Attachment Of Au Nanoparticles Research Articles

Role of oxygen functional groups and attachment of Au nanoparticles on graphene oxide sheets for improved photodetection performance.

Integrating low-dimensional graphene oxide (GO) with conventional Si technology offers innovative strategies for developing ultrafast wideband photodetectors. In this study, we synthesized GO and explored its potential application in broadband photodetection alongside silicon heterostructures. The as-synthesized GO contains various oxygen functional groups, as evidenced by X-ray photoelectron and Fourier transform infrared spectroscopy. These functional groups contribute to increased photo absorption, enhancing photodetection performance. The systematic reduction of these functional groups from the GO surface via thermal annealing decreases photo absorption and consequently lowers the photocurrent. This reduction diminishes photo absorption and amplifies the dark current by approximately 25 times, from 20 nA to 496 nA. This dark current increase is attributed to the electron mobility following the reduction of functional groups. However, attaching plasmonic gold nanoparticles (Au NPs) to the GO surface enhances UV-Vis absorption in the visible region, enabling broadband detection. The even distribution of attached Au NPs on the GO surface is confirmed through field emission transmission electron microscopy. While thermal annealing of GO diminishes the responsivity from 4.6 A W-1 to 3.0 A W-1, the attachment of Au NPs augments the responsivity by more than two-fold, reaching 10.0 A W-1. Thus, it highlights the importance of rich oxygen functional groups in GO and the attachment of Au NPs to achieve more efficient photo-sensing properties.

Visible light sensitive Au–TiO2 nanocomposites formed by effective attachment of Au with TiO2 nanoparticles using liquid-phase pulsed-laser ablation

Liquid-phase pulsed-laser ablation was utilized to grow visible-light-sensitive Au–TiO2 nanocomposites. We performed the nanosecond pulsed-laser ablation of a Ti target in aqueous solution of HAuCl4 of different concentrations varying from 0 mM to 0.24 mM. Structural characterization studies using transmission electron microscopy (TEM) and X ray diffraction (XRD) analyses confirmed formation of the nanoparticles of TiO2 and Au–TiO2 in respective solutions. In Au–TiO2 samples, nanocomposites formation by efficient attachment between Au and TiO2 nanoparticles was confirmed by absorption and X-ray photoelectron spectroscopy (XPS) analyses. Optical absorption analysis revealed that with the attachment of Au, there is a red shift in the onset of the absorption band of TiO2 from the ultraviolet to visible range. This red shift is found to increase from 3.5 to 2.7 eV with respect to the increase in the amount of Au present in Au–TiO2 nanocomposites. While detailed XPS analysis suggested that when the amount of Au attached with TiO2 increased, the number density of oxygen vacancy or Ti3+ states increased. Therefore the attachment of Au nanoparticles and oxygen vacancy or Ti3+ states generations in TiO2 were found to be responsible for the large red shift in the onset of the TiO2 absorption band. Consequently our study showed that single step liquid phase laser ablation method and its subsequent nonequilibrium growth conditions are useful in synthesizing Au and TiO2 nanoparticles simultaneously and also in providing efficient attachment between Au and TiO2 which is responsible for visible range sensitization of Au-TiO2 nanocomposites .

Unraveling the Radiation Damage of n-Dodecanethiol Self-Assembled Monolayers on Au(100) and Au(111): A Prerequisite to Understand the Oriented Attachment of Au Nanoparticles

Unraveling the Radiation Damage of <i>n</i>-Dodecanethiol Self-Assembled Monolayers on Au(100) and Au(111): A Prerequisite to Understand the Oriented Attachment of Au Nanoparticles

Fabrication of Au-CuO hybrid plasmonic nanostructured thin films with enhanced photocatalytic activity

Thin films of Au-CuO plasmonic nanohybrids were fabricated by simple thermal evaporation. SEM and XRD investigations unveiled the impact of annealing on the structural properties and morphology of the synthesized Au-CuO hybrid thin film. Au nanoparticle decoration onto CuO thin film significantly altered the photocatalytic activity, structural and optical properties of CuO thin film. The as-prepared Au-CuO nanostructured hybrid plasmonic thin film showed improved photocatalytic efficiency for decomposition of MG and MB than pristine CuO and annealed Au-CuO thin film samples. The improved photocatalytic efficiency of Au-CuO hybrid nanostructured thin film is attributed to reduction in the recombination of charge carriers in CuO nanostructures and improvement in light utilization capability due to attachment of Au nanoparticles on nanostructured CuO thin film. Cracks in Au-CuO nanohybrid thin film facilitated enhanced adsorption of dye molecules and played an essential role in improving the photocatalytic efficiency.

