We have infused graphene/ionic liquid into block copolymer homoporous membranes (HOMEs), which have highly ordered uniform cylindrical nanopores, to form compact, dense, and continuous graphene/ionic liquid (Gr/IL) lubricating layers at interfaces, enabling a reduction in the friction coefficient. Raman and XPS analyses, confirmed the parallel alignment of the cation of ILs on graphene by the π–π stacking interaction of the imidazolium ring with the graphene layer. This alignment loosens the lattice spacing of Gr in Gr/ILs, leading to a larger lattice spacing of 0.36 nm in Gr of Gr/ILs hybrids than the pristine Gr (0.33 nm). The loose graphene layers, which are caused by the coexistence of graphene and ILs, would make the sliding easier, and favor the lubrication. An increase in the friction coefficient was observed on ILs-infused block copolymer HOMEs, as compared to Gr/ILs-infused ones, due to the absence of Gr and the unstably formed ILs film. Gr/ILs-infused block copolymer HOMEs also exhibit much smaller residual indentation depth and peak indentation depth in comparison with ILs-infused ones. This indicates that the existence of stably supported Gr/ILs hybrid liquid films aids the reduction of the friction coefficient by preventing the thinning of the lubricant layer and exposure of the underlying block copolymer HOMEs.

The release of hydrogen halides in Friedel–Crafts alkylation has long been considered as troublesome and detrimental. Here we demonstrate that the released HCl in alkylation is beneficial and highly demanded to remove poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) templates from the phenolic supramolecules for the preparation of ordered nanoporous phenolic polymers as additional treatment for template removal is no longer necessary. Friedel–Crafts alkylation using bifunctional alkylation agent, 1,4-bis(chloromethyl)benzene, leads to the hyper-cross-linking of phenolic polymers, thus generating micropores in the skeleton of the polymers. HCl in situ generated as the byproduct during alkylation facilely extracts the copolymer because of its enhanced diffusion through the micropores. The prepared phenolic polymers exhibit high surface areas and well-ordered porosities in a hexagonal or gyriodal structure. The in situ cavitation by alkylation takes place at much milder conditions and has higher efficiency than other template-removing methods.

•Polysulfone-block-polyethylene glycol (PEG) are used to prepare UF membranes.•No porogen or additive is required in the membrane-forming process.•PEG blocks deliver both surface seggregation and water-channel effect.•Excellent hydrophilicity, permeablity, and fouling resistance are achieved.Water-soluble polymers are generally required in the process of nonsolvent-induced phase separation (NIPS) as additives or modifiers to enhance the hydrophilicity and permeability of ultrafiltration membranes. In this work, we demonstrate that amphiphilic block copolymers, polysulfone-block-poly (ethyleneglycol) (PSf-b-PEG), dissolved alone in solvents without any additives lead to highly permeable, fouling-resistant membranes via the NIPS process. PEG blocks deliver dual functions in the membranes. Selective enrichment of PEG blocks on the membrane surface as a result of surface segregation enhances the hydrophilicity and consequently fouling resistance of the membranes. Moreover, microscale phase separation of the block copolymers drives the formation of interconnected PEG microdomains distributed throughout the bulk membrane as confirmed by the transmission electron microscopy analysis on stained membrane slices. PEG microdomains serve as water channels facilitating water transport through the membrane. As a result, thus produced membranes exhibit excellent permeability a few times higher than other PSf-based ultrafiltration membranes with similar retentions. For instance, a membrane having the molecular weight cut-off of 70 kDa gives a water permeability as high as 450 m−2 h−1 bar−1. Furthermore, the retentions of the PSf-b-PEG membranes can be tuned in a relatively wide range simply by adjusting the copolymer concentration in the casting solutions. Using amphiphilic block copolymers alone as the base materials for the preparation of ultrafiltration membranes by NIPS not only simplifies membrane manufacturing process but also opens a new avenue to prepare advanced membranes with upgraded permeability and fouling resistance.

Water flow inside polyamide (PA) reverse osmosis (RO) membranes is studied by steady state nonequilibrium molecular dynamics (NEMD) simulations in this work. The PA RO membrane is constructed with the all-atom model, and the density and average pore size obtained thereby are consistent with the latest experimental results. To obtain the time-independent water flux, a steady state NEMD method is used under various pressure drops. The water flux in our simulations, which is calculated under higher pressure drops, is in a linear relation with the pressure drops. Hence, the water flux in lower pressure drops can be reliably estimated, which could be compared with the experimental results. The molecular details of water flowing inside the membrane are considered. The radial distribution function and residence time of water around various groups of polyamide are introduced to analyze the water velocities around these groups, and we find that water molecules flow faster around benzene rings than around carboxyl or amino groups in the membrane, which implies that the main resistance of mass transport of water molecules comes from the carboxyl or amino groups inside the membranes. This finding is in good consistency with experimental results and suggests that less free carboxyl or amino groups should be generated inside RO membranes to enhance water permeance.

