Graphene samples prepared by the exfoliation of graphitic oxide and conversion of nanodiamond exhibit good hydrogen uptake at 1 atm, 77 K, the uptake going up to 1.7 wt %. The hydrogen uptake varies linearly with the surface area, and the extrapolated value of hydrogen uptake by single-layer graphene works out to be just above 3 wt %. The H 2 uptake at 100 atm and 298 K is found to be 3 wt % or more, suggesting thereby the single-layer graphene would exhibit much higher uptakes. Equally interestingly, the graphene samples prepared by us show high uptake of CO 2 , the value reaching up to 35 wt % at 1 atm and 195 K. The firstprinciples calculations show that hydrogen molecules sit alternately in parallel and perpendicular orientation on the six-membered rings of the graphene. Up to 7.7 wt % of hydrogen can be accommodated on singlelayered graphene. CO 2 molecules sit alternatively in a parallel fashion on the rings, giving use to a maximum uptake of 37.93 wt % in single-layer graphene. The presence of more than one layer of graphene in our samples causes a decrease in the H 2 uptake.
Here we report an instantaneous formation of high surface area metal nanosponges through a one-step inexpensive method in a completely green solvent, water. Merely by optimizing the concentration of the precursors and the reducing agent, we were able to generate a three-dimensional porous structure made up of nanowire networks. This is a general process, involves a simple, room temperature reduction of metal salts with sodium borohydride, and is therefore scalable to any amount. Further, these nanoporous metals because of their network structures show optical limiting behavior of a true broadband nature that would find applications in optoelectronic nanodevices.
We present results from our investigations into correlating the styrene-oxidation catalysis of atomically precise mixed-ligand biicosahedral-structure [Au25(PPh3)10(SC12H25)5Cl2](2+) (Au25-bi) and thiol-stabilized icosahedral core-shell-structure [Au25(SCH2CH2Ph)18](-) (Au25-i) clusters with their electronic and atomic structure by using a combination of synchrotron radiation-based X-ray absorption fine-structure spectroscopy (XAFS) and ultraviolet photoemission spectroscopy (UPS). Compared to bulk Au, XAFS revealed low Au-Au coordination, Au-Au bond contraction and higher d-band vacancies in both the ligand-stabilized Au clusters. The ligands were found not only to act as colloidal stabilizers, but also as d-band electron acceptor for Au atoms. Au25-bi clusters have a higher first-shell Au coordination number than Au25-i, whereas Au25-bi and Au25-i clusters have the same number of Au atoms. The UPS revealed a trend of narrower d-band width, with apparent d-band spin-orbit splitting and higher binding energy of d-band center position for Au25-bi and Au25-i. We propose that the differences in their d-band unoccupied state population are likely to be responsible for differences in their catalytic activity and selectivity. The findings reported herein help to understand the catalysis of atomically precise ligand-stabilized metal clusters by correlating their atomic or electronic properties with catalytic activity.
Gold quantum dots exhibit distinctive optical and magnetic behaviors compared with larger gold nanoparticles. However, their unfavorable interaction with living systems and lack of stability in aqueous solvents has so far prevented their adoption in biology and medicine. Here, a simple synthetic pathway integrates gold quantum dots within a mesoporous silica shell, alongside larger gold nanoparticles within the shell's central cavity. This "quantum rattle" structure is stable in aqueous solutions, does not elicit cell toxicity, preserves the attractive near-infrared photonics and paramagnetism of gold quantum dots, and enhances the drug-carrier performance of the silica shell. In vivo, the quantum rattles reduced tumor burden in a single course of photothermal therapy while coupling three complementary imaging modalities: near-infrared fluorescence, photoacoustic, and magnetic resonance imaging. The incorporation of gold within the quantum rattles significantly enhanced the drug-carrier performance of the silica shell. This innovative material design based on the mutually beneficial interaction of gold and silica introduces the use of gold quantum dots for imaging and therapeutic applications.nanomedicine | hybrid nanoparticle | cancer nanotechnology | gold quantum dots | mesoporous silica A lthough gold's potential in nanotechnology has been recognized for many decades (1, 2), new insights into the unique properties of gold nanoparticles (NPs) of less than 2 nm have just recently started to emerge (3, 4). Such extremely small gold NPs could be transformative for a broad set of applications ranging from energy production and storage to catalysis and health care (3). As the size of gold NPs decreases below 2 nm, the quantization of their conduction band leads to molecule-like properties (3). These quantum-sized gold NPs (or gold quantum dots, AuQDs) absorb light in the near-infrared (NIR) biological window (650-900 nm) (2) and convert it into photons and heat (5). Furthermore, whereas bulk gold is diamagnetic, some AuQDs exhibit magnetic properties (4, 6). However, the clear therapeutic and imaging potential of AuQDs in vivo has been undermined by their unfavorable biointeractions and lack of stability in aqueous solvents (5, 7). In biological environments AuQDs tend to aggregate rapidly, reverting to larger gold nanoparticles (AuNPs) (8) and/or bind to protein, which negatively affects their cytotoxicity (7). To retain their advantages, AuQDs require a protective, stabilizing framework that allows proficient biological interactions.Recently, new emphasis has been placed on hybrid NP systems, where multiple nanomaterials are assembled to create multimodal systems that exhibit the combined qualities of the component modules (9-11). These constructs promise to integrate various functionalities by incorporating different nanomaterials into a single, efficient, multimodal system (12, 13). However, these systems usually accumulate the specific functionalities of their component modules through multiple steps in their ...
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