Flow-through Cell Research Articles

Advanced Evaluation of the Long-Term Stability of Oxygen Evolution Electrocatalysts.

Evaluation of the long-term stability of electrocatalysts is typically performed using galvanostatic polarization at a predefined current density. A stable or insignificant increase in the applied potential is usually interpreted as high long-term stability of the tested catalyst. However, effects such as (i) electrochemical degradation of a catalyst due to its oxidation, (ii) blocking of the catalyst surface by evolved gas bubbles, and (iii) detachment of the catalyst from the electrode surface may lead to a decrease of the catalyst's active surface area being exposed to the electrolyte. In order to separate these effects and to evaluate the true electrochemical degradation of electrocatalysts, an advanced evaluation protocol based on subsequently performed electrochemical impedance, double layer capacitance, cyclic voltammetry, and galvanostatic polarization measurements was developed and used to evaluate the degradation of IrO2 particles drop-coated on glassy carbon rotating disk electrode using Nafion as a binder. A flow-through electrochemical cell was developed enabling circulation of the electrolyte leading to an efficient removal of evolved oxygen bubbles even at high current densities of up to 250 mA/cm(2). The degradation rate of IrO2 was evaluated over 225 test cycles (0.733 ± 0.022 mV/h) with a total duration of galvanostatic polarization measurements of over 55 h.

Selection of the Optimal Cathode Material to Synthesize Medical Sodium Hypochlorite Solutions in a Membraneless Electrolyzer

The peculiarities of the cathode reduction of ClO– and ClO–3 ions in a membraneless electrolyzer for the synthesis of sodium hypochlorite solutions to be used in human and veterinary medicine are studied. It is shown that, under the galvanostatic conditions of the electrolysis, the rate of hypochlorite ion reduction depends on the cathode current density, and it is hardly influenced by the cathode material. It is possible to decrease greatly the loss of ClO– on the cathode, especially at high volume current densities, using electrolysis at a cathode current density over 40 mА/сm2. It is demonstrated that, for a flow-through coaxial cell, the most suitable material for the cathode is VT1-0 titanium with polished surface.

Understanding the impact of flow rate and recycle on the conversion of a complex biorefinery stream using a flow-through microbial electrolysis cell

The effect of flow rate and recycle on the conversion of a biomass-derived pyrolysis aqueous phase in a microbial electrolysis cell (MEC) were investigated to demonstrate production of renewable hydrogen in biorefinery. A continuous MEC operation was investigated under one-pass and recycle conditions using the complex, biomass-derived, fermentable, mixed substrate feed at a constant concentration of 0.026g/L, while testing flow rates ranging from 0.19 to 3.6mL/min. This corresponds to an organic loading rate (OLR) of 0.54–10g/L-day. Mass transfer issues observed at low flow rates were alleviated using high flow rates. Increasing the flow rate to 3.6mL/min (3.7min HRT) during one-pass operation increased the hydrogen productivity 3-fold, but anode conversion efficiency (ACE) decreased from 57.9% to 9.9%. Recycle of the anode liquid helped to alleviate kinetic limitations and the ACE increased by 1.8-fold and the hydrogen productivity by 1.2-fold compared to the one-pass condition at the flow rate of 3.6mL/min (10g/L-d OLR). High COD removal was also achieved under recycle conditions, reaching 74.2±1.1%, with hydrogen production rate of 2.92±0.51L/L-day. This study demonstrates the advantages of combining faster flow rates with a recycle process to improve rate of hydrogen production from a switchgrass-derived stream in the biorefinery.

A high-performance flow-field structured iron-chromium redox flow battery

Unlike conventional iron-chromium redox flow batteries (ICRFBs) with a flow-through cell structure, in this work a high-performance ICRFB featuring a flow-field cell structure is developed. It is found that the present flow-field structured ICRFB reaches an energy efficiency of 76.3% with a current density of 120 mA cm−2 at 25 °C. The energy efficiency can be as high as 79.6% with an elevated current density of 200 mA cm−2 at 65 °C, a record performance of the ICRFB in the existing literature. In addition, it is demonstrated that the energy efficiency of the battery is stable during the cycle test, and that the capacity decay rate of the battery is 0.6% per cycle. More excitingly, the high performance of the flow-field structured battery significantly lowers the capital cost at $137.6 kWh−1, which is 28.2% lower than that of the conventional ICRFB for 8-h energy storage.

