Understanding and Designing a High-Performance Ultrafiltration Membrane Using Machine Learning.

Ultrafiltration (UF) as one of the mainstream membrane-based technologies has been widely used in water and wastewater treatment. Increasing demand for clean and safe water requires the rational design of UF membranes with antifouling potential, while maintaining high water permeability and removal efficiency. This work employed a machine learning (ML) method to establish and understand the correlation of five membrane performance indices as well as three major performance-determining membrane properties with membrane fabrication conditions. The loading of additives, specifically nanomaterials (A_wt %), at loading amounts of >1.0 wt % was found to be the most significant feature affecting all of the membrane performance indices. The polymer content (P_wt %), molecular weight of the pore maker (M_Da), and pore maker content (M_wt %) also made considerable contributions to predicting membrane performance. Notably, M_Da was more important than M_wt % for predicting membrane performance. The feature analysis of ML models in terms of membrane properties (i.e., mean pore size, overall porosity, and contact angle) provided an unequivocal explanation of the effects of fabrication conditions on membrane performance. Our approach can provide practical aid in guiding the design of fit-for-purpose separation membranes through data-driven virtual experiments.

Revolutionizing Membrane Design Using Machine Learning-Bayesian Optimization.

Polymeric membrane design is a multidimensional process involving selection of membrane materials and optimization of fabrication conditions from an infinite candidate space. It is impossible to explore the entire space by trial-and-error experimentation. Here, we present a membrane design strategy utilizing machine learning-based Bayesian optimization to precisely identify the optimal combinations of unexplored monomers and their fabrication conditions from an infinite space. We developed ML models to accurately predict water permeability and salt rejection from membrane monomer types (represented by the Morgan fingerprint) and fabrication conditions. We applied Bayesian optimization on the built ML model to inversely identify sets of monomer/fabrication condition combinations with the potential to break the upper bound for water/salt selectivity and permeability. We fabricated eight membranes under the identified combinations and found that they exceeded the present upper bound. Our findings demonstrate that ML-based Bayesian optimization represents a paradigm shift for next-generation separation membrane design.

Two-Dimensional Ti3C2Tx MXene/GO Hybrid Membranes for Highly Efficient Osmotic Power Generation.

Osmotic power has emerged as one of the promising candidates for clean and renewable energy. However, the advancement of present osmotic power-harvesting technologies, specifically pressure-retarded osmosis (PRO) in this work, is hindered by the unsatisfactory membrane transport properties. Herein, we demonstrate the freestanding transition-metal carbides and graphene oxide hybrid membranes as high-performance PRO membranes. Due to the elimination of internal concentration polarization, the freestanding hybrid membrane can achieve a record-high power density up to approximately 56.4 W m-2 with 2.0 M NaCl as the draw solution and river water (0.017 M) as the feed water at an applied hydraulic pressure difference of 9.66 bar. In addition, the hybrid membranes exhibit enhanced antifouling potential and antibacterial activity. The facile fabrication of the hybrid membranes shed light on a new membrane development platform for the highly anticipated osmotic power-harvesting technologies.

Study on the Transport Mechanism of a Freestanding Graphene Oxide Membrane for Forward Osmosis.

Graphene oxide membranes (GOMs) are promising separation technologies. In forward osmosis (FO), we found that the water flux from the feed solution to the draw solution can prevent ions from diffusing to the feed solution in a highly tortuous and porous GOM. In reverse osmosis (RO), we found that the salt rejection is low compared to that in commercially available RO membranes. While this prohibits the use of GOMs for RO and FO water desalination, we believe that such membranes could be used for other water treatment applications and energy production. To examine the transport mechanism, we characterized the physical and chemical properties of GOMs and derived mass transfer models to analyze water and salt transport inside freestanding GOMs. The experimental reverse salt flux was between the largest and smallest theoretical values, which corresponds to the lowest and highest tortuosity, respectively, in FO. Furthermore, the concentration profile for the reverse salt flux shortened as the NaCl draw concentration increased because the water flux increased and the electrical double layer (EDL) decreased with increasing NaCl in the draw solution. We provide insights into the transport mechanisms in GOMs and provide guidance for future exploration of GOMs in efficient water treatment and energy production processes.

