SiO2 Shell Research Articles

Boosting hydroisomerization of n-hexadecane by designing core-shell bifunctional catalysts with partially blocked micropores

Hydroisomerization of long-chain n-alkanes is an indispensable route for upgrading fossil fuels and lubricant oils to meet the state of art regulations. Precisely regulate the distribution of acidic and metal active sites to suppress unwanted cracking reaction is hitherto a difficult task. In this work, we develop a simple coating-carbonation strategy for constructing novel core-shell bifunctional catalysts, comprising ZSM-22 zeolite core with the partially blocked channels and Pt nanoparticles loaded on the mesoporous SiO2 shell. The unique treatment not only adjusted the distribution of acid sites located within the micropore channels and external surface, but also alter the locations and dispersion of Pt nanoparticles. Owing to the short diffusion lengths, nanoscale distance between acid sites and Pt species, and high metal dispersions, the core-shell bifunctional catalyst exhibits outperformed performance in n-hexadecane hydroisomerization, i.e., the yield of isomerized hexadecane can reach 87.9 %, which is among the relatively high level compared with the previous reported Pt/zeolite counterparts. Moreover, the catalyst also displays excellent stability (no deactivation within 100 h). The disclosed structure-catalysis relationship provides rational reference for designing the synergistic meta-acid active sites in the hydroisomerization of long-chain n-alkanes.

Core–Shell–Satellite Au@CeO2–Pd Plasmonical Photocatalysts for Suzuki–Miyaura Coupling Reaction

ABSTRACTIntegration of localized surface plasmon resonance (LSPR) metallic nanocrystals into photocatalysis is an intriguing approach for light‐driven organic transformations. However, uncertain direction of hot carriers is a grand challenge, which fails to take full advantage of the LSPR excitation. In this work, core–shell gold@ceria nanosphere–supported segregated palladium species (Au@CeO2–Pd) have developed to steer the light absorption capability and charge carrier migration. Under simulated solar light irradiation, the core–shell–satellite Au@CeO2–Pd exhibited efficient light harvesting and colossal activity in the Suzuki coupling reaction. The plasmon‐induced hot electrons overpassed the Schottky barrier at the Au@CeO2 interfaces and migrated from Au core to CeO2 shell accordingly. Subsequently, the photogenerated electrons and hot electrons migrated from Au@CeO2 core–shells to Pd, which acted as an electron acceptor. Detailed photocatalytic mechanism studies revealed that both photoexcited electrons and holes were the main active species involved in the photocatalytic Suzuki coupling reaction process. In particular, the diphenyl yield over Au@CeO2–Pd catalyst was ~1.7 times higher than that of core–shell–satellite Au@SiO2–Pd, where a 19‐nm‐thick SiO2 shell was introduced to prevent the migration of hot electrons. This distinctly certified that the hot electrons transfer in the core–shell–satellite Au@CeO2–Pd under illumination played an important role to drive Suzuki reaction. Overall, this design of core–shell–satellite Au@CeO2–Pd plasmonic photocatalyst has the potential in the field of photo‐driven organic transformations.

Preparation, characterization and mechanism of SiO2@SiO2 core-shell microspheres through polymerization-induced colloid aggregation for fast separation using ultra performance liquid chromatography

