Display omitted
•Manual and automated magnet switching methods were coupled to R-MHD microfluidics.•Current between PEDOT-modified electrodes was reversed when oppositely-polarized magnets were ...swapped.•Numerical approximations mapped magnetic flux densities over a magnet switching assembly.•Fluid velocities across a pair of oppositely-polarized magnets were evaluated.•Unlimited, unidirectional R-MHD microfluidics pumping was demonstrated.
A transformative advance in redox-magnetohydrodynamics (R-MHD) microfluidics is demonstrated that indefinitely extends its pumping duration with a miniaturizable approach, while preserving its uniqueness as an internal, self-contained, on-device, active and versatile pump that can also propel fluid in a loop. R-MHD can address the need for fine-tuning microfluidics in micro total analysis systems (μTAS) for multiple functions in an automated fashion that conventional external pumps with channels and/or valves that determine direction cannot fulfill. In MHD, a body force produced by the cross product of ionic current between strategically-activated electrodes and magnetic flux from a permanent magnet or electromagnet drives the fluid. Conducting-polymer-modified electrodes (e.g. with poly(3,4-ethylenedioxythiophene), PEDOT), involve faradaic processes to convert electronic current in the external circuit to ionic current in solution, overcoming bubble generation and electrode corrosion that limited previous MHD microfluidic applications. PEDOT-R-MHD pumping operates with a wider variety of solution compositions and without redox additives. However, pumping stops after complete oxidation/reduction of redox sites in the PEDOT films. The new advance reverses current between PEDOT-modified electrodes to discharge/recharge the polymer while simultaneously swapping permanent magnets of opposite polarities to sustain a constant, unidirectional pumping speed interrupted with brief pauses and without inductive heating. Factors affecting fluid velocities are described, including positions across the magnet assembly, current magnitudes and synchrony with current reversal. A model system (microbeads in biologically-compatible phosphate-buffered saline) is used, which can be generalized more broadly to biological and environmental applications, where starting, stopping, and indefinitely sustaining pumping of a sample are important.
The enhancement of CO
2
reduction in atmospheric-pressure, non-thermal plasma has been shown using a variety of catalyst systems with ranging composition, particle sizes, and morphologies. ...Improvements in CO
2
conversion can be attained by choice of catalyst material. However, inhomogeneity in the material distribution arising from the synthesis affects the catalytically active surface area and dielectric environment that modulates the plasma properties near the catalyst. Atomic layer deposition (ALD) can be used to control the composition of ultra-thin layers on support materials. We used ALD to synthesize metal oxide catalyst coatings on high surface area supports. We found that TiO
2
achieved significantly higher yields of CO
2
conversion (to CO and O
2
) at low reactor power compared to ZnO or Al
2
O
3
, materials commonly used as a support for other catalysts. We also observed an unexpected increase in the catalytic activity on ZnO with increasing power. The results here suggest that ALD can unambiguously isolate the catalytic effects of materials in plasma reactors.
Catalysts prepared by atomic layer deposition allow for comparisons between structurally-identical metal oxide catalysts for CO
2
reduction in non-thermal plasmas.
The enhancement of CO
2
reduction in atmospheric-pressure, non-thermal plasma has been shown using a variety of catalyst systems with ranging composition, particle sizes, and morphologies. ...Improvements in CO
2
conversion can be attained by choice of catalyst material. However, inhomogeneity in the material distribution arising from the synthesis affects the catalytically active surface area and dielectric environment that modulates the plasma properties near the catalyst. Atomic layer deposition (ALD) can be used to control the composition of ultra-thin layers on support materials. We used ALD to synthesize metal oxide catalyst coatings on high surface area supports. We found that TiO
2
achieved significantly higher yields of CO
2
conversion (to CO and O
2
) at low reactor power compared to ZnO or Al
2
O
3
, materials commonly used as a support for other catalysts. We also observed an unexpected increase in the catalytic activity on ZnO with increasing power. The results here suggest that ALD can unambiguously isolate the catalytic effects of materials in plasma reactors.
Based on chemical fingerprinting and other lines of scientific evidence, a former pesticide manufacturing plant in Newark, New Jersey (U.S.A.) has been implicated in numerous journal articles as the ...major source of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the sediments of the Lower Passaic River (LPR). Although the site has been extensively studied for over three decades, no previous study has identified a pathway capable of discharging an amount of 2,3,7,8-TCDD comparable to the mass estimates made for 2,3,7,8-TCDD in the sediments of the LPR and Newark Bay, or examined the timing of specific manufacturing processes at the site in relation to 2,3,7,8-TCDD concentrations in dated sediment cores. A reconstruction of the historical operations at this site was performed, supporting it as the major source of 2,3,7,8-TCDD to the LPR. A 2,4,5-trichlorophenol purification process, utilized prior to September 1954, was specifically identified as a significant source of 2,3,7,8-TCDD to the LPR. This purification process generated a dioxin-rich sludge that was discharged to the river prior to September 1954. Annual 2,4,5-trichlorophenol production, coupled with modeling to predict concentrations of 2,3,7,8-TCDD, indicate that 2,3,7,8-TCDD discharges to the LPR from this one process (20–80 kg) are consistent with mass estimates of 2,3,7,8-TCDD in the river (30–50 kg). 2,3,7,8-TCDD and cesium-137 data from nearby sediment cores support this purification process as a major pathway by which 2,3,7,8-TCDD entered the river.
