Search

A method for accelerating bubble removal in non‐Newtonian liquids by forced stirring is proposed. Numerical simulations based on an Eulerian‐Eulerian multiphase model are performed to test its feasibility for various liquids including shear‐thickening, shear‐thinning, and Newtonian ones. Effects of the rotating speed of the stirrer and rheological properties of liquids on the degassing efficiency are evaluated, and the influencing mechanisms are analyzed in detail. The feasible regions of degassing in shear‐thinning liquids covering a certain range of viscosities are determined, from which one can easily decide the optimal rotating speed given the viscosity of liquids. The results provide a new idea of efficient degassing in shear‐thinning liquids for researchers and engineers. [ABSTRACT FROM AUTHOR]

Detections of telomerase activity in vitro and in living cells are of great importance for clinical diagnosis of cancer. In this work, an AIEgens-based bioprobe with two fluorescent signals for enhanced monitor of extracellular and intracellular telomerase activity is designed. After addition of telomerase, two positively charged AIEgens (Silole-R and TPE-H) bind to quencher group labeled primer (QP) and the extension repeated units, leading enhancement of two telomerase-triggered fluorescent signals. Furthermore, by combination the wider linear range in vitro and lower background in living cells imaging, the bioprobe is used to detect telomerase extracted from various cell lines (MCF-7, HeLa, E-J, and HLF), 50 bladder cancer patients' urine samples, 10 normal people's urine samples, and also applied in mapping telomerase activity inside living cells (MCF-7, HeLa, MDA-MB-231, and HT1080). The results show that this well-designed strategy can successfully detect telomerase activity in vitro and in living cells with high sensitivity, indicating the potential application of this method in cancer cells bioimaging and clinical cancer diagnosis. [ABSTRACT FROM AUTHOR]

Anatase TiO 2 nanosheets (NSs) with high surface area have been prepared via a one-step thermal decomposition of titanium tetraisopropoxide (TTIP) in oleylamine (OM), and their adsorption capacities and photocatalytic activities are investigated by using methylene blue (MB) and methyl orange (MO) as model pollutants. During the synthesis procedure, only one type of surfactant, oleylamine (OM), is used as capping agents and no other solvents are added. Structure and properties of the TiO 2 NSs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N 2 adsorption analysis, UV–vis spectrum, X-ray photoelectron spectroscopy (XPS) and Photoluminescence (PL) methods. The results indicate that the TiO 2 NSs possess high surface area up to 378 m 2 g − 1 . The concentration of capping agents is found to be a key factor controlling the morphology and crystalline structure of the product. Adsorption and photodegradation experiments reveal that the prepared TiO 2 NSs possess high adsorption capacities of model pollutants MB and high photocatalytic activity, showing that TiO 2 NSs can be used as efficient pollutant adsorbents and photocatalytic degradation catalysts of MB in wastewater treatment. [ABSTRACT FROM AUTHOR]

Herein, we report a novel strategy to accelerate the rate of DNA strand replacement reaction (DSRR) by polar organic solvents. DSRR plays a vital role in DNA nanotechnology but prolonged reaction time limits its further advancement. That is why it is extremely important to speed up the rate of DSRR. In this work, we introduce different polar organic solvents in both simple and complicated DSRR systems and observe that the rate constant is much more than in aqueous buffer. The rate acceleration of DSRR by polar organic solvents is very obvious and we believe that this strategy will extend the application of DNA nanotechnology in future. [ABSTRACT FROM AUTHOR]

Two‐step chemical vapor deposition (CVD) method is a promising technique for industrial fabrication of low‐hydroxyl silica glass ingot, in which a porous silica preform is first synthesized by flame hydrolysis deposition, which is subsequently sintered and vitrified to form silica glass. During sintering hydroxyls can be easily removed through the small pores in porous silica preform, which is called dehydroxylation. A deep understanding of the heat and mass transport characteristics involved in the dehydroxylation process is prerequisite to its controlling. In our previous work, a numerical model was developed to simulate the sintering and dehydroxylation of porous silica preform considering heat and mass transfer in porous media at high temperatures, chemical reaction of dehydroxylation, and volume shrinkage of preform. The results revealed that the dehydroxylation effect largely depends on the temperature fields in the furnace. In present work, the influences of thermal environments, including heating curve, heater position, and crucible structure on the dehydroxylation process of porous silica preform are systematically studied by numerical methods. Based on the results, increasing temperature at either stage is helpful for hydroxyl removal as well as increasing the hydroxyl distribution uniformity. However, long‐time exposure to 1500°C will instead worsen the dehydroxylation effect. Compared to top or bottom heating, side heating is more beneficial to hydroxyl removal. To improve the dehydroxylation condition at the bottom of porous silica preform, a novel crucible structure is designed which shows better performance than the ordinary crucible. At last, an optimized heating scheme is proposed in this study, which obtains much better dehydroxylation effect than other cases. [ABSTRACT FROM AUTHOR]

