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Tailored design of high-performance nanofiltration (NF) membranes is desirable because the requirements for membrane performance, particularly ion/salt rejection and selectivity, differ among the various applications of NF technology ranging from drinking water production to resource mining. However, this customization greatly relies on a comprehensive understanding of the influence of membrane fabrication methods and conditions on membrane properties and the relationships between the membrane structural and physicochemical properties and membrane performance. Since the inception of NF, much progress has been made in forming the foundation of tailored design of NF membranes and the underlying governing principles. This progress includes theories regarding NF mass transfer and solute rejection, further exploitation of the classical interfacial polymerization technique, and development of novel materials and membrane fabrication methods. In this critical review, we first summarize the progress made in controllable design of NF membrane properties in recent years from the perspective of optimizing interfacial polymerization techniques and adopting new manufacturing processes and materials. We then discuss the property-performance relationships based on solvent/solute mass transfer theories and mathematical models, and draw conclusions on membrane structural and physicochemical parameter regulation by modifying the fabrication process to improve membrane separation performance. Next, existing and potential applications of these NF membranes in water treatment processes are systematically discussed according to the different separation requirements. Finally, we point out the prospects and challenges of tailored design of NF membranes for water treatment applications. This review bridges the long-existing gaps between the pressing demand for suitable NF membranes from the industrial community and the surge of publications by the scientific community in recent years.

We discuss a recent publication in Energy & Environmental Science that presented a techno-economic analysis of electrochemical water desalination technologies.

Within the last decade, in addition to water desalination, capacitive deionization (CDI) has been used for resource recovery and selective separation of target ions in multicomponent solutions. In this review, we summarize the mechanisms of selective ion removal utilizing different electrode materials, carbon and non-carbon together with or without membranes, from a mixture of salt solutions, by a detailed review of the literature from the beginning until the state-of-the-art. In this venture, we review the advances made in the preparation, theoretical understanding, and the role of electrodes and membranes. We also describe how ion selectivity has been defined and used in literature. Finally, we present a theory of selective ion removal for intercalation materials that, for the first time, considers mixtures of different cations, evidencing the time-dependent selectivity of these electrodes.

Membrane desalination is a promising technology for addressing the global challenge of water scarcity by augmenting fresh water supply. Continuous progress in this technology relies on development of membrane materials. The state-of-the-art membranes used in a wide range of desalination applications are polyamide thin-film composite (TFC) membranes which are formed by interfacial polymerization (IP). Despite the wide use of such membranes in desalination, their real-world application is still hampered by several technical obstacles. These challenges of the TFC membranes largely stem from the inherent limitations of the polyamide chemistry, as well as the IP reaction mechanisms. In the past decade, we have witnessed substantial progress in the understanding of polyamide formation mechanisms and the development of new IP strategies that can potentially lead to the redesign of TFC membranes. In this Tutorial, we first present a brief history of the development of desalination membranes and highlight the major challenges of the existing TFC membranes. We then proceed to discuss the pros and cons of emerging IP-based fabrication strategies aiming at improving the performance of TFC membranes. Next, we present technical obstacles and recent efforts in the characterization of TFC membranes to enable fundamental understanding of relevant mechanisms. We conclude with a discussion of the current gap between industrial needs and academic research in designing high-performance TFC membranes, and provide an outlook on future research directions for advancing IP-based fabrication processes.

As the threat of global water scarcity continues to grow, a myriad of scientific effort is directed towards advancing water desalination technologies. Reverse osmosis (RO), solar thermal desalination (STD), and capacitive deionization (CDI), have dominated recent pressure-, thermal-, and electro-driven desalination research efforts, respectively. Despite being based on distinctive driving forces and separation mechanisms, research of these three processes has primarily shared the same fundamental goal and approach: the minimization of energy consumption for desalination through the development of novel materials. A variety of materials have been studied and proposed to enhance RO membrane permeability, STD solar absorptivity, and CDI electrode capacitance. Here, we critically discuss the advanced materials investigated and assess their efficacy in augmenting the energy efficiency of desalination. Through our systematic analysis, we show that materials have relatively insignificant impact on further increasing energy efficiency, regardless of the process applied. We provide insights into the inherent limitations of advanced materials for improving the energy efficiency of each of the evaluated technologies and propose more effective materials-based research directions. We conclude by highlighting the opportunity for considerable improvement in energy efficiency via system design, reinforcing the critical need for a paradigm shift in desalination research.

