Au Ag Alloy Nanoparticles Research Articles

Synthesis of gold-silver nanoalloys under microwave-assisted irradiation by deposition of silver on gold nanoclusters/triple helix glucan and antifungal activity

Polysaccharides are ideal green synthetic raw materials to improve the biocompatibility of metal nanoparticles. However, polysaccharides generally have weak reducibilities, being challenging supports for the direct preparation of Ag nanoparticles. In this work, gold nanoclusters were prepared using a triple helix glucan (Lentinan) via microwave-assisted synthesis and subsequently employed as seeds for the synthesis of a series of Ag-Au alloy nanoparticles (Ag-AuNPs). The results showed that gold nanoclusters can remarkably speed up the preparation of Ag-AuNPs without the addition of any other chemicals. The particle size of Ag-AuNPs increased at increasing Ag contents in the alloy. Results of UV–vis, transmission electron microscope (TEM) and inductively coupled plasma mass spectrometry (ICP-MS) suggested that Ag+ was quickly reduced to irregular silver nanoparticles (with gold nanoparticles as seeds), then gradually form more regular nano-alloys. Additionally, X-ray diffraction (XRD) and zeta potential results suggested that Ag-AuNPs could entrap the hydrophobic cavity of triple helix polysaccharides during the renaturation process. The nanocomposites exhibited good antifungal activity and low cytotoxicity to RAW264.7, Hela and LO2 cell lines in vitro.

Au–Ag alloy nanoparticles with tunable cavity for plasmon-enhanced photocatalytic H2 evolution

Au–Ag alloy nanoparticles with different cavity sizes have great potential for improving photocatalytic performance due to their tunable plasmon effect. In this study, galvanic replacement was combined with co-reduction with the reaction kinetics processes regulated to rapidly synthesize Au–Ag hollow alloy nanoparticles with tunable cavity sizes. The position of the localized surface plasmon resonance (LSPR) peak could be effectively adjusted between 490 nm and 713 nm by decreasing the cavity size of the Au–Ag hollow nanoparticles from 35 nm to 20 nm. The plasmon-enhanced photocatalytic H 2 evolution of alloy nanoparticles with different cavity sizes was investigated. Compared with pure P25 (TiO 2 ), intact and thin-shelled Au–Ag hollow nanoparticles (HNPs)-supported photocatalyst exhibited an increase in the photocatalytic H 2 evolution rate from 0.48 µmol h −1 to 4 µmol h −1 under full-spectrum irradiation. This improved photocatalytic performance was likely due to the plasmon-induced electromagnetic field effect, which caused strong photogenerated charge separation, rather than the generation of hot electrons. Au–Ag hollow alloy nanoparticles with tunable cavity sizes were constructed by regulating reaction kinetics processes and by combining galvanic replacement with co-reduction. This hollow alloy nanoparticle dramatically enhance the photocatalytic performance.

Target MicroRNA-Responsive DNA Hydrogel-Based Surface-Enhanced Raman Scattering Sensor Arrays for MicroRNA-Marked Cancer Screening.

On the basis of a target microRNA (miRNA)-responsive DNA hydrogel, a novel surface-enhanced Raman scattering (SERS) sensor array with nine sensor units that can detect multiple cancer-related miRNAs in one sample was developed. The target miRNA-responsive DNA hydrogel was first formed in each sensor unit to realize the construction of the DNA hydrogel-based SERS sensor array. Initially, because of the blocking of the streptavidin (SA)-modified sensor units by the formed DNA hydrogel, the SERS tags (biotin/4-mercaptobenzonitrile-functionalized AuAg alloy nanoparticles (B/M-AuAgNPs)) could not pass through the hydrogel and bind to the SA-modified sensor surface; thus, obvious Raman signals could not be observed. After the introduction of the target miRNA, DNA hydrogels of the corresponding sensor unit were disintegrated accordingly, and SERS tags were able to pass through the hydrogel to be captured onto the SA-modified detection surface, thus resulting in strong Raman signals and the detection of target miRNA. The assay is validated under clean buffer conditions as well as in serum. This target miRNA-responsive DNA hydrogel-based SERS sensor array has attractive application prospects in cancer typing via blood miRNA measurements.

