Individual Titanate Nanoribbons Studied by 3D-Resolved Polarization Dependent X‑ray Absorption Spectra Measured with Scanning Transmission X‑ray Microscopy

Polarization dependent X-ray absorption spectroscopy (XAS) is a powerful probe of the anisotropic electronic structure of bulk single crystals, but its application to nanostructured samples is challenging. Here we describe a method for obtaining linearly polarized XAS spectra along three orthogonal axes of an individual nano-object using scanning transmission X-ray microscopy (STXM). The technique is applied to a single sodium titanate nanoribbon [(Na,H)Ti NR]. Significant linear dichroism is observed at both the Ti 2p and O 1s edges. The experimental results are compared with first-principles calculations; good agreement is achieved. The spectral changes among the three axes are attributed to the anisotropic Ti–O bonding of the various Ti and O sites in the monoclinic crystal structure of the nanoribbon. The methodology for 3D dichroic STXM measurements developed in this study is a powerful way to investigate the anisotropic geometric and electronic structure of nanomaterials

Mn²⁺ Substitutional Doping of TiO₂ Nanoribbons: A Three-Step Approach

An in situ doping approach was successfully employed for synthesis of Mn²⁺-doped sodium titanate nanoribbons, which were used as a precursor for preparation of TiO₂ nanoribbons with homogeneous distribution of Mn²⁺ ions. The comprehensive structural characterization using powder X-ray diffraction (XRD) and electron paramagnetic resonance (EPR) provided compelling evidence that the Mn²⁺ ion predominantly substitutes the Ti⁴⁺ ion at octahedral coordination sites in bulk. Measurements performed on individual nanoribbons using near edge X-ray absorption fine structure spectromicroscopy revealed that the strong alkaline environment required for the formation of sodium titanate nanoribbons did not affect the manganese oxidation state. In the next two steps, the ion exchange process in HCl­(aq) solution followed by the thermal treatment in air, lead to the formation of Mn²⁺ doped TiO₂ nanoribbons. Analysis of the manganese content by X-ray photoelectron spectroscopy of several TiO₂ nanoribbon samples calcined in the temperature range from 400 to 700 °C as well as analysis performed at the Ti L_2,3 and Mn L_2,3 edges with electron energy loss spectroscopy (EELS) showed that calcination at elevated temperatures induced the diffusion of manganese ions toward the nanoribbons’ surface. However, transformation of anatase nanoribbons to rutile nanoparticles, this process started at around 580 °C, was also accompanied by the partial oxidation of Mn²⁺ to Mn³⁺ and Mn⁴⁺. Manganese atoms that diffused to the TiO₂ surface preferentially formed MnO_<i>x</i> clusters as observed from characteristic electron paramagnetic resonance spectra and EELS measurements. In addition, the presence of Mn²⁺ reduced the beginning of phase transformation from anatase to rutile to near 120 °C

Nitrogen-Doped Silver-Nanoparticle-Decorated Transition-Metal Dichalcogenides as Surface-Enhanced Raman Scattering Substrates for Sensing Polycyclic Aromatic Hydrocarbons

The modification of transition-metal dichalcogenides (TMDs), incorporating nitrogen (N) doping and silver nanoparticles (Ag_NPs) decoration on the skeleton of exfoliated MoS₂ and WS₂, was accomplished. The preparation of N-doped and Ag_NPs-decorated TMDs involved a one-pot treatment procedure in a vacuum-sputtering chamber under N plasma conditions and in the presence of a silver (Ag) cathode as the source. Two different deposition times, 5 and 10 s, respectively, were applied to obtain N-doped with Ag_NPs-decorated MoS₂ and WS₂ hybrids, abbreviated as N5-MoS₂/Ag_NPs, N10-MoS₂/Ag_NPs, N5-WS₂/Ag_NPs, and N10-WS₂/Ag_NPs, respectively, for each functionalization time. The successful incorporation of N as the dopant within the lattice of exfoliated MoS₂ and WS₂ as well as the deposition of Ag_NPs on their surface, yielding N-MoS₂/Ag_NPs and N-WS₂/Ag_NPs, was manifested through extensive X-ray photoelectron spectroscopy measurements. The observation of peaks at ∼398 eV derived from covalently bonded N and the evolution of a doublet of peaks at ∼370 eV guaranteed the presence of Ag_NPs in the modified TMDs. Also, the morphologies of N-MoS₂/Ag_NPs and N-WS₂/Ag_NPs were examined by transmission electron microscopy, which proved that Ag deposition resulted in nanoparticle growth rather than the creation of a continuous metal film on the TMD sheets. Next, the newly developed hybrid materials were proven to be efficient surface-enhanced Raman scattering (SERS) platforms by achieving the detection of Rhodamine B (RhB). Markedly, N10-MoS₂/Ag_NPs showed the highest sensitivity for detecting RhB at concentrations as low as 10^–9 M. Charge-transfer interactions between RhB and the modified TMDs, together with the polarized character of the system causing dipole–dipole coupling interactions, were determined as the main mechanisms to induce the Raman scattering enhancement. Finally, polycyclic aromatic hydrocarbons such as pyrene, anthracene, and 2,3-dihydroxynaphthalene, coordinated via π–S interactions with N-MoS₂/Ag_NPs, were screened with high sensitivity and reproducibility. These findings highlight the excellent functionality of the newly developed N-MoS₂/Ag_NPs and N-WS₂/Ag_NPs hybrid materials as SERS substrates for sensing widespread organic and environmental pollutants as well as carcinogen and mutagen species

