Crystalline Core Research Articles

Efficient defect engineering and in-situ carbon doping in ultra-fine TiO2 with enhanced visible-light-response photocatalytic performance

The wide bandgap and low photocatalytic efficiency are acknowledged as the main problems of the photocatalytic activities of TiO2. Herein, an effective strategy combing defect engineering and heteroatom doping is developed to expand the region covering visible light response and construct the active surface. A plasma-induced carbon doping (PICD) method is adopted to achieve a binary core-shell structure containing outer defect-layer shell of oxygen vacancy and inside crystalline anatase TiO2 core (~ 5 nm). The outstanding photocatalytic activity for visible-light-driven degradation of RhB and MO originates from narrowed bandgap (~ 2.30 eV) and improved photo-induced charge separation. Moreover, the excellent stability towards RhB degradation (100%) after 4 recycles exhibits the great potential applicability. RhB removal efficiency could reach to 100% even in the wide pH range from 3 to 11. Furthermore, the synergy effect by outside oxygen-vacancies layer and interstitial carbon doping enhanced the photoelectrochemical (PEC) performances significantly. This PICD technology can induce carbon doping and defect layer with active cites, which opens up a new way to design novel visible-light-responsive photocatalysis.

Chemical vapor deposition of germanium-rich CrGe x nanowires.

Chemical vapor deposition was applied to synthetize nanostructured deposits containing several sorts of nanoobjects (i.e., nanoballs, irregular particles, and nanowires). Analytical techniques, that is, high-resolution transmission electron microscopy, scanning electron microscopy, electron dispersive X-ray analysis, selected area electron diffraction, and X-ray photoelectron spectroscopy, showed that unlike nanoballs and particles composed of crystalline germanium, the layer was made of chromium germanide CrGex. The nanowires possessed a complex structure, namely a thin crystalline germanium core and amorphous CrGex coating. The composition of the nanowire coating was [Cr]/[Ge] = 1:(6–7). The resistance of the nanowire–deposit system was estimated to be 2.7 kΩ·cm using an unique vacuum contacting system.

Efficient and Controlled Seeded Growth of Poly(3-hexylthiophene) Block Copolymer Nanofibers through Suppression of Homogeneous Nucleation

Low-dispersity, length-tunable block copolymer nanofibers with spatially controlled functionalization and a crystalline core have recently become accessible using the ambient temperature, living crystallization-driven self-assembly (CDSA) seeded-growth method. The crystallizable π-conjugated polymer, poly(3-hexylthiophene) (P3HT), is of particular interest as a core-forming block as a result of its useful optoelectronic properties. However, attempts to apply the living CDSA method to P3HT diblock copolymers have had limited success as, in addition to seeded growth, homogeneous nucleation events result in the spontaneous formation of new fibers, which leads to a loss of length control. Herein, we demonstrate that by performing detailed variable temperature ultraviolet–visible (UV–vis) spectroscopic studies of the homogeneous nucleation of rrP3HT106-b-rsP3HT47 block copolymer (rr = regioregular and rs = regiosymmetric, respectively) we were able to identify conditions (40 °C) under which spontaneous (homogeneous) nucleation is suppressed. Addition of preformed seeds under these conditions allowed for highly efficient living CDSA to yield nanofibers with a rrP3HT106 core and controllable lengths up to ca. 4 μm with low length dispersity. Analogous use of this technique also allowed the efficient preparation of B-A-B triblock comicelles through the growth of P3HT70-b-PS197 from the termini of rrP3HT106-b-rsP3HT47 nanofibers that function as seed micelles, and also multiarm starlike arrays of fiberlike micelles with variable arm lengths, which were formed when seed micelles derived from rrP3HT150 homopolymer were used.

Solid-state phase transition in n-alkanes of different parity

The kinetics of the first-order solid-state structural transition in monodisperse n-alkanes samples of tricosane C23H48 and tetracosane C24H50 was studied by DSC and FTIR spectroscopy. The initial nuclei location of the new phase was revealed. The process of crystal structure rearrangement is initiated in the interlayers between neighboring lamellar for odd tricosane, while the nanonuclei in even tetracosane arise in the crystalline lamella cores. Thus, the influence of the number evenness of carbon atoms in the n-alkanes chains on the first-order structural phase transition has been proved.

