Engineering Water and Solute Dynamics and MaximalUse of CNT Surface Area for Efficient Water Desalination

<p indent=0mm>Oily water treatment has become an urgent task in our daily life because of the environmental and economic demands. Traditionally, gravity separation, flotation and filtration are used to separate oil/water mixtures successfully, but these methods have some drawbacks, including energy waste, low efficiency and secondary environmental pollution. In recent years, advanced materials with superwetting property involving superhydrophobic/superoleophilic separation materials, superhydrophilic and under-water superoleophobic separation materials, Janus separation materials, smart separation materials with switchable wettability emerge as a new research direction to address these problems. Because of the convenient separation and low-energy consumption, membrane separation material shows great advantages over conventional separation materials, which has a promising choice in the area of oily water treatment. Despite all these progress, most of the membranes separation materials are suffered from several limits for separating surfactant-stabilized oil/water emulsions and surfactant-free oil/water emulsions with micron or nanometer size, which may bring long-term damage to the natural environment. Furthermore, due to the presence of various harmful substances involving organic solvents, bacterial, heavy metal ions in real sewage system, the water pollution has become more serious and thus the resultant water phase is not suitable to put into the water system even after several separation cycles. From this perspective, to construct novel separation membrane materials with multifunction, good separation efficiency, high recyclability and convenient separation process for the separation of oil/water emulsions is passionately desired. Carbon-based (graphene and carbon nanotubes) membranes materials, especially polymer-functionalized carbon-based membrane materials, have gained increasingly attentions attributing to their outstanding physical and chemical properties, therefore are considered as an important choice for the separation of oily wastewater. Until now, there are tremendous advances on the carbon-based materials for oil/water separation, but most of them are focused on the development of three dimensional carbon-based separation materials, whereas the carbon-based membranes which play an important role on the treatment of oily wastewater have been almost neglected. Based on these, the research progress of polymer modified carbon-based films in wastewater treatment in recent years is reviewed in this paper. According to wettability and functions, the carbon-based membranes are divided into five parts: (1) Superhydrophobic carbon-based separation membranes, (2) superhydrophilic carbon-based separation membranes, (3) Janus carbon-based separation membranes, (4) smart carbon-based separation membranes, and (5) multi-functional carbon-based separation membranes. In each part, the influences of design routes, preparation methods and wetting behaviors on the separation efficiency of oily wastewater are discussed in detail. Finally, the development prospects and challenges of carbon-based membranes used for oil-containing wastewater purification are comprehensively discussed.

