Quick Nucleation Research Articles

Fabrication of Self-Standing Porous Foam-like PdM (M = Ni, Fe, Co) Nanocrystals for Boosted Ethanol Oxidation Electrocatalysis

Rational designing of self-standing porous foam-like PdM (M = Ni, Fe and Co) nanocrystals was achieved by a fast aqueous-solution method via the co-reduction of metal precursors using sodium borohydride. This was based on the crystallites’ coalescence growth mechanism, including quick nucleation of Pd that served as starting seeds for the nucleation of M, which attached directly along the specific crystallographic and lowered its high surface energy by diffusion of PdM atoms across the interface via Brownian motion to afford self-standing porous foam-like PdM nanocrystals. Amongst the as-prepared PdM nanocrystals, PdNi nanocrystals showed a superior alkaline ethanol oxidation reaction (EOR) activity and stability compared to PdFe, PdCo, Pd nanospheres (Pd-NSs) and commercial Pd/C (10 wt.%) catalysts. The EOR mass activity of PdNi was 1.32, 1.51, 2.01 and 24.05 times than those of PdFe, PdCo, Pd-NSs and Pd/C, respectively based on equal Pd mass. This was attributed to the lower synergistic effect in PdNi, which enhanced H2O activation/dissociation to give OH- species needed for rapid EOR kinetics, meanwhile, the porous foam-like morphology improved electron mobility and increased accessible active sites. This study revealed that low synergism in porous PdM nanocrystals is beneficial for enhancing the EOR activity and durability, which may allow the design of other binary Pd-based alloys for various electrocatalytic reactions.

Enhancing the polysulfide redox conversion by a heterogeneous CoP-Co3S4 electrocatalyst for Li-S batteries

The development of lithium-sulfur (Li-S) batteries necessitates the creation of efficient cathode materials. By simultaneous phosphating and sulfurating, a spindle-shaped CoP-Co3S4 heterostructure sulfur cathode substrate made up of numerous tiny needle-like structures is created. The benefits of CoP with outstanding conductivity and Co3S4 with great adsorption capacity are combined in the as-prepared CoP-Co3S4 heterostructures, which achieve efficient capture-diffusion-transformation of polysulfides at the interface. The CoP accelerates the redox kinetics toward polysulfide conversion, and the Co3S4 has a considerable adsorption power toward polysulfides. The quick nucleation of polysulfide and increased capture effectiveness are aided by the quick transfer of polysulfide from the Co3S4 surface to the CoP surface. As a result, the CoP-Co3S4 @S cathode battery with a 1.1 mg cm−2 sulfur load achieves a high initial capacity of 1516.9 mAh g−1 at 0.2 C and maintains that capacity after 100 cycles at 750.1 mAh g−1. After 300 cycles, even the 565.1 mAh g−1 specific capacity can be attained at 1 C.

Large ammonium cation-induced controlled mixed-phase of CsPbBr3 perovskites for color tunable perovskite light-emitting diodes

Color tunability is a unique advantage of perovskite light-emitters for next-generation display technologies because controlled dimension and phase of metal halide perovskites can vary the optoelectronic properties of perovskite light-emitting diodes (PeLEDs). Herein, we demonstrate a color tuning of green-emitting CsPbBr3–based PeLEDs to sky-blue by employing n-butylammonium bromide (BABr). The incorporation of BABr, a large ammonium cation, in CsPbBr3 facilitates the formation of 2-dimensional (2D) perovskite structure with band-gap widening that corresponds to fluorescence peak shift from 513 to 406 nm. In addition, the incorporation of BABr is found to restrict the quick nucleation and rapid growth of CsPbBr3 crystals to allow subsequent growth of 2D structure with lower n-phases, affording a smooth and uniform film surface. As a result, the optoelectronic properties of the CsPbBr3-based PeLEDs were significantly improved by BABr with a brightness of 5260 cd m–2, peak external quantum efficiency of 6.72 % and a maximum current efficiency of 27.78 cd A–1. Moreover, the BABr addition also induced a facile color conversion from green to sky-blue, suggesting remarkable potential toward high-performance PeLEDs with tunable emission colors for next-generation display technologies.

