Chapter 2. Synthesis of Core–Shell Polymer-based Colloids

Colloidal nanoparticles (NPs) exhibit unique and tunable physical properties, making them highly attractive for advanced applications in sensing, photonics, flexible electronics, and beyond. Harnessing these properties in functional devices often requires assembling NPs into three-dimensional (3D) microstructures that combine substantial thickness to enhance their functional response, micrometer-scale resolution for precise pattern definition, and high selectivity to minimize material loss. Directed assembly techniques aim to meet these stringent requirements but face significant challenges when NPs are dispersed in non-polar solvents, commonly used for their role in synthesis and colloidal stabilization. Indeed, such solvents hinder NP assembly because of their high wettability and volatility. These limitations are particularly pronounced in Convective Self-Assembly (CSA), which performs efficiently with aqueous dispersions but struggles with non-polar media. In this study, we investigate how the properties of non-polar solvents influence CSA on topographically patterned substrates. To overcome these issues, we propose an upgraded CSA method that combines solvent selection, surface functionalization, and controlled evaporation. This approach enables reproducible and precise assembly of NPs into micrometer-scale 3D structures. The method is versatile, compatible with various nanoparticle types and patterns, and allows sequential co-assembly on a single substrate, offering a scalable route for high-resolution nanomanufacturing of complex multifunctional architectures.

Activity enhancement and selectivity tuneability in aqueous phase hydrodechlorination by use of controlled growth Pd-Rh nanoparticles

Photocatalytic water splitting is an ideal way of generating hydrogen, a renewable energy source, from solar energy that would help solve environmental problems. However, current photocatalysts are far from meeting performance requirements for commercial applications. Recently, increasing attention has been paid to surface plasmon resonance (SPR) enhanced photocatalysis using plasmonic nanoparticles (NPs) because of their superior solar energy harvesting capabilities in the visible and near-infrared spectral region. Herein, based on the common CdS photocatalyst, a series of core–shell plasmonic photocatalysts with different core types and shell layer thicknesses were constructed. By combining experimental results and finite element method (FEM), the near-field enhancement mechanism and plasmon-induced resonance energy transfer mechanism was derived. To further improve the energy conversion efficiency, a core–shell–satellite-type plasmonic nanocomposite photocatalyst, Ag@SiO2@CdS-Au, was designed and constructed. Because of hot electron injection and plasmonic coupling effects, the light absorption of the photocatalyst was effectively expanded, which significantly improved the catalytic performance. Compared with traditional CdS, the photocatalytic performance of the plasmonic nanocomposite photocatalyst was improved by more than 200 times. This work deepens the understanding of the mechanisms in SPR enhanced photocatalysis and provides an effective strategy for designing plasmonic photocatalysts.

Fate and transport of nanoplastics in complex natural aquifer media: Effect of particle size and surface functionalization

Characterization of semiconductor core–shell nanoparticles by resonant Raman scattering and photoluminescence spectroscopy

Core-shell nanoparticles (NPs), which consist in a ferrimagnetic (FIM)/antiferromagnetic (AFM) interface and result in exchange bias coupling, became recently of primary importance in the field of magnetic nanoparticles. The enhancement of some applications such as hyperthermia or magnetic storage media based on the miniaturization of devices is correlated to the size reduction of NPs, which results in the decrease of the magnetocrystalline anisotropy and of the blocking temperature. We present here the synthesis of Fe3-delta O4@CoO core-shell NPs by a one-pot seed-mediated growth process based on the thermal decomposition of metal complexes at high temperature. A 2 nm thick CoO shell was grown homogeneously from the starting Fe3-delta O4 core surface. The Fe3-delta O4@CoO core-shell NP structure has been deeply investigated by performing XRD and advanced techniques based on TEM such as EELS and EFTEM. The high quality of the core-shell interface resulted in the large exchange bias coupling at 5 K (H-E approximate to 4.1 kOe) between the FIM and the AFM components. In comparison to starting Fe3-delta O4 NPs, the dramatic enhancement of the magnetic properties such as a high coercive field (at 5 K, H-C approximate to 15 kOe) were measured. Furthermore, the core-shell structure resulted in the enhancement of the magnetocrystalline anisotropy and the increase of the blocking temperature to 293 K.

Nitrogen heterocyclic carbenes (NHCs) are emerging as effective substitutes for conventional thiol ligands in surface functionalization of nanoparticles (NPs), offering exceptional stability to NPs under harsh conditions. However, the highly reactive feature of NHCs limits their use in introducing chemically active groups onto the NP surface. Herein, we develop a general yet robust strategy for the efficient surface functionalization of NPs with copolymer ligands bearing various functional groups. The polymer ligands consist of a multiple NHCs block, utilized for surface binding on NPs, alongside a poly(reactive ester) block intended for incorporating functional groups. The multiple NHCs block enables NPs with excellent colloidal stability across a broader range of pH values (0-14), temperature variations (-78 °C-100 °C), and electrolyte concentrations (0-1000 mM). Through the in situ ammonolysis of the poly(reactive ester) block, various active functional groups can be individually or together introduced on the NP surface. We further demonstrate the chemical reactivity of these functionalized NPs, including addition polymerization, Diels-Alder and Schiff base reactions. This method is applicable to various types of NPs, including metal NPs, metal oxide NPs, and even upconversion NPs, thereby paving new pathways for the design and creation of nanoparticle-based functional materials.

