Low Ea Research Articles

Sublimation Kinetics for Individual Graphite and Graphene Nanoparticles (NPs): NP-to-NP Variations and Evolving Structure-Kinetics and Structure-Emissivity Relationships

A single nanoparticle (NP) mass spectrometry method was used to measure sublimation rates as a function of nanoparticle temperature (TNP) for sets of individual graphite and graphene NPs. Initially, the NP sublimation rates were ∼400 times faster than those for bulk graphite, and there were large NP-to-NP variations. Over time, the rates slowed substantially, though they remained well above the bulk rate. The initial activation energies (Ea values) were correspondingly low and doubled, as a few monolayers worth of material was sublimed from the surfaces. The high initial rates and low Ea values are attributed to large numbers of edge, defect, and other low coordination sites on the NP surfaces, and the changes are attributed to atomic-scale "smoothing" of the surface by preferential sublimation of the less stable sites. The emissivity of the NPs also changed after heating, more frequently increasing. The emissivity and sublimation rates were anticorrelated, leading to the conclusion that high densities of low-coordination sites on the NP surfaces enhance sublimation but suppress emissivity.

Parametric optimization by Taguchi L9 approach towards biodiesel production from restaurant waste oil using Fe-supported anthill catalyst

Restaurant waste oil is easily obtainable from local restaurants, while anthills grow widely in Oro, Nigeria. The anthills were first carbonized, then steam activated to prepare an inert, porous support capable of functional group adsorption. The support was then doped with Fe (II) using FeSO4 and the Fe/A catalyst was used in biodiesel synthesis from the RWO. L9 Taguchi OA was chosen to optimize the transesterification proves parameters comprising of catalyst concentration, methanol to oil ratio, reaction temperature and reaction time. The optimization revealed that methanol concentration does not affect the biodiesel yield significantly, while reaction time has the highest contribution. A biodiesel yield of 99.73 % was attained at 60 °C for 1.5 h with 1.2 % catalyst and 6:1 methanol:oil ratio. GC analysis showed the product to be rich in methyl esters. Fuel characterization tests show that the product has properties exceeding the standards set by ASTM. Kinetic studies show the process adheres to pseudo 1st order kinetics and has high reaction rate and frequency factor (A) with low EA, while the catalyst shows very efficient retention of functional groups, as evident from its reusability up to 7 times. Thus the process is energy and cost efficient, with a potential for commercialization.

Growth kinetics of hybrid perovskite thin films on different substrates at elevated temperature and its direct correlation with the microstructure and optical properties

We elucidate the growth kinetics and scaling behavior of vacuum deposited CH3NH3PbBr3 thin film on various substrates and correlate the same with its microstructural and optical properties. Analysis of the AFM images reveals an abrupt change in the grain features for thickness, d ≥ 40 nm. Based on the evaluation of the scaling parameters, the perovskite films exhibit an anomalous scaling behavior for, d < 40 nm, and stable growth for, d ≥ 40 nm. Interestingly, the growth exponent (β) is found to be distinctly different, ~0.22 and ~ 0.90, for the films on ITO and SiO2 substrates, respectively. The study of the temperature-dependent growth kinetics yields higher activation energy (Ea) for SiO2 (~0.15 eV) than that of ITO (~0.10 eV). Due to mound-like growth, the film on SiO2 substrate deviates from the conventional scaling law. Structural and photoluminescence (PL) studies reveal better crystallinity of the film on ITO, which is consistent with its low Ea value. Optical absorbance and PL analyses reveal a blue shift in the bandgap with decreasing thickness attributed to the lattice expansion. These findings provide new insights on the growth kinetics and optimum conditions for the vacuum deposition of hybrid perovskite thin films on various substrates.

Core-shell PdO@SiO2/Al2O3 with sinter-resistance and water-tolerance promoting catalytic methane combustion

An Al2O3-supported core–shell-structured PdO@SiO2 catalyst was rationally synthesized for lean-CH4 oxidation with outstanding water-tolerance and sinter-resistance properties. PdO@SiO2 works two parts in promoting the hydrothermally catalytic performance. Firstly, the core–shell configurations with maximized interface and intimate contact bring out the strong metal-support interaction, which leads to the benign oxidation–reduction property and the higher desorption rate of OH–/H2O over the PdO active centres; secondly, the SiO2 shells could isolate PdO nanoparticles from each other and protect them from agglomeration especially at high temperature (>600 °C). As a result, PdO@SiO2/Al2O3 exhibits a 90% CH4 conversion at 380 °C, a low Ea value as 54.0 ± 1.6 kJ/mol and an enhanced hydrothermal stability at 800 °C for 10 h. Such an interface-promoted core–shell-structured catalyst design strategy sheds some light on the stabilization and application of Pd-based catalysts.