The polymerization-induced colloid aggregation (PICA) method is commonly used to create SiO2@SiO2 core–shell silica microspheres (CSSMs), but it often encounters challenges such as incomplete shell coating and poor reproducibility. In this paper, the formation mechanism of the silica shell layer during the preparation of SiO2@SiO2 CSSMs using the PICA method was investigated. It was found that ureido modification can reduce the Zeta potential of the silica core surface, facilitating the deposition of coacervates formed by urea-formaldehyde resin (UF) and silica nanoparticles on the silica core surface to form the SiO2 shell layer when the Zeta potential of the surface is in the range of −20.1 mV to −4.8 mV. By controlling the interfacial state and surface potential of the SiO2 core, the issue of inconsistent reproducibility in preparing SiO2@SiO2 CSSMs can be overcome. Furthermore, optimization of experimental parameters such as pH, reaction temperature, water content, and reaction time can enhance the formation process. The thickness of the shell and pore size of CSSMs can be successfully adjusted by varying the reaction time and the particle size of colloidal silica sol, respectively. With optimal conditions, the semi-scale production yield of SiO2@SiO2 CSSMs can be increased to 50 g. The SiO2@SiO2 CSSMs were modified with octadecyltrichlorosilane (ODS) to be used as stationary phases in reversed phase liquid chromatography (RPLC) for fast separation of small solutes, peptides, and proteins. The superior separation efficiency indicates that the improved PICA method has the potential to be utilized as an alternative to the layer-by-layer method for large-scale production of SiO2@SiO2 CSSMs.

Influence of carbon dots as modifier and SiO2 shell coating as a protecting layer in YAlO3:Cr3+ phosphors for multimodal applications

This study focuses on the synthesis of SiO2-coated carbon dots (CDs) grafted onto YAlO3:Cr3+ (YAP:Cr3+) nanophosphors (NPs) through a combustion method. The CDs enhance the absorption cross-section of Cr3+ ions, significantly boosting the luminescence of YAP:Cr3+ by 19.29-fold. Further improvement is achieved with a SiO2 coating, leading to a 48.73-fold increase in photoluminescence intensity. The NCs are colour tunable, with emissions ranging from pinkish-red to blue, depending on the concentration of CDs and the excitation wavelength. These properties make them suitable for diverse applications, such as ratio metric fluorescence sensors for detecting Fe3+ ions within the 0–350 µM range, with high sensitivity (0.2 µM) and a low detection limit (4.93 μM). Additionally, they serve as material for white light-emitting diodes (W-LEDs), achieving CIE coordinates of (0.31, 0.30) and a rendering index of 94. The NCs also function as an optical thermometer with a sensitivity of 0.31 % K−1 at 320 K, making them ideal for temperature sensing applications. Moreover, their stability and dual-emissive nature make them highly effective in latent fingerprints (LFPs) detection, enabling high-resolution, level III fingerprint analysis. The dual emission properties of CDs and Cr3+ ions position these NCs as multifunctional materials, suitable for optical sensing, lighting, and security applications.

Electrochemical Properties of MIL‐100(Fe) Derived Double‐Shell Coating Anode Materials for Lithium‐Ion Battery

AbstractFe‐based anode materials with a high specific capacity, non‐toxic and abundant resources are among the ideal anode candidates for the new generation of LIBs. But their significant bulk effect causes the problems of the broken electrode structure and short cycle life that seriously hinder their practical applications. Herein, we prepared the core‐shell structure Fe3O4@C@SiO2 for the anode of LIBs by MIL‐101(Fe) derivatization using the solvent thermal method combined with the hydrolytic coating method. The porous carbon layer generated in situ by MOF pyrolysis, together with the coating of the SiO2 shell, can mitigate the volume expansion of ferric tetroxide during the cycling process. With these structural advantages, the Fe3O4@C@SiO2 anode preserves excellent performance with a specific capacity of 716 mAh/g for the 300 cycles at 1 A/g and 428 mAh/g after 2000 cycles as the density is up to 5 A/g. This work presents a promising approach for preparing SiO2‐coated core‐shell structured TMOs composite anodes.

