Noble Metal Nanoparticles Research Articles

A Facile Microwave-Promoted Formation of Highly Photoresponsive Au-Decorated TiO2 Nanorods for the Enhanced Photo-Degradation of Methylene Blue

The integration of noble metal nanoparticles (NPs) effectively modifies the electronic properties of semiconductor photocatalysts, leading to improved charge separation and enhanced photocatalytic performance. TiO2 nanorods decorated with Au NPs were successfully synthesized using a cost-effective, rapid microwave-assisted method in H2O2 and HF media for methylene blue (MB) degradation under visible light illumination. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 physisorption, and UV–vis spectroscopy were employed to characterize the structures, morphologies, compositions, and photoelectronic properties of the as-synthesized materials. The fusing of Au NPs effectively alters the electronic structure of TiO2, enhancing the charge separation efficiency and improved electrical conductivity. The HF treatment promotes the exposure of the highly reactive (001) and (101) crystalline facets. The improved photocatalytic activity of Au/TiO2, achieving 97% efficiency, is attributed to the surface plasmon resonance (SPR) effect of the Au NPs and the presence of oxygen vacancies. The photodegradation of MB using the TiO2/Au photocatalysts follows pseudo-first-order kinetics, highlighting the enhanced catalytic efficiency of the synthesized nanostructures. The exceptional properties of the binary Au/TiO2 photocatalysts, including the SPR effect, exposed crystallographic faces, and efficient charge carrier separation through a decrease in the recombination of electrons and holes, contribute to the photocatalytic degradation of MB.

Unique features of plasmonic absorption in ultrafine metal nanoparticles: unity and rivalry of volumetric compression and spill-out effect

Abstract We present a solution to a longstanding challenge in nanoplasmonics and colloid chemistry: the anomalous optical absorption of noble metal nanoparticles in the ultrafine size range of 2.5–10 nm, characterized by a rapid long-wavelength shift in plasmon resonance as the particle size increases. Our investigation delves into the impact of alterations in electron density along the radial direction of nanoparticles and the resulting variations in dielectric constants on the spectral positioning of the plasmon resonance. We explore the interplay of the spill-out effect, volumetric compression, and their combined impact in different experimental conditions on electron density variation within the particle volume and its blurring at the particle boundary. The latter effectively forms a surface layer with altered dielectric constants and a size-independent extent. As particle size decreases, the influence of the surface layer becomes more pronounced, especially when its extent is comparable to the particle radius. These findings are specific to ultrafine plasmonic nanoparticles and highlight their unique properties.

Opinion: Smart nanofertilizers for growth enhancement and stress resilience in agriculture

Smart nanofertilizers (NFs) represent a promising frontier in agricultural technology, offering precise nutrient delivery and stress resilience to enhance crop growth and productivity while minimizing the environmental impact. This opinion article explores the potential of smart NFs in revolutionizing traditional fertilization practices and addressing the challenges facing modern agriculture. By harnessing the unique properties of nanomaterials, smart NFs including noble metal nanoparticles, green NFs, and novel NFs from industrial waste enable targeted nutrient delivery, enhanced nutrient use efficiency, and stress tolerance in plants. However, their widespread adoption faces regulatory, safety, and scalability challenges that require interdisciplinary collaboration and concerted efforts from stakeholders. Despite these hurdles, smart NFs hold immense promise for promoting sustainable agriculture and ensuring food security in frequently changing global climatic conditions.

Synthesis of concave Au NRs-Pt-CdS plasmonic photocatalyst with efficient hydrogen production rate

Light-driven water photolysis for hydrogen (H2) generation has been proven to be exceptionally efficient in the field of energy transformation. Nevertheless, the practical applications of many single-component semiconductors still suffer from a relatively low energy conversion efficiency. In this work, concave gold nanorods (Au NRs) with three plasmon resonance modes were synthesized using a one-step method in an aqueous solution. Pt nanoparticles and CdS nanocrystals were rational grown onto Au NRs to design the plasmonic photocatalysts with specific morphology and structure characteristic. Photocatalytic test indicated that concave Au NRs-Pt-CdS hetero-nanostructure possess efficient H2 production rate under visible and near-infrared regions. These findings offer a blueprint for creating a novel group of hetero-nanostructures that combine faceted noble metal nanoparticles with semiconductor materials, demonstrating promise for applications across fields such as photocatalysis and energy storage.

