•Thin films of block copolymers with hierarchical microstructures were fabricated.•The fabrication process involves in solution self-assembly and interface adsorption.•The microstructures can be tuned finely by varying the experimental parameters.•The length of the blocks affects the microstructures greatly.•The SERS and catalytic properties of the microstructures were investigated.Hierarchical composite microstructures of block copolymers, polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP)/Ag have been fabricated successfully at the air/liquid interface through a self-assembly and adsorption process. The films with various morphologies including foam, nanorod and nanowire array, hollow sphere, and nanosphere were obtained. These morphologies are closely related to the aggregates formed in the aqueous phase, such as microcapsules, cylindrical micelles, vesicles and spherical micelles, which can be controlled by tuning the critical packing parameters of the amphiphilic block copolymer molecules through changing the concentration of Ag+ ions in the aqueous solution. The length of the P2VP blocks in the PS-b-P2VPs exerts great influences on the self-assembly behavior of the polymers and the final microstructures, which provides a deep insight into the formation mechanism of the microstructures. Additionally, these hybrid films doped with silver nanoparticles provide potential application in surface enhanced Raman scattering (SERS) and catalysis.Download high-res image (203KB)Download full-size image

Hexagonal ultrathin nanoplates of basic lead carbonates were synthesized in aqueous lead acetate solution under ambient conditions. The sizes of the nanoplates were found to reach several hundreds of nanometers to micrometers, whereas the plate thickness was only several nanometers, corresponding to 3, 4, or 5 stacking layers along the c-axis. These nanoplates exhibited effective catalytic properties for the hydrogenation of nitroarenes, such as nitrobenzene, 4-nitroaniline, and 4-nitrophenol, and other organic dyes, such as methylene blue and methyl orange in aqueous solutions in the presence of KBH4. Pb nanoclusters were generated in situ during the catalytic process and were well dispersed on the surface of the nanoplates, leading to the formation of a zero-dimensional/two-dimensional (0D/2D) heterostructure. It was also found that the heterostructure exhibited different catalytic behaviors for the hydrogenation of the compounds mentioned above due to the different molecular structures and different adsorption and desorption abilities of the reactants and products. Such a heterostructure can be also anticipated to be an effective photocatalyst due to its strong UV-light absorption, the ultrathin characteristics of the highly crystalline nanoplates and the transfer abilities of the Pb nanoparticles.

Composite thin films doped with Au species were fabricated at an air/liquid interface via a series of steps, including the mass transfer of polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) across the liquid/liquid interface between a DMF/CHCl3 solution and an aqueous solution containing either AuCl4− or AuCl2−, self-assembly of PS-b-P2VP in a mixed DMF–water solution, and adsorption and further self-organization of the formed aggregates at the air/liquid interface. This is a new approach for fabricating composite polymer films and can be completed within a very short time. AuCl4− and AuCl2− ions were found to significantly influence the self-assembly behavior of the block copolymer and the morphologies of the composite films, leading to the formation of nanowire arrays and a foam structure at the air/liquid interface, respectively, which originated from rod-like micelles and microcapsules that had formed in the respective solutions. The effect of the metal complex was analyzed based on the packing parameters of the amphiphilic polymer molecules in different microenvironments and the interactions between the pyridine groups and the metal chloride anions. In addition, these composite thin films exhibited stable and durable performance as heterogeneous catalysts for the hydrogenation of nitroaromatics in aqueous solutions.

Thin composite films with paralleled nanowire or planar sheet morphologies doped with Ag or Au species were fabricated at the air/liquid interface. The fabrication process involves a series of steps, including the mass transfer of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) across a liquid/liquid interface between a DMF/CHCl3 solution and an aqueous solution containing either Ag+ or AuCl4−, self-assembly of the PS-b-P4VP and the inorganic species in the mixed DMF and water solution, and adsorption and further self-organization of the formed aggregates at the air/liquid interface. Noble metal ions and nanoparticles that formed during the fabrication process can be incorporated into the polymer matrices directly. The film morphology can be controlled through tuning the existential state and critical packing parameter of the polymer molecules. It was also found that the film morphology of PS-b-P4VP is distinctly different from that of PS-b-P2VP, indicating the great influence of the molecular structure on the self-assembly behavior of block copolymers. In addition, these composite thin films exhibit effective heterogeneous catalytic properties for hydrogenation of nitroaromatics in aqueous solutions.

Composite thin films with well-defined and parallel nanowires were fabricated from the binary blends of a diblock copolymer polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) and several homopolystyrenes (h-PSs) at the air/liquid interface through a facile technique, which involves solution self-assembly, interface adsorption, and further self-organization processes. It was confirmed that the nanowires that appeared at the air/water interface came from the cylindrical micelles formed in solution. Interestingly, the diameters of the nanowires are uniform and can be tuned precisely from 45 to 247 nm by incorporating the h-PS molecules into the micellar core. This parallel alignment of the nanowires has potential applications in optical devices and enables the nanowires to be used as templates to prepare functional nanostructures. The extent to which h-PS molecules with different molecular weights are able to influence the diameter control of the nanowires was also systematically investigated.

