Insulator-based dielectrophoretic antifouling of nanoporous membrane for high conductive water desalination

Cell transport and suspension in high conductivity electrothermal flow with negative dielectrophoresis by immersed boundary-lattice Boltzmann method

The transition from the current “linear” economy to a “circular” economy with a strong focus on the recovery and reuse of materials and resources undoubtedly necessitates efficient and effective separation technologies. Membrane technology will play an important role in this transition to a circular economy. In that perspective, separation at the molecular level to separate and fractionate e.g. individual ions and small molecules for reuse is especially essential. Unfortunately, conventional membrane materials and their fabrication methods mostly lack design and control over pore size and selectivity at a true molecular level. In view of this challenge, nanostructured polymer membranes based on self-assembled materials are gaining more and more interest. Using the self-assembly properties of polymerizable liquid crystal molecules ensures control at a molecular level and gives rise to narrow pore size distributions, high pore densities and control of pore size and functionality.In this review, the potential of liquid crystal materials and their self-assembly properties to fabricate nanoporous membranes for water purification, desalination and selective recovery is presented. The basic principles of liquid crystals, the self-assembling characteristics and methods to control pore size and functionality are discussed in the perspective of membrane properties and applications. Efforts reported in the literature highlighting advances and pointing out important limitations for different pore morphologies are discussed. The versatility of liquid crystal based membranes is highlighted by exploring approaches for post-modification of the nanopores to further tune the pore size and control the pore functionality after polymerization of the liquid crystals.The work provides readers with a thorough understanding of the design and fabrication of nanoporous liquid crystal membranes combined with a perspective on the potential of liquid crystal membranes. Next to recent advances, future challenges are presented as well, with the most crucial two: 1) The formation of thin, defect-free nanoporous liquid crystal layers supported on a microporous support; 2) Large-scale production combined with alignment control over longer length scales.

Though above 70% of the Earth is covered by water, most of the seas and oceans are unusable for drinking. Freshwater lakes, rivers and underground aquifers imply 2.5 percent of the global’s whole freshwater supply. Unfortunately, in addition to being scarce, fresh water is dreadfully unevenly spread. Enhanced demand for freshwater is a global concern. In many countries demanding is further than regular reserves. Sensible use of water, reducing spreading losses and upgraded treatment of recycled water to mitigate the concern, though, water scarcity is still presented consequently desalination of seawater is highly required. Graphene, a single sheet of carbon atoms, possibly will deliver the principal for a novel category of extremely permeable membranes for water purification and desalination. Though, a one atom thickness graphene reveals both brilliant mechanical strength and impermeability to atoms as small as helium. High-density, subnanometer pores within graphene have the potential for ultra-fast water permeance and high solute rejection as the atomic thinness makes slight resistance to stream which deters the transfer of solutes bigger than the pores. The two-dimensional, nanoporous membrane is expected to display orders-of-magnitude permeability and selectivity enhancement over current separation membranes for processes such as brackish water, water softening, or nanofiltration. This study is aimed that the existing desalination methods are not adequate to upgrade water sources unless the desalination technologies are improved significantly. Nanotechnology and utilizing graphene will deliver desalination technology to meet the requirements in the near future. Lately, novel procedures have been technologically progressed by means of nanotechnology and applying graphene for water desalination. This research will emphasize the concept of water desalination for the near futures.

Atomic-level engineering of anisotropically nanoporous graphyne membranes for efficient water desalination

The mixing of fluids using AC Electrokinetic is presented in this paper. Both AC electrothermal (ACET) and AC electroosmosis (ACEO) techniques are investigated for mixing operation. AC electrokinetic mixing utilizes the characteristics of short diffusion distance and large specific interface area, and the characteristics of laminar flow and multiphase flow in a microchannel. The proposed mixer will have advantages of easy implementation and compatibility with microchip fabrication. Furthermore low and high conductive fluid has been experimented for mixing operation. In this research, the ACET and ACEO mixing will be optimized by surface modification using a biocompatible hydrophobic nanocomposite monolayer. This coating will modify the mixer surface to a hydrophobic surface and improve the friction losses at the interface, and eventually increase the mixing rate. Both ACEO and ACET flow is a promising technique in microfluidic mixing toward laboratory automation applications, such as clinical diagnostics and high-throughput drug screening. But the mixing efficiency and type of AC electrokinetic usage depends on the conductivity range of the fluids. These mixers can be integrated with the lab-on-a-chip and can provide inexpensive disposable devices.