We report the formation of three-dimensionally interconnected nanoporosities with in situ PEGylated pore walls simply by swelling the block copolymers of polysulfone and poly(ethylene glycol) in paired solvents. The produced nanoporous polymers are expected to find important applications in membranes, batteries, chromatography, and haemodialysis.

•PS/PEO block copolymer was used to produce UF membranes by selective swelling.•Membrane permselectivity was flexibly tuned.•PEO blocks were enriched on the pore walls after swelling.•The membrane exhibit exceptional fouling resistance.•The fouling resistance is expected to be long standing.Ultrafiltration (UF) membranes with high permeability and good fouling resistance hold great promise in water treatment and many industry sectors. Herein, antifouling UF composite membranes with mesoporous films of polystyrene (PS)/poly(ethylene oxide) (PEO) block copolymer as the selective layers were produced by the process of selective-swelling-induced pore generation. We spin-coated thin layers of block copolymer onto macroporous supports, and activated the copolymer layers by soaking them in hot ethanol to induce the selective swelling of the PEO microdomains. The porous structures of the block copolymer selective layers can be continuously modulated simply by varying the swelling durations, resulting in UF membranes with water permeabilities adjustable in the range of ~ 100 to 600 L m-2 h-1 bar-1. Interestingly, the hydrophilic PEO blocks were enriched on the pore walls after swelling, rendering an inherent fouling resistance to the membranes. Protein fouling tests demonstrated that the membrane exhibited exceptional fouling resistance with a recover ratio in water flux of nearly 100%. This fouling resistance is expected to be long-standing as the PEO chains are covalently bonded to the membrane matrix.Download high-res image (223KB)Download full-size image

•Titanicone was firstly ALD-deposited onto the surface of tubular ceramic membranes.•Original dense titanicone was converted to microporous TiO2 by calcination.•The microporous TiO2 layer served as the new selective layer for the membrane.•The membrane properties can be tuned simply by changing the ALD cycles.•The prepared membrane exhibits a MWCO of ~680 Da and flux of 30 L m−2 h−1 bar−1.Ceramic nanofiltration (NF) membranes are of particular significance for molecular separations under harsh conditions. However, they are usually manufactured by the sol-gel process which frequently suffers from low efficiency and poor control in the membrane properties. Herein we demonstrate an efficient and more controllable strategy to produce ceramic tubular NF membranes based on atomic layer deposition (ALD). Tubular ceramic membranes with pore size of ~5 nm are used as the substrates, on which titanium alkoxide (titanicone) is ALD-deposited. Subsequent calcination in air degrades the organic moieties in titanicone, thus converting the dense layer of titanicone into a microporous layer of TiO2. This microporous TiO2 layer serves as a thin separation layer delivering the NF size-sieving function. The thickness of the TiO2 layer can be readily tuned by changing the ALD cycle numbers, and correspondingly the original substrate membranes are progressively tightened with rising ALD cycles, and the membrane with 300 cycles exhibits a molecular-weight-cut-off (MWCO) of ~680 Da and water permeability of 30 L m−2 h−1 bar−1. Such a water permeability is higher than many other ceramic tubular membranes with similar MWCOs because of the ultrathin nature of the microporous TiO2 layer established by titanicone deposition and calcination.Download high-res image (150KB)Download full-size image

•Block copolymer (BCP) solutions are machine-cast to prepare composite membranes.•Cheap and robust polyester nonwoven is used as the support for the membranes.•Nanoporosities are generated in the BCP layers by selective swelling.•Membrane permselectivity is tuned by altering swelling temperatures and durations.•The membranes efficiently narrow down the size distribution of nanoparticles.Block copolymer (BCP) membranes are distinguished for their well-defined porosities, tunable pore geometries, and functionable pore walls. However, it remains challenging to produce robust BCP membranes by affordable, convenient methods. Herein, we demonstrate a facile and easily upscalable approach to produce highly permeable BCP membranes in large areas. The membranes possess a bi-layered composite structure with nanoporous polystyrene-block-poly(2-vinylpyrdine) BCP layers directly supported on macroporous nonwoven substrates. The BCP layers are machine-cast on the water-prefilled nonwoven, and interconnected nanoporosities are created in the BCP layers by ethanol swelling. The nanoporous BCP layers exhibit a thickness of ~10 µm and are tightly adhered to the nonwoven. Changes in the swelling temperatures and durations modulate both pore sizes and surface hydrophilicity of the BCP layers, and consequently the permselectivity of the membranes. By increasing swelling duration from 15 min to 12 h, the permeability of the membrane swollen at 65 °C can be increased from ~100 to ~850 L m−2 h−1 bar−1 with the retention to 15-nm gold nanoparticles reduced from ~93% to ~54%. Moreover, we demonstrate that the composite membrane can efficiently fractionate nanoparticles and narrow down their size distribution from ~3–20 nm to ~3–10 nm.Download high-res image (276KB)Download full-size image

