Characterizations Including Transmission Electron Microscopy Research Articles

Synergy of electronic and steric effects of Br-Ni catalysts for selective hydrogenolysis of diphenyl ether to phenol

Selective hydrogenolysis of 4-O-5 bond in lignin under relatively mild conditions is an important strategy for the production of valuable aromatic products, e.g. phenols, from renewable carbon resources. However, the easy saturation of benzene rings under reductive conditions over metal catalyst reduces the selectivity to aromatics. In this work, we investigated the effect of bromination of supported Ni nanoparticles on the phenol selectivity during the hydrogenolysis of diphenyl ether (DPE), a commonly used lignin model compound. Compared with the unmodified catalysts, Br-Ni/Al2O3 catalyst derived from Ni-Al layered double oxides exhibits enhanced phenol selectivity (37% vs. 15%) under similar DPE conversions (60%). Various characterizations including transmission electron microscopy (TEM), in-situ X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS), and CO-Fourier transform infrared spectroscopy (FTIR) indicate that Br preferentially located at the terrace site of Ni nanoparticles, deactivating the continuous Ni sites for benzene ring hydrogenation. In addition, the electron-withdrawing effect of Br creates positively charged Ni sites at the corners, facilitating the hydrogenolysis of C–O aryl ether bonds. During the hydrogenation of real lignin, the selective poisoning and electronic effects introduced by Br synergistically increased the yield of phenols from 12.20% on the initial Ni/Al2O3 to 30.47% over the Br-Ni/Al2O3 catalyst. This work provides an advanced strategy for the catalytic valorization of lignin by halogen modified metal-based catalysts.

A spark to the powder keg: Microneedle-based antitumor nanomedicine targeting reactive oxygen species accumulation for chemodynamic/photothermal/chemotherapy

Hypothesis.Chemodynamic therapy (CDT) can efficiently kill cancer cells by producing hydroxyl radical (•OH), a kind of high-toxic reactive oxygen species (ROS), via Fenton or Fenton-like reactions. This study involved a versatile nanomedicine, MSN@DOX/GA-Fe/PDA (M@DGP), delivered via microneedles, which was expected to combine chemodynamic/photothermal/chemotherapy and efficiently increase ROS accumulation to achieve significant therapeutic efficacy against melanoma.Experiments.The composition of the synthesized nanoparticles was confirmed by a series of characterizations including transmission electron microscopy, Fourier transform infrared spectroscopy, and zeta potential. The photothermal properties of the nanomedicine was evaluated via infrared imaging, and •OH-producing ability was evaluated by UV–Vis and electron spin resonance. The mechanisms of ROS accumulation were studied in B16 cells by detecting intracellular •OH, glutathione, and ROS levels. The drug-loaded microneedles (M@DGP-MNs) were prepared, and their morphology and mechanical strength were characterized. The in vivo antimelanoma effect and biosafety evaluation of the nanomedicine were investigated in tumor-bearing C57 mice.Findings.M@DGP was successfully prepared and could achieve ROS accumulation through a photothermal-enhanced Fenton reaction, polydopamine-induced glutathione consumption, and doxorubicin-mediated mitochondrial dysfunction which induced oxidative stress and apoptosis of tumor cells. M@DGP-MNs showed superior antitumor efficacy and good biosafety, providing a promising strategy for melanoma treatment.

Exploration of Physicochemical Mechanism for Negative Bias Temperature Instability in GaN‐HEMTs by Extracting Activation Energy of Dislocations

AbstractThe reliability issues caused by negative bias temperature instability (NBTI) impede the rapid expansion of gallium nitride (GaN)‐based high electron mobility transistors (HEMT). Clarifying the physicochemical reactions during the degradation process induced by NBTI is of paramount importance for tracing the origin of NBTI, so as to circumvent the intrinsic reliability problem. However, the investigation of deep‐seated reasons behind NBTI‐related issue still lacks a feasible approach and has not been explored in depth. This paper proposes a conjoint approach that combines electrical measurements, material analysis, and theoretical calculations to comprehensively investigate the molecular basis of degradation presented by NBTI. Extracting the activation energy of dislocations during stress effectively identifies the deep sources of device deterioration. The breaking of NH bonds and migration of hydrogen ions along the dislocations in GaN lattice are primarily responsible for the electrical instabilities according to the theoretical calculation of activation energy, which is also evidenced by material characterizations including transmission electron microscopy, X‐ray photoelectron spectroscopy and Raman analysis. Also, a molecular‐level model that demonstrates the reaction kinetics is well established for the fundamental understanding of the pivotal physicochemical mechanism behind NBTI, thus providing the direction for further optimization of GaN electronics.

