Biomimetic redox-responsive smart coatings with resistance-release functions for reverse osmosis membranes.

Membrane fouling induces catastrophic loss of separation performance and seriously restricts the applications of reverse osmosis (RO) membranes. Inspired by the mussel structure, polydopamine (PDA) and cystamine molecules (CA) with excellent anti-fouling properties were used to prepare accessible, biocompatible, and redox-responsive coatings for RO membranes. The PDA/CA-coated RO membranes exhibit a superior water flux of 65 L m-2 h-1 with a favourable NaCl rejection exceeding 99%. The water permeability through the PDA/CA-coated membrane is much higher than that of most membranes with similar rejection rates. Due to the formed protective hydration layers by PDA/CA coatings, anti-fouling properties against proteins, polysaccharides and surfactants were evaluated separately, and ultralow fouling properties were demonstrated. Moreover, the disulfide linkages in CA molecules can cleave in a reducing environment, yielding the degradation of PDA/CA coatings, thereby removing the foulants deposited on the coatings. The degradation endows the coated membranes with satisfying longtime anti-fouling properties, where the flux recovery reaches up to 90%. The construction of redox-responsive smart coatings not only provided a promising route to alleviate membrane fouling but can also be upscaled for use in numerous practical applications like sensors, medical devices, and drug delivery.

Eco-Friendly Silver Nanoparticles/Chitosan/Poly(vinyl alcohol) Composites Exhibit Remarkable EMI Shielding Capabilities and Outstanding Thermal Conductivities.

The integration and miniaturization of contemporary electronics have led to significant challenges in dealing with electromagnetic (EM) radiation and heat accumulation. Despite these issues, achieving high thermal conductivity (TC) and electromagnetic interference (EMI) shielding effectiveness (SE) in polymer composite films remains an exceptionally difficult task. In this work, we used a straightforward in situ reduction process and a vacuum-drying method to successfully prepare a flexible Ag NPs/chitosan (CS)/PVA nanocomposite with three-dimensional (3D) conductive and thermally conductive network architectures. The 3D silver pathways formed by attaching to the chitosan fibers endow the material with simultaneous exceptional TC and EMI capabilities. At a silver concentration of 25 vol %, the TC of Ag NPs/CS/PVA nanocomposites reaches 5.18 W·m-1·K-1, exhibiting an approximately 25 times increase compared to CS/PVA composites. The electromagnetic shielding performance of 78.5 dB significantly outperforms the specifications of standard commercial EMI shielding applications by a significant margin. Additionally, Ag NPs/CS/PVA nanocomposites have greatly benefited from microwave absorption (SEA), effectively impeding the transmission of EM waves and reducing the reflected secondary EM wave pollution. Meanwhile, the composite material still maintains good mechanical properties and bendability. This endeavor helped develop malleable and durable composites that possess superior EMI shielding capabilities and intriguing heat dissipation properties using innovative design and fabrication methods.

Donnan Effect-Engineered Covalent Organic Framework Membranes toward Size- and Charge-Based Precise Molecular Sieving.

Covalent organic frameworks (COFs), with ordered pores and well-defined topology, are ideal materials for nanofiltration (NF) membranes because of their capacity of transcending the permeance/selectivity trade-off predicament. However, most reported COF-based membranes are focused on separating molecules with different sizes, resulting in low selectivity to similar molecules with different charges. Here, the negatively charged COF layer was fabricated in situ on a microporous support for the separation of molecules with different sizes and charges. Ultrahigh water permeance (216.56 L m-2 h-1 bar-1) was obtained because of the ordered pores and excellent hydrophilicity, which exceeds that of most membranes with similar rejections. For the first time, we used multifarious dyes with different sizes and charges, for the investigation of the selectivity behavior caused by the Donnan effect and size exclusion. The obtained membranes represent superior rejections to negatively and neutrally charged dyes larger than 1.3 nm, while positively charged dyes with a size of 1.6 nm can pass through the membrane, resulting in the separation of negative/positive mixed dyes with similar molecular sizes. This strategy of combining the Donnan effect and size exclusion in nanoporous materials may evolve into a generic platform for sophisticated separation.

One-pot superhydrophilic surface modification of waste polyurethane foams for high-efficiency oil/water separation.