Electronic effect in bromide-modified noble metal catalysts promotes highly stable and selective hydrogenation

Halides with strong affiliation to metals are traditionally viewed as positions in heterogeneous catalysis. This study introduces a method to enhance the selective hydrogenation performance of noble metal nanoparticle catalysts (Pd, Pt, and Rh hosted on N-doped carbon, SiO2, and Al2O3) by gas-phase bromination with 1-bromooctane. Brominated Pd catalysts, particularly those supported on N-doped carbon, show significant improvements in total butene selectivity and stability in butadiene hydrogenation reactions, displaying >97.5 % selectivity to total butenes at complete conversion with 50 h stable performance even at excessive H2 (H2:butadiene = 50) and a high temperature of 473 K. Comprehensive characterizations coupled with density functional theory calculations reveal that bromide species enhance selective hydrogenation by preferentially adsorbing at stepped Pd sites, altering reaction kinetics and preventing over-hydrogenation. Bromination influences reactant and intermediate adsorption, leading to increased competitive adsorption compared to pristine catalysts. Chemisorption studies on butadiene and 1-butene support altered kinetic behaviors post-bromination. X-ray photoelectron spectroscopy analysis demonstrate an increase in surface Pdδ+ species, owing to the electron-pulling character of nearby adsorbed bromide. In situ diffuse reflection infrared Fourier transform spectroscopy with CO probe molecules confirms Br species adsorption at unsaturated Pd sites. Overall, the study provides an effective approach to tuning the electronic properties of metal catalysts and highlights the positive impact of bromination on improving the hydrogenation performance.

Design, Synthesis, and Evaluation of Noble Metal Nanoparticles and In Situ-Decorated Carbon-Supported Nanoparticle Electrocatalysts Using Hypergolic Reactions

Design, Synthesis, and Evaluation of Noble Metal Nanoparticles and In Situ-Decorated Carbon-Supported Nanoparticle Electrocatalysts Using Hypergolic Reactions

Metal nanoparticles encapsulation within multi-shell spongy-core porous microspheres for efficient tandem catalysis

The “one-pot” cascade process involves multiple catalytic conversions followed by a single workup stage. This method has the capability to optimize catalytic efficiency by reducing chemical processes. The key to achieving cascade reactions lies in designing cascade catalysts with well-dispersed, stably immobilized, and accessible noble metal nanoparticles for multiple catalytic conversions. This work presents a strategy for creating long-lasting cascade catalysts by encapsulating Ru and Pd nanoparticles within multi-shell spongy-core porous microspheres (MS-SC-PMs). This cascade catalyst strategy enables the continuous hydrogenation of nitrobenzene to aniline and further to cyclohexylamine, demonstrating both high selectivity and conversion rates. Notably, this approach overcomes the typical challenges associated with noble metal nanoparticles, such as poor stability and recyclability, as it maintains its performance over ten consecutive cycles. Additionally, the MS-SC-PMs have the versatility to encapsulate various metal nanoparticles, providing catalytic versatility, scalability, and a promising avenue for designing long-lasting catalysts loaded with nanoparticles.

High-performance SERS substrate based on gold nanoparticles-decorated micro/nano-hybrid hierarchical structure

Owing to its excellent localized surface plasmon resonance (LSPR) effect, noble metal nanoparticles (NPs) find extensive application in the preparation of surface-enhanced Raman scattering (SERS) substrates. However, due to process limitations, the practicality and testing effectiveness of SERS substrates still leaves much to be desired. Here, a wafer-scale gold (Au) NPs silicon (Si) micro/nano-hybrid structured substrate is prepared. This is achieved through two-step etching, followed by decorating Au-NPs onto the structure via self-assembly process induced by de-wetting. Finite-difference time-domain (FDTD) simulations reveal that the significant enhancement of local electric field in the voids between Au-NPs and Si is crucial for enhancing SERS. Using Rhodamine 6G (R6G) as the probe molecule, performance of the fabricated SERS substrate is investigated. It demonstrates a minimum detection limit of 10−11 M, with a calculated enhancement factor of 4.40 × 108, indicating its high sensitivity. The minimum relative standard deviation for the substrate is 5.254 %. After 20 days of placement, the SERS performance show tiny variation. Even after four cycles of cleaning experiments, it still maintains outstanding SERS performance. This demonstrates its excellent stability, uniformity and reusability. Our research provides guidance for the efficient and low-cost fabrication of high-performance SERS substrates.