A new and facile strategy to fabricate composite thin films with tunable morphologies via self-assembly of block copolymer molecules at the air/liquid interface is first reported. The morphologies (parallel nanowires and foams) of these freestanding thin films can be tuned by varying the molecular structure or other experimental conditions.

•Composite films of block copolymer/Ln3+ were fabricated at liquid/liquid interfaces.•Eu3+ and La3+ have great effects on morphologies and microstructures of the films.•Polymer/Eu3+ and polymer/Eu3+/bpy films exhibit good luminescent properties.An emulsion-directed assembly and adsorption approach has been used to fabricate composite films of polystyrene-b-poly(acryl acid)-b-polystyrene (PS-b-PAA-b-PS) and Eu3+ and La3+ ions at the planar liquid/liquid interface of the polymer DMF/chloroform (1:1, v/v) mixed solution (lower phase) and aqueous solutions of the corresponding salts (upper phase). The lower phase gradually transformed to a water-in-oil (W/O) emulsion via spontaneous emulsification due to the “ouzo effect”. Polymer molecules and the metal ions assembled around emulsion droplets that adsorbed at the planar liquid/liquid interface at last, resulting in formation of composite films. The film morphologies and structures depend on Ln3+ ions: polymer/Eu3+ composite films were foam films composed of microcapsules ranging in size from several hundreds of nanometers to micrometers, while polymer/La3+ composite films were composed of hollow spheres several tens of nanometers in size. Fourier transform infrared (FTIR) spectra revealed that the coordination modes of carboxyl groups to Eu3+ and La3+ were bridging bidentate and ionic, respectively, in the two types of composites. These results indicate that stable microcapsules can be fabricated around droplets for polymer/Eu3+ systems, while microcapsules of polymer/La3+ are unstable. This leads to different film morphologies and structures. Compositions of these films were characterized using energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). In addition, foam films of polymer/Eu3+/2,2′-bipyridine (bpy) were fabricated using this approach, and their photoluminescence properties were investigated.Graphical abstract

A composite polymer/Au nanoparticle multilayer film was fabricated at the air/liquid interface through a new and facile self-assembly and adsorption process. A planar liquid/liquid interface was formed at first by using a DMF/CHCl3 mixed solution of polybutadiene-block-poly(4-vinylpyridine) (PB-b-P4VP) as the lower phase and a HAuCl4 aqueous solution as the upper phase. The PB-b-P4VP molecules self-organized into disk-like micelles in the mixed organic phase. Because DMF is miscible with water, DMF carried the block copolymer molecules and micelles into the upper aqueous phase, and then diffused into the HAuCl4 aqueous solution, leading to further self-assembly of the polymer molecules with the inorganic species and the formation of larger sheet aggregates. These aggregates further adsorbed at the air/liquid interface, resulting in the formation of the multilayer composite film. Most AuCl4− ions were reduced by DMF during this process, and numerous Au nanoparticles were generated and embedded in the composite film. This film exhibited unique heterogeneous catalytic properties due to its unique multilayer structure.

Two approaches have been utilized to fabricate thin composite films of amphiphilic polyisoprene-block-poly(2-vinylpyridine) (PI-b-P2VP) doped with silver and gold nanoparticles. Honeycomb and foam structures were obtained at the interfaces between a chloroform solution of the polymer and aqueous solutions of either AgNO3 or HAuCl4 through the first route. For the second route, porous thin films were obtained at the interfaces between a chloroform solution of the crosslinked polymer by S2Cl2 and pure water, immersed in aqueous solutions of either AgNO3 or HAuCl4 to adsorb metal precursors and then treated with KBH4 aqueous solution to form composite films. The catalytic properties of these films were evaluated by assessing the reduction of 4-nitrophenol by KBH4 in aqueous solutions. It was found that the metal nanoparticles are unstable enough and fused in the film prepared through the first route while the composite film obtained through the second route exhibited good catalytic performance and was more stable during the catalytic reaction. In addition, the porous polymer film is also expected to adsorb other species to form various functional composites.

Diblock copolymers (polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP)) with different molecular weights self-assembled into various supramolecular microstructures at the polymer chloroform solution/aqueous chloroauric acid interface under different conditions. Generally, multilayered foam films composed of microcapsules with walls decorated with or without round interfacial micelles formed when using a higher concentration of aqueous solution; honeycomb monolayers appeared with decreasing aqueous solution concentration; fish net-like or labyrinthine monolayers were generated with a further decrease in aqueous concentration. The appearance of these microstructures reflects the different adsorption and self-assembling behaviors of PS-b-P2VP including interfacial micellization, encapsulation, and microphase separation under different conditions. In addition, the relative molecular weights of the two blocks and the total molecular weight of the polymers had a large effect on the adsorption and self-assembly of the polymers and on the final microstructure architecture. Furthermore, the factors that affect the adsorption rate and intermolecular interactions of the polymers and, consequentially, the self-assembling behavior and final microstructure are discussed. The catalytic activities of these composite microstructures were evaluated.

