Engineering Carbon Nanotube Forest Superstructure for Robust Thermal Desalination Membranes

Desalination by membrane distillation (MD) using low‐grade or waste heat provides a potential route for sustainable water supply. Nonwetting, porous membranes that provide a selective pathway for water vapor over nonvolatile salt are at the core of MD desalination. Conventional water‐repelling MD membranes (i.e., hydrophobic and superhydrophobic membranes) fail to ensure long‐term desalination performance due to pore wetting and surface fouling. To address these challenges, a defect‐free carbon nanotube forest (CNTF) is engineered in situ on a porous electrospun silica fiber substrate. The engineered CNTF forms an ultrarough and porous interface structure, allowing outstanding wetting resistance against water in air and oil underwater. As a result of this antiwetting property, the composite CNTF membrane displays a stable water vapor flux and a near complete salt rejection (>99.9%) in the desalination of highly saline water containing low surface tension contaminants. The antimicrobial property of the composite CNTF membrane imparted by the unique forest‐like architecture and the oxidative effect of carbon nanotubes (CNTs) are further demonstrated. The results exemplify an effective strategy for engineering CNT architecture to elucidate the structure–property–performance relationship of the nanocomposite membranes and to guide the design of robust thermal desalination membranes.     

Extreme pH-Resistant,Highly Cation-Selective Poly(Quaternary Ammonium) Membranes Fabricated via Menshutkin Reaction-Based Interfacial Polymerization

Membrane-based separation technologies have attracted significant interest from various industries owing to their high process efficiency. However, the wider applications of conventional polyamide (PA) thin-film composite (TFC) membranes are limited by their poor pH stability and low cation selectivity, necessitating the development of membranes with advanced chemistries. Herein, an extreme pH-resistant, highly cation-selective TFC membrane is fabricated by synthesizing a crosslinked poly(quaternary ammonium) (PQA) selective layer on a polyethylene support via Menshutkin reaction-based interfacial polymerization (Men-IP). The Men-IP process produces a thin, densely crosslinked, and positively charged PQA permselective layer without hydrolysis-prone functional groups. The fabricated PQA membrane features a highly selective molecular density that significantly exceeds those of previously reported membranes with non-PA chemistries. Moreover, the PQA membrane exhibits remarkably high rejection (>90%) and selectivity for divalent cations owing to the exceptionally strong positive charge imparted by its abundant cationic QA groups. More importantly, the PQA membrane displays ultrahigh pH stability under both extremely acidic (1.5 m H₂SO₄) and alkaline (5 m NaOH) conditions for 28 days. No other membrane reported in the literature demonstrates such excellent pH stability. This strategy opens a new route for fabricating highly selective membranes that can be used in harsh pH environments.     

Dendrimer‐Functionalized Iron Oxide Nanoparticles for Specific Targeting and Imaging of Cancer Cells

We demonstrated a unique approach that combines a layer‐by‐layer (LbL) self‐assembly method with dendrimer chemistry to functionalize Fe₃O₄ nanoparticles (NPs) for specific targeting and imaging of cancer cells. In this approach, positively charged Fe₃O₄ NPs (8.4 nm in diameter) synthesized by controlled co‐precipitation of Fe^II and Fe^III ions were modified with a bilayer composed of polystyrene sulfonate sodium salt and folic acid (FA)‐ and fluorescein isothiocyanate (FI)‐functionalized poly(amidoamine) dendrimers of generation 5 (G5.NH₂‐FI‐FA) through electrostatic LbL assembly, followed by an acetylation reaction to neutralize the remaining surface amine groups of G5 dendrimers. Combined flow cytometry, confocal microscopy, transmission electron microscopy, and magnetic resonance imaging studies show that Fe₃O₄/PSS/G5.NHAc‐FI‐FA NPs can specifically target cancer cells overexpressing FA receptors. The present approach to functionalizing Fe₃O₄ NPs opens a new avenue to fabricating various NPs for numerous biological sensing and therapeutic applications.     

