One of the key challenges in separation science is the lack of precise ion separation methods and mechanistic understanding crucial for efficiently recovering critical materials from complex aqueous matrices. Herein, first‐principles electronic structure calculations and in situ Raman spectroscopy are studied to elucidate the factors governing ion discrimination in an adsorptive membrane specifically designed for transition metal ion separation. Density functional theory calculations and in situ Raman data jointly reveal the thermodynamically favorable binding preferences and detailed adsorption mechanisms for competing ions. How membrane binding preferences correlate with the electronic properties of ligands is explored, such as orbital hybridization and electron localization. The findings underscore the importance of the phenolate group in oxime ligands for achieving high selectivity among competing transition metal ions. In‐depth understanding on which specific atomistic site within the microenvironment of metal‐ligand binding pockets governs the ion discrimination behaviors of the host will build a solid foundation to guide the rational design of next‐generation materials for precision separation essential for energy technologies and environment remediation. In tandem, synthetic controllability is demonstrated to transform 3D micrometer‐scale crystals to a 2D crystalline selective layer in membranes, paving the way for more precise and sustainable advances in separation science.

In this study, a novel fluidized-bed homogeneous granulation (FBHo-G) process was developed to recover lithium (Li) from industrial Li-impacted wastewater. Five important operational variables (i.e., temperatures, pH, [P]0/[Li]0 molar ratios, surface loadings, and up-flow velocities (Umf)) were selected to optimize the Li recovery (TR%) and granulation ratio (GR%) efficiencies of the process. The optimal operational conditions were determined as the following: a temperature of 75 °C, pH of 11.5, [P]0/[Li]0 of 0.5, surface loading of 2.5 kg/m2·h, and Umf of 35.7 m/h). The TR% and GR% at optimal condition could be as much as 90%. The material characterization of the recovery pellet products showed that they were highly crystallized Li3PO4 (purity ~88.2%). The pellets had a round shape and smooth surface with an average size of 0.65 mm, so could easily be stored and transported. The high purity enables them to be further directly reused as raw materials for a wide range of industrial applications (e.g., in the synthesis of cathode materials). Our calculation shows that the FBHo-G process could recover up to 0.1845 kg of lithium per cubic meter of Li-containing wastewater, at a recovery rate of ~90%. A brief technoeconomic analysis shows that FBHG process had economic viability, with an estimate production cost of USD 26/kg Li removed, while the potential gained profit for selling lithium phosphate pellets could be up to USD 48 per the same volume of wastewater and the net profit up to USD 22/m3 Li treated. In all, fluidized-bed homogeneous granulation, a seedless one-step recovery process, opens a promising pathway toward a green and sustainable recycling industry for the recovery and application of the resource-limited lithium element from nonconventional water sources.

Despite the fact that the PSf-b-PEG block copolymer membrane has been widely recognized in literature, the function of PEG block on the membrane formation and rejection capacity has not been fully understood. In this work, we examined the role of PEG blocks with different molecular weight (MW) of 400 Da, 2000 Da, and 6000 Da on the pore structure and separation properties of PSf-b-PEG membrane. Results show that the MW of hydrophilic PEG segments posed significant effects on the PSf-b-PEG membranes’ morphologies, mechanical, and surface properties. PEG blocks with higher MW tend to make membranes with bigger pore size, thinner top skin layer with higher porosity. A linear relationship between the MW of PEG in PSf-b-PEG with either the MWCO or effective membrane pore size suggested the membrane pores can be readily fine-tuned with the length of PEG block polymer. While the PSf-b-PEG400 membrane feature a precise and uniform pore size distribution centered at 2.5 nm, more broad and diverse membrane pore size was observed for the PSf-b-PEG6000 membrane. Regardless of PEG MW, all PSf-b-PEG membranes consistently displayed outstanding separation efficiency as evidenced the rejection rates > 92% for dye Congo Red (CR). Of those considered membrane, PSf-b-PEG2000 outperform the reported polymeric membranes in terms of super-high water permeance (266 LMH/bar) and a high dye rejection (99.1% towards CR), suggesting their high potential for practical applications.

