Solving the problems of the decrease of exposed active surfaces of Pt nanoparticles due to aggregation and their non-uniform dispersion is key to yielding high catalytic activity. In this work, monodisperse Pt nanocrystals (PtNCs) with a small size (2.8 nm in average diameter) and large exposed active surfaces are obtained by designing, inducing and dispersing the PtNCs on a 3D mesopore-rich nitrogen-doped graphene aerogel (NGA) through a facile one-step coassembly. Such a coassembly of PtNCs with NGA (PtNCs@NGA) has a large specific surface area (1750 m2 g−1), rich mesopores (the ratio of mesopores of 2–5 nm to all mesopores is 78%), and a high N content (3.93 at%). The unique structure of PtNCs@NGA not only ensures the exposure of the active PtNCs to O2 and decreases the diffusion time of O2 inside the pore channels, but also increases the adsorption and diffusion of O2 in PtNCs@NGA, consequently increasing the oxygen reduction reaction (ORR) speed and yielding better electrocatalytic activity than those of so far reported metal catalysts on carbon materials. The simple and low-cost preparation of the PtNCs@NGA catalyst renders it the most promising among electrocatalysts for application in fuel cells.

Tuning the porosity of NGAs by tailoring the size of GONSs results in the pore-richest NGA with the best mechanical stability and electrocatalytic biosensing activity by using the smallest sonicated GONSs with DA as precursors, where DA favours high N content and 3D crosslinking capability.

Ultrathin MnO2 hollow nanoballoons (UMHNBs) have a large ratio of interfacial to total atoms, corresponding to expected improved performance. However, their synthesis is a challenge due to difficulty in controlling the concentration of the unit cells. Herein, we describe a strategy to synthesize dry intact UMHNBs through a one-step synthesis by inflating MnO2 (reduced from KMnO4) with CO2 (oxidized from single-layer graphene oxide nanosheets) followed by instant freeze-drying. UMHNBs are 30–500 nm in diameter with a shell thickness of 3.7 nm, packing with laminar [MnO6] unit cells in the form of δ-MnO2. UMHNBs show efficient catalytic activity for decomposing the organic dye methylene blue (MB), 15 times the biggest reported value, and have long-term catalytic efficacy and durability. The described strategy in this paper makes use of graphene nanosheets to assemble durable ultrathin hollow nanoballoons.Keywords: catalytic activity; decomposition; manganese oxide; organic dye; self-assembly

A strategy for inhibiting aggregation of graphene oxide (GO) nanosheets is proposed in this work, which is important to understand the physical chemistry of the stability of GO and related factors. First, GO nanosheets (1.5–2.5 μm wide and 1.0 nm thick) were prepared by a modified Hummers' method. Then layer-by-layer (LbL) self-assembly of polyelectrolytes on GO nanosheets was carried out to obtain nanocapsules, whose premise is aggregation inhibition of GO based on the Debye–Hückel theory by considering the polyelectrolyte chain length and salt concentration. Low molecular weight polyelectrolytes and 0.5 mol L−1 NaCl solution proved to be essential to inhibit the aggregation of GO nanosheets. On the basis of the aggregation inhibition, GO loaded with a hydrophobic drug, paclitaxel (PTX), were encapsulated by polyelectrolytes, showing a high loading capability of 0.4 mg mg−1 and good dispersion stability. By assembling gold nanoparticles (AuNPs) in the shell, PTX was released rapidly from these nanocapsules under near infrared (NIR) irradiation. The strategy for successful aggregation inhibition of GO nanosheets in a polyelectrolyte matrix, as well as the stable loading and controlled rapid release of hydrophobic drugs, paves new paths for GO-based advanced nanomaterials and pharmaceutics.

A strategy of employing gold nanoparticles (AuNPs) is proposed to achieve quick release of paclitaxel (PTX) from GO. Under NIR irradiation, AuNPs absorb and convert NIR lamp energy to local heat, destroying the interactions between GO and PTX, thus enabling the release of PTX from GO.

By AFM we report the successful modulation of shell structure (morphology and shell thickness) of microcapsules through tailoring molecular substituents of chitosan. The shell thickness of hollow (HPCS/SA)n (n = 5, 7, 9) capsules is more than 3 times that of the (QACS/SA)n (n = 5, 7, 9) capsules, due to less charges carried by the neutral –NH2 substituent group and the induced coily conformation in HPCS, while more charges carried by the positively charged –N(CH3)3+ substituent and the induced extended conformation in QACS (HPCS: hydroxyl propyl chitosan; QACS: quaternary ammonium chitosan; SA: sodium alginate). The ultrathin shells of microcapsules assembled in this work by the layer-by-layer (LbL) self-assembly technique rather than the traditional method of mixing CS, SA and CaCl2 enable the thickness modulation characterization by AFM on the atomic scale. These microcapsules with tunable shell thickness provide important guidance for potential drug delivery and sustained release.Graphical abstractHighlights► By AFM we study the morphology of microcapsules through tailoring substituents. ► The thickness of HPCS-capsules is >3 times larger than that of QACS-capsules. ► A scheme is described concerning the molecular conformation and charges carried.

