Photothermal conversion of SiO2@Au nanoparticles mediated by surface morphology of gold cluster layer

Photothermal effects in SiO₂@Au core–shell nanoparticles have demonstrated great potential in various applications for drug delivery, thermo-photovoltaics and photothermal cancer therapy, etc. However, the photothermal conversion of SiO₂@Au nanoparticles partially covered by disconnected gold clusters has rarely been investigated systematically. Here, we control the surface morphology of gold clusters on the photothermal conversion performance of SiO₂@Au core–shell nanoparticles by means of chemically adjusting the synthesis parameters, including amounts of gold salts, pH value and reducing agent. The macroscopic variations of the photothermal heating of different nanoparticle dispersions are significantly influenced by the nanoscale differences of gold cluster morphologies on the silica core. The temperature rise can be enhanced by the strong near-field coupling and collective heating among gold clusters with a relatively uniform distribution on the silica core. A numerical model of the simplified photothermal system is formulated to interpret the physical mechanism of the experimental observation, and shows a similar trend of temperature rise implying a reasonably good agreement with experimental data. Our work opens new possibilities for manipulating the light-to-heat conversion performance of SiO₂@Au core–shell nanoparticles and potential applications of heat delivery with spatial resolution on the nanoscale.

We manipulate the surface morphology of gold clusters on SiO₂@Au nanoparticle and found that macroscopic photothermal conversions of different nanoparticle dispersions are significantly affected by nanoscale differences of gold cluster morphologies.     

Preparation of MoS2-based polydopamine-modified core–shell nanocomposites with elevated adsorption performances

New molybdenum disulfide (MoS₂)-based core–shell nanocomposite materials were successfully prepared through the self-assembly of mussel-inspired chemistry. Characterization by Fourier transform infrared, thermogravimetric analysis, scanning electron microscope and transmission electron microscopy revealed that the surface of the flaked MoS₂ was homogeneously coated with a thin layer of polydopamine (PDA). Dye adsorption performances of the synthesized MoS₂–PDA nanocomposites were investigated at different pH values and reaction times. Compared with pure MoS₂ nanosheets, the obtained core–shell nanocomposites showed elevated adsorption performances and high stability, indicating their potential applications in wastewater treatment and composite materials.

New core–shell MoS₂–PDA nanocomposites are prepared via mussel-inspired chemistry and a simple interfacial self-assembly process, demonstrating potential applications in wastewater treatment and self-assembled core–shell composite materials.     

SiO2@MnOx@Na2WO4@SiO2 core–shell-derived catalyst for oxidative coupling of methane

SiO₂@MnO_x@Na₂WO₄@SiO₂ core–shell catalysts were prepared and their fabrication was confirmed using transmission electron microscopy. The formation of Mn-based nanosheets on the silica spheres is important for the deposition of nanoscopic Na₂WO₄. The SiO₂@MnO_x@Na₂WO₄@SiO₂ core–shell catalysts were used for the oxidative coupling of methane at a temperature of 700–800 °C at which the nanostructures were completely destroyed. Although the core–shell structures did not survive the high-temperature oxidative coupling of methane, the selective production of olefins and paraffins can be attributed to highly dispersed Na₂WO₄ derived from confined core–shell structures.

SiO₂@MnO_x@Na₂WO₄@SiO₂ core–shell catalysts were prepared for the oxidative coupling of methane.     

Effect of core–shell nanocomposites on the mechanical properties and rheological behaviors of cement pastes

SiO₂ nanoparticles (50 nm in diameter) coated with poly(ethylene glycol) methyl ether methacrylate (PEGMA) were synthesized by radical polymerization. The SiO₂/PEGMA nanocomposites were characterised using FITR, ¹HNMR and TGA methods. The load of PEGMA in SiO₂/PEGMA nanocomposites was 72.9 wt%. The hydration products, microstructure, pore structure, density, compressive strengths and rheological properties of cement were investigated. The SiO₂/PEGMA nanocomposite could not only significantly improve the cement hydration and densify the microstructure by reducing the content of calcium hydroxide and promoting the production of calcium silicate hydrate, but also efficiently enhance the fluidity of the cement slurry. The compressive strength of cement with 2 wt% SiO₂/PEGMA nanocomposites was increased by 40.1% curing for 28 days, which was much better than cement with the physical blending of SiO₂ nanoparticles and superplasticizers. The SiO₂/PEGMA nanocomposites with core–shell structure novelly combine the advantages of SiO₂ nanoparticles and superplasticizers to significantly improve the performance of cement pastes. The results obtained provide a new understanding of the effect of the core–shell nanocomposites on cement pastes and demonstrate the potential of the nanocomposites for well cementing applications.

