Au–Ag core–shell composite nanoparticles as a selective and sensitive plasmonic chemical probe for l-cysteine detection in Lens culinaris (lentils)

The present work reported is a simple and selective method for the colorimetrical detection of l-cysteine in Lens culinaris (or lentils) using Au–Ag core–shell (Au core Ag shell) composite nanoparticles as a chemical probe. The phenomenon is based on the color change of composite nanoparticles from yellowish brown to light blue, followed by a shift of the localized surface plasmon resonance (LSPR) absorption band in the UV-visible region (i.e., 200–800 nm) with the addition of l-cysteine into the solution of bimetallic nanoparticles. The mechanism for the detection of l-cysteine is based on the electrostatic interaction of the metal ion with the thiol group of the amino acid, which causes the red shift of the LSPR band at 685 nm. The size distribution, morphology, composition and optical properties of the Au–Ag core–shell composite nanoparticles were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), energy dispersive X-ray diffraction (EDX), UV-visible spectrophotometer and Fourier transform infrared spectroscopy (FTIR) techniques. An excellent linearity range for the present method was observed in the range of 20–140 μg mL⁻¹ with a limit of detection at 1.95 μg mL⁻¹ and correlation coefficient (R²) of 0.986. A good% recovery of 4.0% showed the selectivity of the method for l-cysteine determination from sample matrices. The advantageous features of the present method are being simple, rapid, low cost and selectivity towards the determination of l-cysteine in lentils.

The present work reported is a simple and selective method for the colorimetrical detection of l-cysteine in Lens culinaris (or lentils) using Au–Ag core–shell (Au core Ag shell) composite nanoparticles as a chemical probe.     

Generalized nano-thermodynamic model for capturing size-dependent surface segregation in multi-metal alloy nanoparticles

Multi-metal alloy nanoparticles (NPs) offer new avenues for exploration and design of nanoscale-properties, e.g., catalytic, electronic and optical properties, by virtue of their tunable composition. A method that can aid such exploration by accurately predicting the size-, shape- and composition-dependent elemental distribution associated with nanomaterials is crucially missing. A nano-thermodynamic model based on distribution coefficients Δ is introduced to fill this gap. Δ is employed to predict surface segregation in NPs as a function of the NP size and composition. Interestingly, we find Δ to be independent of size for NPs beyond 2 nm. This key finding motivates the construction of thermodynamic tables for distribution coefficients using segregation observed with one or more NP sizes. The tables can enable accurate prediction of phase diagrams for nanomaterials across a wide-range of sizes. Key concepts of this new theory are demonstrated with Au–Pt–Pd, Ag–Au–Pd and Ni–Pt–Pd, which are found to exhibit complex size-dependent segregation behavior for 2–6 nm NPs and relatively weaker size-dependence beyond 6 nm. Numerically well-converged values of Δ are calculated for small NPs using Monte Carlo simulations in the canonical ensemble. Simulations are based on an embedded atom method (EAM) potential for metal alloys.

Nano-thermodynamic model captures thermodynamic preference of metal species for different regions of a nanoparticle while accounting for size effects.     

Explosives sensing using Ag–Cu alloy nanoparticles synthesized by femtosecond laser ablation and irradiation

Herein we demonstrate the synthesis of Ag–Cu alloy NPs through a consecutive two-step process; laser ablation followed by laser irradiation. Initially, pure Ag and Cu NPs were produced individually using the laser ablation in liquid technique (with ∼50 femtosecond pulses at 800 nm) which was followed by laser irradiation of the mixed Ag and Cu NPs in equal volume. These Ag, Cu, and Ag–Cu NPs were characterised by UV-visible absorption, HRTEM and XRD techniques. The alloy formation was confirmed by the presence of a single surface plasmon resonance peak in absorption spectra and elemental mapping using FESEM techniques. Furthermore, the results from surface enhanced Raman scattering (SERS) studies performed for the methylene blue (MB) molecule suggested that Ag–Cu alloy NPs demonstrate a higher enhancement factor (EF) compared to pure Ag/Cu NPs. Additionally, SERS studies of Ag–Cu alloy NPs were implemented for the detection of explosive molecules such as picric acid (PA – 5 μM), ammonium nitrate (AN – 5 μM) and the dye molecule methylene blue (MB – 5 nM). These alloy NPs exhibited superiority in the detection of various analyte molecules with good reproducibility and high sensitivity with EFs in the range of 10⁴ to 10⁷.

Herein we demonstrate the synthesis of Ag–Cu alloy NPs through a consecutive two-step process; laser ablation followed by laser irradiation.     

Electrooxidation of Pd–Cu NP loaded porous carbon derived from a Cu-MOF

The development of new non-platinum catalysts for alcohol electrooxidation is of utmost importance. In this work, a bimetallic Pd–Cu loaded porous carbon material was first synthesized from a Cu-based metal–organic framework (MOF). The Cu loaded porous carbon was pre-synthesized through calcinating the Cu-based MOF under a N₂ atmosphere. After loading Pd onto the precursor and heating, Pd–Cu loaded porous carbon (Pd–Cu/C) was obtained for alcohol electrooxidation. Electrooxidation experiments revealed that this Pd–Cu bimetal loaded porous carbon assisted steady state electrolysis for alcohol oxidation in alkaline media. Moreover, different alcohols were electrooxidated using the present electrocatalyst for the purposes of discussing the oxidation mechanism. This electrooxidation study of Pd–Cu/C derived from a MOF demonstrates a good understanding of the electrooxidation of different alcohols, and provides useful guidance for developing new electrocatalyst materials for energy conversion and electronic devices.

We have synthesized Pd–Cu NP loaded porous carbon through the direct carbonization of a porous Cu based MOF for efficient electrooxidation.

