Bifunctional 2D superlattice electrocatalysts of alternating layered double hydroxide (LDH)−transition metal dichalcogenide (TMD) heterolayers were synthesized by interstratification of the exfoliated nanosheets. Density functional theory calculations predict an increased interfacial charge transfer between interstratified LDH and TMD nanosheets, which would lead to enhanced electrocatalytic activity. The electrostatically driven self-assembly of oppositely charged 2D building blocks, i.e., exfoliated Ni−Al-LDH/Ni−Fe-LDH and MoS 2 nanosheets, yields mesoporous heterolayered Ni−Al-LDH−MoS 2 /Ni−Fe-LDH−MoS 2 superlattices. The synthesized superlattices show improved electrocatalytic activity with enhanced durability for oxygen and hydrogen evolution reactions and water splitting. The interstratification improves the chemical stability of LDH in acidic media, thus expanding its possible applications. The high electrocatalytic activity of the superlattices may be attributed to an enhanced affinity for OH − /H + , improved electrical conduction and charge transfer, and the increase of active sites. This study indicates that the formation of superlattices via self-assembly of 2D nanosheets provides useful methodology to explore high-performance electrocatalysts with improved stability.

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Very little attention has been focused on the purifi cation of water-soluble pollutants after oil/water separation. [ 4 ] Thus, there is considerable interest in developing novel and facile methods for the simultaneous separation of oil from water and purifi cation of water-soluble pollutants.The practical application of organic micelle catalysts that utilize hydrophilic/ hydrophobic interfaces has been limited by several disadvantages. For example, the stability of organic micelles depends on many parameters, such as the solvent polarity, critical micelle concentration, and reaction conditions, such as pH, water/oil ratio, and temperature. [ 10,11 ] Due to the narrow range of stability of organic micelles, the synthesis of inorganic micelles that have hydrophilic/hydrophobic interfaces, large surface areas, high porosities, tunable surfaces, and high recyclability has recently attracted some attention. [ 12,13 ] For example, Lin and co-workers reported a simple route to hierarchically assembling micelles and inorganic nanoparticles. [ 14 ] Yang and co-workers prepared functionalized mesoporous silica spheres consisting of a hydrophobic core and a hydrophilic micellar shell. [ 15 ] As a fi rst example, Alivisatos and co-workers recently reported resin templates based on the synthesis of inorganic micelles with a hydrophilic cavity and a hydrophobic surface and its application as a catalyst in the bromination of alcohol. [ 16 ] There is still considerable interest in developing novel methods for the exploration of interior/ exterior-functionalized, superhydrophobic, and nanostructured inorganic micelles. To fulfi ll the requirements of oil/water separation and inorganic micellar catalysis mentioned above, the development of hierarchical nanomaterials that have a hydrophilic interior and superhydrophobic/hydrophilic (amphiprotic) exterior is highly desirable, offering signifi cant potential for multiple applications. To the best of our knowledge, this report is the fi rst example of the synthesis of nanomaterials that have a hydrophilic core and amphiprotic shell for multiple applications, such as amphiprotic catalytic reactions, oil/water separation and pollutant purifi cation, and enzyme immobilization with signifi cant stability and effi cient recyclability.Herein, we present the preparation and multiple applications of superhydrophobic hollow SiO 2 micelles (SHSMs) with hydrophilic cores and amphiprotic (superhydrophobic/hydrophilic) shell structures that act as "all-in-one" smart nanomaterials. Our SHSMs are better than hydrophilic@hydrophobic micelles prepared using previously reported methods for several reasons: (i) the polyallylamine hydrochloride (PAH) chains were extended and survived from the core to the shell even Inorganic Micelles (Hydrophilic Core@Amphiprotic Shell) for Multiple Applications Md. Shahinul Islam , Won San Choi , * Sun Ha Kim , Oc Hee Han , and Ha-Jin Lee * A facile approach for synthesizing superhydrophobic hollow silica micelles (SHSMs) with hydrophilic cores and amphiprotic (supe...

We have demonstrated a novel strategy for the synthesis of mesoporous silica nanoparticles (MSNPs) using a surfactant-free method under ambient conditions. By the simple addition of an amine-based polymer (polyethylenimine; PEI) with a high molecular weight to a silica nanoparticle (SNP) solution, two types of MSNPs, including rambutan-like MSNPs (R-MSNPs) and hollow MSNPs (H-MSNPs), were produced. The structural changes of the MSNPs were systematically studied using various reaction conditions (reaction time, molar ratio and molecular weight of PEI, etc.) and were observed using electron microscopic techniques. The formation mechanisms of both MSNPs were carefully investigated using XPS, Raman, and IR spectroscopies. Because the synthesized MSNPs are highly porous materials that contain internal organic/inorganic networks, we investigated the removal/adsorption properties of these MSNPs with respect to pollutants toward possible future use in environmental remediation applications. The H-MSNPs exhibited better environmental remediation capabilities relative to the R-MSNPs because PEI is present between the cobweb-like internal structures of the H-MSNPs, thereby providing a significant number of reaction sites for the adsorption of pollutants. The approach presented here can also be used as a direct method for the preparation of intraconnected networks within the substructures.

Inorganic 2D nanosheets are important building blocks for synthesizing efficient hybrid photocatalysts because of their advantageous characteristics such as highly anisotropic 2D morphology with subnanometer-level thickness, wide surface area, defect-free tunable surface, chemical composition diversity and crystal structure, and tailorable physicochemical properties. Since most of the components in exfoliated nanosheets are exposed on the surface, an unusually strong chemical interaction and a remarkable electronic coupling can occur in the interface between the exfoliated nanosheets and hybridized nanospecies. Such strong electronic coupling is useful in optimizing the photocatalytic activity of the hybrid material via the suppression of electron-hole recombination, increase of the light absorption region, improved transport of excited charge carriers, and increase of surface reactivity. Herein, several representative examples of inorganic 2D nanosheetbased hybrid photocatalysts are introduced to examine the crucial role of 2D nanosheets in the enhancement of the photocatalytic activity of the hybrid materials. Special emphasis is made regarding the unique hybridization effect of exfoliated 2D nanosheets on the optical properties and electron structure of semiconducting species. Future perspectives for the investigation of the 2D nanosheet-based hybrids are discussed to provide valuable insight for the design and synthesis of highly efficient photocatalysts for producing solar fuels.

The mixing of Ag ion-doped poly(ethyleneimine) (PEI) and poly(acrylic acid) (PAA) produced Ag ion-doped polyelectrolyte complex particles (PECs) in solution. Positively charged Ag ion-doped PECs (Ag ion PECs) with a spherical shape were deposited alternatively with PAA to form a multilayer assembly. The multilayered film containing Ag ion PECs was reduced to generate a composite nanostructure. Metal nanoparticle (NP)-enriched nanocomposite films were formed by an additional process of the postadsorption of precursors on PECs within the nanocomposite films, which resulted in the enhancement of the catalytic and electrical properties of the composite films. Because the films contain PECs that are responsive to changes in pH and most of the NPs are embedded in the PECs, interesting catalytic properties, which are unexpected in a particle-type catalyst, were observed upon pH changes. As a result of the reversible structural changes of the films and the immobilization of the NPs within the films, the film-type catalysts showed enhanced performance and stability during catalytic reactions under various pH conditions, compared to particle-type catalysts.

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