•P2VP-b-PS-b-P2VP formed microcapsules and nanobelts at the liquid/liquid interface.•Its self-assembly behavior differs from P4VP-b-PS-b-P4VP at the interface.•This behavior also differs from those in solution, in film and at air/water interface.•The P2VP-b-PS-b-P2VP/Au composites exhibit high and durable catalytic activity.Gold nanoparticle-doped poly(2-vinylpyridine)-block-polystyrene-block-poly(2-vinylpyridine) (P2VP-b-PS-b-P2VP) thin films were prepared at the planar liquid/liquid interface between the chloroform solution of the polymer and aqueous solution of HAuCl4. Transmission electron microscopic (TEM) investigations revealed that foam films composed of microcapsules as well as one-dimensional belts were formed, and numerous Au nanoparticles were incorporated in the walls of the microcapsules and the nanobelts. The walls and the belts have layered structure. The formation mechanism of the foams and the belts was attributed to adsorption of the polymer molecules, combination of the polymer molecules with AuCl4− ions, microphase separation and self-assembly of the composite molecules at the interface. This microstructure is different apparently from those formed in solutions, in casting or spin-coating thin films and at the air/water interface of this triblock copolymer, reflecting unique self-assembly behavior at the liquid/liquid interface. This microstructure is also different from those formed by homo-P2VP and P4VP-b-PS-b-P4VP at the liquid/liquid interface, indicating the effects of molecular structures on the self-assembly behaviors of the polymers. After further treatment by UV-light irradiation and KBH4 aqueous solution, the gold species were reduced completely, as indicated by UV–vis spectra and X-ray photoelectron spectra (XPS). Thermogravimetric analysis indicated that the composite films have high thermal stability, and the content of gold was estimated to be about 9.1%. These composite films exhibited high catalytic activity for the reduction of 4-nitrophenol by KBH4 in aqueous solutions.

The foam films of polystyrene-b-poly(acrylic acid)-b-polystyrene (PS-b-PAA-b-PS) doped with Cd(II) or Pb(II) species were fabricated at the planar liquid/liquid interfaces between a DMF/chloroform (v/v: 1/1) solution of the polymer and aqueous solutions containing cadmium acetate or lead acetate at ambient temperature. Optical microscopic observation shows the thin film is uniform on a larger length scale. Transmission electron microscopic (TEM) investigations reveal that the foam films are made up of microcapsules with the size of several hundreds of nanometers to micrometers. The walls of the microcapsules have a layered structure decorating with nanofibers and hollow nanospheres, where numerous inorganic fine nanoparticles are dispersed homogeneously. The film formation is a result of emulsion droplet-templated assembly and adsorption of the formed microcapsules at the planar liquid/liquid interface. Because of the miscibility of DMF with chloroform and water, DMF migrates to the aqueous phase while water migrates to the organic phase across the interface, resulting in the formation of a W/O emulsion, as revealed by optical microscopic observation, freeze fracture transmission electron microscopic (FF-TEM) observation, and dynamic laser scattering (DLS) investigation. The triblock copolymer molecules and the inorganic species adsorb and self-assemble around the emulsion drops, leading to the formation of the composite microcapsules. X-ray photoelectron spectroscopic (XPS) and FTIR spectroscopic results indicate that two kinds of Cd(II) or Pb(II) species, metal oxide or hydroxide, resulting from the hydrolysis of the metal ions and the coordinated metal ions to the carboxyl groups coexist in the formed thin films, which transform to metal sulfide completely after treating with hydrogen sulfide to get metal sulfide nanoparticle-doped polymer thin films.

An aqueous solution of AgNO3 (upper phase) and a DMF/CHCl3 solution of polystyrene-b-poly(acryl acid)-b-polystyrene (PS-b-PAA-b-PS) or PS-b-PAA-b-PS/1,6-diaminohexane (DAH) (lower phase) constituted a planar liquid/liquid interface. The lower phase gradually transformed to a water-in-oil (W/O) emulsion via spontaneous emulsification due to the “ouzo effect”. Polymer molecules, DAH molecules, and Ag+ ions assembled into microcapsules around emulsion droplets that adsorbed at the planar liquid/liquid interface, resulting in formation of a foam film. DAH acted as a cross-linker during this process. Transmission electron microscopic observations indicated that Ag nanoclusters that were generated through reduction of Ag+ ions by DMF were homogeneously dispersed in the walls of the foam structure. X-ray photoelectron spectroscopic investigations revealed that Ag(I) and Ag(0) coexisted in the film, and Ag(I) transformed to Ag(0) after further treatment. The film formed without DAH was not stable, while the film formed with DAH was very stable due to intermolecular attraction between PAA and DAH and formation of amides, as revealed by FTIR spectra. The film formed with DAH exhibited high and durable catalytic activity for hydrogenation of nitro compounds and, very interestingly, exhibited thermoresponsive catalytic behavior.