Evidence from the Vredefort Granophyre Dikes points to crustal relaxation following basin-size impact cratering

The timescale of the modification stage of basin-sized impact structures is not well understood. Owing to ca. 10 km of erosion since its formation, the Vredefort impact structure, South Africa, is an ideal testing ground for deciphering post-impact modification. Here, we present geophysical and geochemical evidence from the Vredefort Granophyre Dikes, which were derived from the - now eroded - Vredefort impact melt sheet. The dikes have been studied mostly in terms of their composition, while the timing and duration of their emplacement remain controversial. We examined the modern depth extent of five dikes, with three from the inner crystalline core of the central uplift, and two from the boundary between the core and the supracrustal collar of the central uplift, using two-dimensional electrical resistivity tomography. We found that the core dikes terminate near the present erosion surface (i.e., <5 m depth). In contrast, the dikes at the core-collar boundary extend to a depth ≥ 9 m. These observations suggest that the core dikes are exposed near their lowermost terminus. In addition, we obtained bulk geochemical composition of the dikes, finding that the andesitic composition phase is present in the core-collar dikes that is not found in the core dikes. The presence of this phase indicates the episodic emplacement of impact melt into subvertical crater floor fractures.We conclude that the dike formation was protracted and occurred over a time span of at least 104 years. The sequential formation of the Vredefort Granophyre Dikes points to horizontal extension of crust below the impact melt sheet above a kinematic velocity discontinuity, a crustal instability resulting from the dynamic collapse of the transient cavity.

Radiation-induced amorphization of M23C6 in F82H steel: An atomic-scale observation

The purpose of the present study is to clarify the instability behavior of M23C6 under irradiation, specifically the occurrence of radiation-induced amorphization (RIA). Ion irradiation of 10.5 MeV-Fe3+ at elevated temperatures from 573 to 623 K was conducted into the reduced activation ferritic/martensitic steels (F82H) and its model alloy (Fe-8Cr-0.1C). A bilayer contrast of the particle consisting of an amorphous-rim phase and inner crystalline core of M23C6 was observed in the irradiated F82H specimen, but not in the model alloy. From the high-resolution electron microscope observation, the preferential occupation site of W into M23C6 lattice was identified as 8c-site prior to irradiation in F82H specimen, which shifted to other sites due to chemical disordering upon irradiation. Evaluation of the intensity ratio between 8c and another site of M23C6, 8c/4a, then revealed that the extent of chemical disordering of W was mitigated at the amorphous-crystal interface region in comparison with the central of the particle. The hypothesis for the formation mechanism of an amorphous-rim in M23C6 was presumed as the deviation from the stoichiometric composition at the local interface due to the irradiation-enhanced diffusion and/or ballistic mixing under the current circumstances, although the efforts from experimental and/or simulation studies are still necessary to achieve a further understanding of the RIA behavior in M23C6.

An organic crystalline state in ageing atmospheric aerosol proxies: spatially resolved structural changes in levitated fatty acid particles

Abstract. Organic aerosols are key components of the Earth's atmospheric system. The phase state of organic aerosols is known to be a significant factor in determining aerosol reactivity, water uptake and atmospheric lifetime – with wide implications for cloud formation, climate, air quality and human health. Unsaturated fatty acids contribute to urban cooking emissions and sea spray aerosols. These compounds, exemplified by oleic acid and its sodium salt, are surface-active and have been shown to self-assemble into a variety of liquid-crystalline phases upon addition of water. Here we observe a crystalline acid–soap complex in acoustically levitated oleic acid–sodium oleate particles. We developed a synchrotron-based simultaneous small-angle and wide-angle X-ray scattering (SAXS and WAXS)–Raman microscopy system to probe physical and chemical changes in the proxy during exposure to humidity and the atmospheric oxidant ozone. We present a spatially resolved structural picture of a levitated particle during humidification, revealing a phase gradient consisting of a disordered liquid crystalline shell and crystalline core. Ozonolysis is significantly slower in the crystalline phase compared with the liquid phase, and a significant portion (34 ± 8 %) of unreacted material remains after extensive oxidation. We present experimental evidence of inert surface layer formation during ozonolysis, taking advantage of spatially resolved simultaneous SAXS–WAXS experiments. These observations suggest that atmospheric lifetimes of surface-active organic species in aerosols are highly phase-dependent, potentially impacting climate, urban air quality and long-range transport of pollutants such as polycyclic aromatic hydrocarbons (PAHs).

Cubic crystal elastic constants of a white dwarf stellar core determined via modal analysis

In this work, we present the cubic crystal elastic constants of a fully crystallized white dwarf stellar core. Elastic constants were calculated utilizing modal analysis of three-dimensional single-layer and stratified multi-layer crystalline core models. The models were generated using a Fortran based forward calculation algorithm in combination with a finite element modeling software program and were based on the parameters associated with the pulsating crystallized white dwarf BPM 37093. The calculated cubic crystal elastic constants, in comparison with elastic parameters of theoretical Coulomb crystal models of white dwarf matter, differed by, at most, a few orders of magnitude. In addition, the crystallized stellar core elastic parameters produced associated vibrational modes and frequencies that are consistent with the periodicity observed in BPM 37093.