Cancer is a deadly illness with a convoluted pathogenesis. The most prevalent restrictions that frequently result in treatment failure for cancer chemotherapy include lack of selectivity, cytotoxicity, and multidrug resistance. Thus, considerable efforts have been focused in recent years on the establishment of a modernistic sector termed nano-oncology, which offers the option of employing nanoparticles (NPs) with the objective of detecting, targeting, and treating malignant disorders. NPs offer a focused approach compared to conventional anticancer methods, preventing negative side effects. In the present work, a successful synthetic process was used to create magnetic cobalt cores with an AgNPs shell to form bimetallic nanocomposites CoAg, then functionalized with Cis forming novel CoAg@Cis nanohybrid. The morphology and optical properties were determined by TEM, DLS, FTIRs and UV-vis spectroscopy, furthermore, anticancer effect of CoAg and CoAg@Cis nanohybrids were estimated using MTT assay on MCF7 and HCT cell lines. Our results showed that Co@Ag core shell is about 15nm were formed with dark CoNPs core and AgNPs shell with less darkness than the core, moreover, CoAg@Cis has diameter about 25nm which are bigger in size than Co@Ag core shell demonstrating the loading of Cis. It was observed that Cis, CoAg and CoAg@Cis induced a decline in cell survival and peaked at around 65%, 73%and 66% on MCF7 and 80%, 76%and 78% on HCT at 100 µg/ml respectively. Compared to Cis alone, CoAg and CoAg@Cis caused a significant decrease in cell viability. These findings suggest that the synthesized CoAg can be used as a powerful anticancer drug carrier.

The study of metal nanoparticles (NPs) is of great interest due to their ability to enhance optical fields on the nanometric scale, which makes them interesting for various applications in several fields of science and technology. In particular, their optical properties depend on the dielectric function of the metal, its size, shape and surrounding environment.This work analyses the contributions of free and bound electrons to the complex dielectric function of spherical silver NPs and their influence on the optical extinction spectra. The contribution of free electrons is usually corrected for particle size under 10 nm, introducing a modification of the damping constant to account for the extra collisions with the particle's boundary.For the contribution of bound electrons, we considered the interband transitions from the d-band to the conduction band including the size dependence of the electronic density states for radii below 2 nm. Bearing in mind these specific modifications, it was possible to determine optical and band energy parameters by fitting the bulk complex dielectric function. The results obtained from the optimum fit are: Kbulk = 2 × 1024 (coefficient for bound-electron contribution), Eg = 1.91 eV (gap energy), EF = 4.12 eV (Fermi energy), and γb = 1.5 × 1014 Hz (damping constant for bound electrons).Based on this size-dependent dielectric function, extinction spectra of silver particles in the nanometric–subnanometric radius range can be calculated using Mie's theory, and its size behaviour analysed. These studies are applied to fit experimental extinction spectrum of very small spherical particles fabricated by fs laser ablation of a solid target in water. From the fitting, the structure and size distribution of core radius and shell thickness of the colloidal suspension could be determined. The spectroscopic results suggest that the colloidal suspension is composed by two types of structures: bare core and core–shell. The former is composed by Ag, while the latter is composed by two species: silver–silver oxide (Ag–Ag2O) and hollow silver (air–Ag) particles. High-resolution transmission microscopy and atomic force microscopy analysis performed on the dried suspension agree with the sizing obtained by optical extinction spectroscopy, showing that the latter is a very good complementary technique to standard microscopy methods.

We present a memory property study of floating gate structure embedded with Au–SiO2 core–shell nanoparticles (NPs). Herein, the Au–SiO2 core–shell configuration was readily fabricated by a self-assembly (SAM) layer-by-layer process using 3-aminopropyltrimethoxysilane (APTMS) as a versatile mediator. This functional APTMS served as both a binder for adsorbing colloidal Au NPs onto the substrate and to self-organize a SiO2 ultra-thin shell to cover the Au NP cores. A two-run APTMS SAM process was employed to develop the core–shell configuration. The first-run APTMS formed a well-organized monolayer on the substrate which was responsible for the obtained uniform SAM with high density of Au NPs. Next, the second-run APTMS formed an APTMS bilayer around the Au NPs. During the SAM process, a polymerization process simultaneously occurred with the reaction of neighboring silanol groups to form an Si–O–Si network structure. The polymerization was completed by a 400 °C-annealing to form a SiO2 layer within the APTMS bilayer. In addition, the annealing also resulted in the decomposition of the APTMS and released the preformed SiO2 layer from the APTMS bilayer. The ultra-thin SiO2 layer was flexible enough to cover the Au NP cores, eventually constructing the Au–SiO2 core–shell structure. Compared to Au nanocrystal (NC) memory, Au–SiO2 core–shell NCs show a larger memory window and significantly improved retention performance, which are attributed to the SiO2 shell-induced superior NP/oxide interface qualities and the characteristics of the Au NPs.

