Smaller Mass Transfer Resistance Research Articles

Interface-Engineered Hollow Nanospheres with Titanium(IV) Binding Sites and Microwindows as Affinity Probes for Ultrafast and Enhanced Phosphopeptides Enrichment.

Enrichment and identification of phosphopeptides in real biological samples are of great significance in many aspects. Herein, Ti4+-immobilized silica hollow nanospheres were tailored via chelating with phosphonic acid groups produced from dealkylation of phosphonate ester functionalized silica hollow nanospheres, which were synthesized through a single micelle templated method with diethylphosphatoethyltriethoxysilane (DPTES) and tetramethoxysilane (TMOS) as silane precursors under neutral conditions. The characterization results of transmission electron microscopy (TEM), nitrogen sorption isotherms, FT-IR, and energy-dispersive X-ray (EDX) spectroscopy confirmed the successful preparation of Ti4+-immobilized silica hollow nanospheres (SHS-Ti; approximately 17 nm particle size), which possessed a 10 nm hollow cavity with 1.6 nm micropores on the thin shell (about 3.5 nm). Attributed to the immobilized Ti4+ and high specific area (396 m2/g), SHS-Ti was applied as a Ti4+-immobilized metal affinity chromatography (Ti-IMAC) material and showed good specificity, a low limit of detection (5 fmol), high selectivity (tryptic digestion mixture of bovine serum albumin/β-casein, 1000:1 molar ratio), high binding capacity (120 mg/g for pyridoxal 5'-phosphate), and a high binding constant (1.30 × 103 L/mg). Particularly, benefiting from the unique hollow structure with microwindows on the thin shell, a short transport path, and small mass transfer resistance, SHS-Ti exhibited excellent enrichment speed in which both phosphopeptide loading and elution could be completed in 1 min. The 5298 unique phosphopeptides from 1618 unique phosphoproteins were identified after enrichment by SHS-Ti from 100 μg Jurkat cell lysates within three independent replicates. The results showed that SHS-Ti could be utilized as a novel and promising enrichment probe for phosphopeptide characterization in MS-based phosphoproteomics and related fields.

High efficiency three-dimensional electrochemical treatment of amoxicillin wastewater using Mn–Co/GAC particle electrodes and optimization of operating condition

In this work, Mn–Co/GAC particle electrode was prepared by loading Mn and Co as catalysts on granular activated carbon (GAC) and used in a three-dimensional (3D) electrochemical system for mineralization of amoxicillin wastewater. Observation results by SEM, EDS and XRD confirmed that Mn and Co catalysts were successfully loaded onto GAC. The electrochemical properties were measured using an electrochemical workstation. Mn–Co/GAC had a much higher oxygen evolution potential (1.46V) than GAC (1.1V), which demonstrated that it could effectively reduce the oxygen evolution side reaction. In addition, Mn–Co/GAC had an electrochemically active surface area 1.34 times that of GAC and a much smaller mass transfer resistance than GAC, which could provide favorable conditions for the degradation of pollutants. The investigation of the influences of single operating parameters on total organic carbon (TOC) removal rate and electrical energy consumption (EEC) indicated that current density and treatment time had the greatest effect. In order to maximize TOC removal rate and minimize EEC, optimization of operating parameters was also carried out using response surface method in combination with central composite design. The optimal operating parameters were determined as current density of 5.68 mA/cm2, electrolyte concentration of 0.127M, particle electrode dosage of 31.14g and treatment time of 120min. Under this optimum operating condition, TOC removal rate of 85.24% and amoxicillin removal rate of 100% could be achieved with a low EEC of 0.073 kWh/g TOC. In addition, TOC removal rate and EEC were significantly improved compared to the use of bare GAC as particle electrode under the same operating conditions, demonstrating the excellent electrocatalytic ability of the new particle electrode Mn–Co/GAC. A possible mechanism of enhanced amoxicillin and TOC removal was also recommended. In summary, the 3D electrochemical method using Mn–Co/GAC particle electrodes is a suitable choice for amoxicillin wastewater treatment.