Solvent-Free Melting-Assisted Pyrolysis Strategy Applied on the Co/N Codoped Porous Carbon Catalyst

From the current demand for aromatic ketones, economical and environmentally friendly renewable catalysts are highly economical for the efficient selection of aralkyl oxides to form the corresponding aromatic ketone compounds. Yet, since the preparation of the Co–N–C catalyst is complicated at present, it is difficult to be widely applied to the oxidation of arylalkanes. In this study, a one-step solvent-free melting-assisted heat-treatment strategy is adopted to synthesize cobalt and nitrogen codoped carbon catalysts from sucrose, 5-(4-carboxyphenyl)-10,15,20-triphenylcobalt porphyrin (CoCPTPP), and KIT-6. Thanks to the interaction between the silicon hydroxyl of KIT-6 and the carboxyl hydroxyl of CoCPTPP as well as the distinctive properties of CoCPTPP with Co–N4 structures, the Co species in the as-synthesized catalysts are uniformly dispersed on carbon materials. Hereafter, the catalyst showed a high efficiency for the oxidation of arylalkane, e.g., the conversion rate of ethylbenzene is 96% and the selectivity of acetophenone is 99%. According to the characterizations including transmission electron microscopy etc, the results show that a porous special structure and thriving Co–Nx active sites in the catalysts is the main reason for the catalyst’s good catalytic activity and stability. In addition, the catalyst can also be used for the oxidation reaction of various aromatic hydrocarbon substrates with high catalytic activity.

CdSe QD Biosynthesis in Yeast Using Tryptone-Enriched Media and Their Conjugation with a Peptide Hecate for Bacterial Detection and Killing.

The physical and chemical synthesis methods of quantum dots (QDs) are generally unfavorable for biological applications. To overcome this limitation, the development of a novel “green” route to produce highly-fluorescent CdSe QDs constitutes a promising substitute approach. In the present work, CdSe QDs were biosynthesized in yeast Saccharomyces cerevisiae using a novel method, where we showed for the first time that the concentration of tryptone highly affects the synthesis process. The optimum concentration of tryptone was found to be 25 g/L for the highest yield. Different methods were used to optimize the QD extraction from yeast, and the best method was found to be by denaturation at 80 °C along with an ultrasound needle. Multiple physical characterizations including transmission electron microscopy (TEM), dynamic light scattering (DLS), energy-dispersive X-ray spectroscopy (EDX), and spectrophotometry confirmed the optical features size and shape distribution of the QDs. We showed that the novel conjugate of the CdSe QDs and a cell-penetrating peptide (hecate) can detect bacterial cells very efficiently under a fluorescent microscope. The conjugate also showed strong antibacterial activity against vancomycin-resistant Staphylococcus aureus (VRSA), methicillin-resistant Staphylococcus aureus (MRSA), and Escherichia coli, which may help us to cope with the problem of rising antibiotic resistance.