Surface engineering of Fe3O4@SiO2 Core–Shell nanoparticles: Role of CTAB/TEOS ratio

Core– shell Fe3O4@SiO2 nanoparticles with tunable SiO2 shell thickness and porosity were successfully synthesized using cetyltrimethylammonium bromide (CTAB) as the crosslinking agent and tetraethyl orthosilicate (TEOS) as the silica precursor. The increase in the O-H stretching peak intensity observed in the Fe3O4/CTAB and Fe3O4/CTAB/SiO2 nanoparticles was attributable to the increased number of hydroxyl groups resulting from hydrogen bonding between the head of CTAB and water molecules and the increased exposure of the SiO2 surface owing to CTAB dissolution. The shell thickness and porosity of the nanoparticles were controlled by adjusting the TEOS/CTAB ratio. Increasing the CTAB content while maintaining a fixed amount of TEOS resulted in a constant shell thickness but increased porosity. Conversely, increasing the TEOS content while fixing the amount of CTAB led to the formation of a double-shell structure with a new dense silica layer on top of the existing shell at concentrations exceeding a certain threshold. These findings provide valuable insights into the design and application of SiO2-coated nanoparticles tailored for various applications.

Enhanced photocatalytic hydrogen evolution via yolk–heteroshell TiO2@TiO2/SiO2 nanoreactor with confined Pt nanoparticles

The upper limit of photocatalytic efficiency is largely determined by the light-harvesting capability of a semiconductor. To address this challenge, we developed a yolk-heteroshell TiO2@TiO2/SiO2 (T@T/S) nanoreactor, leveraging a novel design based on an in-depth understanding and innovative utilization of light-matter interactions. The T@T/S nanoreactor significantly enhances solar light capture and utilization efficiency through total internal reflection mechanisms facilitated by the heterogeneous shell. This heteroshell, consisting of an outer SiO2 shell an inner monolayer of TiO2 nanoparticles, maximizes light confinement due to the different refractive indices of SiO2 and TiO2, while also minimizing mass transfer resistance due to the thin inner shell layer. These unique structural features result in high photocatalytic activity under simulated solar light. Additionally, we successfully applied a “ship-in-a-bottle” strategy for the confined growth of platinum nanoparticles within T@T/S nanoreactor. The Pt0.5-T@T/S nanoreactors demonstrated excellent hydrogen production, achieving a hydrogen evolution rate of 24.43 mmol g−1h−1 under simulated sunlight and an apparent quantum efficiency (AQE) of 7.8 % at 350 nm. This study highlights the importance of nano-engineered designs in optimizing semiconductor photocatalysts and shows the significant potential of our approach for sustainable energy conversion and environmental protection.

Opal‐Inspired SiO2‐Mediated Carbon Dot Doping Enables the Synthesis of Monodisperse Multifunctional Afterglow Nanocomposites for Advanced Information Encryption

AbstractDespite recent advancements in inorganic and organic phosphors, creating monodisperse afterglow nanocomposites (NCs) remains challenging due to the complexities of wet chemistry synthesis. Inspired by nanoinclusions in opal, we introduce a novel SiO2‐mediated carbon dot (CD) doping method for fabricating monodisperse, multifunctional afterglow NCs. This method involves growing a SiO2 shell matrix on monodisperse nanoparticles (NPs) and doping CDs into the SiO2 shell under hydrothermal conditions. Our approach preserves the monodispersity of the parent NP@SiO2 NCs while activating a green afterglow in the doped CDs with an impressive lifetime of 1.26 s. Additionally, this method is highly versatile, allowing for various core and dopant combinations to finely tune the afterglow through core‐to‐CD or CD‐to‐dye energy transfer. Our findings significantly enhance the potential of SiO2 coatings, transforming them from merely enhancing the biocompatibility of NCs to serving as a versatile matrix for emitters, facilitating afterglow generation and paving the way for new applications.

Opal-Inspired SiO2-Mediated Carbon Dot Doping Enables the Synthesis of Monodisperse Multifunctional Afterglow Nanocomposites for Advanced Information Encryption.