Correction: Preparation of Mo nanopowders through electroreduction of solid MoS2 in molten KCl-NaCl.

Correction for 'Preparation of Mo nanopowders through electroreduction of solid MoS2 in molten KCl-NaCl' by Haiping Gao et al., Phys. Chem. Chem. Phys., 2014, 16, 19514-19521.

Enhanced Ionic Conductivity and Power Generation Using Ion-Exchange Resin Beads in a Reverse-Electrodialysis Stack.

Reverse electrodialysis (RED) is a promising technique for harvesting energy by mixing seawater with river water. The energy production is usually limited by ionic conductivity in dilute compartments of a RED system. Novel tests were conducted in this research, which used ion-exchange resin beads (IERB) to replace nonconductive spacer fabrics in RED compartments with dilute NaCl solution in a modified stack containing Fumasep FKS and Fumasep FAS membranes. We compared the conductivity of an IERB packed bed with that of an inert glass-beads-packed bed as a control to confirm IERB's effectiveness. When applied in a RED system, IERB decreased the stack resistance by up to 40%. The maximum gross power density improved by 83% in the RED stack compared to that in a regular RED stack at 1.3 cm/s average linear flow velocity. IERB-filled stack resistance was modeled. The model results fit well with experimental data, thereby confirming the effectiveness of the new approach presented here. The net power density is also estimated based on the measured pressure drop and pumping energy model. Both gross and net power density was improved by over 75% at higher flow rate. A net power density of 0.44 W/m(2) was achieved at a cell thickness of 500 µm. To the best of our knowledge, this research is the first to study the impact of IERB on power generation and establishes a new approach to improving the power performance of a RED system.

Preparation of Mo nanopowders through electroreduction of solid MoS2 in molten KCl-NaCl.

Electrolysis of MoS2 to produce Mo nanopowders and elemental sulfur has been studied in an equimolar mixture of NaCl and KCl at 700 °C. The reduction mechanism was investigated by cyclic voltammetry (CV), potentiostatic and constant voltage electrolysis together with spectroscopic and scanning electron microscopic analyses. The reduction pathway was identified to be MoS2 → LxMoS2 (x ≤ 1, L = Na or K) → L3Mo6S8 and LMo3S3 → Mo, and the last step to format metallic Mo was found to be relatively slow in kinetics. Electrolysis at a cell voltage of 2.7 V has led to a rapid reduction of MoS2 to nodular Mo nanoparticles (50-100 nm), with the current efficiency and energy consumption being about 92% and 2.07 kW h kg(-1)-Mo, respectively.

Dynamic Marine Atmospheric Corrosion Behavior of AZ91 Mg Alloy Sailing from Yellow Sea to Western Pacific Ocean.

In this work, the dynamic marine atmospheric corrosion behavior of AZ91 Mg alloy sailing from Yellow Sea to Western Pacific Ocean was studied. The corrosion rates were measured using the weight loss method. The microstructure, phase, and chemical composition of corroded samples were investigated by SEM, EDS, XRD, and XPS. The results show that the evolution of corrosion rates of AZ91 Mg alloy was divided into three stages: rapidly increasing during the first 3 months, then remaining stable for the next three months, and finally decreasing after 6 months. The annual corrosion rate of Mg alloy reached 32.50 µm/y after exposure for 12 months in a dynamic marine atmospheric environment, which was several times higher than that of the static field exposure tests. AZ91 magnesium alloy was mainly subjected to localized corrosion with more destructiveness to Mg parts, which is mainly due to the synergistic effect of high relative humidity, the high deposition rate of chloride ion, sulfur dioxide acidic gas produced by fuel combustion, and rapid temperature changes caused by the alternating changes in longitude and latitude during navigation. As the exposure time increased, the corrosion pits gradually increased and deepened. The maximum depth of the corrosion pit was 197 µm after 12 months of exposure, which is almost 6 times the average corrosion depth. This study provides scientific data support for the application of magnesium alloys in shipborne aircraft and electronic equipment. The results could provide guidance for the design of new magnesium alloys and development of anti-corrosion technologies.

Interactions of acidic pharmaceuticals with human serum albumin: insights into the molecular toxicity of emerging pollutants.