There is an immediate need to develop direct alcohol fuel cells (DAFCs), which have been proven to be a fine source of energy, which could probably replace fossil fuels use to fulfil global energy demand. As one of the most significant electrocatalytic procedures, the electrooxidation of alcohols is an important process in DAFCs, and has gathered much attention and is attractive, due to high power density output and low pollutant emissions. Generally, Pt based materials are the most common electrocatalysts for alcohol electrooxidation reactions. However, the high cost and limited supply of Pt severely restricts its commercial application. Therefore, the development of new efficient and inexpensive non-platinum alternative materials to Pt-based catalysts is of utmost importance.Metal–organic frameworks (MOF) are assembled from metal ions linked by organic ligands, and are used in catalysis, guest molecule storage/separation, fluorescence, sensors and other devices.^1–3 Due to their highly ordered porous structures and large surface areas, MOFs can also be used as templates/precursors for preparing porous carbon materials through thermal treatment.^4–8 Several MOF derived carbon materials with good electrical conductivity are reported to show effective electrocatalytic performance,⁹ such as in the oxygen evolution reaction (OER),¹⁰ hydrogen evolution reaction (HER),¹¹ and oxygen reduction reaction (ORR).¹² Recently, a zeolitic imidazolate framework ZIF-8 was calcinated in order to prepare porous carbon with both micro- and meso-pores to support Pd electrocatalysts for methanol electrooxidation.¹³ Unfortunately, this could not efficiently limit the use of the noble metal, which gives challenges to scientists for further exploration.It has been demonstrated that the alloying of noble metals with transition metals has been used for the enhancement of catalytic activity and reduction of cost,¹⁴ because of the low cost and relatively high abundance of transition metals. The use of alloyed metal, Pd–M (where M is Cu, Co or Ni), binary electrocatalysts has been reported for effectively improving the catalytic properties.^15–17 For this purpose, introducing a non-noble metal into a noble metal bimetallic system will fulfil the demand for a new catalyst and become an area of interest nowadays. The second metal (such as Cu) will behave as a donor, while Pd has an empty d orbital to accept electrons, and it is assumed that its electronic properties will be more similar to Pt.¹⁸ Therefore, Pd–Cu bimetal loaded porous carbon derived from a Cu-MOF can provide a good electrocatalyst for alcohol oxidation.In this work, as shown in Scheme 1, we have synthesized Cu loaded porous carbon through the direct carbonization of a porous Cu based MOF. After loading Pd onto the precursor and heating, Pd–Cu bimetal loaded porous carbon (Pd–Cu/C) was obtained. Chronoamperometric studies revealed that this Pd–Cu bimetal loaded porous carbon assisted steady state electrolysis for alcohol oxidation in alkaline media. In addition, alcohols with different numbers of carbon atoms (such as ethanol, 1-propanol and 2-propanol) were also investigated for electrooxidation. It is important to note that the effectiveness of this bimetallic NP loaded carbon means that it can serve as a catalyst for the electrooxidation of low-molecular weight alcohols, which probably can be used as energy sources in portable electronic devices.Open in a separate windowScheme 1The preparation procedure for Pd–Cu/C derived from HKUST-1 and PdCl₂: (a) MOF HKUST-1; (b) Cu/C calcinated from HKUST-1; (c) PdCl₂ loaded on Cu/C; and (d) the Pd–Cu/C material.Here, a 3-D MOF, HKUST-1 (also called Cu₃(BTC)₂, BTC = 1,3,5-benzenetricarboxylate), was chosen as the precursor for preparing the Cu/C material, due to the structure having high porosity and it being a rich Cu source. The as-synthesized HKUST-1 was calcinated at 700 °C for 5 h under a N₂ atmosphere, and the Cu/C material was obtained. In addition, the guest species PdCl₂ was loaded onto the calcinated HKUST-1 through immersing the pre-calcinated HKUST-1 into a PdCl₂ ethanolic solution (1 mM) for 2 h (Scheme 1). The PdCl₂ loaded Cu/C (PdCl₂@Cu/C) was heated at 300 °C for 1 h under a N₂ atmosphere. Finally, an alloy of Pd and Cu loaded porous carbon material (Pd–Cu/C) was obtained and characterized through powder XRD, BET and XPS analyses.The PXRD data (Fig. 1a) from as-synthesized HKUST-1 powder and the bimetallic Pd–Cu NP loaded carbon porous material derived from HKUST-1 show that the samples contain bimetallic palladium and copper mostly. The XRD peak appearing at 43.3° corresponds to the (fcc) (111) facet plane of Cu. Due to Pd being dispersed homogenously at a low concentration through the sample, the XRD pattern could not display the obvious peak from Pd. However, inductively coupled plasma emission spectroscopy (ICP) data (Table S1^†) from the sample showed 0.76% Pd and 36.68% Cu, indicating the existence of Pd and Cu. The porosity of Pd–Cu/C was demonstrated through BET data, which shows N₂ adsorption of ∼150 cm³ g⁻¹. The Pd XPS spectrum showed two definite peaks at 335.5 and 341 eV, respectively assigned to 3d_5/2 and 3d_3/2 and matching well with Pd⁰. XPS peaks at 932.4 and 952.1 eV indicate the valence states of Cu ions in the Cu 2p_3/2 and Cu 2p_1/2 orbitals in the Pd–Cu/C material. Cu²⁺ is present in the porous carbon material, with respective peaks at 933.7 eV and 934.4 eV from CuO and Cu(OH)₂, with a prominent satellite observed in the 938–946 eV range. A few Pd²⁺ ions also exist in the sample due the easy oxidation of the surface. The Raman spectrum of Pd–Cu/C (Fig. S4^†) shows typical graphitic carbon. The results of the characterization studies clearly reveal that the nanoparticles have a Pd and Cu bimetallic nature.Open in a separate windowFig. 1(a) XRD data from HKUST-1 and Pd–Cu/C; (b) N₂ sorption isotherms for Pd–Cu/C; and XPS data from (c) Pd and (d) Cu in a sample of Pd–Cu/C.SEM images with EDS (Fig. 2a and b) results show that the sample contained much more copper than palladium, which clearly suggests that the presence of copper in the sample would probably be the reason for the expected electrooxidation of alcohols. It could be possible to replace the use of high-cost Pd or Pt based catalysts. The morphology of the Pd–Cu NPs was further characterized via TEM imaging and TEM element mapping (Fig. 2c, d and S5^†), demonstrating that the nano-sized NPs were dispersed homogeneously. The HR-TEM image in Fig. 2c gives insight into the bimetallic nature of the synthesized nanoparticles, with two noticeable lattice fringes (0.225 nm for Pd(111) and 0.202 nm for Cu(111)). The mean size of the Pd–Cu NPs was 7.38 nm, as shown in Fig. 2d. The homogenous distribution, with well-defined bimetallic Pd–Cu based carbon material, was good for the electrooxidation of alcohols. The electrochemical active surface area (ECSA) for Pd–Cu/C was high compared with commercial Pd/C, which suggested that the synthesized Pd–Cu/C has ample available surface area, mainly because of synergistic effects from the Cu-MOF based carbon material and the morphology of the electrocatalyst.Open in a separate windowFig. 2(a) SEM image of and (b) EDS data from Pd–Cu/C; (c) a TEM image of Pd–Cu NPs in the hybrid carbon material; and (d) the size distribution of the Pd–Cu NPs.In Fig. 3, CV profiles for commercial Pd/C and the presented Pd–Cu/C show two distinct peaks (forward (iF) and backward (iB) peaks) during the oxidation of methanol-containing 1 M KOH solution. The peak at −0.37 V indicates the oxidation of aforementioned carbonaceous species, such as Pd–CO_ads, along with newly formed alcohol adsorbates, following the removal of surface intermediates at lower potentials.¹⁹ For the forward peak potential, a shift in the iF value is observed, mainly because of Cu existing with Pd in the material. This results in the oxidation of poisonous species, such as Pd adsorbed CO, at higher potentials,²⁰ leading to such high activity. ATR-IR (Fig. S7^†) and GC analyses (Fig. S8^†) show the methanol oxidation reaction (MOR) pathway during the formation of the final CO₂ product. The catalytic activity of Pd–Cu/C is found to be ∼13 times higher than commercial Pd/C for methanol oxidation, demonstrating that the presence of Cu with Pd in Pd–Cu based catalysts increases CO oxidation because of a strong binding ability. Cu binds to CO more strongly than Pd, as a result of electronic structure differences,^21,22 thus preventing the electrode from undergoing CO poisoning, a major issue for Pd-based catalysts during the methanol oxidation reaction (MOR). The mechanism of methanol oxidation is shown in the ESI (eqn (8)–(10)).^† The high iF value for Pd–Cu/C can be ascribed to the fast formation of reactive intermediates, such as Pd–CH₂OH, Pd–COOH, Pd–H, Pd–(CHO)_ads, and Pd–(COOH)_ads.^23–25 The removal of these intermediates is necessary for a high current density. Furthermore, formaldehyde (HCHO), formic acid (HCOOH) and CO₂ would be the final products in the MOR.^26,27 Pd–Cu/C has good catalytic activity for the MOR, leading to further investigation into the electrooxidation of different alcohols, such as ethanol, 1-propanol, and 2-propanol (Fig. 4 and Table S2^†).Open in a separate windowFig. 3CV curves from Pd/C and Pd–Cu/C electrocatalysts during CH₃OH (1 M) oxidation in 1 M KOH solution, at a scan rate of 50 mV s⁻¹, at room temperature.Open in a separate windowFig. 4(a) CV curves from: the Pd–Cu/C electrocatalyst for C₁–C₃ aliphatic alcohol (1 M) oxidation in KOH (1 M) solution; and (b) Pd–Cu/C in 1 M EtOH, 1-propanol and 2-propanol at a scan rate of 50 mV s⁻¹ at room temperature.The current densities for different alcohol oxidation processes are summarized in Fig. 4a and b. The normalized iF (calculated using Pd mass) for the MOR (∼4643 mA mg⁻¹) was higher than for three other alcohols, i.e., it was ∼139, ∼94 and ∼26.5 mA mg⁻¹ for ethanol, 1-propanol and 2-propanol, respectively. The iF/iB ratio for methanol is ∼12 times higher than that for ethanol, ∼13 times that for 1-propanol and ∼4 times that for 2-propanol. The reactivity order for Pd–Cu/C is methanol > ethanol > 1-propanol > 2-propanol. 2-Propanol electrooxidation showed a lower current density on a Pd–Cu/C electrode in alkaline medium, although iF/iB is ∼5.4. The negative shift in the onset of the ethanol oxidation reaction (EOR) suggested that a high copper content with very low amount of Pd was suitable for EOR kinetics using a Pd–Cu/C catalyst. The ethoxy (CH₃CO)_ads was strongly adsorbed, and blocked hydrogen absorption/adsorption. The current intensity of iF increased due to the formation of fresh Pd–OH, through stripping carbonaceous residue from the electrode (eqn (11)–(14)^†). In addition, the increased current at high potentials sharply reached the largest value then started to decline, because a PdO layer formed on the electrode, blocking the further adsorption of reactive species.²⁸ ATR-IR spectra (Fig. S9^†) show the presence of CO₂ and CO_ads, whereas bands appear at 1670 cm⁻¹ and 1390 cm⁻¹ because of the formation of acetic acid.²⁹ The Pd–Cu/C electrocatalyst has the potential to oxidize the intermediate to the final product, CO₂, during EOR to some extent; Cu promotes oxidation through increasing the production of OH_ads⁻/H₂O to eliminate the intermediate CH₃CO_ads simultaneously on Pd.³⁰ The stability of Pd–Cu/C in all four alcohols (methanol, ethanol, 1-propanol and 2-propanol) was studied using chronoamperometry at a potential of −0.25 V, as shown in Fig. S2.^† The slow current decay showed that the stability of the Pd–Cu/C electrocatalyst in methanol is best. Comparing the results, the current for methanol oxidation was higher than that for the other three alcohols. However, the oxidation currents from ethanol and 1-propanol were larger than that from 2-propanol. This suggested that Pd–Cu/C is less stable and shows lower anti-poisoning ability during 2-propanol oxidation in an alkaline medium.During this oxidation, 1-propanol oxidizes to propanal first, and its further oxidation results in the formation of a stable product, propanoic acid (Scheme S1^†). 1-Propanol is converted, with its carboxylate as the major product, as verified using ATR-IR (Fig. S10^†). 2-Propanol forms acetone as an intermediate product, leading to the poisoning of the electrode.³¹ ATR-IR spectra (Fig. S11^†) of Pd–Cu/C also confirm that the electrocatalyst follows a dual pathway through acetone and propene intermediates to oxidize to CO₂ finally (Scheme S2^†).^32–34 However, acetone formation is kinetically favored.³⁵ The results show that the location of the –OH group in the alcohol influences the electrooxidation reaction kinetics. In contrast methanol oxidation using Pd–Cu/C has much higher catalytic activity than ethanol, 1-propanol and 2-propanol oxidation, which makes it a good candidate for direct methanol fuel cells.In summary, we have first synthesized a bimetallic Pd–Cu NP loaded porous carbon material from a Cu-based MOF for alcohol electrooxidation. The Cu loaded porous carbon was pre-synthesized by calcinating the Cu-based MOF HKUST-1 under a N₂ atmosphere. Afterwards, Pd–Cu NP loaded porous carbon was obtained for alcohol electrooxidation. Electrooxidation experiments revealed that Pd–Cu/C was suitable for steady state electrolysis for alcohol oxidation in alkaline media. In addition, different alcohols were electrooxidated using the present electrocatalyst to discuss the oxidation mechanism. This electrooxidation study of Pd–Cu/C derived from a MOF offers good understanding into the electrooxidation of different alcohols and it could provide useful guidance for the development of new electrocatalyst materials.     