Modulating Ni/Ce Ratio in NiyCe100-yOx Electrocatalysts for Enhanced Water Oxidation.

Oxygen evolution reaction (OER) is the key reaction for water splitting, which is used for hydrogen production. Oxygen vacancy engineering is an effective method to tune the OER performance, but the direct relationship between the concentration of oxygen vacancy and OER activity is not well understood. Herein, a series of NiyCe100−yOx with different concentration of oxygen vacancies were successfully synthesized. The larger concentration of oxygen vacancies in Ni75Ce25Ox and Ni50Ce50Ox result in their lower Tafel slopes, small mass-transfer resistance, and larger electrochemical surface areas of the catalysts, which account for the higher OER activities for these two catalysts. Moreover, with a fixed current density of 10 mA/cm2, the potential remains stable at 1.57 V for more than 100 h, indicating the long-term stability of the Ni75Ce25Ox catalyst.

Few-layer N-doped porous carbon nanosheets derived from corn stalks as a bifunctional electrocatalyst for overall water splitting

The environmental crisis of the earth's living has led to in-depth research on energy generation and conversion, and electrocatalytic water splitting appeared suitable for sustainable energy cycles and conversion. Here, a N-doped few-layer porous carbon nanosheets catalyst (labeled as NPCSS) with high specific surface area, enormous active sites and high atom ratio of pyridinic/pyrrolic N was obtained by pyrolysis of mixture of corn stalks soot and melamine. Compared with corn stalks soot during pyrolysis without melamine, the NPCSS is featured with more electrochemically active sites and smaller mass transfer resistance, leading to a superior water splitting activity in 1 M KOH solution. NPCSS shows outstanding water splitting performance with small overpotentials of 195 mV and 358 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at the current density (j) of 10 mA cm−2, respectively. Our method realizes the high value-added utilization of biomass carbon.

Poly(carboxybetaine methacrylate)-grafted silica nanoparticle: A novel carrier for enzyme immobilization

Polymer-coated nanoparticles are favorable carriers for enzyme immobilization for their advantages of high specific surface area, small mass transfer resistance and a large number of active groups for covalent bonding of enzymes. Of the various polymers, zwitterionic polymers have been found to work as protein stabilizers. Inspired by the literature outcomes, we have herein developed a novel nanoparticle-based carrier modified by grafting a highly hydrophilic zwitterionic polymer, poly(carboxybetaine methacrylate) (pCBMA), on silica nanoparticles (SNPs), which was denoted as SNPs-pCBMA. For comparison, an uncharged polymer, poly(glycidyl methacrylate) (pGMA), was also grafted onto SNPs to prepare SNPs-pGMA. The two types of polymer-grafted SNPs were extensively characterized and used for the covalent bonding of two enzymes, catalase and lipase (pGMA-CAT, pCBMA-CRL, pGMA-CRL and pCBMA-CRL). The results revealed that both the immobilized enzymes on SNPs-pCBMA exhibited higher thermal and storage stabilities than those on SNPs-pGMA, due to protective effects of the zwitterionic polymer. For example, by incubation at 50 °C for 20 min, the residual activities of pCBMA-CAT and pCBMA-CRL kept 60.5% and 60.3% of their initial activities, respectively, higher than those of pGMA-CAT and pGMA-CRL (55.6% and 48.3%, respectively). The immobilized enzymes on SNPs-pCBMA also exhibited higher stability under neutral and alkaline conditions and good reusability. Taken together, the research proved that pCBMA-grafted materials were promising support for enzyme immobilizations.

