Bioinspired synthesis of multifunctional, highly stable polymeric templated silver-silica colloids as catalytic and antibacterial coatings for paper

In this paper, a simple, bottom up, bioinspired technique is proposed for the synthesis of highly stable colloids of silica supported spherical silver nanoparticles (SiO2@Ag) that act as efficient catalytic and antimicrobial coatings for an organic substrate, filter paper. The core - shell structure and the highly branched dendritic polymer, poly(ethylene)imine, enabled the precise control of growth rate and morphology of silica and silver nanoparticles. The polymer also enabled the deposition of these nanoparticles onto an organic substrate, filter paper, through immersion by modifying its surface. The catalytic and antibacterial properties of these samples were assessed. The results obtained from this analysis showed a complete degradation of an aqueous pollutant, 4-nitrophenol, for 6 successive catalytic cycles without intermediate purification steps. Furthermore, the polymeric silica-silver suspension proved to express antibacterial activity against both Gram-positive and Gram-negative bacteria (Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa). The antibacterial properties were evaluated according to the disk diffusion method, whereas the Minimum Inhibitory Concentration was also determined. The samples were examined by Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray diffraction analysis, z-potential analysis, Fourier Transform Infrared Spectroscopy and Ultraviolet-visible Spectroscopy.

SERS detection of surface-adsorbent toxic substances of microplastics based on gold nanoparticles and surface acoustic waves

Microplastics adsorb toxic substances and act as a transport medium. When microplastics adsorbed with toxic substances accumulate in the body, the microplastics and the adsorbed toxic substances can cause serious diseases, such as cancer. This work aimed to develop a surface-enhanced Raman spectroscopy (SERS) detection method for surface-adsorbent toxic substances by forming gold nanogaps on microplastics using surface acoustic waves (SAWs). Polystyrene microparticles (PSMPs; 1 μm) and polycyclic aromatic hydrocarbons (PAHs), including pyrene, anthracene, and fluorene, were selected as microplastics and toxic substances, respectively. Gold nanoparticles (AuNPs; 50 nm) were used as a SERS agent. The Raman characteristic peaks of the PAHs adsorbed on the surface of PSMPs were detected, and the SERS intensity and logarithm of the concentrations of pyrene, anthracene, and fluorene showed a linear relationship (R2 = 0.98), and the limits of detection were 95, 168, and 195 nM, respectively. Each PAH was detected on the surface of PSMPs, which were adsorbed with toxic substances in a mixture of three PAHs, indicating that the technique can be used to elucidate mixtures of toxic substances. The proposed SERS detection method based on SAWs could sense toxic substances that were surface-adsorbed on microplastics and can be utilized to monitor or track pollutants in aquatic environments.

Synthesis and Antimicrobial Activity of 3D Micro-Nanostructured Diatom Biosilica Coated by Epitaxially Growing Ag-AgCl Hybrid Nanoparticles

The 3D (three-dimensional) micro-nanostructured diatom biosilica obtained from cultivated diatoms was used as a support to immobilize epitaxially growing AgCl-Ag hybrid nanoparticles ((Ag-AgCl)NPs) for the synthesis of nanocomposites with antimicrobial properties. The prepared composites that contained epitaxially grown (Ag-AgCl)NPs were investigated in terms of their morphological and structural characteristics, elemental and mineral composition, crystalline forms, zeta potential, and photoluminescence properties using a variety of instrumental methods including SEM (scanning electron microscopy), TEM (transmission electron microscopy), EDX (energy-dispersive X-ray spectroscopy), XRD (X-ray powder diffraction), zeta-potential measurement, and photoluminescence spectroscopy. The content of (AgCl-Ag)NPs in the hybrid composites amounted to 4.6 mg/g and 8.4 mg/g with AgClNPs/AgNPs ratios as a percentage of 86/14 and 51/49, respectively. Hybrid nanoparticles were evenly dispersed with a dominant size of 5 to 25 nm in composite with an amount of 8.4 mg/g of silver. The average size of the nanoparticles was 7.5 nm; also, there were nanoparticles with a size of 1-2 nm and particles that were 20-40 nm. The synthesis of (Ag-AgCl)NPs and their potential mechanism were studied. The MIC (the minimum inhibitory concentration method) approach was used to investigate the antimicrobial activity against microorganisms Klebsiella pneumoniae, Escherichia coli, and Staphylococcus aureus. The nanocomposites containing (Ag-AgCl)NPs and natural diatom biosilica showed resistance to bacterial strains from the American Type Cultures Collection and clinical isolates (diabetic foot infection and wound isolates).

