Search

Herein, we have employed a convenient method to study kinetic and thermodynamic parameters of the adsorption of molybdenum from wastewater by using modified Zr‐based metal–organic frameworks, UIO‐66‐NH2‐X, as adsorbents. The frameworks were fabricated with a simple and fast method from terephthalic acids and Zirconium metal ions and modified via introduction of aldehyde groups using imine condensation. This is the first report in which MOFs have been utilized as adsorbents in molybdenum adsorption. The prepared adsorbents show high adsorption efficiency, which is representative of an improvement compared to other literature. The adsorption capacity and molybdenum removal for the modified framework are 667 mg/g and 93%, respectively which is a significant and remarkable value among other previously reported articles. The experimental adsorption data could be well interpreted with the pseudo‐second‐order kinetics and the Langmuir isotherm model. Thermodynamic studies illustrated a spontaneous exothermic mechanism for the adsorption process. [ABSTRACT FROM AUTHOR]

In this work, three bifunctional metal‐organic frameworks (MOFs) were constructed through the introduction of various linear amine functional groups within MIL‐101(Cr). The unsaturated chromium metal center was incorporated with three various ligands including ethylene diamine, diethylene triamine, and diamino butane. The resultant prepared MOFs contain unsaturated chromium centers as Lewis acidic centers and amine groups as basic sites. The contemporary existence of basic and acidic centers allowed prepared bifunctional compounds to be highly effectual heterogeneous catalysts for chemical fixation of CO2 with epoxides, affording cyclic carbonates, under relatively mild conditions and in the absence of either solvent or cocatalyst. High tendency of prepared structures toward CO2 adsorption followed by speeding up the nucleophilic attack resulted in gaining excellent conversion, selectivity, and activity for large epoxide as well as bulky ones. The synthesized catalyst outperforms other reported heterogeneous catalysts. High conversion, TON, recyclability, and mild reaction conditions are some distinctive characteristics of the bifunctional synergetic catalysts. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs) as acid catalysts provide active sites with particularly appropriate for glycerol conversion. In this study, Mil-118-SnO2 was synthesized by doping SnO2 quantum dots with Mil-118. The SnO2 quantum dots were formed through the epoxide-assisted precipitation route as a proton scavenger and following ring-opening that drives hydrolysis and, ultimately, condensation of the hydrated metal. The Mil-118-SnO2 was used as a catalyst for the production of five-member (2, 2-dimethyl-1, 3-dioxolane-4-methanol) and six-member (2,2-dimethyl-dioxane-5-ol, (II)) cycles. The results revealed a higher conversion rate and selectivity for Mil-118-SnO2 than for Mil-118. An increase was observed in conversion and selectivity, which was related to the improvement of the acidic properties of Mil-118 after doping SnO2 quantum dots. The experiments were conducted under mild conditions, producing a 40% increase in conversion and selectivity. This catalyst could be reused up to five times with 97% selectivity during a cycle. Glycerol is produced as the key byproduct in the transesterification process. The as-synthesized Mil-118-SnO2 then was used as a heterogeneous catalyst for the glycerol conversion to solketal. The experiments were carried out under mild conditions, which produced a 40% increase in conversion and selectivity. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) have proved to be particularly appropriate for CO2 conversion. In the present work, we report metalloporphyrin‐based MOFs, PCN‐222(M) (M = Fe, Co, Ni, and Cu), which promote photocatalytic CO2 conversion to valuable chemicals. These ultra‐highly stable frameworks are constructed from Zr6 clusters and metalloporphyrin linkers. Metalloporphyrinic MOF has been synthesized and employed as a visible‐light photocatalyst for carbon dioxide to form formate. The effect of metalloporphyrinic PCN‐222(M) on CO2 reduction has been studied. Remarkably, PCN‐222(M) is highly efficient in visible light‐driven CO2 reduction into formate ion compared with the nonmetal porphyrinic PCN‐222. Metal ions of porphyrinic linkers play a great role in CO2 sorption, light harvesting, bandgap, photoluminescence (pL) intensity, and charge transfer, which influence CO2 reduction. CO2 adsorption and activation over metal ions of porphyrinic linkers play a significant part in the improvement of the conversion efficiency; the product obtained was characterized by gas chromatography/mass spectrometry (GC/MS) and ion mobility spectrometry (IMS) analyses. The reaction mechanism has been discussed in detail. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks with diverse structures and unique properties have demonstrated that can be an ideal substitute for natural enzymes in colorimetric sensing platform for analyte detection in various fields such as environmental chemistry, biotechnology and clinical diagnostics, which have attracted the scientist's attention, recently. In this study, a porous coordination network (denoted as PCN-222) was synthesized as a new biomimetic material from an iron linked tetrakis (4-carboxyphenyl) porphyrin (named as Fe-TCPP) as a heme-like ligand and Zr6 linker as a node. This catalyst shows the peroxidase and catalase activities clearly. The mechanism of peroxidase activity for PCN-222 was investigated using the spectrophotometric methods and its activity was compared with the other nanoparticles which, the results showed a higher activity than the other catalysts. Also, the hydrogen peroxide was detected by PCN-222(Fe) based on the peroxidase-like activity. For detection of hydrogen peroxide a linear range of 3–200 µM and detection of limit (LOD) 1 µM (3σ/slope), under optimal conditions were obtained. Moreover, based on the high tendency of PCN-222(Fe) to combine with the TMB as a chromogenic substrate in the peroxidase-like activity, we developed the sensitive and selective colorimetric assay for glucose detection that was found a detection limit (LOD) of 2.2 µM in the linear range from 12 to 75 µM. Finally due to the good catalytic activity of PCN-222(Fe), it was used to detection of glucose and hydrogen peroxide in real samples. [ABSTRACT FROM AUTHOR]

In contrast to early transition metal complexes of d0 electron configuration, their main group metal analogues are usually poor catalysts for ethylene polymerisation due to their diminished tendency to insert ethylene into an M–R bond. Interestingly, we found that ring strain in the transition structure of the insertion reaction is most likely responsible to set the ease of the process. Ethylene insertion into an M–R bond requires a four-membered ring transition structure. Strain in a four-membered ring was shown to be dependent on the metal identity (transition or main group/d or p block). For early transition metals, due to the presence of empty valence d orbitals, the strain is negligible but, for main group metals, the strain is significant and so destabilizes the corresponding transition structure. Our claim gains support from investigation of ethylene insertion into an M–allyl bond. In this case, the relevant insertion preferentially passes through a six-membered ring transition structure with an accessibly low activation barrier. In contrast to four-membered ring transition structures, six-membered ones do not suffer significantly from ring strain, causing the insertion activation barrier to become independent of the metal identity. It becomes obvious from our study that this previously undisclosed factor should play the pivotal role in determining the reactivity of many catalysts. [ABSTRACT FROM AUTHOR]