Solute Rejection Research Articles

Catalytic template assisted interfacial polymerization for high‐performance acid‐resistant membrane preparation

AbstractHighly permeable acid‐resistant nanofiltration (NF) membranes are of critical significance for the efficient treatment of acidic streams. Enhancing permeability while maintaining the high solute rejection of acid‐resistant NF membranes remains a great challenge due to the low reactivity of monomers. In this work, a novel catalytic template assisted interfacial polymerization (IP) strategy of 3‐aminobenzenesulfonamide (ABSA) and trimesoyl chloride (TMC) was provided to prepare a poly(amide‐sulfonamide) membrane. Aminopyridine doped graphene quantum dots rich in acylation catalytic sites and ZIF‐8 nanoparticles are co‐loaded on a substrate as template. Benefiting from the enhanced phase integrity and self‐inhibition effect of the template assisted IP process, the resulting ultra‐thin acid‐resistant membrane exhibits an excellent water permeance (20.4 Lm−2h−1bar−1) with a high Na2SO4 rejection of 90.5%, which outperforms almost all the reported acid‐resistant NF membranes. Our work paves a versatile way for synthesis of special separation membranes.

Microstructural evolution and phase stability in semi-Heusler NiMnSb and vanadium added equi-atomic NiMnSbV alloys

Phase and microstructure evolution in semi-Heusler NiMnSb and vanadium added quaternary equi-atomic NiMnSbV alloys has been studied in the as solidified state. In the as solidified NiMnSb alloy, cubic semi-Heusler phase and in the as solidified NiMnSbV alloy, Frank-Kasper type cubic SbV3 phase along with the cubic semi-Heusler NiMnSb phase are observed. Nucleation and growth of SbV3 phase takes place in the alloy through solute rejection mechanism, and at the interface of SbV3 and NiMnSb semi-Heusler phase, lamellar structure is observed. While SbV3 phase is stable upto 700 °C, the semi-Heusler NiMnSb phase is not stable beyond 400 °C and it transforms to hexagonal (Ni/Mn)Sb phase. Line defects are observed in the NiMnSb semi-Heusler phase. However, extensive twin like defects are observed in the cubic SbV3 phase. In the SbV3 phase edge sharing 12-fold coordinated icosahedral clusters and 14-fold coordinated clusters are present. Atomic size difference of Sb and V indicates that the clusters are distorted, which might be the viable cause behind the formation of such kind of compound deformation twins. The phase formation and stability in these two alloys has been studied through Miedema’s model. It is observed that apart from atomic size difference, enthalpy of mixing; the ternary and higher order self-interactions, electronic contribution to enthalpy also play an important role. Systematic substitution in the lattice of semi-Heusler NiMnSb phase based on enthalpy of mixing and atomic radius may not be the design strategy for development of semi-Heusler NiMnSb based single phase multicomponent/high entropy alloys.

Leaching of dissolved organic carbon from commercial reverse osmosis membranes exacerbates interferences in organic solute rejection during bench-scale filtration