In-situ observation of the tensile deformation and fracture behaviour of powder-consolidated and as-cast metastable beta titanium alloys

The plastic deformation processes and fracture mechanisms of as-consolidated powder metallurgy (PM) and as-cast ingot metallurgy (IM) metastable beta titanium alloys (Ti-5Al-5V-5Mo-3Cr) were thoroughly investigated by room temperature tensile tests with in-situ scanning electron microscopy (SEM) observations and further microstructure characterizations including transmission electron microscopy (TEM) and atomic force microscopy (AFM). The results suggested that IM alloy has a better compatible deformation capability than PM alloy characterized by varying slip deformation mechanisms and the constantly changing slip modes. The microcracks in PM alloy were observed to be originated at the interfaces of α″/β and grain boundary α/β. Whereas, the microcracks in IM alloy were observed on the grain boundaries and the intracrystalline α precipitation areas, where the slip steps were generated. Particularly, the common defects in PM (residual pores and microvoids) and IM (casting cavity) alloys did not exhibit significant negative effects, contrary to previous awareness. Finally, the coalescence of the grain boundary α and the widened α″/β microcracks led to the sudden brittle transgranular-intergranular mixed fracture of PM alloy. For IM alloy, the serious cracking initiated the V-shape notch made its way through the microcracks at the α/β slip steps, resulting in the gradual transgranular fracture with better ductility.

Shell thickness dependent photocatalytic activity of EDTA-assisted Ag/ZnO core-shell nanoparticles under sunlight irradiation

Functionalized Ag/ZnO core–shell (CS) nanoparticles (NPs) with ethylenediaminetetraacetic acid (EDTA) having same core size but with different shell thickness are successfully prepared through a simple and low cost wet chemical process. Different physiochemical characterizations including transmission electron microscopy, x-ray diffraction, Brunauer-Emment-Teller surface area analysis, zeta potential analysis, thermal gravimetric-differential analysis, UV-visible absorption spectroscopy, Photoluminescence Spectroscopy and Fourier-transform infrared Spectroscopy have been involved to characterize the samples. The thickness of ZnO shell of Ag/ZnO CS NPs is found to be increasing with increasing molar ratio of EDTA/Zn2+. The LSPR wavelength of Ag core is shifting to longer visible wavelength with increasing the shell thickness of Ag/ZnO CS NPs because of the increase in the dielectric constant of the sourrounding environment. The increasing shell thickness of Ag/ZnO CS NPs makes a strong effect on the decrease in the fluorescence intensity of UV emission of ZnO. This quenching of PL intensity has been further verified by transient fluorescence (FL) spectra. The Nyquist plots also provide evidence of higher electron-transfer rate of the Ag/ZnO CS NPs of having higher shell thickness. The photocurrent measurement confirms electron-charging of Ag core in Ag/ZnO CS NPs. Variation of concentration of EDTA as anionic surfactant causes variation of surface charge of Ag/ZnO CS NPs. With increasing the shell thickness, photodegradation efficiency of Ag/ZnO CS NPs towards methylene blue (MB) degradation enhances under sunlight irradiation. This enhancement in photocatalytic efficiency with increasing the shell thickness is achieved due to the higher surface area, higher charge transfer efficiency, extended light absorption towards visible region and more negative zeta potential of Ag/ZnO CS NPs.

Revealing pH-Dependent Activities and Surface Instabilities for Ni-Based Electrocatalysts during the Oxygen Evolution Reaction

Multiple electrochemical processes are involved at the catalyst/electrolyte interface during the oxygen evolution reaction (OER). With the purpose of elucidating the complexity of surface dynamics upon OER, we systematically studied two Ni-based crystalline oxides (LaNiO3−δ and La2Li0.5Ni0.5O4) and compared them with the state-of-the-art Ni–Fe (oxy)hydroxide amorphous catalyst. Electrochemical measurements such as rotating ring disk electrode (RRDE) and electrochemical quartz microbalance microscopy (EQCM) coupled with a series of physical characterizations including transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS) were conducted to unravel the exact pH effect on both the OER activity and the catalyst stability. We demonstrate that for Ni-based crystalline catalysts the rate for surface degradation depends on the pH and is greater than the rate for surface reconstruction. This behavior is unlike that for the amorphous Ni oxyhydroxide catalyst, which is found to be more stable...