•A pore-filling strategy is developed to prepare membranes with tight UF capability.•Phenolic/Pluronic supramolecules are filling into the pores of PVDF MF substrates.•Pluronic is extracted by H2SO4 to produce mesopores in the macropores of PVDF.•The separation performances depend on the dosages of supramolecular solutions.•Tight size-sieving capabilities, e.g. a MWCO of ~2350, are achieved.Mesoporous polymers derived from supramolecules of phenolic resins (PRs) and block copolymers (BCPs) containing highly uniform pores with sizes down to a few nanometers, are expected to deliver promising membrane separation performances. Here we report on the preparation of mesoporous phenolic membranes exhibiting tight ultrafiltration properties through a pore-filling strategy. Solutions of PR/BCP supramolecules are filled into the macropores of polyvinylidene fluoride (PVDF) microfiltration membranes (substrates), followed by thermopolymerization to solidify the solution in the pores. Subsequently, the filled PVDF substrates are treated in hot H2SO4 to remove the BCP components, thus producing mesopores in the PR framework. The produced composite membranes are mechanical robust and ductile as mesoporous phenolic resins are tightly embedded in the pores of the PVDF matrix. The mesoscale porosity in the PR phases endow the composite membrane a tight ultrafiltration performance with the molecular-weight-cut-off (MWCO) down to 2350 Da. The separation properties can be tuned simply by adjusting the dosage of supramolecule solutions used to fill the macroporous substrates. Considering the tight and uniform pore sizes and the robustness of phenolic resins, this strategy opens a new avenue to ultrafiltration membranes with low MWCOs or even nanofiltration membranes.Download high-res image (238KB)Download full-size image

•Polyimide (PI) is synthesized by atomic layer deposition on porous alumina.•Deposition mainly occurs on the pore openings of alumina with short exposure.•Thus-deposited membranes are in the form of thin-film composites.•Retention is greatly upgraded at moderate expense of water permeability.•Long exposure of precursors leads to the uniform thin deposition along pore walls.Polyimide is deposited on the surface of nanoporous anodized alumina by atomic layer deposition (ALD) using pyromellitic dianhydride and ethylenediamine as the two precursors. Such ALD reactions directly produce polyimide rather than the intermediate polyamic acid. The precursor exposure duration plays an important role in determining the growth rate of PI and consequently the reduction of effective pore sizes. ALD with short precursor exposure confines the deposition predominantly around the pore openings of the alumina substrates, producing an asymmetric structure in the form of thin-film composites. This structure efficiently reduces the pore sizes of alumina, and as a result the retention of the membrane is significantly improved. A moderate cycle number of 50 remarkably increases the rejection of the membrane from nearly none to 82% at an acceptable expense of a reduction of 63% in water permeability. Deposition with long precursor exposure results in uniform coating into deep pores of the membranes whereas the effect in tailoring pore sizes and filtration performances are not as pronounced as deposition with short precursor exposure. This work is expected to be adopted to fabricate highly permeable and selective membranes of different materials by leveraging the deposition behavior of ALD on appropriate substrates.Download high-res image (181KB)Download full-size image

