STEM-EDS, as shown in Figs. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e(b) and 3(c), respectively. Their overlay images also shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e(d) represent the Au core and Pt (ca. 1 nm) shell, resulting in the formation of Au@Pt NPs.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2. Nanostructure analyses of NPs synthesized with ultrasonication\u003c/h2\u003e\n \u003cp\u003eFigures \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e(a)-(c) show BF-TEM images of NPs synthesized with ultrasonication at different reaction periods. Compared to the case without ultrasonication, these NPs consist of one core NP and are covered with numerous fine granules. The morphology and size of the ultrasonically treated core NPs were similar to those of the non-ultrasonically treated core NPs shown in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e, with plate-like (triangular, trapezoidal) and polyhedral shapes formed in all reaction periods. This fact suggests that ultrasonication affected only the shell part of Au@Pt, composed of fine Pt granules. The sizes of NPs and those of Au cores synthesized in each reaction period are summarized in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e(d). Although the average size of the Au core was maintained at about 15 nm, the average size of Au@Pt NPs was found to increase with the reaction period, namely the thickness of the shells was found to increase with the reaction period, from 2 nm at 2 hours to 4 nm at 24 hours, respectively. It strongly suggests that the number of granules on the core increased with the reaction period and resulted in a dendritic Pt shell.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e shows HAADF-STEM and STEM-EDS images of the representative Au@Pt NPs at a reaction period of 2 hours with ultrasonication. The high-resolution HAADF-STEM image confirmed the presence of both rough and smooth surfaces on the core. Au-L and Pt-L elemental distribution maps of this NP are shown in Figs. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e(b) and 5(c), respectively. As in the case of the Au@Pt NPs without ultrasonication, a Pt shell layer was found on the Au core. Furthermore, the rough surface region, i.e., the fine granules, was also found to be composed of Pt. The overlay image confirms the formation of Au@Pt dendritic core-shell NPs. Furthermore, the presence of a thin Pt layer was present on the surface of the Au core and seen at the interface between the Pt granules and the Au core.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e shows high-resolution TEM images of the interface between the Pt granules located on the Au core of NPs with a reaction period of 2 hours. Figures \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e(b) to 6(d) confirm the presence of epitaxial growth between the core and shell, as the continuous atomic arrangement between the {111} lattices from the Au core to the Pt shell and then to the Pt granules.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3. Growth mechanism of Au@Pt dendritic core-shell NPs\u003c/h2\u003e\n \u003cp\u003eIn general, the growth model of core-shell NPs is strongly influenced by a complex combination of factors, including the lattice mismatch between core and shell, the ratio of reducing agents per capping agents, and the molar ratio of metal ions [\u003cspan class=\"CitationRef\"\u003e43\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eThere are three representative models when a substance is deposited on a substrate, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e schematically illustrating four different growth models for the epitaxial deposition of two different elements. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e(a) to (c) illustrates the heteroepitaxial layered growth known as F-M mode (Frank-van der Merwe) [\u003cspan class=\"CitationRef\"\u003e55\u003c/span\u003e], the island-like growth known as V-W mode (Volmer-Weber) [\u003cspan class=\"CitationRef\"\u003e56\u003c/span\u003e], and the intermediary process by both F-M and V-W mode known as S-K mode (Stranski-Krastanov) [\u003cspan class=\"CitationRef\"\u003e57\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eIn the case of Au@Pt NPs synthesis without ultrasonication, as seen in Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e(a), a thin layer of Pt was observed on the Au core, which suggested that the Pt layer was grown in the F-M mode. In the case of Au@Pt NPs synthesis with ultrasonication, as seen in Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e(b), fine Pt granules were observed on the thin Pt layer covering the Au core. This fact suggested that the Pt granules grew in a form similar to the S-K mode. The Pt atoms have grown in the form of fine granules as shown in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e(d), not in the case of typical islandic growth forms of the V-W or S-K modes.