Selective Flocculation and H2O2-Free Oxidative Etching-Based Synthesis of Highly Monodisperse Ag Nanospheres for Uniform Quantum Dot Photoluminescence-Enhancing Plasmonic Cavity Applications

Ag nanoparticles have garnered significant attention for their excellent plasmonic properties and potential use as plasmonic cavities, primarily because of their intrinsically low ohmic losses and optical properties in the visible range. These are particularly crucial in systems involving quantum dots that absorb light at low wavelengths, where the need for a high threshold energy of interband transitions necessitates the incorporation of Ag nanostructures. However, the synthesis of Ag nanoparticles still encounters challenges in achieving structural uniformity and monodispersity, along with chemical stability, consequentially inducing inconsistent and poorly reliable optical responses. Here, we present a two-step approach for synthesizing highly uniform spherical Ag nanoparticles involving depletion-induced flocculation and Cu(II)-mediated oxidative etching. We found that the selective flocculation of multitwinned Ag nanocrystals significantly enhances the uniformity of the resulting Ag nanostructures, leaving behind only single-crystalline and single-twinned nanostructures. Subsequent oxidative etching, in which cupric ions are directly involved in the reaction, was designed based on Pourbaix diagrams to proceed following thermodynamically favorable states and circumvent the generation of reactive chemical species such as H2O2. This leads to perfectly spherical shapes of final Ag nanoparticles with a synthetic yield of 99.5% and additionally reduces the overall reaction time. Furthermore, we explore the potential applications of these monodisperse Ag nanospheres as uniform plasmonic cavities. The fabricated Ag nanosphere films uniformly enhanced the photoluminescence of InP/ZnSe/ZnS quantum dots, showcasing their capabilities in exhibiting consistent plasmonic responses across a large area.

Morphologies and magnetic properties of α-Fe2O3 nanoparticles calcined at different temperatures

Different morphologies and sizes of α-Fe2O3 were prepared by a coprecipitation method using polyvinylpyrrolidone as a dispersant. In the preparation process, homogeneous and dispersed nanoscale FeOOH particles were first obtained by the coprecipitation method, and then the FeOOH particles were calcined at high temperature to form α-Fe2O3. The growth and aggregation of the α-Fe2O3 particles at different calcination temperatures resulted in α-Fe2O3 powders with diversiform morphologies (nanoscale microsphere, pinecone ellipsoidal, polyhedral, and quasi-spherical structures). By analyzing the SEM images, it was inferred that the polyhedral structure of α-Fe2O3 particles was formed by the accumulation of rhomboid sheet structures and high-temperature growth. In terms of the magnetic properties, the samples belonged to the class of canted antiferromagnetic materials, and the morphology, particle size, and crystallite size of the α-Fe2O3 particles were important factors affecting the coercivity. Among these, when the calcination temperature was increased from 700 °C to 800 °C, the growth rate of the particle size was significantly faster than that of the crystallite size, and the coercivity increased substantially from 1411 Oe to 2688 Oe.

Systematic Study on the Precursor Reduction Kinetics and Growth Pattern for Size-Tunable Palladium Nanocubes

Unveiling the underlying chemistry during the growth of well-defined nanocrystals is a fundamental but challenging task in materials chemistry. Herein, Pd NCs with tunable sizes ranging from 4.5 to 23.5 nm have been synthesized in the presence of potassium acetate (KOAc). The Pd precursor variation trends of these preparation systems along with reaction time have been determined using a UV-vis spectrometer, and corresponding reduction kinetic parameters, including the apparent reduction rate constant (k) and activation energy (Ea), are calculated by regarding the reduction processes as quasi-first-order reactions. It is confirmed that the introduction of KOAc does not affect the value of the Ea of different reaction systems. The interrelationship of k, product size (d), and reaction temperature (T) is discussed in depth. Results indicate that the three parameters are closely related, and for given reaction systems, they are specified. With the careful investigation of six specific systems (reaction systems with 10 mM, 20 mM KOAc at 55 °C, with 5 mM, 10 mM KOAc at 65 °C, without KOAc at 75 °C, and with 5 mM KOAc at 85 °C), the growth pattern of Pd NCs is described with an empirical expression and is further confirmed as a synergistic result of k and T.

Ultra-mild synthesis of nanometric metal chalcogenides using organyl chalcogenide precursors

Bis(trialkylsilyl) monochalcogenides and diorganyl dichalcogenides, (R₃Si)₂E and R₂E₂ (E = S, Se or Te and R = alkyl, aryl or allyl group), have emerged in the past decade as excellent reagents for the synthesis of metal chalcogenide nanoparticles (NPs) and clusters owing to their ability to transfer the chalcogenide anion (E^2-) under ultra-mild conditions and versatility in reacting even with non-conventional metal reagents or being employed in a variety of synthetic methods. In comparison, the related non-silylated diorganyl monochalcogenides R₂E have received attention only recently for the solution phase synthesis of metal chalcogenide NPs. In spite of sharing many similarities, these three families of organyl chalcogenides are different in their coordination ability and decomposition behavior, and therefore in reactivities towards metal reagents. This feature article provides a concise overview on the use of these three families as synthons for the ultralow-temperature synthesis of metal chalcogenide nanomaterials, deliberating their different decomposition mechanisms and critically assessing their advantages for certain applications. More specifically, it discusses their usefulness in (i) affording molecular precursors with different kinetic and thermal stabilities, (ii) isolating reactive intermediates for comprehending the mechanism of molecule-to-nanoparticle transformation and, therefore, achieving fine control over the synthesis, (iii) stabilizing isolable metastable or difficult-to-achieve phases, and (iv) yielding complex ternary nanoparticles with controlled stoichiometry or composites with sensitive materials without modifying the characteristics of the latter. Besides providing a perspective on the low-temperature synthesis of nanomaterials, this overview is expected to assist further progress, particularly in the field of R₂E, leading to interesting materials including metastable ones for new applications.