Non-enzymatic and non-invasive glucose detection using Au nanoparticle decorated CuO nanorods

Non-enzymatic electrochemical glucose sensors have been fabricated using hydrothermally grown CuO nanorods on fluorine doped tin oxide (FTO) coated glass substrates. The sensing performance has been increased by several times after attaching Au nanoparticles with CuO nanorods. The formation of CuO nanorods and attachment of Au nanoparticles were confirmed using scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) study. The Au decorated CuO nanorod electrodes demonstrated glucose sensitivity of 2009 μAmM-1 cm-2, in the linear detection range 5 μM to 1.325 mM, with detection limit of 0.17 μM. Such Au decorated sensing electrodes are highly selective and exhibited long-term stability. Non-invasive glucose detection has been demonstrated using human saliva samples. The sensitivity of the sensor for salivary glucose detection was found to be 1740 μAmM-1 cm-2. Our present study demonstrated the promising use of Au decorated CuO NR electrodes for low cost, non-enzymatic, non-invasive diabetes monitoring application.

Selective adsorption and degradation of organic pollutants over Au decorated Co doped titanate nanotubes under simulated solar light irradiation

Abstract Au decorated Co doped titanate nanotubes (TNT) was prepared for selective removal of methylene blue (MB) dye followed by selective photocatalytic degradation under solar light in presence of another highly concentrated dyes. The adsorption capacity of Co doped TNT was found to be increased with increasing Co content due to the increase in the number of pores and thus increase in surface area. Due to the high concentration of MB, Co doped TNT was completely covered by MB molecules and become difficult for light to Path though or absorbed by the Co doped TNT catalyst. In order to provide some photocatalytic characteristics for the catalyst, the doped TNTs were calcined to enhance the crystallinity and thus enhancing the photocatalytic activity, but the degradation rate was very low. Thus, another direction was started by reducing the adsorption ability of Co doped TNT through coating its surface by poly(allylamine hydrochloride), which changed the surface charge of the tubes to be positive and facilitate the electrostatic attachment of Au nanoparticles (15 nm). The synergetic effect of plasmonic Au nanoparticles in addition to adsorption and catalytic properties of Co doped TNT make the new composite promising catalyst for degradation of organic pollutants. It shows a good selectivity for adsorption and photocatalytic degradation of MB dye from dyes mixture. The obtained results indicate that Au decorated Co doped TNT will have a great effect on the development of selective environmental water treatment technologies specifically on flow challenges confronted by the wastewater treatment area.

Plasmon mediated enhancement of visible light emission of Au-ZnO nanocomposites

We report on the enhancement of the visible luminescence of Au-ZnO nanocomposites synthesized via a simple photoreduction method. The attachment of Au nanoparticles on the surface of ZnO nanostructures has been observed using transmission electron microscopy. Raman analysis reveals an increase in disorderness via lattice defect formation due to Au attachment and thus results in the appearance of silent modes of ZnO. The photoluminescence spectra of ZnO is found to be dominated by defect related visible emission, which is enhanced with the inclusion of Au nanoparticles. At room temperature, the green emission for nanocomposites has been found to be enhanced by seven times as compared to the pristine ZnO. Temperature dependent photoluminescence of Au-ZnO nanocomposites has been investigated to elucidate the origin of green luminescence and the enhancement of intensity. The gradual dominance of the green emission is originated from the surface plasmon oscillation of Au followed by the electron capture at the singly ionized oxygen vacancies of ZnO. The observed enhancement of visible light emission of ZnO using Au nanoparticles can establish the platform to fabricate efficient ZnO based visible light emitting devices and display systems.