ConspectusPores regulate the entry and exit of substances based on the differences in physical sizes or chemical affinities. Pore uniformity, ordering, and the homogeneity of the surface chemistry of the pore walls are vital for maximizing the performance of a porous material because any scattering in these parameters weakens the capability of pores to discriminate foreign substances. Most strategies for the creation of homogeneous pores are destructive, and sacrificial components in the precursor materials must be selectively removed to generate porosities. The incorporation and subsequent removal of the sacrificial components frequently make the pore-making process complicated and inefficient and impose greater uncertainty in the control of the pore homogeneity.Block copolymers (BCPs) have been demonstrated to be promising precursors in the fabrication of highly ordered nanoporous structures. Unfortunately, BCP-derived porosities are also predominantly dependent on destructive pore-making processes (e.g., etching or extraction). To address this problem, we have developed a swelling-based nondestructive strategy. In this swelling process, one simply needs to immerse BCP materials in a solvent selective for the minority blocks for hours. After removing the BCPs from the solvent followed by air drying, pores are generated throughout the BCP materials in the positions where the minority blocks initially dwell. This Account discusses our recent discoveries, new insights, and emerging applications of this burgeoning pore-making method with a focus on the development of ordered porosities in bulk BCP materials.The initial morphology and orientation of the minority phases in BCPs determine the pore orientation and geometry in the produced porous materials. For nonaligned BCPs, three-dimensionally interconnected pores with sizes scattering in the 10–50 nm range are produced after swelling. There is a morphology evolution of BCP materials from the initial nonporous structure to the increasingly opened nanoporous intermediates, to interconnected networks of micellar nanofibers, and finally to isolated micellar spheres with increasing degrees of swelling. When the BCP films are aligned perpendicularly or in-plane, selective swelling results in uniform “standing” (perpendicular orientation) and “sleeping” (in-plane orientation) pores, respectively. Pore sizes can be tuned by changing molecular weights of the BCPs and swelling conditions without the loss of pore uniformity. Due to the nondestructive nature of this swelling process, nothing in the BCPs is lost during the pore-forming procedure, and consequently the formed pores can be progressively closed also by selective swelling. Such reversible pore opening/closing can be repeated many times, enabling the application of these materials in drug delivery and intelligent antireflective coatings. The monodispersed pore sizes, straight pore profile, and hydrophilic pore walls particularly favor the application of the porous BCPs in separations as homoporous membranes (HOMEs) exhibiting high selectivity, permeability, and inherent stimulus responsiveness.

Extremely permeable ultrafiltration membranes with elongated elliptical pores are fabricated by stretching composite membranes with homoporous selective layers and macroporous supports. With simultaneously increased porosities both for the selective layers and supports and the thinned selective layers, the stretched membranes exhibit multifold-enhanced permeability with little sacrifice in selectivities. Thus the produced membranes enable, for the first time, gravity-driven ultrafiltration and discrimination of similarly sized nanoparticles with diameters down to 30 nm.

We designed spongy monoliths allowing liquid delivery to their surfaces through continuous nanopore systems (mean pore diameter ∼40 nm). These nanoporous monoliths were flat or patterned with microspherical structures a few tens of microns in diameter, and their surfaces consisted of aprotic polymer or of TiO2 coatings. Liquid may reduce adhesion forces FAd; possible reasons include screening of solid–solid interactions and poroelastic effects. Softening-induced deformation of flat polymeric monoliths upon contact formation in the presence of liquids enhanced the work of separation WSe. On flat TiO2-coated monoliths, WSe was smaller under wet conditions than under dry conditions, possibly because of liquid-induced screening of solid–solid interactions. Under dry conditions, WSe is larger on flat TiO2-coated monoliths than on flat monoliths with a polymeric surface. However, under wet conditions, liquid-induced softening results in larger WSe on flat monoliths with a polymeric surface than on flat monoliths with an oxidic surface. Monolithic microsphere arrays show antiadhesive properties; FAd and WSe are reduced by at least 1 order of magnitude as compared to flat nanoporous counterparts. On nanoporous monolithic microsphere arrays, capillarity (WSe is larger under wet than under dry conditions) and solid–solid interactions (WSe is larger on oxide than on polymer) dominate contact mechanics. Thus, the microsphere topography reduces the impact of softening-induced surface deformation and screening of solid–solid interactions associated with liquid supply. Overall, simple modifications of surface topography and chemistry combined with delivery of liquid to the contact interface allow adjusting WSe and FAd over at least 1 order of magnitude. Adhesion management with spongy monoliths exploiting deployment (or drainage) of interfacial liquids as well as induction or prevention of liquid-induced softening of the monoliths may pave the way for the design of artificial surfaces with tailored contact mechanics. Moreover, the results reported here may contribute to better understanding of the contact mechanics of biological surfaces.Keywords: adhesion; atomic layer deposition; bioinspired materials; block copolymers; microspheres; porous materials; surfaces

Poly(ethylene oxide) (PEO) is well-known for its excellent resistance to the nonspecific adsorption of proteins. However, it remains challenging to fabricate surfaces with uniform and robust coverage of PEO chains in a simple and efficient way. Simply by treating the block copolymer polystyrene-block-poly(ethylene oxide) (PS-b-PEO) in ethanol, we obtain nanoporous polymeric films with superior resistance to protein adsorption. The pores are nondestructively formed via the selective swelling-induced pore generation mechanism in which PEO microdomains embedded in PS matrix are selectively swollen in ethanol and collapsed in the subsequent air drying. Pore sizes and porosities can be typically tuned in the ranges ∼20–50 nm and ∼20–70%, respectively, by changing swelling durations and temperatures. Interestingly, the PEO chains are simultaneously migrated on the film surface and pore walls in the selective swelling-induced pore forming process. Atomic force microscopy examinations reveal that PEO chains are solvated when the film is wetted with water, closing the pores in the film. Thus, produced SEO films adsorb much less proteins than PS films without PEO on the surface, and also demonstrate a better fouling resistance than many reported PEO-covered surfaces prepared by other methods.