Nowadays, global fresh water shortage is becoming the most serious problem affecting the economic and social development. Water treatment including seawater desalination and wastewater treatment is the main technology for producing fresh water. Membrane technology is favored over other approaches for water treatment due to its promising high efficiency, ease of operation, chemicals free, energy and space saving. Membrane filtration for water treatment has increased significantly in the past few decades with the enhanced membrane quality and decreased membrane costs. In addition to high permeate flux and high contaminant rejection, membranes for water treatment require good mechanical durability and good chemical and fouling resistances. Thus, investigation of the mechanical behavior of water treatment membranes with underlying deformation mechanisms is critical not only for membrane structure design but also for their reliability and lifetime prediction.Compared to ceramic and metallic membranes, polymer membranes with smaller pore size and higher efficiency for particle removal are widely used in seawater desalination with a high applied pressure. However, polymer membranes are mechanically weaker and have lower thermal and chemical stability compared to inorganic membranes. Blending of polymers with inorganic fillers is an effective method to introduce advanced properties to polymer based membranes to meet the requirements of many practical applications. The reinforced polymeric membranes with inorganic fillers can provide desirable mechanical strength as well as mechanical stability. Carbon nanotubes (CNTs) have received considerable attention from academic and industries over the last twenty years. In addition to their excellent electrical and thermal properties, CNTs exhibit outstanding mechanical characteristics due to its instinct mechanical strength and high aspect ratio. For the application of water treatment membranes, CNTs could be the excellent channels for water to go through and therefore, CNTs have proven to be excellent fillers in polymer membranes improving the permeability and rejection properties. In literature, it is reported that the mechanical strength of the polymer membranes was improved with the embedding of CNTs due to reinforcement effect of the more rigid CNTs. The mechanical responses of polymer_CNTs composites depended on the interfacial adhesion between the CNTs and the membrane-based polymer as well as the dispersion and distribution of the CNTs within the polymer matrix.In this study, a vertical chemical vapor deposition reactor was designed in order to synthesize CNTs of high aspect ratio using continues injection atomization. Bundles of high purity (99%) and high quality CNTs were produced by this system. The produced CNTs had diameters ranging from 20 to 50 nm and lengths ranging from 300 to 500 micron (corresponded aspect ratios ranging from 6000 to 25000). A novel polysulphone (PSF) based nanocomposite membrane incorporated with the produced high aspect ratio CNTs was then casted via phase inversion method, at a wide range of CNTs loading (0–5 wt. %), in polysulphone-dimethylformamide solutions using the Philos casting system. The poly(vinylpyrrolidone) was used as pore-forming additive. To demonstrate the effect of nanocomposite morphology on the mechanical behavior of the prepared membranes, a set of control samples consisted of PSF membranes embedded with commercial CNTs at the same CNTs loading, were casted at the same conditions. The commercial CNTs had a lengths of 1 μm to 10 μm and outer diameters of 10 nm to 20 nm (corresponded aspect ratios ranging from 50 to 1000), with purity &gt;95% and BET surface area of 156 m2/g.The effects of CNTs content and aspect ratio on morphological, water transport and mechanical properties of the prepared PSF-based porous membranes were investigated. The surface and cross-section morphologies of PSF/CNTs porous membranes were examined using scanning electron microscopy (SEM). The orientation, dispersion and distribution of CNTs within polymer membranes were evaluated for the membrane samples with different CNTs content and CNTs aspect ratio. The average membrane pore size was evaluated by using SEM image analysis software.Uniaxial tensile behavior of the membranes was characterized by means of a universal material testing machine under different testing conditions. Wet specimens were carefully cut from the casted membranes by using a razor blade. Elastic, plastic and failure behaviors of the membranes are analyzed with the impacts of CNTs content and aspect ratio. The macroscopic mechanical behaviors of the membranes are correlated with their strain induced microstructure evolution by using SEM. In this, pore shape evolution, pore and CNTs orientations, neighboring pore interaction, interface between the CNTs and PSF matrix and the failure behavior of the deformed porous membranes were analyzed. The macroscopic stress-strain responses of the membranes were correlated with the microstructure of the studied nanocomposites membranes to provide a better understanding of materials' processing-microstructure-properties relationship.

Carbon nanotubes (CNTs) have emerged as promising novel membrane materials for enhancing desalination performance. So far, the salt rejection mechanism of these materials has been through the narrow diameter of these nanotubes that exclude salt and allow the transfer of water. It is challenging to control the inner diameter of all the nanotubes and there is the problem of low permeation after several measurements due to the narrow channels that water molecules have to travel through. There is also the problem of fouling after a few measurements, because even if a low percentage of ions leak through some of the channels, they can easily get stuck there and eventually block the channels. Here, the rejection mechanism of various CNTs, grown on Si hole arrays, is based on the effective surface area of the nanotubes. The rejection of NaCl and MgSO4 ions and the permeability of water were measured across CNT structures grown on micro-fabricated Si hole arrays in a gravity-driven pressure setup. The electric conductivity of the feed and permeate solutions was measured and showed acceptable values for salt rejection and high values for water permeation. A comparison between the performance of bare Si surface and those decorated with CNTs shows the effectiveness of surface modification with CNTs in salt rejection.