Ligand-free attachment of plasmonic Au nanoparticles on ZnO nanowire to make a high-performance broadband photodetector using a laser-based method

We report a new strategy for ligand-free attachment of plasmonic Au nanoparticles on the surface of a ZnO nanowire to make high-performance broadband photodetectors using a pulsed laser ablation technique in a liquid medium. The photoresponse of the ZnO-based photodetector is enhanced and the photodetection limit is broadened from UV to visible, which can be controlled by varying the concentration of Au nanoparticles attached to the ZnO surface. This Au nanoparticle concentration can be tuned by varying the number of laser pulses used in the ablation process. We found that the responsivity of the detector is 10 mA W−1 for and increases to as much as 0.4 A W–1 for λ ≤ 400 nm for the maximum Au concentration. The enhanced responsivity was found to be linked to increased absorption over a broad spectral range arising from direct and indirect plasmonic processes due to Au nanoparticle attachment, and the enhanced absorption also leads to a large increment in photocurrent generation. We also found that the attachment of Au nanoparticles makes the relaxation of the photocurrent (persistence) considerably faster in both the UV and visible regions of the spectrum and that the persistence directly depends on the concentration of Au nanoparticles attached to the ZnO nanowire. This single-step pulsed laser ablation-based nanoparticle attachment process can be further used to make other plasmonic nanoparticle-decorated nanowire devices.

Magnetic GO‐PANI decorated with Au NPs: A highly efficient and reusable catalyst for reduction of dyes and nitro aromatic compounds

Due to the high activity of Au nanoparticles (NPs) for various reactions, many researchers have tried to develop heterogeneous catalysts in order to prevent irreversible agglomeration of Au NPs. Herein, magnetic graphene oxide modified with polyaniline (PANI) was used as a support for Au NPs that brings together advantages including: uniform dispersal of the catalyst in water,alarge surface area related to the graphene oxide; easy electron transfer in chemical reactions and good attachment of Au NPs to the support associated with PANI; and finally facile recovery in the presence of a magnetic field. Catalytic reduction of different analytes (Congo red, methylene blue, rhodamine B and 4‐nitro phenol) was evaluated in the presence of NaBH4 and the results show high catalytic activity of the catalyst. The catalyst was thoroughly characterized using various methods including FTIR, XRD, XPS, FE‐SEM and HRTEM analyses while its catalytic activity was evaluated via reduction of different analytes.

Easily recyclable and highly active rice roll-like Au/SiO2 nanocatalysts from inverse miniemulsion

Rice roll-like (RR-like) Au/SiO2 nanocatalysts (NCs) were synthesized through simultaneous sol–gel process of tetramethoxysilane and 3-aminopropyltriethoxysilane (APTES) and in situ reduction of gold salt in inverse miniemulsions. APTES played an important role in formation of RR-like SiO2 nano-supports, reduction of gold salts to narrowly size-distributed sub–10nm Au nanoparticles (NPs), and improved attachment of Au NPs to the SiO2 nano-supports. The prepared RR-like Au/SiO2 NCs displayed a pH-dependent, reversible colloidal stability in water, which facilitated to recycle them through tuning the pH value of the dispersion. Most importantly, the catalytic activity of the RR-like Au/SiO2 NCs towards reduction of p-nitrophenol was about 7–9 times higher than that of the raspberry-like Au/SiO2 NCs reported in our previous paper (Colloids Surf. A, 489, 2016, 223–233). The formation mechanism of the RR-like Au/SiO2 NCs was also discussed.

Controllable fabrication and photocatalysis of ZnO/Au nanohybrids via regenerative ion exchange and reduction cycles

A facile and convenient approach was introduced to fabricate ZnO/Au nanohybrids with tunable Au contents. The repeated loading of Au nanoparticles on the surface of ZnO nanorods was achieved via 3-aminopropyltriethoxysilane-mediated regenerative exchange of AuCl4− ions and subsequent reduction cycles. X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy were all used to characterize as-prepared ZnO/Au nanohybrids. The attachment of Au nanoparticles onto the ZnO supports significantly altered the interfacial charge transfer process and resulted in a marked decrease in the intensity of photoluminescence peaks. Owing to their special geometry, electronic structure, and particular interphase boundaries, such ZnO/Au nanohybrids exhibited enhanced photocatalytic performance, and hold promising applications in water purification and antibacterial products.