Exploiting the Phenomenon of Liquid-Liquid Phase Separation for Enhanced and Sustained Membrane Transport of a Poorly Water-Soluble Drug.

Recent studies on aqueous supersaturated lipophilic drug solutions prepared by methods including antisolvent addition, pH swing, or dissolution of amorphous solid dispersions (ASDs) have demonstrated that when crystallization is slow, these systems undergo liquid-liquid phase separation (LLPS) when the concentration of the drug in the medium exceeds its amorphous solubility. Following LLPS, a metastable equilibrium is formed where the concentration of drug in the continuous phase corresponds to the amorphous solubility while the dispersed phase is composed of a nanosized drug-rich phase. It has been reasoned that the drug-rich phase may act as a reservoir, enabling the rate of passive transport of the drug across a membrane to be maintained at the maximum value for an extended period of time. Herein, using clotrimazole as a model drug, and a flow-through diffusion cell, the reservoir effect is demonstrated. Supersaturated clotrimazole solutions at concentrations below the amorphous solubility show a linear relationship between the maximum flux and the initial concentration. Once the concentration exceeds the amorphous solubility, the maximum flux achieved reaches a plateau. However, the duration for which the high flux persists was found to be highly dependent on the number of drug-rich nanodroplets present in the donor compartment. Macroscopic amorphous particles of clotrimazole did not lead to the same reservoir effect observed with the nanodroplets formed through the process of LLPS. A first-principles mathematical model was developed which was able to fit the experimental receiver concentration-time profiles for concentration regimes both below and above amorphous solubility, providing support for the contention that the nanodroplet phase does not directly diffuse across the membrane but, instead, rapidly replenishes the drug in the aqueous phase that has been removed by transport across the membrane. This study provides important insight into the properties of supersaturated solutions and how these might in turn impact oral absorption through effects on passive membrane transport rates.

Selection of electrohydraulic grinding parameters for quartz ore

Under analysis is electrohydraulic grinding of rocks under electric charge using nanosecond high-stress pulses to optimize ore pretreatment. A nanosecond high-voltage generator of pulses at a capacity to 500 MW is designed and tested. A flow-through discharge cell at a voltage to 550 kW is developed. The new method of mineral grinding is highly efficient and enables designing commercial plants for electrohydraulic rock processing.

A new X-ray-transparent flow-through reaction cell for a <i>μ</i>-CT-based concomitant surveillance of the reaction progress of hydrothermal mineral–fluid interactions

Abstract. A new flow-through reaction cell consisting of an X-ray-transparent semicrystalline thermoplastic has been developed for percolation experiments. Core holder, tubing and all confining parts are constructed using PEEK (polyetheretherketone) to allow concomitant surveillance of the reaction progress by X-ray microtomography (μ-CT). With this cell setup, corrosive or oversaturated fluids can be forced through rock cores (up to ∅ 19 mm) or powders at pressures up to 100 bar and temperatures up to 200 °C. The reaction progress of the experiment can be monitored without dismantling the sample from the core holder. The combination of this flow-through reaction cell setup with a laboratory X-ray μ-CT system facilitates on-demand monitoring of the reaction progress of (long-term) hydrothermal experiments in the own laboratory, keeping interruption times as short as possible. To demonstrate both the suitability of the cell construction material for X-ray imaging purposes and the experimental performance of the flow-through system, we report the virtually non-existent bias of the PEEK cell setup with distinctive X-ray observations (e.g., differing states of pore fillings: air vs. fluid; detection of delicate fabric elements: filigree zeolite crystals overgrowing weathered muscovite), and the monitoring of the gypsum/anhydrite transition as a case study of a 4-D fabric evolution.

