Hexamolybdenum Clusters Supported on Graphene Oxide: Visible-Light Induced Photocatalytic Reduction of Carbon Dioxide into Methanol

International audienceHexamolybdenum (Mo6) cluster-based compounds namely Cs2Mo6Bri8Bra6 and (TBA)2Mo6Bri8Bra6 (TBA = tetrabutylammonium) were immobilized on graphene oxide (GO) nanosheets by taking advantage of the high lability of the apical bromide ions with oxygen-functionalities of GO nanosheets. The loading of Mo6 clusters on GO nanosheets was probed by Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and elemental mapping analyses. The developed GO-Cs2Mo6Bri8Brax and GO-(TBA)2Mo6Bri8Brax composites were then used as heterogeneous photocatalysts for the reduction of CO2 under visible light irradiation. After 24 h visible light illumination, the yield of methanol was found to be 1644 and 1294 μmol.g-1cat for GO-Cs2Mo6Bri8Brax and GO-(TBA)2Mo6Bri8Brax, respectively. The quantum yields of methanol by using GO-Cs2Mo6Bri8Brax and GO-(TBA)2Mo6Bri8Brax as catalysts with reference to Mo6 cluster units presented in 0.1g amount of catalyst were found to be 0.015 and 0.011, respectively. The role of immobilized Mo6 clusters-based compounds on GO nanosheets is discussed to understand the photocatalytic mechanism of CO2 reduction into methano

Validated Simultaneous Derivative Spectrophotometric Estimation of Azithromycin, Fluconazole and Secnidazole in Bulk and Pharmaceutical Formulation

Two simple, sensitive, accurate and precise spectrophotometric methods were developed and validated for the quantitative determination of Azithromycin (AZI), Fluconazole (FLU) and Secnidazole (SEC) in bulk and tablet dosage form. Method A is based on the first-order derivative (D1) and Method B is based on the second-order derivative (D2) spectrophotometric method. In Method A, absorbance was measured at 215nm, 275nm and 333nm being the zero crossing points for AZI, FLU and SEC respectively. In Method B, absorbance was measured at 220nm, 225nm and 211nm being the zero crossing points for AZI, FLU and SEC respectively. For Method A, all three drugs obey Beer’s law in the concentration range 5-30µg/ml for AZI, 5-60 µg/ml for FLU and 5-40 µg/ml for SEC with correlation coefficients 0.995, 0.998 and 0.998 respectively. For Method B, all three drugs obey Beer’s law in the concentration range 5-35 µg/ml for AZI, 5-40 µg/ml for FLU and 5-40 µg/ml for SEC with correlation coefficients 0.995, 0.999 and 0.998 respectively. Both methods can be used for routine analysis of these three drugs in their pharmaceutical dosage form. Results for analysis of both methods were tested and validated for various parameters according to ICH guidelines.  Keywords: Derivative, Azithromycin, Fluconazole, Secnidazol

Chemically Functionalized Reduced Graphene Oxide as a Novel Material for Reduction of Friction and Wear

Graphene, a lamellar structured material, easily shears at the contact interfaces and exhibits excellent mechanical strength and conductivity, which promises its potential for tribological applications. However, the dispersion of graphene in lube media is a big challenge. Herein, we developed a chemical approach for selective inclusion of long alkyl chains on the edges and defects sites of reduced graphene oxide sheets through the amide linkage, which facilitates their stable dispersion in the lube oil. Chemical and structural features of site-selective chemically functionalized reduced graphene oxide are monitored by FTIR, XPS, XRD, TG-DTA, FESEM, and HRTEM. Tribological test results showed that the chemically functionalized reduced graphene oxide, as an additive to 10W-40 engine oil, significantly reduced both the friction and the wear of steel balls. The stable dispersion of chemically functionalized reduced graphene oxide provides low resistance in a sheared contact owing to weak van der Waals interaction between their lamellas, thus significantly reducing both the friction and the wear

Solvent-free, improved synthesis of pure bixbyite phase of iron and manganese mixed oxides as low-cost, potential oxygen carrier for chemical looping with oxygen uncoupling

Chemical looping with oxygen uncoupling (CLOU) is the tendency of releasing gaseous oxygen of an oxygen carrier upon heating, which is the key property for the efficient and cleaner combustion of solid fuels for their wide exploitation for thermal power applications. The solvent-free, improved synthesis method was developed for the synthesis of pure bixbyite, FeMnO3 (Ia3̅, a = b = c = 0.94 nm) as a low-cost, oxygen carrier by exposing of the abundantly available precursors (Fe3O4 and MnO) under inert- or reduction- atmosphere followed by air at 900 °C. The bixbyite FeMnO3 showed the enhanced, stable multi-cycle CLOU performance than that of the physical mixture and it is converted into FeMn2O4 after the complete exhaustion of reactive oxygen under CLOU conditions. FeMnO3 showed the uniform elemental distribution of Fe, Mn and O, which facilitate the regeneration in air upon heating for multi-cycle performance. 3.2 wt.% of reactive oxygen can be obtained compared to the mass of FeMnO3 which is almost equal to the theoretical value under CLOU conditions. The lattice of FeMnO3 is altered linearly above 100 °C with the increase of temperature, however; without the decomposition of the bixbyite phase and it was reinstated virtually upon cooling in air

Validated Simultaneous Derivative Spectrophotometric Estimation of Diflunisal and Lignocaine in Bulk and Pharmaceutical Formulation