Acidic pharmaceuticals such as diclofenac (DCF), clofibric acid (CA) and ketoprofen (KTP) have been detected frequently in environmental media. In order to reveal the toxicity of such emerging pollutants, their interactions with human serum albumin (HSA) were investigated by capillary electrophoresis, molecular spectrometry, and equilibrium dialysis. The binding constants and sites of these acidic pharmaceuticals with HSA were obtained. The thermodynamic parameters, e.g. enthalpy change and entropy change of these interactions were calculated to characterize that all the reactions resulted from hydrophobic and electrostatic interactions. The static quenching of the fluorescence of HSA was observed when interacted with acidic pharmaceuticals, indicating acidic pharmaceuticals bound to Tryptophan residue of HSA. The 3D fluorescence and circular dichroism confirmed that the secondary conformation of HSA changed after the interactions with the pharmaceuticals. At physiological condition, only 0.12 mM acidic pharmaceuticals reduced the binding of vitamin B(2) to HSA by 37, 30 and 21% for DCF, KTP and CA, respectively. This work provides an insight into non-covalent interactions between emerging contaminants and biomolecule, and is helpful for clarifying the toxic mechanism of such emerging contaminants.

Lipid nanotubes: Formation and applications.

Lipids, the fundamental components of cell membrane, play important roles in the whole cycle of cell life, thus attracting worldwide attention, owing to their physicochemical property and extensive use in the applications based on lipid assemblies. Compared with liposomes, lipid nanotubes (LNTs) usually possess unique properties, such as highly ordered structure, precise molecular recognition, and the possibility of substance transport, thus providing more potential applications in different research fields. However, until now, there are still quite rare cases of LNTs successfully employed in practical applications. Bearing this in mind and based on our own experience in this field, we summarized and discussed the recent progress of the fabrication approaches and representative applications of the LNTs in the past decade, which would potentially provide basic understanding and guidance towards their future development.

Design and synthesis of a new bioactive compound for marine antifouling inspired by natural products.

A marine antifouling compound, N-octyl-2-hydroxybenzamide (OHBA), inspired by ceramide and paeonol molecules, was created. First, methyl salicylate was synthesized with salicylic acid and methanol, followed by n-octylamine through an ester-amine condensation reaction. Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and mass spectrometry confirmed the characteristic structure of the OHBA compound. Bioassays showed that OHBA inhibits the growth of typical marine fouling organisms, such as Vibrio azureus, Navicula subminuscula, Ulva pertusa, Mytilus edulis, and Amphibalanus amphitrite, indicating its broad-spectrum antifouling ability. A one-year marine real-sea test further demonstrated the excellent antifouling properties of OHBA. OHBA is also extremely biodegradable, with a half-life of 6.3 days, making it a less environmentally harmful replacement for widely-used heavy metal-containing antifoulants.

Incorporation of Cellulose Nanocrystals into Graphene Oxide Membranes for Efficient Antibiotic Removal at High Nutrient Recovery.

Two-dimensional (2D) material-based membranes hold great promise in wastewater treatment. However, it remains challenging to achieve highly efficient and precise small molecule/ion separation with pure 2D material-fabricated lamellar membranes. In this work, laminated graphene oxide (GO)-cellulose nanocrystal (CNC) hybrid membranes (GO/CNC) were fabricated by taking advantages of the unique structures and synergistic effects generated from these two materials. The characterization results in physiochemical properties, and the structure of the as-synthesized hybrid membranes displayed enhanced membrane surface hydrophilicity, enhanced crumpling surface structure, and slightly enlarged interlayer-spacing with the incorporation of CNCs. Water permeability increases by two to four times with the addition of different CNC weight ratios in comparison to a pristine GO membrane. The optimal GO/CNC membrane achieved efficient rejection toward three typical antibiotics at 74.8, 90.9, and 97.2% for sulfamethoxazole (SMX), levofloxacin (Levo), and norfloxacin (Nor), respectively, while allowing a high passage of desirable nutrients such as NO3- and H2PO4-. It was found that SMX removal is primarily governed by electrostatic repulsion, while adsorption plays a crucial role in removing Levo and Nor. Moreover, the density functional theory calculations confirmed the increased antibiotic removal in the presence of an organic foulant, humic acid. Such a 2D material-based hybrid membrane offers a new strategy to develop fit-for purpose membranes for resource recovery and water separation.