High Density of Quantum-Sized Silicon Nanowires with Different Polytypes Grown with Bimetallic Catalysts.

When Si nanowires (NWs) have diameters below about 10 nm, their band gap increases as their diameter decreases; moreover, it can be direct if the material adopts the metastable diamond hexagonal structure. To prepare such wires, we have developed an original variant of the vapor–liquid–solid process based on the use of a bimetallic Cu–Sn catalyst in a plasma-enhanced chemical vapor deposition reactor, which allows us to prevent droplets from coalescing and favors the growth of a high density of NWs with a narrow diameter distribution. Controlling the deposited thickness of the catalyst materials at the sub-nanometer level allows us to get dense arrays (up to 6 × 1010 cm–2) of very-small-diameter NWs of 6 nm on average (standard deviation of 1.6 nm) with crystalline cores of about 4 nm. The transmission electron microscopy analysis shows that both 3C and 2H polytypes are present, with the 2H hexagonal diamond structure appearing in 5–13% of the analyzed NWs per sample.

Significantly Enhanced Photocatalytic CO2 Reduction by Surface Amorphization of Cocatalysts.

Rational phase engineering of reduction cocatalyst offers a promising route to modulate the photocatalytic activity and selectivity in the conversion of CO2 to chemical feedstocks. However, it remains a great challenge to choose a suitable phase given that high-crystallinity phase is more conducive to the charge transfer and separation, while amorphous phase is more favorable for the adsorption and activation of CO2 molecules. To resolve this dilemma, herein, with Pd as a well-defined model, a surface amorphization strategy has been developed to fabricate crystalline@amorphous semi-core-shell cocatalysts based on the transformation of outer layer atoms of crystalline cocatalysts to disorder phase. According to the theoretical and experimental analysis, in the heterostructured cocatalysts, crystalline core shuttles the photoexcited electrons from light-harvesting semiconductor to amorphous shell due to its strong electronic coupling with both components. Meanwhile, amorphous shell provides efficient active sites for preferential activation and conversion of CO2 and suppression of undesirable proton reduction. Benefiting from the synergistic effects between crystalline core and amorphous shell, the optimized heterophase cocatalyst with suitable thickness of amorphous shell achieves superior CO (22.2 µmol gcat-1 h-1 ) and CH4 (38.1µmol gcat-1 h-1 ) formation rates with considerable selectivity and high stability in comparison with crystalline and amorphous counterparts.

Oxidation of MBE-Grown ZnTe and ZnTe/Zn Nanowires and Their Structural Properties.

Results of comparative structural characterization of bare and Zn-covered ZnTe nanowires (NWs) before and after thermal oxidation at 300 °C are presented. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, and Raman scattering not only unambiguously confirm the conversion of the outer layer of the NWs into ZnO, but also demonstrate the influence of the oxidation process on the structure of the inner part of the NWs. Our study shows that the morphology of the resulting ZnO can be improved by the deposition of thin Zn shells on the bare ZnTe NWs prior to the oxidation. The oxidation of bare ZnTe NWs results in the formation of separated ZnO nanocrystals which decorate crystalline Te cores of the NWs. In the case of Zn-covered NWs, uniform ZnO shells are formed, however they are of a fine-crystalline structure or partially amorphous. Our study provides an important insight into the details of the oxidation processes of ZnTe nanostructures, which could be of importance for the preparation and performance of ZnTe based nano-devices operating under normal atmospheric conditions and at elevated temperatures.

Anchorage-Dependent Living Supramolecular Self-Assembly of Polymeric Micelles.

Anchorage-dependent contact-inhibited growth usually refers to on-surface cell proliferation inhibited by the proximity of other cells. This phenomenon, prominent in nature, has yet to be achieved with polymeric micelles. Here, we report the control living supra-macromolecular self-assembly of elongated micelles with a liquid crystalline core onto a hydrophobic substrate via the synergetic interactions between the substrate and aggregates dispersed in solution. In this system, seed formation is a transient phenomenon induced by the adsorption and rearrangement of the core-swollen aggregates. The seeds then trigger the growth of elongated micelles onto the substrate in a living controllable manner until the contact with the substrate is disrupted. Brownian dynamic simulations show that this unique behavior is due to the fusion of the aggregates onto both ends of the anchored seeds. More important, the micelle length can be tuned by varying the substrate hydrophobicity, a key step toward the fabrication of intricate structures.