Microstructures bridge the molecular and the macroscopic scales. Disk-patterned microstructures obtained from microcapsules in this work are assembled through layer-by-layer which allowed depositing the natural polysaccharides chitosan (CS) and sodium alginate (SA) on porous CaCO3 microparticles. Besides CS and SA assembled outside CaCO3 microparticles, some CS and SA were also encapsulated by permeation in the pores of CaCO3. During the dissolution of CaCO3, the Ca2 + cations from decomposed CaCO3 were found to interact with alginate (AL) anions and to form Ca2 +–AL scaffolds. The adhesion arising from the OH groups in polysaccharides to solid surfaces was attributed to the disk-patterned microstructures. The calcium content (2.290 × 10− 10 mg) in each (CS/SA)4 microstructure amounts to about 1% of the total mass of the CaCO3 core. This work thus demonstrates the interaction between the decomposed core elements and the polysaccharides existing both inside and outside the porous cores. Such microstructures containing both Ca2 + and natural polysaccharides have potential applications in biological and medical systems.Highlights► Layer-by-layer-assembled capsules of CaCO3∣polysaccharides are employed. ► Ca2 + from decomposed CaCO3 interacts with alginate anions and forms scaffolds. ► Scaffold and adhesion of polysaccharides lead to disk-like microstructures.

Microcapsules with excellent fluorescence enhancement are assembled by using cetyltrimethylammonium bromide (CTAB) micelles to enrich Eu(DBM)3Phen (DBM and Phen are dibenzoylmethane and 1,10-phenanthroline, respectively) on CaCO3 particles by the LbL technique. Compared to microcapsules without micelles, the fluorescence intensity of microcapsules with micelles increases 9 times, larger than the 6 times increase of absorbance. This unexpected fluorescence enhancement is attributed to the “fluorescence protector” effect of CTAB micelles in microcapsules. Energy loss from nonradiative deactivation through energy transfer to high-energy O−H vibrations from the emissive 5D0 state of Eu(III) is greatly prohibited. The new strategy using micelles in this work not only enriches europium complexes during assembly in aqueous solution but also yields a fluorescence enhancement ratio larger than the enrichment ratio.

Fluorescent microcapsules doped with a europium β-diketonate complex were fabricated for the first time by stepwise adsorption of polyelectrolytes and europium complex using the layer-by-layer technique. The influence of temperature and solvent treatment on the morphology of the microcapsules was investigated. Intense red light emission of the microcapsules could be clearly observed by fluorescence microscopy before and after treatment. Remarkable shrinking, decrease of the inner volume and increase of the wall thickness were observed using atomic force microscopy (AFM) and transmission electron microscopy (TEM) after thermal treatment. The shrinkage induced by annealing could be recovered by dissolving in ethanol solution, which was confirmed by AFM and TEM. Morphology variation of the luminescent microcapsules induced by annealing or solvent are both attributed to the molecular rearrangement of polyelectrolytes. While the shrinkage by annealing is an entropy driven process with formation of more coiled conformations of polyelectrolytes the morphology variation by ethanol might be due to the effective screening of electrostatic interaction within the polyelectrolyte multilayers and the changed interaction between hydrophobic fragments present in the polyelectrolytes.

Fluorescent microcapsules doped with europium β-diketone complex were previously fabricated by stepwise adsorption of polyelectrolytes and europium complex using the layer-by-layer (LbL) technique [Chem. Commun. (2007) 1547–1549]. In this work, the influence of thermal treatment on the morphology of rare earth-doped microcapsules was studied by atomic force microscopy (AFM). Remarkable shrinking, increase of wall thickness and decrease of surface roughness were observed after heating the rare earth-doped microcapsules until 70 °C for 30 min. Intense red light emission at 612.0 nm of the microcapsules could be clearly observed by bare eyes after thermal treatment. Diameter variation of the luminescent microcapsules induced by annealing is attributed to the molecular rearrangement of polyelectrolytes. Study on the fluorescent microcapsules with various sizes provides guidance in potential application as biological assay reagents or display elements.

Rare-earth β-diketone complex doped microcapsules with high efficiency fluorescence fabricated by the LbL technique based on electrostatic and charge–dipole interactions are reported.

