Space and time-resolved probing of heterogeneous catalysis reactions using lab-on-a-chip.

Probing catalytic reactions on a catalyst surface in real time is a major challenge. Herein, we demonstrate the utility of a continuous flow millifluidic chip reactor coated with a nanostructured gold catalyst as an effective platform for in situ investigation of the kinetics of catalytic reactions by taking 5-(hydroxymethyl)furfural (HMF) to 2,5-furandicarboxylic acid (FDCA) conversion as a model reaction. The idea conceptualized in this paper can not only dramatically change the ability to probe the time-resolved kinetics of heterogeneous catalysis reactions but also used for investigating other chemical and biological catalytic processes, thereby making this a broad platform for probing reactions as they occur within continuous flow reactors.

No More HF: Teflon-Assisted Ultrafast Removal of Silica to Generate High-Surface-Area Mesostructured Carbon for Enhanced CO2 Capture and Supercapacitor Performance.

An innovative technique to obtain high-surface-area mesostructured carbon (2545 m(2) g(-1)) with significant microporosity uses Teflon as the silica template removal agent. This method not only shortens synthesis time by combining silica removal and carbonization in a single step, but also assists in ultrafast removal of the template (in 10 min) with complete elimination of toxic HF usage. The obtained carbon material (JNC-1) displays excellent CO2 capture ability (ca. 26.2 wt % at 0 °C under 0.88 bar CO2 pressure), which is twice that of CMK-3 obtained by the HF etching method (13.0 wt %). JNC-1 demonstrated higher H2 adsorption capacity (2.8 wt %) compared to CMK-3 (1.2 wt %) at -196 °C under 1.0 bar H2 pressure. The bimodal pore architecture of JNC-1 led to superior supercapacitor performance, with a specific capacitance of 292 F g(-1) and 182 F g(-1) at a drain rate of 1 A g(-1) and 50 A g(-1) , respectively, in 1 m H2 SO4 compared to CMK-3 and activated carbon.

Gold-silica quantum rattles for multimodal imaging and therapy.

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.

Chemically induced magnetism in atomically precise gold clusters.

Comparative theoretical and experimental investigations are reported into chemically induced magnetism in atomically-precise, ligand-stabilized gold clusters Au25 , Au38 and Au55 . The results indicate that [Au25 (PPh3 )10 (SC12 H25 )5 Cl2 ](2+) and Au38 (SC12 H25 )24 are diamagnetic, Au25 (SC2 H4 Ph)18 is paramagnetic, and Au55 (PPh3 )12 Cl6 , is ferromagnetic at room temperature. Understanding the magnetic properties resulting from quantum size effects in such atomically precise gold clusters could lead to new fundamental discoveries and applications.

Millifluidics for chemical synthesis and time-resolved mechanistic studies.

Procedures utilizing millifluidic devices for chemical synthesis and time-resolved mechanistic studies are described by taking three examples. In the first, synthesis of ultra-small copper nanoclusters is described. The second example provides their utility for investigating time resolved kinetics of chemical reactions by analyzing gold nanoparticle formation using in situ X-ray absorption spectroscopy. The final example demonstrates continuous flow catalysis of reactions inside millifluidic channel coated with nanostructured catalyst.

X-ray absorption near-edge structure (XANES) spectroscopy study of the interaction of silver ions with Staphylococcus aureus, Listeria monocytogenes, and Escherichia coli.