The core–shell structure endowed the SiO₂/PEGMA nanocomposite with multiple functions, which could not only significantly improve the cement hydration and densify the microstructure, but also efficiently enhance the fluidity of the cement pastes.     

CNT–TiO2 core–shell structure: synthesis and photoelectrochemical characterization

Porous composite coatings, made of a carbon nanotube (CNT)–TiO₂ core–shell structure, were synthesized by the hybrid CVD-ALD process. The resulting TiO₂ shell features an anatase crystalline structure that covers uniformly the surface of the CNTs. These composite coatings were investigated as photoanodes for the photo-electrochemical (PEC) water splitting reaction. The CNT–TiO₂ core–shell configuration outperforms the bare TiO₂ films obtained using the same process regardless of the deposited anatase thickness. The improvement factor, exceeding 400% in photocurrent featuring a core–shell structure, was attributed to the enhancement of the interface area with the electrolyte and the electrons fast withdrawal. The estimation of the photo-electrochemically effective surface area reveals that the strong absorption properties of CNT severely limit the light penetration depth in the CNT–TiO₂ system.

CNT–TiO₂ core–shell nanostructured coatings were made using a hybrid CVD/ALD process. The evaluation of these films as photoanodes for the photoelectrochemical water splitting reaction reveals a clear benefit from the involvement of CNTs.     

PHB/PCL fibrous membranes modified with SiO2@TiO2-based core@shell composite nanoparticles for hydrophobic and antibacterial applications

In order to prepare multifunctional fibrous membranes with hydrophobicity, antibacterial properties and UV resistance, we used silica and titanium dioxide for preparing SiO₂@TiO₂ nanoparticles (SiO₂@TiO₂ NPs) to create roughness on the fibrous membranes surfaces. The introduction of TiO₂ was used for improving UV resistance. N-Halamine precursor and silane precursor were introduced to modify SiO₂@TiO₂ NPs to synthesize SiO₂@TiO₂-based core@shell composite nanoparticles. The hydrophobic antibacterial fibrous membranes were prepared by a dip-pad process of electrospun biodegradable polyhydroxybutyrate/poly-ε-caprolactone (PHB/PCL) with the synthesized SiO₂@TiO₂-based core@shell composite nanoparticles. TEM, SEM and FT-IR were used to characterize the synthesized SiO₂@TiO₂-based core@shell composite nanoparticles and the hydrophobic antibacterial fibrous membranes. The fibrous membranes not only showed excellent hydrophobicity with an average water contact angle of 144° ± 1°, but also appreciable air permeability. The chlorinated fibrous membranes could inactivate all S. aureus and E. coli O157:H7 after 5 min and 60 min of contact, respectively. In addition, the chlorinated fibrous membranes exhibited outstanding cell compatibility with 102.1% of cell viability. Therefore, the prepared hydrophobic antibacterial degradable fibrous membranes may have great potential application for packaging materials.

Schematic illustration of the synthesis of SiO₂@TiO₂-based core@shell composite nanoparticles (top) and antibacterial hydrophobic behavior of fibrous membranes (bottom).     

Novel mesoporous Ag@SiO2 nanospheres as a heterogeneous catalyst with superior catalytic performance for hydrogenation of aromatic nitro compounds

Mesoporous core–shell structure Ag@SiO₂ nanospheres are constructed to prevent Ag nanoparticles from aggregation during the hydrogenation reaction. The prepared catalyst shows superior catalytic performance for hydrogenation of nitro compounds with 100% conversion and selectivity without any by-products, which also indicates good recycling performance for several times use.

Mesoporous core–shell structure Ag@SiO₂ nanospheres are constructed to prevent Ag nanoparticles from aggregation during the hydrogenation reaction.     