Bimetallic Au–Pd alloy nanoparticles supported on MIL-101(Cr) as highly efficient catalysts for selective hydrogenation of 1,3-butadiene

Gold–palladium (Au–Pd) bimetallic nanoparticle (NP) catalysts supported on MIL-101(Cr) with Au : Pd mole ratios ranging from 1 : 3 to 3 : 1 were prepared through coimpregnation and H₂ reduction. Au–Pd NPs were homogeneously distributed on the MIL-101(Cr) with mean particle sizes of 5.6 nm. EDS and XPS analyses showed that bimetallic Au–Pd alloys were formed in the Au(2)Pd(1)/MIL-101(Cr). The catalytic performance of the catalysts was explored in the selective 1,3-butadiene hydrogenation at 30–80 °C on a continuous fixed bed flow quartz reactor. The bimetallic Au–Pd alloy particles stabilized by MIL-101(Cr) presented improved catalytic performance. The as-synthesized bimetallic Au(2)Pd(1)/MIL-101(Cr) with 2 : 1 Au : Pd mole ratio showed the best balance between the activity and butene selectivity in the selective 1,3-butadiene hydrogenation. The Au–Pd bimetallic-supported catalysts can be reused in at least three runs. The work affords a reference on the utilization of a MOF and alloy nanoparticles to develop high-efficiency catalysts.

Bimetallic Au–Pd alloy particles stabilized by MIL-101(Cr) showed high activity and butene selectivity for 1,3-butadiene hydrogenation reaction.     

Au–Ag and Pt–Ag bimetallic nanoparticles@halloysite nanotubes: morphological modulation,improvement of thermal stability and catalytic performance

In this study, Au–Ag and Pt–Ag bimetallic nanocages were loaded on natural halloysite nanotubes (HNTs) via galvanic exchange based on Ag@HNT. By changing the ratio of Au to Ag or Pt to Ag in exchange processes, Au–Ag@HNT and Pt–Ag@HNT with different nanostructures were generated. Both Au–Ag@HNT and Pt–Ag@HNT systems showed significantly improved efficiency as peroxidase-like catalysts in the oxidation of o-phenylenediamine compared with monometallic Au@HNT and Pt@HNT, although inert Ag is dominant in the composition of both Au–Ag and Pt–Ag nanocages. On the other hand, loading on HNTs enhanced the thermal stability for every system, whether monometallic Ag nanoparticles, bimetallic Au–Ag or Pt–Ag nanocages. Ag@HNT sustained thermal treatment at 400 °C in nitrogen with improved catalytic performance, while Au–Ag@HNT and Pt–Ag@HNT maintained or even had slightly enhanced catalytic efficiency after thermal treatment at 200 °C in nitrogen. This study demonstrated that natural halloysite nanotubes are a good support for various metallic nanoparticles, improving their catalytic efficiency and thermal stability.

