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Chromium inhibition and size-selected Au nanocluster catalysis for the solution growth of low-density ZnO nanowires.

ABSTRACT: The wet chemical synthesis of nanostructures has many crucial advantages over high-temperature methods, including simplicity, low-cost, and deposition on almost arbitrary substrates. Nevertheless, the density-controlled solution growth of nanowires still remains a challenge, especially at the low densities (e.g. 1 to 10 nanowires/100 μm(2)) required, as an example, for intracellular analyses. Here, we demonstrate the solution-growth of ZnO nanowires using a thin chromium film as a nucleation inhibitor and Au size-selected nanoclusters (SSNCs) as catalytic particles for which the density and, in contrast with previous reports, size can be accurately controlled. Our results also provide evidence that the enhanced ZnO hetero-nucleation is dominated by Au SSNCs catalysis rather than by layer adaptation. The proposed approach only uses low temperatures (≤70 °C) and is therefore suitable for any substrate, including printed circuit boards (PCBs) and the plastic substrates which are routinely used for cell cultures. As a proof-of-concept we report the density-controlled synthesis of ZnO nanowires on flexible PCBs, thus opening the way to assembling compact intracellular-analysis systems, including nanowires, electronics, and microfluidics, on a single substrate.

SUBMITTER: Errico V

PROVIDER: S-EPMC4511950 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Exchange Functionals and Basis Sets for Density Functional Theory Studies of Water Splitting on Selected ZnO Nanocluster Catalysts.

Project description:In this communication, we use density functional theory (DFT) to study the structural (geometry) and electronic properties (vertical detachment energy and electron affinity) of ZnO monomers and dimers that can be used to form ZnO clusters of different sizes, with a view to adapting one or more of them as catalysts or photocatalysts, standing alone or on suitable substrates like graphene, to split water. We also investigate different pairs of exchange functionals and basis sets to optimize their choice in our DFT calculations and to compare the singlet-triplet energy gaps of small ZnO clusters of different sizes to select an optimal cluster size for water splitting. We find that the B3LYP/DGDZVP2 exchange functional/basis set is a reliable combination for use with DFT to calculate the geometry and electronic properties of small ZnO nanoclusters from among several other combinations of exchange functionals and basis sets. Comparisons of the singlet-triplet energy gaps show that the trimer (ZnO)3 has an energy gap of 58.66 k cal/mol. which is approximately equal to the energy of a visible photon at a wavelength of 500 nm, and a HOMO-LUMO gap of 4.4 eV, making it a suitable choice of photocatalyst for the oxidation of water from among six (ZnO) n nanoclusters of monomers, with n ranging from 1 to 6. We used this exchange functional/basis set to study the structural and energetic details of hydration and hydrolysis of water absorbed on the (ZnO)3 nanocatalyst and calculated the corresponding potential energy profiles to identify three sets of singlet-triplet pathways for water splitting. Detailed study of a pathway showed that oxygen is produced after hydrogen, and the rate-determining step is the formation of hydrogen.

| S-EPMC9026035 | biostudies-literature

Unconventional seed-mediated growth of ultrathin Au nanowires in aqueous solution.

Project description:Ultrathin Au nanowires have garnered increasing attention in recent years because of their potential use in a range of applications due to their unique optical properties, conductivity, chemical activity, and discrete plasticity. Herein, we report an unconventional seed-mediated growth of ultrathin Au nanowires induced by hydrophobic molecules. Quite intriguingly, by adding a trace amount of hydrophobic molecules (i.e., toluene or chloroform) to the Au growth solution conventionally used for the growth of Au nanorods with cylindrical CTAB micelles as templates, CTAB-capped ultrathin Au nanowires (i.e., water-soluble ultrathin Au nanowires) were crafted. Similarly to the growth of Au nanorods, silver ions and Au seeds were crucially required to yield the water-soluble ultrathin Au nanowires. The growth mechanism of these ultrathin nanowires was also explored.

| S-EPMC6054065 | biostudies-literature

Au@CdS Core-Shell Nanoparticles-Modified ZnO Nanowires Photoanode for Efficient Photoelectrochemical Water Splitting.

Project description:Hydrogen production from water splitting using solar energy based on photoelectrochemical (PEC) cells has attracted increasing attention because it leaves less of a carbon footprint and has economic superiority of solar and hydrogen energy. Oxide semiconductors such as ZnO possessing high stability against photocorrosion in hole scavenger systems have been widely used to build photoanodes of PEC cells but under visible light their conversion efficiencies with respect to incident-photon-to-current conversion efficiency (IPCE) measured without external bias are still not satisfied. An innovative way is presented here to significantly improve the conversion efficiency of PEC cells by constructing a core-shell structure-based photoanode comprising Au@CdS core-shell nanoparticles on ZnO nanowires (Au@CdS-ZnO). The Au core offers strong electronic interactions with both CdS and ZnO resulting in a unique nanojunction to facilitate charge transfer. The Au@CdS-ZnO PEC cell under 400 nm light irradiation without any applied bias provides an IPCE of 14.8%. Under AM1.5 light illumination with a bias of 0.4 V, the Au@CdS-ZnO PEC cell produces H2 at a constant rate of 11.5 μmol h-1 as long as 10 h. This work provides a fundamental insight to improve the conversion efficiency for visible light in water splitting.

| S-EPMC5115296 | biostudies-literature

Fiber optic sensor based on ZnO nanowires decorated by Au nanoparticles for improved plasmonic biosensor.