Advances in carbon isotope analysis of trapped methane and volatile hydrocarbons in crystalline rock cores.

The isotopic composition of hydrocarbons trapped in rocks on the microscale (fluid inclusions, mineral grain boundaries, microfractures) can provide powerful information on geological and biological processes but are an analytical challenge due to low concentrations. We present a new approach for the extraction and carbon isotopic analysis of methane (CH4 ) and hydrocarbons in trapped volatiles in crystalline rocks. An off-line crusher with cryogenic trapping and a custom-made silica glass U-trap were attached to an external injector port on a continuous flow gas chromatograph/combustion/isotope ratio mass spectrometer to demonstrate the accuracy, reproducibility, and sensitivity of δ13 C measurements for CH4 . The method can isotopically characterize CH4 in crushed rock samples with concentrations as low as 3.5 × 10-9 mol/g of rock, and both sample and isotopic standards are analyzed with an accuracy and reproducibility of ±0.5‰. High H2 O/CH4 ratios of 98 to 500 have no effect on measured δ13 CCH4 values. The method is successfully applied to natural samples from the north range of Sudbury Basin, Ontario, Canada. The δ13 C isotopic signatures of CH4 trapped microscopically in rock from the north range overlap significantly with that of CH4 contained in larger scale flowing fracture fluids from the same part of the Sudbury Basin, indicating a potential genetic link. A novel method for δ13 CCH4 analysis was developed for the extraction of nanomole quantities of CH4 trapped microscopically in rocks. The technique has an accuracy and reproducibility comparable to that of on-line crushing techniques but importantly provides the capability of crushing larger rock quantities (up to 100 g). The benefit is improved detection levels for trace hydrocarbon species. Such a capability will be important for future extension of such crushing techniques for measurement of 2 H/1 H for CH4 , clumped isotopologues of CH4 and other trapped volatiles species, such as C2 H6 , C3 H8 , C4 H10 , CO2 and N2 .

Designing Donor-Acceptor Copolymers for Stable and High-Performance Organic Electrochemical Transistors.

Organic electrochemical transistors (OECTs) are oft-used for bioelectronic applications, and a variety of OECT channel materials have been developed in recent years. However, the majority of these materials are still limited by long-term performance and stability challenges. To resolve these issues, we implemented a next-generation design of polymers for OECTs. Specifically, diketopyrrolopyrrole (DPP) building blocks were copolymerized with propylene dioxythiophene-based (Pro-based) monomers to create a donor-acceptor-type conjugated polymer (PProDOT-DPP). These PProDOT-DPP macromolecules were synthesized using a straightforward direct arylation polymerization synthetic route. The PProDOT-DPP polymer thin film exhibited excellent electrochemical response, low oxidation potential, and high crystallinity, as evidenced by spectroelectrochemical measurements and grazing incidence wide-angle X-ray scattering measurements. Thus, the resultant polymer thin films had high charge mobility and volumetric capacitance values (i.e., μC* as high as 310 F cm-1 V-1 s-1) when they were used as the active layer materials in OECT devices, which places PProDOT-DPP among the highest performing accumulation-mode OECT polymers reported to date. The performance of the PProDOT-DPP thin films was also retained for 100 cycles and over 2000 s of ON-OFF cycling, indicating the robust stability of the materials. Therefore, this effort provides a clear roadmap for the design of electrochemically active macromolecules for accumulation-mode OECTs, where crystalline acceptor cores are incorporated into an all-donor polymer. We anticipate that this will ultimately inspire future polymer designs to enable OECTs with both high electrical performance and operational stability.

Magnetoferritin enhances T2 contrast in magnetic resonance imaging of macrophages

Imaging of immune cells has wide implications in understanding disease progression and staging. While optical imaging is limited in penetration depth due to light properties, magnetic resonance (MR) imaging provides a more powerful tool for the imaging of deep tissues where immune cells reside. Due to poor MR signal to noise ratio, tracking of such cells typically requires contrast agents. This report presents an in-depth physical characterization and application of archaeal magnetoferritin for MR imaging of macrophages – an important component of the innate immune system that is the first line of defense and first responder in acute inflammation. Magnetoferritin is synthesized by loading iron in apoferritin in anaerobic condition at 65 °C. The loading method results in one order of magnitude enhancement of r1 and r2 relaxivities compared to standard ferritin synthesized by aerobic loading of iron at room temperature. Detailed characterizations of the magnetoferritin revealed a crystalline core structure that is distinct from previously reported ones indicating magnetite form. The magnetite core is more stable in the presence of reducing agents and has higher peroxidase-like activities compared to the core in standard loading. Co-incubation of macrophage cells with magnetoferritin in-vitro shows significantly higher enhancement in T2-MRI contrast of the immune cells compared to standard ferritin.