Robust and Highly Efficient Free‐Standing Carbonaceous Nanofiber Membranes for Water Purification

The removal of dye and toxic ionic pollutants from water is an extremely important issue. A simple filtration process to decontaminate water by employing a free‐standing fibrous membrane fabricated from highly uniform carbonaceous nanofibers (CNFs) is demonstrated. This process combines the excellent adsorption behavior of CNFs and the advantages of membrane filtration over conventional adsorption techniques, which include simple scale‐up, reduced time, and lower energy consumption. Batch adsorption experiments showed that the CNFs exhibited larger adsorption capacities than commercial granular active carbon (GAC) and carbon nanotubes (CNTs) because of their large surface area, high uniformity, and numerous active sites on the surface of nanofibers. Membrane filtration experiments proved that the CNF membranes could remove methylene blue (MB) efficiently at a very high flux of 1580 L m^?2 h^?1, which is 10–100 times higher than that of commercial nano‐ or ultrafiltration membranes with similar rejection properties. The high permeability of CNF membrane permits stacking of membranes to improve adsorption capacity. In addition, the CNF membranes are easily regenerated and remain unaltered in adsorption performance over six successive cycles of dye adsorption, desorption, and washing. Given the high adsorption and regenerability performance of the CNF membrane, it should have potential applications in water purification.     

Porous Polymersomes with Encapsulated Gd‐Labeled Dendrimers as Highly Efficient MRI Contrast Agents

The use of nanovesicles with encapsulated Gd as magnetic resonance (MR) contrast agents has largely been ignored due to the detrimental effects of the slow water exchange rate through the vesicle bilayer on the relaxivity of encapsulated Gd. Here, the facile synthesis of a composite MR contrast platform is described; it consists of dendrimer conjugates encapsulated in porous polymersomes. These nanoparticles exhibit improved permeability to water flux and a large capacity to store chelated Gd within the aqueous lumen, resulting in enhanced longitudinal relaxivity. The porous polymersomes, ～130 nm in diameter, are produced through the aqueous assembly of the polymers, polyethylene oxide‐b‐polybutadiene (PBdEO), and polyethylene oxide‐b‐polycaprolactone (PEOCL). Subsequent hydrolysis of the caprolactone (CL) block resulted in a highly permeable outer membrane. To prevent the leakage of small Gd‐chelate through the pores, Gd was conjugated to polyamidoamine (PAMAM) dendrimers via diethylenetriaminepentaacetic acid dianhydride (DTPA dianhydride) prior to encapsulation. As a result of the slower rotational correlation time of Gd‐labeled dendrimers, the porous outer membrane of the nanovesicle, and the high Gd payload, these functional nanoparticles are found to exhibit a relaxivity (R1) of 292 109 mM ^?1 s^?1 per particle. The polymersomes are also found to exhibit unique pharmacokinetics with a circulation half‐life of >3.5 h and predominantly renal clearance.     

High‐Efficiency Water‐Transport Channels using the Synergistic Effect of a Hydrophilic Polymer and Graphene Oxide Laminates

Graphene oxide (GO) laminates possess unprecedented fast water‐transport channels. However, how to fully utilize these unique channels in order to maximize the separation properties of GO laminates remains a challenge. Here, a bio‐inspired membrane that couples an ultrathin surface water‐capturing polymeric layer (<10 nm) and GO laminates is designed. The proposed synergistic effect of highly enhanced water sorption from the polymeric layer and molecular channels from the GO laminates realizes fast and selective water transport through the integrated membrane. The prepared membrane exhibits highly selective water permeation with an excellent water flux of over 10 000 g m^?2 h^?1, which exceeds the performance upper bound of state‐of‐the‐art membranes for butanol dehydration. This bio‐inspired strategy demonstrated here opens the door to explore fast and selective channels derived from 2D or 3D materials for highly efficient molecular separation.     

Vapor Sorption and Electrical Response of Au‐Nanoparticle– Dendrimer Composites

Films comprising Au nanoparticles and polyphenylene dendrimers (first and second generation) are deposited onto transducer substrates via layer‐by‐layer self‐assembly and characterized by atomic force microscopy and X‐ray photoelectron spectroscopy. Their sorption behavior is studied by measuring the uptake of solvents from the vapor phase with quartz crystal microbalances (QCMs). The resistance of the films is simultaneously monitored. Both sensor types, QCMs and chemiresistors, give qualitatively very similar response isotherms that are consistent with a combination of Henry‐ and Langmuir‐type sorption processes. The sorption‐induced increase in relative differential resistance scales linearly with the amount of analyte accumulated in the films. This result is in general agreement with an activated tunneling process for charge transport, if little swelling and only small changes in the permittivity of the film occur during analyte sorption (a first‐order approximation). The relative sensitivity of the films to different solvents decreases in the order toluene ≈ tetrachloroethylene > 1‐propanol ? water. Films containing the larger second‐generation dendrimers show higher sensitivity than films containing first‐generation dendrimers.     