Project description:Fiber-optic-based localized surface plasmon resonance (FO-LSPR) sensors with three-dimensional (3D) nanostructures have been developed. These sensors were fabricated using zinc oxide (ZnO) nanowires and gold nanoparticles (AuNPs) for highly sensitive plasmonic biosensing. The main achievements in the development of the biosensors include: (1) an extended sensing area, (2) light trapping effect by nanowires, and (3) a simple optical system based on an optical fiber. The 3D nanostructure was fabricated by growing the ZnO nanowires on the cross-section of optical fibers using hydrothermal synthesis and via immobilization of AuNPs on the nanowires. The proposed sensor outputted a linear response according to refractive index changes. The 3D FO-LSPR sensor exhibited an enhanced localized surface plasmon resonance response of 171% for bulk refractive index changes when compared to the two-dimensional (2D) FO-LSPR sensors where the AuNPs are fixed on optical fiber as a monolayer. In addition, the prostate-specific antigen known as a useful biomarker to diagnose prostate cancer was measured with various concentrations in 2D and 3D FO-LSPR sensors, and the limits of detection (LODs) were 2.06 and 0.51 pg/ml, respectively. When compared to the 2D nanostructure, the LOD of the sensor with 3D nanostructure was increased by 404%.

| S-EPMC6821738 | biostudies-literature

High-performance flexible ultraviolet photoconductors based on solution-processed ultrathin ZnO/Au nanoparticle composite films.

Project description:Transparent ultraviolet (UV) ZnO thin film photoconductors are expected to have great applications in environmental monitoring, large-area displays, and optical communications, and they have drawn enormous interests in recent years. However, at present their performances are not satisfactory: the responsivity R (a parameter characterizing the sensitivity of the device to light) is not high (<1.0 × 10(3) AW(-1)), and the transparency T is not high either (<80%). Realizing high R and high T remains a big challenge today. In this paper, by employing solution-processed ultrathin ZnO/Au nanoparticle composite films, R as high as 1.51 × 10(5) AW(-1) and T of over 90% are achieved. High values for detectivity D* and linear dynamic range LDR are also obtained, which are 2.05 × 10(15) Jones and 60 dB, respectively. Moreover, such high-performance devices can be fabricated on flexible PET (polyethylene terephthalate) substrates.

| S-EPMC3940971 | biostudies-literature

Fingerprints of a size-dependent crossover in the dimensionality of electronic conduction in Au-seeded Ge nanowires.

Project description:We studied the electrical transport properties of Au-seeded germanium nanowires with radii ranging from 11 to 80 nm at ambient conditions. We found a non-trivial dependence of the electrical conductivity, mobility and carrier density on the radius size. In particular, two regimes were identified for large (lightly doped) and small (stronger doped) nanowires in which the charge-carrier drift is dominated by electron-phonon and ionized-impurity scattering, respectively. This goes in hand with the finding that the electrostatic properties for radii below ca. 37 nm have quasi one-dimensional character as reflected by the extracted screening lengths.

| S-EPMC5238664 | biostudies-literature

Nucleation density and pore size tunable growth of ZnO nanowalls by a facile solution approach: growth mechanism and NO<sub>2</sub> gas sensing properties.

Project description:Nanowalls are novel nanostructures whose 3D porous network morphology holds great potential for applications as gas sensors. The realization of such a nanowall-based gas sensor depends directly on the comprehensive understanding of the growth mechanism of the nanowalls. We induced nucleation density and pore size evolution by increasing the dipping and growth times. The investigation indicates that the 3D porous ZnO nanowalls consist of a seed layer of ZnO nanoparticles and a growth layer of the vertically grown ZnO nanosheets. The seed layer nucleation density dominance is driven by the dipping time. The pore size and the height of the as-grown ZnO nanowalls are determined by varying the growth time. Possible growth mechanisms governing the physical characteristics of the synthesized ZnO nanostructures in the solution process are proposed and discussed. The gas sensor that was fabricated from the ZnO nanowall structure exhibited strong dependence on the microstructure, which was mainly determined by the preparation conditions.

| S-EPMC9048435 | biostudies-literature

Antibacterial and Photocatalytic Activity of ZnO/Au and ZnO/Ag Nanocomposites.

