Controlled synthesis of linear and branched Au@ZnO hybrid nanocrystals and their photocatalytic properties

Hydrous ruthenium oxide triggers template-free and spontaneous growth of metal nanostructures

Intrinsically conductive ruthenium oxide is an excellent material for energy storage and conversion. Herein, we present hydrous RuO2 (H-RuO2) as a potent reducing agent to achieve spontaneous growth of multiple noble metals at room temperature. Self-assembled gold and platinum, comprising small-sized nanoparticles, are generated on the surface of H-RuO2 without the need for additional templates. Structural analysis reveals that the disordered structure and the presence of oxygen vacancies trigger interfacial redox reactions between H-RuO2 and oxidative metal salts. The resulting integrated nanostructures, consisting of a metal oxide and different metals (H-RuO2@metal), are subsequently used to treat inflammatory bowel diseases. In addition to biomedical applications, our developed synthetic strategy, using reactive oxides to spontaneously generate multicomponent nanostructures, also holds great significance for other catalysis-based applications.

Colloidal Approaches to Zinc Oxide Nanocrystals

Zinc oxide is an extensively studied semiconductor with a wide band gap in the near-UV. Its many interesting properties have found use in optics, electronics, catalysis, sensing, as well as biomedicine and microbiology. In the nanoscale regime the functional properties of ZnO can be precisely tuned by manipulating its size, shape, chemical composition (doping), and surface states. In this review, we focus on the colloidal synthesis of ZnO nanocrystals (NCs) and provide a critical analysis of the synthetic methods currently available for preparing ZnO colloids. First, we outline key thermodynamic considerations for the nucleation and growth of colloidal nanoparticles, including an analysis of different reaction methodologies and of the role of dopant ions on nanoparticle formation. We then comprehensively review and discuss the literature on ZnO NC systems, including reactions in polar solvents that traditionally occur at low temperatures upon addition of a base, and high temperature reactions in organic, nonpolar solvents. A specific section is dedicated to doped NCs, highlighting both synthetic aspects and structure-property relationships. The versatility of these methods to achieve morphological and compositional control in ZnO is explicated. We then showcase some of the key applications of ZnO NCs, both as suspended colloids and as deposited coatings on supporting substrates. Finally, a critical analysis of the current state of the art for ZnO colloidal NCs is presented along with existing challenges and future directions for the field.

Theoretical and experimental study of the photodegradation of methyl orange in the presence of different morphologies of Au-ZnO using Monte Carlo dynamic simulation

Herein, a simple approach was formed based on synthesizing different morphologies of ZnO and Au-ZnO as photocatalyst. In this study, ZnO and Au-ZnO were synthesized via a co-precipitation method and fully characterized via scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDX). Three different ratios of Zn2+:OH- (1:2, 1:3, and 1:5) controlled the morphology of samples, which were made into spindle, star, and flower structures, respectively. Then, the photocatalytic activity was studied and compared. Their comparison showed that the flower morphology for ZnO and Au-ZnO was more effective in photocatalytic degradation and decolorization of methyl orange dye. Also, quantum and Monte Carlo (MC) calculations were carried out to investigate the adsorption of methyl orange (MO) molecules on ZnO(111) surface in the presence of Au or without Au in aqueous conditions by Monte Carlo adsorption locator simulations in the Materials Studio 2017 software. Au created a tendency to form a relatively strong interaction of MO with the ZnO(111) surface. The adsorption of MO on Au-ZnO(111) in the presence of Au was more significant than that of MO on ZnO(111), suggesting Au could significantly improve the reactivity of the methyl orange toward the ZnO(111).

Shedding Light on Luminescent Janus Nanoparticles: From Synthesis to Photoluminescence and Applications

Luminescent Janus nanoparticles refer to a special category of Janus-based nanomaterials that not only exhibit dual-asymmetric surface nature but also attractive optical properties. The introduction of luminescence has endowed conventional Janus nanoparticles with many alluring light-responsive functionalities and broadens their applications in imaging, sensing, nanomotors, photo-based therapy, etc. The past few decades have witnessed significant achievements in this field. This review first summarizes well-established strategies to design and prepare luminescent Janus nanoparticles and then discusses optical properties of luminescent Janus nanoparticles based on downconversion and upconversion photoluminescence mechanisms. Various emerging applications of luminescent Janus nanoparticles are also introduced. Finally, opportunities and future challenges are highlighted with respect to the development of next-generation luminescent Janus nanoparticles with diverse applications.