S波段温度补偿型FBAR窄带滤波器的研制

研制了一种以SiO2材料作为温度补偿层的S波段温度补偿型薄膜体声波谐振器(FBAR)窄带滤波器.研究了SiO:层厚度对FBAR温度漂移特性的影响,对不同厚度SiO:层时的温度补偿特性进行了仿真.仿真结果表明,当Mo/AlN/Mo的厚度为0.15,1.35和0.15 μm,SiO2层的厚度为10 nm时,FBAR的频率温度系数(TCF)约为3×10-6/℃.采用MEMS工艺制备了温度补偿型FBAR滤波器芯片并进行了测试.测试结果表明,滤波器的中心频率为2 492 MHz,中心插损为3.74 dB,3 dB带宽为17 MHz,相对带宽为0.68％,在2 477和2 507 MHz处阻带抑制分别为27.44和33.81 dBc.在三温(常温25℃、高温85℃、低温-55℃)对该滤波器的S参数进行了测试,计算得出频率温度系数为5×10-6/℃.与未加入温度补偿层的传统滤波器相比,频率温度系数改善明显.     

Cover Picture: Vapor Sorption and Electrical Response of Au‐Nanoparticle– Dendrimer Composites (Adv. Funct. Mater. 6/2007)

The cover shows chemiresistors and mass‐sensitive vapor sensors coated with Au‐nanoparticle/dendrimer composites. The Au nanoparticles provide the film with electrical conductivity and the dendrimers control the chemical selectivity, as reported by Nadjedja Krasteva and co‐workers on p. 881. Analyte sorption follows a combined Henry–Langmuir model, and measurements reveal that sorption‐induced increase in film resistance scales linearly with the concentration of analyte sorbed in the film. The background shows a silicon wafer with lithographically defined microelectrode structures for chemiresistor fabrication. Films comprising Au nanoparticles and polyphenylene dendrimers (first and second generation) are deposited onto transducer substrates via layer‐by‐layer self‐assembly and characterized by atomic force microscopy and X‐ray photoelectron spectroscopy. Their sorption behavior is studied by measuring the uptake of solvents from the vapor phase with quartz crystal microbalances (QCMs). The resistance of the films is simultaneously monitored. Both sensor types, QCMs and chemiresistors, give qualitatively very similar response isotherms that are consistent with a combination of Henry‐ and Langmuir‐type sorption processes. The sorption‐induced increase in relative differential resistance scales linearly with the amount of analyte accumulated in the films. This result is in general agreement with an activated tunneling process for charge transport, if little swelling and only small changes in the permittivity of the film occur during analyte sorption (a first‐order approximation). The relative sensitivity of the films to different solvents decreases in the order toluene ≈ tetrachloroethylene > 1‐propanol ? water. Films containing the larger second‐generation dendrimers show higher sensitivity than films containing first‐generation dendrimers.     

Multilayer Hybrid Films Consisting of Alternating Graphene and Titania Nanosheets with Ultrafast Electron Transfer and Photoconversion Properties

Alternating graphene (G) and titania (Ti_0.91O₂) multilayered nanosheets are fabricated using layer‐by‐layer electrostatic deposition followed by UV irradiation. Successful assemblies of graphene oxide (GO) and titania nanosheets in sequence with polyethylenimine as a linker is confirmed by UV–vis absorption and X‐ray diffraction. Photocatalytic reduction of GO into G can be achieved upon UV irradiation. Ultrafast photocatalytic electron transfer between the titania and graphene is demonstrated using femtosecond transient absorption spectroscopy. Efficient exciton dissociation at the interfaces coupled with cross‐surface charge percolation allows efficient photocurrent conversion in the multilayered Ti_0.91O₂/G films.     