Catalytic reduction of 4-nitrophenol using gold-silver alloy nanoparticles coated on alkali activated sand

Gold-Silver (Au-Ag) bimetallic alloy nanoparticles exhibit improved catalytic activity in comparison to the monometallic nanoparticles due to synergistic effect. In this work Au-Ag bimetallic alloy nanoparticles (BNPs) have been supported on alkali activated sand which acts as an inert support material, stabilizes the nanoparticles and prevents their agglomeration. In addition to providing high surface area for adsorption, sand is inexpensive and environmentally benign. Au-Ag alloy nanoparticles were prepared via co-reduction mechanism using polymer as a stabilising agent. Alkali activated sand was coated with the alloy nanoparticles using surface adsorption method. Efficient reduction of 4-Nitrophenol to 4-Aminophenol by NaBH4 in the presence of BNPs supported on alkali activated sand was investigated. Also, the heterogenous nature of the catalyst makes it highly reusable due to its effortless separation from the reaction medium.

Surface functionalization of ZnO:Ag columnar thin films with AgAu and AgPt bimetallic alloy nanoparticles as an efficient pathway for highly sensitive gas discrimination and early hazard detection in batteries

This work presents the impact of surface decoration on the VOC sensing properties of ZnO:Ag columnar films by AgPt and AgAu bimetallic alloy nanoparticles.

Instantaneous trace detection of nitro-explosives and mixtures with nanotextured silicon decorated with Ag–Au alloy nanoparticles using the SERS technique

The development of recyclable surface enhanced Raman scattering (SERS) based sensors has been in huge demand for trace level explosives detection. A simple, hybrid Silicon (Si) nanotextured target-based SERS platform is fabricated through patterning micro square arrays (MSA) on Si using femtosecond (fs) laser ablation technique at different fluences. Using the hybrid target Si MSA substrate loaded/decorated with Ag–Au alloy NPs (obtained using femtosecond ablation in liquids) we demonstrate the trace level detection of organic nitro-explosives [picric acid (PA), 2,4-dinitrotoluene (DNT), and 1, 3, 5-trinitroperhydro-1, 3, 5-triazine (RDX)] and their mixtures. The microstructures/nanostructures of MSA fabricated at an input fluence of 9.55 J/cm2, and decorated with Ag–Au alloy NPs, exhibited exceptional SERS enhancement factors (EFs) up to ∼1010 for MB, ∼106 for PA, and ∼104 for RDX with the detection limits obtained being ∼5 pM, ∼36 nM, and ∼400 nM for MB, PA and RDX respectively. Furthermore, we demonstrate these SERS substrates possess good reproducibility (RSD values < 15%) and a superior performance compared to a commercial Ag substrate (SERSitive, Poland). Three binary mixtures, i.e. MB-PA, MB-DNT, PA-DNT at different concentrations, were also investigated using the same SERS substrate to test the efficacy. Further, the SERS spectra of dyes, explosives, and complex mixtures were utilized for discrimination/classification using principal component analysis.

Zone-Specific Crystallization and a Porosity-Directed Scaling Marker for the Catalytic Efficacy of Au–Ag Alloy Nanoparticles

Bimetallic Au–Ag hollow nanoprisms (HNPrs) with variable effective surface areas, dynamic atomic compositions (Au:Ag), and distinct stepped surfaces between the central porous region and crystallin...

In Situ Synthesis of Mesoporous TiO2 Nanofibers Surface-Decorated with AuAg Alloy Nanoparticles Anchored by Heterojunction Exhibiting Enhanced Solar Active Photocatalysis.