Controlling Cation Distribution and Morphology in Colloidal Zinc Ferrite Nanocrystals

This paper describes the first synthetic method to achieve independent control over both the cation distribution (quantified by the inversion parameter x) and size of colloidal ZnFe₂O₄ nanocrystals. Use of a heterobimetallic triangular complex of formula ZnFe₂(μ₃-O)(μ₂-O₂CCF₃)₆(H₂O)₃ as a single-source precursor, solvothermal reaction conditions, absence of hydroxyl groups from the reaction solvent, and the presence of oleylamine are required to achieve well-defined, crystalline, and monodisperse ZnFe₂O₄ nanoparticles. The size of the ZnFe₂O₄ nanocrystals increases as the ratio of oleic acid and oleylamine ligands to precursor increases. The inversion parameter increases with increasing solubility of the precursor in the reaction solvent, with the presence of oleic acid in the reaction mixture, and with decreasing reaction temperature. These results are consistent with a mechanism in which ligand exchange between oleic acid and carboxylate ligands bound to the precursor complex influences the degree to which the reaction produces a kinetically trapped or thermodynamically stable cation distribution. Importantly, these results indicate that preservation of the triangular Zn-O-Fe₂ core structure of the precursor in the reactive monomer species is crucial to the production of a phase-pure ZnFe₂O₄ product and to the ability to tune the cation distribution. Overall, these results demonstrate the advantages of using a single-source precursor and solvothermal reaction conditions to achieve synthetic control over the structure of ternary spinel ferrite nanocrystals.

A Brief Review of Carbon Dots-Silica Nanoparticles Synthesis and their Potential Use as Biosensing and Theragnostic Applications

Carbon dots (CDs) are carbon nanoparticles with sizes below 10 nm and have attracted attention due to their relatively low toxicity, great biocompatibility, water solubility, facile synthesis, and exceptional photoluminescence properties. Accordingly, CDs have been widely exploited in different sensing and biomedical applications, for example, metal sensing, catalysis, biosensing, bioimaging, drug and gene delivery, and theragnostic applications. Similarly, the well-known properties of silica, such as facile surface functionalization, good biocompatibility, high surface area, and tunable pore volume, have allowed the loading of diverse inorganic and organic moieties and nanoparticles, creating complex hybrid nanostructures that exploit distinct properties (optical, magnetic, metallic, mesoporous, etc.) for sensing, biosensing, bioimaging, diagnosis, and gene and drug delivery. In this context, CDs have been successfully grafted into diverse silica nanostructures through various synthesis methods (e.g., solgel chemistry, inverse microemulsion, surfactant templating, and molecular imprinting technology (MIT)), imparting hybrid nanostructures with multimodal properties for distinct objectives. This review discusses the recently employed synthesis methods for CDs and silica nanoparticles and their typical applications. Then, we focus on combined synthesis techniques of CD-silica nanostructures and their promising biosensing operations. Finally, we overview the most recent potential applications of these materials as innovative smart hybrid nanocarriers and theragnostic agents for the nanomedical field.

One-step fabrication of Au-Ag alloys and its application for catalysts and SERS sensors

Au-Ag alloy nanoparticles (NPs) with controllable size and composition were synthesized by a facile, one-pot hydrothermal method. Various characterization techniques including TEM, UV-vis, EDX, HAADF-STEM and XPS were used to discuss the influencing factors for the size and composition of Au-Ag alloy NPs. It is obvious that the size and composition of Au-Ag alloy NPs could be adjusted by the experimental parameters. Catalytic and SERS performance of the Au-Ag alloy NPs were further investigated. Ideal catalytic and SERS performance could be also obtained via optimizing the size and composition of Au-Ag alloy. This work is of importance in theory research and practical application of the noble metal nanocomposites.

Challenges and prospects in the selective photoreduction of CO2 to C1 and C2 products with nanostructured materials: a review

Solar fuel generation through CO₂ hydrogenation is the ultimate strategy to produce sustainable energy sources and alleviate global warming. The photocatalytic CO₂ conversion process resembles natural photosynthesis, which regulates the ecological systems of the earth. Currently, most of the work in this field has been focused on boosting efficiency rather than controlling the distribution of products. The structural architecture of the semiconductor photocatalyst, CO₂ photoreduction process, product analysis, and elucidating the CO₂ photoreduction mechanism are the key features of the photoreduction of CO₂ to generate C1 and C2 based hydrocarbon fuels. The selectivity of C1 and C2 products during the photocatalytic CO₂ reduction have been ameliorated by suitable photocatalyst design, co-catalyst, defect states, and the impacts of the surface polarisation state, etc. Monitoring product selectivity allows the establishment of an appropriate strategy to generate a more reduced state of a hydrocarbon, such as CH₄ or higher carbon (C2) products. This article concentrates on studies that demonstrate the production of C1 and C2 products during CO₂ photoreduction using H₂O or H₂ as an electron and proton source. Finally, it highlights unresolved difficulties in achieving high selectivity and photoconversion efficiency of CO₂ in C1 and C2 products over various nanostructured materials.