Phyto-Mediated Copper Oxide Nanoparticles for Antibacterial, Antioxidant and Photocatalytic Performances

The greatest challenge of the current generation and generations to come is antimicrobial resistance, as different pathogenic bacteria have continuously evolved to become resistant to even the most recently synthesized antibiotics such as carbapenems. Resistance to carbapenems limits the therapeutic options of MDR infections as they are the only safe and effective drugs recommended to treat such infections. This scenario has complicated treatment outcomes, even to the commonest bacterial infections. Repeated attempts to develop other approaches have been made. The most promising novel therapeutic option is the use of nanomaterials as antimicrobial agents. Thus, this study examined the efficacy of Camellia sinensis extract (CSE) and Prunus africana bark extract (PAE) green synthesized Copper oxide nanoparticles (CuONPs) against carbapenem-resistant bacteria. Furthermore, the photocatalytic and antioxidant activities of CuONPs were evaluated to determine the potential of using them in a wide range of applications. CuONPs were biosynthesized by CSE and PAE. UV vis spectroscopy, X-ray Diffraction (XRD), Dynamic light scattering (DLS), Fourier Transform Infrared spectroscopy (FTIR), and Scanning Electron Microscopy (SEM) were used to characterize the nanoparticles. CuONPs susceptibility tests were carried out by the agar well diffusion method. The photocatalytic and antioxidant activities of the CuONPs were determined by the methylene blue and DPPH free radical scavenging assays, respectively. UV vis absorbance spectra registered surface plasmon resonance peaks between 272 and 286 nm, confirming the presence of CuONPs. The XRD array had nine strong peaks at 2θ values typical of CuONPs. FTIR spectra exhibited bands associated with organic functional groups confirming capping and functionalization of the CuONPs by the phytochemicals. DLS analysis registered a net zeta potential of +12.5 mV. SEM analysis revealed that the nanoparticles were spherical and clustered with a mean diameter of 6 nm. Phytosynthesized CuONPs exhibited the highest growth suppression zones of 30 mm with MIC ranging from 30 to 125 μg/ml against MDR bacteria. Furthermore, the CuONPs achieved a methylene blue dye photocatalysis degradation efficiency of 85.5% and a free radical scavenging activity of 28.8%. PAE and CSE successfully bio-reduced copper ions to the nanoscale level with potent antimicrobial, photocatalysis, and antioxidant activities.

Green Strategy–Based Synthesis of Silver Nanoparticles for Antibacterial Applications

Antibiotics have been the nucleus of chemotherapy since their discovery and introduction into the healthcare system in the 1940s. They are routinely used to treat bacterial infections and to prevent infections in patients with compromised immune systems and enhancing growth in livestock. However, resistance to last-resort antibiotics used in the treatment of multidrug-resistant infections has been reported worldwide. Therefore, this study aimed to evaluate green synthesized nanomaterials such as silver nanoparticles (AgNPs) as alternatives to antibiotics. UV-vis spectroscopy surface plasmon resonance peaks for AgNPs were obtained between 417 and 475 nm. An X-ray diffraction analysis generated four peaks for both Prunus africana extract (PAE) and Camellia sinensis extract (CSE) biosynthesized AgNPs positioned at 2θ angles of 38.2°, 44.4°, 64.5°, and 77.4° corresponding to crystal planes (111), (200), (220), and (311), respectively. A dynamic light-scattering analysis registered the mean zeta potential of +6.3 mV and +0.9 mV for PAE and CSE biosynthesized nanoparticles, respectively. Fourier transform infrared spectroscopy spectra exhibited bands corresponding to different organic functional groups confirming the capping of AgNPs by PAE and CSE phytochemicals. Field emission scanning electron microscopy imaging showed that AgNPs were spherical with average size distribution ranging from 10 to 19 nm. Biosynthesized AgNPs exhibited maximum growth inhibitory zones of 21 mm with minimum inhibitory concentration and minimum bactericidal concentration of 125 and 250 μg/ml, respectively, against carbapenem-resistant bacteria.

Determination of the LD50 with the chick embryo chorioallantoic membrane (CAM) assay as a promising alternative in nanotoxicological evaluation