\u003c/p\u003e\n \u003cp\u003eAlthough these models were originally developed for the thin film growth, they are beneficial for understanding the Pt deposition behavior on the Au core. There is a possibility that dendritic structures are formed by the deposition of homogeneously synthesized Pt granules, a process that deviates from the classical model. This deviation reflects the complex growth environment caused by ultrasonication, which probably promoted non-classical nucleation and aggregation mechanisms. Three classical models, Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e(a) to 7(c) are shown for the comparison, the current models can also be acknowledged as the unique nature of dendritic formation. A key difference between the classical S-K mode (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e(c)) and the proposed model (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e(d)) lies in the nature of the deposited Pt atoms. In the S-K mode, a layer first forms on the substrate, followed by the nucleation of discrete islands due to accumulated strain energy [\u003cspan class=\"CitationRef\"\u003e57\u003c/span\u003e]. In contrast, in the proposed model (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e(d)), ultrasonication appears to modify the nucleation and growth behavior, leading to the formation of uniformly distributed Pt granules rather than islands. This suggests that ultrasonication enhances the nucleation rate while simultaneously preventing excessive aggregation, resulting in a dendritic morphology rather than discrete islands.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Discussions","content":"\u003cp\u003eNanostructural characterizations by (S)TEM revealed the growth behavior of the thin Pt layer on the Au core during the synthesis without ultrasonication, while Pt granules were found present on the Pt layer with ultrasonication. High-resolution STEM analysis revealed that the surface of NPs was covered entirely by epitaxially grown Pt layer on the Au core, while misfit dislocations were occasionally observed. Moreover, the epitaxial growth of Pt granules on top of the Pt layer was confirmed by HRTEM, where the number of Pt granules was found to be increased with the reaction period. The Pt granules were linked further to form a dendritic Pt shell. Although the synthesis of Au@Pt dendritic core-shell NPs was previously reported by Ataee-Esfahani et al. [\u003cspan class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e48\u003c/span\u003e], the dendritic Pt shells were hardly observed in the sample without ultrasonication, probably due to the low molar ratio of Pt precursor. The formation of dendritic Pt shells through ultrasonication, even at the low molar ratio of the Pt precursor in this study, suggests an increase in the effective molar ratio of the Pt precursor. The yields of Au and Pt were measured for samples with and without ultrasonication at various reaction periods, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e. In the case of NPs synthesized without ultrasonication, the reduction yields remained constant regardless of the reaction periods, with Au at 55% and Pt at 31%, suggesting that the Au@Pt NPs formation was completed within 2 hours. In the case of NPs with ultrasonication, the yield of Au maintained consistently at 55%, while the Pt yield increased with the reaction period, reaching 38%, 45%, and 67% at 2, 4, and 24 hours, respectively. This indicates that ultrasonication promotes the formation of dendritic Pt shells.\u003c/p\u003e\n\u003cp\u003eTwo mechanisms have been proposed for the growth mechanism of metal@Pt dendritic core-shell NPs in the past. One is the growth of Pt granules on the metal core by heterogeneous nucleation [\u003cspan class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e48\u003c/span\u003e], and another one is the growth of Pt clusters nucleated homogeneously by attachment [\u003cspan class=\"CitationRef\"\u003e58\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e60\u003c/span\u003e]. Through the current study, Pt granules were commonly observed on the Au@Pt NPs, which support the latter mechanism strongly. The area where Pt could heterogeneously nucleate on the Au core was insufficient when the Pt precursor was reduced.\u003c/p\u003e\n\u003cp\u003eIt is known that ultrasonication has mechanical effects during the synthesis of NPs driven by shock waves from bubble collapse [\u003cspan class=\"CitationRef\"\u003e61\u003c/span\u003e], as shown in Fig. \u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e, which disrupts the formation of small clusters and facilitates particle collisions, lead to a controlled agglomeration on the primary core particles [\u003cspan class=\"CitationRef\"\u003e49\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e50\u003c/span\u003e]. As a result, the Au core was formed firstly due to its lower reduction potential, then formed Pt layers on the previously formed Au core with the aid of a reducing agent and a surfactant, as schematically shown in Fig. 11. In the case of the sample without ultrasonication, the smooth Pt layer grew via the F-M mode, while in the sample with ultrasonication, the dendritic Pt shell grew similarly to the S-K mode due to the mechanical effects.\u003c/p\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eAu@Pt NPs with/without ultrasonication were synthesized by co-reduction and their nanostructures were characterized by (S)TEM and HRTEM. For the case of NPs without ultrasonication, smooth thin Pt layers were formed on the Au core, while Pt granules are present on the Pt layers for the case of NPs with ultrasonication. The successful synthesis of Au@Pt NPs with dendritic Pt shells was confirmed from the NPs with ultrasonication.