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Surface modification with bactericides is a promising approach to imparting membrane materials with biofouling resistance. However, chemical modification of membranes made from inert materials, such as polyvinylidene fluoride (PVDF) and polysulfone, is challenging because of the absence of reactive functional groups on these materials. In this study, we develop a facile procedure using benzophenone as an anchor to graft biocidal graphene oxide (GO) to chemically inactive membrane materials. GO nanosheets are first functionalized with benzophenone through an amide coupling reaction. Then, benzophenone-functionalized GO nanosheets are irreversibly grafted to the inert membrane surfaces via benzophenone-initiated cross-linking under ultraviolet irradiation. The binding of GO to the membrane surface is confirmed by scanning electron microscopy and Raman spectroscopy. When exposed to a model bacterium (Escherichia coli), GO-functionalized PVDF and polysulfone membranes exhibit strong antibacterial activity, re...

Discovering electrode materials with exceptional capacitance, an indicator of the ability of a material to hold charge, is critical for developing capacitive deionization devices for water desalina...

Biofouling is a major obstacle for the efficient and reliable operation of membrane-based desalination processes. Innovations in membrane materials and fabrication processes are therefore needed to develop antibiofouling strategies. In this study, we utilize the alignability of an emerging two-dimensional nanomaterial, graphene oxide (GO), to fabricate a desalination membrane with enhanced bacterial resistance. GO nanosheets are dispersed in a polymer solution to form a homogeneous mixture, which undergoes slow solvent evaporation in a magnetic field to create a thin nanocomposite membrane with vertically aligned GO nanosheets. The structural characteristics of the fabricated membranes confirm the enhanced exposure of nanosheet edges on the surface through the vertical alignment of GO. Notably, the addition and alignment of GO do not compromise membrane water permeability and water–salt selectivity. When contacted with bacterial cells, membranes with vertically aligned GO nanosheets exhibit enhanced antim...

Water scarcity, expected to become more widespread in the coming years, demands renewed attention to freshwater protection and management. Critical to this effort are the minimization of freshwater withdrawals and elimination of wastewater discharge, both of which can be achieved via zero liquid discharge (ZLD), an aggressive wastewater management approach. Because of the high energetic cost of thermal desalination, ZLD is particularly challenging for high-salinity wastewaters. In this review, we discuss the potential of high-pressure reverse osmosis (HPRO) (i.e., reverse osmosis operated at a hydraulic pressure greater than ∼100 bar) to efficiently desalinate hypersaline brines. We first discuss the inherent energy efficiency of membrane processes compared to that of conventional thermal processes for brine desalination. We then highlight the opportunity of HPRO to reduce energy requirements for desalination of key high-salinity industrial wastewaters. The current state of membrane materials and processe...

Conventional asymmetric or thin-film composite forward osmosis (FO) membranes suffer from severe internal concentration polarization, which significantly hinders process performance and practical applications. Here we report the synthesis of the COOH-derived polyoxadiazole copolymer for the fabrication of a self-standing selective thin film without a support layer. The thickness of the membrane was controlled at merely a few micrometers to achieve a high rate of rejection of the Na2SO4 draw solution, while maintaining acceptable water permeability. Because of the symmetric architecture, the membrane exhibited excellent and identical FO performance at both of its sides. The structural parameter of the fabricated membranes was zero because of the absence of internal concentration polarization in the symmetric FO membranes. Our results highlight the potential of support-free membranes for the further development of FO technology.

This study intends to reinvent classical Fenton chemistry by enabling the Fe(II)/Fe(III) redox cycle to occur on a newly developed FeOCl nanosheet catalyst for facile hydroxyl radical (•OH) generation from H2O2 activation. This approach overcomes challenges such as low operating pH and large sludge production that have prevented a wider use of otherwise attractive Fenton chemistry for practical water treatment, in particular, for the destruction of recalcitrant pollutants through nonselective oxidation by •OH. We demonstrate that FeOCl catalysts exhibit the highest performance reported in the literature for •OH production and organic pollutant destruction over a wide pH range. We further elucidate the mechanism of rapid conversion between Fe(III) and Fe(II) in FeOCl crystals based on extensive characterizations. Given the low-cost raw material and simple synthesis and regeneration, FeOCl catalysts represent a critical advance toward application of iron-based advanced oxidation in real practice.

Recent studies have documented the existence of discrete voids in the thin polyamide selective layer of composite reverse osmosis membranes. Here we present compelling evidence that these nanovoids are formed by nanosized gas bubbles generated during the interfacial polymerization process. Different strategies were used to enhance or eliminate these nanobubbles in the thin polyamide film layer to tune its morphology and separation properties. Nanobubbles can endow the membrane with a foamed structure within the polyamide rejection layer that is approximately 100 nm in thickness. Simple nanofoaming methods, such as bicarbonate addition and ultrasound application, can result in a remarkable improvement in both membrane water permeability and salt rejection, thus overcoming the long-standing permeability–selectivity trade-off of desalination membranes.

The interaction of two-dimensional (2D) nanomaterials with biological membranes has important implications for ecotoxicity and human health. In this study, we use a dye-leakage assay to quantitatively assess the disruption of a model phospholipid bilayer membrane (i.e., lipid vesicles) by five emerging 2D nanomaterials: graphene oxide (GO), reduced graphene oxide (rGO), molybdenum disulfide (MoS2), copper oxide (CuO), and iron oxide (α-Fe2O3). Leakage of dye from the vesicle inner solution, which indicates loss of membrane integrity, was observed for GO, rGO, and MoS2 nanosheets but not for CuO and α-Fe2O3, implying that 2D morphology by itself is not sufficient to cause loss of membrane integrity. Mixing GO and rGO with lipid vesicles induced aggregation, whereas enhanced stability (dispersion) was observed with MoS2 nanosheets, suggesting different aggregation mechanisms for the 2D nanomaterials upon interaction with lipid bilayers. No loss of membrane integrity was observed under strong oxidative condi...