Toxicity tests in rodents are still considered a controversial topic concerning their ethical justifiability. The chick embryo chorioallantoic membrane (CAM) assay may offer a simple and inexpensive alternative. The CAM assay is easy to perform and has low bureaucratic hurdles. At the same time, the CAM assay allows the application of a broad variety of analytical methods in the field of nanotoxicological research. We evaluated the CAM assay as a methodology for the determination of nanotoxicity. Therefore we calculated the median lethal dose (LD₅₀), performed in vivo microscopy and immunohistochemistry to identify organ-specific accumulation profiles, potential organ damage, and the kinetics of the in vivo circulation of the nanoparticles. Zinc oxide nanoparticles were intravascularly injected on day 10 of the egg development and showed an LD₅₀ of 17.5 µM (1.4 µg/mL_eggcontent). In comparison, the LD₅₀ of equivalent amounts of Zn²⁺ was 4.6 µM (0.6 µg/mL_eggcontent). Silica encapsulated ZnO@SiO₂ nanoparticles conjugated with fluorescein circulated in the bloodstream for at least 24 h. Particles accumulated mostly in the liver and kidney. In immunohistochemical staining, organ damage was detected only in liver tissue after intravascular injection of zinc oxide nanoparticles in very high concentrations. Zinc oxide nanoparticles showed a different pharmacokinetic profile compared to Zn²⁺ ions. In conclusion, the CAM assay has proven to be a promising methodology for evaluating nanotoxicity and for the assessment of the in vivo accumulation profiles of nanoparticles. These findings may qualify the methodology for risk assessment of innovative nanotherapeutics in the future.

Janus Nanoparticles: From Fabrication to (Bio)Applications

Janus nanoparticles (JNPs) refer to the integration of two or more chemically discrepant composites into one structure system. Studies into JNPs have been of significant interest due to their interesting characteristics stemming from their asymmetric structures, which can integrate different functional properties and perform more synergetic functions simultaneously. Herein, we present recent progress of Janus particles, comprehensively detailing fabrication strategies and applications. First, the classification of JNPs is divided into three blocks, consisting of polymeric composites, inorganic composites, and hybrid polymeric/inorganic JNPs composites. Then, the fabrication strategies are alternately summarized, examining self-assembly strategy, phase separation strategy, seed-mediated polymerization, microfluidic preparation strategy, nucleation growth methods, and masking methods. Finally, various intriguing applications of JNPs are presented, including solid surfactants agents, micro/nanomotors, and biomedical applications such as biosensing, controlled drug delivery, bioimaging, cancer therapy, and combined theranostics. Furthermore, challenges and future works in this field are provided.

Green Synthesis of Luminescent Gold-Zinc Oxide Nanocomposites: Cell Imaging and Visible Light-Induced Dye Degradation

Green synthesis of gold-zinc oxide (Au-ZnO) nanocomposite was successfully attempted under organic solvent–free conditions at room temperature. Prolonged stirring of the reaction mixture introduced crystallinity in the ZnO phase of Au-ZnO nanocomposites. Luminescence properties were observed in these crystalline Au-ZnO nanocomposites due to in situ embedding of gold nanoparticles (AuNP) of 5–6 nm diameter on the surface. This efficient strategy involved the reduction of Au(III) by Zn(0) powder in aqueous medium, where sodium citrate (NaCt) was the stabilizing agent. Reaction time and variation of reagent concentrations were investigated to control the Au:Zn ratio within the nanocomposites. The reaction with the least amount of NaCt for a long duration resulted in Au-ZnO/Zn(OH)₂ nanocomposite. X-ray photoelectron spectroscopy (XPS) confirmed the formation of Zn(OH)₂ and ZnO in the same nanocomposite. These nanocomposites were reconnoitered as bioimaging materials in human cells and applied for visible light–induced photodegradation of rhodamine-B dye.

Selective Synthesis of Monodisperse CoO Nanooctahedra as Catalysts for Electrochemical Water Oxidation

Thermal decomposition is a promising route for the synthesis of metal oxide nanoparticles because size and morphology can be tuned by minute control of the reaction variables. We synthesized CoO nanooctahedra with diameters of ∼48 nm and a narrow size distribution. Full control over nanoparticle size and morphology could be obtained by controlling the reaction time, surfactant ratio, and reactant concentrations. We show that the particle size does not increase monotonically with time or surfactant concentration but passes through minima or maxima. We unravel the critical role of the surfactants in nucleation and growth and rationalize the observed experimental trends in accordance with simulation experiments. The as-synthesized CoO nanooctahedra exhibit superior electrocatalytic activity with long-term stability during oxygen evolution. The morphology of the CoO particles controls the electrocatalytic reaction through the distinct surface sites involved in the oxygen evolution reaction.