Solution growth of ZnO microwires and grass architectures

• Au nanoparticles with different shapes and sizes were produced. • Au nanoparticles resulted in uniformly dispersed and standing ZnO microwires. • Au nanoparticles serve as heterogeneous nucleation sites for the ZnO microwires. • Au nanoparticles also resulted in ZnO grass architectures. In spite of extensive research in gold (Au) nanoparticles, it remains a challenge to synthesize structurally homogeneous sample-set with controlled morphologies. The latter critically affect the role of Au nanoparticles as a seed/catalyst for the growth of other nanostructures. Here, we systematically studied and quantified the growth of Au nanoparticles in a single-step chemical synthesis approach and observed the effects of growth temperature and duration, metal salt and surfactant concentration, and surfactant type. These parameters strongly influenced morphological evolution, distribution, and heterogeneities in the as-synthesized Au nanoparticles. Next, the synthesized Au nanoparticles were utilized for the growth of zinc oxide (ZnO) microwires in a solution growth approach. It was observed that Au nanoparticles on the substrate did not catalyze the growth of ZnO microwires but facilitated uniform dispersion of standing microwires. Supported by microscopic analysis, the proposed growth mechanism is heterogeneous nucleation of ZnO on the loosely bound Au nanoparticles on the substrates, favored by lattice match between the ZnO and Au. Based on this mechanism, Au nanoparticles only assisted in the initial stages of ZnO microwire growth. For longer growth duration (~10 h), over-deposition of ZnO from the solution on already grown wires led to their micron scale diameters as well as grass architectures and making the growth process independent of size and shape of the Au nanoparticles. The formation of ZnO grass architecture is due to attachment of Au nanoparticles on the growing microwire surface, which further served as a heterogeneous nucleation site for the ZnO growth. These Au nanoparticles detached from the Si wafer due to cleavage of Au S bonds or hydrolysis of Si O bonds on the thiolated Si wafer in presence of the ZnO growth precursor (hexamethylenetetramine) and conditions. As-synthesized Au nanoparticles and ZnO microwires were characterized by high-resolution transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy.

Directing Cluster Formation of Au Nanoparticles from Colloidal Solution

Discrete clusters of closely spaced Au nanoparticles can be utilized in devices from photovoltaics to molecular sensors because of the formation of strong local electromagnetic field enhancements when illuminated near their plasmon resonance. In this study, scalable, chemical self-organization methods are shown to produce Au nanoparticle clusters with uniform nanometer interparticle spacing. The performance of two different methods, namely electrophoresis and diffusion, for driving the attachment of Au nanoparticles using a chemical cross-linker on chemically patterned domains of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) thin films are evaluated. Significantly, electrophoresis is found to produce similar surface coverage as diffusion in 1/6th of the processing time with an ~2-fold increase in the number of Au nanoparticles forming clusters. Furthermore, average interparticle spacing within Au nanoparticle clusters was found to decrease from 2-7 nm for diffusion deposition to approximately 1-2 nm for electrophoresis deposition, and the latter method exhibited better uniformity with most clusters appearing to have about 1 nm spacing between nanoparticles. The advantage of such fabrication capability is supported by calculations of local electric field enhancements using electromagnetic full-wave simulations from which we can estimate surface-enhanced Raman scattering (SERS) enhancements. In particular, full-wave results show that the maximum SERS enhancement, as estimated here as the fourth power of the local electric field, increases by a factor of 100 when the gap goes from 2 to 1 nm, reaching values as large as 10(10), strengthening the usage of electrophoresis versus diffusion for the development of molecular sensors.