Insights into the Synthesis and Kinetics of Silver-on-Silica Core-Shell Particles

In this study, a heterogeneous nucleation and growth model has been developed to explore the formation mechanism of silver-deposited silica core-shell particles based on the reaction kinetics. To validate the core-shell model, the time-dependent experimental data were quantitatively examined and in situ reduction, nucleation, and growth rates were estimated by optimizing the concentration profiles of reactants and deposited silver particles. Using this model, we also attempted to predict the change in the surface area and diameter of core-shell particles. The concentration of the reducing agent, metal precursor, and reaction temperature were found to have a strong influence on the rate constants and morphology of core-shell particles. Higher rates of nucleation and growth often produced thick, asymmetric patches that covered the entire surface, whereas lower rates produced sparsely deposited silver particles with a spherical shape. The result revealed that by simply tuning the process parameters and controlling the relative rates, the morphology of deposited silver particles and the surface coverage can be controlled while retaining the spherical shape of the core. The present study aims to offer comprehensive data pertaining to the nucleation, growth, and coalescence processes of core-shell nanostructures which will aid in the development and understanding of the principles that govern the formation of nanoparticle-coated materials.

Multi-Wavelength-Recognizable Memristive Devices via Surface Plasmon Resonance Effect for Color Visual System

Photoelectric memristor has attracted many attentions thanks to their promising potential in optical communication chips and artificial vision systems. However, the implementation of an artificial visual system based on memristive devices remains a considerable challenge because most photoelectric memristors cannot recognize color. Herein, multi-wavelength recognizable memristive devices based on silver(Ag) nanoparticles (NPs) and porous silicon oxide (SiO_x ) nanocomposites are presented. Rely on the effects of localized surface plasmon resonance (LSPR) and optical excitation of Ag NPs in SiO_x , the set voltage of the device can be gradually reduced. Moreover, the current overshoot problem is alleviated to suppress conducting filament overgrowth after visible light irradiation with different wavelengths, resulting in diverse low resistance states (LRS). Taking advantage of the characteristics of controlled switching voltage and LRS resistance distribution, color image recognition is finally realized in the present work. X-ray photoelectron spectroscopy (XPS) and conductive atomic force microscopy (C-AFM) show that the light irradiation plays an important role on resistive switching (RS) process: the photo-assisted Ag ionization leads to a significant reduction of set voltage and overshoot current. This work provides an effective method toward the development of multi-wavelength-recognizable memristive devices for future artificial color vision system.

Halogen ions modified Ag NPs for ultrasensitive SERS detection of Polycyclic aromatic hydrocarbons

Rapid ultrasensitive detection of trace polycyclic aromatic hydrocarbons (PAHs) is essential and significant for pollution control due to their hazard, persistence, and the wide distribution in the environment. Therefore, rapid detection of PAHs is critical for controlling pollution and protecting the ecology. Considering the advantages of Surface-enhanced Raman spectroscopy (SERS), a simple and reliable SERS method was proposed for detecting PAHs in water in this work. Three chemicals, namely NaCl, KBr, and KI, were chosen to modify Ag NPs for phenanthrene (Phe) detection, and Ag NPs modified with KBr (Ag-BrNPs) show the best SERS response. The mixing sequence and the concentration of KBr were optimized. The addition order of mixing KBr and Ag NPs before Phe solution is best, and the optimal concentration of KBr was 20 mM. Under the optimal condition, the limit of quantification for Phe, pyrene (Pyr), and anthracene (Ant) were 10^-6 M, 10^-7 M, and 10^-7 M, respectively. Mixed PAHs (Phe, Pyr, and Ant) in spiked water samples have been identified and quantified successfully. The proposed method has good application prospects in environmental pollution monitoring.