Materials in contact with purified (e.g., Drinking water, ultrapure-water) water are sources of dissolved organic carbon which can increase the regrowth potential. Reverse osmosis (RO) membrane materials are composed of flexible polymers that are also in contact with treated water, but their contribution to DOC and microbial regrowth in bench-scale filtration studies is not reported. Bench-scale filtration studies use less volumetric throughput compared to pilot and full-scale filtration systems, which likely exacerbates the influence of leachates on for DOC measurement in permeates. This limits our ability to determine if standard membrane preparation procedures ensure sufficient removal of leachable organics. Migration of DOC from 8 different reverse osmosis membrane filters was assessed by two different experimental approaches; (1) Immersion assay—membranes were soaked in a pasteurized, isotonic water solution with a low and constant concentration of DOC. (2) Volume throughput (VT) test—Permeate was collected at defined VT steps to determine the impact of VT on the washout of DOC during system start-up. Test water from the immersion assay and the filtration test were analyzed with respect to (i) DOC (mg/L), (ii) microbial regrowth potential (% increase in bacterial activity), (iii) DOC fractional composition via LC-OCD. The presented study identified variations in the leachability of DOC between commercial RO membranes. Leaching of DOC from RO membranes varied by supplier and membrane composition. Alfa Laval RO98 exhibited the highest release of DOC compared to the other membranes tested during the immersion assay, suggested by an increase in test water DOC from 0.3 mg/L to 7.43 ± 1.54 mg/L, (n = 3) within 48 h. Aquaporin biomimetic-based membranes had the lowest release of DOC after 48 h of immersion (0.702 ± 0.17 mg DOC/L, n = 3). Higher concentrations of leached DOC did not lead to a higher regrowth potential on the released solute. Results of the filtration test demonstrate that DOC leaching from the membrane can exceed the point of flux-stabilisation, which is the common endpoint of membrane preparation. In all membranes tested, the chemical composition of DOC was dominated by low molecular weight acids, indicative of monomers used during membrane interfacial polymerization. The implication of this study suggests that on bench-scale filtration less volumetric throughput compared to pilot-full scale filtration exacerbates the influence of leachates on for example DOC measurement in permeates; promoting interferences in DOC permeate measurement and corresponding rejection coefficient. Relevance for full-scale filtration systems is limited due to higher volume throughputs applied during system start-up and commissioning.

On the edge between organic solvent nanofiltration and ultrafiltration: Characterization of regenerated cellulose membrane with aspect on dendrimer purification and recycling

The performance of commercial cellulose membranes with pore size on the border between ultra- and nanofiltration in selected organic solvents was studied focusing on rejection of small solutes and applicability for dendrimer purification. Organic markers in the MW range 100 – 700 Da and polarity range from nonpolar to polar protic compounds (aliphatics, aromatics, ethers, esters and alcohols) were used for membrane characterization. Transmission experiments in mixtures of methanol and dichloromethane of variable ratio showed the suitability of tested membranes for intended purpose, bringing information on structural factors affecting the rejection. Besides solute molar volume, its polarity type, or affinity, most conveniently expressed by Hansen solubility parameters, was found to be a crucial factor; with increasing size of solute molecule the spatial arrangement becomes also important. Solvent composition influences not only the behavior of solutes, but it also affects the membrane structure: poor solvation of cellulose by less polar solvents causes partial pore collapse, resulting in a decrease of membrane molecular weight cutoff. This effect can be used to improve the retention of a target product, as was shown for the first generation amphiphilic dendron. In addition, a simple mathematical model, allowing to estimate the course of nanofiltration and to optimize its conditions in a semicontinuous dead-end setup, is presented.

Explainable machine learning for unraveling solvent effects in polyimide organic solvent nanofiltration membranes

Understanding the effects of solvents on organic solvent nanofiltration currently depends on results obtained from small datasets, which slows down the industrial implementation of this technology. We present an in-depth study to identify and unify the effects of solvent parameters on solute rejection. For this purpose, we measured the rejection of 407 solutes in 11 common and green solvents using a polyimide membrane in a medium-throughput cross-flow nanofiltration system. Based on the large dataset, we experimentally verify that permeance and electronic effects of the solvent structure (Hildebrand parameters, electrotopological descriptors, and LogP) have strong impact on the average solute rejection. We furthermore identify the most important solvent parameters affecting solute rejection. Our dataset was used to build and test a graph neural network to predict the rejection of solutes. The results were rigorously tested against both internal and literature data, and demonstrated good generalization and robustness. Our model showed 0.124 (86.4% R2) and 0.123 (71.4 R2) root mean squared error for the internal and literature test sets, respectively. Explainable artificial intelligence helps understand and visualize the underlying effects of atoms and functional groups altering the rejection.