Despite of the fact that polymers have brought tremendous convenience to human life, they have also inevitably caused considerable environmental pollution after their service life. Therefore, a feasible strategy that can effectively recycle waste polymers and endow them with high added value is much desired. Superwetting materials have shown great promise in oily wastewater treatment because of their high oil/water separation efficiency. However, most of these materials present some limitations, such as complex preparation procedures and poor salt tolerance, which hamper their practical applications. In this study, an iron hydroxide@polydopamine@waste polyurethane foam (Fe(OH)3@PDA@WPU) was synthesized via a facile and mild "one-pot" reaction. During this process, polymerization of dopamine and in situ growth of Fe(OH)3 were simultaneously realized, and the resultant PDA and Fe(OH)3 nanoparticles were firmly attached to the surface of WPU. Due to the abundant hydrophilic groups from PDA and Fe(OH)3 coupled with the surface roughness created by Fe(OH)3 nanoparticles, the surface properties of the foam could be changed from hydrophobic to superhydrophilic. Remarkably, the Fe(OH)3@PDA@WPU was capable of separating various oil/water mixtures even under some severe conditions (e.g. erosion in a saturated sodium chloride solution and longtime sonication), demonstrating high potential in marine oily sewage treatment. Moreover, this work also paved a new path for reducing the negative impact of waste polymer foams on our environment, and in the meantime realizing their high value utilization.

Eco-friendly chitosan@silver/plant fiber membranes for masks with thermal comfortability and self-sterilization.

The surgical masks have been essential consumables for public in the COVID-19 pandemic. However, long-time wearing masks will make wearers feel uncomfortable and massive discarded non-biodegradable masks lead to a heavy burden on our environment. In this paper, we adopt degradable chitosan@silver (CS@Ag) core-shell fibers and plant fibers to prepare an eco-friendly mask with excellent thermal comfort, self-sterilization, and antiviral effects. The thermal network of CS@Ag core-shell fibers highly improves the in-plane thermal conductivity of masks, which is 4.45 times higher than that of commercial masks. Because of the electrical conductivity of Ag, the fabricated mask can be electrically heated to warm the wearer in a cold environment and disinfect COVID-19 facilely at room temperature. Meanwhile, the in-situ reduced silver nanoparticles (AgNPs) endow the mask with superior antibacterial properties. Therefore, this mask shows a great potential to address the urgent need for a thermally comfortable, antibacterial, antiviral, and eco-friendly mask. Supplementary Information: The online version contains supplementary material available at 10.1007/s10570-022-04582-x.

Temperature-adjustable F-carbon nanofiber/carbon fiber nanocomposite fibrous masks with excellent comfortability and anti-pathogen functionality.

Wearing surgical masks remains the most effective protective measure against COVID-19 before mass vaccination, but insufficient comfortability and low antibacterial/antiviral activities accelerate the replacement frequency of surgical masks, resulting in large amounts of medical waste. To solve this problem, we report new nanofiber membrane masks with outstanding comfortability and anti-pathogen functionality prepared using fluorinated carbon nanofibers/carbon fiber (F-CNFs/CF). This was used to replace commercial polypropylene (PP) nonwovens as the core layer of face masks. The through-plane and in-plane thermal conductivity of commercial PP nonwovens were only 0.12 and 0.20 W/m K, but the F-CNFs/CF nanofiber membranes reached 0.62 and 5.23 W/m K, which represent enhancements of 380% and 2523%, respectively. The surface temperature of the PP surgical masks was 23.9 ℃ when the wearing time was 15 min, while the F-CNFs/CF nanocomposite fibrous masks reached 27.3 ℃, displaying stronger heat dissipation. Moreover, the F-CNFs/CF nanofiber membranes displayed excellent electrical conductivity and produced a high-temperature layer that killed viruses and bacteria in the masks. The surface temperature of the F-CNFs/CF nanocomposite fibrous masks reached 69.2 ℃ after being connected to a portable power source for 60 s. Their antibacterial rates were 97.9% and 98.6% against E. coli and S. aureus, respectively, after being connected to a portable power source for 30 min.

Highly thermally conductive and eco-friendly OH-h-BN/chitosan nanocomposites by constructing a honeycomb thermal network.

More than 110,000,000 tons of mismanaged plastics were to be produced in 2020. Polymers are favored in the preparation of thermally conductive materials due to their excellent comprehensive properties. However, most polymers fabricated for thermally conductive materials are difficult to degrade in the natural environment. To alleviate the increasingly severe environmental problems, we reported a novel eco-friendly material with high thermal conductivity, which was composited of chitosan microspheres (CSM) and hydroxyl-functionalized hexagonal boron nitride (OH-h-BN) nanoplatelets. Utilizing their significant difference in scales, the OH-h-BN nanoplatelets were arranged between each CSM. Their overall structure was similar to the honeycomb: CSM were honeycomb cores, and OH-h-BN nanoplatelets were honeycomb network. The routine-structure OH-h-BN/CS nanocomposites were only 0.94 ± 0.02 W·m-1·K-1 at 50 wt% in thermal conductivity. However, the OH-h-BN/CSM nanocomposites with honeycomb structure can reach 5.66 ± 0.32 W·m-1·K-1 in the same loading, for enhancement of 502% and 1914% than OH-h-BN/CS nanocomposites and pure CS, respectively.