Bimetallic Au–Ag@HNT and Pt–Ag@HNT nanocages showed significantly improved efficiency in the oxidation of o-phenylenediamine as peroxidase-like catalyst compared with corresponding monometallic nanoparticles.     

Spontaneous alloying of ultrasmall non-stoichiometric Ag–In–S and Cu–In–S quantum dots in aqueous colloidal solutions

The effect of spontaneous alloying of non-stoichiometric aqueous Ag–In–S (AIS) and Cu–In–S (CIS) quantum dots (QDs) stabilized by surface glutathione (GSH) complexes was observed spectroscopically due to the phenomenon of band bowing typical for the solid–solution Cu(Ag)–In–S (CAIS) QDs. The alloying was found to occur even at room temperature and can be accelerated by a thermal treatment of colloidal mixtures at around 90 °C with no appreciable differences in the average size observed between alloyed and original individual QDs. An equilibrium between QDs and molecular and clustered metal–GSH complexes, which can serve as “building material” for the new mixed CAIS QDs, during the spontaneous alloying is assumed to be responsible for this behavior of GSH-capped ternary QDs. The alloying effect is expected to be of a general character for different In-based ternary chalcogenides.

The effect of spontaneous alloying of aqueous glutathione-capped Ag–In–S and Cu–In–S quantum dots (QDs) into quaternary Cu(Ag)–In–S QDs is reported.     

Role of composition and texture on bifunctional catalytic performance of extruded Au–Cu alloys

The catalytic activity of Au₂Cu and AuCu samples for the electro-oxidation of CH₃OH and HCOOH, together with their structure and micro-hardness were investigated using various techniques. The addition of Cu can improve the micro-hardness of samples, which is ascribed to the solid solution strengthening effect. The Schmid factor and low angle grain boundary fraction confirm the difference of plastic deformation ability for samples, being consistent with hardness results. The Au–Cu samples exhibit good bifunctional catalytic performance due to the synergistic effect between Au and Cu. In addition, the Au₂Cu sample exhibits a higher catalytic activity than the AuCu sample, suggesting that appropriate preferred orientation plays a key role in the improvement of catalytic activities of Au based catalysts.

Extruded Au–Cu alloys can be used as bifunctional catalysts for the electro-oxidation of CH₃OH and HCOOH, and their catalytic activities can be improved based on alloying and appropriate texture.     

Fullerene–porphyrin hybrid nanoparticles that generate activated oxygen by photoirradiation

The preparation of water-dispersible hybrid nanoparticles comprising fullerene and porphyrin from cyclodextrin complexes is described. In the presence of polyethylene glycol, C₆₀ fullerene and porphyrin were expelled from the cyclodextrin cavity to form fullerene–porphyrin hybrid nanoparticles in water. The fullerene–porphyrin hybrid nanoparticles exhibit improved singlet oxygen generation ability under photoirradiation compared with that of C₆₀ nanoparticles.

Hybrid nanoparticles comprising fullerene and porphyrin are formed via guest exchange reaction of cyclodextrin complexes. The hybrid nanoparticles exhibit singlet oxygen generation ability under photoirradiation.