Facilely controlled synthesis of a core-shell structured MOF composite and its derived N-doped hierarchical porous carbon for CO2 adsorption

A new strategy for controlled synthesis of a MOF composite with a core–shell structure, ZIF-8@resorcinol–urea–formaldehyde resin (ZIF@RUF), is reported for the first time through in situ growth of RUF on the surface of ZIF-8 nanoparticles via an organic–organic self-assembly process by using hexamethylenetetramine as a formaldehyde-releasing source to effectively control the formation rate of RUF, providing the best opportunity for RUF to selectively grow around the nucleation seeds ZIF-8. Compared with the widely reported method for MOF composite synthesis, our strategy not only avoids the difficulty of incorporating MOF crystals into small pore sized materials because of pore limitation, but also effectively guarantees the formation of a MOF composite with a MOF as the core. After carbonization, a morphology-retaining N-doped hierarchical porous carbon characterized by its highly developed microporosity in conjunction with ordered mesoporosity was obtained. Thanks to this unique microporous core–mesoporous shell structure and significantly enhanced porosity, simultaneous improvements of CO₂ adsorption capacity and kinetics were achieved. This strategy not only paves a way to the design of other core–shell structured MOF composites, but also provides a promising method to prepare capacity- and kinetics-increased carbon materials for CO₂ capture.

New strategy for controlled synthesis of core–shell structured ZIF-8 composite and hierarchical N-doped carbon via an effective in situ self-assembly process.     

Hydrophilic and antimicrobial core–shell nanoparticles containing guanidine groups for ultrafiltration membrane modification

Physical blending is a common technique to improve the water flux and antifouling performance of ultrafiltration (UF) membranes. In the present work, a novel hydrophilic and antimicrobial core–shell nanoparticle was synthesized through the chemical grafting of poly(guanidine-hexamethylenediamine-PEI) (poly(GHPEI)) on the surface of silica nanoparticles (SNP). The synthesized core–shell nanoparticles, poly(GHPEI) functionalized silica nanoparticles (SNP@PG), were incorporated into polyethersulfone (PES) to fabricate hybrid UF membranes by a phase inversion process. The chemical composition, surface and cross section morphologies, hydrophilicity, water flux and protein rejection of the membranes were evaluated by a series of characterizations. Results show that the prepared PES/SNP@PG hybrid membrane exhibits not only improved water flux, which is around 2.6 times that of the pristine PES membrane, but also excellent resistance to organic fouling and biofouling.

Hydrophilic and antimicrobial core–shell nanoparticles containing guanidine groups (SNP@PG) were applied to fabricate membranes with improved water flux and fouling resistance.     

One-pot one-step synthesis of Au@SiO2 core–shell nanoparticles and their shell-thickness-dependent fluorescent properties

Herein, we report a one-pot one-step method for the preparation of Au@SiO₂ core–shell nanoparticles (NPs) via a facile heating treatment of an alcoholic-aqueous solution of chloroauric acid (HAuCl₄), 2-methylaminoethanol (2-MAE), cetyltrimethylammonimum bromide (CTAB), and tetraethylorthosilicate (TEOS). The size of the Au core and the thickness of the silica shell can be easily controlled by simply adjusting the volume of HAuCl₄ and TEOS, respectively, which can hardly be achieved by other approaches. The as-prepared Au@SiO₂ core–shell NPs exhibited shell-thickness-dependent fluorescent properties. The optimum fluorescence enhancement of fluorescein isothiocyanate (FITC) was found to occur at a silica shell thickness of 34 nm with an enhancement factor of 5.0. This work provides a new approach for the preparation of Au@SiO₂ core–shell NPs and promotes their potential applications in ultrasensitive analyte detection, theranostics, catalysts and thin-film solar cells.

Au@SiO₂ core–shell nanoparticles with tunable Au core size and silica shell thickness were prepared by a facile one-pot one-step method.     

Epitaxial growth of ultrathin layers on the surface of sub-10 nm nanoparticles: the case of β-NaGdF4:Yb/Er@NaDyF4 nanoparticles

Upconversion core–shell nanoparticles have attracted a large amount of attention due to their multifunctionality and specific applications. In this work, based on a NaGdF₄ sub-10 nm ultrasmall nanocore, a series of core–shell upconversion nanoparticles with uniform size doped with Yb³⁺, Er³⁺ and NaDyF₄ shells with different thicknesses were synthesized by a facile sequential growth process. NaDyF₄ coated upconversion luminescent nanoparticles showed an obvious fluorescence quenching under excitation at 980 nm as a result of energy resonance transfer between Yb³⁺, Er³⁺ and Dy³⁺. NaGdF₄:Yb,Er@NaDyF₄ core–shell nanoparticles with ultrathin layer shells exhibited a better T₁-weighted MR contrast.