Rational design, synthesis, and applications of carbon-assisted dispersive Ni-based composites

Herein, we review recent developments in the rational design and engineering of various carbon-assisted dispersive nickel-based composites, and boosted properties for protein adsorption and nitroaromatics reduction.

Heat-Up Colloidal Synthesis of Shape-Controlled Cu-Se-S Nanostructures-Role of Precursor and Surfactant Reactivity and Performance in N2 Electroreduction

Copper selenide-sulfide nanostructures were synthesized using metal-organic chemical routes in the presence of Cu- and Se-precursors as well as S-containing compounds. Our goal was first to examine if the initial Cu/Se 1:1 molar proportion in the starting reagents would always lead to equiatomic composition in the final product, depending on other synthesis parameters which affect the reagents reactivity. Such reaction conditions were the types of precursors, surfactants and other reagents, as well as the synthesis temperature. The use of 'hot-injection' processes was avoided, focusing on 'non-injection' ones; that is, only heat-up protocols were employed, which have the advantage of simple operation and scalability. All reagents were mixed at room temperature followed by further heating to a selected high temperature. It was found that for samples with particles of bigger size and anisotropic shape the CuSe composition was favored, whereas particles with smaller size and spherical shape possessed a Cu2-xSe phase, especially when no sulfur was present. Apart from elemental Se, Al2Se3 was used as an efficient selenium source for the first time for the acquisition of copper selenide nanostructures. The use of dodecanethiol in the presence of trioctylphosphine and elemental Se promoted the incorporation of sulfur in the materials crystal lattice, leading to Cu-Se-S compositions. A variety of techniques were used to characterize the formed nanomaterials such as XRD, TEM, HRTEM, STEM-EDX, AFM and UV-Vis-NIR. Promising results, especially for thin anisotropic nanoplates for use as electrocatalysts in nitrogen reduction reaction (NRR), were obtained.

Colloidal synthesis of metal chalcogenide nanomaterials from metal-organic precursors and capping ligand effect on electrocatalytic performance: progress, challenges and future perspectives

Renewable and sustainable functional nanomaterials, which can be employed in alternative green energy sources, are highly desirable. Transition metal chalcogenides are potential catalysts for processes resulting in energy generation and storage. In order to optimize their catalytic performance, high phase purity and precise control over shape and size are indispensable. Metal-organic precursors with pre-formed bonds between the metal and the chalcogenide atoms are advantageous in synthesizing phase pure transition metal chalcogenides with controlled shape and sizes. This can be achieved by the decomposition of metal-organic precursors in the presence of suitable surfactants/capping agents. However, the recent studies on electrocatalysis at the nanoscale level reveal that the capping agents attached to their surface have a detrimental effect on their efficiency. The removal of surfactants from active sites to obtain bare surface nanoparticles is necessary to enhance catalytic activity. Herein, we have discussed the properties of different metal-organic precursors and the role of surfactants in the colloidal synthesis of metal chalcogenide nanomaterials. Moreover, the effect of surfactants on their electrocatalytic performance, the commonly used strategies for removing surfactants from the surface of nanomaterials and the future perspectives are reviewed.

Molecular Bottom-Up Approaches for the Synthesis of Inorganic and Hybrid Nanostructures

Chemical routes for the synthesis of nanostructures are fundamental in nanoscience. Among the different strategies for the production of nanostructures, this article reviews the fundamentals of the bottom-up approaches, focusing on wet chemistry synthesis. It offers a general view on the synthesis of different inorganic and hybrid organic–inorganic nanostructures such as ceramics, metal, and semiconductor nanoparticles, mesoporous structures, and metal–organic frameworks. This review article is especially written for a wide audience demanding a text focused on the basic concepts and ideas of the synthesis of inorganic and hybrid nanostructures. It is styled for both early researchers who are starting to work on this topic and also non-specialist readers with a basic background on chemistry. Updated references and texts that provide a deeper discussion and describing the different synthesis strategies in detail are given, as well as a section on the current perspectives and possible future evolution.

In Search of Excellence: Convex versus Concave Noble Metal Nanostructures for Electrocatalytic Applications

Controlling the shape of noble metal nanoparticles is a challenging but important task in electrocatalysis. Apart from hollow and nanocage structures, concave noble metal nanoparticles are considered a new class of unconventional electrocatalysts that exhibit superior electrocatalytic properties as compared with those of conventional nanoparticles (including convex and flat ones). Herein, several facile and highly reproducible routes for synthesizing nanostructured concave noble metal materials reported in the literature are discussed, together with their advantages over noble metal nanoparticles with convex shapes. In addition, possible ways of optimizing the synthesis procedure and enhancing the electrocatalytic characteristics of concave metal nanoparticles are suggested. Nanostructured noble metals with concave features are found to show better catalytic activity and stability hence improve their practical applicability in electrocatalysis.

