Potential and limitations of a T-NIL/UVL hybrid process

A T-NIL/UVL hybrid process offers the potential to combine the advantages of thermal nanoimprint (T-NIL) – to define patterns in the nanometre range in parallel over large areas, with the advantages of photolithography in the ultraviolet range (UVL) – to define large patterns easily. It is attractive for the preparation of e.g. sensors, where typically nm-scaled electrodes are connected to macroscopic contacts. We address the critical issues of such a process that until now have hampered its application in praxis. Major aspects result from the required compatibility of both processes, asking for resists that are imprintable at temperatures well below any deterioration of the photoactive components. Furthermore, the lithography step has to be performed over a pre-patterned surface, which may require overexposure; the pre-patterned surface is also crucial during an eventually required post-exposure bake, where pattern loss may result from unintended viscous flow during crosslinking. Examples with SU-8 as a chemically amplified negative resist demonstrate that the hybrid process works, if some processing parameters are well tuned.     

Measurement of entrainer effects of water and ethanol on solubility of caffeine in supercritical carbon dioxide by FT-IR spectroscopy

The solubilities of caffeine in supercritical CO₂, supercritical CO₂ + water, supercritical CO₂ + ethanol, and supercritical CO₂ + water + ethanol were measured with a circulation-type apparatus combined with an on-line Fourier transform infrared (FT-IR) spectrometer at 313.2 K and 15.0 MPa. The solubilities of caffeine were determined with the peak absorbances of caffeine at 1190 cm⁻¹. The solubilities of caffeine increase until water is saturated in supercritical CO₂. The maximum increase rate is 22%. In CO₂ + caffeine + ethanol system, the solubilities of caffeine increase with increasing the concentration of ethanol. The solubility of caffeine becomes five times when 1000 mol m⁻³ of ethanol is added. In CO₂ + caffeine + water + ethanol system, the solubilities of caffeine are smaller than those with single entrainer of water or ethanol. The shape of the peaks of two CO stretching bands for caffeine were changed by the addition of ethanol. It was confirmed that the interaction species of caffeine interacting with ethanol are produced by deconvolution of the CO stretching bands. The enhancement of solubility for caffeine in supercritical CO₂ by the addition of ethanol is due to the hydrogen bonding between caffeine and ethanol.     

Elucidation the role of Co-MOF on hematite for boosting the photoelectrochemical performance toward water oxidation

Developing an efficient photoanode to convert solar energy into hydrogen fuel confronts big challenges owing to the sluggish water oxidation kinetics. Herein, we proposed a feasible method to coat Co-based metal-organic framework (Co-MOF) on Ti doped α-Fe₂O₃ and revealed its functions on the oxygen evolution reaction (OER) and photoelectrochemical (PEC) water oxidation. The Co-MOF/Ti–Fe₂O₃ showed a photocurrent density of 1.01 mA/cm² (1.23V_RHE) with a low turn-on voltage (V_on) of 0.80 V_RHE. The significant improvement of photocurrent density which was ca. 3 times higher than the pristine Fe₂O₃, was contributed by the improved charge separation efficiency on the surface rather than in the bulk. And this was validated by the increased trapping capacitance (C_trap) and reduced charge transport resistance (R_ct). Additionally, the low V_on was attributable to the compromise of introduced surface states and the catalytic effect of the Co-MOF. In this work, we discovered the Co-MOF not only offered catalysis sites for OER, but shed light on its influence on the overall PEC water oxidation, and led to an in-depth understanding of cocatalysts on the PEC water splitting.     

