The selective synthesis and in situ characterization of aqueous Alcontaining clusters is a long-standing challenge. We report a newly developed integrated platform that combines (i) a selective, atomeconomical, step-economical, scalable synthesis of Al-containing nanoclusters in water via precision electrolysis with strict pH control and (ii) an improved femtosecond stimulated Raman spectroscopic method covering a broad spectral range of ca. T he importance of Al (aluminum) in the biosphere and to human civilization is enormous. The scale of mining and production of Al compounds is second only to that of Fe (iron). Our lives are influenced by its use in electronics (1, 2), cooking and eating utensils, and food packaging, and as structural materials in the construction, automotive, and aircraft industries. Its deposition and migration as a mineral ore are controlled by its aqueous chemistry and speciation. Millions of tons of Al compounds are used worldwide each year for water treatment, and it is found in all drinking water (3). The behavior of Al in water plays significant roles in soil chemistry and plant growth (4, 5), for example, governing Al bioavailability, toxicity, and its overall impact in aquatic ecosystems (6). Meanwhile, aqueous Al clusters are gaining importance as solution precursors for the large-area deposition of Al 2 O 3 coatings with broad technological applications (7,8).Despite more than a century of study (9, 10), the complete portrait of aqueous Al chemistry remains unclear. Studies of aqueous Al chemistry are notoriously difficult because of the variety and complexity of the species that can be formed, encompassing monomeric, oligomeric, and polymeric hydroxides (11-17); colloidal solutions and gels; and precipitates. Synthesis is complicated by the fact that the counter-ions and the method and rate of pH change all have dramatic effects on product formation (18,19). Few methods exist for the in situ determination and assignment of molecular-level structures. For instance, 27 Al NMR can only identify certain Al aqueous species (15). Furthermore, unlike organic compounds, systematic spectroscopic signatures of metal hydroxide clusters are less accessible, making interpretation of experimental spectra challenging. We hereby report a combined synthesis, experiment, and theory platform for the study of aqueous metal clusters. Electrolysis is exploited to control the solution pH and counter-ion content precisely during cluster synthesis without using chemical reagents. The evolution of solution species is followed in situ by an improved femtosecond stimulated Raman (FSR) technique (20-22) that can detect weak signals associated with structure-defining vibrational modes. The resulting pHdependent Raman spectra are interpreted by juxtaposition to quantum mechanically computed vibrational modes to assign specific molecular structures. Through this integrated approach, we have discovered a speciation behavior for Al in water that has not previously been observed. We focus here on the synthesis an...
The prevalence of the condensed phase, interpenetration, and fragility of mesoporous coordination polymers (meso-PCPs) featuring dense open metal sites (OMSs) place strict limitations on their preparation, as revealed by experimental and theoretical reticular chemistry investigations. Herein, we propose a rational design of stabilized high-porosity meso-PCPs, employing a low-symmetry ligand in combination with the shortest linker, formic acid. The resulting dimeric clusters (PCP-31 and PCP-32) exhibit high surface areas, ultrahigh porosities, and high OMS densities (3.76 and 3.29 mmol g, respectively), enabling highly selective and effective separation of CH from CH/CO mixtures at 298 K, as verified by binding energy (BE) and electrostatic potentials (ESP) calculations.
Semiconductor quantum dot (QD) superlattices, which are periodically ordered three-dimensional (3D) array structures of QDs, are expected to exhibit novel photo-optical properties arising from the resonant interactions between adjacent QDs. Since the resonant interactions such as long-range dipole-dipole Coulomb coupling and short-range quantum resonance strongly depend on inter-QD nano space, precise control of the nano space is essential for physical understanding of the superlattice, which includes both of nano and bulk scales. Here, we study the pure quantum resonance in the 3D CdTe QD superlattice deposited by a layer-by-layer assembly of positively charged polyelectrolytes and negatively charged CdTe QDs. From XRD measurements, existence of the periodical ordering of QDs both in the lamination and in-plane directions, that is, the formation of the 3D periodic QD superlattice, was confirmed. The lowest excitation energy decreases exponentially with decreasing the nano space between the CdTe QD layers and also with decreasing the QD size, which is apparently indicative of the quantum resonance between the QDs rather than a dipole-dipole Coulomb coupling. The quantum resonance was also computationally demonstrated and rationalized by the orbital delocalization to neighboring CdTe QDs in the superlattice.
Ethylene (C2H4) purification from multicomponent mixtures by physical adsorption presents a great challenge in the chemical industry. This work successfully uses the postsynthetic method of crystal transformation in boiling alkaline solution to synthesize a trap‐and‐flow channel crystal (namely NTU‐67), the flow channel of which provides an effective shape‐ and size‐dependent sieving path for linear molecules such as acetylene (C2H2) and carbon dioxide (CO2), while the adjacent channel possesses customized space for efficient molecular trapping. The three‐bladed array of the nanospace enables the crystal to afford a record productivity of C2H4 (121.5 mL g−1, >99.95%) from C2H2/CO2/C2H4 (1/9/90, v/v/v) mixtures in a single adsorption–desorption cycle under humid and dynamic conditions, even at a high temperature of 343 K and wide gas ratio. The molecular‐level insight and mechanism of the cooperative role of the trap‐and‐flow channel, found computationally and observed experimentally, demonstrates a new design philosophy toward extending the application boundaries of porous coordination polymers to further challenging tasks.
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