Infiltrated thin film structure with hydrogel-mediated precursor ink for durable SOFCs

The hydrogel of biomolecule-assisted metal/organic complex has the superior ability to form a uniform, continuous, and densely integrated structure, which is necessary for fine thin film fabrication. As a representative of nature-originated polymers with abundant reactive side chains, we select the gelatin molecule as an element for weaving the metal cations. Here, we demonstrate the interaction between the metal cation and gelatin molecules, and associate it with coating quality. We investigate the rheological property of gelatin solutions interacting with metal cation from the view of cross-linking and denaturing of gelatin molecules. Also, we quantitatively compare the corresponding interactions by monitoring the absorbance spectrum of the cation. The coated porous structure is systematically investigated from the infiltration of gelatin-mediated Gd_0.2Ce_0.8O_2-δ (GDC) precursor into Sm_0.5Sr_0.5CoO_3-δ (SSC) porous scaffold. By applying the actively interacting gelatin-GDC system, we achieve a thin film of GDC on SSC with excellent uniformity. Compare to the discrete coating from the typical infiltration process, the optimized thin film coated structure shows enhanced performance and stability.

Catalytically active nanosized Pd9Te4 (telluropalladinite) and PdTe (kotulskite) alloys: first precursor-architecture controlled synthesis using palladium complexes of organotellurium compounds as single source precursors

Several intermetallic binary phases of Pd-Te including Pd3Te2, PdTe, PdTe2, Pd9Te4, Pd3Te, Pd2Te, Pd20Te7, Pd8Te3, Pd7Te2, Pd7Te3, Pd4Te and Pd17Te4 are known, and negligible work (except few studies on PdTe) has been done on exploring applications of such phases and their fabrication at nanoscale. Hence, Pd(ii) complexes Pd(L1)Cl2 and Pd(L2-H)Cl (L1): Ph-Te-CH2-CH2-NH2 and L2: HO-2-C6H4-CH[double bond, length as m-dash]N-CH2CH2-Te-Ph were synthesized. Under similar thermolytic conditions, complex Pd(L1)Cl2 with bidentate coordination mode of ligand provided nanostructures of Pd9Te4 (telluropalladinite) whereas Pd(L2-H)Cl with tridentate coordination mode of ligand yielded PdTe (kotulskite). Bimetallic alloy nanostructures possess high catalytic potential for Suzuki coupling of aryl chlorides, and reduction of 4-nitrophenol. They are also recyclable upto six reaction cycles in Suzuki coupling.

Electrophoretic Deposition of Aged and Charge Controlled Colloidal Copper Sulfide Nanoparticles

Colloidal nanoparticles (NPs) have been recently spotlighted as building blocks for various nanostructured devices. Their collective properties have been exhibited by arranging them on a substrate to form assembled NPs. In particular, electrophoretic deposition (EPD) is an emerging fabrication method for such nanostructured films. To maximize the benefits of this method, further studies are required to fully elucidate the key parameters that influence the NP deposition. Herein, two key parameters are examined, namely: (i) the aging of colloidal NPs and (ii) the charge formation by surface ligands. The aging of Cu_2-xS NPs changes the charge states, thus leading to different NP deposition behaviors. The SEM images of NP films, dynamic light scattering, and zeta potential results demonstrated that the charge control and restoration of interparticle interactions for aged NPs were achieved via simple ligand engineering. The charge control of colloidal NPs was found to be more dominant than the influence of aging, which can alter the surface charges of the NPs. The present results thus reveal that the charge formation on the colloidal NPs, which depends on the surface ligands, is an important controllable parameter in EPD.

Synthesis of highly luminescent Mn-doped CsPbCl3 nanoplatelets for light-emitting diodes

An atmospheric approach is reported to synthesize Mn-doped CsPbCl₃ nanoplatelets with high PLQYs, and their applications in soft polymers and LEDs.

Made-to-Order Heterostructured Nanoparticle Libraries

Nanoparticles that contain multiple materials connected through interfaces, often called heterostructured nanoparticles, are important constructs for many current and emerging applications. Such particles combine semiconductors, metals, insulators, catalysts, magnets, and other functional components that interact synergistically to enable applications in areas that include energy, nanomedicine, nanophotonics, photocatalysis, and active matter. To synthesize heterostructured nanoparticles, it is important to control all of the property-defining features of individual nanoparticles-size, shape, uniformity, crystal structure, composition, surface chemistry, and dispersibility-in addition to interfaces, asymmetry, and spatial organization, which facilitate communication among the constituent materials and enable their synergistic functions. While it is challenging to control all of these nanoscale features simultaneously, nanoparticle cation exchange reactions offer powerful capabilities that overcome many of the synthetic bottlenecks. In these reactions, which are often carried out on metal chalcogenide materials such as roxbyite copper sulfide (Cu_1.8S) that have high cation mobilities and a high density of vacancies, cations from solution replace cations in the nanoparticle. Replacing only a fraction of the cations can produce phase-segregated products having internal interfaces, i.e., heterostructured nanoparticles. By the use of multiple partial cation exchange reactions, multicomponent heterostructured nanoparticles can be synthesized.In this Account, we discuss the use of multiple sequential partial cation exchange reactions to rationally construct complex heterostructured nanoparticles toward the goal of made-to-order synthesis. Sequential partial exchange of the Cu⁺ cations in roxbyite Cu_1.8S spheres, rods, and plates produces a library of 47 derivatives that maintain the size, shape, and uniformity defined by the roxbyite templates while introducing various types of interfaces and different materials into the resulting heterostructured nanoparticles. When an excess of the metal salt reagent is used, the reaction time controls the extent of partial cation exchange. When a substoichiometric amount of metal salt reagent is used instead, the extent of partial cation exchange can be precisely controlled by the cation concentration. This approach allows significant control over the number, order, and location of partial cation exchange reactions. Up to seven sequential partial cation exchange reactions can be applied to roxbyite Cu_1.8S nanorods to produce derivative heterostructured nanorods containing as many as six different materials, eight internal interfaces, and 11 segments, i.e. ZnS-CuInS₂-CuGaS₂-CoS-[CdS-(ZnS-CuInS₂)]-Cu_1.8S. We considered all possible injection sequences of five cations (Zn²⁺, Cd²⁺, Co²⁺, In³⁺, Ga³⁺) applied to all accessible Cu_1.8S-derived nanorod precursors along with simple design criteria based on preferred cation exchange locations and crystal structure relationships. Using these guidelines, we mapped out synthetically feasible pathways to 65 520 distinct heterostructured nanorods, experimentally observed 113 members of this heterostructured nanorod megalibrary, and then made three of these in high yield and in isolatable quantities. By expansion of these capabilities into a broader scope of materials and identification of additional design guidelines, it should be possible to move beyond model systems and access functional targets rationally and retrosynthetically. Overall, the ability to access large libraries of complex heterostructured nanoparticles in a made-to-order manner is an important step toward bridging the gap between design and synthesis.