In-situ experimental investigations of the morphological characteristics of plumes and chimneys formed during the directional solidification of a binary alloy

The defects such as freckles formed during the directional solidification of binary alloys severely affect the performance of cast products. The phenomenon of freckle formation is strongly influenced by the convective flows generated during solidification. The rejection of solute during the solidification at the solid/liquid interface induces the concentration gradients in the liquid. These concentration gradients in combination with existing temperature gradients, may induce buoyancy-driven convection in the mushy zone (plumes) and the parent liquid region (fingers). As the mushy zone evolves, small chimneys are formed, which leads to the formation of discrete plumes of interdendritic liquid. These plumes have a very complex flow structure which leads to the structural and compositional heterogeneities in the final cast product. The current study is an effort to investigate the morphological characteristics of plumes and chimneys formed during the directional alloy solidification. For this, controlled solidification experiments in a bottom-cooled rectangular cavity with an analogue transparent aqua ammonia system (NH4Cl + 74 wt% H2O) are performed. Particle Image Velocimetry (PIV), High Speed (HS) imaging and thermocouples temperature measurement techniques are used for real-time measurement of flow field, solidified and mushy zone dynamics and local temperature during the course of solidification. The dynamical nature of plumes is captured and the morphology of chimneys (shape, size, spacings, etc.) and plumes (velocity magnitude, shape, size, etc.) are quantified. The phase-locking with 180° phase difference due to the coupling between nearby plumes is observed. Also, the evolution of double-diffusive layers (DDLs) is captured and the critical value of thermal Rayleigh number for the onset of DDLs is estimated.

Rigorous determination of pore size non-uniformity for nanofiltration membranes by incorporating the effects on mass transport

The pore size uniformity of a nanofiltration (NF) membrane has an important impact on its rejection capacity and separation selectivity, which remains yet difficult to be scientifically and accurately characterized. In this study, a method was proposed for characterizing the pore size distribution of NF membranes, by assuming its obeyance of the log-normal distribution and incorporating the Donnan and steric pore model to describe water permeation and solute rejection. The distribution parameters are derived through data-fitting the experimental rejections of reference solutes in the model framework. The non-uniformity index is newly defined as the degree of deviation of a special pore size from the median pore size. The index makes that possible to quantitatively compare the non-uniformity among different NF membranes. The fast convergence of the method was verified. Furthermore, we put forward some suggestions on the use of the proposed method for pore size distribution characterization. The determination for the rejections of highly-rejected (∼90 %) solutes and the radii of the lowly-rejected (∼30 %) solutes must be sufficiently accurate. The proposed method is more advantageous over the conventionally adopted method due to the higher accuracy and more convenience in the assessment of membrane pore size distribution as well as membrane performance.

Effects of feed and draw solution temperature on the performance of Aquaporin HFFO.6 membrane in forward osmosis

Recently, forward osmosis (FO) has attracted attention in many potential applications including food processing, fertilizers and manufacturing industries. This study investigates the effects of feed solution (FS) and draw solution (DS) temperature on the water flux, reverse salt flux, and specific reverse salt flux. The temperature of both the DS and FS were varied at the same time. Four typical temperatures such as 20 °C, 25 °C, 30 °C and 35 °C were selected to maintain at FS and DS sides, respectively, for each iteration. Except for the temperature, the other operating conditions like concentration, flow rates, and the type of membrane used were not varied in this experiment. The experiments were performed with tap water as FS and 1.5 M of NaCl as DS. The flow rates of the DS and FS were maintained at 15 L min−1 and 25 L min−1, respectively. The membrane used was the hollow fiber forward osmosis (HFFO.6) membrane procured from Aquaporin A/S, Denmark. The results showed that as temperature increased from 20 °C to 35 °C, the water flux, reserve salt flux (RSF), and specific reverse salt flux were enhanced. This was due to the enhanced diffusion coefficient of both DS and FS on increasing the temperature. This further reduces the concentration polarization and in turn augments the water flux. However, consequently, reverse and specific reverse solute flux also increased on temperature, which is not desirable for an efficient FO system. Hence, it is recommended to operate the FO at a minimum required temperature considering the other influencing other operational parameters such as specific reverse solute flux, recovery and rejection percentage.