Mesoscopic lead halide perovskite solar cells typically use TiO2 nanoparticle films as the scaffolds for electron-transport pathway and perovskite deposition. Here, we demonstrate that swelling-induced mesoporous block copolymers can be templates for producing three-dimensional TiO2 networks by combining the atomic layer deposition technique. Thickness adjustable TiO2 network is an excellent alternative scaffold material for efficient perovskite solar cells. Our best performing cells using such a 270 nm thick template have achieved a high efficiency of 12.5 % with pristine poly-3-hexylthiophene as a hole transport material. The high performance is attributed to the direct transport pathway and high absorption of scaffolds, small leakage current and largely reduced recombination rate at interfaces. The results show that TiO2 network architecture is a promising scaffold for mesoscopic perovskite solar cells.

The selective swelling of amphiphilic block copolymers has been demonstrated to be extremely facile and efficient in producing nanoporous membranes. However, all previous works are limited to diblock copolymers composed of two glassy blocks, suffering from inherent mechanical weakness. Here we elucidate the selective swelling-induced pore generation of triblock terpolymers with a rubbery polyisoprene (PIP) block, polyisoprene-block-polystyrene-block-poly(2-vinylpyridine) (PIP-b-PS-b-P2VP). A short exposure to ethanol turns the initially dense films to nanoporous membranes with well-defined interconnected porosity. We fabricate composite membranes with the nanoporous terpolymer thin films as the selective layers deposited on macroporous substrates. Using PS-b-P2VP diblock copolymer without a rubbery third block for comparison, we identify the role of the rubbery PIP blocks in determining the mechanical properties as well as the swelling behaviors of the terpolymer. The rubbery PIP blocks enhance the mechanical robustness of the nanoporous membranes as revealed by nanoindentation tests on one hand and evidently accelerate the swelling process because of their softening effect to the PS matrix on the other hand, thus leading to 2–3-fold improved permeability. Moreover, the membranes exhibit a fast stimuli-responsive function as well as enhanced hydrophilicity because of the preferential aggregation of P2VP chains on the pore walls.

Extraction homopolymers premixed in aligned films of block copolymers by rinsing with selective solvents has long been used for the preparation of membranes with uniform straight pores (homoporous membranes). It is frequently assumed that only the dissolution of homopolymers contributes to the pore formation. However, in this work, we demonstrate that the effect of swelling plays a significant role in determining the pore sizes. We prepare blended films of block copolymers of polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) and P2VP homopolymers with low molecular weight and anneal the films to perpendicularly align the P2VP microdomains. Rinsing the aligned films in ethanol results in homoporous membranes, and the pore sizes can be tuned by the dosages of P2VP homopolymers. Interestingly, the pore sizes can also be effectively tailored by changing the rinsing temperatures and/or durations because of the significant contribution of the selective swelling of P2VP blocks under strong rinsing conditions in addition to the contribution of the dissolution of P2VP homopolymers. We identify the portion of the contribution from dissolution and from swelling and demonstrate that the pore sizes can be flexibly tuned within a wider range at no expense of pore ordering and uniformity by balancing the effect of dissolution and swelling.

Porous membranes/filters that can remove airborne fine particulates, for example, PM2.5, with high efficiency at low energy consumption are of significant interest. Herein, we report on the fabrication of a new class of unusual superior air filters with ultrahigh efficiency and an interesting antibacterial functionality. We use atomic layer deposition (ALD) to uniformly seed ZnO on the surface of expanded polytetrafluoroethylene (ePTFE) matrix, and then synthesize well-aligned ZnO nanorods with tunable widths and lengths from the seeds under hydrothermal conditions. The presence of ZnO nanorods reduces the effective pore sizes of the ePTFE filters at little expense of energy consumption. As a consequence, the filters exhibit exceptional dust removal efficiencies greater than 99.9999% with much lower energy consumption than conventional filters. Significantly, the presence of ZnO nanorods strongly inhibits the propagation of both Gram positive and negative bacteria on the filters. Therefore, the functionalized filters can potentially overcome the inherent limitation in the trade-off effect and imply their superiority for controlling indoor air quality.Keywords: antibacterial coating; atomic layer deposition; membranes; PM2.5; ZnO nanorods