We designed an electrospinning synthesis protocol to obtain in situ, the mesoporous TiO2 nanofibers, which are surface-decorated with plasmonic AuAg nanoparticles (AuAg-mTNF-H). Such alloy nanoparticles are found to be partially exposed on the surface of the nanofibers. Characterization by HRTEM and EDS confirmed the formation of 1:1 AuAg alloy nanoparticles on the surface of TiO2 nanofibers with heterojunction at the interfaces. On the basis of electron microscopic characterization, we proposed that, during the formation of the nanofibers, the incorporated metal ions with surface capping of negative charges migrated toward the outer surface of the nascent fibers under the influence of high positive voltage required for electrospinning. As a result, after the subsequent thermal treatment, the crystallization of TiO2 nanofibers and the formation of alloy nanoparticles took place, leading to the formation of a deep heterojunction through partial embedment of the nanoparticles. The formation of AuAg alloy also restricted the oxidation of Ag, thus making the nanoparticles highly stable in ambient condition. Accordingly, such unique AuAg-mTNF-H photocatalyst shows strong light absorption property covering the entire range of visible wavelengths with stability. The solar light harvesting property of AuAg-mTNF-H was verified by monitoring solar light induced H2 evolution via water splitting and photodecomposition of MB. In both the cases AuAg-mTNF-H showed excellent H2 evolution and photodecomposition of dye.

Synthesis of Au–Ag Alloy Nanoparticle-Incorporated AgBr Crystals

Nanoscale composites consisting of silver and silver halide (Ag–AgX, X = Cl, Br, I) have attracted much attention as a novel type of visible-light photocatalyst (the so-called plasmonic photocatalysts), for solar-to-chemical transformations. Support-free Au–Ag alloy nanoparticle-incorporated AgBr crystals (Au–Ag@AgBr) were synthesized by a photochemical method. At the initial step, Au ion-doped AgBr particles were prepared by adding an aqueous solution of AgNO3 to a mixed aqueous solution of KBr and HAuBr4. At the next step, UV-light illumination (λ = 365 nm) of a methanol suspension of the resulting solids yielded Au–Ag alloy nanoparticles with a mean size of approximately 5 nm in the micrometer-sized AgBr crystals. The mole percent of Au to all the Ag in Au–Ag@AgBr was controlled below &lt; 0.16 mol% by the HAuBr4 concentration in the first step. Finite-difference time-domain calculations indicated that the local electric field enhancement factor for the alloy nanoparticle drastically decreases with an increase in the Au content. Also, the peak of the localized surface plasmon resonance shifts towards longer wavelengths with increasing Au content. Au–Ag@AgBr is a highly promising plasmonic photocatalyst for sunlight-driven chemical transformations due to the compatibility of the high local electric field enhancement and sunlight harvesting efficiency.

Gold/silver bimetal nanoparticles incorporated graphitic carbon nitride nanohybrid materials for oxygen reduction reaction

A facile method for the preparation of bimetal AuAg (gold/silver) alloy nanoparticles (NPs) incorporated graphitic carbon nitride (g-C3N4) nanohybrids (NHs) materials embedded in Nafion matrix (Nf/g-C3N4/AuAg NHs) and its application towards electrocatalytic reduction of oxygen in alkaline medium are reported. The prepared Nf/g-C3N4/AuAg NHs were characterized by using X-ray diffraction (XRD), absorption spectroscopy, high resolution transmission electron spectroscopy (HRTEM), scanning electron microscopy-energy dispersive X-ray spectrophotometer (SEM-EDX), SEM-EDX elemental mapping, SEM-EDX lines scan spectra and cyclic voltammetry (CV) techniques. The absorption spectra of Nf/g-C3N4/AuAg NHs showed the characteristic surface plasmon resonance (SPR) absorption band for AuAg alloy NPs and was found in between the wavelength regions of the monometal NPs (Au and Ag NPs). The bimetal alloy formation was confirmed from the observation of single SPR absorption band and further a blue shifting in the SPR band was observed with increasing Ag content in the g-C3N4/AuAg NHs. The HRTEM images explicitly demonstrated the formation of Au, Ag and alloy AuAg NPs on g-C3N4 surface where the size of the bimetal AuAg NPs are found to be smaller than the corresponding monometals (Au and Ag NPs). The electrochemical characteristics of bimetal AuAg NPs at the Nf/g-C3N4/Au, Nf/g-C3N4/Ag and Nf/g-C3N4/AuAg NHs modified electrodes were studied using cyclic voltammetry. The combination of Nf/g-C3N4 and bimetal AuAg alloy NPs enhanced the electrocatalytic oxygen reduction reaction at the modified electrode. The GC/Nf/g-C3N4/Au75Ag25 modified electrode showed the highest catalytic current among the other controlled NHs materials towards the electrocatalytic oxygen reduction in alkaline medium. The Koutecky-Levich (K-L) plots obtained from the modified RDE studies showed four-electron transfer of oxygen reduction reaction (ORR) at the GC/Nf/g-C3N4/Au75Ag25 modified electrode.