Improvement of water filtration performance of graphene oxide membranes on Nylon support by UV-assisted reduction treatment: Control of molecular weight cut-off

• Higher rejection values were achieved for GO membranes after UV-reduction. • Molecular weight cut-off between 300 and 150 were achieved. • Rejection increased while permeance decreased with increasing GO loading. • UV-reduction shows a high potential for tuning the properties of GO membranes. Graphene oxide (GO) membranes on Nylon support were modified by UV-assisted reduction to control their behavior in the filtration of water containing organic pollutants. Pyridine, phenol, 2-naphthol and disperse blue 3 were used as probe pollutants to determinate the molecular weight cut-off (MWCO) of the membranes prepared. The membranes were prepared with GO loads of 0.04 and 0.06 mg cm −2 and subjected to UV radiation from a Hg lamp (30 W m −2 ) for 30–60 min. The non-irradiated membranes showed MWCO ca. 300 Da, with rejection values above 90 % for disperse blue 3, while rejection for 2-naphtol reached 64 %. Irradiation resulted in substantial removal of oxygen surface groups, leading to staking of GO sheets and a decrease of interlayer space. These structural changes narrowed the size of pores thus reducing solutes passage. Rejection of 2-naphtol reached 83 %, i.e. decreasing MWCO to ca. 150 Da. The increase in the rejection of solutes was higher for membranes with a GO load of 0.06 mg cm −2 , however similar water permeability was achieved regardless the GO load. UV-reduction shows a high potential for controlling the rejection of solutes by GO membranes on Nylon support while maintaining good permeability.

Mass Transport of Dye Solutions through Porous Membrane Containing Tannic Acid/Fe3+ Selective Layer.

Tannic acid (TA)-Fe3+ membranes have received recent attention due to their sustainable method of fabrication, high water flux and organic solutes rejection performance. In this paper, we present a description of the transport of aqueous solutions of dyes through these membranes using the transport parameters of the Spiegler-Kedem-Katchalsky (SKK) model. The reflection coefficient (σ) and solute permeability (PS) of the considered TA-Fe3+ membranes were estimated from the non-linear model equations to predict the retention of solutes. The coefficients σ and PS depended on the porous medium and dye molecular size as well as the charge. The simulated rejections were in good agreement with the experimental findings. The model was further validated at low permeate fluxes as well as at various feed concentrations. Discrepancies between the observed and simulated data were observed at low fluxes and diluted feed solutions due to limitations of the SKK model. This work provides insights into the mass transport mechanism of dye solutions and allows the prediction of dye rejection by the TFC membranes containing a TA-Fe3+ selective layer using an SKK model.

Molecular Design of the Polyamide Layer Structure of Nanofiltration Membranes by Sacrificing Hydrolyzable Groups toward Enhanced Separation Performance.

Nanofiltration (NF) is an effective technology for removing trace organic contaminants (TrOCs), while the inherent trade-off effect between water permeance and solute rejections hinders its widespread application in water treatment. Herein, we propose a novel scheme of "monomers with sacrificial groups" to regulate the microstructure of the polyamide active layer via introducing a hydrolyzable ester group onto piperazine to control the diffusion and interfacial polymerization process. The achieved benefits include narrowing the pore size, improving the interpore connectivity, enhancing the microporosity, and reducing the active layer thickness, which collectively realized the simultaneous improvement of water permeance and enhancement of TrOCs rejection performance. The resulting membranes were superior to both the control and commercial membranes, especially in water-TrOCs selectivity. The effects of using the new monomers on the membrane physicochemical properties were systematically studied, and underlying mechanisms for the enhanced separation performance were further revealed by simulating the polymerization process through density functional theory calculation and measuring the trans-interface diffusion rate of monomers. This study demonstrates a novel promising NF membrane synthesis strategy by designing the structure of reaction monomers for achieving excellent rejection of TrOCs with a low energy input in water treatment.

Enabling Solution Processable COFs through Suppression of Precipitation during Solvothermal Synthesis.