Self-organized domains in ring pattern of a samarium complex bounded by a β-diketone ligand TTA–Sm(TTA)3Phen (TTA denotes thenoyltrifluoroacetone; Phen denotes 1,10-phenanthroline) were assembled by the Langmuir–Blodgett (LB) film technique. The domain pattern was observed by Brewster angle microscopy (BAM) at the air/liquid interface and by atomic force microscopy (AFM) on mica. A scheme is proposed for the ring domain formation on considering components in aqueous subphase and the structure of samarium complexes. The subphase containing the samarium complex and the ligands is a fundamental condition for the stable existence of this samarium complex at the air/liquid interface. Stearic acid (SA) was mixed with the samarium complex, which formed highly ordered round domains producing a gradient electric field. Sm(TTA)3Phen molecules move towards and nucleate at the edge of the SA domains under electrostatic forces, resulting in the formation of a ring domain.

A strategy for inhibiting aggregation of graphene oxide (GO) nanosheets is proposed in this work, which is important to understand the physical chemistry of the stability of GO and related factors. First, GO nanosheets (1.5–2.5 μm wide and 1.0 nm thick) were prepared by a modified Hummers' method. Then layer-by-layer (LbL) self-assembly of polyelectrolytes on GO nanosheets was carried out to obtain nanocapsules, whose premise is aggregation inhibition of GO based on the Debye–Hückel theory by considering the polyelectrolyte chain length and salt concentration. Low molecular weight polyelectrolytes and 0.5 mol L−1 NaCl solution proved to be essential to inhibit the aggregation of GO nanosheets. On the basis of the aggregation inhibition, GO loaded with a hydrophobic drug, paclitaxel (PTX), were encapsulated by polyelectrolytes, showing a high loading capability of 0.4 mg mg−1 and good dispersion stability. By assembling gold nanoparticles (AuNPs) in the shell, PTX was released rapidly from these nanocapsules under near infrared (NIR) irradiation. The strategy for successful aggregation inhibition of GO nanosheets in a polyelectrolyte matrix, as well as the stable loading and controlled rapid release of hydrophobic drugs, paves new paths for GO-based advanced nanomaterials and pharmaceutics.

Fluorescent microcapsules doped with a europium β-diketonate complex were fabricated for the first time by stepwise adsorption of polyelectrolytes and europium complex using the layer-by-layer technique. The influence of temperature and solvent treatment on the morphology of the microcapsules was investigated. Intense red light emission of the microcapsules could be clearly observed by fluorescence microscopy before and after treatment. Remarkable shrinking, decrease of the inner volume and increase of the wall thickness were observed using atomic force microscopy (AFM) and transmission electron microscopy (TEM) after thermal treatment. The shrinkage induced by annealing could be recovered by dissolving in ethanol solution, which was confirmed by AFM and TEM. Morphology variation of the luminescent microcapsules induced by annealing or solvent are both attributed to the molecular rearrangement of polyelectrolytes. While the shrinkage by annealing is an entropy driven process with formation of more coiled conformations of polyelectrolytes the morphology variation by ethanol might be due to the effective screening of electrostatic interaction within the polyelectrolyte multilayers and the changed interaction between hydrophobic fragments present in the polyelectrolytes.

Rare-earth β-diketone complex doped microcapsules with high efficiency fluorescence fabricated by the LbL technique based on electrostatic and charge–dipole interactions are reported.

A poison-resistant and highly catalytically active Pt(111) lattice on ultrathin Pt nanoplates (Pt(111)NPTs) with a large ratio (28%) of surface active to sum Pt atoms is obtained with a dense small pore N-atom doped aerogel (NGA) featuring a large specific surface area and high N content in the graphene skeleton.

Hierarchical nanostructures are obtained directly on highly oriented pyrolytic graphite (HOPG) by spin coating of dilute chloroform solution of 9-Z-octadecenamide (oleamide), a natural lipid with cis-C═C− conformation, existing in the cerebrospinal fluid of mammal animals and being an additive for medical use and food packaging. Straight separated nanostripes with a length of 70−300 nm exist in the topmost layer and compact nanostripes in the bottom layer contacting HOPG. Compact nanostripes have a periodicity spacing of 3.8 nm, indicating H-bonding between two rows of oleamide molecules. The orientation of the hierarchical nanostructures differs by n60° ± 8° (n = 1 or 2), reflecting the epitaxial ordering along the HOPG substrate. The nanostripes are stable against annealing. A molecular packing scheme for the nanostructures is proposed, where the −C═C bond angle in oleamide is 120° and the plane of the carbon skeleton lies parallel to the HOPG substrate. Nanostripes in the topmost layer are formed from separated rows of oleamide molecules, due to the short-range surface potential of the substrate. The scheme involves direct influence of HOPG on the orientation of oleamide molecules to form nanostripes without any purposely added saturated alkanes and H-bonds between amide groups in adjacent two rows of oleamide molecules.