Au-Ag alloy/porous-SiO2 core/shell nanoparticle-based surface-enhanced Raman scattering nanoprobe for ratiometric imaging analysis of nitric oxide in living cells

2 In this paper, we developed a novel surface-enhanced Raman scattering (SERS) nanoprobe via the assembly of 3,4-diaminobenzene-thiol on the surface of porous SiO2-coated Au-Ag alloy nanoparticles and successfully applied this for ratiometric imaging analysis of NO in living cells. This nanoprobe exhibits excellent biocompatibility and chemical stability, superior SERS enhancement capacity, and good signal reproducibility. To the best of our knowledge, this is the first report of a porous SiO2-coated Au-Ag alloy nanoparticle and ratiometric-based SERS nanosensor to be used for the detection of NO in living cells.

Green synthesis of Au–Ag alloy nanoparticles using Lysimachia christinae polysaccharide and its application for reducing CO in cigarette mainstream smoke

An environmentally friendly and facile method for the synthesis of small-sized Au–Ag alloy nanoparticles is proposed. The method involves the coreduction of HAuCl4 and AgNO3 using Lysimachia christinae polysaccharide as reductant and stabiliser at 85°C. The synthesised alloy nanoparticles with a mean diameter of 3.81 nm are stable in solution due to the stabilising effect of the polysaccharide. Furthermore, Au–Ag nanoparticles have first been introduced into cigarette filter to serve as a synergistic catalyst for reducing CO in mainstream smoke.

Catalytic Hydrogenation of Acetone to Isopropanol on Bimetallic Silver-Gold Nanocatalyst

Silver-gold alloy catalyst for ketones hydrogenation in liquid-phase using NaBH4 as hydrogen source is reported. AgAu alloy nanoparticles are synthesized from common inorganic precursors and mild experimental conditions. To favour the dispersion of the sample in the mixed-aqueous reaction solution a ligand exchange with citric acid was promoted. This citric acid modified AgAu catalyst, thanks to the synergistic effect of Au and Ag, allows for the selective hydrogenation of ketones with to maximum isopropanol yields of 99.7 % within 8 min and shows an excellent reusability after 7 run.

Enhancement of photothermal conversion performance using nanofluids based on bimetallic Ag-Au alloys in nitrogen-doped graphitic polyhedrons

The working fluids with higher solar thermal conversion performance within broadband spectrum ranges are of great concern for direct absorption solar collectors (DASCs). Both metal nanoparticles with localized surface plasmon resonance (LSPR) effects and carbon nanomaterials have unique spectral absorption behaviors and have shown better photothermal performance in DASCs. In this paper, we attempted to prepare composite nanofluids including plasmonic bimetallic alloy and carbon nanomaterials to realize enhanced solar absorption and photothermal conversion performance. By taking ZIF-8-derived nitrogen-doped graphitic polyhedrons (ZNGs) as carrier, plasmonic bimetallic Ag-Au alloy nanoparticles were loaded on them by an impregnation-reduction method successfully. Ag-Au/ZNGs ethylene glycol nanofluids showed significant broadband absorption in the visible and near-infrared spectrum range at a lower concentration. Comparing to ethylene glycol, the photothermal conversion effeiency of all ZNGs nanofluids increased remarkablely. Plasmonic bimetallic Ag-Au alloy nanoparticles further improved the photothermal conversion efficiency, which was up to 74.35% for Ag-Au ZNGs nanofluids compared with 72.41%, 70.35% for Au/ZNGs, Ag/ZNGs respectively. This work presents a new way to enhance solar energy absorption and improve solar thermal conversion efficiency of nanofluids for DASCs.

