Mg-Doped ZnO Nanoparticles for Efficient Sunlight-Driven Photocatalysis

Magnesium-doped ZnO (ZMO) nanoparticles were synthesized through an oxalate coprecipitation method. Crystallization of ZMO upon thermal decomposition of the oxalate precursors was investigated using differential scanning calorimetry (DSC) and X-ray diffraction (XRD) techniques. XRD studies point toward a significant <i>c</i>-axis compression and reduced crystallite sizes for ZMO samples in contrast to undoped ZnO, which was further confirmed by HRSEM studies. X-ray photoelectron spectroscopy (XPS), UV/vis spectroscopy and photoluminescence (PL) spectroscopy were employed to establish the electronic and optical properties of these nanoparticles. (XPS) studies confirmed the substitution of Zn²⁺ by Mg²⁺, crystallization of MgO secondary phase, and increased Zn–O bond strengths in Mg-doped ZnO samples. Textural properties of these ZMO samples obtained at various calcination temperatures were superior in comparison to the undoped ZnO. In addition to this, ZMO samples exhibited a blue-shift in the near band edge photoluminescence (PL) emission, decrease of PL intensities and superior sunlight-induced photocatalytic decomposition of methylene blue in contrast to undoped ZnO. The most active photocatalyst 0.1-MgZnO obtained after calcination at 600 °C showed a 2-fold increase in photocatalytic activity compared to the undoped ZnO. Band gap widening, superior textural properties and efficient electron–hole separation were identified as the factors responsible for the enhanced sunlight-driven photocatalytic activities of Mg-doped ZnO nanoparticles

Room temperature CO2 fixation via cyclic carbonate synthesis over vanadium-MOF catalysts

Vanadium containing 3D MOF, MIL-47 displayed excellent synergistic catalysis with alkyl ammonium halides (TBAX) in the room temperature fixation of CO 2 . Theoretical intrinsic-reaction-coordinate calculations were performed at the level of M06/LACVP**++ implemented in Jaguar v8.5 software to ascertain the mechanistic pathways of catalysis. A homogeneous complex of vanadium, vanadium acetyl acetonato [VO(acac) 2 ], was used as a model system to investigate the mechanism behind the synergistic activity of the MIL-47/TBAX, which indeed shows that the activation energy of the CO 2 fixation is considerably lowered by about 30–35 kcal compared to the uncatalyzed reactions. © 2019, The Korean Institute of Chemical Engineers.1

Inverse relationship of dimensionality and catalytic activity in CO2 transformation: a systematic investigation by comparing multidimensional metal-organic frameworks

The correlation between dimensionality and active sites on deciding the catalytic performance of an MOF catalyst in CO2-epoxide cycloaddition reactions has been studied. Seven In(iii) based MOFs built from carboxylic and N-donor ligands possessing different dimensionalities and distinct coordination environments were chosen as solid acid catalysts for this study. The origin of the catalytic activity of an In3+/TBAB bifunctional system in a CO2-PO reaction was studied in detail by performing density functional theory (DFT) calculations at the M06/LACVP∗∗++ level. The energy barrier of the propylene oxide ring opening in the presence of In3+/Br- is 11.5 kcal mol-1, which is significantly lower than those of un-catalyzed (55-63 kcal mol-1) and Br--catalyzed (19.5 kcal mol-1) reactions, which confirms the importance of the In3+/Br- binary catalytic system in the CO2-epoxide cycloaddition reactions. The one-dimensional (1D) MOF with unsaturated metal centers exhibited higher catalytic activity (PO conversion: 91%, temperature: 50 °C, and time: 12 h) than the two- and three-dimensional MOFs. The roles of dimensionality and unsaturated metal centers in cycloaddition reactions were explained on the basis of the results of activity testing and structural investigations. In addition, a plausible reaction mechanism for the catalytic activity of the 1D MOF was proposed with reference to our structure-density functional theory correlations. © 2017 The Royal Society of Chemistry.1

Rapid, Microwave-Assisted Synthesis of Cubic, Three-Dimensional, Highly Porous MOF-205 for Room Temperature CO₂ Fixation via Cyclic Carbonate Synthesis

A dual-porous, three-dimensional, metal–organic framework [Zn₄O­(2,6-NDC)­(BTB)_4/3] (MOF-205, BET = 4200 m²/g) has been synthesized using microwave power as an alternative energy source for the first time, and its catalytic activity has been exploited for CO₂–epoxide coupling reactions to produce five-membered cyclic carbonates under solvent-free conditions. Microwave synthesis was performed at different time intervals to reveal the formation of the crystals. Significant conversion of various epoxides was obtained at room temperature, with excellent selectivity toward the desired five-membered cyclic carbonates. The importance of the dual porosity and the synergistic effect of quaternary ammonium salts on efficiently catalyzed CO₂ conversion were investigated using various experimental and physicochemical characterization techniques, and the results were compared with those of the solvothermally synthesized MOF-205 sample. On the basis of literature and experimental inferences, a rationalized mechanism mediated by the zinc center of MOF-205 for the CO₂–epoxide cycloaddition reaction has been proposed