Surface wettability of vertical harps for fog collection

Surface wettability is an influential property and plays a pivotal role in fog harvesting. Two types of surfaces i.e., hydrophilic and hydrophobic are generally used for fog harvesting. A hydrophilic surface provides quick nucleation whereas a hydrophobic surface carries rapid transportation of water droplets. Animals and plants live in arid environment, control their surface wetting through their naturally grown surfaces in their biological structures. These patterns provide extremely high affinity of fog collection for these surfaces by reducing the friction and pinning force of water droplets sliding down towards storage. In this study, a comparison of hydrophilic and hydrophobic surfaces is carried out and the results are expressed in terms of wetting behavior. Hydrophilic and hydrophobic vertical harps are developed by plasma treated and silane treated monofilament polyesters respectively. Traditional raschel mesh is replaced with polyester monofilament-based prototype developed in this study. The reason to replace raschel mesh (standard fog collector element) with a harp design is to capture the maximal fog by avoiding clogging. It is revealed that fog collector element(FCE) treated with hydrophobic coating improve the collection rate, however, hydrophilic treatment shows adverse effects. In addition, we examined the contact angle hysteresis (CAH) of our prototypes to verify the wettability effect.

Speedy Hydration of Carbon Dioxide Hydration in an Immediate Coolant of Ice Granules.

Hydrate-based carbon capture (HBCC) has been considered as a promising technique in recent times. However, large exothermic heat of hydration and lower solubility of the gas in water cause a slower hydration rate and poor gas uptake during hydration. In the present work, a phase change heat removal method was applied, in which ice granules surrounded by normal alkanes were used as an immediate coolant and quick nucleation center to intensify the carbon dioxide capture through hydrate formation. Normal alkanes have great potential to enhance gas–water contact due to their high solubility with CO2 and thus may enhance the hydration rate. The slurries of ice in normal alkanes from cooling three different W/O emulsions were prepared to perform all the hydration experiments in a batch autoclave at a constant temperature of 267.15 K and pressure range of 1.9–2.5 MPa with a stirring speed of 600 rpm. Kinetics of CO2 hydrate formation such as induction time, hydration duration, molar gas uptake, and hydrate growth rate were determined using a mole balance (PVT) model. Compared to earlier investigations of hydrate formation, in present work, the hydrate growth rate increased by 7–39 times and enlarged to 352 times as compared to pure water while gas uptake per mole of water increased by 1.6–10 times.

Ultrafast Catalyst-Free Graphene Growth on Glass Assisted by Local Fluorine Supply.

High-quality graphene film grown on dielectric substrates by a direct chemical vapor deposition (CVD) method promotes the application of high-performance graphene-based devices in large scale. However, due to the noncatalytic feature of insulating substrates, the production of graphene film on them always has a low growth rate and is time-consuming (typically hours to days), which restricts real potential applications. Here, by employing a local-fluorine-supply method, we have pushed the massive fabrication of a graphene film on a wafer-scale insulating substrate to a short time of just 5 min without involving any metal catalyst. The highly enhanced domain growth rate (∼37 nm min-1) and the quick nucleation rate (∼1200 nuclei min-1 cm-2) both account for this high productivity of graphene film. Further first-principles calculation demonstrates that the released fluorine from the fluoride substrate at high temperature can rapidly react with CH4 to form a more active carbon feedstock, CH3F, and the presence of CH3F molecules in the gas phase much lowers the barrier of carbon attachment, providing sufficient carbon feedstock for graphene CVD growth. Our approach presents a potential route to accomplish exceptionally large-scale and high-quality graphene films on insulating substrates, i.e., SiO2, SiO2/Si, fiber, etc., at low cost for industry-level applications.

Unravelling the growth mechanism of hierarchically structured Ni1/3Co1/3Mn1/3(OH)2 and their application as precursors for high-power cathode materials

A hydroxide co-precipitation method is used to synthesize transition metal hydroxide (Ni1/3Co1/3Mn1/3(OH)2), which is the precursor for layer-structured LiNi1/3Co1/3Mn1/3O2. The optimum pH range for the preparation of Ni1/3Co1/3Mn1/3(OH)2 using a continuous stirred-tank reactor is calculated by taking into account the underlying chemical equilibria. The entire growth process of the Ni1/3Co1/3Mn1/3(OH)2 particles is investigated by monitoring the structure, morphology, particle size distribution, and tap density as a function of the reaction time. The results confirm that the co-precipitation reaction in the presence of ammonia started with the formation of crystal nuclei and (001) plane dominated nanosheets. The reaction ended with spherical and dense hydroxide precursors. The crystal growth mechanism was interpreted during the co-precipitation process, which involved the quick nucleation of primary particles followed by its slow aggregation and crystallization. The electrochemical properties of the final cathode materials with different morphologies are also studied. The results show that the electrochemical performances of the final LiNi1/3Co1/3Mn1/3O2 are strongly affected by the hierarchical structure of Ni1/3Co1/3Mn1/3(OH)2.