Despite recent advancements in inorganic and organic phosphors, creating monodisperse afterglow nanocomposites (NCs) remains challenging due to the complexities of wet chemistry synthesis. Inspired by nanoinclusions in opal, we introduce a novel SiO2-mediated carbon dot (CD) doping method for fabricating monodisperse, multifunctional afterglow NCs. This method involves growing a SiO2 shell matrix on monodisperse nanoparticles (NPs) and doping CDs into the SiO2 shell under hydrothermal conditions. Our approach preserves the monodispersity of the parent NP@SiO2 NCs while activating a green afterglow in the doped CDs with an impressive lifetime of 1.26 s. Additionally, this method is highly versatile, allowing for various core and dopant combinations to finely tune the afterglow through core-to-CD or CD-to-dye energy transfer. Our findings significantly enhance the potential of SiO2 coatings, transforming them from merely enhancing the biocompatibility of NCs to serving as a versatile matrix for emitters, facilitating afterglow generation and paving the way for new applications.

Photothermal Dry Reforming of Methane on Yolk‐Shell Co–Ni Alloy@SiO2 Catalyst

Photothermal dry reforming of methane (PT‐DRM) is an appealing pathway to convert carbon dioxide and methane into synthesis gas, a mixture of carbon monoxide and hydrogen, via photothermal heating induced by concentrated sunlight. Coke formation and sintering of active metal nanoparticles, however, are a key issue for catalyst stability. In the present study, we demonstrated Co–Ni alloy nanoparticles encapsulated with a porous SiO2 shell exhibited improved catalytic activity and stability for PT‐DRM using visible/near‐IR light irradiation without any other external heating. The addition of a trace amount of Co (1–5 mol% relative to total metal) and SiO2 encapsulation enhanced the stability by simultaneously suppressing coke formation and sintering of the metal nanoparticles. Furthermore, we revealed that the position of the light irradiation spot has a crucial role in the conversions of methane and carbon dioxide and product selectivity, presumably due to large temperature gradient under the light irradiation. These findings would contribute to designing for effective PT‐DRM catalysts with improved activity and enhanced resistance for both coke formation and sintering and emphasize the significant contribution of the temperature gradients to the performance in PT‐DRM.

Investigation of long-range plasmonic field effects in Au@SiO2 nanostructures using p-nitrophenol reduction

As an emerging field, plasmonic photocatalysis has gradually garnered attention from researchers. It is generally accepted that localized surface plasmonic resonance (LSPR) in noble metallic nanostructures enhances photocatalysis through the induction of a long-range plasmonic field. Furthermore, nanostructures in close proximity can enhance the electromagnetic (EM) field via plasmonic coupling, which also contributes to improved photocatalytic activity. In this study, core-shell nanostructures composed of Au nanorods (AuNRs) with pinhole-free SiO2 shells (pf-AuNRs@SiO2) are synthesized as non-contact, long-range photocatalysts. By tuning the aspect ratios (ARs) of the AuNRs to match the LSPR peaks with the wavelength of the irradiation light source, an optimized photocatalytic effect was achieved in the reduction of p-nitrophenol (p-NP). Additionally, by comparing shell thicknesses of 5 nm and 10 nm, it was observed that the 5 nm thickness exhibited superior catalytic efficiency. This enhancement is attributed to the thinner shell allowing reactants to be placed within a stronger plasmonic field.

Optimization and performance assessment of Ag@SiO2 core–shell nanofluids for spectral splitting PV/T system: Theoretical and experiment analysis

Ag@SiO2 nanofluid is widely used in spectral splitting PV/T system. Its core–shell structure has great influence on the optical properties. In this work, we focus on the comprehensive analysis and structure optimization of Ag@SiO2 nanofluid to achieve its optimal spectral performance. DDA method is used to predict the optical properties of Ag@SiO2 nanofluid and an optimization model based on filter efficiency is proposed. The effect of the SiO2 shell thickness and Ag core mass concentration is analyzed. It indicates that the spectral performance of Ag@SiO2 nanofluid can be improved with SiO2 shell thickness of 15–40 nm and Ag core mass concentration of 81–135 mg/L. To achieve the same theoretical merit function of 1.46, the usage of Ag mass can be reduced by 25/33/44/62 % with SiO2 coating of 10/20/40/70 nm. The optimal structure to achieve the highest filter efficiency η of 37.8 % is with a shell thickness of 20 nm and a mass concentration of 113.9 mg/L. An indoor PV/T operation testing is conducted to verify the optimization results. The merit function of Ag-based nanofluids increases from 1.58 to 1.598 and a reduction in Ag usage of 17 % is achieved with a SiO2 coating shell of 17.8 nm. Operation stability is also enhanced with no aggregation observed during the working cycle and 7-day static experiment.

