The small-pore zeolite with the chabazite framework topology, SSZ-13, is found to be an active catalyst in the carbonylation of dimethyl ether to methyl acetate (MA). The production of MA over SSZ-13 after 24 h on stream at 165 °C and 1 bar approaches that obtained from mordenite and is significantly higher than from ferrierite at comparable Si/Al of ca. 10. To understand the origin of the activity, SSZ-13 materials are synthesized with variable Si/Al, characterized via several techniques including multinuclear magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, and evaluated for their carbonylation activity. While MA production rates increase with decreasing Si/Al, the correlation is nonlinear due to the effect of Si/Al on the acid site distribution within different confining environments, and the associated impact of the latter on the rate-determining transition state barrier. Enhanced MA production rates trend with acid sites located at the eight-membered ring (8MR) that are increasingly populated as framework Al content increases. Density functional theory analyses of transition state energies as a function of active site location support the experimental findings, where the lowest apparent barriers are associated with the methoxy groups that orient within the plane of the 8MR window. This is due to an optimal charge stabilization of the cationic transition states with the negatively charged oxygens within the 8MR window. The effects of catalyst chemical composition, separate from framework topology, are also investigated using SAPO-34 (the silicoaluminophosphate analog of SSZ-13). Analyses of the 1 H MAS NMR signals and carbonylation activity suggest that the higher acid site strength of SSZ-13 compared to that of the SAPO material is required for effective Brønsted acid catalysis of Koch-type carbonylation pathways.

This paper presents a fully-continuous novel liquid-liquid-extraction (LLE) platform for the purification of nanoparticles. The use of multistage operation enhances the purity of the final stream without the expense of high solvent consumption. Two case studies, purification of CdSe quantum dots in organic solvent and that of gold nanoparticles in water, demonstrate that the LLE platform is versatile, non-destructive, and highly efficient.

Mesoporous carbon nitride is synthesized in a one-pot approach using different nonionic surfactants (Pluronic F-127, Pluronic P-123, and Triton X-100) and a melamine cyanurate hydrogen-bonded complex using just water as the solvent. We obtain three-dimensional assembled nanostructures from low-dimensional carbon nitride sheets by taking advantage of supramolecular assembly of melamine and cyanuric acid, moderate interactions between the surfactant and precursors, structure directing effects of the surfactants, and the good thermal stability of the melamine cyanurate sheets formed around the micelles. Different morphologies, including sheetlike, hollow spherical, and tubular or highly porous networks, result depending upon the synthesis approach and the surfactant/precursor ratio. Pseudoternary phase diagrams map the composition of the starting solution to the resultant carbon nitride morphology. Increasing the amount of surfactant leads to a higher carbon residue (C/N ∼ 1) and large BET surface areas (≤300 m2/g). Further tuning of the synthesis parameters as well as addition of HCl produces uniformly porous nanostructures with a high porosity (up to 0.8 cm3/g), a high surface area (>200 m2/g), and yet a stoichiometric C/N ratio (∼0.75). The synthesized high-surface area carbon nitrides show improved light absorption and enhanced photocatalytic activity in a rhodamine B dye degradation reaction under visible light irradiation compared to those of bulk melamine-derived carbon nitride.

We describe the controlled colloidal synthesis and characterization of ZnSe quantum dots using a continuous-flow microfluidic reactor. A systematic investigation of the synthetic route reveals a possible two-stage pathway for ZnSe nanocrystal formation. The first stage corresponds to the formation of zinc selenide nuclei at low temperatures (160 °C), followed by the growth of ZnSe nanocrystals at higher temperatures (340 °C). The quantum dots exhibit sharp exciton absorption, with tunable emission spectra between 370 and 430 nm. The photoluminescence of ZnSe nanocrystals is characterized by narrow emission linewidths of 14–21 nm. For the first time, we report luminescent emission from ZnSe nanocrystals upon X-ray excitation, revealing that radioluminescence emission is associated to confined excitons, and that the radioluminescence intensity is a linear function of the fluence/dose rate of X-rays. The precise control of the synthesis of particles with uniform sizes and excellent optical properties associated with the microfluidic synthesis opens a new avenue for the controlled production of heavy-metal-free luminescent and radioluminescent nanocrystals in flow.

The continuous liquid–liquid extraction of the PET radioisotope 45Ti using a membrane-based separator allows for efficient 45Ti recovery and radiolabeling.