Water-dispersible colloidal fullerene assemblies, referred to as fullerene nanoparticles (NPs), have recently received increasing attention.^1–3 Fullerene NPs are negatively charged and can be dispersed in water in the absence of any solubilizer. Fullerene NPs demonstrate promise within biological and medical applications, as radical scavengers and photosensitizers for photodynamic therapy. To further extend the applications of fullerene NPs, additional hybridization with desired functional molecules is required. Porphyrin and associated derivatives are highly promising candidates for hybridization with fullerenes to increase photoactivity.⁴ Numerous studies on the complexation of fullerenes with porphyrin molecules using synthetic organic chemistry^5–7 or supramolecular chemistry^8–10 have been reported. Although fullerene NPs have been intensively studied over the last decade, no reliable method to achieve the hybridization of porphyrins with fullerene NPs has been proposed.Poly(ethylene glycol) monomethyl ether (PEG) was recently observed to accelerate the decomposition of fullerene C₆₀–γ-CD complexes in water, which leads to the rapid aggregation of C₆₀ to form water-dispersible C₆₀ NPs.¹¹ In this method, C₆₀–γ-CD complexes can exist as stable isolated molecules in water, enabling the precise size control and step-wise growth of C₆₀ NPs.^12,13 Herein, the preparation of hybrid NPs comprising C₆₀ and hydrophobic porphyrin molecules are reported. C₆₀–γ-CD and porphyrin-trimethyl-β-cyclodextrin (por–TMe-β-CD) complexes are mixed in water in the presence of PEG. Both complexes decompose through the interaction of PEG with the CDs, leading to the formation of C₆₀–porphyrin hybrid NPs (denoted as C₆₀–por NPs). The C₆₀–por NPs are negatively charged and easily disperse in water. Additionally, the ability of C₆₀–por NPs to generate activated oxygen is also evaluated.The C₆₀–γ-CD complex^14,15 and 1–TMe-β-CD complex (Fig. 1)^16–18 were prepared according to a previously described procedure (see the ESI^† for details). The ¹H NMR spectrum of the mixed solution comprising the C₆₀–γ-CD complex and PEG after 1 h incubation at 80 °C shows that the peaks attributed to the C₆₀–γ-CD complexes completely disappeared (Fig. S1^†). Hence, the ¹H NMR data confirm the decomposition of the C₆₀–γ-CD complexes and the formation of water-dispersible C₆₀ NPs, as previously reported.^11–13 The effect of PEG on 1–TMe-β-CD complexes was also investigated by ¹H-NMR as shown in Fig. S2.^† After incubating the mixed solution of 1–TMe-β-CD complex and PEG ([1] = 0.1 mM, [PEG] = 5.0 g L⁻¹) for 1 h at room temperature, peaks attributed to the 1–TMe-β-CD complex were still evident at 4.97 ppm and above 7.7 ppm (Fig. S2(i)^†). Hence, PEG has no influence upon the 1–TMe-β-CD structure at room temperature. Conversely, after incubating for 1 h at 80 °C, a dark purple precipitate formed and the aforementioned ¹H NMR peaks completely disappeared (Fig. S2(ii)^†). In the absence of PEG, the 1–TMe-β-CD complex was stable in water both at room temperature (Fig. S2(iii)^†) and 80 °C (Fig. S2(iv)^†). These results suggest a decomposition route of 1–TMe-β-CD by interaction with PEG at 80 °C, with a concomitant formation of non-dispersible large aggregates.Open in a separate windowFig. 1Chemical structures of porphyrin derivatives used in this study.To obtain hybrid NPs comprising C₆₀ and 1 (C₆₀–1 NPs), PEG (M_w = 2000) was added to an aqueous solution containing C₆₀–γ-CD and 1–TMe-β-CD complexes ([C₆₀] = [1] = 0.1 mM, [PEG] = 5.0 g L⁻¹), which were thereafter incubated at room temperature or 80 °C. The ¹H NMR spectrum of the mixed solution at room temperature shows peaks attributed to γ-CD in the C₆₀–γ-CD complex at 5.03 ppm, TMe-β-CD in the 1–TMe-β-CD complex at 4.97 ppm, and 1 in the 1–TMe-β-CD complex in the region of 7.6–8.5 ppm (Fig. 2a(i)). The data indicate that PEG fails to induce the decomposition of the C₆₀–γ-CD and 1–TMe-β-CD complexes at room temperature. Conversely, after the mixture was heated at 80 °C for 1 h, the peaks attributed to the C₆₀–γ-CD and 1–TMe-β-CD complexes completely disappeared (Fig. 2a(ii)). Hence, C₆₀–γ-CD and 1–TMe-β-CD were decomposed at 80 °C, in the presence of PEG. The solution after being subjected to heat treatment at 80 °C for 1 h, was dark purple in the absence of any precipitate. The hydrodynamic diameter and ζ-potential of the reacted solution were 125 nm (polydispersity index = 0.21) and −20.2 mV, respectively. Water dispersible fullerene NPs typically exhibit negative ζ-potentials, the origin of which still requires elucidating.^19,20 Hence, the formation of water-dispersible nano-composites, C₆₀–1 NPs, is suggested.Open in a separate windowFig. 2(a) ¹H NMR spectra of mixed solutions comprising fullerene C₆₀–γ-cyclodextrin (CD) and 1–trimethyl (TMe)-β-CD complexes ([C₆₀] = [1] = 0.1 mM) (i) before and (ii) after heating at 80 °C for 1 h, in the presence of polyethylene glycol (PEG) (5 g L⁻¹). Open circles: free γ-CD, filled circles: C₆₀–γ-CD, open diamonds: free TMe-β-CD, and filled diamonds: porphyrin–TMe-β-CD (por–TMe-β-CD) complex. The spectra at 7.6–8.5 ppm, are amplified five-fold. (b) Ultraviolet-visible (UV/Vis) absorption spectra of the mixed solution comprising C₆₀–γ-CD and 1–TMe-β-CD complexes ([C₆₀] = [1] = 0.1 mM) with PEG (5 g L⁻¹), before (dashed line) and after (solid line) heating at 80 °C for 1 h. (c) UV/Vis absorption spectra of the mixed solution comprising the C₆₀–γ-CD complex as a function of the 1–TMe-β-CD complex concentration ([C₆₀] = 0.1 mM, [1] = 0–0.2 mM) with PEG (5 g L⁻¹) after heating at 80 °C for 1 h.The por–TMe-β-CD complexes using 2–6 (Fig. 1), were also prepared adopting the same procedure as that for the 1–TMe-β-CD complex. Each por–TMe-β-CD complex solution was mixed with C₆₀–γ-CD and PEG ([C₆₀] = [por] = 0.1 mM, [PEG] = 5.0 g L⁻¹). The ¹H NMR spectrum of each individual mixed solution after being incubated for 1 h at 80 °C, is shown in Fig. S3.^† In the ¹H NMR spectrum of the mixture comprising C₆₀–γ-CD and 2–TMe-β-CD, the peaks attributed to these complexes at 5.03, 4.98, and 7.60–8.50 ppm, completely disappeared after being subjected to incubation for 1 h at 80 °C, without precipitation (Fig. S3a^†). Similar changes in the ¹H NMR spectrum of the mixture comprising C₆₀–γ-CD and 3–TMe-β-CD complexes are observed, as shown in Fig. S3b.^† The data suggest that the 2–TMe-β-CD and 3–TMe-β-CD complexes can be decomposed in a similar manner as the C₆₀–γ-CD complexes, and imply the formation of C₆₀–2 and C₆₀–3 NPs.The ¹H NMR spectra of the mixed solutions comprising C₆₀–γ-CD and 4, 5, or 6–TMe-β-CD complexes failed to show peaks attributed to the C₆₀–γ-CD complex, and peaks associated with the respective por–TMe-β-CD complexes were observed after incubation for 1 h at 80 °C (Fig. S3c–e,^† respectively). Hence, the data suggest that the C₆₀–γ-CD complex decomposed in the presence of PEG, and the 4, 5, and 6–TMe-β-CD complexes were observed to be stable without decomposition at 80 °C. There have been reports suggesting the strong interaction of water-soluble tetraphenyl porphyrins with TMe-β-CDs.^21,22 Polar substituents prompt the penetration of the polarized porphyrin rims into the TMe-β-CD cavity. Porphyrins 4–6 possess polar substituents, which are suggested to enable the formation of stable TMe-β-CD complexes. Furthermore, the size of the β-CD cavity is sufficiently narrow to prevent any strong interaction with PEG.²³ Thus, PEG-induced decomposition of the 4, 5, and 6–TMe-β-CD complexes is not possible.The absorption behavior of C₆₀–1 NPs was investigated using ultraviolet-visible (UV/Vis) spectroscopy. In the UV/Vis spectra, the characteristic peak of solvated C₆₀–γ-CD, at 333 nm shifted to 344 nm after heating at 80 °C for 1 h (Fig. 2b). An additional broad absorption at 400–550 nm is also apparent, which is characteristic of solid-state crystalline C₆₀ and arises from the electronic interactions between adjacent C₆₀ molecules.^24,25 The characteristic peak of the solvated 1–TMe-β-CD complex at 415 nm, shifted to 432 nm, with induced broadening after being subjected to heat treatment at 80 °C for 1 h (Fig. 2b). In the absence of C₆₀–γ-CD complexes, the characteristic absorption peak attributed to the solvated 1–TMe-β-CD complex completely disappeared after heating for 1 h at 80 °C, in the presence of PEG (Fig. S4^†). The data show that 1, when expelled from the TMe-β-CD cavities, forms non-dispersible precipitates in the absence of C₆₀. For 1 dispelled from the TMe-β-CD cavities to be stably dispersed in water, formation of co-aggregates with C₆₀ may be a prerequisite. C₆₀–2 and C₆₀–3 NPs also show similar UV-Vis absorption spectra after being subjected to heating at 80 °C for 1 h, as shown in Fig. S5a and b,^† respectively.To further elucidate the composite formation of C₆₀ and 1, the influence of 1 concentration on C₆₀–1 NP formation was investigated by UV/Vis spectroscopy (Fig. 2c). The intensity of the absorption peak at 432 nm increased as a function of 1 concentration from 0.05 to 0.1 mM. Conversely, the absorption peak at 345 nm, derived from the formation of fullerene NPs, shifted to 338 nm, with increasing concentration of 1. This absorption peak derives from the fullerene nanoparticle size, and as the size decreased (i.e., the NPs became smaller), the peak blue-shifted.