Heat Conduction and Antibacterial Hexagonal Boron Nitride/Polypropylene Nanocomposite Fibrous Membranes for Face Masks with Long-Time Wearing Performance.

Wearing surgical masks is one of the best protective measures to protect humans from viral invasion during the 2019 coronavirus (COVID-19) outbreak. However, wearing surgical masks for extended periods will cause uncomfortable sweltering sense to users and are easy to breed bacteria. Here, we reported a novel fibrous membrane with outstanding comfortability and antibacterial activity prepared by PP ultrafine fiber nonwovens and antibacterial functionalized h-BN nanoparticles (QAC/h-BN). The thermal conductivity of commercial PP nonwovens was only 0.13 W m-1 K-1, but that of the QAC/h-BN/PP nanocomposite fibrous membranes can reach 0.88 W m-1 K-1, an enhancement of 706.5% than commercial PP nonwovens. The surface temperature of commercial PP surgical masks was 31.8 °C when the wearing time was 60 min. In contrast, QAC/h-BN/PP surgical masks can reach 33.6 °C at the same tested time, exhibiting stronger heat dissipation than commercial PP surgical masks. Besides, the antibacterial rates of QAC/h-BN/PP nanocomposite fibrous membranes were 99.3% for E. coli and 96.1% for S. aureus, and their antibacterial mechanism was based on "contact killing" without the release of unfavorable biocides. We think that the QAC/h-BN/PP nanocomposite fibrous membranes could provide better protection to people.

Biodegradable all-cellulose composite membranes for simultaneous oil/water separation and dye removal from water.

While of enormous scientific interests, the super-wetting materials capable of one-step separation of oils and dyes from water are rare on the market. Besides, the disposal of the used materials themselves is still a challenge, mainly ascribed to their non-biodegradation. Herein, we report an all-cellulose composite membrane that can simultaneously remove oil and dye from water. The membrane was fabricated via a simple dip-coating process during which the filter paper was coated by a cellulose hydrogel layer. This cellulose hydrogel coating was discovered to play an essential role in the separation of oil/water emulsion. Meanwhile, the incorporation of citric acid remarkably improved the mechanical and adsorption properties of the membrane as it served as both the crosslinking agent and the active species for methylene blue adsorption. This work demonstrated a new strategy on the development of fully biodegradable materials for both high-efficiency oil/water separation and dye removal.

An l-cystine/l-cysteine impregnated nanofiltration membrane with the superior performance of an anchoring heavy metal in wastewater.

Considerable efforts are being made to develop new materials and technologies for the efficient and fast removal of toxic ions in drinking water. In this work, we developed a sulfur-complexed strategy to enhance the removal capability of heavy metal ions using the polyamide nanofiltration membrane by the covalent anchoring of l-cystine and l-cysteine. The sulfur-functionalized polyamide nanofiltration membrane exhibits superior complexation of heavy metal ions and can efficiently remove them from high-concentration wastewater. As a result, the sulfur-functionalized nanofiltration membrane not only showed excellent desalination performance but also achieved a record removal rate of heavy metal ions (99.99%), which can effectively reduce Hg(ii) concentration from 10 ppm to an extremely low level of 0.18 ppb, well below the acceptable limits in drinking water (2 ppb). Moreover, the sulfur-functionalized nanofiltration membrane showed an exciting long-term stability and can be easily regenerated without significant loss of Hg(ii) removal efficiency even after six cycles. Such outstanding performances were attributed to the synthetic effect of Hg-S coordinative interaction, electrostatic repulsion, and the sieving action of nanopores. These results highlight the tremendous potential of thiol/disulfide-functionalized NF active layer as an appealing platform for removing heavy metal ions from polluted water with high performance in environmental remediation.

Sulfaguanidine nanofiltration active layer towards anti-adhesive and antimicrobial attributes for desalination and dye removal.

A novel sulfaguanidine (SG)-modified polyamide thin-film composite (TFC) nanofiltration (NF) membrane was constructed by the strategy referred to as co-solvent assisted interfacial polymerization (CASIP), which involves the respective interfacial polymerization (IP) of piperazine (PIP) and SG with trimesoyl chloride (TMC) on porous polysulfone (PSf) supports. CASIP enables the formation of a defect-free thin dense active layer and favors higher water permeance up to 79.0 L m-2 h-1 with rejection above 98.3% for Na2SO4. The resulting PA membrane also demonstrates a high flux recovery ratio of nearly 98.9% to bovine serum albumin protein after being cleaned. More importantly, the current membrane shows excellent anti-adhesive and antimicrobial performances against Gram-negative Escherichia coli, Gram-positive Bacillus pumilus LDS.33 and Aspergillus parasiticus JFS. This promises great potential application of the PA membrane for practical water/wastewater treatment. The prospect of using the co-solvent mediated SG-modified layer as a next-generation anti-fouling/antimicrobial membrane is very encouraging.