Interaction between Molnupiravir and noble metal substrates in SERS detection: A DFT method and Raman characteristic study

Molnupiravir, a nucleoside analogue (EIDD-2801), is an RNA polymerase inhibitor that effectively treats infections caused by novel coronaviruses and can be administered orally. Therefore, it is necessary to monitor the distribution of Molnupiravir in vivo after oral administration. Surface-enhanced Raman spectroscopy (SERS) is a suitable detection method, so it is necessary to understand the interaction between Molnupiravir and noble metal nanoparticles in the SERS effect. Therefore, we used density functional theory combined with surface-enhanced Raman spectroscopy to investigate the interaction between Molnupiravir and noble metal/composite nanoparticles in the SERS effect. To study the interaction sites of Molnupiravir and the substrate in the SERS effect, the molecular electrostatic potential (MEP) of Molnupiravir was calculated. Considering the significant role of binding energy in studying molecular docking, the binding energy between Molnupiravir and Metal6 (Au6, Ag6, Au3Ag3) atomic clusters was calculated. The calculated results of the frontier orbitals and relevant molecular parameters of Molnupiravir and Molnupiravir-Metal6 complexes reveal the changes in the molecular properties of Molnupiravir in the SERS effect. Finally, the theoretical Raman spectra differences between Molnupiravir and complexes were compared and analyzed, and the adsorption structure of Molnupiravir on the substrate surface was determined based on the surface selection rules of SERS. The research results will provide insights into the interaction between Molnupiravir and the substrate in the SERS effect, and also offer theoretical support for the application of SERS methods in biomedical detection.

Cyanobacterial Silver Nanoparticles and Their Potential Utility-Recent Progress and Prospects: A Review.

The current situation involves an increase in interest in nanotechnology, in particular the ways in which it can be applied in the commercial and medical fields. However, traditional methods of synthesizing nanoparticles have some drawbacks, including the generation of harmful byproducts, high energy consumption, and cost. As a result, researchers have shifted their focus to "green" nanoparticle synthesis to circumvent these drawbacks. Because of their exceptional physiochemical properties, silver nanoparticles (Ag Nps) are the noble metal nanoparticles that are used most frequently. The green approach to Ag NP synthesis is environmentally friendly, non-toxic, and cost-effective, and it makes use of a variety of biological entities. Cyanobacteria, in particular, have garnered the most attention because of the abundance of bioactive substances that they contain, which serve both as reducing agents and as stabilizing agents during the process of biosynthesis. This review article discusses the current state of cyanobacteria-mediated Ag NP synthesis, the potential mechanisms that are involved, nanoparticle characterization, the various applications of Ag NP in different fields, and their prospects.

Fast tailoring the ZIF-8 surface microenvironment at ambient temperature to boost glucose oxidase-like activity of AuNPs for biosensing

Rational design and tailoring of the surface microenvironment surrounding the catalytic sites, such as noble metal nanoparticles, is an effective way to enhance the catalytic activity of mimicking enzymes. However, it remains on-going challenges to regulate the microenvironment of the catalytic sites due to the lack of tunable variability in structural precision of conventional solid catalysts. Herein, three types of zeolitic imidazolate framework-8 (ZIF-8) with different major crystal facet orientations, i.e., cubic with (100) facets (denoted ZIF-8c), truncated dodecahedral with (100), (110) facets (denoted ZIF-8tr), and dodecahedral with (110) facets (denoted ZIF-8r), were developed facilely using an electrochemical method by switching the potential at ambient temperature. Because the Zn2+ nodes were predominantly exposed on the (100) facets of ZIF-8, while the ligands were mainly exposed on the (110) facets. Hence, gold nanoparticles (AuNPs) showed differential glucose oxidase (GOx)-like activities when anchored in situ on different crystal facets of ZIF-8 and obeyed the following order ZIF-8c/Au>ZIF-8tr/Au>ZIF-8r/Au. Notably, both the metal nodes and aromatic linkers of ZIF-8 interacted with AuNPs through coordination and π-π interactions. The Zn2+ nodes facilitated the formation of the electron-deficient Au species. The electron transfer from AuNPs to Zn2+ sites effectively boosted the catalytic activity. It was known that directly tailoring the microenvironment at the supporting sites of noble metal catalysts to boost catalysis through a facile electrochemical method was not reported. Based on the favorable GOx-like activity and long-term stability of ZIF-8tr/Au, a highly sensitive electrochemical biosensing platform for assaying squamous cell carcinoma antigen (SCCA) was developed. It enabled fg-level detection of cancer marker.