Dual-shell protection enables highly efficient and stable all-inorganic perovskite composites for light-emitting-diodes

Lead-halide perovskite nanocrystals (NCs) present superior photoelectric properties, but the poor stability seriously hinders their practical application. The encapsulation of perovskite NCs inside mesoporous silica (m-SiO2) matrix is considered as one of the most feasible pathways to improve the stability of NCs. However, the challenges of loose encapsulation structure, aggregation of particles, high energy consumption during the preparation of CsPbX3@m-SiO2 composites have not yet been overcome, which throw a shadow over the large-scale commercial applications. Here, we present a dual-shell encapsulation strategy that enables the formation of highly emissive CsPbBr3@m-SiO2@SiO2 composites, achieving an exceptional photoluminescence quantum yield (PLQY) of 97.37 %. The reaction parameters for the preparation of composites are meticulous investigated. The CsPbBr3 NCs can be well formed inside the pores of m-SiO2 as the m-SiO2 is introduced into the precursor solution. The secondary SiO2 shells can effectively seal the open pores of m-SiO2. As a result, the as-prepared CsPbBr3@m-SiO2@SiO2 composites present excellent stability, in which the composites can maintain 93.16 % of initial intensity after storage for 84 days. Besides, a series of CsPbX3@m-SiO2@SiO2 composites with tunable emission wavelength in the range of 428.6–630.6 nm are prepared through facile designing the halide ratios of precursor solution, which present a wide color gamut (148.48 % of the National Television Standards Committee). In addition, a white light-emitting diode (LED) is fabricated by combining CsPbBr3@m-SiO2@SiO2 composites and K2SiF6:Mn4+ phosphors with a 455 nm LED chip, which exhibits good photoelectric performances. This facile low-temperature dual-shell encapsulation strategy reported here provides a new pathway for preparing high-performance perovskite composites, facilitating their practical photoelectric application.

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The in‐situ post‐synthetic treatment of CsPbBr₃ nanocrystals confined within nanoporous silica microspheres enhances their optical properties, addressing key challenges in lead halide perovskites. Surface passivation with Br⁻ ions boosts photoluminescence quantum yield, while Mn²⁺ doping introduces a new emission band, enabling precise control of optical properties. Coating with a SiO₂ shell further enhances the stability of the nanocrystals in polar solvents, expanding their potential for diverse applications. More details are discussed in the article by Huang et al. on pages 2779—2787. image

Double Layer SiO2-Coated Water-Stable Halide Perovskite as a Promising Antimicrobial Photocatalyst under Visible Light.

Halide perovskite nanocrystals (HPNCs) have emerged as promising materials for various light harvesting applications due to their exceptional optical and electronic properties. However, their inherent instability in water and biological fluids has limited their use as photocatalysts in the aqueous phase. In this study, we present highly water-stable SiO2-coated HPNCs as efficient photocatalysts for antimicrobial applications. The double SiO2 layer coating method confers long-term structural and optical stability to HPNCs in water, while the in situ synthesis of lead- and bismuth-based perovskite NCs into the SiO2 shell enhances their versatility and tunability. We demonstrate that the substantial generation of singlet oxygen via energy transfer from HPNCs enables efficient photoinduced antibacterial efficacy under aqueous conditions. More than 90% of Escherichia coli was inactivated under mild visible light irradiation for 6 h. The excellent photocatalytic antibacterial performance suggests that SiO2-coated HPNCs hold great potential for various aqueous phase photocatalytic applications.