تحضیرمتراكبات Au/Ag النانویة بواسطة التبخر الانفجاري للیزرالنبضي في الماء واستخدامها في السيطرة على فعالية انزيم AIP في دم الانسان

تم الحصول على محاليل مائيه غرويه عالقه لمتراكبات الفضة والذهب النانوية بأستخدام طريقة التبخر الانفجاري لقطع معدنية فائقة النقاوة من الذهب والفضة المغموره في ماء لاأيوني ثنائي التقطير وبأستخدام طولين موجيين 1064nm,532nmمن ليزر الياك النبضي بطاقة 100-900mj)). طيف الامتصاص لرنين البلازموني تم الحصول علية بأستخدام مطياف الاشعة المرئية-فوق البنفسجية دعمت النتائج باستخدام تقنية الاشعة السينية والمجهر الالكتروني النافذ. اظهرت اطياف الامتصاص الاشعة المرئية-فوق البنفسجية قمة حادة لكل معدن (400nm)للفضة (525nm) للذهب واظهرت الفحوصات تولد جسيمات نانوية تراوحت قياسها من (5-45nm) للفضة و(8-55nm)للذهب و(10-170nm)للمتراكب فضة- ذهب وبشكل عام بينت الفحوصات بأن الجسيمات النانوية اخذت الشكل الكروي وهيئة بلورية تدعى المكعب مركزي الوجة يعرف ب .(fcc). ان هذا العمل يمثل دراسة تأثير عدد نبضات الليزرعلى خواص سبائك الذهب والفضة النانوية وكذلك دراسة التأثير البايولوجي لهذه السبائك على فعالية انزيم الالكالاين فوسفاتيزفي دم الانسان.

Correlation between the work function of Au–Ag nanoalloys and their electrocatalytic activity in carbon dioxide reduction

The electrocatalytic reduction of carbon dioxide (CO2) on Au–Ag bimetallic alloy nanoparticles was scrutinized. This system provides a good model to investigate the correlation between the electrocatalytic activity and the composition of the nanoparticles. The CO Faradaic efficiency (and thus the forming CO:H2 ratio) was changed linearly by controlling the Au:Ag ratio in the alloy. This trend was attributed to the changes in the electronic properties, as there was a monotonous shift in the Fermi level away from the vacuum level with increasing Au content. This shift correspondingly reduces the binding energy of the intermediates (*COOH and *CO), resulting in the gradually enhanced CO2-reduction activity. Finally, comparison of the catalytic activity of Ag@Au core–shell particles to that of pure Ag (which bears similar electronic properties), and to Au–Ag alloy nanoparticles (with similar bulk composition), emphasized the importance of both geometric and electronic effects on the CO2 reduction activity.

One-step gamma radiation aided diffusion of Ag-Au alloy nanoparticles into polycarbonate and its application towards the reduction of 4-Nitrophenol

One-step gamma radiation aided method was adopted to synthesize face centre cubic structured Silver-Gold alloy nanoparticles (Ag-AuNPs) having particle size ∼10 nm and simultaneously diffused into Polycarbonate (PC). The depth of diffusion of Ag-AuNPs in PC was found to be 93 nm at a dose of 600 kGy. A broad peak around 492 nm in absorbance spectra was due to the surface plasmon resonance of Ag-AuNPs. X-ray Photoelectron spectroscopic results showed blue shift in Au 4f and Ag 3d peaks indicating the possible interaction of Ag-AuNPs with PC. The Ag-AuNPs diffused PC showed enhancement in catalytic reduction activity due to more adsorption and effective electron transfer from Ag-AuNPs to 4-Nitrophenol.

