Regulating C₂H₂/CO₂ adsorption selectivity by electronic-state manipulation of iron in metal-organic frameworks

The separation of C2H2 from C2H2/CO2 mixture is of great importance, yet highly challenging in the petrochemical industry due to their similar physicochemical properties. While open-metal sites (OMSs) in metal-organic frameworks (MOFs) are known to possess high affinity toward C2H2, its selective adsorption performance regulated by the electronic state of the same OMSs remains unexplored. Here, we report a metal electronic-state manipulation approach to construct a pair of isostructural Fe-MOFs, namely LIFM-26(Fe[II]/Fe[III]) and LIFM-27(Fe[III]) with different Fe[II] or Fe[III] oxidation states on the Fe centers, which display mixed-valent Fe[II]/Fe[III] centers in the former and sole Fe[III] centers in the latter. Remarkably, LIFM-26(Fe[II]/Fe[III]) shows significantly enhanced C2H2 uptake capacity than LIFM-27(Fe[III]), attested by adsorption isotherms and IAST calculations, as well as simulated and experimental breakthrough experiments. Furthermore, in situ infrared (IR) and molecular calculations unveil that the presence of Fe[II] in LIFM-26(Fe[II]/Fe[III]) results in stronger Fe[II]–C2H2 interactions than Fe[III]–C2H2, which plays a key role in the C2H2/CO2 separation

Tetrabenzoporphyrin and -mono-, - Cis -di- and tetrabenzotriazaporphyrin derivatives: Electrochemical and spectroscopic implications of meso CH Group replacement with nitrogen

Nonperipherally hexyl-substituted metal-free tetrabenzoporphyrin (2H-TBP, 1a) tetrabenzomonoazaporphyrin (2H-TBMAP, 2a), tetrabenzo-cis-diazaporphyrin (2H-TBDAP, 3a), tetrabenzotriazaporphyrin (2H-TBTAP, 4a), and phthalocyanine (2H-Pc, 5a), as well as their copper complexes (1b-5b), were synthesized. As the number of meso nitrogen atoms increases from zero to four, Îmax of the Q-band absorption peak becomes red-shifted by almost 100 nm, and extinction coefficients increased at least threefold. Simultaneously the blue-shifted Soret (UV) band substantially decreased in intensity. These changes were related to the relative electron-density of each macrocycle expressed as the group electronegativity sum of all meso N and CH atom groups, âχR. X-ray photoelectron spectroscopy differentiated between the three different types of macrocyclic nitrogen atoms (the Ninner, (NH)inner, and Nmeso) in the metal-free complexes. Binding energies of the Nmeso and Ninner,Cu atoms in copper chelates could not be resolved. Copper insertion lowered especially the cathodic redox potentials, while all four observed redox processes occurred at larger potentials as the number of meso nitrogens increased. Computational chemical methods using density functional theory confirmed 1b to exhibit a Cu(II) reduction prior to ring-based reductions, while for 2b, Cu(II) reduction is the first reductive step only if the nonperipheral substituents are hydrogen. When they are methyl groups, it is the second reduction process; when they are ethyl, propyl, or hexyl, it becomes the third reductive process. Spectro-electrochemical measurements showed redox processes were associated with a substantial change in intensity of at least two main absorbances (the Q and Soret bands) in the UV spectra of these compounds

Sub-ppt level voltammetric sensor for Hg2+ detection based on nafion stabilized l-cysteine-capped Au@Ag core-shell nanoparticles