Currently, over a billion people around the world lack access to clean drinking water, industrial wastewater treatment and reuse is limited, and conventional water treatment systems cannot adequately treat all contaminants of concern. Nanotechnology-enabled water treatment (NWT) has begun to emerge as a viable option to address many of the problems facing the water treatment status quo, either through cost reducing performance enhancements or filling unmet niches. Advancements in fundamental nanoscience allow unprecedented use of catalysis and energy from across the broad electromagnetic spectrum, as well as unique physicochemical properties, to purify drinking water, treat industrial wastewater, and access unconventional water supplies. However, before fully adopting NWT, it is imperative that the devices are both safe and sustainable, enhancing acceptance from consumers, government, non-government organizations, and industry. We suggest that we are in a unique window of time to “do nano right” by making key sustainability considerations very early in nano-water technology development. To this end, we have developed a framework based on three guiding research questions aimed at understanding the breadth of sustainability considerations for NWT at each of the four major life cycle stages – extraction, production, use, and end-of-life. In following this framework, researchers and product developers can design nano-enabled water treatment devices that perform well and are both safe and sustainable. By presenting the current state of sustainable NWT and specifying gaps in the literature, the present review aims to further develop NWT to be the best alternative to conventional water treatment across a variety of sectors.

Microbial contamination and biofilm formation present major challenges in numerous applications. Many types of nanoparticles possess high antibacterial activity and thus are being investigated to combat environmental microbial contamination, limit bacterial deposition, and inhibit or destroy biofilms. In addition to finding nanoparticles with high and broad antibacterial activity, the synthesis of nanoparticles must also be sustainable and the nanoparticles should have low toxicity and low environmental impact. In this study, we developed a simple one-step probe sonication method to synthesize a ZnO nanoparticle functionalized reduced graphene oxide (rGO–ZnO) nanocomposite by exfoliating oxidized graphite in the presence of Zn2+. The antibacterial activity of the nanocomposite was higher than that of graphene oxide (GO) and rGO against Gram-negative (Escherichia coli and Serratia marcescens) and Gram-positive (Bacillus subtilis) bacteria. Direct intracellular reactive oxygen species (ROS) and Zn2+ leaching measurements indicated that the high antibacterial activity against different bacteria of the nanocomposite arises from the formation of ROS, whereas the effect of Zn2+ is negligible. Furthermore, incorporating rGO–ZnO nanocomposite into a polyethersulfone (PES) membrane inhibited biofilm growth compared with a pristine PES membrane. Leaching experiments of Zn2+ from the incorporated rGO–ZnO membrane during synthetic wastewater filtration revealed that Zn2+ concentration in the effluent was below the environmental standards for potable and non-potable uses. Our research presents an effective, fast, and low-cost preparation method for developing nanocomposites with high antimicrobial activities. Also, it shows that a nanocomposite incorporated polymeric membrane can be safely applied for water and wastewater treatment with minimum environmental impact.

Low-grade heat from geothermal sources and industrial plants is a significant source of sustainable power that has great potential to be converted to electricity. The two main approaches that have been extensively investigated for converting low-grade heat to electrical energy, organic Rankine cycles and solid-state thermoelectrics, have not produced high power densities or been cost-effective for such applications. Newer, alternative liquid-based technologies are being developed that can be categorized by how the heat is used. Thermoelectrochemical cells (TECs), thermo-osmotic energy conversion (TOEC) systems, and thermally regenerative electrochemical cycles (TRECs) all use low-grade heat directly in a device that generates electricity. Other systems use heat sources to prepare solutions that are used in separate devices to produce electrical power. For example, low-temperature distillation methods can be used to produce solutions with large salinity differences to generate power using membrane-based systems, such as pressure-retarded osmosis (PRO) or reverse electrodialysis (RED); or highly concentrated ammonia solutions can be prepared for use in thermally regenerative batteries (TRBs). Among all these technologies, TRECs, TOEC, and TRBs show the most promise for effectively converting low-grade heat into electrical power mainly due to their high power productions and energy conversion efficiencies.

Waterborne pathogens are a major health threat and must be eliminated to guarantee safe usage of water for potable purposes. For this purpose, a new carbon-based nanomaterial composed of single-walled carbon nanotubes (SWCNTs) and iron oxides was constructed for bacterial inactivation. Owing to its magnetic properties, the SWCNT–iron oxide nanocomposite may serve as a reusable antimicrobial agent. The nanocomposite material exhibited high antimicrobial activity against Escherichia coli. Successful reuse of the nanocomposite material was achieved by washing with calcium chloride and distilled water, which restored its performance for several successive cycles. To investigate the cytotoxicity mechanisms of the nanocomposite material, we exposed it to single-gene knockout mutant strains of E. coli. Mutants bearing shorter lipopolysaccharide (LPS) layers in the outer membrane (ΔrfaC and ΔrfaG) demonstrated an increased sensitivity in comparison to the wildtype strain, exemplified in enhanced removal by the nanocomposite material. This finding suggests that the LPS acts as a protective shield against the nanocomposite material. Inactivation of mutants impaired in specific oxidative stress defense mechanisms (ΔsodA, ΔkatG and ΔsoxS) emphasized that oxidative stress plays a significant role in the inactivation mechanism of the nanocomposite. This study sheds light on the mechanisms of bacterial inactivation by carbon-based nanomaterials and advances their potential implementation for water disinfection.