Wastewater treatment by high-growth bioreactor integrated with settling-cum-membrane separation

A different approach of wastewater treatment has been investigated in this study by operating bioreactor at low mixed liquor suspended solids (MLSS) concentrations, thereby maintaining high F/ M ratio to target higher nutrient removal through higher biomass yield. A 10-L capacity laboratory-scale bioreactor followed by settling-cum-membrane separation employing hollow fiber membrane module (pore size: 0.1 μm) was set up and operated under batch mode at a hydraulic retention time (HRT) of 24 h using simulated domestic wastewater as feed. Average removal efficiencies of bioreactor were approximately 84% soluble chemical oxygen demand (SCOD), 95.5% total COD (TCOD), 90% NH 4 +–N, and 87% total Kjeldahl nitrogen (TKN). True yield coefficient ( Y T ) and decay coefficient ( K d ) for bioreactor were estimated at 0.397 kg VSS/kg SCOD and 0.0549 day − 1 , respectively. Significant proliferation of non-flocculating microorganisms was observed in the system with decreasing solids retention time (SRT) and thereby deteriorating biomass settling property indicated by enhanced sludge volume index (SVI). Significant proliferation of non-flocculating microorganisms with better ability to access substrate from bulk solution through smaller mass transfer resistance most probably contributed to better organics removal. The modified approach of wastewater treatment can be a good basis to develop high-growth membrane bioreactor (MBR) as opposed to conventional MBR operation.

Effect of Gas Diffusion Layer Composition on the Performance of Direct Methanol Fuel Cells

The effect of the cathode gas diffusion layer compositions on the performance of direct methanol fuel cells has been investigated. Morphological and textural properties of different diffusion layers have been characterized. Experiments in a single cell show that the use of a microporous layer (MPL) made with acetylene black instead of furnace carbon black results in higher cell voltages and power densities. This has been explained by a smaller mass-transfer resistance in the cathode diffusion layer due to a more suitable structure of the MPL when using acetylene black.

Effects of baffles on separation of aqueous ethanol solution with hollow fibers

The effects of baffles on the operation and mass-transfer characteristics in novel hollow fiber membrane contactor used in distillation were investigated. Hollow fiber membranes, coated with a 7 μm polydimethyl-siloxane, were operated as structural packing in the separation of ethanol-water solutions. The parallel flow mode was chosen for separation due to the stronger driving force of the concentration difference, in which liquid flows through the lumens of the fibers and vapor flows countercurrent-wise outside the fibers. Two baffles were installed on the shell side of the membrane contactors to enhance separation, which had a round shape with a semi-lunar hole. The results show that both baffled and unbaffled membrane contactors gave better, more productive separations than traditional packing in distillation, such as the excellent Sulzer Gauze BX structured packing. The baffled membrane contactors performed better than unbaffled ones, especially at high vapor velocities. The minimal HTU of membrane contactor with baffles could reach as low as 4.5 cm, and almost all the contactors could work well above the limit where flooding normally occurs in conventional cases. Theoretical analysis predicted that baffles helped membrane module to obtain a higher masstransfer coefficient and a smaller mass-transfer resistance. Finally, theoretical mass-transfer coefficient and experimental value were compared as well as the contribution of each individual mass-transfer coefficients among liquid, gas and membrane.

Separation of kinetics and mass-transport effects for a fast reaction: the selective hydrogenation of functionalized alkynes

A kinetic study has been made into the hydrogenation of 3-methyl-1-pentyn-3-ol over palladium on silica catalysts. This reaction already proceeds at very high rates under mild reaction conditions and, therefore, mass-transfer inside the catalyst particle inevitably influences the reaction progress, making the determination of the reaction kinetics difficult. To be able to determine the reaction mechanism and the kinetic parameters, a model has been drawn up in which both mass-transfer and kinetics are modeled simultaneously. This model is able to accurately describe the reaction progress. The model can also be used to explain the effect of commonly used reaction modifiers like quinoline on the reaction. Quinoline can be added to increase the selectivity to the desired alkene intermediate. From the calculations it is shown that the primary function of this type of modifier is to decrease the reaction rate. The lower reaction rate and thereby relatively smaller mass-transfer resistance in the catalyst is most likely a primary cause for the increased selectivity when a reaction modifier is used.