Synthesis of Au, Ag, and Au-Ag Bimetallic Nanoparticles Using Pulicaria undulata Extract and Their Catalytic Activity for the Reduction of 4-Nitrophenol

Plant extract of Pulicaria undulata (L.) was used as both reducing agent and stabilizing ligand for the rapid and green synthesis of gold (Au), silver (Ag), and gold–silver (Au–Ag) bimetallic (phase segregated/alloy) nanoparticles (NPs). These nanoparticles with different morphologies were prepared in two hours by stirring corresponding metal precursors in the aqueous solution of the plant extracts at ambient temperature. To infer the role of concentration of plant extract on the composition and morphology of NPs, we designed two different sets of experiments, namely (i) low concentration (LC) and (ii) high concentration (HC) of plant extract. In the case of using low concentration of the plant extract, irregular shaped Au, Ag, or phase segregated Au–Ag bimetallic NPs were obtained, whereas the use of higher concentrations of the plant extract resulted in the formation of spherical Au, Ag, and Au–Ag alloy NPs. The as-prepared Au, Ag, and Au–Ag bimetallic NPs showed morphology and composition dependent catalytic activity for the reduction of 4-nitrophenol (4-NPh) to 4-aminophenol (4-APh) in the presence of NaBH₄. The bimetallic Au–Ag alloy NPs showed the highest catalytic activity compared to all other NPs.

Facile Sonochemical Preparation of Au-ZrO2 Nanocatalyst for the Catalytic Reduction of 4-Nitrophenol

High-intensity ultrasonic waves have great potential for the green synthesis of various nanomaterials under mild conditions and offer an excellent alternative for hazardous chemical methods. Herein a facile approach for the eco-friendly synthesis of Au-ZrO2 nanocatalyst with a high catalytic activity using a facile ultrasonic method is presented. Gold (Au) in the nanosize regime was successfully deposited on the surface of solvothermally synthesized monodispersed ZrO2 nanoparticles (ZrO2 NPs) in a very short period of time (5 min) at room temperature. Spherical shape small size Au nanoparticles that are uniformly dispersed on the surface of ZrO2 nanoparticles were obtained. Notably, in the absence of ZrO2 nanoparticles, HAuCl4 could not be reduced, indicating that nano-sized ZrO2 not only acted as support but also helped to reduce the gold precursor at the surface. The as-prepared Au-ZrO2 nanocatalyst was characterized by various techniques. The Au-ZrO2 nanocatalyst served as a highly efficient reducing catalyst for the reduction of 4-nitrophenol. The reaction time decreased with increasing the amount of catalyst.

Bioactivities of Geranium wallichianum Leaf Extracts Conjugated with Zinc Oxide Nanoparticles

This study attempts to obtain and test the bioactivities of leaf extracts from a medicinal plant, Geranium wallichianum (GW), when conjugated with zinc oxide nanoparticles (ZnONPs). The integrity of leaf extract-conjugated ZnONPs (GW-ZnONPs) was confirmed using various techniques, including Ultraviolet-visible spectroscopy, X-Ray Diffraction, Fourier Transform Infrared Spectroscopy, energy-dispersive spectra (EDS), scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The size of ZnONPs was approximately 18 nm, which was determined by TEM analysis. Additionally, the energy-dispersive spectra (EDS) revealed that NPs have zinc in its pure form. Bioactivities of GW-ZnONPs including antimicrobial potentials, cytotoxicity, antioxidative capacities, inhibition potentials against α-amylase, and protein kinases, as well as biocompatibility were intensively tested and confirmed. Altogether, the results revealed that GW-ZnONPs are non-toxic, biocompatible, and have considerable potential in biological applications.

Oxidative nucleation and growth of Janus-type MnOx-Ag and MnOx-AgI nanoparticles

Janus nanoparticles (NPs) containing two chemically distinct materials in one system are of great significance for catalysis in terms of harnessing catalytic synergies that do not exist in either component. We herein present a novel synthetic method of two Janus-type MnOx-Ag and MnOx-AgI NPs. The synthesis of Janus-type MnOx-AgI NPs is based on the oxidative nucleation and growth of Ag domains on MnO first and the subsequent iodization of Ag. A mild and non-disruptive iodization strategy is developed to yield Janus MnOx-AgI NPs, in which converting Ag to AgI domains with iodomethane (CH3I) is achieved through partial iodization. Simultaneously, Mn2+ species in the primary MnO octahedra are oxidized during the growth of Ag NPs, leading to the formation of amorphous p-type MnOx domains. Therefore, the as-resultant Janus-type MnOx-AgI NPs combining two semiconductors into an integrated nanostructure can be used as an efficient photocatalyst for visible-light-driven water oxidation. Janus MnOx-AgI NPs show an expected photocatalytic activity even in the absence of Ru(bpy)3Cl2 as an electron mediator. This intriguing synthesis may offer a new opportunity to develop asymmetric nanostructures of two semiconductors that will potentially be efficient photocatalysts for solar-driven water splitting.

