Polyamine nanofiltration membranes have a high stability at extreme pH conditions. In contrast to polyamides, polyamines do not contain the carbonyl group that is susceptible to nucleophilic attack. A previous study has shown that polyamine membranes can be prepared from the interfacial polymerization reaction of polyethylenimine and cyanuric chloride, and that indeed these membranes have a high resistance towards hydrolysis. In the present study, the potential of a variety of other multifunctional amine / cyanuric chloride combinations is screened for the formation of stable polyamine nanofiltration membranes. For several traditional amine precursors it is found that the moderate reactivity of the cyanuric chloride hampers the formation of thin selective membrane films. For two linear amine monomers, both of which are precursors to polyethylenimine, the formation of well-defined, thin, stable, and selective polyamine films is observed. In particular, diethylene triamine is identified as a suitable monomer for the interfacial reaction. The membranes derived from this amine have a higher salt rejection and water permeability as compared to the previously studied polyethylenimine based membranes, and show a comparably high stability at extreme pH conditions. Cross-flow filtration of different salts and neutral solutes at different pH indicates that both steric effects as well as Donnan exclusion effects are relevant for the rejection of solutes. The membrane skin layer is very dense at neutral pH (MWCO of about 200Da), and becomes slightly more open at extreme alkaline conditions.

In this work polyamine membranes are presented that are prepared by the interfacial polymerisation of polyethylenimine and cyanuric chloride on porous polyethersulfone supports. The thin film composite polyamine membranes have superior pH stability as compared to conventional polyamide membranes that are derived from polyethylenimine and trimesoyl chloride. The polyamine membranes show exceptionally strong resistance towards nucleophilic attack induced by extreme pH conditions. This is verified by the stable salt rejection and molecular weight cut off performance after five weeks of treatments at pH=1 and pH=13. The polyamine membranes exhibit a persisting separation performance over this entire pH range, whereas hydrolysis of the conventional polyamide membranes at high pH conditions causes a tremendous drop in their salt rejection. Their isoelectric points of both the polyamide and polyamine membranes are around pH=7.5. The polyamine membrane is tighter. It has a fivefold lower permeance as compared to the polyamide membrane, and a sodium chloride rejection of 65%, exceeding that of the polyamide by ~10%.

Water treatment is one of the main battlegrounds in the world's effort to reduce greenhouse gas emission and global warming: ever greater amounts of energy are required in developed countries to treat water to ever increasing quality standards; wastewater treatment and sea-water desalination plants are often out of reach of those developing countries that need it the most, due to high energy and capital requirements. In this opinion paper we argue that nanotube membranes have the potential to change this dynamic by lowering overall costs of filtration processes. We discuss current limitations and the latest developments toward commercialization of this technology.

Since their discovery, carbon nanotubes have been considered as a potential material for filtration applications due to low tortuosity, smooth structure and the possibility of fine tuning their diameter. Measurements of fluid flow in nanotubes, with diameters ranging from 0.6 to 100nm dramatically raised interest in them, with very high water flow rates promising to deliver orders-of-magnitude higher performance compared to other membranes. This promise was based on reports of flow enhancement, defined as a ratio of the measured flow compared to a no-slip Poiseuille flow, ranging from 10 to 100,000 with the underlying assumption that commercial membranes would exhibit the no-slip behavior. The concept of flow enhancement, though, is of little help for actual filtration applications where one is interested in a membrane׳s performance in terms of selectivity and permeability. In this work, the flow enhancement and permeability of UF carbon nanotube–anodic alumina membranes (CNT–AAM) with a large range of diameters is reported. Using a recently developed model, it is shown that the permeability is directly related to the solid–liquid molecular interactions between the liquid and the nanotubes. Finally, the performance of these CNT membranes and others in the literature has been analyzed in terms of permeability, comparing them to commercial membranes in the RO, NF and UF ranges. Results show that in fact, carbon nanotube membranes have a higher pure water permeability than commercial polymer membranes.

With a large number of experimental and modelling papers reporting higher than expected liquid flow rates in both hydrophobic and hydrophilic nanochannels published in the last few years, there is a need to develop a coherent theoretical framework to explain these phenomena. In this work we will introduce a complete modelling and present a comparison between experimental data and predicted flows, showing good agreement.

Tubular anodic alumina membranes, containing self-ordered and circular pores below 100 nm, were used to produce sunflower oil in water emulsions. Span 80 and Tween 20 were used as surfactants in the dispersed phase and continuous phase, respectively. Both dead-end and cross-flow processes were investigated. Membrane pore diameter and cross-flow velocity dominated the final droplet size. The droplet size yielded was consistently in the nanometer range and exhibited low polydispersity (<0.2). In particular, the smallest average droplet size range of approximately 120 nm was obtained when a 25 nm membrane was used in a cross-flow configuration. Models developed for micrometer-sized emulsions produced an overestimation of the nanoemulsion droplets in this work of up to 180 times. A modified version of the model developed by Peng and Williams is proposed here with good agreement for nanometer-sized emulsion droplets.

Tubular alumina membranes exhibiting symmetric and asymmetric morphology were fabricated via electrochemical anodization of aluminium and studied for ultrafiltration application. By controlling the anodization conditions, the pore structure can be precisely controlled at the nanometre scale. Via reduction of the anodization voltage in a sudden or gradual manner, two types of asymmetric cross-section morphologies were obtained. The membranes were characterized by MWCO, pure water permeability, bovine serum albumin (BSA) rejection and fouling tests. The breakdown of linear relationship between anodization voltage and pore diameter was observed for anodization below 10V. The selectivity-permeability analysis was compared to the framework developed by Metha and Zydney (JMS, 2005). The analysis shows the asymmetric membranes still suffering from low permeability despite providing good rejection properties. Most of the resistance to water permeability is, however, contributed by the thickness of the support layer of the membranes. The flux decline during BSA filtration can be modelled using combined complete pore blocking–cake filtration model. Although the membranes show good rejection performance and potential for scale-up application by fabrication in tubular form, further improvement in permeability and fouling mitigation could be achieved by developing a more porous support layer and surface modification.

