Nanoscale Bubble Valves on MWCNT Membranes for Chemical Energy Storage

Electrophoretic transport of proteins across electrochemically oxidized multi-walled carbon nanotube (MWCNT) membranes has been investigated. A small charged protein, lysozyme, was successfully pumped across MWCNT membranes by an electric field while rejecting larger bovine serum albumin (BSA). Transport of lysozome was reduced by a factor of about 30 in comparison to bulk mobility and consistent with the prediction for hindered transport. Mobilities between 0.33 and 1.4 × 10(-9) m(2) V(-1) s(-1) were observed and are approximately 10-fold faster than comparable ordered nanoporous membranes and consistent with continuum models. For mixtures of BSA and lysozyme, complete rejection of BSA is seen with electrophoretic separations.

Effects of modification groups and defects on the desalination performance of multi-walled carbon nanotube (MWNT) membranes

Separation of hydrogen isotopic water by multi-walled carbon nanotube (MWCNT) membrane and graphene oxide (GO)-MWCNT composite membranes

An electric field was applied across a deionized water droplet placed on a multi-walled carbon nanotube (MWCNT) membrane. Droplets of different size were tested by varying the voltage applied from 3 to 25 V during the electrowetting process. After electrowetting, it was observed that the topography of the membrane deformed from vertical alignment to a grouped pattern due to bubbles appearing during the electrowetting process, indicating the occurrence of electrolysis. For the droplet size ranging from 2 to 3.5 μl, the contact angle (CA) for smaller droplets reduced more dramatically than for larger droplets at the same voltage, and the contact angle saturation condition also varied in response to the droplet size. To reveal the droplet size effect, the Young-Lippmann equation is modified to simulate CA reduction on a MWCNT membrane.

Carbon Nanotubes Applications on Electron Devices 406 of the active membrane pore density.In contrast, there are few, if any, reports of "bamboo" structure formation or catalyst migration in SWNTs or double-walled carbon nanotubes (DWNTs).However, it has been difficult to produce vertically aligned carbon nanotubes of this size uniformly and at large scale (Kalra 2003;Hata, Futaba et al. 2004).The major challenges also lie in finding a conformal deposition process to fill the gaps in this nanotube array, as well as in designing a selective etching process to open up the nanotube channels without producing voids in the membrane.These challenges in nanomanufacturing are one of the major reasons for the imbalance between the number of reports from computational and experimental studies, offering great research opportunities in the area of experimental Carbon Nanotube Nanofluidics.This book chapter is intended to provide an intermediate level overview of Carbon Nanotube Nanofluidics to the beginners and scientists who are interested in this emerging research field.For that purpose, we write discussions of Carbon Nanotube Nanofluidics with respect to transporting entities.In section 2, we discuss water transport under the CNT nanoconfinement in view of the unique transport phenomena including spontaneous water filling, fast water transport and mechanisms behind it.In section 3, we discuss the various aspects of gas transport in CNT.We present fundamental findings of Carbon Nanotube Nanofluidics for the gas transport, followed by a perspective of gas separation using CNT membranes.In section 4, we introduce recent achievements made by theoretical and experimental studies focusing on the behavior of ions in CNT including transport of ions under the CNT nanoconfinement, and ion exclusion and selectivity in association with CNT membrane technology.Finally, we will conclude several aspects of Carbon Nanotube Nanofluidics in section 5.

Multiwalled carbon nanotube membranes for water purification

Application and characterization of electroactive membranes based on carbon nanotubes and zerovalent iron nanoparticles

We present a simple and versatile technique to fabricate and transfer multi-walled carbon nanotube (MWCNT) membranes to virtually any substrate, including devices and a large variety of materials with different shapes. First, a mesoporous silica (Mobil Composite material MCM-41)/MWCNT composite is deposited by spin coating on SiO2. Immersion of the wafer in HF solution, releases a floating MWCNT membrane that strongly adheres to any surface that makes contact with it. The process does not require functionalization or surfactants, thus avoiding contamination and additional cleaning steps, and has potential to be extended to allow the fabrication and transfer of membranes of other carbon materials, including other CNT types, fullerenes and graphene.

Calcium-enhanced retention of humic substances by carbon nanotube membranes: Mechanisms and implication

Self-supported supercapacitor membranes: Polypyrrole-coated carbon nanotube networks enabled by pulsed electrodeposition

The fouling behavior of carbon nanotube (CNT) membranes is investigated for large protein biomolecules and a wide variety of small molecules. The CNT membranes are largely fouling resistant, even to untreated river water, due to size exclusion and an inert graphitic core that supports fast fluid flow. However, it is found that bovine serum albumin (BSA) and naphthalene significantly foul membranes due to solution coagulation and π–π stacking, respectively. Small single‐walled (SW) CNTs (<1.5 nm i.d.) are difficult to foul with BSA when precipitation is prevented, showing that size exclusion at SWCNT tips can prevent fouling. Electrochemical oxidation, bubble generation and ionic pumping are shown to recover membrane performance. Electrochemical oxidation at greater than +1.4 V is seen to oxidize CNTs as well as biofoulants, but H2 bubble generation at –2 V lifts foulants without damage to the membrane allowing for repeated cycles. Ionic pumping using large cations is seen to remove small molecule foulants adsorbed to the CNT core. The relatively narrow class of foulants and three complementary methods of membrane defouling make the CNT membrane platform a potentially robust system for a wide variety of chemical separations and environmental water treatments.