¹¹ The results suggest that in the presence of 1, the fullerene interaction might be disturbed, or smaller C₆₀ NPs might form. For C₆₀–1 NPs formulated with 0.2 mM of 1 ([C₆₀] = 0.1 mM, [1] = 0.2 mM), the absorption peak derived from the Soret band of 1 split into two peaks (Fig. 2c). The absorption peak at the shorter wavelength of 415 nm is consistent with that of the 1–TMe-β-CD complex. The absorption peak at the longer wavelength of 431 nm is almost consistent with the absorption peaks in the UV/Vis spectra of C₆₀–1 NPs fabricated with 0.05 and 0.1 mM of 1. The findings indicate that in the sample comprising 0.2 mM of 1, a portion of the 1–TMe-β-CD complexes remained in the complex state after heating for 1 h at 80 °C, in the presence of PEG. The absorption peak at 338 nm, which reflects the state of fullerene NPs, is similar to that of C₆₀–1 NPs fabricated with 0.1 mM of 1. When C₆₀ and 1 form co-aggregated NPs, the ratio of 1 to C₆₀ is thought to be limited to ∼1 : 1.Morphological observations of the hybrid NPs were also undertaken. In the absence of the por–TMe-β-CD complex, C₆₀ NPs possessing fairly monodisperse size distributions were observed (Fig. S6a^†). The average diameter of the individual NPs, determined from the transmission electron microscopy (TEM) images, is 82 nm. C₆₀ NPs have been previously reported to exhibit lattice fringes and diffraction patterns, which suggests that C₆₀ NPs maintain the face-centered cubic (fcc) crystalline structure.¹¹ C₆₀–1 NPs prepared with 0.05 mM C₆₀ and 0.1 mM 1, possessed irregular shapes (Fig. 3a and b, respectively). The average diameter of C₆₀–1 NPs, determined by TEM, is 119 nm (Fig. 3a and S6b^†), demonstrating the larger C₆₀–1 NP size than that of the C₆₀ NPs (82 nm). Increasing the concentration of 1 to 0.1 mM results in the average diameter of C₆₀–1 NPs to increase to 131 nm (Fig. 3b and S6c^†). Similar morphology is observed from the TEM micrographs of C₆₀–2 and C₆₀–3 NPs having average diameters of 109 nm and 144 nm, respectively (Fig. 3c and d, respectively). A lower PEG molecular weight or a lower reaction temperature during C₆₀ NP formation via C₆₀–γ-CD complexes have been reported to induce an increase in the diameter of the C₆₀ NPs.^11,12 Thus, the findings suggest that slower reaction conditions result in less nucleation and a larger NP formation. Porphyrin 3 possesses a methoxy substituent at the para position of the phenyl group and is more polar than 1 or 2. Previous reports have demonstrated that the higher the polarity of the phenyl group, the more stable the complex with TMe-β-CD,^21,22 which indicates that 3–TMe-β-CD is more stable than 1– or 2–TMe-β-CD in water. Thus, the aforementioned decomposition, which results from the interaction with PEG, is slower in 3 with a concomitant increase in the NP size.Open in a separate windowFig. 3Transmission electron microscopy (TEM) images of C₆₀–1 nanoparticles (NPs) prepared with (a) 0.05 and (b) 0.1 mM of the 1–TMe-β-CD complex. TEM images of (c) C₆₀–2 and (d) C₆₀–3 NPs. Scale bars in images (a–d) are 100 nm. (e) High resolution TEM micrograph and selected-area electron diffraction pattern of C₆₀–1 NP. Scale bar is 10 nm. (f) ¹³C NMR spectra of (i) C₆₀ NPs and (ii) C₆₀–1 NPs. (g) Illustration of a C₆₀–por NP. A portion of C₆₀ form crystalline structures, while a portion of the porphyrin molecules interact with C₆₀ at the molecular level.In the high-resolution TEM micrograph (Fig. 3e), the C₆₀–1 NPs only exhibited partial lattice fringes, and hence did not show clear diffraction patterns compared with the C₆₀ NPs (inset in Fig. 3e).¹¹ The findings demonstrate the highly amorphous nature of the C₆₀–1 NPs, and that the C₆₀ crystal structure was only retained in part. ¹³C NMR spectra also provide important information about the structure of the C₆₀–1 NPs. A characteristic C₆₀ cluster signal at 142.4 ppm was detected in both C₆₀ NPs and C₆₀–1 NPs (Fig. 3f).²⁶ The C₆₀–1 NP dispersions also exhibited several small new signals at 141.5, 143.3, and 143.7 ppm, as shown in Fig. 3f(ii). When a fullerene and a porphyrin molecule form a stable complex in solution, the C₆₀ signal shifts depending on the interaction type between the fullerene and the porphyrin molecule.²⁷ Thus, the porphyrin molecule interacted with the aggregate of C₆₀ in C₆₀–1, as illustrated in Fig. 3g.Some porphyrin molecules can form a co-crystal with fullerene C₆₀.²⁸ To form a crystal structure, not only the interaction between molecules but also the relationship with the solvent, such as gradually changing the polarity of the solvent or removing the solvent, are important. In our system, porphyrin molecules that are pseudo-dissolved by TMe-β-CDs are added to water, which is a poor solvent for porphyrins, through the interaction of PEG with TMe-β-CDs. The porphyrin molecule should immediately aggregate and have difficulty forming a crystal structure. Furthermore, because water is also a poor solvent for fullerene C₆₀, C₆₀ also immediately aggregates in water. Thus, it should be extremely difficult for C₆₀ and porphyrin molecules to regularly associate to form a co-crystal structure.The concentration of singlet oxygen molecules (¹O₂, Type-II energy transfer pathway) generated by photoirradiation was measured according to a chemical method using 9,10-anthracenediyl-bis(methylene) dimalonic acid (ABDA)^15,29 as a marker to determine the biological activities of C₆₀ NPs, C₆₀–1 NPs, C₆₀–2 NPs, and C₆₀–3 NPs. The absorption of ABDA at the absorption maximum (380 nm) was monitored as a function of irradiation time ([C₆₀] = 0.1 mM, [por] = 0 or 0.1 mM). Under visible-light irradiation at wavelengths > 620 nm, C₆₀–1 NPs, C₆₀–2 NPs, and C₆₀–3 NPs generated higher levels of ¹O₂ than C₆₀ (Fig. 4a). These results show that the ¹O₂ photoproduction abilities of the C₆₀–por NPs were higher than that of the C₆₀ NPs. There are no significant differences in the ¹O₂ photoproduction abilities of C₆₀–1 NPs, C₆₀–2 NPs, and C₆₀–3 NPs, which suggests that the structure of the porphyrin has an insignificant influence on the ability of the hybrid NPs. The generation of formazan, via the reduction of nitroblue tetrazolium (NBT) by oxygen radicals (O₂˙⁻), is observed as an increase of absorption intensity at 560 nm.³⁰ The reduction of NBT by O₂˙⁻ was scarcely detected in solutions containing C₆₀–1 NPs, C₆₀–2 NPs, and C₆₀–3 NPs under photoirradiation, even though formazan was readily detected in the positive control sample in the presence of reduced nicotinamide adenine dinucleotide (NADH) (Fig. 4b). The results suggest that the reactive oxygen species produced by C₆₀–1 NPs, C₆₀–2 NPs, and C₆₀–3 NPs are predominantly ¹O₂ generated by a Type-II reaction.¹⁸Open in a separate windowFig. 4(a) ¹O₂ generation by NPs. Bleaching of 9,10-anthracenediyl-bis(methylene) dimalonic acid (ABDA) was monitored as a function of the decrease in the absorbance at 380 nm, for C₆₀ NPs (black circles and solid line), C₆₀–1 NPs (red circles and solid line), C₆₀–2 NPs (blue circles and solid line), and C₆₀–3 NPs (green circles and solid line) ([C₆₀] = 15 μM, [por] = 0 or 15 μM, [ABDA] = 25 μM). (b) O₂˙⁻ generation by NPs. The amount of formazan generated by the reduction of nitroblue tetrazolium (NBT) in the presence of O₂˙⁻ was analyzed by the absorbance at 560 nm, of C₆₀–1 NPs (red circles) and C₆₀–2 NPs (blue circles) in the absence (solid lines) and presence (dashed lines) of NADH ([C₆₀] = 15 μM, [por] = 15 μM, [NBT] = 200 μM, [NADH] = 0 or 625 μM). All samples were photoirradiated at >620 nm, in O₂-saturated aqueous solutions.In summary, the preparation of hybrid C₆₀–porphyrin NPs was achieved via a guest exchange reaction comprising porphyrin CD complexes and C₆₀. Seven C₆₀–por NP derivatives with various moieties were prepared. CD porphyrin complexes possessing phenyl and methoxyphenyl moieties were decomposed in the presence of PEG at the same time as C₆₀–γ-CD complexes and formed NPs with C₆₀. Porphyrins containing a hydrophilic moiety form stable complexes with TMe-β-CD and fail to co-aggregate with C₆₀. The C₆₀–por NPs are negatively charged and are easily dispersed and stable in water. The ¹O₂ generation ability of C₆₀–por NPs under photoirradiation (>620 nm) is greater than that of C₆₀ NPs. The findings herein demonstrate a new method to fabricate fullerene–porphyrin composite materials, which provides a route to highly functional fullerene-based materials.     