A thin-felt Pd–MgO–Al2O3/Al-fiber catalyst for catalytic combustion of methane with resistance to water-vapor poisoning

Thin-sheet microfibrous-structured Pd–MgO–Al2O3/Al-fiber catalysts were developed for high-throughput catalytic methane combustion with 3–15 vol% water vapor in feed gas. The catalysts were obtained by hydrothermally growing Mg–Al mixed-oxide precursors (e.g., layered double hydroxides (LDHs) plus MgCO3) on Al-fiber surfaces followed by placing 0.5 wt% Pd on the as-obtained substrates by impregnation. Transformation of Pd/MgAl-LDH–MgCO3 mounted on the Al-fiber into Pd-MgO-Al2O3 via in situ reaction activation markedly enhances the catalyst basicity and electron density of metallic Pd, thus weakening support electrophilicity and stabilizing PdO against the formation of inactive Pd4+ species. This preferred catalyst with high intrinsic activity (turnover frequency 135 h−1 at 290 °C and 3 vol% water vapor) achieves a very low Ea of only 57 kJ mol−1, a third that (170 kJ mol−1) for the Pd/AlOOH/Al-fiber. This catalyst can stably run for feed gases of 1 vol% methane and 3–15 vol% water vapor in air.

Prussian Blue Analogue-derived co/fe bimetallic nanoparticles immobilized on S/N-doped carbon sheet as a magnetic heterogeneous catalyst for activating peroxymonosulfate in water.

While Co is the most effective metal for activating PMS, extensive efforts are made to develop Co/Fe species (CF) (e.g., CoFe2O4) for imparting magnetic properties and facilitating recovery of catalysts. When carbon substrates are doped with heteroatoms (e.g., S and N) and CF is embedded within the heteroatom-doped carbon matrix, synergies can occur to boost catalytic activities. This study proposes an alternative CF-bearing carbonaceous composite, a cobalt-containing Prussian Blue Analogue (PBA) (Co3[Fe(CN)6]2) is employed as a precursor for preparing CF species embedded in N-doped carbon matrix and immobilized on S/N-co-doped carbon (SNC). Specifically, PBA in-situ grows on SNC by a heat treatment of trithiocyanuric acid to form PBA@SNC, which is then carbonized into CF species@SNC (CF@SNC). By adopting Amaranth degradation as a model reaction, CF@SNC shows a higher catalytic activity (kapp=0.230 min-1) than CF (kapp=0.152 min-1) and SNC (kapp=0.016 min-1) for activating PMS. In comparison with Co3O4, CF@SNC exhibits a higher catalytic activity for PMS activation. CF@SNC renders a relatively low Ea value (53kJ/mol) for Amaranth degradation in comparison to other reported catalysts. These comparisons demonstrate the advantageous features of CF@SNC as a magnetic and efficient catalyst for PMS activation.

Sulfonated catalytic esterification of Madhuca indica oil using waste Delonix regia: L16 Taguchi optimization and kinetics

The reported study discusses fuel-grade mahua oil methyl esters production from Madhuca indica oil, utilizing Delonix regia pods as a precursor to develop activated carbon support for preparing sulfonated carbon catalyst by H2SO4 impregnation. Raw pods were found to be thermally stable based on TGA analysis, making it suitable as raw material for catalyst synthesis. The catalyst is characterized using BET, XRD, SEM and FT-IR to check desired properties like surface area, porosity enhancement and doping of required functional groups. MOME production is optimized through L16 Taguchi design. Optimum yield of 97.04% is observed at 50 °C for 1 h with 4% w/w catalyst, methanol:oil of 6:1 and 1000 rpm. Catalyst load (1−4% w/w) affects the reaction most prominently, while methanol to oil molar ratio (3:1–12:1) is insignificant. The optimal product is characterized through ASTM standardized tests and gas chromatography analysis and conforms to acceptable biodiesel properties. The reaction adheres to pseudo-first order kinetics with low EA (4.257 kJ/mol) and high A (174.66 min−1). Catalyst shows appreciable reusability with >85% yield after 4 uses. Cost analysis of catalyst preparation shows that indigenously developed catalyst cuts down biodiesel production costs, thus the production process discussed is lucrative for commercialization.