Raman spectroscopy has been used to investigate ethane, propane, and SF6 interactions with an aligned multiwalled carbon nanotube (MWNT) membrane. Pressures of 7.5-9.3 atm and temperatures of 293-333 K were examined for propane and SF6, whereas slightly lower temperatures (263-293 K) and pressures (6.7-7.5 atm) were used for ethane. Red-shifting and broadening is seen for the C-C stretching vibrations of the two hydrocarbons, as well as for the A1g symmetric vibration (nu1) of SF6. These spectral features indicate that the interaction between the gas and the nanotube membrane is capable of perturbing molecular vibrations and creating red-shifted features. Control experiments done on polycrystalline graphite and a polystyrene blank indicate that this spectral behavior is unique to gases interacting with the nanotubes in the membrane.

Towards mimicking natural protein channels with aligned carbon nanotube membranes for active drug delivery

ABSTRACTA NEMD simulation system is constructed to simulate at two-dimensional (2D) periodic boundary conditions (PBCs) and to create two different pressures on two sides of the carbon nanotube (CNT) membrane. The simulation results show that water permeation through the same CNT membrane driven by different pressure differences exhibit similar transport phenomenon including unusually fast water permeation and a periodic (non-parabolic) radial velocity distribution unlike the parabolic form characteristic of continuum flow in the CNT membrane. A three-dimensional (3D) PBC system is also constructed to simulate water permeation through the same CNT membrane at the same pressure differences, to show the effect of PBC and simulation methodologies on transport phenomenon. The two systems both show that the forward/backward water flux increases/decreases with increasing the pressure difference from 1.0 MPa to 8.0 MPa. However, the net flux is higher for the 3D PBC system, especially at higher pressure difference is high. In general, the NEMD simulation method using the 2D PBC system is shown to be a feasible and valuable tool for studying pressure-driven permeation processes such as nanofiltration through these studies with model CNT membrane.

Objectives The reversible electrical modulation of chemical delivery is crucial for various biomedical engineering applications, enabling a tailored drug delivery profile. Electroosmosis flow (EOF) represents a significant electrokinetic phenomenon where a bulk flow is induced through narrow channels including capillaries or microfluidic devices or porous medium, under the influence of an applied electric field (Fig. 1a). Since the velocity of EOF is directly proportional to the applied current density ( I ) and the EOF strength ( K eo ), a standardized indicator related to the zeta potential of the channel walls, it provides the possibility of controlling the direction and velocity of EOF by simply adjusting the surface zeta potential.[1] Herein, a novel concept of electrically modulated delivery utilizing EOF generated within the porous network of the carbon nanotube (CNT) membrane is reported. The charge sign and magnitude of the micropores inside the CNT membrane are altered by applying varying voltages, leading to corresponding changes in the direction and velocity of the EOF. Results and Discussion The multi-walled carbon nanotubes powered are first treated with ozone and dispersed in ethanol. Then, the suspension is formed into the random alignment and cohesive CNT membrane by vacuum-assisted filtration (Fig. 1b-c). The experimental setup consists of symmetrically positioned reservoirs at both ends and a CNT membrane placed between the two reservoirs filled with 0.1 M KCl solution. The electrically modulated system is comprised of two circuits: the main circuit that generates an axial electric field to drive the EOF and the sub-circuit that varies the sign and magnitude of charges on the CNT membrane. The controllability of the EOF direction and velocity is evaluated by observing the movement of the liquid column in the reservoirs (Fig. 1d -e). Based on the established experimental setup, the voltage at which EOF is unobserved is referred to as the neutral voltage (or bias voltage) and is used as the reference for electrical modulation. Significant differences in the direction and velocity of EOF can be observed and measured on the CNT membrane when a positive (or negative) voltage relative to the bias voltage is applied. The EOF under the main circuit of + 0.25 mA and the sub-circuit voltage of + 0.5 V and - 0.5 V relative to the bias voltage, indicating a mobility rate of - 0.781 μL/mm2·min and + 0.972 μL/mm2·min, respectively (Fig. 1f). The plus and minus means that opposite directions of EOF are generated with applied voltages. Next, to demonstrate the effect of applied voltages on the EOF rate, the sub-circuit voltage of + 0.5 V and + 0.25 V relative to the neutral voltage was applied (with the same main circuit of + 0.25 mA), generating a mobility rate of - 0.781 μL/mm2·min and - 0.431 μL/mm2·min. The difference in velocity is due to the differential surface zeta potential within the microchannels of the CNT membrane. Conclusion Here, this study introduces a novel concept of a chemical delivery system by focusing on the electrically modulated EOFs generated in the microchannels of the CNT membrane. According to the results of the experiments, it can be demonstrated that altering the direction and velocity of EOF through electrical modulation is achievable. Additionally, the electrical modulation on EOF is feasible under varying axial electric field strengths and concentration solution environments. Reference [1] Kusama, S., Sato, K., Matsui, Y., Kimura, N., Abe, H., Yoshida, S., & Nishizawa, M. (2021). Transdermal electroosmotic flow generated by a porous microneedle array patch. Nature communications , 12 (1), 658. Fig. 1 Experimental setup and electrical modulation performance. (a) The mechanism of EOF. (b) Optical and SEM images of CNT membrane. (c) Schematic illustration of EOF generated in the micropores of CNT membrane. (d) An experimental setup consisting of Franz Cells with insertion of CNT membrane and the EOF direction and velocity were analyzed by observing the liquid movement. (e) Electrical modulation. (f) The relationship between the applied voltages (relative to the neutral voltage) and flow rates. Figure 1