Covalent organic frameworks (COFs) are crystalline, nanoporous materials of interest for various applications, but current COF synthetic routes lead to insoluble aggregates which precludes processing for practical implementation. Here, we report a COF synthesis method that produces a stable, homogeneous suspension of crystalline COF nanoparticles that enables the preparation of COF monoliths, membranes, and films using conventional solution-processing techniques. Our approach involves the use of a polar solvent, diacid catalyst, and slow reagent mixing procedure at elevated temperatures which altogether enable access to crystalline COF nanoparticle suspension that does not aggregate or precipitate when kept at elevated temperatures. On cooling, the suspension undergoes a thermoreversible gelation transition to produce crystalline and highly porous COF materials. We further show that the modified synthesis approach is compatible with various COF chemistries, including both large- and small-pore imine COFs, hydrazone-linked COFs, and COFs with rhombic and hexagonal topologies, and in each case, we demonstrate that the final product has excellent crystallinity and porosity. The final materials contain both micro- and macropores, and the total porosity can be tuned through variation of sample annealing. Dynamic light scattering measurements reveal the presence of COF nanoparticles that grow with time at room temperature, transitioning from a homogeneous suspension to a gel. Finally, we prepare imine COF membranes and measure their rejection of polyethylene glycol (PEG) polymers and oligomers, and these measurements exhibit size-dependent rejection and adsorption of PEG solutes. This work demonstrates a versatile processing strategy to create crystalline and porous COF materials using solution-processing techniques and will greatly advance the development of COFs for various applications.

Complete parametric investigation of a forward osmosis process using sodium chloride draw solution

The design and operation of FO systems require accurate prediction of performance according to the operating parameters. Performance parameters such as water flux, reverse solute flux (RSF), specific reverse solute flux (SRSF), recovery and rejection are influenced by operating parameters including temperature, concentration difference (CD), and flow rates of feed solution (FS) and draw solution (DS). Whereas previous studies analysed the effect of only one or two operating parameters on one or two output parameters, this study provides a complete investigation into the effects of all operating parameters on all output parameters important for performance. A bench-scale FO setup using an advanced FO membrane and NaCl draw solution has been studied and compared to a predictive model, giving agreement within 10 %. Water flux and RSF increased with temperature, CD and flow rate. SRSF decreased with temperature, increased with CD, and increased as flow rates of FS and DS increased. Increasing temperature or CD increased the recovery; whereas increasing the flow rate of FS or DS reduced the recovery. Rejection dropped at higher CD and flow rates. Hence, it is recommended to operate at lower CD and flow rates to achieve higher recovery and rejection.

Can Hindered Transport Models for Rigid Spheres Predict the Rejection of Single Stranded DNA from Porous Membranes?

In this paper, predictions from a theoretical model describing the rejection of a rigid spherical solute from porous membranes are compared to experimental results for a single stranded DNA (ssDNA) with 60 thymine nucleotides. Experiments were conducted with different pore size track-etched membranes at different transmembrane pressures and different NaCl concentrations. The model includes both hydrodynamic and electrostatic solute-pore wall interactions; predictions were made using different size parameters for the ssDNA (radius of gyration, hydrodynamic radius, and root mean square end-to-end distance). At low transmembrane pressures, experimental results are in good agreement with rejection predictions made using the hard sphere model for the ssDNA when the solute size is described using its root mean square end-to-end distance. When the ssDNA size is characterized using the radius of gyration or the hydrodynamic radius, the hard sphere model under-predicts rejection. Not surprisingly, the model overestimates ssDNA rejection at conditions where flow induced elongation of the DNA is expected. The results from this study are encouraging because they mean that a relatively simple hindered transport model can be used to estimate the rejection of a small DNA from porous membranes.

Antibacterial studies of Ag@HPEI@GO nanocomposites and their effects on fouling and dye rejection in PES UF membranes