Synthesis and luminescent properties of multi-mode core-shell-shell LaPO4:RE (RE³⁺ = Er³⁺, Eu³⁺) microspheres for anti-counterfeiting ink applications

To meet the demands for product and consumer protection, we developed biocompatible multi-mode emitting core-shell-shell rare earth phosphates for anti-counterfeiting inks. These core-shell-shell structures feature SiO2 microspheres as the core, with LaPO4 nanocrystals doped with erbium (Er) and europium (Eu) as the interlayer, and an outer SiO2 shell. The SiO2@LaPO4:Er0.1,Eux@SiO2 (x = 0.01, 0.02, 0.03, 0.04, 0.05) microspheres display dual emissions when excited by 254 nm and 365 nm UV light, offering a novel anti-counterfeiting approach. Another core-shell-shell structure was created with LaPO4:Er3+ and LaPO4:Eu3+ separately coated on SiO2 cores, mixed, and then covered with a SiO2 shell. Under 980 nm near-infrared laser excitation, these structures emit bright upconverted green light, while 254/365 nm UV light induces red/yellow down-conversion luminescence. This design minimizes up-conversion luminescence quenching of Er3+ ions from cross-relaxation with Eu3+ ions. The SiO2 core minimizes energy loss, regulates particle size, and enhances luminescence. A certain thickness of the silicon shell layer also protects against luminescence quenching. The inks exhibit high dispersibility, non-reproducibility, and excellent luminescence, making them effective for anti-counterfeiting.

Preparation, pore structure and properties of uniformly porous glass-ceramics sintered from granite powder using SiC@SiO2 foaming agent

Granite sludge produced during the processing of granite blocks should be efficiently recycled for environmental protection and as a sustainable resource. In this work, porous glass-ceramics were prepared by stepwise sintering of granite powder using core-shell SiC@SiO2 foaming agent. The SiC and SiC@SiO2 foaming agents were compared in terms of the sintering and foaming behaviors of the powder compacts by thermal expansion, thermogravimetry and mass spectroscopy. The foaming agent and foaming temperature were investigated to study their effects on the pore structure and properties of the porous glass-ceramics. The SiO2 shells of the SiC@SiO2 particles inhibited the oxidation of the SiC cores and the release of CO2 at the early stage of the sintering process, thus preventing pore coalescence and increasing the densification and specific strength of the sintered glass-ceramics. As the foaming temperature increased, the porous glass-ceramics exhibited a linear relationship between pore size and foaming temperature, and the specific strength first increased and then decreased due to pore coalescence and reduced crystallinity. Furthermore, the linear relationship between thermal conductivity and porosity indicates a closed pore structure, as demonstrated by computed tomography. At a foaming temperature of 1220 °C, the porous glass-ceramic has a porosity of 50.1 %, a specific strength of 16.6 kN⋅m/kg and a thermal conductivity of 0.747 W/(m⋅K). Numerical simulation confirms that lightweight glazed glass-ceramics have potential applications in energy-efficient building tiles.

Hydrophobic surface modification and morphology tuning of supported KNiMoS-based catalyst for synergistically enhanced higher alcohols synthesis via CO hydrogenation