Ru clusters and sulfoacids are isolated in a yolk-shell nanoreactor to balance hydrolysis, isomerization, hydrogenolysis and hydrogenation well, yielding 38% of 1,2-propylene glycol from cellulose valorization, corresponding to a high productivity of 342.86 mol/h g Ru –1 and a large TON of 173264. [Display omitted] • Isolated Ru clusters and sulfoacids are integrated in a yolk-shell nanoreactor. • Cellulose hydrogenolysis to 1,2-propylene glycol with 38% yield. • High productivity of 342.86 mol 1,2-PG h−1 g Ru –1 and turnover number of 173264. • Enhanced metal-acid synergism, diffusion pathway and optimized acidity/basicity. • Intermediate reactions are banlanced to render high yield 1,2-propylene glycol. Direct conversion of cellulose to high yield 1,2-propylene glycol (1,2-PG) is amazing in the biomass valorization to diols, since this process is atom-economic, carbon neutral, and the produced 1,2-PG has a large market demand. However, it is very challenging to control cellulose hydrogenolysis owing to high reactivity of intermediates (like glucose) and metal-acid repelling, leading to decreased selectivity of metal-acid multi-functional catalysts. Aimed at this, we herein developed a highly selective metal-acid catalyst (Ru/NC@void@MC-SO 3 H) with site isolated Ru clusters (1.4 nm) on the core and sulfoacids on the shell in a yolk-shell nanoreactor by a layer-by-layer assembly before chemical transformation. The spatial isolation of metal and acid sites integrated in a mesoporous yolk-shell nanoreactor not only facilitates the metal-acid synergism in hydrolysis, isomerization/hydrogenolysis and hydrogenation cascade reactions, but also provides a designated diffusion pathway that is favorable for reaction species. As expected, the elaborately fabricated Ru/NC@void@MC-SO 3 H proves to be highly selective to 1,2- PG (38 % yield), delivering a productivity of 342.86 mol h−1 g Ru –1 and an extremely high turnover number of 173264, outperforming the state-of-art metal-acid catalysts for cellulose hydrogenolysis to 1,2-PG. Our characterization and performance test suggest that sulfoacids are mainly responsible for cellulose hydrolysis, while N -stabilized Ru centers contribute to the glucose isomerization to fructose and its further hydrogenolysis to dihydroxyacetone, followed by hydrogenation to 1,2-PG on metallic Ru species. The acidity and basicity optimized for site isolated Ru/NC@void@MC-SO 3 H is beneficial to balance intermediate reactions, rendering a higher selectivity to target 1,2-PG. The concept illustrated in this study will provide a guide for the development of other site isolated multi- functional catalysts towards cellulosic biomass conversion and other cascade reactions. [ABSTRACT FROM AUTHOR]

A brand-new Co catalyst with precisely tailored Co nanoparticle/single atom (NP/SA) ratio was encapsulated into a hollow carbon sphere for aqueous levulinic acid hydrogenation to γ-valerolactone. Synergism between carbonyl activation and hydrogen dissociation was realized over the Co catalyst with an isoatomic ratio of NPs and SAs, and superior stability was achieved due to the unique yolk-structure. [Display omitted] • Yolk-shell Co catalysts with a raspberry core and a hollow N -doped carbon shell. • Co nanoparticle/single atom ratio was controlled precisely. • Superior activity and stability of the Co catalyst for LA hydrogenation. • The synergism between Co nanoparticles and single atoms. • Co single atoms and nanoparticles facilitate C O and H 2 activation, respectively. Precise and facile tailoring of metal nanoparticle/single-atom ratio to optimize the catalytic hydrogenation activity and durability is important yet challenging, owing to the lack of efficient synthetic methodology. Herein, we report a brand-new Co catalyst with precisely tailored Co NP/Co SA ratio encapsulated into a hollow carbon sphere, skillfully fabricated by stepwise coating of bimetallic Zn/Co zeolitic imidazole frameworks with silica and 8-quinolinol modified chitosan before pyrolysis and acid washing. The transformation of the target catalyst and the tailoring of Co NP/Co SA ratio are well investigated by various characterization techniques including TEM, aberration-corrected scanning TEM (AC-STEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS), etc. It is found that the yolk-shell structured Co catalyst integrated with nearly equivalent nanoparticles and sing-atoms are highly active and stable towards aqueous levulinic acid (LA) hydrogenation to γ-valerolactone (GVL). Combined with H 2 -TPD and LA adsorbed FT-IR investigations, it is revealed that the superior activity originates from the synergism of Co nanoparticles and single-atoms, since H 2 dissociation and C O adsorption are facilitated by Co nanoparticles and single-atoms, respectively, leading to a lowered energy barrier during the hydrogenation reaction. This study will shed light on the precise tailoring of metal nanoparticle/single-atom ratio and also provides a new insight into the development of highly efficient non-noble metal catalysts for sustainable biomass conversion. [ABSTRACT FROM AUTHOR]