Aerosol-Assisted CVD-Grown WO₃ Nanoneedles Decorated with Copper Oxide Nanoparticles for the Selective and Humidity-Resilient Detection of H₂S

A gas-sensitive hybrid material consisting of Cu₂O nanoparticle-decorated WO₃ nanoneedles is successfully grown for the first time in a single step via aerosol-assisted chemical vapor deposition. Morphological, structural, and composition analyses show that our method is effective for growing single-crystalline, n-type WO₃ nanoneedles decorated with p-type Cu₂O nanoparticles at moderate temperatures (i.e., 380 °C), with cost effectiveness and short fabrication times, directly onto microhot plate transducer arrays with the view of obtaining gas sensors. The gas-sensing studies performed show that this hybrid nanomaterial has excellent sensitivity and selectivity to hydrogen sulfide (7-fold increase in response compared with that of pristine WO₃ nanoneedles) and a low detection limit (below 300 ppb of H₂S), together with unprecedented fast response times (2 s) and high immunity to changes in the background humidity. These superior properties arise because of the multiple p–n heterojunctions created at the nanoscale in our hybrid nanomaterial

Biobased Epoxy Resin with Low Electrical Permissivity and Flame Retardancy: From Environmental Friendly High-Throughput Synthesis to Properties

Recent years have witnessed significant advances in biobased epoxy resins to replace their petroleum-based counterparts, especially diglycidyl ether of bisphenol A type epoxy resin (DGEBA). However, for meeting a great variety of the requirements, long-standing challenges include environmentally friendly preparation of epoxy resin with few toxic byproducts and improving their properties. Herein, we report a facile method to synthesize new silicone-bridged difunctional epoxy monomers in high yield. They are derived from naturally occurring eugenol by introducing the methylsiloxane and phenylsiloxane linkers of different chain lengths into their molecular backbones. These synthesized liquid epoxy monomers have definitive molecular structure with high purity. These silicone-bridged difunctional epoxy monomers exhibit much lower viscosity (<2.5 Pa s) than commercial DGEBA epoxy (10.7 Pa s) suitable for composites and prepregs. After curing, they exhibit a dielectric permittivity as low as 2.8 and good intrinsic flame retardancy with LOI value higher than 31, far outperforming DGEBA. All these advantages are stemmed from their siloxane-contained segments characterized by low polarity, very high dissociation energy, helical molecular structure, and high molecular volume. Overall, this work provides a very facile and scalable route access to a family of the multifunctional eugenol-based epoxy monomers with low dielectric constant and enhanced flame retardancy

Lattice Mismatch Drives Spatial Modulation of Corannulene Tilt on Ag(111)

We investigated the adsorption of corannulene (C₂₀H₁₀) on the Ag(111) surface by experimental and simulated scanning tunneling microscopy (STM), X-ray photoemission (XPS), and near-edge X-ray absorption fine structure (NEXAFS). Structural optimizations of the adsorbed molecules were performed by density functional theory (DFT) and the core excited spectra evaluated within the transition-potential approach. Corannulene is physisorbed in a bowl-up orientation displaying a very high mobility (diffusing) and dynamics (tilting and spinning) at room temperature. At the monolayer saturation coverage, molecules order into a close-compact phase with an average intermolecular spacing of ∼10.5 ± 0.3 Å. The lattice mismatch drives a long wavelength structural modulation of the molecular rows, which, however, could not be identified with a specific superlattice periodicity. DFT calculations indicate that the structural and spectroscopic properties are intermediate between those predicted for the limiting cases of an on-hexagon geometry (with a 3-fold, ∼8.6 Å unit mesh) and an on-pentagon geometry (with a 4-fold, ∼11.5 Å unit mesh). We suggest that molecules smoothly change their equilibrium configuration along the observed long wavelength modulation of the molecular rows by varying their tilt and azimuth in between the geometric constraints calculated for molecules in the 3-fold and 4-fold phases