\u003c/p\u003e \u003cp\u003eMoreover, HR-TEM characterization confirmed the epitaxial growth of Pt granules on thin Pt layer under ultrasonication, which resulted in the formation of the dendritic Pt shell. This study opens a new possibility for the controlled synthesis of NPs with complex nanostructures through facile and ultrasonication. In addition, understanding the precise role of ultrasonication in NP synthesis could lead to innovative approaches in nanotechnology, materials science, catalysis, electronics, and medicine.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eDeclaration of competing interest\u003c/h2\u003e \u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eHu-Jun LEE: Investigation, Data curation, Formal analysis, Writing - original draft.Daisuke HANYU: Investigation, Data curation, Formal analysis, Writing - review and editing. Anh Thi Ngoc DAO and Kenji KANEKO: Conceptualization, Methodology, Data curation, Formal analysis, Resources, Funding acquisition, Writing - review and editing, Supervision.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThis work was partially supported by JSPS KAKENHI (Grant Numbers JP 22K14742 to A.T.N.D.). The authors would like to acknowledge the Ultramicroscopy Research Center (URC) of Kyushu University for providing facilities and scientific and technical assistance for electron microscopy measurements.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eData is provided within the manuscript or supplementary information files.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eX. Ren, Q. Lv, L. Liu, B. Liu, Y. Wang, A. Liu, G. 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Wang, Sonochemical catalysis as a unique strategy for the fabrication of nano-/micro-structured inorganics, Nanoscale Adv 3 (2021) 41\u0026ndash;72. https://doi.org/10.1039/d0na00753f.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Core-shell nanoparticle, Ultrasonication, Noble metal nanoparticle, Transmission electron microscopy","lastPublishedDoi":"10.21203/rs.3.rs-6398480/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6398480/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eBimetallic Au@Pt dendritic core-shell nanoparticles were synthesized via co-reduction with ultrasonication, and their nanostructures were characterized to gain insights into the formation mechanism of the Pt shell on the Au core. Two types of nanoparticles, one with ultrasonication and another without, were prepared and examined by scanning transmission electron microscopy to understand the role of ultrasonication. With or without ultrasonication, a thin layer of Pt shell was present on the Au core. The ultrasonication resulted in the Pt cluster formation from precursors, the Pt cluster dispersion, the Pt granule formation, and the Pt granule collision with the Au core. Consequently, Au@Pt nanoparticles were synthesized with the Pt dendritic shell consisting of Pt granules. These findings highlight the potential of ultrasonication in the controlled synthesis of nanoparticles with unique nanostructures.\u003c/p\u003e","manuscriptTitle":"Insights into the formation of Au@Pt dendritic core-shell nanoparticles with the aid of ultrasonication","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-05 11:27:29","doi":"10.21203/rs.3.rs-6398480/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-05-22T13:26:36+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-21T09:54:56+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-20T09:12:05+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-20T08:46:42+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-19T10:39:56+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-10T15:56:55+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"185388520730899653115350505938956384961","date":"2025-05-04T13:09:38+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"200058410133376690392623235471757841128","date":"2025-05-01T03:35:07+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"62547481158115703031959223658592936637","date":"2025-05-01T01:00:02+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"202750031946755030241489245137700653685","date":"2025-04-29T13:18:17+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"173529944953874790442592258928286441050","date":"2025-04-29T10:04:37+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"254702031072395104606111635808915875514","date":"2025-04-29T03:41:04+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-04-29T00:30:44+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-04-29T00:16:46+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-04-28T18:00:43+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-04-09T23:14:33+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-04-09T23:13:32+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"8292b009-d2f6-4bff-a441-69f1885a883e","owner":[],"postedDate":"May 5th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":48042007,"name":"Physical sciences/Materials science"},{"id":48042008,"name":"Physical sciences/Nanoscience and technology"}],"tags":[],"updatedAt":"2025-08-18T16:09:11+00:00","versionOfRecord":{"articleIdentity":"rs-6398480","link":"https://doi.org/10.1038/s41598-025-09572-0","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-08-12 15:57:23","publishedOnDateReadable":"August 12th, 2025"},"versionCreatedAt":"2025-05-05 11:27:29","video":"","vorDoi":"10.1038/s41598-025-09572-0","vorDoiUrl":"https://doi.org/10.1038/s41598-025-09572-0","workflowStages":[]},"version":"v1","identity":"rs-6398480","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6398480","identity":"rs-6398480","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}