Laser-Based Synthesis of Au Nanoparticles for Optical Sensing of Glyphosate: A Preliminary Study

Nowadays, gold nanoparticles Au nanoparticles (AuNPs) capture great interest due to their chemical stability, optical properties and biocompatibility. The success of technologies based on the use of AuNPs implies the development of simple synthesis methods allowing, also, the fine control over their properties (shape, sizes, structure). Here, we present the AuNPs fabrication by nanosecond pulsed laser ablation in citrate-solution, that has the advantage of being a simple, economic and eco-sustainable method to fabricate colloidal solutions of NPs. We characterized the stability and the absorbance of the solutions by Ultraviolet-Visible (UV-Vis) spectroscopy and the morphology of the AuNPs by Transmission Electron Microscopy. In addition, we used the AuNPs solutions as colorimetric sensor to detect the amount of glyphosate in liquid. Indeed, glyphosate is one of the most widely used herbicides which intensive use represents a risk to human health. The glyphosate presence in the colloidal AuNPs solutions determines the aggregation of the AuNPs causing the change in the color of the solution. The variation of the optical properties of the colloidal solutions versus the concentration of glyphosate is studied.

The role of pre-nucleation clusters in the crystallization of gold nanoparticles

The syntheses of metal nanoparticles by reduction in apolar solvents in the presence of long chain surfactants have proven to be extremely effective in the control of the particle size and shape. Nevertheless, the elucidation of the nucleation/growth mechanism is not straightforward because of the multiple roles played by surfactants. The nucleation stage, in particular, is very difficult to describe precisely and requires in situ and time-resolved techniques. Here, relying on in situ small angle X-ray scattering (SAXS), X-ray absorption spectroscopy (XAS) and high-energy X-ray diffraction (HE-XRD), we propose that ultra-small gold particles prepared by reduction of gold chloride in a solution of oleylamine (OY) in hexane with triisopropylsilane do not follow a classical nucleation process but result from pre-nucleation clusters (PNCs). These PNCs contain Au(iii) and Au(i) precursors; they are almost stable in size during the induction stage, as shown by SAXS, prior to undergoing a very fast shrinkage during the nucleation stage. The gold speciation as a function of time deduced from the XAS spectra has been analyzed through multi-step reaction pathways comprising both highly reactive species, involved in the nucleation and growth stages, and poorly reactive species acting as a reservoir for the reactive species. The duration of the induction period is related to the reactivity of the gold precursors, which is tuned by the coordination of OY to the gold complexes, while the nucleation stage was found to depend on the size and reactivity of the PNCs. The role of the PNCs in determining the final particle size and structure is also discussed in relation to previous studies. The multiple roles of OY, as the solubilizing agent of the gold salt, the ligand of the gold complexes determining both the size of the PNCs and the reactivity of the gold precursors, and finally the capping agent of the final gold particles as oleylammonium chloride, have been clearly established. This work opens new perspectives to synthesize metal NPs via metal-organic PNCs and to define new synthesis routes for nanoparticles that may present structure and morphologies different from those obtained by the classical nucleation routes.

A Versatile Route to Assemble Semiconductor Nanoparticles into Functional Aerogels by Means of Trivalent Cations

3D nanoparticle assemblies offer a unique platform to enhance and extend the functionality and optical/electrical properties of individual nanoparticles. Especially, a self-supported, voluminous, and porous macroscopic material built up from interconnected semiconductor nanoparticles provides new possibilities in the field of sensing, optoelectronics, and photovoltaics. Herein, a method is demonstrated for assembling semiconductor nanoparticle systems containing building blocks possessing different composition, size, shape, and surface ligands. The method is based on the controlled destabilization of the particles triggered by trivalent cations (Y³⁺ , Yb³⁺ , and Al³⁺ ). The effect of the cations is investigated via X-ray photoelectron spectroscopy. The macroscopic, self-supported aerogels consist of the hyperbranched network of interconnected CdSe/CdS dot-in-rods, or CdSe/CdS as well as CdSe/CdTe core-crown nanoplatelets is used to demonstrate the versatility of the procedure. The non-oxidative assembly method takes place at room temperature without thermal activation in several hours and preserves the shape and the fluorescence of the building blocks. The assembled nanoparticle network provides longer exciton lifetimes with retained photoluminescence quantum yields, that make these nanostructured materials a perfect platform for novel multifunctional 3D networks in sensing. Various sets of photoelectrochemical measurements on the interconnected semiconductor nanorod structures also reveal the enhanced charge carrier separation.