ATR-FTIR spectrokinetic analysis of the CO adsorption and oxidation at water/platinum interface

Attenuated total reflection infrared (ATR-IR) spectroscopy is a powerful tool to investigate reaction pathways in liquid(reactive)/solid(catalyst) systems. Catalysts are commonly deposited on an internal reflection elements (IRE) as layers of powders or as films (e.g. metal film), and they are exposed to the liquid phase reactants. To obtain quantitative information of intrinsic reaction rates, the chemical engineering aspects of an ATR flow-through cell must be evaluated. Particularly, mass transport in the ATR cell has to be characterized. We present here an analysis of the mass transfer from the flowing solution to the surface of the ATR crystal, where the catalyst is deposited. Criteria to determine kinetic parameters under chemical control were developed on the base of non-dimensional Péclet (Pe) and Sherwood (Sh) numbers, and Thiele modulus (φcl). A Pt thin film deposited on a ZnSe IRE by vapor deposition and a layer of Pt/Al2O3 porous catalyst were used to study the adsorption of carbon monoxide and oxidation of preadsorbed carbon monoxide on aqueous phase. Experimental data of the evolution of the linearly adsorbed CO (2048cm−1) were fitted using a microkinetic model to obtain reaction constants. Results reported here serve as a practical guide to quickly determine the operational limits of an ATR cell with a porous layer of catalyst deposited onto the IRE.

Degradation of Carbon Nanomaterials Using Electrochemical Oxidation on BDD Electrodes

Toxic potential of carbon nanomaterials (CN) to environmental species and humans is well documented. As carbon nanomaterials are produced in kiloton quantities worldwide, so is the risk of environmental contamination through industrial discharge and use (1). Eventually such discharge may diffuse through aquifers and residential drinking water. Significant challenges exist in decontaminating the effluent water, containing carbon nanomaterials. Carbon nanomaterials can be destroyed or degraded by incineration, however it requires the ability to locate, collect and concentrate carbon nanomaterial sample from the environment, which is often quite complicated. We have investigated the way to rapidly and significantly decrease the CN concentration in aqueous suspensions, thus reducing its toxic potential. Carbon nanomaterial degradation is based on generating strong oxidizing agents on a boron doped diamond anode, combined with a vigorous solution turbulence due to gas evolution inside a thin layer flow-through cell at high current densities. These agents react with carbon nanomaterials, damage them through multiple oxidations, destroy their structural integrity and rapidly reduce their concentration in aqueous solvents. In addition, the inert cathode surface facilitates hydrogen peroxide production due to the dissolved oxygen reduction reaction. As a result of strong oxidative reactions between nanomaterials and oxidative radicals, the outflowing water has a significantly lower concentration of suspended nanomaterials and, consequently is less toxic to the environment. The method was tested with pristine single and multiwall carbon nanotube, graphene and fullerene aqueous suspensions. UV-VIS-NIR absorbance show that CN concentration is reduced below 1% in a single pass through the single compartment electrochemical cell, thus offering a much faster way to degrade environmental toxicants compared to enzymatic or Fenton reaction approaches (2). Raman spectroscopy and analysis of the reaction products shows that oxidative attack on CN sp 2 –based structure by electrochemically generated reactive oxygen species leads to nanoparticle integrity loss and subsequent oxidation to CO2 . References Petersen, E. J. et al., Environ. Sci. Technol. 2011, 45, 9837-9856.Allen, B. L. et al., J. Am. Chem. Soc. 2009, 131, 17194-17205.

Determination of mineral dissolution regimes using flow-through time-resolved analysis (FT-TRA) and numerical simulation

Flow-through time resolved analysis (FT-TRA) involves subjecting small mineral samples (<10mg) inserted in a miniature flow-through cell (50μL) to controlled flows of eluent analyzed on-line by ICP-MS. In this study, FT-TRA is used to empirically determine the dissolution regimes for the two well-studied minerals forsterite and calcite, representing minerals with relatively slow and fast dissolution kinetics. A proportional increase in steady-state effluent [Mg, Si] concentrations with increasing flow-through cell eluent residence times confirms a dominantly surface-controlled dissolution regime for a powdered forsterite sample at pH2.3, implying that transport limitations are negligible. In contrast, the relationship between flow rates and dissolution rates for single grain calcite samples at pH2.3–4 reveals that transport limitations affect the rate of calcite dissolution. To provide a quantitative and process-based assessment of the effect of diffusive transport limitations, simulations of the calcite experiments were performed with a high resolution, pore-scale model that considers the geometry of the calcite grain and the FT-TRA flow-through reactor. The pore-scale model reproduces the observed effluent [Ca] concentrations for all experimental conditions using a single set of surface kinetic parameters, by accounting for the formation of a diffusive boundary layer (DBL) that varies in thickness as a function of flow rates. These results demonstrate that combining FT-TRA with pore-scale modeling makes it possible to obtain unprecedented insights not achievable by either method separately, including quantification of DBL thicknesses and the determination of transport controls as a function of pH, flow velocity and residence times.

