Other affiliations: California NanoSystems Institute
Bio: Xiaofei Huang is an academic researcher from University of California, Los Angeles. The author has contributed to research in topics: Membrane & Fouling. The author has an hindex of 11, co-authored 12 publications receiving 2815 citations. Previous affiliations of Xiaofei Huang include California NanoSystems Institute.
TL;DR: In this article, a new concept for formation of mixed matrix reverse osmosis membranes by interfacial polymerization of nanocomposite thin films in situ on porous polysulfone supports is reported.
Abstract: Here, we report on a new concept for formation of mixed matrix reverse osmosis membranes by interfacial polymerization of nanocomposite thin films in situ on porous polysulfone supports. Nanocomposite films created for this study comprise NaA zeolite nanoparticles dispersed within 50–200 nm thick polyamide films. Hand-cast pure polyamide membranes exhibit surface morphologies characteristic of commercial polyamide RO membranes, whereas nanocomposite membranes have measurably smoother and more hydrophilic, negatively charged surfaces. At the highest nanoparticle loadings tested, hand-cast nanocomposite film morphology is visibly different and pure water permeability is nearly double that of hand-cast polyamide membranes with equivalent solute rejections. Comparison of membranes formed using pore-filled and pore-opened zeolites suggest nanoparticle pores play an active role in water permeation and solute rejection. The best performing nanocomposite membranes exhibit permeability and rejection characteristics comparable to commercial RO membranes. As a concept, thin film nanocomposite membrane technology may offer new degrees of freedom in tailoring RO membrane separation performance and material properties. © 2007 Elsevier B.V. All rights reserved.
TL;DR: In this paper, the impacts of organic solvent properties, reaction conditions, and curing conditions on polyamide composite reverse osmosis membrane separation performance, film structure, and interfacial properties are reported.
Abstract: Here we report on the impacts of organic solvent properties, reaction conditions, and curing conditions on polyamide composite reverse osmosis membrane separation performance, film structure, and interfacial properties. We provide direct experimental evidence that: (1) MPD diffusivity in the organic phase governs MPD–TMC thin film water permeability, (2) MPD diffusivity and solubility influence MPD–TMC thin film crosslinking in competing ways, (3) water permeability correlates most strongly with MPD–TMC film structure (i.e., crosslinking), and (4) salt rejection correlates most strongly with MPD–TMC film thickness and morphology. Overall, higher flux membranes with good salt rejection appear to comprise thinner, more heavily crosslinked film structures. Such high performance RO membranes are obtained by (1) selecting high surface tension, low viscosity solvents, (2) controlling protonation of MPD and hydrolysis of TMC during interfacial polymerization, and (3) optimizing curing temperature and time based on organic solvent volatility. Finally, although more research is necessary, our results suggest the rugose morphology and relative hydrophobicity of high performance MPD–TMC membranes might enhance concentration polarization and exacerbate surface fouling.
TL;DR: The data presented offer additional support for the hypothesis that zeolite crystals alter polyamide thin film structure when they are present during the interfacial polymerization reaction.
Abstract: Zeolite-polyamide thin film nanocomposite membranes were coated onto polysulfone ultrafiltration membranes by interfacial polymerization of amine and acid chloride monomers in the presence of Linde type A zeolite nanocrystals. A matrix of three different interfacial polymerization chemistries and three different-sized zeolite crystals produced nanocomposite thin films with widely varying structure, morphology, charge, hydrophilicity, and separation performance (evaluated as reverse osmosis membranes). Pure polyamide film properties were tuned by changing polymerization chemistry, but addition of zeolite nanoparticles produced even greater changes in separation performance, surface chemistry, and film morphology. For fixed polymer chemistry, addition of zeolite nanoparticles formed more permeable, negatively charged, and thicker polyamide films. Smaller zeolites produced greater permeability enhancements, but larger zeolites produced more favorable surface properties; hence, nanoparticle size may be considered an additional "degree of freedom" in designing thin film nanocomposite reverse osmosis membranes. The data presented offer additional support for the hypothesis that zeolite crystals alter polyamide thin film structure when they are present during the interfacial polymerization reaction.
TL;DR: These simple, but systematic studies--enabled by high-throughput screening--reveal the inherent complexity associated with understanding silver nanoparticle antibacterial efficacy as well as potential environmental impacts of silver nanoparticles.
Abstract: Although silver nanoparticles are being exploited widely in antimicrobial applications, the mechanisms underlying silver nanoparticle antimicrobial properties in environmentally relevant media are not fully understood. The latter point is critical for understanding potential environmental impacts of silver nanoparticles. The aim of this study was to elucidate the influence of inorganic aquatic chemistry on silver nanoparticle stability (aggregation, dissolution, reprecipitation) and bacterial viability. A synthetic “fresh water” matrix was prepared comprising various combinations of cations and anions while maintaining a fixed ionic strength. Aggregation and dissolution of silver nanoparticles was influenced by electrolyte composition; experimentally determined ionic silver concentrations were about half that predicted from a thermodynamic model and about 1000 times lower than the maximum dispersed silver nanoparticle concentration. Antibacterial activity of silver nanoparticles was much lower than Ag+ io...
TL;DR: A facile approach is presented for quantifying the impacts of specific ion interactions on aquatic colloid stability, aggregation, and deposition for seawater RO membrane fouling by alginic acid.