High‐Performance CO2 Capture through Polymer‐Based Ultrathin Membranes

Thin film composite (TFC) membranes have attracted great research interest for a wide range of separation processes owing to their potential to achieve excellent permeance. However, it still remains challenging to fully exploit the superiority of thin selective layers when mitigating the pore intrusion phenomenon. Herein, a facile and generic interface‐decoration‐layer strategy collaborating with molecular‐scale organic–inorganic hybridization in the selective layer to obtain a high‐performance ultrathin film composite (UTFC) membrane for CO₂ capture is reported. The interface‐decoration layer of copper hydroxide nanofibers (CHNs) enables the formation of an ultrathin selective layer (≈100 nm), achieving a 2.5‐fold increase in gas permeance. The organic part in the molecular‐scale hybrid material contributes to facilitating CO₂‐selective adsorption while the inorganic part assists in maintaining robust membrane structure, thus remarkably improving the selectivity toward CO₂. As a result, the as‐prepared membrane shows a high CO₂ permeance of 2860 GPU, superior to state‐of‐the‐art polymer membranes, with a CO₂/N₂ selectivity of 28.2. The synergistic strategy proposed here can be extended to a wide range of polymers, holding great potential to produce high‐efficiency ultrathin membranes for molecular separation.     

Versatile Surface Functionalization of Metal–Organic Frameworks through Direct Metal Coordination with a Phenolic Lipid Enables Diverse Applications

A novel strategy for the versatile functionalization of the external surface of metal‐organic frameworks (MOFs) has been developed based on the direct coordination of a phenolic‐inspired lipid molecule DPGG (1,2‐dipalmitoyl‐sn‐glycero‐3‐galloyl) with metal nodes/sites surrounding MOF surface. X‐ray diffraction and Argon sorption analysis prove that the modified MOF particles retain their structural integrity and porosity after surface modification. Density functional theory calculations reveal that strong chelation strength between the metal sites and the galloyl head group of DPGG is the basic prerequisite for successful coating. Due to the pH‐responsive nature of metal‐phenol complexation, the modification process is reversible by simple washing in weak acidic water, showing an excellent regeneration ability for water‐stable MOFs. Moreover, the colloidal stability of the modified MOFs in the nonpolar solvent allows them to be further organized into 2 dimensional MOF or MOF/polymer monolayers by evaporation‐induced interfacial assembly conducted on an air/water interface. Finally, the easy fusion of a second functional layer onto DPGG‐modified MOF cores, enabled a series of MOF‐based functional nanoarchitectures, such as MOFs encapsulated within hybrid supported lipid bilayers (so‐called protocells), polyhedral core‐shell structures, hybrid lipid‐modified‐plasmonic vesicles and multicomponent supraparticles with target functionalities, to be generated. for a wide range of applications.     

Engineering a Robust,Versatile Amphiphilic Membrane Surface Through Forced Surface Segregation for Ultralow Flux‐Decline

Unlike biofoulants/pollutants, oil foulants/pollutants are prone to coalesce, spread and migrate to form continuous fouling layer covering on the surfaces. Therefore, such kind of fouling can not be simply alleviated by hydrophilic modification with currently extensively used antifouling materials such as poly(ethylene glycol) (PEG)‐based or zwitterionic polymers etc. In the present study, an amphiphilic porous membrane surface, comprising hydrophilic fouling resistant domains and hydrophobic fouling release microdomains, is explored via a "forced surface segregation" approach. The resultant membranes exhibit both superior oil‐fouling and bio‐fouling resistant property: membrane fouling is exquisitely suppressed and the permeation flux‐decline is decreased to an ultralow level. It can be envisaged that the present study may open a novel avenue to the design and construction of robust, versatile antifouling surfaces.     

Synthesis of Thin,Oriented Zeolite A Membranes on a Macroporous Support

Continuous, thin, oriented zeolite A membranes are produced by a two‐step synthesis on macroporous α‐Al₂O₃ supports. In the first step, zeolite A nano‐cubes with ～350‐nm edges are prepared as a native impurity phase in zeolite Y synthesis dispersions, the support surface is pre‐modified with a cationic polymer having a selective affinity for zeolite A. The thus‐treated support is contacted with a colloidally stable dispersion of zeolite A and Y mixture in water, which results in selective, dense‐packed deposition of the zeolite A cubes with one face aligned to the average support surface. In a second step of hydrothermal epitaxial growth, the seed layer grows epitaxially into a continuous, meso‐defect free, ～1 µm thick zeolite A layer, already after 1 h of treatment. This microstructure of the membrane compares very favorably to what is commonly obtained. The pH value of the zeolite mixture suspension is found to have a major influence on seed layer morphology, and thereby, on the quality and orientation of zeolite A membrane after short synthesis times. The final zeolite A membrane thickness and morphology is controlled by varying secondary growth synthesis time. The approach presented is thought to be of generic use for the preparation of oriented zeolite membranes.     

