RESUMEN
This paper presents a fast CO2 laser synthesis and writing technique - laser photothermal synthesis and writing (LPSW) - to generate and write a high concentration of unaggregated, spherical sub-10 nm metal nanoparticles (sMNPs). The method is generic, and we demonstrate the fabrication of Ni, Cu, and Ag directly in polymer thin films. A partly IR-absorbing thin polymer film can be heated by the laser to high temperatures in a short time, triggering metal-reduction, nucleation, and growth. Rapid quenching of polymer films suppresses particle diffusion and traps the generated sMNPs in the polymer film. As a result, these particles are immobilized in the laser illuminated spot ("written" by the laser) on quenching. Here, Ag-polymer films are used as a model to demonstrate how laser parameters - pulse duration, laser energy flux, and number of pulses (pulsed thermal load) - can be varied to tune particle size distributions of metal sMNPs. Using this approach, we have been able to generate 4-12 nm Ag sMNPs with thermal pulses as short as 35 ms. Fast heating timescales employed in this approach allow for the scalable manufacturing of high yields of metal sMNPs, which we estimate to be around 1 g min-1. This rapid, general synthesis and writing technique may have potentially important applications in fast, large-scale additive manufacturing and patterning of metal-loaded polymer multilayers, flexible electronics, and sensors.
RESUMEN
Two-dimensional (2D) layered zeolites are new forms of 3D zeolite frameworks. They can be pillared to form more open porous structures with increased access for reactants that are too big for the micropores of zeolites. The current pillaring procedure, however, requires intercalation of pillaring precursors by dispersing 2D zeolite in an alkoxide liquid and hydrolizing entrapped alkoxide to form inorganic oxide pillars in an aqueous alkaline solution. Both steps use excess solvents, generate significant waste, and require multiple synthesis and separation steps. Here we report a vapor-phase pillarization (VPP) process to produce pillared zeolites from 2D layered zeolite structures. The VPP process has â¼100% efficiency of alkoxide usage in the intercalation step, requires less (and, in some cases, zero) water addition in the hydrolysis step, does not require separation for product recovery, and generates no liquid waste. Furthermore, synthesis of pillared zeolites via the VPP process can be accomplished within a single apparatus with one-time operation. The pillared zeolite prepared by the VPP method preserved the zeolitic layered structure as well as acidity and showed enhancement in catalytic alkylation of mesitylene with benzyl alcohol compared to 2D layered zeolite without pillarization treatment.
RESUMEN
Ultrasmall metal nanoparticles are inherently unstable because of their high specific surface area. This work investigates how growth and aggregation of these nanostructures can be circumvented by incorporating them into a polymer matrix in an on-the-fly growth process. We demonstrate the formation of sub-5 nm particles of Ni, Co, and Cu nanoparticles in a polymer matrix using an aerosol single-drop reactor approach. The rapid thermal pulse given to the aerosol particles enables the formation of nuclei and growth, with subsequent rapid quenching to freeze in the structure. The role of the temperature as well as the precursor concentration of the resulting size and morphology is discussed. A characteristic time analysis and an analysis of the particle size distributions lead to the conclusion that growth is governed by nucleation and surface growth, with little coagulation or Ostwald ripening. Finally, we note that this aerosol route is amenable to scale-up for large-scale production of nanoclusters that can either be used as is within the polymer or released by solvent extraction, depending on the application.
RESUMEN
In this study, we determine effective adsorption capacities and desorption energies for DMMP with highly ordered mesoporous carbons (OMCs), 1D cylindrical FDU-15, 3D hexagonal CMK-3, 3D bicontinuous CMK-8, and as a reference, microporous BPL carbon. After exposure to DMMP vapor at room temperature for approximately 70 and 800 h, the adsorption capacity of DMMP for each OMC was generally proportional to the total surface area and pore volume, respectively. Desorption energies of DMMP were determined using a model-free isoconversional method applied to thermogravimetric analysis (TGA) data. Our experiments determined that DMMP saturated carbon will desorb any weakly bound DMMP from pores >2.4 nm at room temperature, and no DMMP will adsorb into pores smaller than 0.5 nm. The calculated desorption energies for high surface coverages, 25% DMMP desorbed from pores ≤2.4 nm, are 68-74 kJ mol-1, which is similar to the DMMP heat of vaporization (52 kJ mol-1). At lower surface coverages, 80% DMMP desorbed, the DMMP desorption energies from the OMCs are 95-103 kJ mol-1. This is overall 20-30 kJ mol-1 higher in comparison to that of BPL carbon, due to the pore size and diffusion through different porous networks.
RESUMEN
Quantitative determination of Ca, Mg, and Zn in fingernails was performed with laser-induced breakdown spectroscopy. Two different methods of producing solid standards for calibration were explored - preparation of keratin pellets and deposition of aqueous solutions to filter papers. Measurements of the temperature and electron density of the plasma produced on keratin pellets, filter paper, and nails were performed, and it was determined that the standards prepared on filter paper gave plasma temperatures and electron densities closer to those observed on the nails. The ablation rate of the filter paper was also more similar to that of the nails. Using calibration curves produced using these filter paper standards, Ca, Mg, and Zn were determined in fingernails of 11 subjects. For comparison, the same samples were digested and atomic absorption was used to determine the same three elements. The differences in results are discussed in light of sample homogeneity and instrumental precision; the best agreement was obtained for determination of Zn. The work suggests that the filter paper method of standard preparation may be appropriate for LIBS analysis of other samples that give relatively low temperature, low electron density plasmas (i.e., polymers).