In this work, a series of core–shell upconversion nanoparticles with uniform size doped with Yb³⁺, Er³⁺ and NaDyF₄ shells with different thicknesses were synthesized by a facile sequential growth process.     

Non-photochemical catalytic hydrolysis of methyl parathion using core–shell Ag@TiO2 nanoparticles

Highly water-dispersible core–shell Ag@TiO₂ nanoparticles were prepared and shown to be catalytically active for the rapid degradation of the organothiophosphate pesticide methyl parathion (MeP). Formation of the hydrolysis product, p-nitrophenolate was monitored at pH 7.5 and 8.0, using UV-Vis spectroscopy. ³¹P NMR spectroscopy confirmed that hydrolysis is the predominant pathway for substrate breakdown under non-photocatalytic conditions. We have demonstrated that the unique combination of TiO₂ with silver nanoparticles is required for catalytic hydrolysis with good recyclability. This work represents the first example of MeP degradation using TiO₂ doped with AgNPs under mild and ambient conditions. Analysis of catalytic data and a proposed dark mechanism for MeP hydrolysis using core–shell Ag@TiO₂ nanoparticles are described.

Ag@TiO₂ non-photochemical catalyzed degradation of organophosphosphates.     

Enhanced visible transmittance and reduced transition temperature for VO2 thin films modulated by index-tunable SiO2 anti-reflection coatings

The low visible transmission is one of the bottleneck problems for the application of vanadium dioxide films since the high refractive index (RI) of VO₂ films results in strong reflection in the visible wavelength. To address this problem, in this paper, high-purity VO₂ films were deposited on fused silica by DC reactive magnetron sputtering at low temperature of 320 °C. Silica sol–gel coatings with tunable refractive index (RI) coated onto VO₂ films have been fabricated to enhance visible transmittance with the potential application in the field of smart windows. SiO₂ coatings with tunable RI (1.16–1.42 at λ = 700 nm) were prepared by sol–gel dip-coating technique. The double structure SiO₂/VO₂ films were characterized through several techniques, including X-ray diffraction, UV-VIS-NIR spectrophotometry and scanning electron microscopy. Compared with the single-layer VO₂ film (ΔT_sol of 6.25% and T_lum of 38.58%), the three kinds of SiO₂/VO₂ bilayer films had higher T_lum (41.93–50.44%) and larger ΔT_sol (8.15–8.51%) simultaneously due to significantly decreased reflectance. Moreover, the crystallization properties of VO₂ films are essentially unchanged by applying a SiO₂ top layer, while the phase transition temperature and thermal hysteresis width of sample S116 are lower than those of pure VO₂ film. The presented RI-tunable SiO₂ coatings, can regulate optical properties continuously for various VO₂ substrates, paving the way for practical applications of VO₂ films in the field of smart windows or others.

Index-tunable anti-reflection SiO₂ coatings prepared on the surface of VO₂ films by sol–gel dip-coating technique to enhance the visible and infrared transmittance of SiO₂/VO₂ films.     

Synthesis of TiO2–ZnS nanocomposites via sacrificial template sulfidation and their ethanol gas-sensing performance

TiO₂–ZnS core–shell composite nanorods were synthesized by using ZnO as a sacrificial shell layer in a hydrothermal reaction. ZnO thin films of different thicknesses were sputter-deposited onto the surfaces of TiO₂ nanorods as templates for hydrothermally synthesizing TiO₂–ZnS core–shell nanorods. Structural analysis revealed that crystalline TiO₂–ZnS composite nanorods were formed without any residual ZnO phase after hydrothermal sulfidation in the composite nanorods. The thickness of the ZnO sacrificial shell layer affected the surface morphology and sulfur-related surface defect density in hydrothermally grown ZnS crystallites of TiO₂–ZnS composite nanorods. Due to the distinctive core–shell heterostructure and the heterojunction between the TiO₂ core and the ZnS shell, TiO₂–ZnS core–shell nanorods exhibited ethanol gas-sensing performance superior to that of pristine TiO₂ nanorods. An optimal ZnO sacrificial shell layer thickness of approximately 60 nm was found to enable the synthesis of TiO₂–ZnS composite nanorods with satisfactory gas-sensing performance through sulfidation. The results demonstrated that hydrothermally derived TiO₂–ZnS core–shell composite nanorods with a sputter-deposited ZnO sacrificial shell layer are promising for applications in gas sensors.