Single atom iron carbons supported Pd–Ni–P nanoalloy as a multifunctional electrocatalyst for alcohol oxidation

Exploring high-performance and multifunctional electrocatalysts for alcohols oxidation is the key to develop alkaline fuel cells. Herein, we prepared a novel palladium-nickel-phosphorus catalyst supported on single atom iron carbons (SAICs) with different diameter sizes (1000 nm, 200 nm, 100 nm, 50 nm, and 20 nm), which were synthesized by direct carbonization of Fe-doped Zeolitic Imidazolate Framework-8 (ZIF-8). Electrochemical tests reveal that the as-prepared PdNiP/50nmSAIC exhibited excellent electrooxidation activity and stability to the various alcohols (methanol, glycerol, and especially ethylene glycol) electrooxidation in the alkaline solution, which is much higher than that of commercial Pd/C and other advanced Pd-based catalysts. Meanwhile, the rotating disk electrode (RDE) and CO-stripping results proves that PdNiP/50nmSAIC possesses a faster kinetic process of ethylene glycol oxidation and enhanced anti-CO poisoning ability. Our efforts provide a new strategy for the development of MOFs-derived multielement electrocatalyst with excellent activity and stability, and a bright future for alcohol oxidation.     

The influence of Gd/Ce substitution on the magnetic properties,electronic structure and the valence of cerium in the solid solution CexGd1−xNi3

The polycrystalline compounds Ce_xGd_1−xNi₃ with a rhombohedral PuNi₃ (x ≤ 0.2) and hexagonal CeNi₃ (x ≥ 0.8) – type of crystal structures have been obtained. The change of the lattice parameters may suggest an unstable valence of cerium in the studied system. The effect of partial substitution of Gd by Ce is reflected in a change of the cell volume V(x), the Curie temperature T_C(x) and in the temperature dependence of the magnetic susceptibility and electrical resistivity. Thus, T_C(x) decreases from 115 K (x = 0) to ∼6.8 K (x = 0.8). The XPS spectra have been measured at room temperature. The valence band spectra (VB) as well as the core level lines have been analysed as influence of the Gd/Ce substitution on the electronic structure. The VB near the Fermi level (E_F) is dominated by Ni3d states. In the VB region some slight effects of hybridization and changes of intensity of states on E_F have been noticed. The analysis of Ce core level lines reveals the occurrence of possible intermediate valence. The values of the Ce4f - state occupation parameter (n_f) and the hybridization energy (Δ) have been estimated. The gradual filling of the Ni3d band is revealed by a reduction of the 6 eV satellite intensities in the Ni2p core level spectrum. All these effects can modify the magnetic properties of the investigated compounds.     

Thermal oxidation‐induced long chain branching and its effect on phase separation kinetics of a polyethylene blend

Thermal oxidation‐induced long chain branching (LCB) during the molding processes for polyolefin copolymer poly(ethylene‐co‐butene) (PEB) and its blend with another polyolefin copolymer poly(ethylene‐co‐hexene) (PEH/PEB 50/50 blend, denoted as H50) was investigated mainly by rheological measurements. LCB with different levels could be introduced on PEB backbones by changing the molding temperature and/or molding time, which could be sensitively characterized by changes of rheological parameters, that is, storage modulus G′ and complex viscosity η*. Thermal oxidation‐induced LCB of PEB in H50 samples could largely influence the phase separation kinetics. Rheological measurements and phase‐contrast optical microscope observations coherently indicated that thermal oxidation‐induced LCB of PEB more or less retarded the development of phase separation and once it reached a certain level, the reduced chain diffusion even arrested phase separation. The decrease of mass‐averaged molecular mass in H50 with high LCB level was ascribed to the reduced hydrodynamic volume. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation of Au-loaded niobate nanosheets and their plasmon-driven photochemical reaction

Niobate nanosheets prepared by exfoliation of layered hexaniobate K₄Nb₆O₁₇ were sequentially decorated with two noble metal nanoparticles, gold and silver, through two-step photochemical reactions. First, cationic bis(ethylenediamine)gold(III) ions were electrostatically adsorbed on the anionic niobate nanosheets, and reduced to gold nanoparticles by UV excitation of the photocatalytically active niobate nanosheets. Then, the surface plasmon band of the photodeposited gold nanoparticles was excited with visible light, by which the silver cations introduced to the system together with citrate anions were reduced to silver nanoparticles. Spectroscopic and transmission electron microscopic observations indicated the formation of morphologically different silver nanoparticles, for example nanorods and core-shell particles.     