Determination of Pb(II) by sequential injection/stripping analysis at all-plastic electrochemical fluidic cells with integrated composite electrodes

This work reports the development of a sequential injection/stripping analysis method for the determination of trace Pb(II) at injection-moulded electrochemical fluidic cells. Conducting carbon fibre–loaded polystyrene electrodes were integrated within the plastic cells. The flow-through cells were incorporated into a home-made sequential injection analysis (SIA) manifold. Different experimental parameters for the detection of Pb(II) were investigated including the type and concentration of the supporting electrolyte, the conditions of the stripping step, the volume of the sample, the flow rate and the accumulation potential. The LOD for Pb(II) was 0.5μgL−1, the within-cell % relative standard deviation (n=8) was 3.1% and the between-cell % relative standard deviation (n=5) was 8.9% for 25μgL−1 Pb(II). The cells were applied to the determination of Pb(II) in tapwater and a phosphate fertilizer sample.

Merits of online electrochemistry liquid sample desorption electrospray ionization mass spectrometry (EC/LS DESI MS).

A new online electrochemistry/liquid sample desorption electrospray ionization mass spectrometry (EC/LS DESI MS) system with a simple electrochemical thin-layer flow-through cell was developed and tested using N,N-dimethyl-p-phenylenediamine (DMPA) as a model probe. Although oxidation of DMPA is observed as a result of ionization of LS in positive ion mode LS DESI, application of voltage to the online electrochemical (EC) cell in EC/LS DESI MS increases yields of oxidation products. An advantage of LS DESI MS is its sensitivity in aqueous electrolyte solutions, which improves efficiency of electrochemical reactions in EC/LS DESI MS. In highly conductive low pH aqueous buffer solutions, oxidation efficiency is close to 100%. EC/ESI MS typically requires mixed aqueous/organic solvents and low electrolyte concentrations for efficient ionization in MS, limiting efficiency of electrochemistry online with MS. Independently, the results verify higher electrochemical oxidation efficiency during positive mode ESI than during LS DESI.

Effects of Pump Pulsation on Hydrodynamic Properties and Dissolution Profiles in Flow-Through Dissolution Systems (USP 4).

To clarify the effects of pump pulsation and flow-through cell (FTC) dissolution system settings on the hydrodynamic properties and dissolution profiles of model formulations. Two FTC systems with different cell temperature control mechanisms were used. Particle image velocimetry (PIV) was used to analyze the hydrodynamic properties of test solutions in the flow-through dissolution test cell. Two pulsation pumps (semi-sine, full-sine) and a non-pulsatile pump were used to study the effects of varied flows on the dissolution profiles of United States Pharmacopeia standard tablets. PIV analysis showed periodic changes in the aligned upward fluid flow throughout the dissolution cell that was designed to reduce the temperature gradient during pump pulsation (0.5s/pulse). The maximum instantaneous flow from the semi-sine pump was higher than that of the full-sine pump under all conditions. The flow from the semi-sine wave pump showed faster dissolution of salicylic acid and prednisone tablets than those from other pumps. The semi-sine wave pump flow showed similar dissolution profiles in the two FTC systems. Variations in instantaneous fluid flow caused by pump pulsation that meets the requirements of pharmacopoeias are a factor that affects the dissolution profiles of tablets in FTC systems.

An approach to discriminatively determine thoron and radon emanation rates for a granular material with a scintillation cell

A powder sandwich technique was applied to determine thoron (220Rn) and radon (222Rn) emanation rates for a granular material. The feature of this technique is the sample preparation, in which a granular material is put and fixed between two membrane filters. Airflow is directly given to this sandwich sample, will include thoron and radon emanated from the material, and then is transferred to the detector. This method makes sure that thoron and radon emanated are not retained in pore space within the sample volume, which is crucial for the appropriate emanation test. This technique was first introduced by Kanse et al. (2013) with the intention to measure the emanation of thoron - but not of radon - from materials having much higher 224Ra activity than 226Ra. In the present study, the methodology for the discriminative determination of thoron and radon emanation rates from a granular material has been examined using a flow-through scintillation cell and sandwich sample. The mathematical model was developed to differentiate total alpha counts into thoron- and radon-associated counts. With a sample of uranium ore, this model was experimentally validated by comparison between the scintillation cell and a reference detector that can discriminatively measure thoron and radon concentrations. Furthermore, the detection limits and uncertainties were evaluated to discuss the characteristics of this method. Key parameters for improving the determination of thoron and radon emanations were found to be the background radon concentration and the leakage of radon from the measurement system, respectively. It was concluded that the present method is advantageous to a sample that has much higher 226Ra activity than 224Ra.