Bimetallic nanoparticles (BMNPs) have received considerable attention due to their distinctive properties when compared to the corresponding monometallic NPs and their bulk counterpart. In this report, the formation of gold@silver core-shell nanoparticles (Au@AgCSNPs) was achieved via a one-pot synthetic approach after mixing 1:1 M solutions of Au and Ag ions. L-cysteine was used as reducing as well as capping agent for preparing Au@AgCSNPs. Ultraviolet-visible (UV-Vis) spectroscopy was employed for surface plasmon study while Fourier-transform infrared (FTIR) spectroscopy gave insights for interaction of NPs with specific functionality of the capping material. Surface morphology of the fabricated Au@AgCSNPs, probed by atomic force microscopy (AFM), indicated an average height of nanoparticles around 43 ± 3 nm and their crystallinity were confirmed via powder X-ray diffraction (PXRD) study. Significantly, the as synthesized Au@AgCSBMNPs were fabricated onto the conductive surface of glassy carbon electrode (GCE), stabilized with nafion, and then utilized as an extremely sensitive/greatly selective sensor for voltammetric detection of Hg2+. The developed sensor responded linearly to Hg2+ between 0.001 and 19 ppb with limit of detection (LOD) as low as 0.0001 ppb (0.1 ppt). Finally, the sensor was effectively applied for Hg2+ detection in different groundwater samples and is workable at concentrations undetectable by several sensing tools. [Figure not available: see fulltext.]

MnOx nanoparticle-dispersed CeO2 nanocubes: A remarkable heteronanostructured system with unusual structural characteristics and superior catalytic performance

Understanding the interface-induced effects of heteronanostructured catalysts remains a significant challenge due to their structural complexity, but it is crucial for developing novel applied catalytic materials. This work reports a systematic characterization and catalytic evaluation of MnOx nanoparticle-dispersed CeO2 nanocubes for two important industrial applications, namely, diesel soot oxidation and continuous-flow benzylamine oxidation. The X-ray diffraction and Raman studies reveal an unusual lattice expansion in CeO2 after the addition of MnOx. This interesting observation is due to conversion of smaller sized Ce4+ (0.097 nm) to larger sized Ce3+ (0.114 nm) in cerium oxide led by the strong interaction between MnOx and CeO2 at their interface. Another striking observation noticed from transmission electron microscopy, high angle annular darkfield scanning transmission electron microscopy, and electron energy loss spectroscopy studies is that the MnOx species are well-dispersed along the edges of the CeO2 nanocubes. This remarkable decoration leads to an enhanced reducible nature of the cerium oxide at the MnOx/CeO2 interface. It was found that MnOx/CeO2 heteronanostructures efficiently catalyze soot oxidation at lower temperatures (50% soot conversion, T50 ∼660 K) compared with that of bare CeO2 nanocubes (T50 ∼723 K). Importantly, the MnOx/CeO2 heteronanostructures exhibit a noticeable steady performance in the oxidation of benzylamine with a high selectivity of the dibenzylimine product (∼94-98%) compared with that of CeO2 nanocubes (∼69-91%). The existence of a strong synergistic effect at the interface sites between the CeO2 and MnOx components is a key factor for outstanding catalytic efficiency of the MnOx/CeO2 heteronanostructures

Easy, one-step synthesis of CdTe quantum dots via microwave irradiation for fingerprinting application

A novel one-step microwave irradiation method has been introduced to synthesize 3-mercaptopropionic acid capped CdTe QDs (Quantum dots). The synthesis process required no special conditions such as an inert nitrogen atmosphere but was carried out using TeO2(Tellurium oxide) as opposed to the Te powder, Na2TeO3or Al2TeO3usually used for the tellurium source. The characterization of the QDs revealed that they were 2-3 nm in size. The application of aqueous synthesis of capped CdTe QDs for latent fingerprinting was explored and fast turnaround times were achieved

Voltammetric studies on the inter-relationship between the redox chemistry of TTF, TTF+, TTF2+ and HTTF+ in acidic media

The electrochemistry of TTF, TTF+, TTF2+ and HTTF+ (TTF = tetrathiafulvalene) has been studied in acetonitrile (0.1 M Bu4NPF6) solutions containing ethereal HBF4 or trifluoroacetic acid (TFA) using transient and steady-state voltammetric techniques. In the absence of acid, the oxidation of TTF occurs via two, diffusion controlled, chemically and electrochemically reversible, one-electron processes with reversible formal potentials of -74 and 311 mV vs. Fc0/+ (Fc = ferrocene). The voltammetry in the presence of acid is far more complex. Voltammetric and UV-vis data reveal that the parent TTF undergoes facile protonation to yield the structurally modified HTTF+ cation in the presence of acid. In contrast, detailed analysis of the data show that electrochemically generated TTF+ and TTF2+ do not react with acid. The voltammetry in the presence of acid has been simulated to provide a thermodynamic and kinetic description of the acid-base chemistry coupled to electron transfer