Current postcombustion CO2 capture technologies are energy intensive, require high-temperature heat sources, and dramatically increase the cost of power generation. In this work, we introduce a new carbon capture process requiring significantly lower temperatures and less energy, creating further impetus to reduce CO2 emissions from power generation. In this process, high-purity CO2 is generated through the addition of an organic solvent (acetone, dimethoxymethane, or acetaldehyde) to a CO2 rich, aqueous ammonia/carbon dioxide solution under room-temperature and -pressure conditions. The organic solvent and CO2-absorbing solution are then regenerated using low-temperature heat. When acetone, dimethoxymethane, or acetaldehyde was added at a concentration of 16.7% (v/v) to 2 M aqueous ammonium bicarbonate, 39.8, 48.6, or 86.5%, respectively, of the aqueous CO2 species transformed into high-purity CO2 gas over 3 h. Thermal energy and temperature requirements for recovering acetaldehyde, the best-performing o...

Desalination membranes are essential for the treatment of unconventional water sources, such as seawater and wastewater, to alleviate water scarcity. Promising research efforts on novel membrane materials may yield significant performance gains over state-of-the-art thin-film composite (TFC) membranes, which are constrained by the permeability–selectivity trade-off. However, little guidance currently exists on the practical impact of such performance gains, namely enhanced water permeability or enhanced water–solute selectivity. In this critical review, we first discuss the performance of current TFC membranes. We then highlight and provide context for recent module-scale modeling studies that have found limited impact of increased water permeability on the efficiency of desalination processes. Next we cover several important examples of water treatment processes in which inadequate membrane selectivity hinders process efficacy. We conclude with a brief discussion of how the need for enhanced selectivity ...

Understanding the interactions of graphene oxide (GO) with biological membranes is crucial for the evaluation of GO’s health and environmental impacts, its bactericidal activity, and to advance graphene-based biological and environmental applications. In an effort to understand graphene-induced bacterial inactivation, we studied the interaction of GO with bacterial (Escherichia coli) cell membranes using atomic force microscopy (AFM). Toward this goal, we devised a polydopamine-assisted experimental protocol to functionalize an AFM probe with GO nanosheets, and used AFM-based force spectroscopy to measure cell membrane–GO interaction forces. Our results show that GO–cell interactions are predominantly repulsive, with only sporadic adhesion forces being measured upon probe pull-off, which we attribute to lipopolysaccharide bridging. We provide evidence of the acellular oxidation of glutathione by GO, underscoring the role of oxidative pathways in GO-mediated bacterial cell inactivation. Our force spectrosc...

In this work, we fabricate an omniphobic microporous membrane for membrane distillation (MD) by modifying a hydrophilic glass fiber membrane with silica nanoparticles followed by surface fluorination and polymer coating. The modified glass fiber membrane exhibits an anti-wetting property not only against water but also against low surface tension organic solvents that easily wet a hydrophobic polytetrafluoroethylene (PTFE) membrane that is commonly used in MD applications. By comparing the performance of the PTFE and omniphobic membranes in direct contact MD experiments in the presence of a surfactant (sodium dodecyl sulfate, SDS), we show that SDS wets the hydrophobic PTFE membrane but not the omniphobic membrane. Our results suggest that omniphobic membranes are critical for MD applications with feed waters containing surface active species, such as oil and gas produced water, to prevent membrane pore wetting.

We demonstrate the simultaneous extraction of phosphorus and clean water from digested sludge centrate using a forward osmosis (FO)–membrane distillation (MD) hybrid process. In this FO–MD hybrid process, FO concentrates orthophosphate and ammonium for subsequent phosphorus recovery in the form of struvite (MgNH4PO4·6H2O), while MD is used to recover the draw solution and extract clean water from the digested sludge centrate. A decline in water flux was observed during the FO process, but fouling was largely reversible after a brief, simple membrane flushing using deionized water. The FO process also provides an effective pretreatment capacity to the subsequent MD process, which exhibited stable water flux. The use of MgCl2 as the draw solute for the FO process is another novel aspect of the system. The reverse salt flux of magnesium to the concentrated digested sludge across the FO membrane and the diffusion of protons away from the digested sludge create favorable conditions for the formation of struvit...

Fouling of membranes by microorganisms is a major limiting factor in membrane separation processes. Novel strategies are therefore required to decrease the extent of bacterial growth on membranes. In this study, we confer strong antimicrobial properties to thin-film composite polyamide membranes by a simple graphene oxide surface functionalization. Using amide coupling between carboxyl groups of graphene oxide and carboxyl groups of the polyamide active layer, graphene oxide is irreversibly bound to the membrane. Surface binding of graphene oxide is demonstrated by scanning electron microscopy and Raman spectroscopy. Direct contact of bacteria with functionalized graphene oxide on the membrane surface results in 65% bacterial inactivation after 1 h of contact time. This bactericidal effect is imparted to the membrane without any detrimental effect to the intrinsic membrane transport properties. Our results suggest that functionalization of thin-film composite membranes with graphene oxide nanosheets is a ...