Lattice Mismatch Drives Spatial Modulation of Corannulene Tilt on Ag(111)

We investigated the adsorption of corannulene (C₂₀H₁₀) on the Ag(111) surface by experimental and simulated scanning tunneling microscopy (STM), X-ray photoemission (XPS), and near-edge X-ray absorption fine structure (NEXAFS). Structural optimizations of the adsorbed molecules were performed by density functional theory (DFT) and the core excited spectra evaluated within the transition-potential approach. Corannulene is physisorbed in a bowl-up orientation displaying a very high mobility (diffusing) and dynamics (tilting and spinning) at room temperature. At the monolayer saturation coverage, molecules order into a close-compact phase with an average intermolecular spacing of ∼10.5 ± 0.3 Å. The lattice mismatch drives a long wavelength structural modulation of the molecular rows, which, however, could not be identified with a specific superlattice periodicity. DFT calculations indicate that the structural and spectroscopic properties are intermediate between those predicted for the limiting cases of an on-hexagon geometry (with a 3-fold, ∼8.6 Å unit mesh) and an on-pentagon geometry (with a 4-fold, ∼11.5 Å unit mesh). We suggest that molecules smoothly change their equilibrium configuration along the observed long wavelength modulation of the molecular rows by varying their tilt and azimuth in between the geometric constraints calculated for molecules in the 3-fold and 4-fold phases

Plasma Fluorination of Vertically Aligned Carbon Nanotubes

Functionalization of vertically aligned multiwalled carbon nanotube carpets was performed via exposure to CF₄ or Ar:F₂ RF plasmas. Rapid fluorination was observed via X-ray photoelectron spectroscopy (XPS) with surface fluorine concentration, bonding type, and patterning dependent on gas mixture and exposure time. Surface properties of the v-MWCNTs forests have been changed by the introduction of fluorine-containing groups, as demonstrated via surface wettability studies, while scanning electron microscopy shows that overall nanotube alignment and separation is conserved. Scanning X-ray photoelectron spectromicroscopy (SPEM) shows that the plasma treatment results in selective functionalization of the surface tips of the nanotubes. This opens the way to nanotube carpet structures with activated surfaces, which maintain the desirable conductive properties of the pristine nanotubes near to the substrate

Electron Beam Nanosculpting of Kirkendall Oxide Nanochannels

The nanomanipulation of metal nanoparticles inside oxide nanotubes, synthesized by means of the Kirkendall effect, is demonstrated. In this strategy, a focused electron beam, extracted from a transmission electron microscope source, is used to site-selectively heat the oxide material in order to generate and steer a metal ion diffusion flux inside the nanochannels. The metal ion flux generated inside the tube is a consequence of the reduction of the oxide phase occurring upon exposure to the e-beam. We further show that the directional migration of the metal ions inside the nanotubes can be achieved by locally tuning the chemistry and the morphology of the channel at the nanoscale. This allows sculpting organized metal nanoparticles inside the nanotubes with various sizes, shapes, and periodicities. This nanomanipulation technique is very promising since it enables creating unique nanostructures that, at present, cannot be produced by an alternative classical synthesis route

Knitting the Catalytic Pattern of Artificial Photosynthesis to a Hybrid Graphene Nanotexture

The artificial leaf project calls for new materials enabling multielectron catalysis with minimal overpotential, high turnover frequency, and long-term stability. Is graphene a better material than carbon nanotubes to enhance water oxidation catalysis for energy applications? Here we show that functionalized graphene with a tailored distribution of polycationic, quaternized, ammonium pendants provides an sp² carbon nanoplatform to anchor a totally inorganic tetraruthenate catalyst, mimicking the oxygen evolving center of natural PSII. The resulting hybrid material displays oxygen evolution at overpotential as low as 300 mV at neutral pH with negligible loss of performance after 4 h testing. This multilayer electroactive asset enhances the turnover frequency by 1 order of magnitude with respect to the isolated catalyst, and provides a definite up-grade of the carbon nanotube material, with a similar surface functionalization. Our innovation is based on a noninvasive, synthetic protocol for graphene functionalization that goes beyond the ill-defined oxidation–reduction methods, allowing a definite control of the surface properties