Abstract: Organic fouling plagues many environmental membrane processes. In this study, well-controlled laboratory experiments were performed to elucidate seawater RO membrane fouling by alginic acid. Interfacial free energies derived from multiple probe liquid contact angle analyses (including different seawater matrices) correlated strongly with the rates of membrane fouling. More importantly, the Lewis acid-base interfacial free energy quantitatively described the impacts of calcium-carboxylate complex formation and predicted membrane fouling and cleaning behavior. Calcium ions made polyamide composite RO membranes (and alginic acid) more hydrophobic, enhanced the rate and extent of flux decline, and reduced the effectiveness of chemical cleaning. The implications for seawater RO membrane fouling are clear. Selective removal of calcium ions via pretreatment can reduce the gel forming ability of carboxylate rich biomacromolecules and, hence, the extent to which they foul RO membranes. In addition, RO membranes should be produced with smooth, hydrophilic interfaces comprising monopolar electron-donor functionality and no carboxylic acid residue. More broadly, this paper presents a facile approach for quantifying the impacts of specific ion interactions on aquatic colloid stability, aggregation, and deposition.
TL;DR: A review of the antibacterial effects of silver nanomaterials, including proposed antibacterial mechanisms and possible toxicity to higher organisms, is presented in this paper, where the authors suggest that further research is warranted given the already widespread and rapidly growing use of silver nanoparticles.
Abstract: Here, we present a review of the antibacterial effects of silver nanomaterials, including proposed antibacterial mechanisms and possible toxicity to higher organisms. For purpose of this review, silver nanomaterials include silver nanoparticles, stabilized silver salts, silver–dendrimer, polymer and metal oxide composites, and silver-impregnated zeolite and activated carbon materials. While there is some evidence that silver nanoparticles can directly damage bacteria cell membranes, silver nanomaterials appear to exert bacteriocidal activity predominantly through release of silver ions followed (individually or in combination) by increased membrane permeability, loss of the proton motive force, inducing de-energization of the cells and efflux of phosphate, leakage of cellular content, and disruption DNA replication. Eukaryotic cells could be similarly impacted by most of these mechanisms and, indeed, a small but growing body of literature supports this concern. Most antimicrobial studies are performed in simple aquatic media or cell culture media without proper characterization of silver nanomaterial stability (aggregation, dissolution, and re-precipitation). Silver nanoparticle stability is governed by particle size, shape, and capping agents as well as solution pH, ionic strength, specific ions and ligands, and organic macromolecules—all of which influence silver nanoparticle stability and bioavailability. Although none of the studies reviewed definitively proved any immediate impacts to human health or the environment by a silver nanomaterial containing product, the entirety of the science reviewed suggests some caution and further research are warranted given the already widespread and rapidly growing use of silver nanomaterials.
TL;DR: Recent development in nanotechnology for water and wastewater treatment is reviewed, covering candidate nanomaterials, properties and mechanisms that enable the applications, advantages and limitations as compared to existing processes, and barriers and research needs for commercialization.
Abstract: Providing clean and affordable water to meet human needs is a grand challenge of the 21st century. Worldwide, water supply struggles to keep up with the fast growing demand, which is exacerbated by population growth, global climate change, and water quality deterioration. The need for technological innovation to enable integrated water management cannot be overstated. Nanotechnology holds great potential in advancing water and wastewater treatment to improve treatment efficiency as well as to augment water supply through safe use of unconventional water sources. Here we review recent development in nanotechnology for water and wastewater treatment. The discussion covers candidate nanomaterials, properties and mechanisms that enable the applications, advantages and limitations as compared to existing processes, and barriers and research needs for commercialization. By tracing these technological advances to the physicochemical properties of nanomaterials, the present review outlines the opportunities and limitations to further capitalize on these unique properties for sustainable water management.
TL;DR: In this article, a semi-quantitative ranking system was proposed considering projected performance enhancement (over state-of-the-art analogs) and state of commercial readiness, while commercial readiness was based on known or anticipated material costs.
Abstract: Nanotechnology is being used to enhance conventional ceramic and polymeric water treatment membrane materials through various avenues. Among the numerous concepts proposed, the most promising to date include zeolitic and catalytic nanoparticle coated ceramic membranes, hybrid inorganic–organic nanocomposite membranes, and bio-inspired membranes such as hybrid protein–polymer biomimetic membranes, aligned nanotube membranes, and isoporous block copolymer membranes. A semi-quantitative ranking system was proposed considering projected performance enhancement (over state-of-the-art analogs) and state of commercial readiness. Performance enhancement was based on water permeability, solute selectivity, and operational robustness, while commercial readiness was based on known or anticipated material costs, scalability (for large scale water treatment applications), and compatibility with existing manufacturing infrastructure. Overall, bio-inspired membranes are farthest from commercial reality, but offer the most promise for performance enhancements; however, nanocomposite membranes offering significant performance enhancements are already commercially available. Zeolitic and catalytic membranes appear reasonably far from commercial reality and offer small to moderate performance enhancements. The ranking of each membrane nanotechnology is discussed along with the key commercialization hurdles for each membrane nanotechnology.
TL;DR: A review of the development of reverse osmosis (RO) membrane materials can be found in this paper, where an overview of RO performance in relation to membrane materials and methods of synthesis is provided.
Abstract: 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.