Zinc–Acetate–Amine Complexes as Precursors to ZnO and the Effect of the Amine on Nanoparticle Morphology, Size, and Photocatalytic Activity

Zinc oxide is an environmentally friendly and readily synthesized semiconductor with many industrial applications. ZnO powders were prepared by alkali precipitation using different [Zn(acetate)2(amine)x] compounds to alter the particle size and aspect ratio. Slow precipitations from 95 °C solutions produced micron-scale particles with morphologies of hexagonal plates, rods, and needles, depending on the precursor used. Powders prepared at 65 °C with rapid precipitation yielded particles with minimal morphology differences, but particle size was dependent on the precursor used. The smallest particles were produced using precursors that yielded crystals with low aspect ratios during high-temperature synthesis. Particles produced during rapid synthesis had sizes ranging from 21–45 nm. The materials were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, BET, and diffuse reflectance. The materials prepared using precursors with less-volatile amines were found to retain more organic material than ZnO produced using precursors with more volatile amines. The amount of organic material associated with the nanoparticles influenced the photocatalytic activity of the ZnO, with powders containing less organic material producing faster rate constants for the decolorizing of malachite green solutions under ultraviolet illumination, independent of particle size. [Zn(acetate)2(hydrazine)2] produced ZnO with the fastest rate constant and was recycled five times for dye degradation studies that revealed minimal to no reduction in catalytic efficiency

Zinc–Acetate–Amine Complexes as Precursors to ZnO and the Effect of the Amine on Nanoparticle Morphology, Size, and Photocatalytic Activity

Zinc oxide is an environmentally friendly and readily synthesized semiconductor with many industrial applications. ZnO powders were prepared by alkali precipitation using different [Zn(acetate)2(amine)x] compounds to alter the particle size and aspect ratio. Slow precipitations from 95 °C solutions produced micron-scale particles with morphologies of hexagonal plates, rods, and needles, depending on the precursor used. Powders prepared at 65 °C with rapid precipitation yielded particles with minimal morphology differences, but particle size was dependent on the precursor used. The smallest particles were produced using precursors that yielded crystals with low aspect ratios during high-temperature synthesis. Particles produced during rapid synthesis had sizes ranging from 21–45 nm. The materials were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, BET, and diffuse reflectance. The materials prepared using precursors with less-volatile amines were found to retain more organic material than ZnO produced using precursors with more volatile amines. The amount of organic material associated with the nanoparticles influenced the photocatalytic activity of the ZnO, with powders containing less organic material producing faster rate constants for the decolorizing of malachite green solutions under ultraviolet illumination, independent of particle size. [Zn(acetate)2(hydrazine)2] produced ZnO with the fastest rate constant and was recycled five times for dye degradation studies that revealed minimal to no reduction in catalytic efficiency

Role of Oxygen Defects on the Magnetic Properties of Ultra-Small Sn\u3csub\u3e1−x\u3c/sub\u3eFe\u3csub\u3ex\u3c/sub\u3eO\u3csub\u3e2\u3c/sub\u3e Nanoparticles

Although the role of oxygen defects in the magnetism of metal oxide semiconductors has been widely discussed, it is been difficult to directly measure the oxygen defect concentration of samples to verify this. This work demonstrates a direct correlation between the photocatalytic activity of Sn1−xFexO2 nanoparticles and their magnetic properties. For this, a series of ~2.6 nm sized, well characterized, single-phase Sn1−xFexO2 crystallites with x = 0−0.20 were synthesized using tin acetate, urea, and appropriate amounts of iron acetate. X-ray photoelectron spectroscopy confirmed the concentration and 3+ oxidation state of the doped Fe ions. The maximum magnetic moment/Fe ion, μ, of 1.6 × 10−4 μB observed for the 0.1% Fe doped sample is smaller than the expected spin-only contribution from either high or low spin Fe3+ ions, and μ decreases with increasing Fe concentration. This behavior cannot be explained by the existing models of magnetic exchange. Photocatalytic studies of pure and Fe-doped SnO2 were used to understand the roles of doped Fe3+ ions and of the oxygen vacancies and defects. The photocatalytic rate constant k also showed an increase when SnO2 nanoparticles were doped with low concentrations of Fe3+, reaching a maximum at 0.1% Fe, followed by a rapid decrease of k for further increase in Fe%. Fe doping presumably increases the concentration of oxygen vacancies, and both Fe3+ ions and oxygen vacancies act as electron acceptors to reduce e−-h+ recombination and promote transfer of electrons (and/or holes) to the nanoparticle surface, where they participate in redox reactions. This electron transfer from the Fe3+ ions to local defect density of states at the nanoparticle surface could develop a magnetic moment at the surface states and leads to spontaneous ferromagnetic ordering of the surface shell under favorable conditions. However, at higher doping levels, the same Fe3+ ions might act as recombination centers causing a decrease of both k and magnetic moment μ