Simultaneous Analysis of Monovalent Anions and Cations with a Sub-Microliter Dead-Volume Flow-Through Potentiometric Detector for Ion Chromatography.

A microliter dead-volume flow-through cell as a potentiometric detector is described in this article for sensitive, selective and simultaneous detection of common monovalent anions and cations in single column ion chromatography for the first time. The detection cell consisted of less selective anion- and cation-selective composite membrane electrodes together with a solid-state composite matrix reference electrode. The simultaneous separation and sensitive detection of sodium (Na(+)), potassium (K(+)), ammonium (NH4 (+)), chloride (Cl(-)) and nitrate (NO3 (-)) in a single run was achieved by using 98% 1.5 mM MgSO4 and 2% acetonitrile eluent with a mixed-bed ion-exchange separation column without suppressor column system. The separation and simultaneous detection of the anions and cations were completed in 6 min at the eluent flow-rate of 0.8 mL/min. Detection limits, at S/N = 3, were ranged from 0.2 to 1.0 µM for the anions and 0.3 to 3.0 µM for the cations, respectively. The developed method was successfully applied to the simultaneous determination of monovalent anions and cations in several environmental and biological samples.

Dissolution and Persistence of Copper-Based Nanomaterials in Undersaturated Solutions with Respect to Cupric Solid Phases.

Dissolution of copper-based nanoparticles (NPs) can control their environmental persistence and toxicity. Previous research has generally reported limited dissolution of Cu-based NPs at circumneutral pH, but the environmentally important case of dissolution in solutions that are undersaturated with respect to copper mineral phases has not been investigated thoroughly. In this study, immobilized Cu-based NPs were fabricated on solid supports. Metallic copper (Cu), cupric oxide/hydroxide (Cuox), and copper sulfide (CuxS) NPs were investigated. Dissolution rate constants were measured in situ by an atomic force microscope equipped with a flow-through cell. A mass-balance model indicated that the flowing solution was consistently undersaturated with respect to cupric solid phases. Based on the measured rate constants, Cuox NPs are expected to dissolve completely in these undersaturated conditions within a matter of hours, even at neutral to basic pH. The expected persistence of metallic Cu NPs ranges from a few hours to days, whereas CuxS NPs showed no significant dissolution over the time scales studied. Field deployment of Cu-based NP samples in a freshwater stream confirmed these conclusions for a natural aquatic system. These results suggest that Cu and Cuox NPs will be short-lived in the environment unless dissolution is hindered by a competing process, such as sulfidation.

In vitro human skin penetration model for organophosphorus compounds with different physicochemical properties

A flow-through diffusion cell was validated for in vitro human epidermal penetration studies of organophosphorus compounds (OPCs) applied by infinite dosing. By testing OPCs with similar molecular weight but different physicochemical properties, it was shown that hydrophilic and lipophilic properties are major determinants for the penetration rate. Lipophilic OPCs displayed maximum cumulative penetration in the 20–75% agent concentration range whereas the hydrophilic OPCs displayed maximum cumulative penetration at 10 or 20% agent concentration. Low penetration was observed for all agents at 1% agent concentration or when applied as neat agents. The impact of the receptor solution composition was evaluated by comparing the penetration using receptor solutions of different ratios of ethanol and water. For diluted OPCs, a high concentration of ethanol in the receptor solution significantly increased the penetration compared to lower concentrations. When OPCs were applied as neat agents, the composition of the receptor solution only affected the penetration for one of four tested compounds. In conclusion, the flow-through diffusion cell was useful for examining the penetration of OPCs through the epidermal membrane. It was also demonstrated that the penetration rates of OPCs are strongly influenced by dilution in water and the receptor fluid composition.