•Composite films with different structures were formed at the liquid/liquid interface.•These films are composed of diblock or triblock copolymers and inorganic species.•PS-b-P4VP/Au and PS-b-P4VP/Ag have honeycomb and foam structure, respectively.•P4VP-b-PS-b-P4VP/Au forms a free-standing film with a nanosphere array structure.•Co-adsorption and self-assembly of polymer and the ions lead to the film formation.The adsorption and self-organization behaviors of two kinds of block copolymers, polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) and poly(4-vinylpyridine)-block-polystyrene-block-poly(4-vinylpyridine) (P4VP-b-PS-b-P4VP), at planar liquid/liquid interfaces were investigated. A gel film decorating with honeycomb-like microstructures forms at the liquid/liquid interface between PS-b-P4VP chloroform solution and chloroauric acid aqueous solution. However, foam films were developed when the chloroauric acid aqueous solution was replaced by a chloroplatinic acid solution or a silver nitrate solution. Furthermore, a free-standing film containing the ordered arrays of nanospheres appeared at the liquid/liquid interface between P4VP-b-PS-b-P4VP chloroform solution and chloroauric acid aqueous solution. The formation of these microstructures was attributed to the adsorption of polymer molecules, combining with inorganic ions and the self-assembly of the composite species at the interface. The doped metal ions and complex ions were transformed to metal nanoparticles after further treatment. This is a facile and convenient method to prepare polymer/inorganic nanoparticle composites. These results also indicate the great influences of the polymer structures and the inorganic species in the aqueous phases on the self-assembly behaviors of the polymers at the interfaces, the final morphology, and structure of the composites. In addition, the formed thin composite films doped with well-dispersed, homogeneous small noble metal nanoparticles exhibit great and durable catalytic activities for the reduction of 4-nitrophenol (4-NP) by potassium borohydride.

Free-standing films of poly(2-vinylpyridine) doped with Ag+ ions were fabricated at the planar liquid/liquid interface of an aqueous solution of AgNO3 and a chloroform solution of the polymer through adsorption of the polymer molecules, combination with Ag+ ions, and self-assembly of the composite species. Transmission electron microscopic (TEM) investigations indicated that the films were composed of planar thin layers decorated with separated microcapsules and foam structures of conglutinated microcapsules, and no Ag nanoparticles formed in the pristine films. After UV-light irradiation and KBH4 aqueous solution treatment, Ag nanoparticles with the average size of 3.2 nm appeared and incorporated in the polymer matrices. X-ray photoelectron spectra (XPS) and UV–vis spectra are consistent with the TEM observations. Thermogravimetric analysis (TGA) showed good thermal stability of the composite films. The silver content was estimated to be 24.0% from the TG curve, closing to the calculated value. The catalytic performance of the composite films was evaluated by using the reduction of nitro-compounds, including nitrobenzene, 4-nitrophenol, and 4-nitrobenzoic acid by KBH4 in aqueous solutions. The results indicated that the composite films have high and durable catalytic activity. The apparent reaction constants are related to the size of the nitro-compounds, suggesting that the Ag nanoparticles were incorporated in the matrices, and the diffusion of the reactant molecules has a great influence on the catalytic reaction.Graphical abstractHighlights► Free-standing composite polymer/Ag+ foam film formed at the liquid/liquid interface. ► Co-adsorption, combination and self-assembly of P2VP/Ag+ leads to the film formation. ► Transformed Ag nanoparticles exhibit high and durable catalytic activity. ► The diffusion of reactants is important for catalytic reactions.

•Composite films of block copolymer doped with noble metal ions were fabricated.•Interfacial adsorption and self-assembly are responsible for film formation.•The composite film has foam and honeycomb microstructure.•The transformed noble metal nanoparticles exhibit high catalytic activity.Composite thin films of poly(t-butyl methacrylate)-block-poly(2-vinyl pyridine) (PtBMA-b-P2VP) doped with silver or gold nanoclusters or nanoparticles were fabricated at the liquid/liquid interface between the polymer chloroform solution and AgNO3 or HAuCl4 aqueous solution. The formation of the thin films results from the adsorption of the polymer molecules at the interface, combination with the inorganic species in the water phases, and self-assembly of the composite molecules. Different from homo-P2VP and polystyrene-block-poly(2-vinyl pyridine) (PS-b-P2VP) that self-assemble into foam film and honeycomb structure, respectively, two kinds of morphologies (foam and honeycomb structures) are formed simultaneously for PtBMA-b-P2VP, reflecting different assembling behaviors of these polymers at the interface. Silver or gold nanoclusters or nanoparticles were generated in the polymer films during the assembly process and further reduction of the combined precursors, which show high catalytic activity and durability for the reduction of 4-nitrophenol and other nitro-compounds.