TiO₂–ZnS core–shell composite nanorods were synthesized by using ZnO as a sacrificial shell layer in a hydrothermal reaction.     

Facile synthesis of silver nanocatalyst decorated Fe3O4@PDA core–shell nanoparticles with enhanced catalytic properties and selectivity

In this work, we have successfully prepared core–shell nanoparticles (Fe₃O₄@PDA) wrapped with Ag using a simple and green synthesis method. Without an external reducing agent, silver nanoparticles (Ag NPs) with good dispersibility were directly reduced and deposited on a polydopamine (PDA) layer. Fe₃O₄@PDA@Ag showed excellent catalytic activity and recyclability for 4-nitrophenol, and also exhibited good catalytic selectivity for organic dyes (MO and MB). This simple and green synthesis method will provide a platform for other catalytic applications.

In this work, we have successfully prepared core–shell nanoparticles (Fe₃O₄@PDA) wrapped with Ag using a simple and green synthesis method.     

Fabrication and excellent electroresponsive properties of ideal PMMA@BaTiO3 composite particles

A series of core–shell-structured poly(methylmethacrylate)@BaTiO₃ (PMMA@BT) composite particles were constructed via the self-assembly of BT nanoparticles on the surfaces of PMMA cores through the covalent bonding of siloxane groups at room temperature. The PMMA@BT composite particles were characterized by scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, X-ray diffraction, video-based optical contact angle measurement, thermogravimetric analysis, and impedance analysis. The electroresponses of the obtained PMMA@BT composite particles were all stronger than that of pure BT, and the electroresponse depended on the weight percentage of the BT shell. The PMMA@BT particles with the optimal core–shell structure contained 58.14 wt% of BT shell. The surface hydrophilicity of the optimal particles was close to that of pure BT, and the dielectric constant was the greatest among the series of synthesized PMMA@BT particles. Thus, the optimized PMMA@BT particles demonstrated the strongest electroresponsive behavior in gelatin hydrogel elastomer, as demonstrated by polarized microscopy and dynamic mechanical analysis. The excellent electroresponsive property of the optimal PMMA@BT particles is reflected by the large sensitivity of the increase in storage modulus for the gelatin hydrogel elastomer containing the composite particles (21% at E = 0.8 kV mm⁻¹ and a particle loading of 1.0 wt%), far greater than that of pure BT particles (4.7%). Based on the sensitive electroresponsive properties, the PMMA@BT particles have potential applications as electroresponsive materials.

A series of core–shell-structured poly(methylmethacrylate)@BaTiO₃ (PMMA@BT) composite particles were constructed via the self-assembly of BT nanoparticles on the surfaces of PMMA cores through the covalent bonding of siloxane groups at room temperature.     

Upconversion luminescence in sub-10 nm β-NaGdF4:Yb3+,Er3+ nanoparticles: an improved synthesis in anhydrous ionic liquids

Sub-10 nm β-NaGdF₄:18% Yb³⁺,2% Er³⁺ nanoparticles were synthesized in ethylene glycol and various ionic liquids under microwave heating. The products were characterized by powder X-ray diffraction, electron microscopy, and upconversion (UC) luminescence spectroscopy. After Yb³⁺ excitation at 970 nm, Er³⁺ ions are excited by energy transfer upconversion and show the typical green and red emission bands. The UC luminescence intensity was optimized with respect to reactant concentrations, solvents, and reaction temperature and time. The strongest UC emission was achieved for sub-20 nm core–shell nanoparticles which were obtained in the ionic liquid diallyldimethylammonium bis(trifluoromethanesulfonyl)amide from a two-step synthesis without intermediate separation. Strictly anhydrous reaction conditions, a high fluoride/rare earth ion ratio, and a core–shell structure are important parameters to obtain highly luminescent nanoparticles. These conditions reduce non-radiative losses due to defects and high energy acceptor modes of surface ligands. A low power excitation of the core–shell particles by 70 mW at 970 nm results in an impressive UC emission intensity of 0.12% compared to the bulk sample.