A series of polyethersulfone membranes containing Ag@HPEI@GO composite was fabricated using non-solvent induced phase separations (NIPS) to mitigate against biofilm causing bacteria and modulate solute rejection. All materials produced and used were fully characterised using a combination of appropriate physicochemical techniques including FTIR, XRD, BET, SEM, AFM. The GO-based fillers exhibited bactericidal activities. The bactericidal activities of GO, HPEI@GO against Escherichia Coli (E. coli) were observed at 8 mg mL−1 whilst Ag@HPEI@GO composites exhibit bactericidal activities against E. coli at 4 mg mL−1. Against Klebsiella pneumonia (K. pneumonia), GO bactericidal activities were observed at 8 mg mL−1, whilst HPEI@GO and Ag@HPEI@GO bactericidal activities on K. pneumonia were observed at 4 mg mL−1. Against Staphylococcus aureus (S. aureus), GO exhibit bactericidal activities at 8 mg mL−1, HPEI@GO and Ag@HPEI@GO composites exhibit bactericidal activities on S. aureus at 4 mg mL−1. The aforementioned microorganisms are among the microorganism that causes biofilm formation on surfaces. The membrane performance was assessed by measuring pure water flux, solute rejections and fouling propensity with three different organic dye molecules and bovine serum albumin (BSA). All composite membranes (GO/PES, HPEI@GO/PES, and Ag@HPEI@GO/PES) exhibited increased hydrophilicity and higher pure water flux compared to the baseline PES membranes with concomitant increase in fouling resistance, The observed flux recovery ratios (FRR) were 80% (GO/PES), 70% (HPEI@GO/PES) and 69% (Ag@HPEI@GO/PES) respectively compared to the 45% FRR observed for the baseline PES membrane after BSA fouling. Congo red (CR) used as an indicator for molecular cut-off of UF membranes was rejected above 95% by all nanocomposite membranes. Furthermore, the nanocomposite membranes-maintained rejection for the positively charged methylene blue (MB) of above 90% whilst rejection observed for amaranth (AR) dye decreased from 80 to 58% with increasing filler content in the PES matrix. The results demonstrate the positive influence of GO, HPEI@GO and Ag/HPEI@GO nanofillers on flux, fouling and solute rejection performance of resultant PES nanocomposite membranes.

Recovery of water and valuable metals using low pressure nanofiltration and sequential adsorption from acid mine drainage

Acid mine drainage (AMD) contains an array of valuable resources such as Rare Earth Elements (REE) and Copper (Cu) which can be recovered along with fresh water. Low pressure nanofiltration with NF90 membrane was first studied to recover fresh water from synthetic AMD and concentration of dissolved metals for subsequent efficient selective recovery. Organic matter (OM) present in AMD was found to cause membrane fouling which resulted in significant flux decline. Powdered eggshell was investigated as a low-cost adsorbent for OM removal. The study showed that a 0.2 mg/l dose of powdered eggshell adsorbed 100% of OM and Fe with no significant loss of other dissolved metals. A steady permeate flux of 15.5 ± 0.2 L/m 2 h (LMH) was achieved for pre-treated AMD with a solute rejection rate of more than 98%. A chromium-based metal organic framework (MOF) modified with N - (phosphonomethyl) iminodiacetic acid (PMIDA) and an amine-grafted mesoporous silica (SBA15) material was synthesized for selective recovery of REE and Cu, respectively. The two adsorbents were used sequentially to selectively adsorb REE (91%) and Cu (90%) from pH adjusted concentrated feed. The formation of coordinating complexes with carboxylate and phosphonic groups on MOF was found to be the primary driving force for selective REE adsorption. Selective uptake of Cu onto amine-grafted SBA15 was due to the formation of strong chelating bonds between Cu and amine ligands. Both adsorbents remained structurally stable over 5 regeneration cycles. The findings here highlight the practical potential of membrane/adsorption hybrid systems for water and valuable metal (REE) recovery from AMD. • Low pressure NF achieved 80% permeate recovery while concentrating dissolved ions. • Modified MOF and SBA15-NH 2 selectively adsorbed 91% of REE and 90% of Cu. • REE show high affinity to deprotonated phosphonic and carboxyl groups in MOF. • Chelating bonds between Cu and amine groups in SBA15 promotes high selectivity. • High reuse capacity over multiple cycles recorded for both adsorbents.

Tight UF membranes with ultrahigh water flux prepared by in-situ growing ZIF particles in NIPS process for greatly enhanced dye removal efficiency

Tight ultra-filtration (TUF) membranes with in-situ grown zeolitic imidazole framework (ZIF) particles embedded in and packed under porous polysulfone (PSF) separating layers were prepared using non-solvent induced phase separation (NIPS) processes. Imidazole ligands contained in casting solutions were released and reacted with divalent Zn2+ cations pre-loaded on non-woven fabric supporting layers. The capillary filling pore size and molecular-weight-cut-off (MWCO) Stokes solute rejection pore size of the formed ZIF/PSF TUF were tuned by varying the loading levels of Zn (II), polyvinylpyrrolidone (PVP) and imidazole, as well as the NIPS reaction time. With thinned PSF separating layer (200–500 nm) and embedding water permeating short-cuts from the ZIF particles, ZIF/PSF TUF membranes showed 7 times higher water permeance (up to 250 L/(m2 h bar)) and greatly enhanced dye/salt retention selectivity, bearing high potential for applications in dye and textile waste water treatment processes.