Ideal membrane configurations for efficient separation at high flux rates consist of thin size-selective layers connected to macroporous supports for mechanical stabilization. We show that micelle-derived (MD) composite membranes combine efficient separation of similarly sized proteins and water flux 5–10 times higher than that of commercial membranes with similar retentions. MD composite membranes were obtained by filtration of solutions of amphiphilic block copolymer (BCP) micelles through commercially available macroporous supports covered by sacrificial nanostrand fabrics followed by annealing and removal of the nanostrand fabrics. Swelling-induced pore generation in the BCP films thus covering the macroporous supports yielded ∼210 nm thin nanoporous size-selective BCP layers with porosities in the 40% range tightly connected to the macroporous supports. Permselectivity and flux rates of the size-selective BCP layers were adjusted by the BCP mass deposited per membrane area and by proper selection of swelling times. The preparation methodology described here may pave the way for a modular assembly system allowing the design of tailored separation membranes.Keywords: block copolymers; membranes; micelles; porous materials; separation

•Isoporous membranes with gradient porosity were fabricated using block copolymers.•The inner pores can be tuned separately by UV crosslinking and secondary swelling.•The membranes showed superior permeation and separation properties.•The membranes showed a sensitive and reversible pH-responsive property.Selective swelling of amphiphilic block copolymers (BCPs) is an effective and nondestructive pore-making strategy. Here we coupled swelling-induced pore generation with UV crosslinking to fabricate BCP isoporous membranes with gradient porosity. Polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) solutions were coated onto macroporous supporting membranes to achieve composite films, which were then annealed in solvent vapor for the perpendicular alignment of the P2VP phases near the surface of the coating BCP layer. After swelling of BCP in hot ethanol and drying, isopores of ~8 nm formed at the surface of BCP layer following the selective swelling-induced pore-formation mechanism. Then UV exposure and subsequent secondary swelling at stronger condition of the membranes were conducted to enlarge the inner pores while maintaining the surface structures. With balanced UV crosslinking and secondary swelling, the finally obtained membranes showed ordered perpendicular pores at the outmost layer and gradient porosity with enlarged interconnected pores inside the BCP layer. Due to the gradient structures, the membranes exhibited much higher flux while the surface structures and retention remained essentially unchanged. Moreover, compared to the membranes without UV treatment, the membranes showed better performances in discriminating polyethylene glycol molecules with different molecular weights and still kept a sensitive pH-responsive property.

•ALD deposition of PI followed by crosslinking was used to modify PES membranes.•Diamines were fixed into deposited PI layers, leading to shrinkage of pore sizes.•Retention of the modified PES membrane was remarkably enhanced.•The modified PES membrane showed improved hydrophilicity and fouling resistance.•The thermal, mechanical, and corrosion properties of the membrane were also upgraded.Polyimide (PI) has been uniformly deposited and chemically crosslinked to form a hydrophilic and robust coating layer wrapping the skeleton of the macroporous polyethersulfone (PES) substrate membranes. PI is coated along all the exposed surfaces including the free surfaces and also the pore walls of the PES membranes by atomic layer deposition. The PI-deposited PES membranes are immersed in the excessive methanolic solution of ethylenediamine to initiate the crosslinking of PI chains. The crosslinked PES membranes exhibit synergistically enhanced performances in multiple aspects. They obtain enhanced hydrophilicity due to the formation of polar amide bonds. Control experiments on smooth PI films deposited on nonporous substrates reveal that crosslinking progressively increases the thickness of the PI films. Consequently, we are able to well control and tune the pore sizes by changing the crosslinking durations. The selectivity is enhanced by larger amplitude than the reduction of permeability as a result of reduced pore size and enhanced hydrophilicity after crosslinking. In addition, crosslinking also efficiently improves the thermal and mechanical stability and corrosion resistance of the PES membranes.

•Nitric acid mildly activates the surface of porous polypropylene membranes.•Noticeably improved water permeability is achieved by the surface activation.•Atomic layer deposition of metal oxides further upgrades activated membranes.•The 100-cycle-deposited membrane shows doubled water permeability.•Al2O3 is more efficient in improving hydrophilicity and permeation than TiO2.Activation by nitric acid oxidation has been combined with atomic layer deposition (ALD) to modify microporous polypropylene (PP) membranes. Nitric acid oxidation with prewetting of t-butanol generates active groups on the inert surface of PP membranes. Metal oxides including Al2O3 and TiO2 are subsequently ALD-deposited on the activated membrane. Nitric acid oxidation is a mild approach to activate PP membranes. A short immersion in nitric acid for 10 min is able to generate oxygen/nitrogen-containing active species on the membrane surface, which leads to an evident increase (38%) in the membrane permeability. The mechanical stability and the integrity of the porous structure are well preserved after activation. Surface elemental analyses and microscopy observations confirm the successful deposition of metal oxides thin layers onto the activated membranes. In the deposition of either Al2O3 or TiO2, the hydrophilicity of the deposited membranes is continuously improved with increasing ALD cycles, resulting in further increase in water flux. After 100 ALD cycles, the flux is doubled compared to that of the bare membrane. Al2O3 is more efficient in enhancing the hydrophilicity and permeation than TiO2 under identical deposition conditions because of the faster growth of Al2O3 on the activated PP surface.