Robust cellulose-based composite adsorption membrane for heavy metal removal.

Adsorptive membranes offer an effective mode to remove heavy metal ions from contaminated water, due to the synergies made possible by low-cost, high-affinity adsorbents and highly scalable filtration in one system. However, the development of adsorptive membranes is hampered by their instability in the aqueous phase and low binding affinity with a broad spectrum of heavy metals in a reasonable flux. Herein, a regenerated cellulose support membrane is strongly grafted with stable and covalent-bonded polyelectrolyte active layers synthesized by a reactive layer-by-layer (LBL) assembly method. The LBL assembled layers have been successfully tested by scanning electron microscopy, Fourier-transform infrared spectroscopy and X-ray photo-electron spectroscopy. The covalent bonding provides the membrane with long-term stability and a tunable water flux compared to a membrane assembled by electrostatic bonding. The maximum adsorption capacity of the membrane active layers can reach up to 194 mg/g, showing more efficient adsorption at lower heavy metal concentration and higher pH value of feed solution. The membrane can remove multiple ions, such as Cu, Pb, and Cd, by adsorption and is easy to be regenerated and recovered. The strong covalent bonding can extend the membrane lifetime in water purification to remove multiple heavy metals at high efficiency.

Low-Grade Waste Heat Recovery via an Osmotic Heat Engine by Using a Freestanding Graphene Oxide Membrane.

The osmotic heat engine represents a new and promising technology for the harvesting of low-grade waste heat from various sources. However, the lack of an adequate semipermeable membrane hinders the technology's advancement. In this study, we investigated the application of a freestanding graphene oxide membrane (GOM) for energy generation in an osmotic heat engine. The synthesized GOM has a water permeability coefficient of 4.4 L m-2 h-1 bar-1 (LMH-bar). The internal concentration polarization in the osmosis filtration system can be minimized because no membrane support layer is needed for the freestanding GOM. As a result, high water flux and high power density are obtained. For example, under an applied hydraulic pressure of 6.90 bar, with a 2 M draw solution of ammonium bicarbonate solution, a power density of 20.0 W/m2 is achieved. This study shows that the freestanding GOM is promising for application in the osmotic heat engine. Future research regarding improving the mechanical properties and water stability of the GOM is beneficial for further advancing the technology.

Behavior and Potential Impacts of Metal-Based Engineered Nanoparticles in Aquatic Environments.

The specific properties of metal-based nanoparticles (NPs) have not only led to rapidly increasing applications in various industrial and commercial products, but also caused environmental concerns due to the inevitable release of NPs and their unpredictable biological/ecological impacts. This review discusses the environmental behavior of metal-based NPs with an in-depth analysis of the mechanisms and kinetics. The focus is on knowledge gaps in the interaction of NPs with aquatic organisms, which can influence the fate, transport and toxicity of NPs in the aquatic environment. Aggregation transforms NPs into micrometer-sized clusters in the aqueous environment, whereas dissolution also alters the size distribution and surface reactivity of metal-based NPs. A unique toxicity mechanism of metal-based NPs is related to the generation of reactive oxygen species (ROS) and the subsequent ROS-induced oxidative stress. Furthermore, aggregation, dissolution and ROS generation could influence each other and also be influenced by many factors, including the sizes, shapes and surface charge of NPs, as well as the pH, ionic strength, natural organic matter and experimental conditions. Bioaccumulation of NPs in single organism species, such as aquatic plants, zooplankton, fish and benthos, is summarized and compared. Moreover, the trophic transfer and/or biomagnification of metal-based NPs in an aquatic ecosystem are discussed. In addition, genetic effects could result from direct or indirect interactions between DNA and NPs. Finally, several challenges facing us are put forward in the review.

Developmental toxicity of diclofenac and elucidation of gene regulation in zebrafish (Danio rerio).