Prediction of single salt rejection in PES/CMS based membranes

This study explains the modeling of synthesized membranes using the Donnan Steric Pore model (DSPM) based on the Extended Nernst Planck Equation (ENP). Conventionally, structural parameters required to predict the performance of the membranes were determined through tedious experimentation, which in this study are found using a new MATLAB technique. A MATLAB program is used to determine the unknown structural parameters such as effective charge density (Xd), effective pore radius (rp), and effective membrane thickness to porosity ratio (Δx/Ak) by using the single solute rejection and permeation data. It was found that the model predicted the rejection of studied membranes accurately, with the E5C1 membrane exceeding the others (E5, E5C5) for rejection of single and divalent salt's aqueous solutions. The rejection of 100 ppm aqueous solution of NaCl for E5C1 was around 60%, whereas, for an aqueous solution of 100 ppm, CaCl2 rejection reached up to 80% at 10 bar feed pressure. The trend of salt rejection for all three membranes was found to be in the following order: E5C1 > E5C5 > E5, confirming that their structural parameters-controlled ion transport in these membranes. The structural parameters, such as effective pore radius, effective membrane thickness to porosity ratio, and effective charge density for the best performing membrane, i.e., E5C1, were determined to be 0.5 nm, 16 μm, and −6.04 mol/m3,respectively. Finally, it can be asserted that this method can be used to predict the real performance of membranes by significantly reducing the number of experiments previously required for the predictive modeling of nanofiltration-type membranes.

Controllable preparation of novel “ridge-valley shaped” poly(p-phenylene terephthamide) (PPTA) hollow fiber nanofiltration membrane for thermal dye/salt wastewater separation

In this study, two novel poly(p-phenylene terephthamide) (PPTA) hollow fiber composite nanofiltration (NF) membranes with excellent thermal stability and antifouling performance were synthesized on the homogeneous reinforced PPTA hollow fiber membranes by interfacial polymerization and the robust chemical vapor deposition separately. The effect of fabrication conditions, substrate properties on the NF performance was systematically investigated and optimized. Interestingly, SEM images presented that the two different composite membranes had relatively rough surfaces containing globular or striped structures, which was the same as the reported Turing-type structures. Meanwhile, the formation mechanism of the rough globular and striped morphologies on the surface of the membranes was also discussed. Moreover, both membranes were compared through filtration experiments such as permeate flux, solute rejection, heat stability, and anti-fouling property. The results presented that both membranes displayed high removal capacity for low molecular weight dyes (200–1000 Da), meanwhile, they exhibited high rejections (98.4 %) for negative dyes. However, they possessed complicated and diverse rejective behaviors for dye removal in different aqueous environments, such as diverse solute concentrations and diverse operating conditions. It was worth noting that PPTA/PA composite membrane showed higher separation efficiency, thermal stability, and antifouling performance compared to PPTA/PPy composite membrane, due to the significantly increased negative charge density and hydrophilicity on the membrane surface. Besides, this study offered new insights and strategies for exploring next-generation NF membranes for high temperature dye wastewater treatment.

Optimisation of design and operating parameters of reverse osmosis process for the removal of phenol from wastewater

Reverse Osmosis (RO) is widely used for separating organic and inorganic pollutants in wastewater. In this research, the one-dimensional steady state model of a spiral wound RO for the removal of phenol from wastewater, was simulated using gPROMS software to identify optimal design and operating parameters. The design parameters included the membrane length, width and feed spacer channel and operating conditions included temperature and pressure of the RO process. The optimal design parameters were able to maximise the removal of phenol from wastewater. The simulation results showed that the removal of phenol from wastewater was significantly influenced by the combination of membrane width, operating pressure, and feed temperature. The four main parameters (permeate concentration, solute flow, solute rejection, and water flux) that govern the performance of a reverse osmosis membrane were found to be influenced by the design and operating conditions.