Theoretical design of new triphenylamine based dyes for the fabrication of DSSCs: A DFT/TD-DFT study

A series of rigid triphenylamine (TPA) dyes have been designed with the donor(D)-π-acceptor(A) architecture. The rigid TPA unit is designed by locking the two phenyl rings with alkyl and ethylene chain to attain better planarity and to minimize its rotation. Four different acceptor units viz. BTz, BBTz, PzT and PyT are used to design four parent dye systems. The study reveals that all four dyes show low ΔH−L values whereas only BTz, PyT and PzT dyes show small dihedral angles. Moreover, excited state calculation of these three dyes show excellent electronic transition properties with a sharp absorption (λmax) in the range of 507–540 nm at the UV–vis spectra. The λmax values of BTz, PyT and PzT dyes show a red shift to that of the reference dye which signifies better electronic transition from HOMO to LUMO orbitals. It is further supported by the MO diagrams of the dyes where the MOs of BBTz dye shows less overlap between the occupied and unoccupied orbitals. It is also evident from the low EA and IP values that the three dye systems (excluding BBTz) should show excellent transfer of injected electron to the semiconducting surface. Low λ+ and high kCT+ values imply the hole transporting nature of the designed dyes. Hence, these dyes will act as potential candidates for fabrication of dye-sensitized solar cells (DSSCs).

Facile Fabrication of NiPt/CNTs as an Efficient Catalyst for Hydrogen Production from Hydrous Hydrazine

AbstractHydrogen generation through catalytically hydrous hydrazine has recently emerged as a promising strategy to meet the ever‐increasing demand for sustainable energy. However, it remains a challenging obstacle to design highly active catalysts as well as low‐cost. In this work, we designed a series of NiPt/CNTs catalysts, which were prepared via a facile wet chemical reduction method, employed it in the dehydrogenation of hydrous hydrazine. The crystalline structure, chemical states and morphology of the catalysts were also characterized in detail. Among these catalysts, Ni0.4Pt0.6/CNTs exhibits highest activity with a turnover frequency (TOF) of 1725.3 h−1 at 50 °C and a low Ea of 36.3 kJ/mol. Considering its cost‐effective and high performance, the Ni0.4Pt0.6/CNTs represent a promising catalyst to hydrolyze hydrous hydrazine for hydrogen generation.

Thermosalient Amphidynamic Molecular Machines: Motion at the Molecular and Macroscopic Scales

Summary The supramolecular amphidynamic rotor 1, composed of two carbazole molecules acting as the stator and a DABCO rotator, exhibits remarkable thermosalience above 316 K. During this process, the crystals spontaneously transduce collective molecular displacements into macroscopic movement due to a phase transition, which is described by single-crystal X-ray analyses from 100 K to 320 K. The fast rotation in the low-temperature phase (I) occurs with a low activation energy Ea(I) ≈ 2.6 kcal mol−1 and a pre-exponential factor A(I) ≈ 1012 s−1. Increased symmetry of the cavity in the high-temperature phase (II) resulted in slower dynamics, regardless of a smaller rotational barrier, Ea(II) ≈ 0.5 kcal mol−1, due to the large reduction in the pre-exponential factor to A(II) ≈ 107 s−1. These results demonstrate that a relatively small distortion of lattice framework leads to drastic dynamic effects at both molecular and macroscopic scales, helping us to understand responsive crystalline materials.