Free-standing thin films of poly(2-vinylpyridine) (P2VP) doped with platinum complex ions were fabricated at the planar aqueous solution of H2PtCl6/chloroform solution of P2VP interface. The formation of the free-standing thin films was attributed to the adsorption and combination of the polymer molecules and the complex ions at the interface, and self-assembly of the composites. The films were composed of thin layers decorated with separated and conglutinated microcapsules. After treatment with KBH4 aqueous solution, the platinum complex ions incorporated in the polymer matrices transformed to platinum nanoparticles with the mean size of 2.2 nm, which was confirmed by transmission electron microscopic investigations and X-ray photoelectron spectroscopic (XPS) analysis of the samples. Both the contents of the platinum element in the untreated and treated composite films estimated based on the thermagravimetric analysis (TGA) were close to each other, indicating no loss of platinum during the treatment process. The catalytic activity of the composite films was evaluated by using the reduction of 4-nitrophenol by KBH4 in aqueous solutions. The results indicated that the composite films have high and durable catalytic activity.Highlights► Free-standing composite polymer foam film formed at the liquid/liquid interface. ► The film formation was attributed to self-assembly of the adsorbed species. ► Doped platinum complex anions transformed to Pt nanoparticles after treatment. ► Pt nanoparticles in the composite films exhibit high and durable catalytic activity.

•Composite network and microporous P2VP/Cu(II) structures were fabricated.•Composite nano-shuttle and microbelt of P2VP/Cu(OH)2 were obtained.•These nanostructures were fabricated at the liquid/liquid interface.•Adsorption, hydrolysis and self-assembly processes were involved in the fabrication.•The two kinds of nanostructures exhibited different catalytic properties.Two kinds of microstructures, microporous film of poly(2-vinylpyridine) (P2VP)/Cu2+ and thin film composed of P2VP and nano-shuttles and microbelts of Cu(OH)2 were fabricated at the planar liquid/liquid interface formed by chloroform solutions of P2VP and aqueous solutions of cupric sulfate (CuSO4) and cupric acetate (Cu(CH3COO)2), respectively. The formation of the microporous film of P2VP/Cu2+ was associated with the adsorption and combination of P2VP molecules with Cu2+ ions, and self-assembly of the composite species at the liquid/liquid interface, while the formation of the composite P2VP/Cu(OH)2 structure was attributed to the adsorption of the polymer molecules and the hydrolysis of Cu2+ ions at the liquid/liquid interface when Cu(CH3COO)2 aqueous solution was used. The incorporated Cu2+ ions and Cu(OH)2 nanoparticles transformed to Cu nanoparticles after reduction by KBH4. These composite nanostructures exhibit different catalytic behaviors for the reduction of 4-nitrophenol (4-NP). The catalytic activity of the microporous structure of polymer doped with Cu nanoparticles increased and then decreased gradually for different cycles, which was due to the gradually outward diffusion and part leaching and/or aggregation of the incorporated Cu nanoparticles because the interaction of Cu nanoparticles with the polymer is weak. While the nano-shuttle and microbelt structures composed of Cu nanoparticles exhibited higher and durable catalytic activity.

Regular one-dimensional (1D) parallel chains composed of CdS nanoparticles with cubic zinc blende crystal structure were prepared at the air/water interface via one-step synthesis and assembly process. These nanostructures were produced through an interfacial reaction between Cd2+ ions in the aqueous solution of cadmium acetate and H2S in the gaseous phase under Langmuir monolayers of 10,12-pentacosadiynoic acid (PDA). It was demonstrated that PDA molecules self-assembled into parallelly aligned linear supermolecules at the air/water interface with the aid of π–π interactions and acted as templates for the formation of the superstructures. The experimental conditions including temperature and reaction time have great influences on the superstructure formation and the parameters of the parallel chains.Graphical abstractHighlights► Parallel 1D chains of CdS nanoparticles were prepared at the air/water interface. ► These nanostructures were produced through one-step synthesis and assembly process. ► 10,12-pentacosadiynoic acid supermolecules in Langmuir monolayers acted as templates. ► The parameters of the nanostructures can be tuned.

Gold nanoparticle-doped poly(2-vinylpyridine) (P2VP) microcapsules and foam films were synthesized and assembled at the P2VP chloroform solution/HAuCl4 aqueous solution interface at 25 °C. It was found that Au nanoparticles with the average diameter of 2.1 nm were homogeneously embedded in and adsorbed on the walls of the capsules and foams, the nanoparticles were composed of Au(0) and Au(III) with the molar ratio of about 75/25, and the mass percent of Au elements was measured to be 19.65%. The formation of the nanostructures was attributed to the self-assembly of P2VP at the liquid/liquid interface, the simultaneous reduction of AuCl4- ions by a small amount of ethanol in the chloroform and adsorption of AuCl4- ions. After irradiated by UV-light for 1 h, the average diameter of the nanoparticles was found to be 2.2 nm, and the AuCl4- ions were transformed to Au(0) completely. The catalytic performance of these composite nanostructures were evaluated by using the reduction of 4-nitrophenol (4-NP) by potassium borohydride in aqueous solutions. The catalytic activity was very high in the first cycle, decreased rapidly and slightly in the second and third cycles, respectively, due to the aggregation of some nanoparticles, and stabilized after the third cycle.Graphical abstractFoam films of P2VP doped with Au nanoparticles were fabricated at the liquid/liquid interface. The composite films exhibit effective catalytic activity.Highlights► Gold nanoparticle-doped foam-like P2VP film formed at the liquid/liquid interface. ► UV-light treatment led to further reduction of AuCl4- and cross-linking of P2VP. ► The self-assembly of P2VP-AuCl4- complexes resulted in the formation of the film. ► The composite films exhibited effective catalytic activity. ► Durable catalytic activity was achieved after the third cycle.