Influence of Phase Composition and Pretreatment on the Conversion of Iron Oxides into Iron Carbides in Syngas Atmospheres

CO2 Fischer–Tropsch synthesis (CO2–FTS) is a promising technology enabling conversion of CO2 into valuable chemical feedstocks via hydrogenation. Iron–based CO2–FTS catalysts are known for their high activities and selectivities towards the formation of higher hydrocarbons. Importantly, iron carbides are the presumed active phase strongly associated with the formation of higher hydrocarbons. Yet, many factors such as reaction temperature, atmosphere, and pressure can lead to complex transformations between different oxide and/or carbide phases, which, in turn, alter selectivity. Thus, understanding the mechanism and kinetics of carbide formation remains challenging. We propose model–type iron oxide films of controlled nanostructure and phase composition as model materials to study carbide formation in syngas atmospheres. In the present work, different iron oxide precursor films with controlled phase composition (hematite, ferrihydrite, maghemite, maghemite/magnetite) and ordered mesoporosity are synthesized using the evaporation–induced self–assembly (EISA) approach. The model materials are then exposed to a controlled atmosphere of CO/H2 at 300 °C. Physicochemical analysis of the treated materials indicates that all oxides convert into carbides with a core–shell structure. The structure appears to consist of crystalline carbide cores surrounded by a partially oxidized carbide shell of low crystallinity. Larger crystallites in the original iron oxide result in larger carbide cores. The presented simple route for the synthesis and analysis of soft–templated iron carbide films will enable the elucidation of the dynamics of the oxide to carbide transformation in future work.

Thermosetting supramolecular polymerization of compartmentalized DNA fibers with stereo sequence and length control

Thermosetting supramolecular polymerization of compartmentalized DNA fibers with stereo sequence and length control

Sonication assisted advanced oxidation process: hybrid method for deagglomeration of detonation nanodiamond particles

ABSTRACT In the present paper, a new approach for detonation nanodiamond (DND) deagglomeration is proposed. DND agglomerates of the size from 20 to 200 nm have been exposed to wet sonication assisted oxidative treatment with ozone under UV irradiation (Advanced Oxidation Process). Subsequent sonication and centrifugation gave a stable hydrosol of individual DND particles with negative zeta potential of −65 mV. The yield of the desired 4–5 nm fraction reached 33 wt%. Powder X-Ray Diffraction study showed no signs of DND crystalline core degradation, while the surface of particles was enriched significantly with carboxyl functional groups according to the data of Diffuse Reflectance Infrared Fourier Transform Spectroscopy, that gave boost to the stability of DND hydrosol. The approach provides relatively high yield of deagglomerated detonation nanodiamond without impact of high temperatures on the DND particles. It also allows avoiding gas phase processes sticking to wet-chemistry that could be useful for process scalability.

Cubosomes as Potential Nanocarrier for Drug Delivery: A Comprehensive Review

Lyotropic liquid crystalline cores are characterized as soft nanoparticles and referred as cubosomes. They are prepared to activate the natural self-assembly capability of lipids (e.g., monoolein or phytantriol) in water. Cubosomes are crystalline isotropic lipidic nanoparticles stabilized by Poloxamers such as F127, F108. It is made up of a network of two separate aqueous channels formed by a three-dimensional, non-intersecting lipid bilayer imposed over an indefinite periodic minimum surface of cubic symmetry. Cubosomes constitute unique features such as their special cubic structure which permits to incorporate highly lipophilic, hydrophilic, and amphiphilic drugs. Also, the lipids excipients used in the preparation of cubosomes such as monoolein, phytantriol are biodegradable and biocompatible so these cubic nanoparticles are referred as safe carrier for drug delivery. Cubic lipid nanoparticles have a highly stable cubic shape that allows for a slower rate of dissociation, improved drug retention, and site-specific drug delivery. The architecture of cubic particles provides suitability in the drug delivery as compared to other lipids-based drug delivery systems such as solid lipid nanoparticles (SLN), liposomes due to their drug expulsion to the surface of nanoparticles. Cubosomes with these loaded features/architectural composition led to an array of desired performance. Solvent evaporation, ultrasonication, hydrotrope, spray drying, melt dispersion emulsifying methods are used to prepare these carrier systems.

Cargo Encapsulation in Uniform, Length-Tunable Aqueous Nanofibers with a Coaxial Crystalline and Amorphous Core

Cargo Encapsulation in Uniform, Length-Tunable Aqueous Nanofibers with a Coaxial Crystalline and Amorphous Core