Electrocatalytic CO2 Reduction by [Re(CO)3Cl(3-(pyridin-2-yl)-5-phenyl-1,2,4-triazole)] and [Re(CO)3Cl(3-(2-pyridyl)-1,2,4-triazole)].

The exploration of novel electrocatalysts for CO2 reduction is necessary to overcome global warming and the depletion of fossil fuels. In the current study, the electrocatalytic CO2 reduction of [Re(CO)3Cl(N-N)], where N-N represents 3-(2-pyridyl)-1,2,4-triazole (Hpy), 3-(pyridin-2-yl)-5-phenyl-l,2,4-triazole (Hph), and 2,2'-bipyridine-4,4' dicarboxylic acidic (bpy-COOH) ligands, was investigated. In CO2-saturated electrolytes, cyclic voltammograms showed an enhancement of the current at the second reduction wave for all complexes. In the presence of triethanolamine (TEOA), the currents of Re(Hpy), Re(Hph), and Re(bpy-COOH) enhanced significantly by approximately 4-, 2-, and 5-fold at peak potentials of -1.60, -150, and -1.69 VAg/Ag+, respectively (in comparison to without TEOA). The reduction potential of Re(Hph) was less negative than those of Re(Hpy) and Re(COOH), which was suggested to cause its least efficiency for CO2 reduction. Chronoamperometry measurements showed the stability of the cathodic current at the second reduction wave for at least 300 s, and Re(COOH) was the most stable in the CO2-catalyzed reduction. The appearance and disappearance of the absorption band in the UV/vis spectra indicated the reaction of the catalyst with molecular CO2 and its conversion to new species, which were proposed to be Re-DMF + and Re-TEOA and were supposed to react with CO2 molecules. The CO2 molecules were claimed to be captured and inserted into the oxygen bond of Re-TEOA, resulting in the enhancement of the CO2 reduction efficiency. The results indicate a new way of using these complexes in electrocatalytic CO2 reduction.

Enhancing the remarkable adsorption of Pb2+ in a series of sulfonic-functionalized Zr-based MOFs: a combined theoretical and experimental study for elucidating the adsorption mechanism.

A series of Zr-based metal-organic frameworks was prepared via the solvothermal route using sulfonic-rich linkers for the efficient capture of Pb2+ ions from aqueous medium. The factors affecting adsorption such as the solution pH, adsorbent dosage, contact time, adsorption isotherms, and mechanism were studied. Consequently, the maximum adsorption capacity of Pb2+ on the acidified VNU-23 was determined to be 617.3 mg g-1, which is much higher than that of previously reported adsorbents and MOF materials. Furthermore, the adsorption isotherms and kinetics of the Pb2+ ion are in good accordance with the Langmuir and pseudo-second-order kinetic model, suggesting that the uptake of Pb2+ is a chemisorption process. The reusability experiments demonstrated the facile recovery of the H+⊂VNU-23 material through immersion in an HNO3 solution (pH = 3), where its Pb2+ adsorption efficiency still remained at about 90% of the initial uptake over seven cycles. Remarkably, the adsorption mechanism was elucidated through a combined theoretical and experimental investigation. Accordingly, the Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, scanning electron microscopy connected to energy-dispersive X-ray mapping (SEM-EDX-mapping), and X-ray photoelectron spectroscopy (XPS) analysis of the Pb⊂VNU-23 sample and comparison with H+⊂VNU-23 confirmed that the electrostatic interaction occurs via the interaction between the SO3- moieties in the framework and the Pb2+ ion, leading to the formation of a Pb-O bond. In addition, the density functional theory (DFT) calculations showed the effective affinity of the MOF adsorbent toward the Pb2+ ion via the strong driving force mentioned in the experimental studies. Thus, these findings illustrate that H+⊂VNU-23 can be employed as a potential adsorbent to eliminate Pb2+ ions from wastewater.