Ultrathin Active Layer for Transparent Electromagnetic Shielding Window.

Recently, electromagnetic (EM) shielding (EMS) window, especially the ultrathin, transparent EMS active layer, has been the primary objective of extensive studies because of its widely potential applications in stealth technology, high radiation pollution, and others. However, several defects, including opacity and large thickness, have severely restricted the application in optical EMS devices. Herein, we developed an ultrathin and highly transparent EMS active layer on a rigid glass and a flexible polyethylene terephthalate substrate by chemical doping CVD (chemical vapor deposition) graphene with nitric acid (HNO3) as the P-type dopant, which has a 91% transmittance and 1/1000 thickness compared to the conventional EMS active layer. The HNO3-treated graphene shows excellent EMS efficiency by a factor of 4.5, significantly compensating for the adverse effects of the grain boundaries between CVD graphene crystals. Additionally, 55% HNO3 is the most suitable for achieving high EMS effectiveness, which can be significantly improved by treating for only 5 min. This unique chemical-doping CVD graphene holds potential for being exploited as a transparent active layer in numerous EMS applications.

Progress and Challenges in Transfer of Large-Area Graphene Films.

Graphene, the thinnest, strongest, and stiffest material with exceptional thermal conductivity and electron mobility, has increasingly received world-wide attention in the past few years. These unique properties may lead to novel or improved technologies to address the pressing global challenges in many applications including transparent conducting electrodes, field effect transistors, flexible touch screen, single-molecule gas detection, desalination, DNA sequencing, osmotic energy production, etc. To realize these applications, it is necessary to transfer graphene films from growth substrate to target substrate with large-area, clean, and low defect surface, which are crucial to the performances of large-area graphene devices. This critical review assesses the recent development in transferring large-area graphene grown on Fe, Ru, Co, Ir, Ni, Pt, Au, Cu, and some nonmetal substrates by using various synthesized methods. Among them, the transfers of the most attention kinds of graphene synthesized on Cu and SiC substrates are discussed emphatically. The advances and the main challenges of each wet and dry transfer method for obtaining the transferred graphene film with large-area, clean, and low defect surface are also reviewed. Finally, the article concludes the most promising methods and the further prospects of graphene transfer.

Metastable region of phase diagram: optimum parameter range for processing ultrahigh molecular weight polyethylene blends.

Numerous studies suggest that two-phase morphology and thick interface are separately beneficial to the viscosity reduction and mechanical property maintainence of the matrix when normal molecular weight polymer (NMWP) is used for modification of ultrahigh molecular weight polyethylene (UHMWPE). Nevertheless, it is very difficult to obtain a UHMWPE/NMWP blend which may demonstrate both two-phase morphology and thick interface. In this work, dissipative particle dynamics simulations and Flory-Huggins theory are applied in predicting the optimum NMWP and the corresponding conditions, wherein the melt flowability of UHMWPE can be improved while its mechanical properties can also be retained. As is indicated by dissipative particle dynamics simulations and phase diagram calculated from Flory-Huggins theory, too small Flory-Huggins interaction parameter (χ) and molecular chain length of NMWP (N(NMWP)) may lead to the formation of a homogeneous phase, whereas very large interfacial tension and thin interfaces might also appear when parameters N(NMWP) and χ are too large. When these parameters are located in the metastable region of the phase diagram, however, two-phase morphology occurs and interfaces of the blends are extremely thick. Therefore, metastable state is found to be advisable for both the viscosity reduction and mechanical property improvement of the UHMWPE/NMWP blends.

Theoretical study on the identity ion pair SN2 reactions of LiX with CH3SX (X=Cl, Br, and I): structure, mechanism, and potential energy surface.

Three archetypal ion pair nucleophilic substitution reactions at the methylsulfenyl sulfur atom LiX+CH3SX-->XSCH3+LiX (X=Cl, Br, and I) are investigated by the modified Gaussian-2 theory. Including lithium cation in the anionic models makes the ion pair reactions proceed along an SN2 mechanism, contrary to the addition-elimination pathway occurring in the corresponding anionic nucleophilic substitution reactions X-+CH3SX-->XSCH3+X-. Two reaction pathways for the ion pair SN2 reactions at sulfur, inversion and retention, are proposed. Results indicate the inversion pathway is favorable for all the halogens. Comparison of the transition structures and energetics for the ion pair SN2 at sulfur with the potential competition ion pair SN2 reactions at carbon LiX+CH3SX-->XCH3+LiXS shows that the SN2 reactions at carbon are not favorable from the viewpoints of kinetics and thermodynamics.