Construction of chitosan-supported nickel cobaltite composite for efficient electrochemical capacitor and water-splitting applications

Abstract The construction of highly efficient electrode material is of considerable interest, particularly for high capacitance and water-splitting applications. Herein, we present the preparation of a NiCo2O4-Chitosan (NC@Chit) nanocomposite using a simple hydrothermal technique designed for applications in high capacitance and water-splitting. The structure/composition of the NC@Chit composite was characterized using different analytical methods, containing electron microscope (SEM and TEM), and powder X-ray diffraction (XRD). When configured as an anode material, the NC@Chit displayed a high capacitance of 234 and 345 F g−1 (@1Ag−1 for GC/NC and NC@Chit, respectively) in an alkaline electrolyte. The direct use of the catalyst in electrocatalytic water-splitting i.e., HER and OER achieved an overpotential of 240 mV and 310 mV at a current density of 10 mA cm−2, respectively. The obtained Tafel slopes for OER and HER were 62 and 71 mV dec−1, respectively whereas the stability and durability of the fabricated electrodes were assessed through prolonged chronoamperometry measurement at constant for 10 h. The electrochemical water splitting was studied for modified nickel cobaltite surface using an impedance tool, and the charge transfer resistances were utilized to estimate the electrode activity

Silver/gold core/shell nanowire monolayer on a QCM microsensor for enhanced mercury detection

The formation of a silver nanowire monolayer (Ag NWML) galvanically replaced with gold (Au) directly on the electrodes of a quartz crystal microbalance (QCM) transducer for non-spectroscopic based elemental mercury (Hg0) vapor sensing is reported in this study. The modification of Ag NWML to Ag/Au alloyed (Ag/Au NWML) structures through galvanic replacement (GR) reaction was found to enhance the sensitivity and selectivity of the sensors. Following GR reaction, the morphology of the Ag nanowires was found to change without deforming the monolayer packing arrangement. Interestingly, the selectivity of the sensor toward Hg0 vapor was increased by increasing the Au concentration during the GR reaction. The Ag/Au NWML based sensor which was modified using a 2 mM Au solution was found to produce 3 times higher sensitivity compared to the Au control QCM as well as having more than 95% accuracy and >90% repeatability. This was found to be due to the formation of Ag/Au alloys (Ag/Au NWML) with active sites that had a high affinity toward Hg0 vapor

Ceria-zirconia modified MnOx catalysts for gaseous elemental mercury oxidation and adsorption

A series of MnOx/CeO2 (Mn/Ce), MnOx/ZrO2 (Mn/Zr), and MnOx/Ce0.75Zr0.25O2 (Mn/CZ) catalysts prepared by an impregnation method were tested for their ability to catalyse the oxidation of Hg0 at relatively low temperature (423 K). Various characterization techniques, namely, Brunauer-Emmett-Teller (BET) surface area analysis, X-ray diffraction (XRD), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), and H2-temperature programmed reduction (H2-TPR) were employed to understand the structural, surface, and redox properties of the prepared catalysts. Specific aspects of the catalysis of Hg0 oxidation that were investigated included the influence of MnOx loading (5, 15, and 25%) and the influence of HCl and O2. Among the catalysts tested, the 15Mn/CZ catalyst achieved the best Hg0 oxidation performance (~83% conversion of Hg0 to Hg2+) in the presence of HCl and O2. The higher activity of the 15Mn/CZ catalyst was most likely due to the presence of more oxygen vacancies, enhanced Mn4+/Mn4+ + Mn3+ + Mn2+ ratio and more surface adsorbed oxygen, which were proved by XRD, BET, Raman, and XPS. H2-TPR results also show that the strong interaction between the Ce0.75Zr0.25O2 support and MnOx improved the redox properties significantly as compared to pure CeO2 and ZrO2 supported MnOx catalysts