Silver ions are widely used as antibacterial agents, but the basic molecular mechanism of this effect is still poorly understood. X-ray absorption near-edge structure (XANES) spectroscopy at the Ag LIII, S K, and P K edges reveals the chemical forms of silver in Staphylococcus aureus and Escherichia coli (Ag(+) treated). The Ag LIII-edge XANES spectra of the bacteria are all slightly different and very different from the spectra of silver ions (silver nitrate and silver acetate), which confirms that a reaction occurs. Death or inactivation of bacteria was observed by plate counting and light microscopy. Silver bonding to sulfhydryl groups (Ag-S) in cysteine and Ag-N or Ag-O bonding in histidine, alanine, and DL-aspartic acid was detected by using synthesized silver-amino acids. Significantly lower silver-cysteine content, coupled with higher silver-histidine content, in Gram-positive S. aureus and Listeria monocytogenes cells indicates that the peptidoglycan multilayer could be buffering the biocidal effect of silver on Gram-positive bacteria, at least in part. Bonding of silver to phosphate groups was not detected. Interaction with DNA or proteins can occur through Ag-N bonding. The formation of silver-cysteine can be confirmed for both bacterial cell types, which supports the hypothesis that enzyme-catalyzed reactions and the electron transport chain within the cell are disrupted.

Carbon spheres assisted synthesis of porous oxides with foam-like architecture.

Herein, we report a facile route for the synthesis of foam-like porous oxides using carbon spheres and polyvinylpyrrolidone (PVP) as sacrificial templates. The as-prepared porous structures were characterized by XRD, FESEM, TEM and BET methods. These foam-like macroporous oxides are formed through the fusion of oxide nanoparticles around the gas bubbles liberated during the combustion of composites and show good BET surface areas.

Ligand-stabilized and atomically precise gold nanocluster catalysis: a case study for correlating fundamental electronic properties with catalysis.

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.

Lab-on-a-chip synthesis of inorganic nanomaterials and quantum dots for biomedical applications.

The past two decades have seen a dramatic raise in the number of investigations leading to the development of Lab-on-a-Chip (LOC) devices for synthesis of nanomaterials. A majority of these investigations were focused on inorganic nanomaterials comprising of metals, metal oxides, nanocomposites and quantum dots. Herein, we provide an analysis of these findings, especially, considering the more recent developments in this new decade. We made an attempt to bring out the differences between chip-based as well as tubular continuous flow systems. We also cover, for the first time, various opportunities the tools from the field of computational fluid dynamics provide in designing LOC systems for synthesis inorganic nanomaterials. Particularly, we provide unique examples to demonstrate that there is a need for concerted effort to utilize LOC devices not only for synthesis of inorganic nanomaterials but also for carrying out superior in vitro studies thereby, paving the way for faster clinical translation. Even though LOC devices with the possibility to carry out multi-step syntheses have been designed, surprisingly, such systems have not been utilized for carrying out simultaneous synthesis and bio-functionalization of nanomaterials. While traditionally, LOC devices are primarily based on microfluidic systems, in this review article, we make a case for utilizing millifluidic systems for more efficient synthesis, bio-functionalization and in vitro studies of inorganic nanomaterials tailor-made for biomedical applications. Finally, recent advances in the field clearly point out the possibility for pushing the boundaries of current medical practices towards personalized health care with a vision to develop automated LOC-based instrumentation for carrying out simultaneous synthesis, bio-functionalization and in vitro evaluation of inorganic nanomaterials for biomedical applications.

Shape assisted fabrication of fluorescent cages of squarate based metal-organic coordination frameworks.

Micronic cage structures of squarate based metal-organic coordination frameworks (MOCFs) have been fabricated for the first time by specific anion selective etching of metal squarate cubes. Time and stoichiometry dependent synthesis and the corresponding microscopic studies have provided mechanistic insight into the cage formation. Furthermore, a non-covalent post-synthetic strategy has been adopted to functionalize the micronic cubes or cages with chromophores rendering the resulting hybrids green fluorescent.

Mixing does the magic: a rapid synthesis of high surface area noble metal nanosponges showing broadband nonlinear optical response.

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.

ZnO: a versatile template to obtain unusual morphologies of silica, gold and carbon nanostructures.

Unusual morphologies of silica, gold and carbon were obtained by using ZnO nanostructures as templates. Microdrums and pencil-shaped ZnO nanostructures are successfully replicated into silica, gold and carbon analogues which are otherwise difficult to make.