A Flow-Through Cell Electroporation Device for Rapidly and Efficiently Transfecting Massive Amounts of Cells in vitro and ex vivo.

Continuous cell electroporation is an appealing non-viral approach for genetically transfecting a large number of cells. Yet the traditional macro-scale devices suffer from the unsatisfactory transfection efficiency and/or cell viability due to their high voltage, while the emerging microfluidic electroporation devices is still limited by their low cell processing speed. Here we present a flow-through cell electroporation device integrating large-sized flow tube and small-spaced distributed needle electrode array. Relatively large flow tube enables high flow rate, simple flow characterization and low shear force, while well-organized needle array electrodes produce an even-distributed electric field with low voltage. Thus the difficulties for seeking the fine balance between high flow rate and low electroporation voltage were steered clear. Efficient in vitro electrotransfection of plasmid DNA was demonstrated in several hard-to-transfect cell lines. Furthermore, we also explored ex vivo electroporated mouse erythrocyte as the carrier of RNA. The strong ability of RNA loading and short exposure time of freshly isolated cells jointly ensured a high yield of valid carrier erythrocytes, which further successfully delivered RNA into targeted tissue. Both in vitro and ex vivo electrotransfection could be accomplished at high cell processing speed (20 million cells per minute) which remarkably outperforms previous devices.

Development and Validation of a Discriminating Dissolution Method for Atorvastatin Delayed-Release Nanoparticles Using a Flow-Through Cell: A Comparative Study Using USP Apparatus 4 and 1

Atorvastatin, an HMG CoA reductase inhibitor, is widely used for the treatment of dyslipidemia and prevention of cardiovascular disease. It belongs to Class 2 of the Biopharmaceutics Classification System owing to its low solubility and high permeability. In vitro dissolution testing is an essential tool for the design of a dosage form. Appropriate selection of dissolution test conditions is essential since it will help establish an appropriate in vitro-in vivo correlation (IVIVC), which is imperative for a waiver of costly bioequivalence studies. Compounds belonging to BCS Class 2 are suitable for establishing a significant IVIVC. USP Apparatus 4 (flow-through cell) is an attractive alternative to conventional dissolution methods like Apparatus 1 and 2. The ability of the apparatus to maintain sink conditions over a longer period of time has proved useful in the development of dissolution methods for poorly soluble drugs, making the development of IVIVCs easier for such drugs. Nanoparticles of atorvastatin were formulated by an emulsion-solvent evaporation method to overcome its bioavailability problems. Development of a discriminatory dissolution method for the same was attempted using a flow-through cell (Apparatus 4) because dissolution performed using Apparatus 1 did not provide complete release of the drug within 60 min. Phosphate buffer pH 6.8 with 1.5% SLS was selected as the dissolution medium based on the results of the solubility studies. Various parameters such as flow rate and sample-loading method were optimized. The dissolution method was validated with respect to various parameters as per ICH guidelines.

Nano-Crystalline Cellulose as a Novel Tablet Excipient for Improving Solubility and Dissolution of Meloxicam

Article history: Received on: 13/10/2015 Revised on: 15/11/2015 Accepted on: 02/12/2015 Available online: 27/02/2016 This study explored the effect of nano-crystalline cellulose (NCC) on Meloxicam (MX) solid dispersion (SD) prepared by co-grinding technique compared to micro-crystalline cellulose (MCC) in presence of lactose. MXtablets were prepared by direct compression of different co-ground SDs or physical mixtures. The solubility, dissolution, SEM and DSC of different preparations were studied. Flow-through cell apparatus (FTC) was used to study the dissolution of MX from tablets at pH 7.4. Generally, the results revealed that increasing NCC loadings showed a direct increase in both the solubility and dissolution of MX. MCC did not improve either the solubility or the dissolution of MX in the physical mixture, while, co-grinding dramatically decreased the dissolution rate of MX. It was interesting to find that grinding of MX-powder alone or in a mixture with lactose highly increased MX solubility and dissolution. SEM as well as DSC were found to be very good tools, without a single exception, to describe the observed solubility and dissolution of MX in these proposed preparations. SEM-images showed the particle size reduction upon grinding or co-grinding techniques. While DSC-data proved that the crystalline structure of MX has been changed to an amorphous state.