Metal/Semiconductor Nanocomposites for Photocatalysis: Fundamentals, Structures, Applications and Properties

Due to the capability of utilizing light energy to drive chemical reactions, photocatalysis has been widely accepted as a green technology to help us address the increasingly severe environment and energy issues facing human society. To date, a large amount of research has been devoted to enhancing the properties of photocatalysts. As reported, coupling semiconductors with metals is one of the most effective methods to achieve high-performance photocatalysts. The excellent properties of metal/semiconductor (M/S) nanocomposite photocatalysts originate in two aspects: (i) improved charge separation at the metal-semiconductor interface; and (ii) increased absorption of visible light due to the surface plasmon resonance of metals. So far, many M/S nanocomposite photocatalysts with different structures have been developed for the application in environmental remediation, selective organic transformation, hydrogen evolution, and disinfection. Herein, we will give a review on the M/S nanocomposite photocatalysts, regarding their fundamentals, structures (as well as their typical synthetic approaches), applications and properties. Finally, we will also present our perspective on the future development of M/S nanocomposite photocatalysts.

Magnetic-Plasmonic Heterodimer Nanoparticles: Designing Contemporarily Features for Emerging Biomedical Diagnosis and Treatments

Magnetic-plasmonic heterodimer nanostructures synergistically present excellent magnetic and plasmonic characteristics in a unique platform as a multipurpose medium for recently invented biomedical applications, such as magnetic hyperthermia, photothermal therapy, drug delivery, bioimaging, and biosensing. In this review, we briefly outline the less-known aspects of heterodimers, including electronic composition, interfacial morphology, critical properties, and present concrete examples of recent progress in synthesis and applications. With a focus on emerging features and performance of heterodimers in biomedical applications, this review provides a comprehensive perspective of novel achievements and suggests a fruitful framework for future research.

Zinc overload mediated by zinc oxide nanoparticles as innovative anti-tumor agent

The predicted global cancer burden is expected to surpass 20 million new cancer cases by 2025. Despite recent advancement in tumor therapy, a successful cancer treatment remains challenging. The emerging field of nanotechnology offers great opportunities for diagnosis, imaging, as well as treatment of cancer. Zinc oxide nanoparticles (ZnO NP) were shown to exert selective cytotoxicity against tumor cells via a yet unknown mechanism, most likely involving the generation of reactive oxygen species (ROS). These nanoparticles are a promising therapeutic opportunity as zinc is a nontoxic trace element and its application in medically-related products is considered to be safe. We could show that ZnO NP can exert cytotoxic effects on several human tumor cell lines. There can be found ZnO NP concentrations which selectively damage tumor cells while human fibroblasts do not sustain lasting damage. Cytotoxicity is attributable to the release of zinc ions from the nanoparticles outside the cells as well as to a direct cell-nanoparticle interaction. This involves uptake of the particles into the tumor cells. With a silica shell the cytotoxicity can be delayed which can help in the future for a safe transport in the blood stream. Cellular damage finally cumulates in apoptotic cell death via zinc overload within 48 h after treatment with ZnO NP. A therapeutical perspective could be the targeted accumulation of ZnO NP at the tumor side to induce local zinc overload that substantially damages the tumor cells with no or low side effects. We suggest further studies to explore the potential of ZnO NP as an innovative anti-tumor agent.

Photocatalysis with Pt-Au-ZnO and Au-ZnO Hybrids: Effect of Charge Accumulation and Discharge Properties of Metal Nanoparticles

Metal-semiconductor hybrid nanomaterials are becoming increasingly popular for photocatalytic degradation of organic pollutants. Herein, a seed-assisted photodeposition approach is put forward for the site-specific growth of Pt on Au-ZnO particles (Pt-Au-ZnO). A similar approach was also utilized to enlarge the Au nanoparticles at epitaxial Au-ZnO particles (Au@Au-ZnO). An epitaxial connection at the Au-ZnO interface was found to be critical for the site-specific deposition of Pt or Au. Light on-off photocatalysis tests, utilizing a thiazine dye (toluidine blue) as a model organic compound, were conducted and confirmed the superior photodegradation properties of Pt-Au-ZnO hybrids compared to Au-ZnO. In contrast, Au-ZnO type hybrids were more effective toward photoreduction of toluidine blue to leuco-toluidine blue. It was deemed that photoexcited electrons of Au-ZnO (Au, ∼5 nm) possessed high reducing power owing to electron accumulation and negative shift in Fermi level/redox potential; however, exciton recombination due to possible Fermi-level equilibration slowed down the complete degradation of toluidine blue. In the case of Au@Au-ZnO (Au, ∼15 nm), the photodegradation efficiency was enhanced and the photoreduction rate reduced compared to Au-ZnO. Pt-Au-ZnO hybrids showed better photodegradation and mineralization properties compared to both Au-ZnO and Au@Au-ZnO owing to a fast electron discharge (i.e. better electron-hole seperation). However, photoexcited electrons lacked the reducing power for the photoreduction of toluidine blue. The ultimate photodegradation efficiencies of Pt-Au-ZnO, Au@Au-ZnO, and Au-ZnO were 84, 66, and 39%, respectively. In the interest of effective metal-semiconductor type photocatalysts, the present study points out the importance of choosing the right metal, depending on whether a photoreduction and/or photodegradation process is desired.