Bimetallic Nanoparticles Supported on Cr2O3 Microspheres As Heterogeneous Photocatalysts for Light-Induced Alcohol Oxidation

The development of environmentally benign photocatalytic processes with high reaction rate and high selectivity has always been a significant challenge. Plasmonic metal nanoparticles have been promising light-driven photocatalysts in chemical transformations due to their localized surface plasmon resonance (LSPR). In this study, bimetallic catalysts with various loadings and Ag/Au ratios supported on Cr2O3 microspheres were synthesized and evaluated as heterogeneous photocatalysts for benzyl alcohol oxidation under monochromatic 532 nm laser irradiation. Au and Ag nanoparticles were uniformly decorated on Cr2O3 microspheres by deposition precipitation and wet impregnation method respectively. The optical and physical properties of the as-prepared photocatalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-Ray spectroscopy (EDX), diffuse reflectance spectroscopy (DRS), X-Ray diffraction (XRD) and RAMAN spectroscopy. The bimetallic Ag-Au-Cr2O3 catalysts presented an enhanced photocatalytic activity compared to monometallic catalysts. It should be noted that the enhanced photocatalytic activity was dependent on Ag-Au ratio. Specifically, 0.5 wt.% Ag - 3 wt.% Au /Cr2O3 photocatalyst showed the highest photocatalytic activity, achieving up to 91.2% conversion and 98.5 % selectivity of the targeted benzaldehyde. The remarkable photocatalytic performance over bimetallic nanoparticles can be ascribed to the synergistic effect of Ag-Au alloy nanoparticles under visible light irradiation. Phototelectrochemical tests were performed to further evaluate the role of plasmon mediated charge transfer in the activity of bimetallic nanoparticles.

Nanocomposite thin films based on Au-Ag nanoparticles embedded in a CuO matrix for localized surface plasmon resonance sensing

Nanocomposite thin films, composed of monometallic Au and Ag, and bimetallic AuAg nanoparticles, dispersed in a CuO matrix were prepared, characterised and tested for Localized Surface Plasmon Resonance (LSPR) sensing. The films were deposited by reactive magnetron sputtering, followed by a post-deposition thermal annealing to modify the size and shape of the nanoparticles distribution within the oxide matrix. Regarding the main results of the monometallic systems, the Au:CuO films showed LSPR bands from 800 nm to 650 nm, which reveal a progressive narrowing and a continuous blue-shift with increasing temperature (400–700 °C). The Ag:CuO films evidenced plasmonic bands at about 400 nm for temperatures of 500 °C and above. The bimetallic system, Au-Ag:CuO, showed LSPR bands in the range between those of the corresponding monometallic systems, due to the presence of Ag enriched AuAg alloy nanoparticles, taking part of Janus-like structures in some cases. In terms of LSPR sensing, Au:CuO films revealed the highest values of refractive index sensitivity since the nanoparticles are more exposed to the surrounding environment.

Cyclic Voltammetry Characterization of Au, Pd, and AuPd Nanoparticles Supported on Different Carbon Nanofibers

Three types of carbon nanofibers (pyrolytically stripped carbon nanofibers (PS), low-temperature heat treated carbon nanofibers (LHT), and high-temperature heat treated carbon nanofibers (HHT)) with different graphitization degrees and surface chemistry have been used as support for Au, Pd, or bimetallic AuPd alloy nanoparticles (NPs). The carbon supports have been characterized using Raman, X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV). Moreover, the morphology of the metal nanoparticles was investigated using transmission electron microscopy (TEM) and CV. The different properties of the carbon-based supports (particularly the graphitization degree) yield different electrochemical behaviors, in terms of potential window widths and electrocatalytic effects. Comparing the electrochemical behavior of monometallic Au and Pd and bimetallic AuPd, it is possible to observe the interaction of the two metals when alloyed. Moreover, we demonstrate that carbon surface has a strong effect on the electrochemical stability of AuPd nanoparticles. By tuning the Au-Pd nanoparticles’ morphology and modulating the surface chemistry of the carbon support, it is possible to obtain materials characterized by novel electrochemical properties. This aspect makes them good candidates to be conveniently applied in different fields.