Membranes are widely used in industrial separation processes, particularly for gas separation and desalination processes. To develop membrane materials with improved permeability, selectivity can achieve more energy-efficient membrane separations and reduce costs. Since composite membranes offer improved performance, the aim of this research is to develop polymer-based composite membranes with improved performance for gas separation and water desalination applications. First, in order to obtain a composite membranes with high chlorine tolerance, a carbonaceous poly(furfuryl alcohol) (PFA) composite membrane was synthesized at a low temperature carbonation by formation and post-treatment of a thin PFA layer on porous polymer substrates. The carbonaceous PFA membrane exhibits high selectivity and excellent chemical stability in seawater desalination. The low-temperature carbonization method developed in this study is promising for developing a wide range of other carbonaceous polymer composite membranes for water desalination. Next, in order to apply PFA to other applications, understanding the effects of polymerization conditions on the properties of the PFA composite membrane is required. The PFA membrane was fully characterized in terms of microstructure and separation properties. Suitable synthesis conditions for the preparation of PFA composite membranes with smooth surfaces and uniform structure were (1) FA/ H2SO4 molar ratios: 74-300, (2) polymerization temperatures: 80-100°C and (3) solvents: ethanol and acetone. The preparation conditions were also optimized. The PFA composite membrane prepared with a FA/ H2SO4 molar ratio of 250, a polymerization temperature of 80°C and with ethanol as the solvent exhibited the highest H2/N2 ideal selectivity (αH2/N2=24.9), and a H2 permeability of 206 Barrers. This work led to a better understanding of the effect of the preparation procedures on the membrane performance. In order to investigate the effects of the incorporation of molecular sieve nanoparticles on the membrane structure and membrane performance, silicalite-poly(furfuryl alcohol) (PFA) mixed matrix composite membranes were successfully synthesized based on the best synthesis condition obtained previously. The silicalite-PFA mixed matrix composite membrane with 20% w/w silicalite loading had a high ideal selectivity (αo2/N2= 3.5 and αco2/N2= 5.4) and a good permeability (Po2= 821.2, Pco2= 1263.7, PN2= 233.3 Barrers) at room temperature. This membrane can be a good candidate for oxygen enrichment applications. Finally, in order to investigate the effects of the incorporation of silicalite nanocrystals on the desalination property of polyamide membranes, silicalite nanocrystals were also incorporated into polyamide matrix to synthesize silicalite-polyamide mixed matrix membranes. With an increase in the loading of silicalite nanocrystals, the water flux of silicalite-polyamide mixed matrix composite membranes increased whereas the salt selectivity significantly decreased. The silicalite-polyamide mixed matrix composite membrane prepared from TMC-hexane with 0.5% (w/v) silicalite had water flux of 2.7×10-6 m3/m2·s and NaCl rejection of 50% at a feed pressure of 34.5 bar which 2000 ppm salt solution was used as the feed. The silicalite-polyamide mixed matrix composite membrane is promising for developing high water flux composite membranes for water desalination. In this research, composite membranes with improved permeability, selectivity and chemical resistance were successfully synthesized for desalination and gas separation. For desalination, carbonaceous PFA composite membranes with high chlorine tolerance and silicalite-PA mixed matrix composite membranes with high salt rejection and water flux were successfully obtained. For gas separation, an optimized composite membranes PFA synthesis condition was found and silicalite-PFA mixed matrix composite membranes with high O2/N2 separation were successfully synthesized.

Bioinspired humic acid-based membranes for water desalination: Mechanistic insights from molecular simulations

Support based novel single layer nanoporous graphene membrane for efficacious water desalination

Molecular dynamics simulation-directed rational design of nanoporous graphitic carbon nitride membranes for water desalination

Mechanical properties of water desalination and wastewater treatment membranes

Super square (SS) carbon nanotube (CNT) networks, acting as a new kind of nanoporous membrane, manifest excellent water desalination performance. Nanopores in SS CNT network can efficiently filter NaCl from water. The water desalination ability of such nanoporous membranes critically depends on the pore diameter, permitting water molecule permeatration while salt ion obstruction. On the basis of the systematical analysis on the interaction among water permeability, salt concentration limit and pressure on the membranes, an empirical formula is developed to describe the relationship between pressure and concentration limit. In the meantime, the nonlinear relationship between pressure and water permeability is examined. Hence, by controlling pressure, optimal plan can be easily made to efficiently filter the saltwater. Moreover, steered molecular dynamics (MD) method uncovers bending and local buckling of SS CNT network that leads to salt ions passing through membranes. These important mechanical behaviours are neglected in most MD simulations, which may overestimate the filtration ability. Overall, water permeability of such material is several orders of magnitude higher than the conventional reverse osmosis membranes and several times higher than nanoporous graphene membranes. SS CNT networks may act as a new kind of membrane developed for water desalination with excellent filtration ability.