Plant extracts as green reductants for the synthesis of silver nanoparticles: lessons from chemical synthesis

From conventional synthesis to green transformations: a brief literature overview and insight for the synthesis of Ag nanoparticles.

Ternary hybrid nanostructures of Au-CdS-ZnO grown via a solution-liquid-solid route using Au-ZnO catalysts

Multi-component nanostructures of Au-CdS-ZnO with a novel morphology were synthesized by a non-conventional strategy where seeded growth is combined with solution-liquid-solid (SLS) growth. Each of these synthetic routes is used for growing a different domain of the final heterostructure, where ZnO rods are grown first on Au nanoparticles via heterogeneous nucleation while CdS is later grown between these two domains via SLS, using the Au tip of the preformed Au-ZnO as a catalyst. The in situ alloying of the Au tip with Cd enabled the metal tip to function as an SLS catalyst at a relatively mild reaction temperature which is lower than the melting point of pure Au.

In situ SERS study of surface plasmon resonance enhanced photocatalytic reactions using bifunctional Au@CdS core-shell nanocomposites

Surface plasmon resonance (SPR) has been utilized in many fields, such as surface-enhanced Raman spectroscopy (SERS) and solar energy conversion. Here we developed an Au@CdS core-shell nanostructure, a bifunctional nanoparticle, used as an efficient catalyst for SPR enhanced photocatalytic degradation, and as a substrate for in situ SERS detection of methylene blue (MB) and p-nitrophenol (pNTP). With integration of an Au nanoparticle into a CdS shell, the degradation process was significantly accelerated under 500 nm long-pass (λ > 500 nm) visible light irradiation, which was caused by the injection of hot electrons. Moreover, a highly uniform, monolayer film of Au@CdS nanoparticles (NPs) has been prepared and used as both a SERS substrate and catalyst. The decomposition of MB molecules and nitrogen coupling reaction of pNTP were observed during the 638 nm laser illumination. We demonstrate that a plasmonic core-semiconductor shell nanocomposite can be a promising material for photocatalysis and in situ SERS study.

Bioengineered silver nanoparticles using Curvularia pallescens and its fungicidal activity against Cladosporium fulvum

Microorganisms based biosynthesis of nanomaterials has triggered significant attention, due to their great potential as vast source of the production of biocompatible nanoparticles (NPs). Such biosynthesized functional nanomaterials can be used for various biomedical applications. The present study investigates the green synthesis of silver nanoparticles (Ag NPs) using the fungus Curvularia pallescens (C. pallescens) which is isolated from cereals. The C. pallescens cell filtrate was used for the reduction of AgNO₃ to Ag NPs. To the best of our knowledge C. pallescens is utilized first time for the preparation of Ag NPs. Several alkaloids and proteins present in the phytopathogenic fungus C. pallescens were mainly responsible for the formation of highly crystalline Ag NPs. The as-synthesized Ag NPs were characterized by using UV–Visible spectroscopy, X-ray diffraction and transmission electron microscopy (TEM). The TEM micrographs have revealed that spherical shaped Ag NPs with polydisperse in size were obtained. These results have clearly suggested that the biomolecules secreted by C. pallescens are mainly responsible for the formation and stabilization of nanoparticles. Furthermore, the antifungal activity of the as-prepared Ag NPs was tested against Cladosporium fulvum, which is the major cause of a serious plant disease, known as tomato leaf mold. The synthesized Ag NPs displayed excellent fungicidal activity against the tested fungal pathogen. The extreme zone of reduction occurred at 50 μL, whereas, an increase in the reduction activity is observed with increasing the concentration of Ag NPs. These encouraging results can be further exploited by employing the as synthesized Ag NPs against various pathogenic fungi in order to ascertain their spectrum of fungicidal activity.