Two simple, sensitive, accurate and precise spectrophotometric methods were developed and validated for the quantitative determination of Diflunisal (DIF) and Lignocaine (LIG) in bulk and pharmaceutical dosage form. Method A is based on the first-order derivative (D1), and Method B is based on the second-order derivative (D2) spectrophotometric method. In Method A, absorbance was measured at 224nm and 264nm being the zero crossing points for DIF and LIG, respectively. In Method B, absorbance was measured at 232nm and 273nm being the zero crossing points for DIF and LIG, respectively. For Method A, the two drugs obeyed Beer's law in the concentration range of 3-39µg/ml for DIF and 4-40 µg/ml for LIG with correlation coefficients 0.999 and 0.995, respectively. For Method B, the two drugs obeyed Beer’s law in the concentration range of 3-30µg/ml for DIF and 4-48µg/ml for LIG with correlation coefficients 0.998 and 0.996, respectively. Both methods can be used for routine analysis of these two drugs in their pharmaceutical dosage form. Results for analysis of both methods were tested and validated for various parameters according to ICH guidelines.  Keywords: Derivative, Diflunisal, Lignocaine, first order, second orde

Copper–manganese mixed oxides: CO2- selectivity, stable, and cyclic performance for chemical looping combustion of methane

Chemical looping combustion (CLC) is a key technology for oxy-fuel combustion with inherent separation of CO2 from a flue gas, in which oxygen is derived from a solid oxygen carrier. Multi-cycle CLC performance and the product selectivity towards CO2 formation were achieved using mixed oxide of Cu and Mn (CuMn2O4) (Fd%3m, a = b = c = 0.83 nm) as an oxygen carrier. CuMn2O4 was prepared by the co-precipitation method followed by annealing at 900 1C using copper(II) nitrate trihydrate and manganese(II) nitrate tetrahydrate as metal precursors. CuMn2O4 showed oxygen-desorption as well as reducibility at elevated temperatures under CLC conditions. The lattice of CuMn2O4 was altered significantly at higher temperature, however, it was reinstated virtually upon cooling in the presence of air. CuMn2O4 was reduced to CuMnO2, Mn3O4, and Cu2O phases at the intermediate stages, which were further reduced to metallic Cu and MnO upon the removal of reactive oxygen from their lattice. CuMn2O4 showed a remarkable activity towards methane combustion reaction at 750 1C. The reduced phase of CuMn2O4 containing Cu and MnO was readily reinstated when treated with air or oxygen at 750 1C, confirming efficient regeneration of the oxygen carrier. Neither methane combustion efficiency nor oxygen carrying capacity was altered with the increase of CLC cycles at any tested time. The average oxygen carrying capacity of CuMn2O4 was estimated to be 114 mg g�1, which was not altered significantly with the repeated CLC cycles. Pure CO2 but no CO, which is one of the possible toxic by-products, was formed solely upon methane combustion reaction of CuMn2O4. CuMn2O4 shows potential as a practical CLC material both in terms of multi-cycle performance and product selectivity towards CO2 formation

Combustion of volatile organic compounds over Cu–Mn based mixed oxide type catalysts supported on mesoporous Al2O3, TiO2 and ZrO2

A series of supported Cu–Mn based catalysts have been synthesized using three different supports mesoporous Al2O3, mesoporous TiO2 and mesoporous ZrO2. Cu–Mn precursors were incorporated on mesoporous supports using wet impregnation method. These catalyst supports were prepared by templating method using a natural biopolymer namely, chitosan. The catalytic activity for benzene and acetaldehyde combustion was studied for these catalysts. The synthesized catalysts have been characterized by XRD, BET-SA, O2-TPD and H2-TPR in a view of material characterization, as well as to investigate the mechanistic aspects of catalytic reactions. The bimetallic supported catalysts follow the activity sequence—Cu–Mn/TiO2 > Cu–Mn/ZrO2 > Cu–Mn/Al2O3 for both the reactions studied. These results interestingly show, that the catalytic activity is dependent on the support used, however, quite independent of the surface area of these supports. The better activity of TiO2 and ZrO2 based catalysts is likely due to their redox properties. The existence of low temperature peaks in both O2-TPD and H2-TPR explain better redox properties as well as catalytic performance of TiO2 and ZrO2 supported catalysts as compared to those Al2O3 supported mixed oxides

Mechanically Stable Mixed Metal Oxide of Cu and Mn as Oxygen Carrier for Chemical Looping Syngas Combustion

Chemical looping combustion possesses an inherent advantage of separation of CO2 from the carbon based fuels including thermal power plants that would offer effective mitigation of CO2 emissions through carbon capture and sequestration. In this study, a stable and regenerative mixed transition metal oxide of Cu and Mn (CuMn2O4) is synthesized through coprecipitation method and tested for multi-cycle performance for the oxidation of syngas as fuel. It was observed that, 90% of oxygen carrying capacity of CuMn2O4 can be utilized for the oxidation of syngas with almost 100% conversion efficiency in a packed bed reactor. Theconversion efficiency of both CO and H2 was not altered significantly in all the tested cycles. CO2 and H2O were the sole products of syngas conversion. The phase of CuMn2O4 can be regenerated solely by aerial oxidation of the reduced products (Cu and MnO) at 800° C. Utilization of maximum oxygen carrying capacity can reduce the circulation frequency of oxygen carrier between air and fuel fluidized bed reactors that can reduce the energy penalty significantly. The pelletized oxygen carrier possess appreciable mechanical strength that showed micro-hardness up to 2186 N/mm2 which is suitable for fluidized bed CLC reactors