Green Synthesis of Silver-Decorated Magnetic Particles for Efficient and Reusable Antimicrobial Activity

Metal and metal hybrid nanostructures have shown tremendous application in the biomedical and catalytic fields because of their plasmonic and catalytic properties. Here, a green and clean method was employed for the synthesis of silver nanoparticle (Ag NP)-SiO₂-Fe₂O₃ hybrid microstructures, and biomolecules from green tea extracts were used for constructing the hybrid structures. The SiO₂-Fe₂O₃ structures were synthesized using an ethanolic green tea leaf extract to form Bio-SiO₂-Fe₂O₃ (BSiO₂-Fe₂O₃) structures. Biochemical studies demonstrated the presence of green tea biomolecules in the BSiO₂ layer. Reduction of the silver ions was performed by a BSiO₂ layer to form Ag NPs of 5–10 nm in diameter in and on the BSiO₂-Fe₂O₃ microstructure. The reduction process was observed within 600 s, which is faster than that reported elsewhere. The antimicrobial activity of the Ag-BSiO₂-Fe₂O₃ hybrid structure was demonstrated against Staphylococcus aureus and Escherichia coli, and the nanostructures were further visualized using confocal laser scanning microscopy (CLSM). The magnetic properties of the Ag-BSiO₂-Fe₂O₃ hybrid structure were used for studying reusable antimicrobial activity. Thus, in this study, we provide a novel green route for the construction of a biomolecule-entrapped SiO₂-Fe₂O₃ structure and their use for the ultra-fast formation of Ag NPs to form antimicrobial active multifunctional hybrid structures.

Effect of Graphene Characteristics on Morphology and Performance of Composite Noble Metal-Reduced Graphene Oxide SERS Substrate

Graphene/noble metal substrates for surface enhanced RAMAN scattering (SERS) possess synergistically improved performance, due to the strong chemical enhancement mechanism accounted to graphene and the electromagnetic mechanism raised from the metal nanoparticles. However, only the effect of noble metal nanoparticles characteristics on the SERS performance was studied so far. In attempts to bring a light to the effect of quality of graphene, in this work, two different graphene oxides were selected, slightly oxidized GOS (20%) with low aspect ratio (1000) and highly oxidized (50%) GOG with high aspect ratio (14,000). GO and precursors for noble metal nanoparticles (NP) simultaneous were reduced, resulting in rGO decorated with AgNPs and AuNPs. The graphene characteristics affected the size, shape, and packing of nanoparticles. The oxygen functionalities actuated as nucleation sites for AgNPs, thus GOG was decorated with higher number and smaller size AgNPs than GOS. Oppositely, AuNPs preferred bare graphene surface, thus GOS was covered with smaller size, densely packed nanoparticles, resulting in the best SERS performance. Fluorescein in concentration of 10^-7 M was detected with enhancement factor of 82 × 10⁴. This work demonstrates that selection of graphene is additional tool toward powerful SERS substrates.