Formulation and Aerosol Jet Printing of Nickel Nanoparticle Ink for High-Temperature Microelectronic Applications and Patterned Graphene Growth

Aerosol jet printing (AJP) is an advanced manufacturing technique for directly writing nanoparticle inks onto target substrates. It is an emerging reliable, efficient, and environmentally friendly fabrication route for thin film electronics and advanced semiconductor packaging. This fabrication technique is highly regarded for its rapid prototyping, the flexibility of design, and fine feature resolution. Nickel is an attractive high-temperature packaging material due to its electrical conductivity, magnetism, and corrosion resistance. In this work, we synthesized nickel nanoparticles and formulated an AJP ink, which was printed on various material surfaces. Thermal sintering experiments were performed on the samples to explore the redox behavior and to optimize the electrical performance of the devices. The nickel devices were heated to failure under an argon atmosphere, which was marked by a loss of reflectance and electrical properties due to the dewetting of the films. Additionally, a reduction mechanism was observed from these studies, which resembled that of nucleation and coalescence. Finally, multilayer graphene was grown on a custom-printed nickel thin film using chemical vapor deposition (CVD), establishing a fully additive manufacturing route to patterned graphene

Novel Magnetic and Optical Properties of Sn\u3csub\u3e1−x\u3c/sub\u3eZn\u3csub\u3ex\u3c/sub\u3eO\u3csub\u3e2\u3c/sub\u3e Nanoparticles

In this work, we report on the effects of doping SnO2 nanoparticles with Zn2+ ions. A series of ∼2–3 nm sized Sn1−x ZnxO2 crystallite samples with 0 ≤ x ≤ 0.18 were synthesized using a forced hydrolysis method. Increasing dopant concentration caused systematic changes in the crystallite size, oxidation state of Sn, visible emission, and band gap of SnO2 nanoparticles. X-ray Diffraction studies confirmed the SnO2 phase purity and the absence of any impurity phases. Magnetic measurements at room temperature showed a weak ferromagnetic behavior characterized by an open hysteresis loop. Their saturation magnetization Ms increases initially with increasing Zn concentrations; however for x \u3e 0.06, Ms decreases. Samples with the highest Ms values (x = 0.06) were analyzed using an Inductively Coupled Plasma Mass Spectrometer, looking for traces of any magnetic elements in the samples. Concentrations of all transition metals (Fe, Co, Mn, Cr, and Ni) in these samples were below ppb level, suggesting that the observed magnetism is not due to random inclusions of any spurious magnetic impurities and it cannot be explained by the existing models of magnetic exchange. A new visible emission near 490 nm appeared in the Zn doped SnO2 samples in the photoluminescence spectra which strengthened as x increased, suggesting the formation of defects such as oxygen vacancies. X-ray Photoelectron Spectroscopy (XPS) confirmed the nominal Zn dopant concentrations and the 2+ oxidation state of Zn in the Sn1−x ZnxO2 samples. Interestingly, the XPS data indicated the presence of a small fraction of Sn2+ ions in Sn1−xZnxO2 samples in addition to the expected Sn4+, and the Sn2+ concentration increased with increasing x. The presence of multi-valent metal ions and oxygen defects in high surface area oxide nanoparticles has been proposed as a potential recipe for weak ferromagnetis

Dopant Spin States and Magnetism of Sn\u3csub\u3e1−x\u3c/sub\u3eFe\u3csub\u3ex\u3c/sub\u3eO\u3csub\u3e2\u3c/sub\u3e Nanoparticles

This work reports detailed investigations of a series of ∼2.6 nm sized, Sn1−xFexO2 crystallites with x = 0–0.10 using Mossbauer spectroscopy, x-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance spectroscopy (EPR), and magnetometry to determine the oxidation state of Fe dopants and their role in the observed magnetic properties. The magnetic moment per Fe ion μ was the largest ∼6.48 × 10−3 μB for the sample with the lowest (0.001%) Fe doping, and it showed a rapid downward trend with increasing Fe doping. Majority of the Fe ions are in 3+ oxidation state occupying octahedral sites. Another significant fraction of Fe dopant ions is in 4+ oxidation state and a still smaller fraction might be existing as Fe2+ ions, both occupying distorted sites, presumably in the surface regions of the nanocrystals, near oxygen vacancies. These studies also suggest that the observed magnetism is not due to exchange coupling between Fe3+ spins. A more probable role for the multi-valent Fe ions may be to act as charge reservoirs, leading to charge transfer ferromagnetism