Strongly emitting and long-lived silver indium sulfide quantum dots for bioimaging: Insight into co-ligand effect on enhanced photoluminescence

Nanoscale ternary chalcogenides have attracted increasing research interest due to their merits of tunable properties and diverse applications in energy and biomedical fields. In this article, silver indium sulfide quantum dots supported by glutathione and polyethyleneimine as dual-ligands have been synthesized through an environmentally friendly and reproducible aqueous method. An emission quantum yield up to 37.2% has been achieved by glutathione as co-ligand bearing electron-rich groups, much higher than that of polyethyleneimine coated quantum dots (4.97%). Both spectroscopic and structural characterizations demonstrate that the photoluminescence enhancement is attributed to change of surface properties by glutathione as co-ligand. Dynamic light scattering (DLS) results and thermogravimetric analysis (TGA) reveal that glutathione covers the QDs with a higher density on the nanocrystal surface than other co-ligands. Therefore, it can effectively passivate the surface trap centers, thus decreasing the non-radiative emission. Moreover, the resultant silver indium sulfide quantum dots present surprisingly long lifetime of 3.69 μs, excellent fluorescent stability and low cytotoxicity, which enables them to be ideal candidate for real-time bioimaging.

Preparation of cobalt crystals with various morphologies and the catalytic performance of platinum-on-cobalt crystal for the selective hydrogenation of nitrobenzene

The Pt/Co-No catalyst exhibited the best catalytic property (yield to aniline-95.8%) due to high Pt dispersion and nano-synergy effect between Pt- and Co-related species.

A size-controlled green synthesis of silver nanoparticles by using the berry extract of Sea Buckthorn and their biological activities

Herein, by using the Sea Buckthorn berry extract, we present a new eco-friendly approach for green synthesis of AgNPs, which reveal superior antioxidation and anticancer but poor antimicrobial activities.

Toward greener methods of producing branched metal nanostructures

This review highlights the use of biogenic resources (i.e., plant extracts, microorganisms, and biomolecules) as green reagents for the production of technologically promising branched metal nanomaterials.

Spontaneous Crystallization of Perovskite Nanocrystals in Nonpolar Organic Solvents: A Versatile Approach for their Shape-Controlled Synthesis

The growing demand for perovskite nanocrystals (NCs) for various applications has stimulated the development of facile synthetic methods. Perovskite NCs have often been synthesized by either ligand-assisted reprecipitation (LARP) at room temperature or by hot-injection at high temperatures and inert atmosphere. However, the use of polar solvents in LARP affects their stability. Herein, we report on the spontaneous crystallization of perovskite NCs in nonpolar organic media at ambient conditions by simple mixing of precursor-ligand complexes without application of any external stimuli. The shape of the NCs can be controlled from nanocubes to nanoplatelets by varying the ratio of monovalent (e.g. formamidinium+ (FA+ ) and Cs+ ) to divalent (Pb2+ ) cation-ligand complexes. The precursor-ligand complexes are stable for months, and thus perovskite NCs can be readily prepared prior to use. Moreover, we show that this versatile synthetic process is scalable and generally applicable for perovskite NCs of different compositions.

Janus to Core-Shell to Janus: Facile Cation Movement in Cu2-xS/Ag2S Hexagonal Nanoplates Induced by Surface Strain Control

Nanocrystals with multiple compositions and heterointerfaces have received great attention due to promising multifunctional and synergistic physicochemical properties. In particular, heterointerfaces have been at the focal point of nanocatalyst research because the strain caused by lattice mismatches between different phases is the dominant determinant of surface energy and catalytic activity. The ensemble effects of different material phases have also contributed to the interest in heterointerfaced multicomponent materials. Until now, heterointerfaces have largely been regarded as static, and the dynamic movement of components within the multicomponent material phases has received little attention, although the dynamic movement of individual components within multicomponent materials can revise the interpretation of the catalytic behaviors of these materials and lead to fascinating opportunities for nanostructure synthesis. In this study, we demonstrate unprecedented cation migrations within a sulfide matrix induced by surface strain modulation initiated by cation exchange. Specifically, Cu and Ag cations in the sulfide matrix were initially segregated to form a Janus structure. This Janus configuration was then transformed into a core-shell Cu_2-xS@Ag₂S structure via surface Pt doping. When the surface strain was relieved by a reduced Pt concentration at the nanoparticle surface, the core-shell transitioned back into a Janus structure. We expect that the facile composition fluctuations in multiphasic nanostructures will expand synthetic methodologies for the design and synthesis of intricate nanostructures with useful physicochemical properties.