Decoration of SiO2 and Fe3O4 Nanoparticles onto the Surface of MWCNT-Grafted Glass Fibers: A Simple Approach for the Creation of Binary Nanoparticle Hierarchical and Multifunctional Composite Interphases

We report on a versatile method for chemically grafting multiwalled carbon nanotubes (MWCNTs) onto the surface of conventional glass fibers (GFs), as well as depositing further silica (SiO2) or superparamagnetic (SPM) magnetite (Fe3O4) nanoparticles (NPs) creating novel hierarchical reinforcements. The CNT-grafted GFs (GF-CNT) were utilized further as the support to decorate nano-sized SiO2 or Fe3O4 via electrostatic interactions, resulting finally into double hierarchy reinforcements. SiO2 NPs were first used as model nano-particulate objects to investigate the interfacial adhesion properties of binary coated GFs (denoted as GF-CNT/SiO2) in epoxy matrix via single fiber pull-out (SFPO) tests. The results indicated that the apparent interfacial shear strength (IFSS or τapp) was significantly increased compared to the GF-CNT. Fe3O4 NPs were assembled also onto CNT-grafted GFs resulting into GF-CNT/Fe3O4. The fibers exhibited a magnetic response upon being exposed to an external magnet. Scanning electron microscopy (SEM) revealed the surface morphologies of the different hierarchical fibers fabricated in this work. The interphase microstructure of GF-CNT and GF-CNT/SiO2 embedded in epoxy was investigated by transmission electron microscopy (TEM). The hybrid and hierarchical GFs are promising multifunctional reinforcements with appr. 85% increase of the IFSS as compared to typical amino-silane modified GFs. It could be envisaged that, among other purposes, GF-CNT/Fe3O4 could be potentially recyclable reinforcements, especially when embedded in thermoplastic polymer matrices.

Three-Dimensional Printed Polylactic Acid (PLA) Surgical Retractors with Sonochemically Immobilized Silver Nanoparticles: The Next Generation of Low-Cost Antimicrobial Surgery Equipment

A versatile method is reported for the manufacturing of antimicrobial (AM) surgery equipment utilising fused deposition modelling (FDM), three-dimensional (3D) printing and sonochemistry thin-film deposition technology. A surgical retractor was replicated from a commercial polylactic acid (PLA) thermoplastic filament, while a thin layer of silver (Ag) nanoparticles (NPs) was developed via a simple and scalable sonochemical deposition method. The PLA retractor covered with Ag NPs (PLA@Ag) exhibited vigorous AM properties examined by a reduction in Staphylococcus aureus (S. aureus), Pseudomonas aeruginosa (P. aeruginosa) and Escherichia coli (E. coli) bacteria viability (%) experiments at 30, 60 and 120 min duration of contact (p < 0.05). Scanning electron microscopy (SEM) showed the surface morphology of bare PLA and PLA@Ag retractor, revealing a homogeneous and full surface coverage of Ag NPs. X-Ray diffraction (XRD) analysis indicated the crystallinity of Ag nanocoating. Ultraviolent-visible (UV-vis) spectroscopy and transmission electron microscopy (TEM) highlighted the AgNP plasmonic optical responses and average particle size of 31.08 ± 6.68 nm. TEM images of the PLA@Ag crossection demonstrated the thickness of the deposited Ag nanolayer, as well as an observed tendency of AgNPs to penetrate though the outer surface of PLA. The combination of 3D printing and sonochemistry technology could open new avenues in the manufacturing of low-cost and on-demand antimicrobial surgery equipment.

Highly Efficient Mesoporous Core-Shell Structured Ag@SiO2 Nanosphere as an Environmentally Friendly Catalyst for Hydrogenation of Nitrobenzene

The size-uniformed mesoporous Ag@SiO₂ nanospheres’ catalysts were prepared in one-pot step via reducing AgNO₃ by different types of aldehyde, which could control the size of Ag@SiO₂ NPs and exhibit excellent catalytic activity for the hydrogenation of nitrobenzene. The results showed that the Ag core size, monitored by different aldehydes with different reducing abilities, together with the ideal monodisperse core-shell mesoporous structure, was quite important to affect its superior catalytic performances. Moreover, the stability of Ag fixed in the core during reaction for 6 h under 2.0 MPa, 140 °C made this type of Ag@SiO₂ catalyst separable and environmentally friendly compared with those conventional homogeneous catalysts and metal NPs catalysts. The best catalyst with smaller Ag cores was prepared by strong reducing agents such as CH₂O. The conversion of nitrobenzene can reach 99.9%, the selectivity was 100% and the catalyst maintained its activity after several cycles, and thus, it is a useful novel candidate for the production of aniline.

