Integration in a soft material of all molecular components necessary to generate storable fuels is an interesting target in supramolecular chemistry. The concept is inspired by the internal structure of photosynthetic organelles such as plant chloroplasts which co-localize molecules involved in light absorption, charge transport, and catalysis to create chemical bonds with light energy. We report here on the light-driven production of hydrogen inside a hydrogel scaffold built by the supramolecular self-assembly of a perylene monoimide amphiphile. The charged ribbons formed can electrostatically attract a nickel-based catalyst, and electrolyte screening promotes gelation. We found the emergent phenomenon that screening by the catalyst or the electrolytes led to two-dimensional crystallization of the chromophore assemblies and enhanced the electronic coupling among the molecules. Photocatalytic production of hydrogen is observed in the three-dimensional environment of the hydrogel scaffold and the material is easily placed on surfaces or in the pores of solid supports. The development of soft materials that integrate all necessary molecular components to generate storable fuels in the presence of sunlight is an unexplored area of chemistry with potential impact in renewable energy. Such systems could have advantages over the use of large volumes of liquids, dispersions of expensive or toxic inorganic particles, or complex devices. The use of such soft materials with integrated functions and high water content is bioinspired by the internal structure of chloroplasts in plants. These photosynthetic organelles have evolved to co-localize within stacked lipid bilayers in their stroma the protein machinery which integrates light-absorption, charge transport, and the catalytic functions necessary to convert light energy into chemical bonds1,2. Efforts to emulate natural photosynthetic systems over the past several decades have concentrated on the development of efficient catalysts for water oxidation and proton reduction3-7. In other recent work, catalysts have been coupled to light absorbing CdSe quantum dots8, Si microrods9, and organic dyes10,11 to create artificial photosynthetic systems. Also functional devices capable of performing water-splitting and fuel-generating reactions using earth-abundant resources have been demonstrated12. The development of bionspired soft materials that can be shaped into forms and integrate light-harvesting, charge transport, and catalytic functions to produce solar fuels is an obvious gap. This gap can be addressed through self-assembly strategies for materials in which a bottom-up approach fine tunes all functional aspects of a catalytic system13. Organic systems may have shorter lifetimes than their inorganic counterparts, but could have their own niche in sustainable energy given their soft matter nature and low energy requirements for production. We report here on a strategy to create supramolecular hydrogels that integrate both light-absorbing chromophores and catalysts into a m...

Exfoliated two-dimensional (2D) sheets can readily stack to form flexible, free-standing films with lamellar microstructure. The interlayer spaces in such lamellar films form a percolated network of molecularly sized, 2D nanochannels that could be used to regulate molecular transport. Here we report self-assembled clay-based 2D nanofluidic channels with surface charge-governed proton conductivity. Proton conductivity of these 2D channels exceeds that of acid solution for concentrations up to 0.1 M, and remains stable as the reservoir concentration is varied by orders of magnitude. Proton transport occurs through a Grotthuss mechanism, with activation energy and mobility of 0.19 eV and 1.2 Â 10 À 3 cm 2 V À 1 s À 1 , respectively. Vermiculite nanochannels exhibit extraordinary thermal stability, maintaining their proton conduction functions even after annealing at 500°C in air. The ease of constructing massive arrays of stable 2D nanochannels without lithography should prove useful to the study of confined ionic transport, and will enable new ionic device designs.

T he remarkable electronic properties of graphene and related two-dimensional (2D) materials result from the confi nement of electrons within the material. Similarly, the interstitial space between 2D materials can enable the 2D confi nement of ions and electrolytes and alter their transport. Many dif erent 2D sheets can be obtained by exfoliation of natu-ral layered materials (1), and an exfoliationreconstruction strategy can convert powders of layered materials into continuous, robust bulk forms in which lamellar nanochannels occupy a substantial volume fraction (up to several tens of percent). Nanofl uidics, which enables the manipulation of confi ned ions and electrolytes, has applications in electrochemical energy conversion and storage, biosensing, and water purifi cation.Electrolytes exhibit drastically dif erent properties when confi ned in nanochannels. IONIC TRANSPORT Two-dimensional nanofl uidicsRestacked exfoliated sheets create interconnected nanofl uidic channels for ion transport Exfoliation Powders of layered material Debye length determined by ionic strength Reconstruction creates continuous channels for ions Reconstruction Debye length A B COO -COO -COO -COO -Debye length Vertical transport Horizontal transport Electric feldIon fow is mainly along the sheets but can fow across them at defectsConf ning ion f ow. (A) Lamellar f lm with massive arrays of 2D nanof uidic channels can be made by the exfoliationreconstruction approach, as illustrated with models of graphene oxide (GO) sheets that are terminated with negatively charged carboxyl groups. (B) Debye layers of neighboring sheets overlap to create unipolar 2D ion channels with greatly enhanced cation conductivity.suring structural and electronic properties of materials. Thus, "computer experiments" can be used on a par with experimental investigation. Users of DFT codes now have a dependable estimate for the level of precision of their results and a confi dence of reproducibility by other DFT codes. This work has farreaching implications, as it af ects the entire community of DFT users, in fi elds as diverse as metallurgy and biochemistry.Being able to do such accurate quantum calculations is insuf cient when the goal is to solve complex problems of technological relevance. Molecules, biomolecules, and materials are neither isolated nor at a temperature of 0 K. On the contrary, they interact heavily with each other and their environment (for example, a solvent) and are in constant thermal motion. To make an impact in grand challenges such as understanding the function of a living cell or a nanodevice, we will need to tackle much larger (thousands to millions of atoms) length scales than can be approached with conventional DFT. Part of the answer to this challenge will be provided by linear-scaling DFT approaches (11), which can treat much larger numbers of atoms. Inevitably, however, multiscale methods that couple DFT with coarser descriptions such as classical atomistic force fi elds (12), and eventually continuum models, will be needed. The...