Exploring non-precious-metal catalysts (NPMCs) for highly-efficient oxygen reduction reactions (ORRs) in fuel cells holds great potential to ease the global energy challenge. Recent developments regarding state-of-the-art Fe–N–C catalysts in terms of precursor development, synthesis innovation, and active site identification are compelling. Here, an efficient and sustainable Fe–N–C catalyst was successfully synthesized by temperature-programmed N2-pyrolysis from a ferrous ethylenediaminetetraacetic acid (EDTA) chelate. The unique structural properties were characterized by a wide existence of FeN4/C species encapsulated by a N–C coat, multiple porous morphologies, and a defective graphitic matrix, all of which greatly enhanced their intrinsic conductivities and prevented the aggregation of active moieties. The best Fe–N–C–800 catalysts promoted the ORR peak potential to −0.21 V with a nearly four-electron transfer pathway, only facilitating ∼14% H2O2 production. Both the Mossbauer fingerprints and X-ray absorption near edge structure (XANES) analysis revealed the origin of the ORR features derived from the structural compositions and corresponding hyperfine interaction. Interestingly, the embedding of oxygen in the Fe–N–C structure was found favorable for boosting durability and methanol endurance, which also hints at a strategy for rationally designing and producing promising ORR electrocatalysts from proper approaches and precursors.

The enormous potential of harvesting energy from salinity gradients has been discussed for decades, and pressure-retarded osmosis (PRO) is being increasingly investigated as a method to extract this energy. Despite advancements in membranes and system components, questions still remain regarding the overall viability of the PRO process. Here, we review PRO focusing on the net energy extractable and the ultimate feasibility of the most widely explored configurations. We define the maximum energy that can be obtained from the process, quantify losses and energetic costs that will reduce the net extractable energy, and explain how membrane modules can be improved. We then explore the potential of three configurations of PRO: systems designed to control mixing where rivers meet the sea, power plants that utilize the high concentration gradients available from hypersaline solutions, and PRO systems incorporated into reverse osmosis desalination plants to reduce electricity requirements. We conclude by considering the overall outlook of the process and identifying the most pressing challenges for future research.

One of the greatest challenges to the sustainability of modern society is an inadequate supply of clean water. Due to its energy-saving and cost-effective features, membrane technology has become an indispensable platform technology for water purification, including seawater and brackish water desalination as well as municipal or industrial wastewater treatment. However, membrane fouling, which arises from the nonspecific interaction between membrane surface and foulants, significantly impedes the efficient application of membrane technology. Preparing antifouling membranes is a fundamental strategy to deal with pervasive fouling problems from a variety of foulants. In recent years, major advancements have been made in membrane preparation techniques and in elucidating the antifouling mechanisms of membrane processes, including ultrafiltration, nanofiltration, reverse osmosis and forward osmosis. This review will first introduce the major foulants and the principal mechanisms of membrane fouling, and then highlight the development, current status and future prospects of antifouling membranes, including antifouling strategies, preparation techniques and practical applications. In particular, the strategies and mechanisms for antifouling membranes, including passive fouling resistance and fouling release, active off-surface and on-surface strategies, will be proposed and discussed extensively.

When repulsive colloidal interactions are involved, calculating the rate of particle deposition becomes particularly difficult. To overcome the difficulty, a new (constant migration flux) boundary condition and a sophisticated numerical procedure are introduced. With these procedures, smooth solutions of the equation are obtained for the entire domain, including the region beyond the energy barrier adjacent to the collector surface. Numerical calculations demonstrate that the dependence of particle deposition rate on flow velocity is quite different from that reported previously. The difficulty of using the ‘perfect-sink’ boundary condition in numerical solutions and the inadequacy of previous numerical methods are discussed.

A novel theory is developed for concentration polarization of non-interacting particles in crossflow-filtration systems. This theory reveals that the extent of concentration polarization, as well as the behaviour of the permeate flux, are characterized by an important dimensionless filtration number (NF= 4πa3pΔP/3kT). There is a critical value of the filtration number for a given suspension and operational conditions. When the filtration number is smaller than the critical value, a polarization layer exists directly over the membrane surface and the wall particle concentration is determined by the pressure and temperature. At higher filtration numbers, a cake layer of retained particles forms between the polarization layer and the membrane surface. Mathematical models are constructed for both cases and analytical solutions for the permeate flux are derived. An increase in permeate flux with increasing pressure is predicted for all operational conditions.

Collision efficiencies of latex colloids with glass surfaces have been determined experimentally. An anomalous decrease of collision efficiencies with increasing electrolyte concentration at high ionic strengths was observed. The results provide indirect evidence for the presence of repulsive hydration forces.