One-step controllable synthesis of three-dimensional WO3 hierarchical architectures with different morphologies decorated with silver nanoparticles: enhancing the photocatalytic activity

Hierarchical architecture self-assembled three-dimensional WO₃ and WO₃·Ag with high uniformity have been successfully obtained using peroxopolytungstic acid as precursor and silver in a morphological engineering approach under moderate hydrothermal conditions.

A magnetic SERS immunosensor for highly sensitive and selective detection of human carboxylesterase 1 in human serum samples

Hepatocellular carcinoma (HCC) is a common and lethal cancer. New serum markers for detecting HCC are urgently needed. Human carboxylesterase 1 (hCE1) is an important member of the serine hydrolase superfamily and is closely related to the occurrence of HCC. It can be used as a good serum marker for early diagnosis of HCC. Here, we developed a surface enhanced Raman scattering (SERS)- based magnetic immunosensor that specifically recognizes and detects trace amounts of hCE1 in human serum via a sandwich structure consisting of a SERS tags, magnetic supporting substrates, and target antigen (hCE1). The SERS tags are 4-mercaptobenzoic acid (4-MBA)-labeled AgNPs, and the SERS supporting substrates are composed of a raspberry-like morphology of Fe₃O₄@SiO₂@AgNPs magnetic nanocomposites surface-functionalized with a hCE1 antibody. The prepared SERS magnetic immunosensor exhibits excellent selectivity and extremely high sensitivity for hCE1 detection. The SERS signal and logarithm of hCE1 concentration presented a wide linear response range of 0.1 ng mL^-1 to 1.0 mg mL^-1, and the detection limit of hCE1 was 0.1 ng mL^-1. The results indicate that the immunosensor can be used for the rapid determination of hCE1 in human serum without a complicated sample pre-treatment. Furthermore, the immunosensor has good reproducibility and stability, and has a promising prospect for the quantitative detection of other tumor markers in early clinical diagnosis.

Temperature-Controlled Catalysis by Core-Shell-Satellite AuAg@pNIPAM@Ag Hybrid Microgels: A Highly Efficient Catalytic Thermoresponsive Nanoreactor

A novel wet-chemical protocol is reported for the synthesis of "temperature-programmable" catalytic colloids consisting of bimetallic core@shell AuAg nanoparticles encapsulated into poly(N-isopropylacrylamide) (pNIPAM) microgels with silver satellites (AgSTs) incorporated within the microgel structure. Spherical AuNPs of 50 nm in diameter are initially synthesized and used for growing a pNIPAM microgel shell with temperature stimulus response. A silver shell is subsequently grown on the Au core by diffusing Ag salt through the hydrophilic pNIPAM microgel (AuAg@pNIPAM microgel). The use of allylamine as a co-monomer during pNIPAM polymerization facilitates the coordination of Ag⁺ with the NH₂ nitrogen lone pair of electrons, which are reduced to Ag seeds (∼14 nm) using a strong reducing agent, obtaining thus AuAg@pNIPAM@Ag hybrid microgels. The two systems are tested as catalysts toward the reduction of 4-nitrophenol (4-Nip) to 4-aminophenol (4-Amp) by NaBH₄. Both exhibit extremely sensitive temperature-dependent reaction rate constants, with the highest K₁ value of the order of 0.6 L/m² s, which is one of the highest values ever reported. The presence of plasmonic entities is confirmed by UV-vis spectroscopy. Dynamic light scattering proves the temperature responsiveness in all cases. Transmission electron microscopy and energy-dispersive X-ray (EDX) elemental mapping highlight the monodispersity of the synthesized hybrid nanostructured microgels, as well as their size and metallic composition. The amount of gold and silver in both systems is obtained by thermogravimetric analysis and the EDX spectrum. The reduction reaction kinetics is monitored by UV-vis spectroscopy at different temperatures for both catalytic systems, with the AuAg@pNIPAM@Ag microgels showing superior catalytic performance at all temperatures because of the synergistic effect of the AuAg core and the AgSTs. The principal novelty of this study lies in the "hierarchical" design of the metal-polymer-metal core@shell@satellite nanostructured colloids exhibiting synergistic capabilities of the plasmonic NPs for, among others, temperature-controlled catalytic applications.