Biocompatible synthesis of reduced graphene oxide from Euphorbia heterophylla (L.) and their in-vitro cytotoxicity against human cancer cell lines

•

A simple and facile biocompatible method for the reduction of graphene oxide (GO).

•

Reduction of graphene oxide (rGO) from leaves extract of Euphorbia heterophylla (L.).

•

The rGO shows significant cytotoxicity on A549- Human Lung Cancer cell line and HepG2-Human Hepatocarcinomatous Cell lines.

•

Green synthesis of rGO is very easy, in expensive, cheap, non-toxic, biocompatibility and ecofriendly.

Facile and biocompatible synthesis of reduced graphene oxide from graphene oxide as a precursor and aqueous leaves extract of Euphorbia heterophylla (L.), act as a reducing /capping /stabilizing agent by green chemistry approaches. The obtained product was analyzed by Ultraviolet-Visible spectroscopy (UV–vis), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy and Scanning electron Microscopy (SEM). In addition to this, the significant cytotoxicity of rGO studied against cancerous cell lines such as A549- Human Lung cancer cell line and HepG2-Human Hepatocarcinoma Cell lines in-vitro. These results indicate that the biocompatible synthesis of rGO is straightforward, inexpensive and environmentally friendly for promising large-scale production of industrial purpose and then finding further biomedical applications.

Ion exchange: an advanced synthetic method for complex nanoparticles

There have been tremendous efforts to develop new synthetic methods for creating novel nanoparticles (NPs) with enhanced and desired properties. Among the many synthetic approaches, NP synthesis through ion exchange is a versatile and powerful technique providing a new pathway to design complex structures as well as metastable NPs, which are not accessible by conventional syntheses. Herein, we introduce kinetic and thermodynamic factors controlling the ion exchange reactions in NPs to fully understand the fundamental mechanisms of the reactions. Additionally, many representative examples are summarized to find related advanced techniques and unique NPs constructed by ion exchange reactions. Cation exchange reactions mainly occur in chalcogenide compounds, while anion exchange reactions are mainly involved in halogen (e.g. perovskite) and metal-chalcogenide compounds. It is expected that NP syntheses through ion exchange reactions can be utilized to create new devices with the required properties by virtue of their versatility and ability to tune fine structures.

Noble Metal Composite Porous Silk Fibroin Aerogel Fibers

Nobel metal composite aerogel fibers made from flexible and porous biopolymers offer a wide range of applications, such as in catalysis and sensing, by functionalizing the nanostructure. However, producing these composite aerogels in a defined shape is challenging for many protein-based biopolymers, especially ones that are not fibrous proteins. Here, we present the synthesis of silk fibroin composite aerogel fibers up to 2 cm in length and a diameter of ~300 μm decorated with noble metal nanoparticles. Lyophilized silk fibroin dissolved in hexafluoro-2-propanol (HFIP) was cast in silicon tubes and physically crosslinked with ethanol to produce porous silk gels. Composite silk aerogel fibers with noble metals were created by equilibrating the gels in noble metal salt solutions reduced with sodium borohydride, followed by supercritical drying. These porous aerogel fibers provide a platform for incorporating noble metals into silk fibroin materials, while also providing a new method to produce porous silk fibers. Noble metal silk aerogel fibers can be used for biological sensing and energy storage applications.

Seed-assisted synthesis of fcc Ru–Cu bimetallic nanostructures and their catalytic properties for the hydrogen evolution reaction

Adjusting the chemical composition and/or crystal structures is an important approach to tune the activity of catalysts.

Enhanced catalytic and SERS performance of shape/size controlled anisotropic gold nanostructures

Au nanostars of different sizes and shapes prepared using a simple method and their applications.

Palygorskite Supported AuPd Alloy Nanoparticles as Efficient Nano-Catalysts for the Reduction of Nitroarenes and Dyes at Room Temperature

In this work, AuPd alloy palygorskite based Pal-NH₂@AuPd nano-catalysts were prepared and used as catalysts for the reduction of nitroarenes and dyes at room temperature. The surface of palygorskite (Pal) was first modified with 3-aminpropyltriethoxysilane, and then covered with AuPd alloy nanoparticles through co-reduction of HAuCl₄ and K₂PdCl₄. The morphology and structures of the Pal-NH₂@AuPd nano-catalysts were characterized by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The as-synthesized Pal-NH₂@AuPd nano-catalysts displayed excellent catalytic performance in reducing 4-nitrophenol (4-NP) and various other nitroaromatic compounds. Moreover, the catalytic activities of the Pal-NH₂@AuPd nano-catalysts were adjustable via changing the atomic ratio of AuPd alloy nanoparticles, leading to the Pal-NH₂@Au₄₈Pd₅₂ component as having the best atomic ratio. The Pal-NH₂@Au₄₈Pd₅₂ continued to display good catalytic stability after being reused for several cycles and there were no obvious changes, either of the morphology or the particle size distribution of the nano-catalysts. Furthermore, these Pal-NH₂@Au₄₈Pd₅₂ nano-catalysts also provided a convenient and accessible way for the degradation of dyes in artificial industrial wastewater.