Numerical simulation of transesterification reaction was carried out in Y-shaped microreactor. The effects of inlet pressures, temperatures and oil molar ratio towards conversion of triglyceride was examined. The inlet pressure ranging from 0.001 to 0.1 Pa, three different temperature of 25, 50 and 75 ℃ together with alcohol to oil molar ratio of 12:1, 9:1 and 6:1 was simulated via COMSOL Multiphysics software. The temperature of 50 ℃ and alcohol to oil molar ratio of 12:1 shows high biodiesel yield at lowest inlet pressure of 0.001 Pa applied. On top of that, the inlet pressure has substantial impact of the biodiesel yield which is the conversion of triglyceride measured in this studied.KeywordsBiodieselY-shaped microreactorCFD

Self-Healing Hydrophilic Porous Photothermal Membranes for Durable and Highly Efficient Solar-Driven Interfacial Water Evaporation

In this study, we present a computational model utilizing a Newtonian fluid assumption to investigate blood flow characteristics in arteries with single and double stenosis. We have used COMSOL Multiphysics software with a suitable validation to evaluate the hemodynamic parameters. The geometry of the arterial segment with single and double stenosis has been considered to analyze their effects on flow patterns, wall shear stress distribution, velocity, and pressure gradients. Results reveal the significant alterations in flow velocity profiles and pressure gradients downstream of the stenotic regions, leading to changes in wall shear stress distribution along the arterial wall for the higher severity. Greater stenosis severity results in higher wall shear stress at the constricted region; and in the case of double stenosis, the wall shear stress is slightly lower for the second stenosis than that of the first. For single stenosis with severity levels of 45%, 60%, and 75%, the results of inlet pressures are 773.49 Pa, 1001.1 Pa, and 2041.9 Pa, respectively. In the double stenosis configuration, inlet pressures have been increased to 874.57 Pa, 1304.5 Pa, and 3055.6 Pa for the same severity levels. The study has shown that both increasing stenosis severity and the presence of multiple stenoses significantly elevate inlet pressure. Further, for single stenosis, results indicate that as stenosis severity increases, the separation point moves upstream, the reattachment point shifts downstream, and the recirculation length expands significantly (0.99 mm for 45% stenosis, 3.20 mm for 60%, and 9.30 mm for 75%). In the double stenosis case, a second recirculation zone is observed, with larger and more prolonged disturbed flow regions compared to single stenosis. The first and second stenoses exhibit distinct separation and reattachment points, with recirculation lengths increasing as severity progresses (e.g., 4.76 mm and 10.44 mm for 75% severity). These findings highlight the hemodynamic significance of stenosis severity and location, as larger recirculation zones and flow disturbances may contribute to vascular complications, endothelial damage, and plaque progression.

Design and optimization of a microneedle with skin insertion analysis for transdermal drug delivery applications

In this study, porous polymers of intrinsic microporosity (PIM-1) membranes were prepared by non-solvent induced phase inversion (NIPS) and investigated for water vapor transport in view of their application in membrane distillation (MD). Due to the lack of high boiling point solvents for PIM-1 that are also water miscible, the mixture of tetrahydrofuran (THF) and N-methyl-2-pyrrolidone (NMP) was found to be optimal for the formation of a membrane with a developed porous system both on the membrane surface and in the bulk. PIM-1 was synthesized by using low and high temperature methods to observe how molecular weight effects the membrane structure. Low molecular weight PIM-1 was produced at low temperatures, while high molecular weight PIM-1 was obtained at high temperatures. Several membranes were prepared, including PM-6, PM-9, and PM-11 from low molecular weight PIM-1, and PM-13 from high molecular weight PIM-1. Scanning electron microscopy (SEM) was used to image the surface and cross-section of different porous PIM-1 membranes. Among all the PIM-1 membranes (PM) obtained, PM-6, PM-9, PM-11 and PM-13 showed the most developed porous structure, while PM-13 showed large voids in the bulk of the membrane. Contact angle measurements showed that all PIM-1 porous membranes are highly hydrophobic. Liquid water flux measurements showed that PM-6, PM-9 and PM-11 showed minimal water fluxes due to small surface pore size, while PM-13 showed a high water flux due to a large surface pore size. Water vapor transport measurements showed high permeance values for all membranes, demonstrating the applicability of the developed membranes for MD. In addition, a thin film composite (TFC) membrane with PIM-1 selective layer was prepared and investigated for water vapor transport to compare with porous PIM-1 membranes. The TFC membrane showed an approximately 4-fold lower vapor permeance than porous membranes. Based on these results, we postulated that the use of porous PIM-1 membranes could be promising for MD due to their hydrophobic nature and the fact that the porous membranes allow vapor permeability through the membrane but not liquid water. The TFC membrane can be used in cases where the transfer of water-soluble contaminants must be absolutely avoided.