Nanostructures as color-tunable luminescent markers have become major, promising tools for bioimaging and biosensing. In this paper separated molybdate/Gd2O3 doped rare earth ions (erbium, Er3+ and ytterbium, Yb3+) core–shell nanoparticles (NPs), were fabricated by a one-step homogeneous precipitation process. Emission properties were studied by cathodo- and photoluminescence. Scanning electron and transmission electron microscopes were used to visualize and determine the size and shape of the NPs. Spherical NPs were obtained. Their core–shell structures were confirmed by x-ray diffraction and energy-dispersive x-ray spectroscopy measurements. We postulated that the molybdate rich core is formed due to high segregation coefficient of the Mo ion during the precipitation. The calcination process resulted in crystallization of δ/ξ (core/shell) NP doped Er and Yb ions, where δ—gadolinium molybdates and ξ—molybdates or gadolinium oxide. We confirmed two different upconversion mechanisms. In the presence of molybdenum ions, in the core of the NPs, Yb3+– (∣2F7/2, 3T2〉) dimers were formed. As a result of a two 980 nm photon absorption by the dimer, we observed enhanced green luminescence in the upconversion process. However, for the shell formed by the Gd2O3:Er, Yb NPs (without the Mo ions), the typical energy transfer upconversion takes place, which results in red luminescence. We demonstrated that the NPs were transported into cytosol of the HeLa and astrocytes cells by endocytosis. The core–shell NPs are sensitive sensors for the environment prevailing inside (shorter luminescence decay) and outside (longer luminescence decay) of the tested cells. The toxicity of the NPs was examined using MTT assay.

Green synthesis of silver-protein (core–shell) nanoparticles using Piper betle L. leaf extract and its ecotoxicological studies on Daphnia magna

Hydrolytic dehydrogenation of ammonia borane and methylamine borane catalyzed by graphene supported Ru@Ni core–shell nanoparticles

Designing low-cost, highly efficient, and stable electrocatalysts for oxygen evolution reactions is of great significance for water splitting, which is a green and sustainable method of producing hydrogen. Herein, a series of transition metal sulphide-based nanostructures, including Au–CoNi2S4 core–shell, Au–NiS core–shell, Au–Co3S4 core–shell, and bare CoNi2S4 nanoparticles (NPs), have been rationally designed. Among them, the Au–CoNi2S4 core–shell NPs exhibit superior electrocatalytic properties for oxygen evolution. It requires an overpotential of only 264 mV to reach a current density of 10 mA cm−2, while the Tafel slope (35.6 mV dec−1) is also the lowest among the as-prepared nanostructures. X-ray photoelectron spectra and electrochemical impedance spectra demonstrate that the electronic structure and chemical state of Au–CoNi2S4 core–shell heterostructure are regulated by the delicate structural design. The enhanced electrocatalytic performance of the Au–CoNi2S4 core–shell heterostructure can be attributed to the combined effects of constructing bimetallic sulphide instead of its monometallic counterparts and forming metal–sulphide core–shell interface. It provides a way to develop a superior electrocatalyst by constructing a metal–bimetallic sulphide core–shell heterostructure.

Cu is the cheapest plasmonic metal showing plasmonic resonance in the visible region, which makes it highly attractive in various fields (e.g., sensing, surface-enhanced Raman scattering, and photocatalysis). However, its poor chemical stability severely restricts its application. Herein, we develop a seed-mediated approach to synthesize ultrastable Cu-based nanoparticles (NPs) stabilized with a thin, completely covered shell. By precisely controlling the reaction conditions, we are able to achieve uniform plasmonic Cu–Au core–shell NPs with significantly enhanced chemical stability even in a harsh environment in the presence of a strong oxidizing acid (HNO3) solution. In-depth characterizations and analysis allow us to identify the critical role of the external crystalline Au layer, as compared to the AuCu alloy layer, in achieving superior stability. Furthermore, a deeper understanding of the plasmonic spectra was obtained by correlating the theoretical calculations on NPs of different core–shell dimensions with experimental results. Transient absorption measurements reveal that the plasmon dynamics and the heat transfer coefficients are not affected with the shell formation. As a proof of concept, these NPs demonstrate high photothermal efficiency and chemical stability for solar steam generation. This work offers a general strategy for the synthesis of ultrastable cost-effective, plasmonic Cu-based NPs, which show great potential in catalysis, electronics, and optics.