Enhanced photoreduction efficiency of Cr(VI) driven by visible light in a new Zr-based metal-organic framework modified by hydroxyl groups.

While metal-organic framework (MOF) photocatalysts have demonstrated a unique Cr(VI) photoreduction capability in recent decades, their performance is still insufficient for practical applications because of their low Cr(VI) uptake and poor visible light response. To cope with these drawbacks, a new OH-modified Zr-based MOF, termed HCMUE-1, was successfully prepared via a solvothermal method in this work. The complete characterization of HCMUE-1 was performed through various techniques, including powder X-ray diffraction (PXRD), Raman spectroscopy, Fourier transform infrared (FT-IR), thermogravimetric analysis and differential scanning calorimetry (TGA-DSC), scanning electron microscopy combined with energy-dispersive X-ray (SEM-EDX), and X-ray photoelectron spectroscopy (XPS). The obtained data exhibited the excellent Cr(VI) photoreduction efficiency of HCMUE-1, reaching up to 98% after 90 min and almost 100% after 120 min under visible light illumination in a low acidic medium. Noteworthily, HCMUE-1 retained the same Cr(VI) removal rate for at least seven cycles without considerable loss. Further experimental investigations demonstrated that the structural stability and surface morphology of HCMUE-1 were retained after photoreduction. Moreover, the photocatalytic reduction mechanism of Cr(VI) to Cr(III) was interpreted through a series of systematic experimental measurements. These results indicate that HCMUE-1 possesses potential as an efficient photocatalyst for reducing toxic Cr(VI) species from wastewater in real-life conditions.

[Mo2 S12 ]2- Complex as a Precursor for In-situ Generation of Molybdenum Sulfide Catalyst During the H2 Evolution.

For decades, the sulfido molybdenum complexes like [MoS4 ]2- , [Mo2 S12 ]2- , [Mo3 S13 ]2- have gained great attention because of their chemical versatility as well as their structural similarity to the edge-plan of the molybdenum disulfide (MoS2 ) which shows promising catalytic ability for the H2 generation. In this work, we report on the investigation of the dinuclear complex [Mo2 S12 ]2- in both organic and aqueous solution. We demonstrate that [Mo2 S12 ]2- is not intact during the H2 evolution catalysis when it is assayed as a homogeneous catalyst in an electrolyte solution (e. g. in DMF or water solvent) nor when it is immobilized on an electrode surface (e. g. mesoporous carbon black). It transforms into the polymeric amorphous molybdenum sulfide [MoS] which subsequently acts as an actual catalyst. We discuss on the possible [Mo2 S12 ]2- to [MoS] transformation mechanism by employing an arsenal of electrochemical analysis, spectroscopic analyses and microscopic analyses. Effects of the electrochemical operating conditions to the [Mo2 S12 ]2- to [MoS] transformation as well as to the chemical nature and the catalytic performance of the [MoS] product are also emphasized.

Electrocatalytic H2 evolution using binuclear cobalt complexes as catalysts.

We report herein on the use of two binuclear cobalt complexes with the N,N'-bis(salicylidene)-phenylmethanediamine ligand as catalysts for the H2 evolution in DMF solution with acetic acid as proton source. Both experimental analyses (electrochemical analysis, spectroscopy analysis) and theoretical analysis (foot-of-the wave analysis) were employed. These catalysts required an overpotential of ca. 470 mV to catalyze the H2 evolution and generated H2 gas with a faradaic efficiency of 85-95% as calculated on the basis of after 5 hour bulk electrolysis. The kinetic investigation showed the maximal TOF value of 50 s-1 on the basis of an ECEC mechanism. Two cobalt centers, standing at a long distance of 4.175 Å, operated independently during catalysis without a synergetic effect or cooperation capability.

N(4)-Morpholinothiosemicarbazide-Modified Cellulose: Synthesis, Structure, Kinetics, Thermodynamics, and Ni(II) Removal Studies.

In this study, cellulose extracted from straw was modified using N(4)-morpholinothiosemicarbazide to generate a novel adsorbent as a chelate-complex-based material. The effects of pH, time, temperature, and mass ratios of KIO4: cellulose on the yield of the oxidation were analyzed using iodometric titration and photometric methods. The accuracy and precision of the above two methods were evaluated using Student and Fisher statistical distribution. The structure of the material was characterized by Fourier-transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and Brunauer-Emmett-Teller surface area analysis. The kinetic order of Ni(II) adsorption was dependent on the concentration of Ni(II). The surface response design enabled to optimize the condition for Ni(II) adsorption at 58 °C, pH of 4.98, within 106 min. The maximum Ni(II) adsorption capacity was 90 mg g-1. This kind of adsorbent can be reused at least five times without a significant decrease in its adsorption efficiency.

Thiosemicarbazone-Modified Cellulose: Synthesis, Characterization, and Adsorption Studies on Cu(II) Removal.

Thiosemicarbazide-modified cellulose (MTC) has been studied for removing heavy metals in the water source or for extracting some precious metals. The conditions of synthesis of MTC and Cu(II) removal were optimized by single-variable analysis through oxidation-reduction on titration and photometry. The results of Fourier-transform infrared spectroscopy, Brunauer-Emmett-Teller, and thermogravimetric analyses show that MTC exists in the thioketone form with a high surface area and heat durability. The Cu(II) removal was of pseudo-second order and the isotherm equation correlated best with the Langmuir equation. MTC has the maximum capacity of adsorption, which is q m = 106.3829 mg g-1. Furthermore, MTC can be regenerated without the loss of adsorption efficiency after ten cycles of adsorption and desorption.