Large-Scale Fabrication of Ultrasensitive and Uniform Surface-Enhanced Raman Scattering Substrates for the Trace Detection of Pesticides

Technology transfer from laboratory into practical application needs to meet the demands of economic viability and operational simplicity. This paper reports a simple and convenient strategy to fabricate large-scale and ultrasensitive surface-enhanced Raman scattering (SERS) substrates. In this strategy, no toxic chemicals or sophisticated instruments are required to fabricate the SERS substrates. On one hand, Ag nanoparticles (NPs) with relatively uniform size were synthesized using the modified Tollens method, which employs an ultra-low concentration of Ag⁺ and excessive amounts of glucose as a reducing agent. On the other hand, when a drop of the colloidal Ag NPs dries on a horizontal solid surface, the droplet becomes ropy, turns into a layered structure under gravity, and hardens. During evaporation, capillary flow was burdened by viscidity resistance from the ropy glucose solution. Thus, the coffee-ring effect is eliminated, leading to a uniform deposition of Ag NPs. With this method, flat Ag NPs-based SERS active films were formed in array-well plates defined by hole-shaped polydimethylsiloxane (PDMS) structures bonded on glass substrates, which were made for convenient detection. The strong SERS activity of these substrates allowed us to reach detection limits down to 10⁻¹⁴ M of Rhodamine 6 G and 10⁻¹⁰ M of thiram (pesticide).

Controlling the 3D Electromagnetic Coupling in Co-Sputtered Ag⁻SiO₂ Nanomace Arrays by Lateral Sizes

Ag–SiO₂ nanomace arrays were prepared on a two-dimensional ordered colloidal (2D) polystyrene sphere template by co-sputtering Ag and SiO₂ in a magnetron sputtering system. The lateral size of the nanomaces and the distance between the neighbor nanomaces were controlled by adjusting the etching time of the 2D template. The nanomaces were composed of SiO₂-isolated Ag nanoparticles, which produced surface-enhanced Raman scattering (SERS) enhancement, and 3D hot spots were created between the neighbor nanomaces. When the distance between the nanomaces was sufficiently large, triangle-shaped nanostructures on silicon substrate were observed, which also contributed to the enhancement of the SERS signals. The finite-difference time-domain (FDTD) method was used to calculate the electromagnetic field distributions in the Ag–SiO₂ nanomace arrays, which generated physical reasons for the change of the SERS signals.

Shape control of nickel crystals and catalytic hydrogenation performance of ruthenium-on-Ni crystals

Nickel crystals with various shapes were obtained via hydrothermal synthesis. The effect of temperature and surfactant on nickel morphology was studied.

Fabrication of Semiconductor ZnO Nanostructures for Versatile SERS Application

Since the initial discovery of surface-enhanced Raman scattering (SERS) in the 1970s, it has exhibited a huge potential application in many fields due to its outstanding advantages. Since the ultra-sensitive noble metallic nanostructures have increasingly exposed themselves as having some problems during application, semiconductors have been gradually exploited as one of the critical SERS substrate materials due to their distinctive advantages when compared with noble metals. ZnO is one of the most representative metallic oxide semiconductors with an abundant reserve, various and cost-effective fabrication techniques, as well as special physical and chemical properties. Thanks to the varied morphologies, size-dependent exciton, good chemical stability, a tunable band gap, carrier concentration, and stoichiometry, ZnO nanostructures have the potential to be exploited as SERS substrates. Moreover, other distinctive properties possessed by ZnO such as biocompatibility, photocatcalysis and self-cleaning, and gas- and chemo-sensitivity can be synergistically integrated and exerted with SERS activity to realize the multifunctional potential of ZnO substrates. In this review, we discuss the inevitable development trend of exploiting the potential semiconductor ZnO as a SERS substrate. After clarifying the root cause of the great disparity between the enhancement factor (EF) of noble metals and that of ZnO nanostructures, two specific methods are put forward to improve the SERS activity of ZnO, namely: elemental doping and combination of ZnO with noble metals. Then, we introduce a distinctive advantage of ZnO as SERS substrate and illustrate the necessity of reporting a meaningful average EF. We also summarize some fabrication methods for ZnO nanostructures with varied dimensions (0–3 dimensions). Finally, we present an overview of ZnO nanostructures for the versatile SERS application.

Luminophore Configuration and Concentration-Dependent Optoelectronic Characteristics of a Quantum Dot-Embedded DNA Hybrid Thin film

To be useful in optoelectronic devices and sensors, a platform comprising stable fluorescence materials is essential. Here we constructed quantum dots (QDs) embedded DNA thin films which aims for stable fluorescence through the stabilization of QDs in the high aspect ratio salmon DNA (SDNA) matrix. Also for maximum luminescence, different concentration and configurations of core- and core/alloy/shell-type QDs were embedded within SDNA. The QD-SDNA thin films were constructed by drop-casting and investigated their optoelectronic properties. The infrared, UV-visible and photoluminescence (PL) spectroscopies confirm the embedment of QDs in the SDNA matrix. Absolute PL quantum yield of the QD-SDNA thin film shows the ~70% boost due to SDNA matrix compared to QDs alone in aqueous phase. The linear increase of PL photon counts from few to order of 5 while increasing [QD] reveals the non-aggregation of QDs within SDNA matrix. These systematic studies on the QD structure, absorbance, and concentration- and thickness-dependent optoelectronic characteristics demonstrate the novel properties of the QD-SDNA thin film. Consequently, the SDNA thin films were suggested to utilize for the generalised optical environments, which has the potential as a matrix for light conversion and harvesting nano-bio material as well as for super resolution bioimaging- and biophotonics-based sensors.