Gold Nanoparticles Decoration of Zinc Oxide Nanowalls on Flexible Substrates

Metal oxide nanostructures decorated with noble metal nanoparticles are hybrid structures with a special interface that combines the unique properties of those two materials. Noble metal nanoparticles exhibit useful catalytic properties, and they can be functionalized with biomaterials. In this work, we use gold nanoparticles that can be functionalized using thiolated molecules bound to the metal surface. Zinc oxide nano-walls (NWs) are a high surface-to-volume ratio wide-bandgap semiconductor nanostructures that, due to their biocompatibility and non-toxicity characteristics, can be used in biosensing applications that involve contact with tissues and cells. ZnO nano-walls can be deposited from aqueous solutions at low temperatures, both on rigid and flexible substrates, using a simple and low-cost process that can be upscaled to high-volume production. In this work, we study the nucleation and growth of the ZnO nano-walls and we describe the gold nanoparticles decoration at three different schemes of surface functionalization. Among these schemes, we found that the process where ZnO nano-walls were deposited on polyimide substrates followed by activation using a self-assembled monolayer, resulted in a decoration with uniform size and distribution of gold nano-particles. That process was studied as a function of the growth temperature, solution concentration, and time. The morphology of the ZnO nano-walls was studied by Scanning Electron microscope imaging and the crystal structure was studied by X-ray diffraction.

Effect of surface charge on laser-produced silver nanoparticles for dye reduction and surface-enhanced Raman spectroscopy

Silver nanoparticles (Ag NPs) are widely used in biological, chemical, and physical fields due to their distinct properties. However, the effect of surfactants with different polarities on the catalytic and surface-enhanced Raman spectroscopy (SERS) performance of Ag NPs has not been thoroughly studied. Here, we tailor the surface charge of laser-synthesized Ag NP without changing their morphology and investigate their catalytic and SERS capabilities. The surfactant-free silver nanoparticles (NPBare), synthesized via pulsed laser ablation in liquid (PLAL), are subsequently coated with ionic surfactants sodium dodecyl sulfate (NPSDS) and cetyltrimethylammonium bromide (NPCTAB). The synthesis and morphology of Ag NPs are confirmed using UV-Vis absorption spectroscopy and scanning electron microscopy. The surface charge of fabricated NPs is determined using zeta potential (ZP) measurements. The ZP values of NPBare, NPSDS, and NPCTAB are determined to be -17 mV, 28.7 mV, and 5.58 mV, respectively. The catalytic activity of bare and coated Ag NPs was tested against the cationic and anionic dyes, Methylene blue (MB) and Methyl orange (MO) respectively. The reduction rate of both dyes was highest when using NPBare. However, in the case of coated nanoparticles, the rate of MB and MO reduction depends on the difference between the ZP of the dye and nanoparticles: the rate of reduction increases with the difference between the zeta potentials of the dye and coated nanoparticles increases. The SERS capability of bare and coated NPs was evaluated for anionic (MO) and cationic (MB, Rhodamine B, and Crystal Violet) dyes. The SERS intensity of dyes strongly enhanced with the increase in ZP difference between the dye molecules and NPs. Surface charge modified NPs shown excellent SERS sensitivity with detection limit up to nanomolar for dye molecules as well as the homogeneity of NPs demonstrated in Raman mapping results with relative standard deviation of 17%. The results suggest that the electrostatic interaction between the nanoparticles and dye molecules plays a dominant role in SERS enhancement. These findings highlight the significance of surface charge in improving the catalytic and sensing properties of noble metal nanoparticles.

