Photon upconversion in core-shell nanoparticles.

Review: tutorial review; 53 refs.

Core-shell nanoparticles have unusual physical, chemical and biological properties. Until now, for the Ag and TiO2 combination, only Ag core and TiO2 shell nanoparticles have been practically demonstrated. In this investigation, novel TiO2@Ag core-shell (TiO2 core and Ag shell) nanoparticles were produced via ultrasonic vibration of Ag-TiO2 compound nanoparticles. A bulk Ti/Ag alloy plate was used to generate colloidal Ag-TiO2 compound nanoparticles via picosecond laser ablation in deionised water. The colloidal nanoparticles were then sonicated in an ultrasonic bath to generate TiO2@Ag core-shell nanoparticles. They were characterised using a UV-VIS spectrometer, transmission electron microscopy (TEM), high-angle annular dark-field-Scanning transmission electron microscopy (HAADF-STEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The Ag-TiO2 compound and the TiO2@Ag core-shell nanoparticles were examined for their antibacterial activity against Escherichia coli (E. coli) JM109 strain bacteria and compared with those of Ag and TiO2 nanoparticles. The antibacterial activity of the core-shell nanoparticles was slightly better than that of the compound nanoparticles at the same concentration under standard laboratory light conditions and both were better than the TiO2 nanoparticles but not as good as the Ag nanoparticles.

Electrochemical reduction of CO2 (CO2RR) to produce valuable chemicals is promising in simultaneously controlling the CO2 concentration and storing renewable energy. However, its wide adoption still needs highly selective and reactive catalysts. In this study, Au-Pd core-shell (CS) nanoparticles consisting of a Au-rich core and Pd-rich shell were synthesized by wet methods. The nanoparticle composition and shell thickness were adjusted to evaluate their impacts on CO2-to-CO electrocatalytic conversion performance. The CS nanoparticles have a uniform morphology with an average size between 7 to 9 nm. As compared to pure Pd and Au nanoparticles with a similar size, all the synthesized CS nanoparticles exhibited a significantly increased CO selectivity (Figure 1). The CS nanoparticles also have superior mass and specific activities, which are highly dependent on the composition and structure. The best catalyst showed an ultrahigh mass activity of 99.8 mA mg-1 at -0.5 V along with a superior CO faradaic efficiency of 94.7%. In situ infrared spectroscopic studies with an attenuated total reflection configuration (ATR) and density functional theory calculations (DFT) were conducted to reveal the combined structure and composition impacts on the activity. It was found that the scaling relation between *COOH and *CO binding strength was broken on the core-shell nanoparticles and led to the high selectivity and activity toward CO production. The authors acknowledge the support from Hong Kong Research Grant Council (26206115 and 16309418). Figure 1. Faradaic efficiency of CO measured on synthesized Au-Pd core-shell, Pd and Au nanoparticles. Figure 1

Photon upconversion towards applications in energy conversion and bioimaging

Photocatalytic Degradation of Effluent water by CuO@Ag Core–shell Nanoparticles as Effective Catalyst under Irradiation of UV-light

In this article, the relationship between the states of Ag core-Au shell (core-shell) nanoparticles (NP) and the intensity of Raman scattering of analytes dissolved in the water and adsorbed on the NP was studied. The core-shell NP were synthesised by coating Au layers over Ag seeds by the method of "seed-growth". To highlight the advantage of the core-shell NP, Ag colloid and Au colloid were chosen for contrasting. The analyte that were chosen for this testing were methylene blue (MB) for the reason that MB has very strong signal in surface-enhanced Raman scattering (SERS). The SERS activity of optimalizing states of Ag and Au colloids were compared with that of core-shell NP when MB was used as analyte. In this study, sodium chloride, sodium sulfate and sodium nitrate were used as aggregating agents for Ag, Au colloids and core-shell NP, because anions have a strong influence on the SERS efficiency and the stability of colloids. The results indicate that core-shell NP can obviously enhance the SERS of MB. The aim of this study is to prove that compared with the metal colloid, the core-shell NP is a high efficiency SERS active substrate.

Photon upconversion, the process of converting lower-energy light to higher-energy, has attracted a lot of attention in biological applications, like phototherapy and bio-imaging. Among different photon upconversion mechanisms, triplet−triplet annihilation (TTA) based photon upconversion enables this process at low incident excitation power. Recently, I reported a 7% upconversion quantum yield with nontoxic and earth-abundant silicon nanocrystals as photosensitizer. However, ambient oxygen is an obstacle in further applications of photon upconversion as the triplet excitons involved in TTA can be quenched by oxygen in the air. Here, we discuss an air-stable photon upconversion system with silicon nanocrystals as sensitizer to upconvert red/green light to violet light. This hydrophobic silicon-based system has been incorporated into the aqueous phase with size-tunable micelles to enable applications in the water. An 11% photon upconversion quantum yield in micelles is achieved.

Given their versatile nature and wide range of possible applications, core–shell nanoparticles (NPs) have received considerable attention. This paper proposes a novel method for synthesizing ZnO@NiO core–shell nanoparticles using a hybrid technique. The characterization demonstrates the successful formation of ZnO@NiO core–shell nanoparticles, which have an average crystal size of 13.059 nm. The results indicate that the prepared NPs have excellent antibacterial activity against both Gram-negative and Gram-positive bacteria. This behavior is primarily caused by the accumulation of ZnO@NiO NPs on the bacteria's surface, which results in cytotoxic bacteria and a relatively increased ZnO, resulting in cell death. Moreover, the use of a ZnO@NiO core–shell material will prevent the bacteria from nourishing themselves in the culture medium, among many other reasons. Finally, the PLAL is an easily scalable, cost-effective, and environmentally friendly method for the synthesis of NPs, and the prepared core–shell NPs could be used in other biological applications such as drug delivery, cancer treatment, and further biomedical functionalization.