Adsorption of micropollutants onto fibrous activated carbon: association of ultrafiltration and fibers

The adsorption of polluted solutions is performed by different kinds of activated carbon: grains, powder and fibers (cloth or felt). The adsorption is carried out in a batch reactor. Classic models are applied and kinetic constants are calculated. Results showed that the performance of fiber activated carbon (FAC) is significantly higher than that of granular activated carbon (GAC). Moreover, FAC's adsorption capacities of phenol are greater than GAC's. Therefore the application of FAC adsorbers may lead to smaller adsorption reactors. The breakthrough curves obtained with FAC adsorbers are particularly steep, suggesting a smaller mass transfer resistance than GAC. The adsorption zone in the FAC bed is about 3.4 mm and is not dependent on the flow rate within the range 0.67 - 2.07 m.h−1. The selectivity of the FAC between different size of soluble molecules is shown. Then, an Ultrafiltration (UF) membrane is coupled with FAC to remove successively macromolecules (humic substances) and phenols present together in an aqueous solution. This new and original approach to a water treatment compact process successfully put to use. Industrial developments are put forward.

Simulation of oxygen concentration profile in calcium alginate gel beads entrapping microbes during biological phenol degradation

Numerical simulation was carried out to elucidate the effects of gel-bead diameter, initial cell density, initial phenol concentration, and oxygen concentration in the bulk liquid on the change in the oxygen concentration profile in a gel bead during biological aerobic phenol degradation with activated sludge entrapped in the calcium alginate gel bead. The results of simulation show that oxygen-limiting occurs in the central parts of the gel beads under most conditions examined in this study. After phenol degradation starts, the oxygen concentration in the beads is found to be immediately reduced and slightly increased instantly, and then slowly decreased linearly to a minimum value as the degradation proceeds. Finally, the oxygen concentration rapidly recovers to the same level of the bulk liquid. For small-sized gel beads, at low initial cell densities no oxygen-limiting is found to occur even in the core of the gel beads due to the small mass transfer resistance for oxygen diffusion, low oxygen consumption rate, or both. The critical gel-bead diameter for freedom from oxygen depletion is about 1 mm. At high phenol concentrations, oxygen may penetrate to the central parts of the gel beads as a result of reduction of the oxygen consumption rate by substrate inhibition. The effectiveness factors for small-sized cell-loaded gel beads were found to be unity at relatively high phenol concentrations in the bulk liquid and to decrease with increasing cell density. Further, it is found that at higher initial cell densities or for large-sized gel beads a high cell density layer will be formed around the surface of the gel beads during phenol degradation periods.

A study of flow boiling heat transfer with refrigerant mixtures

Mixture effects are studied on horizontal flow boiling heat transfer with both azeotropic and non-azeotropic refrigerant mixtures. More than 2000 local heat transfer coefficients are obtained with the azeotropie R 12/R 152a mixture and compared against the previously measured data with the non-azeotropic R22/R114 mixture. In a convective evaporation region, small mass transfer resistance is found for mixtures. The variation of physical properties due to mixing is responsible for almost all of the heat transfer degradation. In a partial boiling region, however, severe degradation of heat transfer with mixtures, similar to that in nucleate pool boiling heat transfer with mixtures, is found. A suppression of nucleate boiling at lower qualities due to loss of wall superheat with mixtures is responsible for this degradation. An analysis is developed to predict a transition quality by using Hsu's onset of nucleate boiling theory. The prediction agreed well with observed transition qualities for both pure and mixed refrigerants. Correlations, based on the supposition of Chen and using only phase equilibrium data to consider mixture effects, are developed with mean deviations of 7.2 and 9.6% for pure and mixed refrigerants.