This paper investigates the effect of surface structure and chemistry on the wetting properties of nanostructured porous anodic alumina (PAA). Measurements of the equilibrium apparent contact angle (APCA) were first taken on as produced hydrophilic nanoporous alumina with a range of pore diameters from 10 to 170 nm, yielding a range of contact angles from 10 to 100°. The PAAs were then coated with a fluorosilane to change the surface chemistry of the nanostructures. The same trend was observed as in the hydrophilic case, but the contact angles increased from 106 to 150° for pores sizes ranging from 10 to 100 nm for the hydrophobic PAA. These results probe the limits of the current wetting models such as the Cassie-Baxter and Wenzel equations for nanostructured materials. A geometric model has been developed using the equation proposed by Marmur to explain the wetting properties of the bareand silanized-PAA.

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All published reports on fluid flow enhancement and water slippage are associated with hydrophobic surfaces, such as carbon nanotubes. Here, we investigate water flow in hydrophilic alumina nanochannels with diameters ranging from 20 nm to 100 nm. For the smallest channels tested, the water permeability is more than double than the theoretical prediction using the Hagen-Poiseuille equation. Though such an enhancement is significantly smaller than what has been measured in carbon nanotubes, it clearly shows that flow enhancement and water slippage occurs on hydrophilic surfaces as well, contrary to existing theoretical models. To the authors' knowledge, it is the first experimental demonstration of water slippage on hydrophilic surfaces. The results show the dependence of the flow enhancement on the surface chemistry, diameter and length of the nanochannel.

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Reverse osmosis (RO) is currently the most important desalination technology and it is experiencing significant growth. The objective of this paper is to review the historical and current development of RO membrane materials which are the key determinants of separation performance and water productivity, and hence to define performance targets for those who are developing new RO membrane materials. The chemistry, synthesis mechanism(s) and desalination performance of various RO membranes are discussed from the point of view of membrane materials science. The review starts with the first generation of asymmetric polymeric membranes and finishes with current proposals for nano-structured membrane materials. The paper provides an overview of RO performance in relation to membrane materials and methods of synthesis. To date polymeric membranes have dominated the RO desalination industry. From the late 1950s to the 1980s the research effort focussed on the search for optimum polymeric membrane materials. In subsequent decades the performance of RO membranes has been optimised via control of membrane formation reactions, and the use of poly-condensation catalysts and additives. The performance of state-of-the-art RO membranes has been highlighted. Nevertheless, the advances in membrane permselectivity in the past decade has been relatively slow, and membrane fouling remains a severe problem. The emergence of nano-technology in membrane materials science could offer an attractive alternative to polymeric materials. Hence nano-structured membranes are discussed in this review including zeolite membranes, thin film nano-composite membranes, carbon nano-tube membranes, and biomimetic membranes. It is proposed that these novel materials represent the most likely opportunities for enhanced RO desalination performance in the future, but that a number of challenges remain with regard to their practical implementation. (C) 2010 Elsevier B.V. All rights reserved.

Boron is extensively used in the ceramic industry for enhancing mechanical strength of the tiles. The discharge of boron containing wastewater to the environment causes severe pollution problems. Boron is also dangerous for human consumption and causes organisms' reproductive impediments if the safe intake level is exceeded. Current methods to remove boron include ion-exchange, membrane filtration, precipitation-coagulation, biological and chemical treatment. These methods are costly to remove boron from the wastewater and hence infeasible for industrial wastewater treatment. In the present research, adsorption-flocculation mechanism is proposed for boron removal from ceramic wastewater by using Palm Oil Mill Boiler (POMB) bottom ash and long chain polymer or flocculant. Ceramic wastewater is turbid and milky in color which contains 15 mg/L of boron and 2000 mg/L of suspended solids. The optimum operating conditions for boron adsorption on POMB bottom ash and flocculation using polymer were investigated in the present research. Adsorption isotherm of boron on bottom ash was also investigated to evaluate the adsorption capacity. Adsorption isotherm modeling was conducted based on Langmuir and Freundlich isotherms. The results show that coarse POMB bottom ash with particle size larger than 2 mm is a suitable adsorbent where boron is removed up to 80% under the optimum conditions (pH=8.0, dosage=40 g bottom ash/300 ml wastewater, residence time=1h). The results also show that KP 1200 B cationic polymer is effective in flocculating the suspended solids while AP 120 C anionic polymer is effective in flocculating the bottom ash. The combined cationic and anionic polymers are able to clarify the ceramic wastewater under the optimum conditions (dosage of KP 1200 B cationic polymer=100 mg/L, dosage of AP 120 C anionic polymer=50 mg/L, mixing speed=200 rpm). Under the optimum operating conditions, the boron and suspended solids concentration of the treated wastewater were reduced to 3 mg/L and 5 mg/L respectively, satisfying the discharge requirement by Malaysia Department of Environment (DOE). The modeling study shows that the adsorption isotherm of boron onto POMB bottom ash conformed to the Freundlich Isotherm. The proposed method is suitable for boron removal in ceramic wastewater especially in regions where POMB bottom ash is abundant.