Antimicrobial Activity of Biosynthesized Silver Nanoparticles Decorated Silica Nanoparticles

The production of cheap and effective compound for medicinal application is a major challenge for scientific community. So, several biological materials have been explored for the possible application in material synthesis which are useful in biomedical uses. Here, biomolecules from green tea leaves were functionalized on the surface of silicon dioxide nanoparticles (GSiO₂ NPs). Next, the decoration silver (Ag) NPs on the surface of the GSiO₂ NPs was observed in very short time of incubation in aqueous AgNO₃. Ultraviolet-visible spectroscopy confirmed the formation of Ag NPs and the high-resolution transmission and scanning electron microscopies confirmed the decoration of spherical Ag NPs of 10 to 15 nm size on the surface of GSiO₂ NPs. The antimicrobial activity of the Ag-GSiO₂ NPs was determined against Staphylococcus aureus and Escherichia coli. The Ag-GSiO₂ NPs displayed sustainable antimicrobial activity compared to Ag ions. The results indicate the potential value of Ag-GSiO₂ NPs in surgical material and food processing.

Surface-Enhanced Raman Scattering-Fluorescence Dual-Mode Nanosensors for Quantitative Detection of Cytochrome c in Living Cells

During apoptosis process, the release of cytochrome c (Cyt c) is considered to be a key factor in the intrinsic pathway and is often defined as no regression point. Quantitative detection of intracellular Cyt c remains a challenge. Herein, we have developed surface-enhanced Raman scattering (SERS)-fluorescence dual-mode nanosensors for the quantitative assay of Cyt c in living cells. Dual signal detection was achieved by constructing gold nanotriangles (AuNTs) nanosensors capable of specifically recognizing Cyt c. The nanosensors were prepared by modifying the aptamer of Cyt c on AuNTs and connecting the complementary strands modified with Cy5. The AuNTs provided both enhanced SERS signals and fluorescence quenching effects. Once cells were induced by external stimulus (such as toxins) to release Cyt c, Cyt c would specifically bind to its aptamer, and the complementary strands modified with Cy5 would detach which would result in weakened SERS signal and recovery of fluorescence signal. The experimental results showed that the nanosensors not only had excellent selectivity and sensitivity but also realized real-time monitoring of Cyt c translocation event from mitochondria to cytoplasm. The SERS and fluorescence intensity showed good linear relationship with Cyt c concentration ranging from 0.044 to 9.95 μM and achieved a minimum limit of detection (LOD) of 0.02 μM in living cells. The accuracy of intracellular Cyt c quantitative results was more than 90% compared with the ELISA results.

Effect of hybrid SiO2@Ag nanoparticles with raspberry-like morphology on the excited states of the photosensitizers Rose Bengal and riboflavin

Ag⁺ is released due to a charge transfer process from the triplet state of adsorbed riboflavin to the silver nanoparticles.