Suppressed recombination of a flexible TiO2 nanowires photoanode by coupling of plasmonic Ag nanoparticles in the photoelectrochemical ultraviolet photodetector

The noble metal nanoparticles can improve the efficiency of photoelectric conversion via enhancement of light harvesting for the localized surface plasmon resonance (LSPR) effect. Here, TiO2 nanowires were constructed on carbon fiber cloth as a flexible photoanode for photoelectrochemical (PEC) ultraviolet (UV) photodetector. By decorated noble metal Ag nanoparticles on TiO2 nanowires, the photocurrent was improved from 35.9 μA cm−2 to 268.4 μA cm−2, and the rise and decay time were increased by 0.14 s and 0.12 s, respectively. Moreover, the recombination of photon-generated electrons and holes was also decreased in photoanode due to the Schottky barrier between Ag and TiO2. This work provided an approach to promote the performances of the PEC UV photodetector.

Fabrication of sandwich nanostructured substrates with Au@Ag NCs/Graphene/AgMP for ultrasensitive SERS detection

This paper presents the design of a bottom-up "sandwich" configuration substrate via electrostatic self-assembly. A silver microplate (AgMP) serves as the stable structural base, onto which monolayer graphene is wet-transferred. Au@Ag nanocubes (Au@Ag NCs) are then assembled on the upper layer through liquid-liquid three-phase self-assembly, forming a Au@AgNCs/G/AgMP “sandwich” substrate. The combination of electromagnetic enhancement from noble metal nanoparticles and chemical enhancement from graphene synergistically amplifies the signal of detected molecules, leading to significant Surface-Enhanced Raman Scattering (SERS) enhancement. Experimental results demonstrate that this substrate can detect Rhodamine 6 G (R6G) at concentrations as low as 10–12 M and Crystal Violet (CV) at 10–9 M. Moreover, the substrate can detect Aspartame (APM) at concentrations as low as 0.0625 g/L, well below the typical daily intake levels for humans. These findings indicate that the substrate exhibits excellent SERS performance and holds significant potential for broad applications.

Controlling size and distribution of Au nano-particles on C3N4 for high-efficiency photocatalytic hydrogen production.

With advantages such as low cost, high stability, and ease of production, visible light photocatalytic C3N4 with a unique microscopic layered structure holds significant potential for development. However, its hydrogen production efficiency remains low due to the pronounced recombination of photo-generated charge carriers and limited surface reaction sites. Normally, the photocatalytic performance of C3N4 can be enhanced by loading noble metals with surface plasmon resonance. It is worth noting that the size of noble metal nanoparticles has a great influence on photocatalytic performance. In this study, accurate controlling of the size and distribution of Au nanoparticles was achieved on the surface of C3N4 by introducing amino groups to improve photocatalytic performance. Results show that uniformly distributed Au nanoparticles in the range of 2-6nm can be obtained on C3N4 with a remarkable enhancement of hydrogen production efficiency, which is about 114 times the property of pure C3N4. The small-sized and uniformly distributed Au nanoparticles can provide more reaction sites and increase the separation of photo-generated charge carriers, in turn improving Au/NH3-C3N4 photocatalytic hydrogen release rate to 6.85 mmol g-1h-1. This work offers a facile way to enhance photocatalytic performance by controlling the size of metal nanoparticles on C3N4 precisely.

Pentatwinned AuAg Nanorattles with Tailored Plasmonic Properties for Near-Infrared Applications.