Colloidal synthesis of Cu-ZnO and Cu@CuNi-ZnO hybrid nanocrystals with controlled morphologies and multifunctional properties

Metal-semiconductor hybrid nanocrystals have received extensive attention owing to their multiple functionalities which can find wide technological applications. The utilization of low-cost non-noble metals to construct novel metal-semiconductor hybrid nanocrystals is important and meaningful for their large-scale applications. In this study, a facile solution approach is developed for the synthesis of Cu-ZnO hybrid nanocrystals with well-controlled morphologies, including nanomultipods, core-shell nanoparticles, nanopyramids and core-shell nanowires. In the synthetic strategy, Cu nanocrystals formed in situ serve as seeds for the heterogeneous nucleation and growth of ZnO, and it eventually forms various Cu-ZnO hetero-nanostructures under different reaction conditions. These hybrid nanocrystals possess well-defined and stable heterostructure junctions. The ultraviolet-visible-near infrared spectra reveal morphology-dependent surface plasmon resonance absorption of Cu and the band gap absorption of ZnO. Furthermore, we construct a novel Cu@CuNi-ZnO ternary hetero-nanostructure by incorporating the magnetic metal Ni into the pre-synthesized colloidal Cu nanocrystals. Such hybrid nanocrystals possess a magnetic Cu-Ni intermediate layer between the ZnO shell and the Cu core, and exhibit ferromagnetic/superparamagnetic properties which expand their functionalities. Finally, enhanced photocatalytic activities are observed in the as-prepared non-noble metal-ZnO hybrid nanocrystals. This study not only provides an economical way to prepare high-quality morphology-controlled Cu-ZnO hybrid nanocrystals for potential applications in the fields of photocatalysis and photovoltaic devices, but also opens up new opportunities in designing ternary non-noble metal-semiconductor hybrid nanocrystals with multifunctionalities.

Hierachical Ni@Fe2O3 superparticles through epitaxial growth of γ-Fe2O3 nanorods on in situ formed Ni nanoplates

One endeavour of nanochemistry is the bottom-up synthesis of functional mesoscale structures from basic building blocks. We report a one-pot wet chemical synthesis of Ni@γ-Fe2O3 superparticles containing Ni cores densely covered with highly oriented γ-Fe2O3 (maghemite) nanorods (NRs) by controlled reduction/decomposition of nickel acetate (Ni(ac)2) and Fe(CO)5. Automated diffraction tomography (ADT) of the Ni-Fe2O3 interface in combination with Mössbauer spectroscopy showed that selective and oriented growth of the γ-Fe2O3 nanorods on the Ni core is facilitated through the formation of a Fe0.05Ni0.95 alloy and the appearance of superstructure features that may reduce strain at the Ni-Fe2O3 interface. The common orientation of the maghemite nanorods on the Ni core of the superparticles leads to a greatly enhanced magnetization. After functionalization with a catechol-functional polyethylene glycol (C-PEG) ligand the Ni@γ-Fe2O3 superparticles were dispersible in water.

Advances in biogenic synthesis of palladium nanoparticles

Due to their catalytic activity, biogenic synthesis of Pd nanparticles is of significant importance.

Enhanced photophysical properties of plasmonic magnetic metal-alloyed semiconductor heterostructure nanocrystals: a case study for the Ag@Ni/Zn1−xMgxO system

Multiple plasmonic magnetic Ag@Ni core–shell metal nanocrystal decorated Zn_1−xMg_xO nanoheterostructures have been synthesized and enhanced photophysical properties were found.

Maximizing the photo catalytic and photo response properties of multimodal plasmonic Ag/WO(3-x) heterostructure nanorods by variation of the Ag size

High quality nearly monodisperse colloidal WO3-x nanorods with an aspect ratio ∼18 were synthesized using the thermal decomposition technique. The effects of a capping agent and an activating agent on the nanorod aspect ratio have been studied. Excess carrier concentration due to large oxygen vacancy and smaller width of the nanorods compared to the Bohr exciton radius gives rise to an increase of the band gap. Shape anisotropy in nanorods results in two plasmonic absorbance bands at about 890 nm and 5900 nm corresponding to short axis and long axis plasmon modes. The short axis mode reveals an excellent plasmonic sensitivity of ∼345 nm per refractive index. A plasmonic photocatalysis process based on WO3-x nanorods has been developed to synthesize Ag/WO3-x heterostructures consisting of multiple Ag dots with ∼2 nm size, randomly decorated on the surface of the WO3-x nanorods. Long time irradiation leads to an increase in the size (5 nm) of Ag nanocrystals concomitant with decrease in the number of Ag nanocrystals attached per WO3-x nanorod. Plasmonic photocatalysis followed by thermal annealing produces only one Ag nanocrystal of size ∼10 nm on each WO3-x nanorod. Red shifting and broadening of plasmon bands of Ag nanocrystals and WO3-x nanorods confirm the formation of heterostructures between the metal and semiconductor. Detailed transmission electron micrograph analysis indicates the epitaxial growth of Ag nanocrystals onto WO3-x nanorods. A high photocurrent gain of about 4000 is observed for Ag (10 nm)/WO3-x heterostructures. The photodegradation rate for Rhodamine-B and methylene blue is maximum for Ag (10 nm)/WO3-x heterostructures due to efficient electron transfer from WO3-x nanorods to Ag nanocrystals. Metal plasmon-semiconductor exciton coupling, prominent plasmon absorbance of metal nanoparticles, and formation of an epitaxial interface are found to be the important factors to achieve the maximum photocatalytic activity and fabrication of a high speed photodetector device by employing the heterostructures.