Project description:The use of a combination of nanoparticles as antimicrobial agents can be one strategy to overcome the tendency of microbes to become resistant to antibiotic action. Also, the optimization of nano-photocatalysts to efficiently remove persistent pollutants from wastewater is a hot topic. In this study, two composites ZnO/Au (1% wt.) and ZnO/Ag (1% wt.) were synthesized by simple aqueous solution methods. The structure and morphology of the r nanocomposites were analyzed by structural and optical characterization methods. The formation of AuNPs and AgNPs in these experiments was also discussed. The antimicrobial properties of ZnO, ZnO/Au, and ZnO/Ag nanomaterials were investigated against Gram-negative bacteria (Pseudomonas aeruginosa) and Gram-positive bacteria (Staphylococcus aureus). The results showed an increase of 80% in the antimicrobial activity of ZnO/Au against Pseudomonas aeruginosa compared with 30% in the case of ZnO/Ag. Similarly, in the case of the S. aureus strain tests, ZnO/Au increased the antimicrobial activity by 55% and ZnO/Ag by 33%. The photocatalytic tests indicated an improvement in the photocatalytic degradation of methylene blue (MB) under UV irradiation using ZnO/Au and ZnO/Ag nanocomposites compared to bare ZnO. The photocatalytic degradation efficiency of ZnO after 60 min of UV irradiation was ∼83%, while the addition of AuNPs enhanced the degradation rate to ∼95% (ZP2), and AgNP presence enhanced the efficiency to ∼98%. The introduction of noble metallic nanoparticles into the ZnO matrix proved to be an effective strategy to increase their antimicrobial activity against P. aeruginosa and S. aureus, and their photocatalytic activity was evaluated through the degradation of MB dye. Comparing the enhancing effects of Au and Ag, it was found that ZnO/Au was a better antimicrobial agent while ZnO/Ag was a more effective photocatalyst under UV irradiation.

| S-EPMC10706707 | biostudies-literature

Nanowarming using Au-tipped Co35Fe65 ferromagnetic nanowires.

Project description:Ferromagnetic Co35Fe65, Fe, Co, and Ni nanowires have high saturation magnetizations (Ms) and magnetic anisotropies, making them ideal for magnetic heating in an alternating magnetic field (AMF). Here, Au-tipped nanowires were coated with polyethylene glycol (PEG) and specific absorption rates (SAR) were measured in glycerol. SAR increased when using metals with increasing Ms (Co35Fe65 > Fe > Co > Ni), reaching 1610 ± 20 W g-1 metal at 1 mg metal per ml glycerol for Co35Fe65 nanowires using 190 kHz and 20 kA m-1. Aligning these nanowires parallel to the AMF increased SAR up to 2010 W g-1 Co35Fe65. Next, Co35Fe65 nanowires were used to nanowarm vitrified VS55, a common cryoprotective agent (CPA).Nanowarming rates up to 1000 °C min-1 (5 mg Co35Fe65 per ml VS55) were achieved, which is 20× faster than the critical warming rate (50 °C min-1) for VS55 and other common CPAs. Human dermal fibroblast cells exposed to VS55, and Co35Fe65 nanowire concentrations of 0, 1 and 2.5 mg Fe per ml all showed similar cell viability, indicating that the nanowires had minimal cytotoxicity. With the ability to provide rapid and uniform heating, ferromagnetic nanowires have excellent potential for nanowarming cryopreserved tissues.

| S-EPMC6709862 | biostudies-literature

Effect of the Electronic State of Cu, Ag, and Au on Diesel Soot Abatement: Performance of Cu/ZnO, Ag/ZnO, and Au/ZnO Catalysts.

Project description:Noble metals such as Au, Ag, and Cu supported over semiconducting ZnO are well-known heterogeneous oxidation catalysts. All of them have been utilized for the oxidation of diesel soot with varied success. However, Au-supported ZnO is seen to be superior among them. Here, we present a comparative study of all these three catalysts for diesel soot oxidation to explain why Au/ZnO is the best among them, demonstrating the contribution of electronic states of metals in composite catalysts. The electronic states of Cu, Ag, and Au determined by X-ray photoelectron spectroscopy on 1 wt % Cu/ZnO, 1 wt % Ag/ZnO, and 1 wt % Au/ZnO catalysts were correlated with their diesel soot oxidation activities. Although all three catalysts present reasonable diesel soot oxidation activities at relatively low temperature, 1% Cu/ZnO and 1% Ag/ZnO oxidize only about 60% of the deposited diesel soot around 250 °C and 1% Au/ZnO oxidizes 100% of the deposited diesel soot, at a temperature as low as 230 °C. The activity of the catalysts is attributed to the formation of stable M0-Mδ+ bifunctional catalytic sites at the metal-ZnO interface, which enhances the contact efficiency of solid diesel soot on Mδ+ and generates the superoxide species on M0 moieties. The stability of the bifunctional M0-Mδ+ sites is controlled by the electronic interactions between the metal (M) and n-type semiconductor ZnO at their interface. Very high activity of 1% Au/ZnO is attributed to the presence of Au3+ at the catalyst surface, which generates a stronger Coulombic force with diesel soot electrons. We demonstrate a direct relation between the diesel soot oxidation activity of these three metals and their electronic states at the catalyst surface.

| S-EPMC6648296 | biostudies-literature

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