Plasmon-enhanced upconversion fluorescence in NaYF4:Yb/Er/Gd nanorods coated with Au nanoparticles or nanoshells

We investigate plasmon-enhanced upconversion (UC) fluorescence in Yb3+-Er3+-Gd+3 codoped sodium yttrium fluoride (NaYF4:Yb/Er/Gd) nanorods using gold nanoparticles or nanoshells. A simple method was proposed for the preparation of core/shell NaYF4/Au structures, with dispersed Au nanoparticles or uniform Au coating on the surface of the UC nanorod. Pure hexagonal-phase NaYF4:Yb/Er/Gd nanorods were synthesized via a liquid-solid reaction in oleic acid and ethanol solvent. A one-step approach was introduced to modify the hydrophobic surfaces of the as-deposited NaYF4:Yb/Er/Gd nanorods. After this surface modification, Au nanoparticles or nanoshells were successfully attached on the surfaces of NaYF4:Yb/Er/Gd nanorods. The as-deposited UC nanorods showed a strong UC emission in green and red bands under 980 nm laser excitation. The attachment of Au nanoparticles onto NaYF4:Yb/Er/Gd nanorods resulted in a more than three-fold increase in UC emissions, whereas the formation of continuous and compact Au shells around the nanorods suppressed the emissions. The related interaction mechanisms of the UC emission of NaYF4:Yb/Er/Gd nanorods with plasmon modes in Au nanostructures are analyzed and discussed.

Surface-Enhanced Raman Spectroscopy of Carbon Nanotubes in Aqueous Solution

Carbon nanotubes (CNTs) exhibit intrinsic spectroscopic properties and are potential Raman and NIR florescence probes for bioimaging. However, the weak Raman intensity greatly obstructs such applications. Surface-enhanced Raman scattering (SERS) has shown to be an effective way to increase the Raman signal. SERS has been widely studied for solid samples. However, solid state is distinctly different from the environment in biosystems. Herein, we studied the SERS of Au- nanoparticle-decorated CNTs in aqueous solution, which offers a similar environment to biosystems. We found that the func- tionalization of CNTs with -SH groups can improve the attachment of Au nanoparticles on tube surfaces thus benefit the SERS effect. The particle size is another important issue for SERS. Particles of 50 nm show much stronger enhancement than those of 12 nm. The Raman intensity of CNTs increases with the increase of the concentration of Au nanoparticles. Hexame- thylene diamine molecules can act as the bi-linkers between Au nanoparticles, compressing the interparticle distance. This was proved by the red-shift of the band at ca. 540 nm and the appearance of a broad band around 700 nm in the absorption spectra of Au nanoparticles. Therefore the addition of hexamethylene diamine can further increase the Raman signal of CNTs by the strong coupling of the surface plasma from the Au nanoparticles with very small interparticle distances. Two kinds of commonly used small molecule Raman probes p-aminothiophenol and Rhodamine B both show remarkably enhanced Raman intensity when added to the aqueous dispersion of Au/CNT hybrids. This shows that these Raman probe molecules can ab- sorb onto the Au/CNT hybrids and their Raman spectra are able to be greatly enhanced by Au nanoparticles decorated on CNTs. Because various Raman bands from either CNTs or Raman probe molecules can be used for Raman imaging, this kind of Raman probe molecule/Au/CNT tri-component hybrid systems may be used as a potential nanostructured platform for multiplexed Raman imaging based on SERS effect. Keywords carbon nanotubes; gold nanoparticles; surface enhanced Raman scattering (SERS); Raman spectroscopy for aqueous solution

In Situ Synthesis of Reduced Graphene Oxide and Gold Nanocomposites for Nanoelectronics and Biosensing.

In this study, an in situ chemical synthesis approach has been developed to prepare graphene–Au nanocomposites from chemically reduced graphene oxide (rGO) in aqueous media. UV–Vis absorption, atomic force microscopy, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy were used to demonstrate the successful attachment of Au nanoparticles to graphene sheets. Configured as field-effect transistors (FETs), the as-synthesized single-layered rGO-Au nanocomposites exhibit higher hole mobility and conductance when compared to the rGO sheets, promising its applications in nanoelectronics. Furthermore, we demonstrate that the rGO-Au FETs are able to label-freely detect DNA hybridization with high sensitivity, indicating its potentials in nanoelectronic biosensing.