Structural Relaxation in Polyanionic Sodium Fluorophosphate Glasses

Structural heterogeneity is a common feature of all glasses, however, little is known about the underlying contributions of chemical fluctuations and modulations in free volume in concrete glass forming systems. In this investigation, we relate the dynamics of structural relaxation of (100-x)NaPO3–xAlF3 glasses to their heterogeneous structure as determined from multinuclear magnetic resonance spectroscopic analysis. For this, we evaluate differential scanning calorimetry (DSC) data using the integral isoconversional method to determine the variation in activation energy, Ea, of the glass transition as a function of temperature and conversion progress. Specific heat measurements from DSC allow for the determination of the effective size of the cooperatively rearranging region (CRR). From 31P, 19F and 27Al NMR, we observe that the introduction of AlF3 into the NaPO3 network increases the average connectivity (i.e., the number of heteronuclear Al—O—P bonds), rationalizing the higher Ea determined from the DSC measurements. We find highly constrained regions of Al(OP)4F2 with Al—F—Al cross-linking (high Ea) and, simultaneously, more flexible regions of phosphate chains containing P—F··(Na+)n bonds (low Ea); this results in a topologically and dynamically heterogeneous structure as evidenced by the increased variability in Ea with higher AlF3 content. The decreasing size of the CRR reflects the increased heterogeneity: at low AlF3 the CRR is large, while at high AlF3 (high heterogeneity), the CRR is significantly smaller (by a factor of 103). Finally, we relate the heterogeneity to other macroscopic properties, such as Tg and mechanical properties.

The Effects of Endurance Training Under Low Energy Availability on Muscle Glycogen Contents

PURPOSE:Some previous studies demonstrated that acute bout of exercise suppressed appetite and reduced energy intake among athletes. However, the accumulative effects of reduced energy intake during consecutive days of training period remains unclear. The purpose of the present study was to investigate the influences of 3 days of endurance training under low energy availability on muscle glycogen content, endocrine responses and endurance capacity. METHODS:Seven male long distance runners (19.9 ± 0.4 years, 175.6 ± 1.8 cm, 61.4 ± 2.0 kg, 67.5 ± 1.6 ml/kg/min) completed 3 consecutive days of endurance training under low energy availability trial (LEA, 18.9 ± 0.7 kcal/kg FFM/day) and normal energy availability trial (NEA, 52.9 ± 1.9 kcal/kg FFM/day). The order of two trials was randomized with two weeks interval between trials. The experiment consisted of 3 consecutive days of endurance training (days 1-3) and exercise performance test on the following morning (day 4). The endurance training consisted of 75 min of treadmill running at 70% of maximal oxygen uptake (VO2max) in both trials. Muscle glycogen contents, respiratory gas variables, subjective parameters, blood and urinal variables were evaluated in the morning during 3 days of training periods (day 1-day 3) and on the following morning after the training (day 4). As an indication of endurance capacity, time to exhaustion during submaximal running test was determined on day 4. RESULTS:LEA trial showed that body weight, free fat mass and skeletal muscle volume were significantly reduced during training period (P < 0.05). Also, muscle glycogen contents were significantly decreased in LEA (P < 0.001) with significant lower values than those in NEA trial (P < 0.001). Blood glucose, serum free testosterone and insulin like growth factor-1 concentrations were significant lowered with training under LEA (P < 0.05). On the other hand, serum leptin concentration did not change significantly in LEA trial during training period (P > 0.05). Time to exhaustion during submaximal running test evaluated on day 4 was not significantly different between LEA trial (1170 ± 127 s) and NEA trial (1361 ± 196 s, P > 0.05). CONCLUSION:Three consecutive days of endurance training under Low EA reduced muscle glycogen content. However, endurance capacity was not attenuated.

Copigmentation of cyanidin 3-O-glucoside with phenolics: Thermodynamic data and thermal stability

The intermolecular copigmentation of cyanidin-3-O-glucoside (C3G) with three colorless phenolic compounds and its thermal stability were investigated. The influence of the copigment (ferulic acid, dopamine, or (+)-catechin), the pigment-to-copigment molar ratio (1 : 1, 1 : 10, and 1 : 100), the pH value (pH 3–7), and the temperature (20, 30, 40, and 50 °C) on the copigmentation effect, stoichiometric ratio (n), the equilibrium constant (K), and thermodynamic parameters (ΔG°, ΔH°, and ΔS°) were obtained. The strongest immediate copigmentation reactions were observed at pH 3 and 1 : 100 molar ratio, being significantly higher with (+)-catechin, followed by ferulic acid and then dopamine. The greatest hyperchromic shift was found in the complex of C3G/(+)-catechin, which was reasonable for its n and K values of 0.7 and 17.1, respectively. Moreover, the reactions were favored at low temperature. The thermodynamic data indicated that all these complexes were formed by spontaneous exothermic reactions. The C3G/(+)-catechin complex at the molar ratio 1 : 100 exhibited the greatest thermodynamic properties, with negative values of ΔG° (−6.92 kJ/mol), ΔH° (−38.7 kJ/mol), and ΔS° (−108.0 J/K/mol). The C3G/(+)-catechin complex exhibited a low Ea value (78 J/mol), indicating greater thermal stability against temperature change compared with those with the other phenolic pigments. In addition, copigmentation of anthocyanins in mulberry juice with (+)-catechin significantly reduced the loss of anthocyanins during pasteurization (80 °C for 15 min).