Alternating current (AC) electrokinetics have many applications in engineering fields, among which the efficient delivery of bioparticles in a continuous flow is significant for further biomedical manipulations. To avoid the cell lyse caused by low electrical conductivity environment, the AC electrothermal (ACET) phenomenon which effectively drives the physiological fluid with high electrical conductivity becomes attractive. In addition, negative dielectrophoresis (nDEP) is usually induced on the polarized bioparticles immersed in physiological fluid with a non-uniform electric field. In the current work, a novel AC electrokinetic micro-device with castellated electrodes is designed for delivering bioparticles in high electrical conductivity fluid without the use of a mechanical micropump. The ACET flow vortex could be eliminated by replacing the interdigitated electrodes with the castellated electrodes. Besides, by appropriately choosing the phases of AC voltages, a nDEP force is induced to repel the bioparticles from the electrode edges and the microchannel surfaces. Under this circumstance, the bioparticle transport efficiency is highly improved, and the cell adhension on the micropump surfaces is also reduced. The effects of AC voltage magnitudes, electrical conductivities of solution and bioparticles, bioparticle size, and bioparticle initial position on the multi-physical bioparticle transport process are investigated by immersed boundary-lattice Boltzmann method. The results demonstrate that the hybrid AC electrokinetics using castellated electrodes is an efficient technique of delivering bioparticles in a lab-on-a-chip device.

Water desalination using positively and negatively charged single-layer nanoporous graphene membranes are investigated using molecular dynamics (MD) simulations. Pressure-driven flows are induced by the motion of specular reflection boundaries with a constant speed, resulting in a prescribed volumetric flow rate. Simulations are performed for 14.40 Å hydraulic pore diameter membrane with four different electric charges distributed on the pore edges. Salt rejection efficiencies and the resulting pressure drops are compared with the previously obtained base-line case of 9.9 Å diameter pristine nanoporous graphene membrane, which exhibits 100% salt rejection with 35.02 MPa pressure drop at the same flow rate. Among the positively charged cases, q = 9e shows 100% and 98% rejection for Na+ and Cl- ions respectively, with 35% lower pressure drop than the reference. For negatively charged pores, optimum rejection efficiencies of 94% and 93% are obtained for Na+ and Cl- ions for the q = -6e case, which requires 60.6% less pressure drop than the reference. The results indicate the high potential of using charged nanoporous graphene membranes in reverse osmosis (RO) desalination systems with enhanced performance.

Efficient pumping of whole blood is an essential task in biomedical engineering, especially for point-of-care diagnostics using lab-on-a-chip devices. Alternating current (AC) electrokinetics have been widely used for several different applications among which pumping fluids using the precisely controlled electric field without any moving mechanical parts is significant. Due to its high conductive characteristic, it is difficult to drive the blood flow using the AC electroosmosis phenomenon because the electric double layer is highly compressed. Fortunately, the AC electrothermal (ACET) phenomenon occurs due to the variation of temperature-dependent permittivity and conductivity caused by Joule heating effects or other heat sources making it powerful for driving high electrical conductivity physiological fluids in biomedical devices. Compared with Newtonian fluids like saline solutions or urine, the non-Newtonian rheological nature and AC frequency-dependent dielectric property of blood make its ACET driving mechanism more complicated and attractive. In this paper, ACET induced blood flow in the 3D microfluidic channel is modeled by the lattice Boltzmann method accelerated using graphics processor units. The Carreau-Yasuda model is applied to simulate the shear-thinning behavior of blood flow, and its electrothermal pumping efficiency is investigated with respect to the AC electrode configuration, AC voltage magnitude, and AC signal frequency by comparing it with the ACET pumping of Newtonian fluids using scaling law analysis. The results demonstrate that the ACET phenomenon is effective for pumping non-Newtonian whole blood flow in microfluidic devices with ring electrodes which will contribute to the point-of-care diagnostic of bacterial bloodstream infections or rapid detection of circulating tumor cells.

This paper presents a new PDMS micro chip with pre-concentration unit by insulated dielectrophoresis and patterned nanoporous membrane for low frequency impedance spectroscopy that has the potential to decrease the time needed to screen industrial and clinical samples for total bacterial content. This device is tested to concentrate Escherichia coli (E. coli) O157:H7 on the microwells with nanoporous membrane from a dilute sample using insulator-based dielectrophoresis (IDEP). Bacteria identification is determined by impedance spectrum of antibody modified nanoporous alumina membrane.