Dehydroxylation of porous silica preform plays a key role in two-step chemical vapor deposition (CVD) method for low-hydroxyl silica glass fabrication, the good control of which requires a clear understanding of the heat and mass transport characteristics involved in this process. For this purpose, a coupled numerical model is developed in this paper to simulate the sintering and dehydroxylation of porous silica preform, which considers the main phenomena including dehydroxylation reaction, heat and mass transfer in porous silica preform at high temperatures and shrinkage of porous silica preform. Numerical simulations are performed with this model in the configuration of a practical industrial heating furnace. Model verification is carried out by comparing the simulated hydroxyl concentration with experimental measurements at the end of sintering, which shows reasonable agreements. Based on the simulation results, variations of key parameters during heating, including temperature, porosity, hydroxyl concentration, gas pressure and gas velocity are analyzed in detail. Different transport modes of water vapor in porous silica preform are compared which shows that diffusion is the dominant way for its expelling. According to the sensitivity analysis, activation energy and frequency factor of dehydroxylation reaction have significant influences on the simulated hydroxyl concentration. Heat transfer coefficient and intrinsic permeability has little influences on the variation history of hydroxyl concentration, but has certain influences on the final hydroxyl distribution. Finally, the effects of preform size and heating curve on the dehydroxylation effect are determined, which could provide useful guidance for better controlling of the dehydroxylation of porous silica preform. [ABSTRACT FROM AUTHOR]

Carbon-based non-precious metal/oxide catalysts always face the dilemma of a trade-off between high activity and long-term stability in hydrogenation reactions, detrimental to their practical applications. Herein we propose a unique and uniform feather duster-type catalyst as a promising concept to solve this activity-stability trade-off. The feather duster is composed of both exposed and embedded active sites, that can facilitate substrate adsorption/activation and can be resistant against site leaching during the non-neutral aqueous phase reactions. We constructed a uniform one-dimensional hierarchical transition metal oxide-containing N-doped carbon (TMO-N-C), especially for CoO x -N-C (x = 1.0 or 1.3), based on a controlled depolymerization-reassembly strategy before morphology-conserved pyrolysis. The uniform, thermally stable feather duster-type precursor was induced in view of the interaction between cobalt 2-methylimidazolate framework (ZIF-67) polyhedron and zinc-trimesic acid (ZnBTC) fiber in water. And subsequent pyrolysis leads to a uniform CoO x -N-C nanoarchitecture with numerous nanorods planted on a single fiber. The resulting CoO x -N-C proves to be highly efficient for 4-nitrophenol reduction, delivering a high activity factor of 7.32 s −1 g −1 with exceptional long life over 10 cycles, thus ranking CoO x -N-C one of the best transition metal oxide catalysts for hydrogenation reactions. This research overcomes the dilemma that either high activity contributed by surface active sites or superior stability provided by embedded ones, offering valuable guidance for rational design of efficient metal/oxide catalysts. Based on the acid-base interaction, ZIF-67 polyhedron and ZnBTC fiber were depolymeried in water and reassembled into a feather duster-type precursor for uniform one-dimensional hierarchical CoO x -N-C, which breaks the activity-stability trade-off. [Display omitted] • Controlled depolymerization-reassembly strategy. • Uniform one-dimensional hierarchical CoO x -N-C feather duster. • CoO x sites located both outside and inside. • Breaking the activity-stability trade-off for hydrogenation reactions. [ABSTRACT FROM AUTHOR]