Light harvesting supramolecular assemblies are potentially useful structures as components of solar-to-fuel conversion materials. The development of these functional constructs requires an understanding of optimal packing modes for chromophores. We investigated here assembly in water and the photocatalytic function of perylene monoimide chromophore amphiphiles with different alkyl linker lengths separating their hydrophobic core and the hydrophilic carboxylate headgroup. We found that these chromophore amphiphiles (CAs) self-assemble into charged nanostructures of increasing aspect ratio as the linker length is increased. The addition of salt to screen the charged nanostructures induced the formation of hydrogels and led to internal crystallization within some of the nanostructures. For linker lengths up to seven methylenes, the CAs were found to pack into 2D crystalline unit cells within ribbon-shaped nanostructures, whereas the nine methylene CAs assembled into long nanofibers without crystalline molecular packing. At the same time, the different molecular packing arrangements after charge screening led to different absorbance spectra, despite the identical electronic properties of all PMI amphiphiles. While the crystalline CAs formed electronically coupled H-aggregates, only CAs with intermediate linker lengths showed evidence of high intermolecular orbital overlap. Photocatalytic hydrogen production using a nickel-based catalyst was observed in all hydrogels, with the highest turnovers observed for CA gels having intermediate linker lengths. We conclude that the improved photocatalytic performance of the hydrogels formed by supramolecular assemblies of the intermediate linker CA molecules likely arises from improved exciton splitting efficiencies due to their higher orbital overlap.

Ultrafine particles are often used as lubricant additives because they are capable of entering tribological contacts to reduce friction and protect surfaces from wear. They tend to be more stable than molecular additives under high thermal and mechanical stresses during rubbing. It is highly desirable for these particles to remain well dispersed in oil without relying on molecular ligands. Borrowing from the analogy that pieces of paper that are crumpled do not readily stick to each other (unlike flat sheets), we expect that ultrafine particles resembling miniaturized crumpled paper balls should selfdisperse in oil and could act like nanoscale ball bearings to reduce friction and wear. Here we report the use of crumpled graphene balls as a high-performance additive that can significantly improve the lubrication properties of polyalphaolefin base oil. The tribological performance of crumpled graphene balls is only weakly dependent on their concentration in oil and readily exceeds that of other carbon additives such as graphite, reduced graphene oxide, and carbon black. Notably, polyalphaolefin base oil with only 0.01-0.1 wt % of crumpled graphene balls outperforms a fully formulated commercial lubricant in terms of friction and wear reduction.

Some earlier studies suggested that graphene oxide (GO) sheets adopt a crumpled configuration in water, similar to the shape of a paper ball, which turns into an even more compact, collapsed form upon addition of a poor solvent due to enhanced intrasheet affinity. Although those results have been debated in studies concerning membrane configurations, they are now often used to justify the existence of folds and wrinkles in solution-processed GO-based structures. This has led to a misconception that wrinkled and crumpled features may be intrinsic to solution processing and unavoidable. Here, we connect this problem to experimental observations of the liquid crystallinity of GO dispersions, which clearly show that the sheets are neither crumpled nor collapsed, with or without poor solvent. The sheets can simply fold flat or restack to hide their surfaces from poor solvent, without incurring the energetic cost of severe deformations to crumple.

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Kirigami nanofluidics is demonstrated here, where ionic transport through 2D laminar films can be manipulated by tailor-cutting the film shape.