Achieving Color and Function with Structure: Optical and Catalytic Support Properties of ZrO2 Inverse Opal Thin Films

Taking inspiration from natural photonic crystal architectures, we report herein the successful fabrication of zirconia inverse opal (ZrO₂ IO) thin-film photonic crystals possessing striking iridescence at visible wavelengths. Poly(methyl methacrylate) (PMMA) colloidal crystal thin films (synthetic opals) were first deposited on glass microscope slides, after which the interstitial voids in the films were filled with a Zr(IV) sol. Controlled calcination of the resulting composite films yielded iridescent ZrO₂ IO thin films with pseudo photonic band gaps (PBGs) along the surface normal at visible wavelengths. The PBG position was dependent on the macropore diameter (D) in the inverse opals (and thus proportional to the diameter of the PMMA colloids in the sacrificial templates), the incident angle of light with respect to the surface normal (θ), and also the refractive index of the medium filling the macropores, all of which were accurately described by a modified Bragg's law expression. Au/ZrO₂ IO catalysts prepared using the ZrO₂ IO films demonstrated outstanding performance for the reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH₄, which can be attributed to the interconnected macroporosity in the films, which afforded a high Au nanoparticle dispersion and also facile diffusion of 4-nitrophenol to the catalytically active Au sites.

Silver oxide decomposition mediated direct bonding of silicon-based materials

Silicon-based materials are widely promising electronic components by the combination with metals in power electronics field. However, bonding metal and silicon-based materials generally requires specific surface modification due to their different chemical bonds. Here, we demonstrate a process for directly bonding metals to silicon-based materials that does not require surface treatment, based on the in situ decomposition of Ag₂O paste, forming Ag nanoparticles (AgNPs). We demonstrate sound joints of Ag/silicon-based materials at 300–500 °C with the formation of a silicon oxide interlayer containing AgNPs. We propose that Ag in the interlayer attracted other Ag particles to the interface, playing a unique role in this direct bonding process. This process is suitable for various bonding applications in electronics, as well the fabrication of conducting paths for photovoltaic and other applications.

Lignin Nanosphere-Supported Cuprous Oxide as an Efficient Catalyst for Huisgen [3+2] Cycloadditions under Relatively Mild Conditions

In this work, low-cost lignin nanospheres were fabricated and further applied as an efficient and sustainable support for preparing cuprous oxide (Cu₂O) "green" catalyst by using electrospraying technology. The unalloyed lignin, a special three-dimensional molecular structure, was successfully processed into uniform nanospheres under an electrospraying condition. The synthesized lignin-supported Cu₂O catalyst had a well-defined nanosphere structure, and Cu₂O nanoparticles with sizes less than 30 nm were supported by exposed layers of lignin nanospheres. There were C⁻O⁻Cu bonds formed between the lignin nanospheres and the metallic nanoparticles. The lignin nanospheres and the lignin nanosphere-supported catalyst werfe characterized by utilizing XRD, SEM, TEM, XPS, EDS, and TGA. The immobilization of Cu₂O nanoparticles on the lignin nanospheres was beneficial for dispersion of the Cu₂O nanoparticles and preventing their aggregation, which could cause catalyst deactivation, which favored the Huisgen [3+2] cycloaddition reaction. The triazole synthesis results indicated that the lignin nanosphere-supported Cu₂O catalyst had a high catalytic performance with 99% yield under solvent-free conditions. Furthermore, the as-synthesized catalyst could be recycled for four times without significantly losing its catalytic activity.

Seeded Growth Synthesis of Gold Nanotriangles: Size Control, SAXS Analysis, and SERS Performance