Synthesis of bi-phase dispersible core-shell FeAu@ZnO magneto-opto-fluorescent nanoparticles

Bi-phase dispersible core-shell FeAu@ZnO magneto-opto-fluorescent nanoparticles were synthesized by a modified nanoemulsion process using poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEO-PPO-PEO) as the surfactant. The morphology and crystal structure of the nanoparticles were studied by TEM/HRTEM and XRD. The nanoparticles manifest soft ferromagnetic and/or near superparamagnetic behavior with a small coercivity of ~19 Oe at room temperature. The corresponding magnetic hysteresis curves were elucidated by the modified Langevin equation. The FTIR study confirms the PEO-PPO-PEO molecules on the surface of the nanoparticles. The UV-vis and PL results reveal the well-behaved absorption bands including surface plasmon resonance and multiple visible fingerprint photoluminescent emissions of the nanoparticles dispersed in both hydrophilic and hydrophobic solvents. Moreover, the processes of solvent dispersion-collection of the nanoparticles were demonstrated for application readiness of such core-shell nanostructures.

Synthesis and photocatalytic properties of multi-morphological AuCu3-ZnO hybrid nanocrystals

Noble metal-semiconductor hybrid nanocrystals represent an important class of materials for many potential applications, especially for photocatalysis. The utilization of transition metals to form alloys with noble metals can not only reduce the preparation costs, but may also offer tunable optical and catalytic properties for a broader range of applications. In this study, we report on the solution synthesis of AuCu3-ZnO hybrid nanocrystals with three interesting morphologies, including urchin-like, flower-like and multipod-like nanocrystals. In the synthetic strategy, Au-Cu bimetallic alloy seeds formed in situ are used to induce the heteroepitaxial growth of ZnO nanocrystals on the surface of bimetallic alloy cores; thus different types of morphologies can be achieved by controlling the reaction conditions. Through high-resolution transmission electron microscopy observations, well-defined interfaces between ZnO and AuCu3 are observed, which indicate that ZnO has a (0001) orientation and prefers to grow on AuCu3 {111} facets. The as-prepared hybrid nanocrystals demonstrate morphology- and composition-dependent surface plasmon resonance (SPR) absorption bands. In addition, much higher photocatalytic efficiency than pure ZnO nanocrystals is observed for the hybrid nanocrystals in the degradation of methylene blue. In particular, the multipod-like AuCu3-ZnO hybrid nanocrystals show the highest catalytic performance, as well as more than three times higher photocurrent density than the pure ZnO sample. The reported synthetic strategy provides a facile route to the effective combination of a plasmonic alloy with semiconductor components at the nanoscale in a controlled manner.

Synthesis of Ni-Au-ZnO ternary magnetic hybrid nanocrystals with enhanced photocatalytic activity

The functional synergy between the metal and the semiconductor in metal-semiconductor hybrid nanocrystals with specific structures and morphologies makes them suitable candidates for a wide range of applications. To date, the synthesis and the corresponding properties of ternary metal-semiconductor hetero-nanostructures, especially for hybrid nanocrystals containing magnetic metals, are seldom discussed and thus worthy of extensive research. In this study, we report a nonaqueous approach for the synthesis of Ni-Au-ZnO ternary hybrid nanocrystals with three morphologies, including nanomultipods, matchstick-like nanorods and nanopyramids. In the synthetic strategy, the Ni precursor dissolved in oleylamine was injected into a hot solution containing preformed Au-ZnO nanocrystals with specific morphologies. Then Ni prefers to grow on the unoccupied surfaces of Au, thus forming a hybrid hetero-nanostructure which retains the main morphologies of Au-ZnO nanocrystals. The ultraviolet-visible spectra not only show the band gap absorption of ZnO but also exhibit a broadened and weakened surface plasmon resonance (SPR) band of Au. The Ni-Au-ZnO nanocrystals exhibit much higher photocatalytic efficiency than pure ZnO in the degradation of Rhodamine B. Meanwhile, these hybrid nanocrystals are superparamagnetic at room temperature and can be readily recycled by a magnetic field for reuse. The as-prepared ternary Ni-Au-ZnO hybrid nanocrystals possess plasmonic, magnetic and enhanced photocatalytic properties, and thus are expected to find wide applications in the future.