Tuning domain size and crystallinity in isoindigo/PCBM organic solar cells via solution shearing

Despite having achieved the long sought-after performance of 10% power conversion efficiency, high performance organic photovoltaics (OPVs) are still mostly constrained to lab scale devices fabricated by spin coating. Efforts to produce printed OPVs lag considerably behind, and the sensitivity to different fabrication methods highlights the need to develop a comprehensive understanding of the processing-morphology relationship in printing methods. Here we present a systematic experimental investigation of a model low bandgap polymer/fullerene system, poly-isoindigo thienothiophene/PC₆₁BM, using a lab-scale analogue to roll-to-roll coating as the fabrication tool in order to understand the impact of processing parameters on morphological evolution. We report that domain size and polymer crystallinity can be tuned by a factor of two by controlling the temperature and coating speed. Lower fabrication temperature simultaneously decreased the phase separation domain size and increased the relative degree of crystallinity in those domains, leading to improved photocurrent. We conclude that domain size in isoindigo/PCBM is dictated by spontaneous phase separation rather than crystal nucleation and growth. Furthermore we present a model to describe the temperature dependence of domain size formation in our system, which demonstrates that morphology is not necessarily strictly dependent on the evaporation rate, but rather on the interplay between evaporation and diffusion during the printing process.     

Adsorption kinetics and mechanism of cationic methyl violet and methylene blue dyes onto sepiolite

The use of low-cost and ecofriendly adsorbents was investigated as an ideal alternative to the current expensive methods of removing dyes from wastewater. Sepiolite was used as an adsorbent for the removal of methyl violet (MV) and methylene blue (MB) from aqueous solutions. The rate of adsorption was investigated under various parameters such as contact time, stirring speed, ionic strength, pH and temperature for the removal of these dyes. Kinetic study showed that the adsorption of dyes on sepiolite was a gradual process. Quasi-equilibrium reached within 3 h. Adsorption rate increased with the increase in ionic strength, pH and temperature. Pseudo-first-order, the Elvoich equation, pseudo-second-order, mass transfer and intra-particle diffusion models were used to fit the experimental data. The sorption kinetics of MV and MB onto sepiolite was described by the pseudo-second-order kinetic equation. Intra-particle diffusion process was identified as the main mechanism controlling the rate of the dye sorption. The diffusion coefficient, D, was found to increase when the ionic strength, pH and temperature were raised. Thermodynamic activation parameters such as ΔG¹, ΔS¹ and ΔH¹ were also calculated.     

Highly efficient visible-light driven AgBr/Ag3PO4 hybrid photocatalysts with enhanced photocatalytic activity

Highly efficient visible-light-driven AgBr/Ag₃PO₄ hybrid photocatalysts with different mole ratios of AgBr were prepared via an in-situ anion-exchange method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) technique. Under visible light irradiation (>420 nm), the AgBr/Ag₃PO₄ photocatalysts displayed the higher photocatalytic activity than pure Ag₃PO₄ and AgBr for the decolorization of acid orange 7 (AO 7). Among the hybrid photocatalysts, AgBr/Ag₃PO₄ with 60% of AgBr exhibited the highest photocatalytic activity for the decolorization of AO 7. X-ray photoelectron spectroscopy (XPS) results revealed that AgBr/Ag₃PO₄ readily transformed to be Ag@AgBr/Ag₃PO₄ system while the photocatalytic activity of AgBr/Ag₃PO₄ remained after 5 recycling runs. In addition, the quenching effects of different scavengers displayed that the reactive h⁺ and O₂^∙− play the major role in the AO 7 decolorization. The photocatalytic activity enhancement of AgBr/Ag₃PO₄ hybrids can be ascribed to the efficient separation of electron–hole pairs through a Z-scheme system composed of Ag₃PO₄, Ag and AgBr, in which Ag nanoparticles act as the charge separation center.