Micro‐ and Nanopatterning of Functional Organic Monolayers on Oxide‐Free Silicon by Laser‐Induced Photothermal Desorption

The photothermal laser patterning of functional organic monolayers, prepared on oxide-free hydrogen-terminated silicon, and subsequent backfilling of the laser-written lines with a second organic monolayer that differs in its terminal functionality, is described. Since the thermal monolayer decomposition process is highly nonlinear in the applied laser power density, subwavelength patterning of the organic monolayers is feasible. After photothermal laser patterning of hexadecenyl monolayers, the lines freed up by the laser are backfilled with functional acid fluoride monolayers. Coupling of cysteamine to the acid fluoride groups and subsequent attachment of Au nanoparticles allows easy characterization of the functional lines by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Depending on the laser power and writing speed, functional lines with widths between 1.1 μm and 250 nm can be created. In addition, trifluoroethyl-terminated (TFE) monolayers are also patterned. Subsequently, the decomposed lines are backfilled with a nonfunctional hexadecenyl monolayer, the TFE stripes are converted into thiol stripes, and then finally covered with Au nanoparticles. By reducing the lateral distance between the laser lines, Au-nanoparticle stripes with widths close to 100 nm are obtained. Finally, in view of the great potential of this type of monolayer in the field of biosensing, the ease of fabricating biofunctional patterns is demonstrated by covalent binding of fluorescently labeled oligo-DNA to acid-fluoride-backfilled laser lines, which--as shown by fluorescence microscopy--is accessible for hybridization.

Electrografted Poly(N‐mercaptoethyl acrylamide) and Au Nanoparticles‐Based Organic/Inorganic Film: A Platform for the High‐Performance Electrochemical Biosensors

In this study, we describe the use of the combination of eletrografting poly(N-mercaptoethyl acrylamide) and Au nanoparticles in the construction of high-performance biosensors. The poly(N-mercaptoethyl acrylamide) was electrografted onto the glassy carbon electrode surface, which provided a strongly adhering primer film for the stable attachment of Au nanoparticles and horseradish peroxidase (HRP) enzymes. The performances of the biosensors based on the HRP immobilized in the Au/poly(N-mercaptoethyl acrylamide) composite film were investigated. A couple of redox peaks were obtained, indicating that the Au nanoparticles could facilitate the direct-electron transfer between HRP and the underlying electrode. The biosensor showed an excellent electrocatalytic activity toward the reduction of hydrogen oxide and long-term stability, owing to the stable electrografted film and biocompatible Au nanoparticles. Our results demonstrate that the combination of electrografting and Au nanoparticles provides a promising platform for the immobilization of biomolecules and analysis of redox enzymes for their sensing applications.

Nanocomposites of size-controlled gold nanoparticles and graphene oxide: Formation and applications in SERS and catalysis

In this paper, we describe the formation of Au nanoparticle-graphene oxide (Au-GO) and -reduced GO (Au-rGO) composites by noncovalent attachment of Au nanoparticles premodified with 2-mercaptopyridine to GO and rGO sheets, respectively, viaπ-π stacking and other molecular interactions. Compared with in situ reduction of HAuCl4 on the surface of graphene sheets that are widely used to prepare Au-GO composites, the approach developed by us offers well controlled size, size distribution, and morphology of the metal nanoparticles in the metal-GO nanohybrids. Moreover, we investigated surface enhanced Raman scattering (SERS) and catalysis properties of the Au-graphene composites. We have demonstrated that the Au-GO composites are superior SERS substrates to the Au NPs. Similarly, a comparative study on the catalytic activities of the Au, Au-GO, and Au-rGO composites in the reduction of o-nitroaniline to 1,2-benzenediamine by NaBH4 indicates that both Au-GO and Au-rGO composites exhibit significantly higher catalytic activities than the corresponding Au nanoparticles.

Nanoscale Heterostructures with Molecular-Scale Single-Crystal Metal Wires

Creating nanoscale heterostructures with molecular-scale (<2 nm) metal wires is critical for many applications and remains a challenge. Here, we report the first time synthesis of nanoscale heterostructures with single-crystal molecular-scale Au nanowires attached to different nanostructure substrates. Our method involves the formation of Au nanoparticle seeds by the reduction of rocksalt AuCl nanocubes heterogeneously nucleated on the substrates and subsequent nanowire growth by oriented attachment of Au nanoparticles from the solution phase. Nanoscale heterostructures fabricated by such site-specific nucleation and growth are attractive for many applications including nanoelectronic device wiring, catalysis, and sensing.