Noble metal nanoparticles, particularly gold and silver nanoparticles, have garnered significant attention due to their ability to manipulate light at the nanoscale through their localized surface plasmon resonance (LSPR). While their LSPRs below 1100 nm were extensively exploited in a wide range of applications, their potential in the near-infrared (NIR) region, crucial for optical communication and sensing, remains relatively underexplored. One primary reason is likely the limited strategies available to obtain highly stable plasmonic nanoparticles with tailored optical properties in the NIR region. Herein, we synthesized AuAg nanorattles (NRTs) with tailored and narrow plasmonic responses ranging from 1000 to 3000 nm. Additionally, we performed comprehensive characterization, employing advanced electron microscopy and various spectroscopic techniques, coupled with finite difference time domain (FDTD) simulations, to elucidate their optical properties. Notably, we unveiled the main external and internal LSPR modes by combining electron energy-loss spectroscopy (EELS) with surface-enhanced Raman scattering (SERS). Furthermore, we demonstrated through surface-enhanced infrared absorption spectroscopy (SEIRA) that the NRTs can significantly enhance the infrared signals of a model molecule. This study not only reports the synthesis of plasmonic NRTs with tunable LSPRs over the entire NIR range but also demonstrates their potential for NIR sensing and optical communication.

Photon avalanche effect and spectral control of single LiYF4:Yb3+/Pr3+microparticle

Photon avalanche is a special phenomenon of upconversion that the luminescence emission intensity exhibits a significant nonlinear response to the excitation power. Traditional photon avalanche is typically observed in bulk materials, which is not enough to meet requirements of modern techniques as it expect smaller in size and stronger in signal response. In this study, photon avalanche effect is obtained from single LiYF4: Yb3+/Pr3+ microparticle. The emission intensity demonstrates a 16-order nonlinear coefficient with excitation intensity change under 835 nm laser excitation. By utilizing the plasmonic effect of noble metal nanoparticles, we successfully modulate the photon avalanche of the particle. Obvious reduction in the threshold of photon avalanche is detected when plasmonic gold nanorods are assembled to the surface of LiYF4: Yb3+/Pr3+ microparticle.

Ag@ZIF-8 core-shell nanocomposites as sensitive and stable SERS substrates: Synthesis, optimization, and application in pollutant detection

Although surface-enhanced Raman scattering (SERS) is a powerful spectral analysis technique, its practical application is restricted due to the poor chemical stability of some noble metal nanoparticles. In this work, Ag@ZIF-8 nanocomposites with different ZIF-8 core-shell thicknesses were prepared by coating AgNP surfaces with polyvinylpyrrolidone and adjusting the dosage of zinc nitrate and 2-methylimidazole. Several characterizations have confirmed that the Ag@ZIF-8 nanocomposites was successfully prepared. Based on transmission electron microscopy images and SERS spectral intensity, it was determined that Ag@ZIF-8 nanocomposites with a ZIF-8 shell thickness of 30 nm exhibited optimal SERS performance. As a result of evaluating the uniformity and stability of the composite with 4-ATP as the probe molecule, it showed a relative standard deviation of 6.91 % and a decrease in SERS intensity of 4.5 % after 28 days. Based on the results obtained with Ag@ZIF-8 nanocomposites as the SERS substrate, the detection limits of 4-mercaptopyridine and thiram were as low as 5.87×10−9 M and 6.61×10−8 M, respectively. Furthermore, the finite-difference time-domain simulation reveals an enhancement factor of 2.6×106, which is in good agreement with the experimental value of 1.8×106, confirming its effectiveness as a SERS substrate.

Strong Electronic Metal-Support Interactions Enable the Increased Spin State of Co-N4 Active Sites and Performance for Acidic Oxygen Reduction Reaction.

Nonprecious metal catalysts, particularly M-N-C catalysts, are widely recognized as promising contenders for the oxygen reduction reaction (ORR). However, a notable performance gap persists between M-N-C catalysts and Pt-based catalysts under acidic conditions. In this study, hybrid catalysts comprising single Co atoms and ultralow concentrations of Pt3Co intermetallic nanoparticles (NPs) are introduced to enhance ORR performance. Under acidic conditions, these hybrid catalysts demonstrate ORR efficiency with a half-wave potential of 0.895 V, negligible decay even after 80 000 cycles, and a high maximum power density of 1.34 W cm-2 in fuel cells. This performance surpasses those of Co-N-C and Pt/Co-N-C catalysts. Both experimental findings and theoretical computations suggest that the heightened ORR activity stems from an increase in the spin density of Co sites induced by noble metal NPs, facilitating the activation of O-O bonds via side-on overlapping and enabling a transition in the reaction pathway from associative to dissociative processes. This research offers a promising avenue for the systematic design of M-N-C cathodes with an enhanced performance for acidic fuel cells.