In this article, it is shown that the efficiency of an electrochemical aptasensing device is influenced by the use of different nanoparticles (NPs) such as gold nanoparticles (Au), silver nanoparticles (Ag), hollow gold nanospheres (HGN), hollow silver nanospheres (HSN), silver–gold core shell (Ag@Au), gold–silver core shell (Au@Ag), and silver–gold alloy nanoparticles (Ag/Au). Among these nanomaterials, Ag@Au core shell NPs are advantageous for aptasensing applications because the core improves the physical properties and the shell provides chemical stability and biocompatibility for the immobilization of aptamers. Self-assembly of the NPs on a cysteamine film at the surface of a carbon paste electrode is followed by the immobilization of thiolated aptamers at these nanoframes. The nanostructured (Ag@Au) aptadevice for Escherichia coli as a target shows four times better performance in comparison to the response obtained at an aptamer modified planar gold electrode. A comparison with other (core shell) NPs is performed by cyclic voltammetry and differential pulse voltammetry. Also, the selectivity of the aptasensor is investigated using other kinds of bacteria. The synthesized NPs and the morphology of the modified electrode are characterized by UV-Vis absorption spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis, and electrochemical impedance spectroscopy.

In this study we investigate the structure-mechanical property relationships for nanostructured ionomer films containing ionically crosslinked core-shell polymer nanoparticles based on poly(n-butyl acrylate) (PBA). Whilst nanostructured ionomer films of core-shell nanoparticles have been previously shown to have good ductility [Soft Matter, 2014, 10, 4725], the modulus values were modest. Here, we used BA as the primary monomer to construct core-shell nanoparticles that provided films containing nanostructured polymers with much higher glass transition temperature (Tg) values. The core-shell nanoparticles were synthesised using BA, acrylonitrile (AN), methacrylic acid (MAA) and 1,4-butanediol diacrylate (BDDA). Nanostructured ionomer films were prepared by casting aqueous core-shell nanoparticle dispersions in which the shell -COOH groups were neutralised with KOH and ZnO. The film mechanical properties were studied using dynamic mechanical analysis and tensile stress-strain measurements. The use of BA-based nanoparticles increased the Tg values to close to room temperature which caused a strong dependence of the film mechanical properties on the AN content and extent of neutralisation of the -COOH groups. The Young's modulus values for the films ranged from 1.0 to 86.0 MPa. The latter is the highest modulus reported for cast films of nanostructured ionomer films prepared from core-shell nanoparticles. The films had good ductility with strain-at-break values of at least 200%. The mechanical properties of the films were successfully modelled using the isostrain model. From comparison with an earlier butadiene-based system this study demonstrates that the nature of the primary monomer used to construct the nanoparticles can profoundly change the film mechanical properties. The aqueous nanoparticle dispersion approach used here provides a simple and versatile method to prepare high modulus elastomer films with tuneable mechanical properties.

Photon upconversion, which converts low-energy photons into high-energy photons, provides a strategy for overcoming the limitations imposed by excitation wavelengths in energy and biology applications. Recent advancement in triplet-triplet annihilation-based photon upconversion (TTA-UC) witnesses the importance of the bulkiness of the substituents in chromophores to avoid quenching of the singlet and triplet. One of the simplest bulky substituents, the tert-butyl (tBu) group, has been introduced into acene derivatives and shown both positive and negative effects on UC performance, underscoring the importance of further structure-property investigations. Here, we systematically synthesized anthracene derivatives of 9,10-bis(phenylethynyl)anthracene (BPEA) and 9,10-bis[(triisopropylsilyl)ethynyl]anthracene (TIPS-Ac), each bearing bulky tBu substituents. The relationship between the excluded volume imparted by these substituents and UC performance in both solution and the solid state was investigated. A moderate intermolecular distance effectively suppressed singlet and triplet quenching, yielding high UC quantum yields of approximately 15% in the solution state with both chromophores. A significant extension of the triplet lifetime was also observed in a donor-acceptor bilayer solid film, demonstrating the simple yet positive effects of tBu on the anthracene backbone, thereby boosting the UC performances in versatile material forms.

Photon upconversion based on triplet–triplet annihilation using thermally activated delayed fluorescence sensitizers

Enhancement of red upconversion emission intensity of Ho3+ ions in NaLuF4:Yb3+/Ho3+/Ce3+@NaLuF4 core–shell nanoparticles

Review: 234 refs.

Core–shell nanoparticles are nanosized particles that consist of a core and a shell, constructed from different metallic elements. Core–shell nanoparticles have received extensive attention, owing to their various potential applications such as paints, optical films and catalysts. Herein, we investigate the melting behaviours of different core–shell nanoparticles under continuous heating using molecular dynamics simulation. Different metallic elements were examined as core–shell and pure nanoparticles. Five different processes were observed during the melting of core–shell nanoparticles. In contrast, only one process was identified during the melting of pure nanoparticles. These processes were influenced by the nanoparticle size, shell thickness and differences between the lattice constants and melting point temperatures of the metallic elements. Our simulation provides microscopic insights into the melting behaviours of existing and proposed core–shell nanoparticles that would be highly beneficial towards the fabrication of materials with different chemical coatings.