MoS2-based catalysts have gained significant attention in higher alcohols synthesis (HAS) via CO hydrogenation. However, the water–gas shift (WGS) to produce CO2 in HAS is undesirable reaction, which will reduce the efficiency of carbon utilization. Here, we provide a facile strategy with hydrophobic surface modification and metal-support interaction modulation to design a series of KNiMoS/MgAl catalysts. The organic modified SiO2 shell with excellent hydrophobicity effectively shortens the residence of water formed in HAS, and further suppress the generation of CO2 and low-chain hydrocarbons. Moreover, the moderate metal-support interaction between MoS2-based active species and MgAl support can regulate the dispersion and sulfidation extent of MoS2 slabs to provide more active sites for alcohol formation. The MoS2 slabs with predominant double-layer structure enhance the C–C propagation and CO insertion in HAS. And as a result, the optimal KNiMoS/MgAl@Si(c)-5 achieves total alcohols selectivity of 74.7 %, C2+OH selectivity of 85.8 % in total alcohols, and C2+ alcohols space–time yield of 107.8 mg gcat-1h−1, where C2+ alcohols space–time yield is 3.50 and 2.71 times than those on KNiMoS/MgAl(H) and KNiMoS/MgAl, respectively. Notably, the total selectivity of CO2 and hydrocarbons is less than 23.2 %, and selectivity ratio of C2-4OH to methanol can be overturned from 1.9 to 6.0. The dependence of HAS performance on the morphology of MoS2 slabs were also demonstrated to get insight into the structure-performance relationship. This work provides a facile strategy with tunable hydrophobic surface and metal-support interaction of MoS2-based catalysts for further improvement of catalytic performance.

Titania-Cored Janus Multipods as UV-Protective Pickering Emulsifiers for Sunscreens.

Pickering emulsifiers have gained significant interest as alternatives for conventional surfactants in various applications that includes pharmaceutics, food, homecare products, and cosmetics. However, their function is primarily focused on enhancing emulsion stability of which still remains to be resolved. Herein, Janus multipods are presented that simultaneously shield UV while offering high emulsion stability. These particles are prepared by growing multiple silicon dioxide (SiO2) nanopods using sol-gel method on a spherical titanium dioxide (TiO2) core with a thin SiO2 shell. The incorporation of high refractive index TiO2 in the core is shown to effectively shield UV while the SiO2 shell suppresses the photocatalytic activity. Moreover, by utilizing wax colloidosomes as templates, these multipod nanoparticles are further modified to exhibit Janus characteristics. This leads to strong adsorption of the Janus multipods at the oil/water emulsion interface where the multipod feature additionally reinforces the interfacial stabilization by interdigitation and interlocking of the Janus multipods to suppress detachment of the highly dense particles from the interface. As these Janus multipods offer effective UV protection as well as excellent emulsion stability, it is envisioned that they have great potential in advanced cosmetic formulations which require both enhanced sunscreen performance and better feeling in skincare products.

Formation mechanism and luminescence properties of silicon carbide nanowires with core-shell structure

For the preparation of SiC nanowires (SiC NWs) by carbothermal reduction, it is of great significance to study the formation mechanism of sic nanowires for process optimization and the controllable preparation. Although first-principles molecular dynamics (FPMD) can simulate systems of hundreds of atoms on a picosecond time scale, the results of FPMD are still insufficient to elucidate the formation mechanism of core-shell SiC nanowires. To make up this deficiency, this article has conducted Deep Potential Molecular Dynamics (DPMD) simulation on nanoseconds timescales with near FPMD accuracy for systems containing thousands of atoms, the results more concretively show the formation process of core-shell SiC nanowires. DPMD simulation results show when CO molecules react with SiO molecules, CO molecules are wrapped by SiO molecules to form agglomerates, SiO molecules in the agglomerates that can come into contact with the wrapped CO molecules will react with wrapped CO molecules to form the SiC core, and SiO molecules that in the outer layer of the agglomerates will disproportionate into the amorphous SiO2 shell. Furthermore, the formation mechanism of SiC nanowires was validated in combination with thermodynamics and experimental methods. Thermodynamic results show that vacuum conditions are favorable for the formation of SiO and CO and lower the temperature of SiC preparation. Finally, the core-shell structure of SiC NWs with good luminescence properties were successfully prepared by carbothermal reduction method using carbon black and silicon dioxide as raw materials under the pressure of less than 5 kPa.