3D Multiscale Superhydrophilic Sponges with Delicately Designed Pore Size for Ultrafast Oil/Water Separation

Developing novel filtering materials with both high permeation flux and rejection rate presents an enticing prospect for oil/water separation. In this paper, robust porous poly(melamine formaldehyde) (PMF) sponges with superwettability and controlled pore sizes through introducing layered double hydroxides (LDH) and SiO₂ electrospun nanofibers are reported. The LDH nanoscrolls endow the sponge with inherent superhydrophilicity and the SiO₂ nanofibers act as pore size regulators by overlapping the PMF mainframe. This approach allows the intrinsic large pores in the pristine sponge to decrease quickly from 109.50 to 23.35 µm, while maintaining porosity above 97.8%. The resulting modified sponges with varied pore sizes can effectively separate a wide range of oil/water mixtures, including the surfactant‐stabilized emulsions, solely by gravity, with ultrahigh permeation flux (maximum of 3 × 10⁵ L m^?2 h^?1 bar^?1) and satisfactory oil rejection (above 99.46%). Moreover, separation of emulsions stabilized by different surfactants, such as anionic, nonionic, and cationic surfactants has been investigated for further practical evaluation. It is expected that such a pore size tuning technology can provide a low cost and easily scaled‐up method to construct a series of filtering materials for high‐efficient separation of target oil/water mixtures.     

Beetle‐Inspired Assembly of Heterostructured Lamellar Membranes with Polymer Cluster–Patterned Surface for Enhanced Molecular Permeation

2D lamellar membranes hold great promise in efficient molecular separations of liquid and gas mixtures. However, the simultaneous realization of high permeation and precise sieving (i.e., overcoming the permeation–rejection tradeoff) of membranes poses a great challenge. Inspired by the structures and functions of the beetle's back, the heterostructured lamellar membranes fabricated through facile and controllable electrostatic atomization method are reported. Particularly, hydrophobic polymer clusters are patterned on hydrophilic laminate (graphene oxide) surfaces to realize the hydrophilic/hydrophobic heterostructure. It shows that the fast dissolution for nonpolar solvents is achieved by the strong affinity polymer clusters, and the ultralow‐barrier diffusion is achieved by the weak affinity laminate channels. Therefore, the permeance is remarkably enhanced (over 7 times for nonpolar solvents), while fully retaining membrane rejection. In contrast, hydrophilic clusters are patterned on hydrophobic laminate (reduced graphene oxide) surfaces and exhibit similar behaviors toward polar solvents. Furthermore, the lamellar membrane displays highly ordered layer‐by‐layer stacking, affording precise molecular rejection. Besides, the lamellar membrane acquires lower thermodynamic energy and hence superior stability under ultrasonic and strong acid or alkali environments, manifesting great potential for long‐term practical operation.     

Ultrathin MnO2/Graphene Oxide/Carbon Nanotube Interlayer as Efficient Polysulfide‐Trapping Shield for High‐Performance Li–S Batteries

Ultrathin MnO₂/graphene oxide/carbon nanotube (G/M@CNT) interlayers are developed as efficient polysulfide‐trapping shields for high‐performance Li–S batteries. A simple layer‐by‐layer procedure is used to construct a sandwiched vein–membrane interlayer of thickness 2 µm and areal density 0.104 mg cm^?2 by loading MnO₂ nanoparticles and graphene oxide (GO) sheets on superaligned carbon nanotube films. The G/M@CNT interlayer provides a physical shield against both polysulfide shuttling and chemical adsorption of polysulfides by MnO₂ nanoparticles and GO sheets. The synergetic effect of the G/M@CNT interlayer enables the production of Li–S cells with high sulfur loadings (60–80 wt%), a low capacity decay rate (?0.029% per cycle over 2500 cycles at 1 C), high rate performance (747 mA h g^?1 at a charge rate of 10 C), and a low self‐discharge rate with high capacity retention (93.0% after 20 d rest). Electrochemical impedance spectroscopy, cyclic voltammetry, and scanning electron microscopy observations of the Li anodes after cycling confirm the polysulfide‐trapping ability of the G/M@CNT interlayer and show its potential in developing high‐performance Li–S batteries.     