Switchable nanoporous films, which can repeatedly alternate their porosities, are of great interest in a diversity of fields. Currently these intelligent materials are mostly based on polyelectrolytes and their porosities can change only in relatively narrow ranges, typically under wet conditions, severely limiting their applications. Here we develop a new system, which is capable of reversibly switching between a highly porous state and a nonporous state dozens of times regulated simply by exposure to selective solvents. In this system nanopores are created or reversibly eliminated in films of a block copolymer, polystyrene-block-poly(2-vinyl pyridine) (PS-b-P2VP), by exposing the films to P2VP-selective or PS-selective solvents, respectively. The mechanism of the switch is based on the selective swelling of the constituent blocks in corresponding solvents, which is a nondestructive and easily controllable process enabling the repeatable and ample switch between the open and the closed state. Systematic microscopic and ellipsometric characterization methods are performed to elucidate the pore-closing course induced by nonsolvents and the cycling between the pore-open and the pore-closed state up to 20 times. The affinity of the solvent for PS blocks is found to play a dominating role in determining the pore-closing process and the porosities of the pore-open films increase with the cycling numbers as a result of loose packing conditions of the polymer chains. We finally demonstrate the potential applications of these films as intelligent antireflection coatings and drug carriers.

•Both CaCO3 and CTAB are used to synthesize mesoporous carbon nanosheet (MCS).•The capacitance of MCS is 90.7 μF cm−2 at 0.05 A g−1 in ionic liquid electrolyte.•The energy density of MCS capacitor remains at 22.19 Wh kg−1 at 4267 W kg−1.•All the MCS electrodes show good cycle stability in the ionic liquid electrolyte.Interconnected mesoporous carbon sheets (MCSs) were prepared from cheap coal tar pitch with low-cost CaCO3 nanoparticles and cetyltrimethyl ammonium bromide (CTAB) as porogens for supercapacitors. The results show that the surface area of MCSs can be tuned in the range of 87–167 m2 g−1. The interconnected MCS2–1–1 made at 2:1:1 of CaCO3/coal tar pitch/CTAB mass ratio retains a capacitance of 87 F g−1 at 0.1 A g−1 after 100 cycles in ionic liquid electrolyte with high retention of 93.1%, showing excellent cycle stability. The energy density of MCS2–1–1 capacitor only drops from 64.18 Wh kg−1 to 22.19 Wh kg−1 with the average power density increasing from 115 W kg−1 to 4267 W kg−1, demonstrating good rate performance. This work suggests a low-cost way to synthesize high performance MCS for energy storage materials.Interconnected mesoporous carbon nanosheets are prepared from cheap coal tar pitch with low-cost CaCO3 nanoparticles and cetyltrimethyl ammonium bromide (CTAB) as porogens and exhibit a high energy density for supercapacitor.

We develop a retarded evaporation approach for the alignment of cylinder-forming block copolymer supramolecular monoliths, 3-n-pentadecylphenol (PDP) hydrogen-bonded polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP). A variety of highly ordered, aligned morphologies are produced by varying the dosages of PDP in the supramolecules. Treatment of the aligned supramolecular monoliths in hot ethanol leads to the dissolution of PDP and the selective swelling of P4VP, yielding enlargeable ordered mesopores along the original P4VP/PDP domains. Particularly, from supramolecular monoliths aligned in the morphology of perpendicular cylinders and gyroids, we obtain highly ordered monolithic membranes containing enlarged straight pores and bicontinuous pores, respectively. The straight and gyroidal pores were filled with phenol–formaldehyde resol and further carbonized to produce well-defined carbon nanostructures including nanofibers and reversed gyroids, demonstrating the pore accessibility and the promising templating functionality of the resulted monolithic membranes.

Long and narrow slit-shaped pores are predicted to have enhanced permeation and selectivity. We report, for the first time, the efficient production of membranes containing densely packed slitted pores with a pore width of <15 nm from block copolymers (BCPs). Such membranes exhibit sharp selectivity and ultrahigh water flux.