Temperature-swing solvent extraction (TSSE) is a cost-effective, simple, versatile, and industry-ready technology platform capable of desalinating hypersaline brines toward zero liquid discharge. In this work, we demonstrate the potential of TSSE in the effective removal of selenium oxyanions and traces of mercury with the coexistence of high contents of chloride and sulfate often encountered in flue gas desulfurization wastewater streams. We compare the rejection performance of the two common solvents broadly used for TSSE, decanoic acid (DA) and diisopropylamine (DPA), and correlate those with the solvent physicochemical properties (e.g., dielectric constant, polarity, molecular bulkiness, and hydrophobicity) and ionic properties (e.g., hydrated radii and H-bonding). The results show that TSSE can remove >99.5% of selenium oxyanions and 96%-99.6% of mercury traces coexisting with sulfate (at a sixfold Se concentration) and chloride (at a 400-fold Se concentration) in a synthetic wastewater stream. Compared to diisopropylamine, decanoic acid is more effective in rejecting ions for all cases, ranging from a simple binary system to more complex multicomponent systems with highly varied ionic concentrations. Furthermore, the H-bonding interaction with water and the hydrated radii of the oxyanions (i.e., selenate vs. selenite) along with the hindrance effects caused by the molecular bulkiness and hydrophobicity (or lipophilicity) of the solvents play important roles in the favorable rejection of TSSE. This study shows that TSSE might provide a technological solution with a high deionization potential for the industry in complying with the Environmental Protection Agency regulations for discharge streams from coal-fired power facilities.

Background: The last few decades have seen the critical role of global cattle industry in agricultural development. However, while giving prosperity and significant benefits to the countryside, the industry also produces wastewater streams, that cause eutrophication in water bodies. The streams, if treated effectively, could act as a valuable nonconventional water source to help address the global freshwater crisis. Moreover, resources recovered from these wastewater streams, e.g., potassium (K) and phosphorus (P), could be converted to valuable commodities such as fertilizers. We, therefore, propose to use a continuous K-struvite granulation process as an effective method for the treatment of swine wastewater (SW) and recovery of K-struvite. Results show that the P and K were efficiently removed and that wastewater-derived K-struvite is a promising green chemistry agent for a slow-release, reinforcing a promising pathway to global P and K conservation. Methods: The fluidized-bed homogeneous granulation (FBHG) has recently emerged as an advanced metal re-covery technology with high efficiencies for several metals and low moisture products. Based on the principle of chemical precipitation, FBHG technology requires less chemicals while producing insignificant amounts of sludge, thereby alleviating burden on sludge management often encountered in conventional chemical precipitation and others. Significant findings: Herein, we investigate the potential use of FBHG technology for simultaneous recovering K and P while treating swine wastewater. The recovered products are in the form of K-struvite pellets having a studded quasi-spherical form with a rough surface and sharp spikes that resemble sea urchins. The pellets are almost free of heavy metals, which make them promising candidates for use as fertilizer without significant harm. We observed that the release of K was faster than that of P. The formation, size, morphology, purity, and crushing strength of the pellets greatly affected the up-flow velocity value condition. The FBHG could potentially be scaled up for more extensive nutrient recovery.

Technologies that can efficiently purify nontraditional water sources are needed to meet rising global demand for clean water. Water treatment plants typically require a series of costly separation units to achieve desalination and the removal of toxic trace contaminants such as heavy metals and boron. We report a series of robust, selective, and tunable adsorptive membranes that feature porous aromatic framework nanoparticles embedded within ion exchange polymers and demonstrate their use in an efficient, one-step separation strategy termed ion-capture electrodialysis. This process uses electrodialysis configurations with adsorptive membranes to simultaneously desalinate complex water sources and capture diverse target solutes with negligible capture of competing ions. Our methods are applicable to the development of efficient and selective multifunctional separations that use adsorptive membranes.

Computational methods with real-time forecasting of embedded energy and water networks are critical for resource management and conservation. In the August 1, 2021 issue of Energy & Environmental Science, Liu and Mauter propose a high-resolution computational framework of the embedded energy in water delivery systems to guide efficient management of water resources.