The role of different functional groups and the nature of the functional group on multiwalled carbon nanotube (MWCNT) surface were thoroughly studied for silver nanoparticles (AgNPs) loading and on the mechanism of decontamination and disinfection. The surfactant free method for grafting of AgNPs on MWCNT surface followed by vacuum annealing was adapted to enhance the interfacial interactions of nanomaterials with bacteria. The best performing functionalized MWCNT was selected for the fabrication of functional composite membrane for further insight into the interfacial interaction of polymer–nanomaterials. It has been shown that at an optimized weight percentage loading of functionalized MWCNTs, nanotube scaffolds were generated inside the pores of polysulfone membrane to sieve out toxic metal ions and bacteria by physical and chemical elimination without compromising the flux rate of filtration. The structure property relationship of the nanocomposite membrane has been thoroughly evaluated by the morphological, surface area, and contact angle measurement studies. The modified surface of MWCNTs by Ag nanoparticles and polar functional groups placed on the pores of the membrane was thus further exposed for interfacial interaction with the decontaminated and disinfected water, which in turn enhances the efficiency of filtration.

Production of lactobionic acid by BMED process using porous P84 co-polyimide anion exchange membranes

Modelling the rejection of nanofiltration membranes using zeta potential measurements

Effect of hydrodynamic diameter on the sieving of waterborne carbon nanotubes by porous membranes

Water in carbon nanotubes is surrounded by hydrophobic carbon surfaces and shows anomalous structural and fast transport properties. However, the dynamics of water in hydrophobic nanospaces is only phenomenologically understood. In this study, water dynamics in hydrophobic carbon nanotubes is evaluated based on water relaxation using nuclear magnetic resonance spectroscopy and molecular dynamics simulations. Extremely fast relaxation (0.001 s) of water confined in carbon nanotubes of 1 nm in diameter on average is observed; the relaxation times of water confined in carbon nanotubes with an average diameter of 2 nm (0.40 s) is similar to that of bulk water (0.44 s). The extremely fast relaxation time of water confined in carbon nanotubes with an average diameter of 1 nm is a result of frequent energy transfer between water and carbon surfaces. Water relaxation in carbon nanotubes of average diameter 2 nm is slow because of the limited number of collisions between water molecules. The dynamics of interfacial water can therefore be controlled by varying the size of the hydrophobic nanospace.

Despite the recent progress in creating photothermal agents of various compositions and morphologies, there is a strong need to further develop photothermal transducers that absorb light in the near-infrared region, which corresponds to the biological window, and enhance the local heat generation at the cellular level. One of the major limitations of photothermal therapy is the nonselective and uncontrolled heating of tumor tissues that lead to the heat diffusion in the normal cells. Therefore, we propose to fill these gaps by designing and developing decorated multiwalled carbon nanotubes (MWCNTs) with plasmonic nanoparticles that enhance the light-to-heat conversion in the therapeutic window through the localized surface plasmon resonance on the carbon nanotube surface. These novel hybrid nanostructures used as plasmonic photothermal transducers will provide efficient thermal ablation as well as minimal damage to normal cells compared to the current plasmonic nanostructures. Here, we focus on optimizing the near-infrared optical absorption of multiwalled carbon nanotubes by decorating their surfaces with gold nanorods. First, we present the synthesis process of this hybrid plasmonic nanostructure as well as their characterization employing high-resolution microscopic and spectroscopic tools such as TEM, FTIR, Raman spectroscopy and UV-Vis spectroscopy. Then, we report the numerical evaluation of the optical spectra distribution of decorated multiwall carbon nanotubes in a water environment using COMSOL Multiphysics software. Finally, near infrared photothermal measurements and quantitative analysis (more particularly using a laser wavelength of 808 nm) of this hybrid carbon nanostructure will be discussed.

Preparation and performance of magnetic carbon nanotubes modified PVC substrate composite nanofiltration membranes