We studied the controlled growth of triangular prismatic Au nanoparticles with different beveled sides for surface-enhanced Raman spectroscopy (SERS) applications. First, in a seedless synthesis using 3-butenoic acid (3BA) and benzyldimethylammonium chloride (BDAC), gold nanotriangles (AuNTs) were synthesized in a mixture with gold nanooctahedra (AuNOCs) and separated by depletion-induced flocculation. Here, the influence of temperature, pH, and reducing agent on the reaction kinetics was initially investigated by UV-vis and correlated to the size and yield of AuNT seeds. In a second step, the AuNT size was increased by seed-mediated overgrowth with Au. We show for the first time that preformed 3BA-synthesized AuNT seeds can be overgrown up to a final edge length of 175 nm and a thickness of 80 nm while maintaining their triangular shape and tip sharpness. The NT morphology, including edge length, thickness, and tip rounding, was precisely characterized in dispersion by small-angle X-ray scattering and in dry state by transmission electron microscopy and field-emission scanning electron microscopy. For sensor purposes, we studied the size-dependent SERS performance of AuNTs yielding analytical enhancement factors between 0.9 × 10⁴ and 5.6 × 10⁴ and nanomolar limit of detection (10^-8-10^-9 M) for 4-mercaptobenzoic acid and BDAC. These results confirm that the 3BA approach allows the fabrication of AuNTs in a whole range of sizes maintaining the NT morphology. This enables tailoring of localized surface plasmon resonances between 590 and 740 nm, even in the near-infrared window of a biological tissue, for use as colloidal SERS sensing agents or for optoelectronic applications.

Control of the Size of Silver Nanoparticles and Release of Silver in Heat Treated SiO₂-Ag Composite Powders

The growth of silver nanoparticles, the activation energy for silver particle growth, and the release of silver species in heat treated SiO2-Ag composite powders are investigated. The silver particle growth is controlled by heat treatment for 75 min of the as-synthesized SiO2-Ag composite powder at 300–800 °C. During heat treatment the mean size of the Ag particles increases from 10 nm up to 61 nm with increasing temperature, however, the particle size distribution widens and the mean size increases with increasing heat treatment temperature. Based on X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) studies, silver particles are crystalline and in a metallic state after annealing in all SiO2-Ag composite powders. The growth of Ag particles is suggested to take place via diffusion and Ostwald ripening. The activation energy for particle growth was determined as 0.14 eV. The dissolution of silver in aqueous solutions from the SiO2-Ag composites heat treated, at 300 °C, 600 °C, and 700 °C, was investigated by varying pH and temperature. The dissolution was reduced in all conditions with increasing silver particle size, i.e., when the total surface area of Ag particles is reduced. It is suggested that the dissolution of silver from the composite powders can conveniently be adjusted by controlling the Ag particle size by the heat treatment of the composite powder.

Broadband light absorption by silver nanoparticle decorated silica nanospheres

Ag NPs decorated SiO₂ nanospheres for plasmon enhanced light absorption.

Synthesis of catalytically active gold clusters on the surface of Fe3O4@SiO2 nanoparticles

This work proposes a novel method to obtain catalytically active gold clusters by using the water-soluble 5,10,15,20-Tetrakis(4-trimethyl-ammonio-phenyl)porphyrin under mild conditions instead of using strong reducing agents.

Facile preparation of highly electrically conductive films of silver nanoparticles finely dispersed in polyisobutylene-b-poly(oxyethylene)-b-polyisobutylene triblock copolymers and graphene oxide hybrid surfactants

The melted morphologies revealed that the AgNPs possessed mobility, and melted on the film surface, giving a high electrical conductivity of 5.2 × 10⁻² Ω sq⁻¹ when heat-treated at 350 °C.

Highly monodispersed Ag embedded SiO2 nanostructured thin film for sensitive SERS substrate: growth, characterization and detection of dye molecules

Highly monodispersed Ag embedded SiO₂ nanostructured thin films have been synthesized and their sensitivity towards SERS investigated.

Synthesis and characterization of an AgI/Ag hybrid nanocomposite with surface-enhanced Raman scattering performance and photocatalytic activity

Novel AgI/Ag hybrid nanocomposites with good SERS performance and excellent photocatalytic activity were prepared.

SERS performance of graphene oxide decorated silver nanoparticle/titania nanotube array

A schematic illustrates the preparation of recyclable GO/Ag/TiO₂ NTA substrate keeping both active SERS detection and photocatalytic self-cleaning properties.