Value of natriuretic peptides and tissue Doppler imaging in the estimation of left ventricular filling pressure in patients with cardiac amyloidosis

BackgroundEstimation of left ventricular filling pressures (LVFP) is a determining factor in the follow-up of patients with cardiac amyloidosis (CA). Natriuretic peptides (NPs) and tissue Doppler imaging may be used...

The use of M@p(4‐VP) and M@p (VI) (M:Co, Ni, Cu) cryogel catalysts as reactor in a glass column in the reduction of p‐nitrophenol to p‐aminophenol under gravity

AbstractIn this study, metal@p(4‐Vinyl pyridine) (M@p(4‐VP)) and metal@p (vinyl imidazole) (M@p (VI)) (M: Co, Ni, and Cu) cryogel catalysts as continuous reactor were used in reduction of p‐nitrophenol (p‐NP) to p‐amino phenol (p‐AP). The aqueous solution of p‐NP passed through these super porous cryogel catalysts under gravity, and reaction kinetic for p‐AP generation was investigated. The effect of metal species, amount of p‐NP solution, amount of metal nanoparticle (increased by loading/reducing cycles), and temperature on the reduction reaction for p‐NP to p‐AP catalyzed by M@p(4‐VP) and M@p (VI) cryogel catalysts were investigated. It was found that Co@p(4‐VP) and Co@p (VI) cryogel catalysts provided the best catalytic performances than the other used metal species with 2.19 and 1.37 mol p‐NP/(mol catalyst.min)−1 turn‐over frequency (TOF) values. Furthermore, in addition better TOF values, low Ea values of the prepared Co@p(4‐VP) and Co@p (VI) cryogel catalysts with the values of 18.9 ± 1.3, and 25.4 ± 1.8 kJ/mol were found to be better than most of the similar works reported in the literature.

Electrochemical performance of sulfide solid electrolyte Li10GeP2S12 synthesized by a new method

Solid electrolyte Li10GeP2S12 (LGPS) was successfully synthesized by optimizing the mechanical ball milling process and subsequent heat treatment process using Li, Ge, P and S as raw materials. The synthesis method has the advantages of low cost, simple process, short cycle and high efficiency. The synthesized LGPS possesses regular morphology and uniform particle distribution without agglomeration. Simultaneously, it presents a wide electrochemical voltage window of over 6.0 V (vs. Li+/Li), a low activation energy Ea of 25.5 kJ mol−1 and the room temperature conductivity σLi of 3.27 × 10−3 S cm−1. The synthesized LGPS solid electrolyte exhibits good electrochemical stability and compatibility with lithium metal electrodes, making it possible to apply in all solid state batteries.

Purification and biochemical characterization of a novel copper, zinc superoxide dismutase from liver of camel (Camelus dromedarius): An antioxidant enzyme with unique properties