The microwave-assisted synthesis of β-NaGdF₄:Er³⁺,Yb³⁺ in anhydrous ionic liquids yields efficient upconversion luminescence nanoparticles. A core–shell structure raises the nanoparticle emission intensity to 0.12% of the bulk material.     

Oriented exchange-coupled L10-FePt/Co core-shell nanoparticles with variable Co thickness

Exchange-coupled core–shell nanoparticles are expected to be the new generation of permanent magnets, where the orientation of the hard magnetic phase is supposed to play a key role in improving their magnetic performance. In this work, L1₀-FePt/Co core–shell nanoparticles with Co thickness ranging from 0.6 to 2.2 nm have been synthesized by a seed-mediated growth method. The exchange coupling effect between the hard core and soft shell led to a 60% improvement of the maximum magnetic energy product ((BH)_max), compared with the pure L1₀-FePt core. By tuning the amount of precursor, nanoparticles with different Co shell thicknesses were synthesized. Furthermore, the L1₀-FePt/Co core–shell nanoparticles were dispersed in epoxy resin and oriented under an external magnetic field. The (BH)_max of the anisotropic nanocomposite magnet with a Co thickness of 1 nm is 7.1 MGOe, enhanced by 117% compared with the isotropic L1₀-FePt magnet, which paves the way for the development of high-performance permanent magnets for energy conversion applications.

With the increase of Co layer thickness, the outer layer Co and the core gradually decoupled.     

High-sensitivity refractive index of Au@Cu2−xS core–shell nanorods

A high refractive index sensitivity of Au@Cu_2−xS core–shell nanorods working in the near-infrared is theoretically demonstrated. The sensitivity of our sensor reaches 1200 nm per Refractive Index Unit (RIU), which is higher than that of other metal–metal core–shell nanorods. The reason is that the new materials and structure of Au@Cu_2−xS core–shell nanorods lead to a unique sensing principle. It is noteworthy that the refractive index (RI) sensitivity is more susceptible to the effects of the shell-thickness to core-radius ratio than to the aspect ratio. These results show that the excellent sensitivity performance of Au@Cu_2−xS core–shell nanorods working in the near-infrared can be treated as a new tool to detect the minute variations in refractive index for small amounts of chemicals and biomolecules.

A high refractive index sensitivity of Au@Cu_2−xS core–shell nanorods working in the near-infrared is theoretically demonstrated.     

Double-exponential refractive index sensitivity of metal–semiconductor core–shell nanoparticles: the effects of dual-plasmon resonances and red-shift

In order to improve the refractive index sensitivity of a localized surface plasmon resonance (LSPR) sensor, we present a new type of LSPR sensor whose refractive index sensitivity can be improved by greatly increasing the plasmon wavelength red-shift of metal–semiconductor core–shell nanoparticles (CSNs). Using extended Mie theory and Au@Cu_2−xS CSNs, we theoretically investigate the optical properties of metal–semiconductor CSNs in the entire near-infrared band. Compared with dielectric–metal and metal–metal CSNs under the same conditions, the metal–semiconductor CSNs have a higher double-exponential sensitivity curve because their core and shell respectively support two LSPRs that greatly increase the LSPR red-shift to the entire near-infrared range. It is worth noting that the sensitivity can be improved effectively by increasing the ratio of the shell-thickness to core-radius, instead of decreasing it in the case of the dielectric–metal CSNs. The underlying reason for the enhancement of sensitivity is the increase of repulsive force with the enlargement of shell thickness, which is different from the dielectric–metal CSNs. This design method not only paves the way for utilizing metal–semiconductor CSNs in biology and chemistry, but also proposes new ideas for the design of sensors with high sensitivity.

We present a new type of localized surface plasmon resonance (LSPR) sensor whose refractive index sensitivity can be improved by greatly increasing the plasmon wavelength red-shift of metal–semiconductor core–shell nanoparticles (CSNs).