Palladium nanoparticles supported on mesoporous silica microspheres for enzyme-free amperometric detection of H2O2 released from living cells

An enzyme-free sensitive hydrogen peroxide (H2O2) amperometric sensor is developed to detect H2O2 released from living cells using palladium nanoparticles supported on sulfonic acid functionalized mesoporous silica microspheres (Pd@SO3H-MSM). It is synthesized by an easy and facile method and is subsequently used for fabrication of an electrochemical sensing scaffold via drop-casting modification of a glassy carbon electrode (represented as GC/Pd@SO3H-MSM). Comprehensive characterizations including transmission electron microscopy, scanning electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, UV–vis spectrophotometry and electrochemical impedance spectroscopy to confirm the existence and nature of Pd nanoparticles in Pd@SO3H-MSM. GC/Pd@SO3H-MSM electrode demonstrates electrocatalytic activity for H2O2 reduction in phosphate buffer, leading to a sensitive H2O2 amperometric sensor with wide linear range (47.0 nM-1.0 mM), low detection limit (14.0 nM) and high sensitivity (0.36 μA mM−1 cm-2). It exhibits high selectivity, good reproducibility and long-term stability. More importantly, Pd@SO3H-MSM exhibits no toxicity to living cells and based on its remarkable analytical advantages, it is further unswervingly used to execute real-time detection of H2O2 released from living tumor cells and healthy normal cells. Thus Pd@SO3H-MSM acts as promising material for amperometric determination of H2O2 as well as used to accomplish real-time quantitative detection of H2O2 in biological environment.

Fabrication and characterization of ZnS/ZnO core shell nanostructures on silver wires

In this research, ZnS nanoparticles were synthesized on ZnO/silver wires to form ZnS/ZnO core shell structures. Various outward appearance and colors could be observed by different ZnO growth and sulfurization conditions. To evaluate the properties of these nanostructures, optical properties and chemical bindings were analyzed by photoluminescence, Raman analysis, and X-ray photoelectron spectroscopy. Furthermore, material characterizations including transmission electron microscopy and X-ray diffraction confirmed that cubic ZnS (311)/ZnO nanostructures were grown on silver wires for the first time. ZnS/ZnO core shell structures on silver wires are promising for future optoelectronic and biomedical applications.

Silver Nanoparticle/Boron-Doped Graphene Nanoribbon Nanocomposite for Effective Surface Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) provides high sensitivity and selectivity on molecule detection, making it attractive for biomedical and chemical detections. Generally there are two mechanisms to influence the SERS enhancement: electromagnetic mechanism (EM) created by the metals with surface plasmon resonance (SPR) property and chemical mechanism (CM) due to the charge transfer between the molecule and the substrate. The development of synthetic method to produce nanostructures with controllable EM and CM properties will lead to important advances on both fundamental study and innovative applications for SERS-based biomedical detections. Graphene nanoribbons (GNRs) represent a unique structure of carbon nanomaterials with controlled electronic properties by tuning their widths, making them can be potentially useful as the SERS-active substrate and used in other applications including energy, composites, biomedical and electronics. Here we report a rational design to develop a SERS-active nanocomposite with improved EM and CM properties. Toward this goal, we prepared silver (Ag)/Boron-doped GNR (B-GNR) composites using a sequential reaction route. First we synthesized GNRs with averaged width around 4 to 5 nm by the chemical unzipping of singled-walled carbon nanotubes (SWCNTs). Additionally, the prepared GNRs were doped with B atoms by a controlled carbonthemic reaction under argon (Ar) flow at atmospheric pressure and the B dopant concentration was about 1.4 atomic percentage (atom%) according to the X-ray photoelectron spectroscopy (XPS) analysis. Ag NPs with 10 nm averaged size were decorated onto the B-GNRs surface through an atmospheric-pressure microplasma-assisted redox reaction. Detailed materials characterizations including transmission electron microscopy and UV-Vis spectroscopy show that Ag/B-GNR composites were successfully synthesized in our experiment. We further systematically studied the Raman response of the Ag/B-GNR composite using Rhodamine 6G (R6G) as the Raman probe molecules. The result indicates that the Ag/GNR composite shows superior SERS performance with low detection concentration of 10-12 M of R6G and high enhance factor (EF) of 1.9x1012. We furthermore systematically studied the CM enhancement via different probing molecules and substrates. Results show that SERS performance is strongly influenced by the charge transfer mechanism induced by the energy gap between the substrate Fermi level and the LUMO energy of probing molecules. Our study provide the conception to design the applicable SERS substrates. Figure 1