A novel copper, zinc superoxide dismutase (CuZnSOD) was purified to homogeneity from the liver of an animal well adapted to the stressful living conditions of the desert, the camel (Camelus dromedarius). The biochemical properties of camel liver CuZnSOD were examined. The purified enzyme had a native molecular weight of 28 kDa, as judged by gel filtration chromatography, and showed a single band at 27 kDa on SDS-PAGE, indicating that it is a monomeric protein. Optimal activity of the purified enzyme occurred at 43 °C and pH 6.0, and the activation energy was 1.42 kJ/mol. CuZnSOD activity was strongly inhibited by β-ME, DTT, H2O2 and SDS and slightly inhibited by EDTA, NaN3 and PMSF. Al3+, Ca2+, Cd2+, Mg2+ and Zn2+ stimulated CuZnSOD activity, whereas Ba2+, Co2+, Fe2+ and Ni2+ inhibited it. The purified enzyme contained 0.010 µg of Cu and 0.69 µg of Zn per mg of protein. Km, Vmax, kcat and kcat/Km values for NBT and riboflavin were 16.27 and 0.16 µM, 20.85 and 21.54 U/mg, 9.65 and 9.97 s−1, and 0.59 and 62.33 s-1 µM−1, respectively. Camel liver CuZnSOD exhibited unique biochemical properties compared to those of other CuZnSODs, including lower molecular weight with a monomeric structure, higher optimum temperature, very low Ea, very low optimum pH, very low contents of Cu and Zn, and higher affinity, turnover number and catalytic efficiency for riboflavin. These unique properties of camel liver CuZnSOD might be related to the ability of this animal to inhabit stressful desert conditions.

An environmentally-benign NaNbO3 based perovskite antiferroelectric alternative to traditional lead-based counterparts

NaNbO3-based lead-free AFE R-phase ceramics with Pnma space group and nanoscale stripe domain exhibit completely reversible field induced AFE–FE phase transition, featuring a relatively low EA–F of ∼8 kV mm−1 and a large repeatable strain of ∼0.29%.

Water diffusion with temperature enabling predictions for sorption and transport behavior in thermoset materials

Water desorption kinetics for a number of epoxy materials (five amine and one anhydride cured), with glass transitions from below room temperature to 245 °C, were studied using thermogravimetry and near-infrared spectroscopy between ambient and 200 °C. Computational models based on 1D finite difference or 3D finite element Fickian diffusion processes were then applied to determine the underlying diffusivity. Classical Fickian diffusion with a constant D was sufficient to describe the water desorption behavior for all evaluated materials and conditions, with water induced swelling affecting the diffusion process no more than through small dimensional changes. The temperature dependence for diffusivity displayed mostly a single activation energy (Ea) between 44 and 62 kJ mol−1 for all materials except one, which showed a change from 75 kJ mol−1 below Tg (∼65 °C), to 53 kJ mol−1 above. The obtained diffusivities and their Ea were then used to predict and illustrate the sorption behavior for other geometries and temperatures. The trends for these materials were discussed within the existing theories for fractional free volume, effective crosslink density and chemical composition. Unexpectedly, this study shows that Tg has no or only limited influence on water diffusivity in contrast with the Cohen-Turnbull model. Water sorption (solubility in the material) is of similar magnitude independent of temperature (i.e. low Ea) as anticipated. Only a fraction of the water uptake was found to be associated with free volume utilization, with the majority of water resulting in material volume changes, which as a consequence means that dynamic water uptake and drying will result in changing stress conditions (expansion and contraction) for glassy thermosets even under ambient conditions.

Bimetallic palladium–iridium alloy nanoparticles as highly efficient and stable catalyst for the hydrogen evolution reaction

Addressed herein, a highly efficient, durable and uniformly dispersed activated carbon supported palladium–iridium nanomaterials (3.42 ± 0.34 nm) were reported for the first time as a catalyst in dimethylamine-borane dehydrogenation reaction at the room temperature. The activated carbon supported palladium-iridium nanosheet (Pd–Ir NPs) is obtained by a simple ultrasonic reduction method, and the fabricated nanocatalyst have been defined by Ultra-Violet-Visible (UV–VIS), Raman spectroscopy, X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM) and High-Resolution Transmission Electron Microscopy (HR-TEM). These newly prepared Pd–Ir nanocomposites were found to be highly efficient and stable for dehydrocoupling of dimethylamine borane. The catalytic activity of the Pd–Ir NPs was excellent by showing the one of the best catalytic activity with a very high turnover frequency (295.1 h−1) and low Ea value of 36.6 ± 2 kJ/mol for DMAB dehydrocoupling. Another important fact about the prepared catalyst is the reusability of the catalyst was very high and easily reused five times without any significant decrease in their catalytic performance. In the current work, the synthesize, characterization and the catalytic performance of the Pd–Ir nanoparticles for the dehydrogenation of the DMAB reaction will be discussed in detail.