From energy storage to separation applications, performances of nanoporous membranes are typically limited by an inherent trade-off between transport rate and selectivity. For example, conventional protective garments sacrifice breathability to prevent exposure to harmful agents, and this trade-off severely hinders the duration of their active use. The discovery of enhanced fluid flow in single-walled carbon nanotubes (SWCNT) has provided a path toward combining the diametric properties of high selectivity and permeability into a single SWCNT-based material, yet successful demonstration of this promise remains elusive. Using as example the design of novel materials for protective clothing applications, herein we demonstrate a smart, nanoporous, SWCNT membrane that overcomes the limitation of conventional protective garments. Specifically, we show that the adoption of nanometer-wide SWCNTs for ultrafast moisture conduction [1] enables a simultaneous boost in size-sieving selectivity and water-vapor permeability by decreasing nanotube diameter, thereby overcoming the breathability/protection trade-off [2].Our membrane platform can rapidly and selectively transition from a highly breathable state in a safe environment to a protective state when exposed to a chemical threat. Dynamic response to chemical stimuli is achieved through the physical collapse of an ultrathin copolymer layer on the membrane surface, which efficiently gates transport through the SWCNT membrane pores [2].Multifunctional SWCNT membranes such these present exciting opportunities in many other areas including energy-efficient separations, energy storage, and smart delivery. References 1. N. Bui, E. R. Meshot, S. Kim, J. Peña, P. W. Gibson, K. J. Wu, F. Fornasiero, Adv. Mater., 28 (2016) 5871. 2. Y. Li, C. Chen, E. R. Meshot, S. F. Buchsbaum, M. Herbert, R. Zhu, O. Kulikov, B McDonald, N. Bui, M. L. Jue, S. J. Park, C. Valdez, S. Hok, C. J. Doona, K. J. Wu, T. M. Swager, F. Fornasiero, submitted (2019) This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Herein, we present a scalable approach for the synthesis of a hydrogen-bonded organic–inorganic framework via coordination-driven supramolecular chemistry, for efficient remediation of trace heavy metal ions from water. In particular, using copper as our model ion of interest and inspired by nature’s use of histidine residues within the active sites of various copper binding proteins, we design a framework featuring pendant imidazole rings and copper-chelating salicylaldoxime, known as zinc imidazole salicylaldoxime supramolecule. This material is water-stable and exhibits unprecedented adsorption kinetics, up to 50 times faster than state-of-the-art materials for selective copper ion capture from water. Furthermore, selective copper removal is achieved using this material in a pH range that was proven ineffective with previously reported metal–organic frameworks. Molecular dynamics simulations show that this supramolecule can reversibly breathe water through lattice expansion and contraction, and that water is initially transported into the lattice through hopping between hydrogen-bond sites.

Forward osmosis (FO) is an emerging desalination technology that has garnered an increasing amount of attention in recent years. In FO, water is driven across a semi-permeable membrane by an osmotic pressure gradient that is generated by a draw solution. The membrane rejects dissolved contaminants, much like they are in reverse osmosis. The draw solution is comprised of highly soluble solutes that are easily removed and reused in the process. When designed with an appropriate membrane and draw solution, FO promises to enable low cost desalination with improved recovery and fouling resistance. The road to commercialization still contains a number of technical hurdles. Membranes must be designed specifically for FO while retaining the high permselectivity of conventional reverse osmosis membranes. Draw solutes must be designed for high solubility, easy removal, and low toxicity. These challenges, while considerable, have not deterred a substantial worldwide research effort on forward osmosis. Commercialization of FO hinges on continued work in these area while eventual successful demonstration on the pilot scale will secure FO in its place among conventional desalination technologies.