Enhanced photoelectrochemical biosensing performance for Au nanoparticle–polyaniline–TiO2 heterojunction composites

A new photoelectrochemical (PEC) sensing platform comprising TiO₂ nanotube arrays (TiONTAs), polyaniline (PANI), and gold nanoparticles (AuNPs) was successfully fabricated. After loading the enzyme, this Au–PANI–TiONTA electrode showed excellent response to glucose at a linear range of 2–36 mM with a 0.02 mM detection limit. Good PEC performance was obtained due to the following advantages of the material: high visible-light harvesting ability for excellent light trapping capacity of PANI and AuNPs, good separation of the photo-induced charges related to the specific Au–PANI–TiONTA heterostructure, efficient electrode surface reaction kinetics derived from the large specific surface area of TiONTAs and improved electrode catalytic activity. This work proposed a new and general PEC enzymatic format and can be extended to prepare different PEC biosensors for biomolecules such as DNA, proteins and substrates of oxidases.

A novel photoelectrode for glucose PEC biosensing composed of TiONTAs, PANI, and AuNPs was successfully obtained. The GOx@Au–PANI–TiONTA electrode exhibited a wide response range (2–36 mM) with a low detection limit (0.02 mM) and good stability.     

Enhanced thermal conductivity and tensile strength of Al–17Si–3.5Cu with SiC-nanoparticle addition

The morphology and size of primary Si has a significant influence on the thermal conductivity (TC) and strength of Al–17Si–3.5Cu. In this study, the effect of a 1–3 wt% SiC nanoparticle (SiC_nps) addition on TC and tensile strength of Al–17Si–3.5Cu was investigated. Nanoparticles distributed at the interface between primary Si and Al led to a significant refinement of primary Si; for example, a primary Si size of 2 μm with 3 wt% SiC_nps addition was achieved. TC of SiC_nps/Al–17Si–3.5Cu improved with an increase in nanoparticle content. Nanoparticles distributed at the interface between Si and Al reduced the interfacial thermal resistance. Thus, the effective TC of eutectic Si increased. Owing to the refinement of the primary Si and the increased interfacial thermal resistance, originating from the high content of SiC_nps at the interface, the effective TC of primary Si decreased. Compared with Al–17Si–3.5Cu, contribution to the improvement of the TC of SiC_nps/Al–17Si–3.5Cu resulted mainly from eutectic Si. Due to the refinement of primary Si, the tensile strength of SiC_nps/Al–17Si–3.5Cu improved with an increase in SiC_nps content. When the SiC_nps content was 3 wt%, the yield strength, ultimate tensile strength and elongation of SiC_nps/Al–17Si–3.5Cu were ∼176 MPa, 418 MPa and 7%, respectively, which were improved by 37.5%, 53.7% and 218%, respectively, when compared with Al–17Si–3.5Cu.

An interfacial nanocomposite layer was proposed to investigate the effect of SiC_nps on interfacial thermal resistance between Si and Al.     

Magnetic–plasmonic Ni@Au core–shell nanoparticle arrays and their SERS properties

In this paper, large-area magnetic–plasmonic Ni@Au core–shell nanoparticle arrays (NPAs) with tunable compositions were successfully fabricated by a direct laser interference ablation (DLIA) incorporated with thermal dewetting method. The magnetic properties of the Ni@Au core–shell NPAs were analyzed and the saturation magnetization (M_s) of the Ni₈₀@Au₂₀ nanoparticles was found to be higher than that of nickel-only nanoparticles with the same diameter. Using Rhodamine 6G (R6G) as a Raman reporter molecule, the surface enhanced Raman scattering (SERS) property of the Ni@Au core–shell NPAs with a grain size distribution of 48 ± 42 nm and a short-distance order of about 200 nm was examined. A SERS enhancement factor of 2.5 × 10⁶ was realized on the Ni₅₀@Au₅₀ NPA substrate, which was 9 times higher than that for Au nanoparticles with the same size distribution. This was due to the enhanced local surface plasmon resonance (LSPR) between the ferromagnetic Ni cores and the surface polariton of the Au shells of each nanoparticle. The fabrication of the Ni@Au core–shell NPAs with different compositions offers a new avenue to tailor the optical and magnetic properties of the nanostructured films for chemical and diagnostic applications.

In this paper, large-area magnetic–plasmonic Ni@Au core–shell nanoparticle arrays (NPAs) with tunable compositions were successfully fabricated by a direct laser interference ablation (DLIA) incorporated with thermal dewetting method.     

Cu–Ag alloy for engineering properties and applications based on the LSPR of metal nanoparticles

Efficient generation of high-energy hot carriers from the localized surface plasmon resonance (LSPR) of noble metal (Ag, Au and Cu) nanoparticles is fundamental to many applications based on LSPR, such as photovoltaics and photocatalysis. Theoretically, intra- and inter-band electron transitions in metal nanoparticles are two important channels for the non-radiative decay of LSPR, which determine the generation rate and energy of hot carriers. Therefore, on the basis of first-principles calculations and Drude theory, in this work we explore the potential role of alloying Ag with Cu in modulating the generation rate and energy of hot carriers by studying the intra- and inter-band electron transitions in Cu, Ag and Cu–Ag alloys. It is meaningful to find that the d-sp inter-band electron transition rates are notably increased in Cu–Ag alloys. In particular, the inter-band electron transition rates of Cu_0.5Ag_0.5 become larger than that of single Cu and Ag across the whole energy range between 1.5 and 3.2 eV. In contrast, intra-band electron transition rates of Cu–Ag alloys become smaller than that of single Cu and Ag. Because the intra-band electron transitions mainly contribute to the resistive loss in metals, which finally results in a thermal effect rather than high-energy hot carriers, the reduction of intra-band electron transitions in Cu–Ag alloy is beneficial for the transforming the energy absorbed by LSPR into high-energy hot carriers through other non-radiative channels. These results indicate that alloying of Ag and Cu can effectively improve the generation rates of high-energy hot carriers through the inter-band electron transition, but decrease the resistive loss through intra-band transition of electrons, which should be used as a guide in optimizing the non-radiative decay processes of LSPR.

Alloying Ag with Cu can effectively improve the generation rates of high-energy hot carriers.     

Modified graphene supported Ag–Cu NPs with enhanced bimetallic synergistic effect in oxidation and Chan–Lam coupling reactions

Herein, well dispersed Ag–Cu NPs supported on modified graphene have been synthesized via a facile and rapid approach using sodium borohydride as a reducing agent under ambient conditions. Dicyandiamide is selected as an effective nitrogen source with TiO₂ as an inorganic material to form two kinds of supports, labelled as TiO₂–NGO and NTiO₂–GO. Initially, the surface area analysis of these two support materials was carried out which indicated that N-doping of GO followed by anchoring with TiO₂ has produced support material of larger surface area. Using both types of supports, ten nano-metal catalysts based on Ag and Cu were synthesized. Benefiting from the bimetallic synergistic effect and larger specific surface area of TiO₂–NGO, Cu@Ag–TiO₂–NGO is found to be a highly active and reusable catalyst out of other synthesized catalysts. It exhibits excellent catalytic activity for oxidation of alcohols and hydrocarbons as well as Chan–Lam coupling reactions. The nanocatalyst is intensively characterized by BET, SEM, HR-TEM, ICP-AES, EDX, CHN, FT-IR, TGA, XRD and XPS.