Mesoporous Tantalum Oxide Photocatalyst: Structure and Activity Evaluation

AbstractMesoporous nanostructured pure tantalum pentoxide and Eu‐doped Ta2O5 were produced by facile and reproducible one‐pot procedure not involving structure directing agents. The as‐produced material is poorly crystalline and catalytically inactive. Photoluminescence behavior of the doped oxide indicates that it is formed by quick nucleation of pure Ta2O5, leaving the Eu‐dopant only on the surface of the formed material. Further thermal treatment leads to crystallization and structural transformation as revealed by in situ X‐Ray Diffraction (XRD) and Rietveld refinement used to identify and quantify the emerging phases as well as Diffuse Reflectance UV‐vis Spectroscopy (DR‐UV‐Vis) and Raman Spectroscopy studies. The thermally induced transformation results in generation of surface oxygen vacancies that provide the material with pronounced photocatalytic activity in selective oxidation of aromatic amine compounds. The processes of generation and curing of the vacancies have been followed and quantified by temperature programmed oxidation and reduction and photoluminescence studies, offering in depth insight into the reaction mechanism.

Electrodeposition of silver nanoparticle arrays on ITO coated glass and their application as reproducible surface-enhanced Raman scattering substrate

In this paper, a double-potentiostatic method is used for preparation of highly efficient and uniform surface-enhanced Raman scattering (SERS) substrate. The method takes advantage of the quick nucleation and slow growth process, yielding silver nanoparticle arrays (NAs) containing large amount of hot spots, which bring about these dense silver NAs for reproducible SERS application.

Study of mullite formation in porcelain stoneware applying isoconversional and IKP methods

Abstract The growth process of mullite in a porcelain stoneware body has been studied under isoconversional, isokinetic relationship and invariant kinetic parameters. Activation energy for mullite crystallisation of over 589–628 kJ mol −1 and a Ln A over 50–59 min −1 was obtained. The model was Johnson–Melh–Avrami with n = 1.5. The model chosen implies quick nucleation and subsequent one or three-dimensional growth. Isoconversional methods show an independent activation energy variation in mid range conversion degrees. Lower and higher conversion degrees show different reactions in mullite formation. Results obtained with the methods employed here are in agreement with a previous paper where the Kissinger non-isothermal method and Ligero et al. approximation were applied.

A straight way toward phase pure complex oxides

Great majority of the electroceramic materials to date are complex oxides. Phase purity, high crystallinity and small grains with narrow size distribution are almost always required. Quick nucleation and limited growth are essential for that purpose. The author concentrates himself on a straight way toward this goal by taking three components into account, i.e. (1) active nucleation sites in high concentration, (2) short diffusion path for growth and (3) achievement of kinetic stabilization. Soft-mechanochemical synthesis is one of the best shortcuts to the goal. The main spirit is the incipient chemical reaction at the boundary between dissimilar particles through homogenization of the starting mixture by exerting as small mechanical energy as possible. Case studies are devoted to the syntheses of various complex perovskites, recently carried out in the author's own laboratory.

Rad51 Protein from the Thermotolerant Yeast Pichia angusta as a Typical but Thermodependent Member of the Rad51 Family

The Rad51 protein from the methylotrophic yeast Pichia angusta (Rad51(Pa)) of the taxonomic complex Hansenula polymorpha is a homolog of the RecA-RadA-Rad51 protein superfamily, which promotes homologous recombination and recombination repair in prokaryotes and eukaryotes. We cloned the RAD51 gene from the cDNA library of the thermotolerant P. angusta strain BKM Y1397. Induction of this gene in a rad51-deficient Saccharomyces cerevisiae strain partially complemented the survival rate after ionizing radiation. Purified Rad51(Pa) protein exhibited properties typical of the superfamily, including the stoichiometry of binding to single-stranded DNA (ssDNA) (one protomer of Rad51(Pa) per 3 nucleotides) and DNA specificity for ssDNA-dependent ATP hydrolysis [poly(dC) > poly(dT) > phiX174 ssDNA > poly(dA) > double-stranded M13 DNA]. An inefficient ATPase and very low cooperativity for ATP interaction position Rad51(Pa) closer to Rad51 than to RecA. Judging by thermoinactivation, Rad51(Pa) alone was 20-fold more thermostable at 37 degrees C than its S. cerevisiae homolog (Rad51(Sc)). Moreover, it maintained ssDNA-dependent ATPase and DNA transferase activities up to 52 to 54 degrees C, whereas Rad51(Sc) was completely inactive at 47 degrees C. A quick nucleation and an efficient final-product formation in the strand exchange reaction promoted by Rad51(Pa) occurred only at temperatures above 42 degrees C. These reaction characteristics suggest that Rad51(Pa) is dependent on high temperatures for activity.