Forward osmosis (FO) has emerged as a new technology for desalination and exhibits potentials for applications where reverse osmosis is incapable or uneconomical for treating streams with high salinity or fouling propensity. However, most of current draw agents in FO are salts and difficult to be recycled cost- and energy-effectively. In this work, we demonstrate a new and facile approach to efficiently recover water from the FO process with enhanced water purity by using a binary ion liquid/hydrogel system. The hybrid ion liquid/hydrogel draw solution system demonstrated in this work synergistically leverages the thermoresponsive properties of both the ionic liquid (IL) and hydrogel to improve the overall FO performance. Our findings corroborate that the hydrogel mitigates the water flux decline of the IL as the draw agent and provide a ready route to contiguously and effectively regenerate water from the FO process. Such a route allows for an efficient recovery of water from the draw solute/water mixture with enhanced water purity, compared with conventional thermal treating of lower critical solution temperature IL draw solute/water. Furthermore, hydrogels can be used in a continuous and readily recyclable process to recover water without heating the entire draw solute/water mixture. Our design principles open the door to use low-grade/waste heat or solar energy to regenerate draw agents and potentially reduce energy in the FO process considerably.

Ultrafast fluid transport through the core of single-wall carbon nanotube (SWNT) channels promises to advance membrane applications, from efficient water purification and low-cost separation of high-value components, to next-generation protective garments. For the last application, we recently demonstrated cm2-area, vertically-aligned, SWNT-polymer composite membranes that combined both high breathability and protection in a single functional material, thus breaking the typically elusive trade-off between the two.1 As we seek to further enhance the performance of these membranes, we target vertically-aligned SWNT “forest” growth toward: a) minimizing SWNT diameter to maximize protection via size exclusion; b) maximizing SWNT number density to maximize breathability; and c) scaling up SWNT growth area to eventually incorporate into garments. We perform low-pressure chemical vapor deposition (CVD) in an AIXTRON® Black Magic cold-wall furnace, featuring a wafer-scale, local heater stage and gas showerhead. The combination of a low flux of carbon precursors with sub-nm Fe/Mo catalyst films on alumina-coated Si wafers maintains small-diameter SWNTs. High-resolution TEM and X-ray scattering2 confirm that our forests contain >99% SWNTs below 3.5 nm diameter (on wafers up to 4 inches). Consistent with literature reports, 6 at% Mo optimally preserves small, densely packed particles, templating growth of forests with high number densities up to 1.4x1012 cm-2. In an effort to control the forest thickness and uniformity across large substrate areas, we investigate the area-dependent growth kinetics and temporal density decay. Despite exhibiting a growth rate that is initially uniform across the substrate, growth at the center self-terminates first, while edge growth continues at a sublinear rate for tens of minutes. Understanding these varying reaction lifetimes that arise on a single substrate is key to engineering large-area SWNT membranes with highly uniform transport characteristics. To scale SWNT forest production and overcome non-uniformities in wafer-scale growth, we seek to simplify the catalyst film formulation. While wafer-scale growth from Fe films of equal thickness in the absence of Mo is markedly more robust over multiple sequential batches, the SWNT diameter distributions have larger means and tails, which are detrimental to the rejection properties of our membranes. Tuning the Fe thickness down renders smaller SWNTs, but the range of densities grown from these Fe-only films is 0.2-0.6x1012 cm-2, regardless of thicknesses studied (0.35-0.65 nm). This challenge of accessing a parameter space that co-optimizes growth yield of small, monodisperse diameter, high-density SWNT forests highlights a deficiency in conventional catalyst design and suggests a need for improved designs that could unlock a range of SWNT applications. This work is supported by the Defense Threat Reduction Agency (DTRA) D[MS]2 project under Contract No. BA12PHM123 and was performed under the auspices of U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Bui, N.; Meshot, E. R.; Kim, S.; Peña, J.; Gibson, P. W.; Wu, K. J.; Fornasiero, F., Ultrabreathable and Protective Membranes with Sub-5 nm Carbon Nanotube Pores. Advanced Materials 2016, 28 (28), 5871-5877. Meshot, E.; Zwissler, D. W.; Bui, N.; Kuykendall, T. R.; Wang, C.; Hexemer, A.; Wu, K. J. J.; Fornasiero, F. Quantifying the Hierarchical Order in Self-Aligned Carbon Nanotubes from Atomic to Micrometer Scale. ACS Nano 2017, 11 (6), 5405-5416.