A facile “polystyrene-dissolving” strategy to hollow periodic mesoporous organosilica with flexible structure-tailorability

A facile “template dissolving” strategy has been developed for the fabrication of hollow periodic mesoporous organosilica (HPMO) particles with perpendicularly ordered mesopores, where polystyrene (PS) is used as sacrifice template for the generation of hollow cavity. Systematic characterizations including transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and N2 adsorption/desorption analysis clearly reveal that the HPMO particles have an excellent monodispersity with a high specific surface area of 1246.7 m2 g−1, large pore volume of 1.38 cm3 g−1 and uniformly ordered mesopores of 2.48 nm. The pre-encapsulation of a core into PS (SiO2, Fe3O4@SiO2) results in a yolk-shell (Y-S) particle with high tunable shell thickness (30–60 nm) and cavity size (230–450 nm). The magnetically recyclable Fe3O4-YS-PMO was further utilized to adsorb 2, 4-dichlorophenol (2, 4-DCP) and the controlled release of camptothecin (CPT). Up to 81 mg of CPT was loaded per gram of the Fe3O4-YS-PMO particles, followed with a continuously release of 76% within 5 days.

Controlled-release drug carriers based mesoporous silica spheres with hierarchical hollow/nano structure

Mesoporous silica spheres with hierarchical hollow/nano structure (MSSH-H/N) have been successfully prepared by a template-guided approach, in which cetyltrimethyl ammonium bromide (CTAB) and polystyrene (PS) emulsion was used as the template of mesopores and hollow core, respectively. A consecutive template mechanism and the formation of the hierarchical hollow/nano structure were proposed on basis of the combined characterizations including transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction patterns (XRD) and nitrogen sorption analysis, which showed that the hierarchical structure is composed of mesoporous hollow SiO2 spheres and discrete mesoporous SiO2 nanoparticles coating on the shell. Ibuprofen (IBU) was chosen as a drug model in delivery and release experiments, and these MSSH-H/N samples exhibited higher drug loading capacity, desired low initial IBU release rate and typical two-phase drug release behavior compared with conventional single-structure (single-shelled) hollow mesoporous silica spheres due to their unique hierarchical hollow/nano structure.

Synthesis of Ultralong Polyaniline Nanorods by Magnetic Nanoparticles as Templates Under External Magnetic Field.

We report the successful synthesis of ultralong polyaniline nanorods (UL-PANI-NRs) via using water-soluble magnetic Fe3O4 nanoparticles as soft templates under the assistance of external magnetic field. It was found that the concentration of Fe3O4 nanoparticles, the aniline concentration and the use of an external magnetic field significantly affect the morphology of the PANI products. The following characterizations including transmission electron microscopy (TEM), Fourier-Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD). and thermogravimetric analysis (TGA) were conducted to investigate the electronic structure and composition of as-prepared UL-PANI-NRs. Our preliminary result indicates that complicated polymer structures (such as ultralong rods with vertical branches) may be prepared by water-soluble magnetic Fe3O4 nanoparticles as soft templates under the assistance of alternatively external magnetic fields.

Tuning the surface charge of 2D oxide nanosheets and the bulk-scale production of superlatticelike composites.

The surface charge of various anionic unilamellar nanosheets, such as graphene oxide (GO), Ti0.87O2(0.52-), and Ca2Nb3O10(-) nanosheets, has been successfully modified to be positive by interaction with polycations while maintaining a monodispersed state. A dilute anionic nanosheet suspension was slowly added dropwise into an aqueous solution of high molecular weight polycations, which attach on the surface of the anionic nanosheets via electrostatic interaction. Surface modification and transformation to positively charged nanosheets were confirmed by various characterizations including atomic force microscopy and zeta potential measurements. Because the sizes of the polycations used are much larger than the nanosheets, the polymer chains may run off the nanosheet edges and fold to the fronts of the nanosheets, which could be a reason for the continued dispersion of the modified nanosheets in the suspension. By slowly adding a suspension of polycation-modified nanosheets and pristine anionic nanosheet dropwise into water under suitable conditions, a superlatticelike heteroassembly can be readily produced. Characterizations including transmission electron microscopy and X-ray diffraction measurements provide evidence for the formation of the alternately stacked structures. This approach enables the combination of various pairs of anionic nanosheets with different functionalities, providing a new opportunity for the creation of unique bulk-scale functional materials and their applications.