Cu@Ag–TiO₂–NGO prepared from modified graphene by simple methodology exhibits enhanced catalytic activity towards oxidation and Chan–Lam coupling due to the synergistic effect between Ag and Cu NPs.     

Green synthesis of biocompatible core–shell (Au–Ag) and hybrid (Au–ZnO and Ag–ZnO) bimetallic nanoparticles and evaluation of their potential antibacterial,antidiabetic, antiglycation and anticancer activities

The fabrication of bimetallic nanoparticles (BNPs) using plant extracts is applauded since it is an environmentally and biologically safe method. In this research, Manilkara zapota leaf extract was utilized to bioreduce metal ions for the production of therapeutically important core–shell Au–Ag and hybrid (Au–ZnO and Ag–ZnO) BNPs. The phytochemical profiling of the leaf extract in terms of total phenolic and flavonoid content is attributed to its high free radical scavenging activity. FTIR data also supported the involvement of these phytochemicals (polyphenols, flavonoids, aromatic compounds and alkynes) in the synthesis of BNPs. Whereas, TEM and XRD showed the formation of small sized (16.57 nm) spherical shaped core–shell Au–Ag BNPs and ZnO nano-needles with spherical AuNPs (48.32 nm) and ZnO nano-rods with spherical AgNP (19.64 nm) hybrid BNPs. The biological activities of BNPs reinforced the fact that they show enhanced therapeutic efficacy as compared to their monometallic components. All BNPs showed comparable antibacterial activities as compared to standard tetracycline discs. While small sized Au–Ag BNPs were most effective in killing human hepato-cellular carcinoma cells (HepG2) in terms of lowest cell viability, highest intracellular ROS/RNS production, loss of mitochondrial membrane potential, induction of caspase-3 gene expression and enhanced caspase-3/7 activity. BNPs also effectively inhibited advanced glycation end products and carbohydrate digesting enzymes which can be used as a nano-medicine for aging and diabetes. The most important finding was the permissible biocompatibility of these BNPs towards brine shrimp larvae and human RBCs, which suggests their environmental and biological safety. This research study gives us insight into the promise of using a green route to synthesize commercially important BNPs with enhanced therapeutic efficacy as compared to conventional treatment options.

Graphical demonstartion of the Manikara zapota-mediated biosynthesis of Bimetallic nanoparticles (BNPs) and evalution of their biological activities.     

Synthesis of Ni–Ag–ZnO solid solution nanoparticles for photoreduction and antimicrobial applications

ZnO is one of the most promising and efficient semiconductor materials for various light-harvesting applications. Herein, we reported the tuning of optical properties of ZnO nanoparticles (NPs) by co-incorporation of Ni and Ag ions in the ZnO lattice. A sonochemical approach was used to synthesize pure ZnO NPs, Ni–ZnO, Ag–ZnO and Ag/Ni–ZnO with different concentrations of Ni and Ag (0.5%, 2%, 4%, 8%, and 15%) and Ni doped Ag–ZnO solid solutions with 0.25%, 0.5%, and 5% Ni ions. The as-synthesized Ni–Ag–ZnO solid solution NPs were characterized by powdered X-ray diffraction (pXRD), FT-IR spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), UV-vis (UV) spectroscopy, and photoluminescence (PL) spectroscopy. Ni–Ag co-incorporation into a ZnO lattice reduces charge recombination by inducing charge trap states between the valence and conduction bands of ZnO and interfacial transfer of electrons. The Ni doped Ag–ZnO solid solution NPs have shown superior 4-nitrophenol reduction compared to pure ZnO NPs which do not show this reaction. Furthermore, a methylene blue (MB) clock reaction was also performed. Antibacterial activity against E. coli and S. aureus has inhibited the growth pattern of both strains depending on the concentration of catalysts.

The synergic effect of Ni and Ag in Ni–Ag–ZnO solid solutions has tuned the optoelectronic properties of ZnO for photoreduction reactions.     

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

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

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

Zr–Cu alloy filler metal for brazing SiC ceramic

The Zr–Cu filler metal is mainly used for the joining of SiC ceramic as a nuclear fuel cladding material. The physical and chemical properties of the alloy, the interfacial reaction between the Zr–Cu filler metal and SiC ceramic, the residual stress of the SiC joint and the thermal neutron absorption cross section of the filler metal are considered during the design of the Zr–Cu filler metal. 80Zr–20Cu (wt%) is used as the filler metal in these experiments, showing good wettability and brazing properties with SiC ceramic.

The Zr–Cu filler metal is mainly used for the joining of SiC ceramic as a nuclear fuel cladding material.     

Biosynthesis of Ag–Pd bimetallic alloy nanoparticles through hydrolysis of cellulose triggered by silver sulfate

We report a simple but efficient biological route based on the hydrolysis of cellulose to synthesize Ag–Pd alloy nanoparticles (NPs) under hydrothermal conditions. X-ray powder diffraction, ultraviolet-visible spectroscopy and scanning transmission electron microscopy-energy dispersive X-ray analyses were used to study and demonstrate the alloy nature. The microscopy results showed that well-defined Ag–Pd alloy NPs of about 59.7 nm in size can be biosynthesized at 200 °C for 10 h. Fourier transform infrared spectroscopy indicated that, triggered by silver sulfate, cellulose was hydrolyzed into saccharides or aldehydes, which served as both reductants and stabilizers, and accounted for the formation of the well-defined Ag–Pd NPs. Moreover, the as-synthesized Ag–Pd nanoalloy showed high activity in the catalytic reduction of 4-nitrophenol by NaBH₄.

We report a simple but efficient biological route based on the hydrolysis of cellulose to synthesize Ag–Pd alloy nanoparticles (NPs) under hydrothermal conditions.     

Natural phosphate-supported Cu(ii), an efficient and recyclable catalyst for the synthesis of xanthene and 1,4-disubstituted-1,2,3-triazole derivatives

Cu(NO₃)₂ supported on natural phosphate, Cu(ii)/NP, was prepared by co-precipitation and applied as a heterogeneous catalyst for synthesizing xanthenes (2–3 h, 85–97%) through Knoevenagel–Michael cascade reaction of aromatic aldehydes with 1,3-cyclic diketones in ethanol under refluxing conditions. It was further used for regioselective synthesis of 1,4-disubstituted-1,2,3-triazoles (1–25 min, 95–99%) via a three-component reaction between organic halides, aromatic alkynes and sodium azide in methanol at room temperature. The proposed catalyst, Cu(ii)/NP, was characterized using X-ray fluorescence, X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, Brunauer–Emmett–Teller, Barrett–Joyner–Halenda and inductively coupled plasma analyses. Compared to other reports in literature, the reactions took place through a simple co-precipitation, having short reaction time (<3 hours), high reaction yield (>85%), and high recyclability of catalyst (>5 times) without significant decrease in the inherent property and selectivity of catalyst. The proposed protocols provided significant economic and environmental advantages.

Cu(NO₃)₂ supported on natural phosphate, Cu(ii)/NP, was prepared by co-precipitation and characterized. The Cu(ii)/NP catalyzed the synthesis of xanthenes and triazoles. The proposed protocols provided significant economic and environmental advantages.