Correlative Imaging of Three-Dimensional Cell Culture on Opaque Bioscaffolds for Tissue Engineering Applications

Three-dimensional (3D) tissue engineering (TE) is a prospective treatment that can be used to restore or replace damaged musculoskeletal tissues, such as articular cartilage. However, current challenges in TE include identifying materials that are biocompatible and have properties that closely match the mechanical properties and cellular microenvironment of the target tissue. Visualization and analysis of potential 3D porous scaffolds as well as the associated cell growth and proliferation characteristics present additional problems. This is particularly challenging for opaque scaffolds using standard optical imaging techniques. Here, we use graphene foam (GF) as a 3D porous biocompatible substrate, which is scalable, reproducible, and a suitable environment for ATDC5 cell growth and chondrogenic differentiation. ATDC5 cells are cultured, maintained, and stained with a combination of fluorophores and gold nanoparticles to enable correlative microscopic characterization techniques, which elucidate the effect of GF properties on cell behavior in a 3D environment. Most importantly, the staining protocol allows for direct imaging of cell growth and proliferation on opaque scaffolds using X-ray MicroCT, including imaging growth of cells within the hollow GF branches, which is not possible with standard fluorescence and electron microscopy techniques

ZnO Nanoparticles Modulate the Ionic Transport and Voltage Regulation of Lysenin Nanochannels

Background: The insufficient understanding of unintended biological impacts from nanomaterials (NMs) represents a serious impediment to their use for scientific, technological, and medical applications. While previous studies have focused on understanding nanotoxicity effects mostly resulting from cellular internalization, recent work indicates that NMs may interfere with transmembrane transport mechanisms, hence enabling contributions to nanotoxicity by affecting key biological activities dependent on transmembrane transport. In this line of inquiry, we investigated the effects of charged nanoparticles (NPs) on the transport properties of lysenin, a pore-forming toxin that shares fundamental features with ion channels such as regulation and high transport rate. Results: The macroscopic conductance of lysenin channels greatly diminished in the presence of cationic ZnO NPs. The inhibitory effects were asymmetrical relative to the direction of the electric field and addition site, suggesting electrostatic interactions between ZnO NPs and a binding site. Similar changes in the macroscopic conductance were observed when lysenin channels were reconstituted in neutral lipid membranes, implicating protein-NP interactions as the major contributor to the reduced transport capabilities. In contrast, no inhibitory effects were observed in the presence of anionic SnO2 NPs. Additionally, we demonstrate that inhibition of ion transport is not due to the dissolution of ZnO NPs and subsequent interactions of zinc ions with lysenin channels. Conclusion: We conclude that electrostatic interactions between positively charged ZnO NPs and negative charges within the lysenin channels are responsible for the inhibitory effects on the transport of ions. These interactions point to a potential mechanism of cytotoxicity, which may not require NP internalization

Assessment of Wafer Scale MoS\u3csub\u3e2\u3c/sub\u3e Atomic Layers Grown by Metal–Organic Chemical Vapor Deposition Using Organo-Metal, Organo-Sulfide, and H\u3csub\u3e2\u3c/sub\u3eS Precursors

Transition Metal Dichalcogenides (TMDs) are a unique class of materials that exhibit attractive electrical and optical properties which have generated significant interest for applications in microelectronics, optoelectronics, energy storage, and sensing. Considering the potential of these materials to impact such applications, it is crucial to develop a reliable and scalable synthesis process that is compatible with modern industrial manufacturing methods. Metal–organic chemical vapor deposition (MOCVD) offers an ideal solution to produce TMDs, due to its compatibility with large-scale production, precise layer control, and high material purity. Optimization of MOCVD protocols is necessary for effective TMD synthesis and integration into mainstream technologies. Additionally, improvements in metrology are necessary to measure the quality of the fabricated samples more accurately. In this work, we study MOCVD of wafer-scale molybdenum disulfide (MoS2) utilizing two common chalcogen precursors, H2S and DTBS. We then develop a metrology platform for wafer scale samples quality assessment. For this, the coalesced films were characterized using Raman spectroscopy, atomic force microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Kelvin probe force microscopy. We then correlate the structural analysis of these grown films with electrical performance by using aerosol jet printing to fabricate van der Pauw test structures and assess sheet resistance