Synthesis of polyaniline-coated carbon nanotubes and study on their pH-sensitive conductivity.

We report the synthesis of polyaniline-coated-carbon nanotubes (PANI-c-CNTs) composites by using water-soluble CNTs with phenyl sulfonate groups as templates. A series of characterizations including transmission electron microscopy (TEM), Fourier-Transform Infrared Spectroscopy (FTIR) and UV-vis spectroscopy were conducted to investigate the formation of PANI coating on the surfaces of the CNTs. The thickness of PANI coating in the PANI-c-CNTs composites was controlled by adjusting concentrations of aniline and CNTs. The conductivities of PANI-c-CNTs composites were measured by using conductive atomic force microscopy (c-AFM). It was found that the conductivities of PANI-c-CNTs composites were remarkably affected after doping and dedoping process of PANI coating by different pH solution. Therefore, our preliminary result indicates that as-prepared PANI-c-CNTs composites may be used as gas sensor such as HCl and NH3 vapor.

A facile vesicle template route to multi-shelled mesoporous silica hollow nanospheres

Multi-shelled mesoporous silica hollow nanospheres (MMSHNs) with uniform size distribution (∼150 nm), tuneable shell thickness (7–20 nm) and layer number (1–4 layers) have been successfully synthesized through a facile vesicle template approach derived from a self-assembly of surfactants [C3F7O(CFCF3CF2O)2CFCF3CONH(CH2)3N+(C2H5)2CH3I−] (FC4) and EO106PO70EO106 (F127). The formation of these hollow nanospheres was monitored by dynamic light scattering. A vesicle template mechanism for the molecular build-up of these silica hollow nanospheres was proposed based on the dynamic light scattering data in combination with material characterizations including transmission electron microscopy (TEM), scanning electron microscopy (SEM) and nitrogen sorption analysis. Through this method, CdTe quantum dots (QDs) were in situ encapsulated into the hollow nanospheres. These hollow nanospheres demonstrated a good selective adsorption capacity for Methylene Blue dye, and can effectively load drug molecules for delivery. It is expected these hollow nanospheres have great potential for the application in fluorescence biological probes, bio-imaging, drug delivery and water purification.

Triangle-shape ZnO prepared by thermal decomposition

Using oleic acid as surfactant, triangle-shape ZnO with an average diameter of 250 nm can be synthesized by thermal decomposition of precursor zinc acetate (Zn(CH 3CH 2COO) 2) in the high boil-point solvent trioctylamine (TOA). Fundamental characterizations including transmission electron microscopy, X-ray diffraction, high-resolution transmission electron microscopy, scanning electron microscopy and photoluminescence were conducted for the as-synthesized ZnO particles. The effects of refluxing time and the content of surfactant on size and morphology of ZnO particles were studied. It is found that the shape of ZnO particles changes from round-shape, disk-shape to triangle-shape. Based on experimental observations and surface and attachment energies simulation for various crystallographic planes, a possible growth mechanism was put forward to explain the formation of triangle-shape ZnO particles.

A methodology for the preparation of nanoporous polyimide films with low dielectric constants

A method to generate nanoporous polyimide films with low dielectric constants was proposed. The preparation consisted of two steps. Firstly, a polyimide/silica hybrid film was prepared via sol–gel process. Secondly, the hybrid film was treated with hydrofluoric acid to remove the dispersed silica particles, leaving pores with diameters between 20 and 120 nm, depending on the size of silica particles. Both hybrid and porous films were subjected to a variety of characterizations including transmission electron microscopy observation, dielectric constant measurement and tensile strength measurement.