Environmental pollution by emerging contaminants, e.g. pharmaceuticals, has become a matter of widespread concern in recent years. We investigated the membrane transport of diclofenac and its toxic effects on gene expression and the development of zebrafish embryos. The association of diclofenac with the embryos conformed to the general partition model at low concentration, the partition coefficient being 0.0033 ml per embryo. At high concentration, the interaction fitted the Freundlich model. Most of the diclofenac remained in the extracellular aqueous solution with less than 5% interacting with the embryo, about half of which was adsorbed on the membranes while the rest entered the cytoplasm. Concentrations of diclofenac over 10.13 µM were lethal to all the embryos, while 3.78 µM diclofenac was teratogenic. The development abnormalities at 4 day post treatment (dpt) include shorter body length, smaller eye, pericardial and body edema, lack of liver, intestine and circulation, muscle degeneration, and abnormal pigmentation. The portion of the diclofenac transferred into the embryo altered the expression of certain genes, e.g. down-regulation of Wnt3a and Gata4 and up-regulation of Wnt8a. The alteration of expression of such genes or the regulation of downstream genes could cause defects in the cardiovascular and nervous systems.

Potential toxicity of sulfanilamide antibiotic: binding of sulfamethazine to human serum albumin.

Antibiotics are widely used in daily life but their abuse has posed a potential threat to human health. The interaction between human serum albumin (HSA) and sulfamethazine (SMZ) was investigated by capillary electrophoresis, fluorescence spectrometry, and circular dichroism. The binding constant and site were determined to be 1.09×10(4) M(-1) and 1.14 at 309.5 K. The thermodynamic determination indicated that the interaction was driven by enthalpy change, where the electrostatic interaction and hydrogen bond were the dominant binding force. The binding distance between SMZ and tryptophan residue of HSA was obtained to be 3.07 nm according to Fǒrster non-radioactive energy transfer theory. The site marker competition revealed that SMZ bound into subdomain IIA of HSA. The binding of SMZ induced the unfolding of the polypeptides of HSA and transferred the secondary conformation of HSA. The equilibrium dialysis showed that only 0.13 mM SMZ decreased vitamin B(2) by 38% transported on the HSA. This work provides a new quantitative evaluation method for antibiotics to cause the protein damage.

Binding of triclosan to human serum albumin: insight into the molecular toxicity of emerging contaminant.

PURPOSE: The interaction between triclosan (TCS) and human serum albumin (HSA) was investigated in order to obtain the binding mechanism, binding constant, the type of binding force, the binding distance between the donor and acceptor, and the effect of TCS on the conformation change of HSA. METHODS: A HSA solution was added to the quartz cell and then titrated by successive addition of TCS. The fluorescence quenching spectra and synchronous spectra were recorded with the excitation and emission slits of the passage of band set at 10 and 20 nm. Three-dimensional fluorescence spectra of HSA were recorded before and after the addition of TCS. The capillary electrophoresis was conducted with the pressure injection mode at 0.5 psi for 5 s, separation under 25 kV, and detection at 214 nm. RESULTS: Fluorescence data indicated the fluorescence quenching of HSA by TCS was static quenching, and the quenching constants (K ( a )) were 1.14 × 10(5), 8.75 × 10(4), 6.67 × 10(4), and 5.00 × 10(4) at 293, 298, 303, and 309 K, respectively. The thermodynamic parameters, enthalpy change (ΔH) and entropy change (ΔS) for the interaction were calculated to be -37.9 kJ mol(-1) and 32.6 J mol(-1) K(-1). The binding distance between TCS and tryptophan residues of HSA was obtained to be 1.81 nm according to Fǒrster nonradioactive energy transfer theory. The UV-Vis absorption spectroscopy, the synchronous fluorescence spectroscopy, three-dimensional fluorescence spectroscopy, and circular dichroism spectroscopy revealed the alterations of HSA secondary structure in the presence of TCS. Finally, the interaction between TCS and HSA was further confirmed by capillary electrophoresis. CONCLUSIONS: TCS was bound to HSA to form the TCS-HSA complex, with the binding distance of 1.81 nm. Hydrophobic interaction and hydrogen bond were dominated in the binding. TCS could change the secondary conformation of HSA. This work provides an insight into noncovalent interaction between emerging pollutants and protein, helping to elucidate the toxic mechanism of such pollutants.