Oils and organic solvents that leak into water bodies must be promptly removed to avoid ecological disasters, for example, by selective absorption using oleophilic absorbents. However, it remains a challenge for the low-cost synthesis of efficient and recyclable absorbents for oily pollutants. By surface functionalization to inexpensive polyurethane (PU) foams, we synthesize oil absorbents exhibiting the highest absorption capacity and the best recyclability among all polymeric absorbents. The synthesis is enabled by atomic layer deposition of ∼5 nm-thick Al2O3 transition layer onto the skeleton surface of PU foams, followed by coupling a single-molecule layer of silanes to the Al2O3 layer. The sub-10 nm functionalization layer provides the PU foam an outstanding water-repelling and oil-absorbing functionality without compromising its high porosity and elasticity. The functionalized foam is able to quickly absorb oily pollutants spread on water surfaces or precipitated in water with a capacity more than 100 times its own weight. This ultrathin-layer-functionalization method is also applicable to renewable porous biomaterials, providing a sustainable solution for oil spills. Moreover, we propose devices than can continuously operate to efficiently collect oil spills from water surfaces based on the functionalized PU foam developed in this work.Keywords: absorption; atomic layer deposition; oil spill; oleophilicity; polyurethane foam; silanization

It remains a great challenge for the simple and affordable production of membranes for oil/water separation. We prepare low-cost but highly efficient paper-based membranes for oil/water separation through hydrophobic modification to filter papers. The simple modification contains only two steps: a thin layer of aluminum oxide is first coated on the surface of the filter paper by atomic layer deposition, and silane molecules are subsequently coupled on the precoated aluminum oxide layer via their reaction with hydroxyl groups on the surface. Both the alumina layer and the silanization layer are very thin with a total thickness less than 10 nm. The modified filter paper is endowed with strong hydrophobicity and oleophilicity, therefore exhibits strongly retarded permeation to water and enhanced permeation to nonpolar oils. The modified filter paper is demonstrated to show excellent separation efficiencies greater than 90% in the separation of various types of oils and organic solvents from their mixtures with water. The paper-based membranes prepared in this work are distinguished among others for their low-cost substrates and simple modification route. This modification method is expected to be easily extended to hydrophobize a diversity of other substrates.

Nanofluidics in hydrophilic nanopores is a common issue in many natural and industrial processes. Among all, the mass transport of nanofluidics is most concerned. Besides that, the heat transfer of a fluid flow in nano or micro channels is always considered with adding nanoparticles into the flow, so as to enhance the heat transfer by convection between the fluid and the surface. However, for some applications with around 1 nm channels such as nano filtration or erosion of rocks, there should be no nanoparticles included. Hence, it is necessary to figure out the heat transfer mechanism in the single phase nanofluidics. Via non-equilibrium molecular dynamics simulations, we revealed the heat transfer inside nanofluidics and the one between fluid and walls by setting simulation into extremely harsh condition. It was found that the heat was conducted by molecular motion without temperature gradient in the area of low viscous heat, while it was transferred to the walls by increasing the temperature of fluids. If the condition back to normal, it was found that the viscous heat of nanofluidics could be easily removed by the fluid-wall temperature drop of less than 1 K.Download full-size image

Mesoscopic lead halide perovskite solar cells typically use TiO2 nanoparticle films as the scaffolds for electron-transport pathway and perovskite deposition. Here, we demonstrate that swelling-induced mesoporous block copolymers can be templates for producing three-dimensional TiO2 networks by combining the atomic layer deposition technique. Thickness adjustable TiO2 network is an excellent alternative scaffold material for efficient perovskite solar cells. Our best performing cells using such a 270 nm thick template have achieved a high efficiency of 12.5 % with pristine poly-3-hexylthiophene as a hole transport material. The high performance is attributed to the direct transport pathway and high absorption of scaffolds, small leakage current and largely reduced recombination rate at interfaces. The results show that TiO2 network architecture is a promising scaffold for mesoscopic perovskite solar cells.

Long and narrow slit-shaped pores are predicted to have enhanced permeation and selectivity. We report, for the first time, the efficient production of membranes containing densely packed slitted pores with a pore width of <15 nm from block copolymers (BCPs). Such membranes exhibit sharp selectivity and ultrahigh water flux.

Extremely permeable ultrafiltration membranes with elongated elliptical pores are fabricated by stretching composite membranes with homoporous selective layers and macroporous supports. With simultaneously increased porosities both for the selective layers and supports and the thinned selective layers, the stretched membranes exhibit multifold-enhanced permeability with little sacrifice in selectivities. Thus the produced membranes enable, for the first time, gravity-driven ultrafiltration and discrimination of similarly sized nanoparticles with diameters down to 30 nm.