Carbon nanotubes (CNTs) exhibit truly nm-scale size, easily functionalized openings, uniquely smooth walls, and a well-defined structure which sets them apart from other types of synthetic nanopores in the literature. As a result, they show remarkable fluidic properties which make them very attractive building blocks for next-generation biomimetic materials. Towards this end, we have developed a fabrication process to generate free-standing and flexible single-walled CNT based membranes with well-aligned, high-density tubes. Through the use of these membranes we have studied the unique fluidic transport behavior seen in CNTs under multiple driving forces, including pressure, concentration, and voltage gradients. In some cases, remarkable transport rates were seen that are several orders of magnitude above typical continuum models. In addition, we have combined our CNT membrane fabrication with focused ion beam (FIB) nanomachining to create a platform that allows for activation of individual (or a few) tubes. By employing this platform, we analyzed voltage-driven ionic transport through CNTs and show giant ionic currents and a power-law increase in conductance with KCl concentration, a behavior that seems unique to CNTs. Moreover, we demonstrated that this power-law relationship can be pH dependent, which helps explain a possible origin of the large electroosmotic flow thought to be present in the tubes.

Fundamental understanding of structure-property relationships in hierarchically organized nanostructures is crucial for the development of new functionality, yet quantifying structure across multiple length scales is challenging. In this work, we used nondestructive X-ray scattering to quantitatively map the multiscale structure of hierarchically self-organized carbon nanotube (CNT) "forests" across 4 orders of magnitude in length scale, from 2.0 Å to 1.5 μm. Fully resolved structural features include the graphitic honeycomb lattice and interlayer walls (atomic), CNT diameter (nano), as well as the greater CNT ensemble (meso) and large corrugations (micro). Correlating orientational order across hierarchical levels revealed a cascading decrease as we probed finer structural feature sizes with enhanced sensitivity to small-scale disorder. Furthermore, we established qualitative relationships for single-, few-, and multiwall CNT forest characteristics, showing that multiscale orientational order is directly correlated with number density spanning 109-1012 cm-2, yet order is inversely proportional to CNT diameter, number of walls, and atomic defects. Lastly, we captured and quantified ultralow-q meridional scattering features and built a phenomenological model of the large-scale CNT forest morphology, which predicted and confirmed that these features arise due to microscale corrugations along the vertical forest direction. Providing detailed structural information at multiple length scales is important for design and synthesis of CNT materials as well as other hierarchically organized nanostructures.

A flexible membrane with sub-5 nm single-walled carbon nanotube (SWNT) pores is developed by F. Fornasiero and co-workers, as described on page 5871, for application as a key component of protective, yet breathable fabrics. The SWNTs are shown to enable exceptionally fast transport of water vapor under a concentration driving force. Thus, membranes having SWNTs as moisture-conductive pores feature outstanding breathability and provide a high degree of protection from biological threats by size exclusion.

Small-diameter carbon nanotubes (CNTs) are shown to enable exceptionally fast transport of water vapor under a concentration gradient driving force. Thanks to this property, membranes having sub-5 nm CNTs as conductive pores feature outstanding breathability while maintaining a high degree of protection from biothreats by size exclusion.

Engineered osmosis (e.g., forward osmosis, pressure-retarded osmosis, direct osmosis) has emerged as a new platform for applications to water production, sustainable energy, and resource recovery. The lack of an adequately designed membrane has been the major challenge that hinders engineered osmosis (EO) development. In this study, nanotechnology has been integrated with membrane science to build a next generation membrane for engineered osmosis. Specifically, hydrophilic nanofiber, fabricated from different blends of polyacrylonitrile and cellulose acetate via electrospinning, was found to be an effective support for EO thin film composite membranes due to its intrinsically wetted open pore structure with superior interconnectivity. The resulting composite membrane exhibits excellent permselectivity while also showing a reduced resistance to mass transfer that commonly impacts EO processes due to its thin, highly porous nanofiber support layer. Our best membrane exhibited a two to three times enhanced water flux and 90% reduction in salt passage when compared to a standard commercial FO membrane. Furthermore, our membrane exhibited one of the lowest structural parameters reported in the open literature. These results indicate that hydrophilic nanofiber supported thin film composite membranes have the potential to be a next generation membrane for engineered osmosis.