The composite poly(2-vinylpyridine) (P2VP)-Ag+ foam-like thin films were prepared at the interface between AgNO3 aqueous solution and polymer chloroform solution at 25 °C. An X-ray photoelectron spectroscopy (XPS) investigation indicated that Ag+ ions in the composite films were partially transformed to Ag atoms after irradiated by UV-light and completely transformed to Ag atoms after being treated with KBH4 aqueous solution. Ag nanoparticles with the average sizes of 2.71 ± 0.82 and 3.28 ± 1.20 nm were generated in these two transferred films with different treatments, respectively. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) images showed clearly that the composite films were composed of microcapsules whose walls had multilayer structures, and the nanoparticles were incorporated in the walls. The formation of the composite films at the liquid–liquid interface was attributed to the adsorption of the polymer molecules at the interface, coordination between the pyridine groups and Ag+ ions, and self-assembly of the composite molecules. Furthermore, the catalytic activity of the composite films was evaluated using the reduction of 4-nitrophenol (4-NP) by KBH4. The results demonstrated that the composite thin films have high and durable catalytic activity.

Flowerlike, dendritic and snowflake-like gold hierarchical nanostructures were prepared at the carbon-coated copper grid/Langmuir monolayer/HAuCl4 aqueous solution interfaces under different Langmuir monolayers through an electroless deposition process. The morphology and structure of these nanostructures were characterized by using transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and scanning electron microscopy (SEM), and the surface enhanced Raman scattering performance of these nanostructures was tested. It was found Langmuir monolayers between the copper grids and the aqueous solutions played an important role in the formation of the nanostructures and affected the morphology and structure of the nanostructures greatly. The formation of these nanostructures was attributed to the galvanic reduction between AuCl4− and Cu and electrochemical deposition, the conductivity of the carbon layer for electrons, non-equilibrium growth of the nanostructures, and templating effect of the Langmuir monolayers. These nanostructures exhibited high surface enhanced Raman scattering (SERS) performance.Graphical abstractHighlights► Gold nanostructures formed at the solid/liquid interface via electroless deposition. ► The interface formed by carbon-coated copper grid and HAuCl4 aqueous solution. ► Langmuir monolayers between them guided the formation of the nanostructures. ► Langmuir monolayers affected the morphology and structure of the nanostructures. ► These nanostructures exhibited good SERS performance.

Nanoparticles with different shapes were prepared at the air/water interface via hydrolysis of Pb2+ ions under Langmuir films of poly(N-vinylcarbazole) (PVK) at 30–50 °C. It was found that round or irregular nanoparticles with the size of several to several tens of nanometers were formed when the PbCl2 aqueous solution with the concentration of 1 × 10−3 mol L−1 was used as subphase, while single-crystalline quasi-hexagonal nanoplates, nanostars and dendrites with the size of several hundreds of nanometers were obtained when the subphase concentration was 1 × 10−4 mol L−1. Analysis on the selective-area electron diffraction (SAED) patterns revealed that the formed nanoparticles are β-PbO. The formation of the nanostructures should be attributed to the formation and dehydration of lead hydroxide, diffuse-limited growth and aggregation of nanoparticles at the air/water interface.Graphical abstractResearch highlights▶ PVK forms monolayers at the interface of air/aqueous solution of PbCl2. ▶ Pb2+ ions enriches in the interfacial phase. ▶ Pb2+ ions hydrolyze to form Pb(OH)2 that dehydrate to form β-PbO. ▶ Nanoplates, nanostars and nanodendrites of PbO nucleate and grow at the interface. ▶ These nanoparticles are single nanocrystals.