Display omitted
•2,4,5-TCP operations at a former pesticide plant in Newark, NJ, were reviewed.•Waste sludge containing 2,3,7,8-TCDD was discharged to Lower Passaic River (LPR).•Estimated 2,3,7,8-TCDD mass discharge is similar to mass of 2,3,7,8-TCDD in the LPR.•2,3,7,8-TCDD and Cs-137 sediment data support a major discharge pathway to the LPR.•The findings supported this plant as the major source of 2,3,7,8-TCDD to the LPR.
Continuous microfluidic pumping is an important requirement for numerous applications, such as lab-on-a-chip separation and imaging cytometry. To satisfy this necessity we have developed a strategy ...to indefinitely push fluid in a single direction by Redox-Magnetohydrodynamics (R-MHD). R-MHD is a phenomenon where fluid flows between electrodes by a net body force (
F
B
), followed by the equation
F
B
= j
×
B
, where
j
and
B
are the ionic current and magnetic flux densities, respectively
.
1,2
Ionic current density (
j
) converts from electronic current through the redox reaction of chemical species (K
3
Fe(CN)
6
/ K
4
Fe(CN)
6
) or electrode confined conducting polymer (CP) whereas magnetic field (
B
) comes from a permanent or electromagnet. CP, such as Poly(3,4-ethylenedioxythiophene) or PEDOT can be electropolymerized on the electrode surface with good spatial resolution, adherence, uniformity, and controlled thickness.
3
These characteristics along with high electronic conductivity and capacitance have made them perfect candidates as redox center in R-MHD pumping. CP generates high ionic current density
(
j
)
in the electrolyte solution and avoids the interference issue of solution redox species.
4-6
R-MHD pumping has unique advantages; such as flat flow profile, valve and channel less device, tunability, portability, circular flow capability, and low voltage requirement.
6
Therefore, it is of interest in different microfluidic applications including chemical analysis, mixing, synthesis, detection, imaging cytometry and separation. To satisfy these growing needs, achieving longer pumping with a high speed is a primary requirement. Deposition parameters such as types of monomers, the number of redox centers or polymer loading, choice of deposition method, and electrolytic strength of the pumping solution affect both the current and charge density of polymer films that limits pumping speed and duration. PEDOT deposited by the potentiostatic technique, propylene carbonate solvent, and TBAPF
6
electrolyte exhibited the best combination for maximum electrochemical response and mechanical stability. The improved polymer showed 80% retention of its capacity even after 500 pumping cycles.
7,8
Though the optimized PEDOT film could pump for 211.70 ± 8.0 sec with a moderate 49.40 ± 6.0 µm/s fluid speed through a cross section of 760 µm × 3 mm pumping region, the fluid can only flow in one direction until the charge in the PEDOT film is consumed (discharging). Polymer film recharges by applying a reverse current but owing to have the same magnetic field orientation underneath the electrodes, the fluid flows in the reverse direction. This periodic reversed flow was useful in image cytometry application of leukocytes in post cancer monitoring.
5,9
Some microfluidic applications such as on-chip separation require even longer pumping, at a high speed, and in a single direction. To address this limitation, we built a raspberry pi-controlled translational device that synchronizes magnetic field with opposite bias current. The continuous change in current bias recharges the polymer film after the initial discharge but the simultaneous position switching of two permanent magnets with opposite field directions maintains a unidirectional MHD force. This programmable R-MHD offers several advantages over AC-MHD approach, such as higher magnetic field, simplified instrumentation, and less fluidic disruption.
10
Results will be reported on a newly developed smaller device where galvanostat can trigger a translational stage with opposing orientation of magnets through a single board computer so that, magnets can be switched automatically when a target voltage is reached or within a wait time (open circuit potential).
References
(1) Grant, K. M.; Hemmert, J. W.; White, H. S.
Journal of the American Chemical Society
2002
,
124
, 462-467.
(2) Leventis, N.; Gao, X.
Analytical Chemistry
2001
,
73
, 3981-3992.
(3) Poverenov, E.; Li, M.; Bitler, A.; Bendikov, M.
Chemistry of Materials
2010
,
22
, 4019-4025.
(4) Nash, C. K.; Fritsch, I.
Analytical Chemistry
2016
,
88
, 1601-1609.
(5) Khan, F. Z.; Hutcheson, J. A.; Hunter, C. J.; Powless, A. J.; Benson, D.; Fritsch, I.; Muldoon, T. J.
Analytical Chemistry
2018
,
90
, 7862-7870.
(6) Sahore, V.; Fritsch, I.
Analytical Chemistry
2013
,
85
, 11809-11816.
(7) Khan, F. Z.; Fritsch, I.
Meeting Abstracts
2016
,
MA2016-01
, 2064-2064.
(8) Khan, F. Z.; Fritsch, I.
Meeting Abstracts
2017
,
MA2017-01
, 2017-2017.
(9) Hutcheson, J. A.; Khan, F. Z.; Powless, A. J.; Benson, D.; Hunter, C.; Fritsch, I.; Muldoon, T. J. In
High-Speed Biomedical Imaging and Spectroscopy: Toward Big Data Instrumentation and Management
; International Society for Optics and Photonics, 2016, p 97200U.
(10) Nash, C. K.
The Electrochemical Society Interface
2014
,
23
, 79-80.