Hierarchical NiCo2S4 Nanowire Arrays Supported on Ni Foam: An Efficient and Durable Bifunctional Electrocatalyst for Oxygen and Hydrogen Evolution Reactions

A recent approach for solar‐to‐hydrogen generation has been water electrolysis using efficient, stable, and inexpensive bifunctional electrocatalysts within strong electrolytes. Herein, the direct growth of 1D NiCo₂S₄ nanowire (NW) arrays on a 3D Ni foam (NF) is described. This NiCo₂S₄ NW/NF array functions as an efficient bifunctional electrocatalyst for overall water splitting with excellent activity and stability. The 3D‐Ni foam facilitates the directional growth, exposing more active sites of the catalyst for electrochemical reactions at the electrode–electrolyte interface. The binder‐free, self‐made NiCo₂S₄ NW/NF electrode delivers a hydrogen production current density of 10 mA cm^–2 at an overpotential of 260 mV for the oxygen evolution reaction and at 210 mV (versus a reversible hydrogen electrode) for the hydrogen evolution reaction in 1 m KOH. This highly active and stable bifunctional electrocatalyst enables the preparation of an alkaline water electrolyzer that could deliver 10 mA cm^–2 under a cell voltage of 1.63 V. Because the nonprecious‐metal NiCo₂S₄ NW/NF foam‐based electrodes afford the vigorous and continuous evolution of both H₂ and O₂ at 1.68 V, generated using a solar panel, they appear to be promising water splitting devices for large‐scale solar‐to‐hydrogen generation.     

Template‐Free Sol‐Gel Preparation of Superhydrophobic ORMOSIL Films for Double‐Wavelength Broadband Antireflective Coatings

A double‐layer double‐wavelength antireflective (AR) coating with 100% transmittance at both 1064 nm and 532 nm, which is very important in high power laser systems, is designed using thin film design software (TFCalc). The refractive indices for the bottom and top layers of the designed AR coating are about 1.30 and 1.14. A simple, template‐free sol‐gel route is proposed to prepare the superhydrophobic ORMOSIL (organically modified silicate) thin film, which has an ultralow refractive index, by silica particle surface modification using hexamethylisilazane (HMDS); this treatment decreases the refractive index of the silica thin film from 1.23 to 1.13. The formation mechanism of the ultralow refractive index thin film is proposed. The particle surface modification with HMDS significantly improves the hydrophobicity of the coated film; the water contact angle of the film increases from 23.4° to 160°. The bottom layer, which has a refractive index of 1.30, is prepared from acid‐catalyzed and base‐catalyzed mixed silica sol. A double‐layer silica AR coating is obtained with transmittances of 99.6% and 99.8% at 532 nm and 1064 nm, respectively.     

Ultrathin Graphene Nanofiltration Membrane for Water Purification

A method of fabricating ultrathin (≈22–53 nm thick) graphene nanofiltration membranes (uGNMs) on microporous substrates is presented for efficient water purification using chemically converted graphene (CCG). The prepared uGNMs show well packed layer structure formed by CCG sheets, as characterized by scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. The performance of the uGNMs for water treatment was evaluated on a dead end filtration device and the pure water flux of uGNMs was high (21.8 L m^?2 h^?1 bar^?1). The uGNMs show high retention (>99%) for organic dyes and moderate retention (≈20–60%) for ion salts. The rejection mechanism of this kind of negatively charged membranes is intensively studied, and the results reveal that physical sieving and electrostatic interaction dominate the rejection process. Because of the ultrathin nature of uGNMs, 34 mg of CCG is sufficient for making a square meter of nanofiltration membrane, indicating that this new generation graphene‐based nanofiltration technology would be resource saving and cost‐effective. The integration of high performance, low cost, and simple solution‐based fabrication process promises uGNMs great potential application in practical water purification.