Platinum nanoparticle-doped polymer foam-like thin films were prepared via a synthesis and assembly process at the liquid/liquid interface of a chloroform solution of poly(2-vinylpyridine) and an aqueous solution of chloroplatinic acid hydrate and a subsequent UV-light irradiation process. Transmission electron microscopy, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy investigations indicated that the foam-like thin films formed at the interface were composed of polymer molecules, and Pt(II) and Pt(IV) ions. Platinum nanoparticles with average diameter of 2.70 ± 0.35 nm appeared after UV-light irradiation, which were embedded in and adsorbed on the walls of the foams. The formation of the composite nanostructures at the interface was attributed to self-assembly of the polymer molecules at the liquid/liquid interface, reduction of PtCl62−, and interaction between PtCl62−/intermediate PtCl42− ions and the protonated pyridine groups. The catalytic activity of the composite film for the reduction of methylene blue by potassium borohydride in aqueous solutions was evaluated. The apparent rate constant decreased gradually with increasing the number of runs due to the partially leaching of Pt nanoparticles and became stable after the fifth cycle, indicating that the composite film can be used as an effective, stable and reusable catalyst.Graphical abstractHighlights► Foam-like composite film of P2VP–platinum formed at the liquid/liquid interface. ► The film was formed via combination of platinum complex ions with P2VP and their self-assembly. ► Pt nanoparticles formed and doped in the films after UV-light irradiation. ► The composite films exhibited effective catalytic. ► Durable catalytic activity was achieved after the fourth cycle.

Ordered two-dimensional (2D) arrays of β-HgS nanocrystal aggregates were prepared successfully at the air/water interface through the interfacial reaction between Hg2+ ions in the subphase and H2S in the gaseous phase under the direction of liquid-expanded monolayers of arachidic acid (AA). These 2D arrays are composed of hexagonal or quasi-hexagonal aggregates with the size of several hundreds of nanometers that consist of several tens of HgS nanocrystals with the size of several nanometers. The formed HgS nanocrystals together with AA molecules self-assembled into round aggregates due to the interactions between the species, and the aggregates self-assembled into 2D arrays further due to the attractions between them. During the self-assembly process, the soft round aggregates transformed into hexagonal or quasi-hexagonal ones. The experimental conditions, especially the phase states of the AA monolayers and temperature, have great influences on the formation of the 2D arrays. To the best of our knowledge, this is the first case to get 2D ordered arrays at the air/water interface through a one-step synthesis and assembly process.

Silver dendritic nanostructures and nanoplates were prepared at the solid/liquid interfaces via electroless deposition. Langmuir monolayers of 5,10,15,20-tetra-4-oxy(2-stearic acid) phenyl porphyrin (TSPP) and arachidic acid (AA) were formed at the air/AgNO3 aqueous solution interface. These nanostructures were produced when carbon-coated copper grids were covered on the Langmuir monolayers at lower (<20 °C) and higher (20–50 °C) temperature, respectively, and the branches are composed of parallel aligned nanobelts with their (110) face parallel to the interface. The formation of the nanostructures should be attributed to the galvanic reduction of Ag+ ions by copper, the electronic conductivity of the carbon layer, the templating effect of the Langmuir monolayer, and the non-equilibrium growth and aggregation of silver nanoparticles at the interface. This is a convenient avenue to produce metal nanostructures.

Triangular single-crystalline nanorings of PbS were prepared at the air/water interface and characterized by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV−vis spectroscopy. The nanorings were transformed from triangular PbS nanopyramids that were formed under Langmuir monolayers of arachidic acid (AA) through interfacial reactions between Pb2+ ions in the subphases and H2S in the gaseous phase. The basal plane of the pyramids is a (111) face of PbS crystals with rock salt crystal structure, which is parallel to the air/water interface. The tips of the pyramids beneath the interface dissolved gradually due to selective etching of Pb2+ in the nanocrystals by Cl− ions in the subphase because of their higher surface energy, resulting in the formation of the rings. The size of the rings could be tuned by changing the experimental conditions, and the optical properties changed when the rings formed.

Triangular, hexagonal, and truncated triangular single-crystal gold nanoplates are successfully synthesized under Langmuir monolayers of long-chain ionic liquid molecules 1-hexadecyl-3-methylimidazolium bromide (C16mimBr) through interfacial reduction of AuCl4− by formaldehyde gas. The Au nanoparticles are characterized using transmission electron microscopy (TEM), selected-area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), and UV−vis spectroscopy. It is found that the size of the Au plates varies from several hundred nanometers to several micrometers, up to 20 μm, and the thickness is ca. 35 nanometers. The atomically flat planar surfaces of the Au nanoplates correspond to {111} planes and the lateral surfaces are {110} planes. The concentration of HAuCl4 aqueous solution strongly influences the formation of the Au nanoplates. The formation of the nanoplates should be attributed to the preferential adsorption of 1-hexadecyl-3-methylimidazolium cations onto the {111} planes of Au nuclei and the connection of small, triangular nanoplates.

PbS nanocrystals with different shapes were synthesized at the air/PbCl2 aqueous solution interface via reaction between Pb2+ and H2S gas under poly(9-vinylcarbazole) (PVK) thin films and characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), electron diffractometry (ED), scanning electron microscopy (SEM), and UV−vis spectroscopy. It was found that the shapes of the nanocrystals depend on the experimental conditions, such as temperature, subphase concentration, and H2S amount. Triangular nanopyramids and nanoplates/nanorods were formed at ca. 20 and 30 °C, respectively. The (111) plane of the nanopyramid is parallel to the water surface, and the other three sides are (100), (010), and (001) faces, respectively. For the rectangular nanoplates and nanorods, the (001) planes are parallel to the water surface. The formation of the nanopyramids should be related to lattice matching between the two-dimensional arrays of nitrogen atoms in PVK Langmuir monolayers at 20 °C with the (111) crystal face of PbS, while the formation of nanoplates and nanorods at 30 °C would be ascribed to the variation of the Langmuir monolayer structure. In addition, the shapes of nanoplates/nanorods changed with the subphase concentrations and H2S volumes.

Gold nanorings were prepared at the air/water interface through reduction of AuCl4− ions by UV-light irradiation or formaldehyde gas treatment at room temperature templated by thin films of phthalocyanine derivatives. Silver nanorings were produced at the air/water interface via reduction of Ag+ ions by UV-light irradiation templated by poly(9-vinylcarbazole) (PVK) thin films. These nanostructures were investigated by transmission electron microscopy (TEM), selective-area electron diffractometry (SAED), and high-resolution TEM (HRTEM). It was found that the gold nanorings are composed of close-packed nanoplates whose (1 1 0) crystal planes are parallel to the air/water interface; while silver rings are composed of nanoparticles. It is demonstrated that the ring-like aggregates formed by parallel linear supramolecules of the phthalocyanine derivatives and the ring-like structure of PVK supramolecules are responsible for the formation of the gold and silver nanorings, respectively.

One-dimensional (1D) silver oxide nanoparticle arrays were synthesized by illuminating the composite Langmuir–Blodgett monolayers of porphyrin derivatives/Ag+ and n-hexadecyl dihydrogen phosphate (n-HDP)/Ag+ deposited on carbon-coated copper grids with daylight and then exposing them to air. Transmission electron microscopy (TEM) observation shows that the nanoparticle size is around 3 nm, with the separation of about 2–3 nm. High-resolution TEM (HRTEM) investigation indicates that the particles are made up of Ag2O. Ag nanorods with the width of 15–35 nm and the length of several hundreds of nanometers were synthesized by irradiating the composite Langmuir monolayers of porphyrin derivatives/Ag+ and n-HDP/Ag+ by UV-light directly at the air/water interface at room temperature. HRTEM image and selected-area electron diffraction (SAED) pattern indicate that the nanorods are single crystals with the (110) face of the face-centered cubic (fcc) silver parallel to the air/water interface. The formation of the 1D arrays and the nanorods should be attributed to the templating effect of the linear supramolecules formed by porphyrin derivative or n-HDP molecules in Langmuir monolayers through non-covalent interactions.One-dimensional ordered arrays of silver oxide nanoparticles formed in composite porphyrin derivative/Ag+ Langmuir–Blodgett monolayers.

Europium complex Eu(DB-bpy)phenCl3(H2O)2 (phen: 1,10-phenanthroline, DB-bpy: 4,4′-di-tert-butyl-2,2′-dipyridyl) was doped in poly(methyl methacrylate) (PMMA) and poly(vinyl pyrrolidone) (PVP). The composite systems with various molar ratios of CO groups/Eu3+ ions were characterized by photoluminescent (PL) spectroscopy, X-ray diffractometry (XRD) and luminescent lifetime measurements. It was found that Eu3+ ions have more than one kind of symmetrical sites in Eu/PMMA composites and the PL spectra of Eu(III) change with the compositions. However, the composites of Eu/PVP with different molar ratios show similar PL spectra, indicating different influence of matrices on luminescent properties.

Composite thin films doped with Au species were fabricated at an air/liquid interface via a series of steps, including the mass transfer of polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) across the liquid/liquid interface between a DMF/CHCl3 solution and an aqueous solution containing either AuCl4− or AuCl2−, self-assembly of PS-b-P2VP in a mixed DMF–water solution, and adsorption and further self-organization of the formed aggregates at the air/liquid interface. This is a new approach for fabricating composite polymer films and can be completed within a very short time. AuCl4− and AuCl2− ions were found to significantly influence the self-assembly behavior of the block copolymer and the morphologies of the composite films, leading to the formation of nanowire arrays and a foam structure at the air/liquid interface, respectively, which originated from rod-like micelles and microcapsules that had formed in the respective solutions. The effect of the metal complex was analyzed based on the packing parameters of the amphiphilic polymer molecules in different microenvironments and the interactions between the pyridine groups and the metal chloride anions. In addition, these composite thin films exhibited stable and durable performance as heterogeneous catalysts for the hydrogenation of nitroaromatics in aqueous solutions.

A new and facile strategy to fabricate composite thin films with tunable morphologies via self-assembly of block copolymer molecules at the air/liquid interface is first reported. The morphologies (parallel nanowires and foams) of these freestanding thin films can be tuned by varying the molecular structure or other experimental conditions.