Single-layer metal dichalcogenides are two-dimensional semiconductors that present strong potential for electronic and sensing applications complementary to that of graphene.

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Electronics and optoelectronics of two-dimensional transition metal dichalcogenides.

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Since the time of the industrial revolution, the atmospheric CO(2) concentration has risen by nearly 35 % to its current level of 383 ppm. The increased carbon dioxide concentration in the atmosphere has been suggested to be a leading contributor to global climate change. To slow the increase, reductions in anthropogenic CO(2) emissions are necessary. Large emission point sources, such as fossil-fuel-based power generation facilities, are the first targets for these reductions. A benchmark, mature technology for the separation of dilute CO(2) from gas streams is via absorption with aqueous amines. However, the use of solid adsorbents is now being widely considered as an alternative, potentially less-energy-intensive separation technology. This Review describes the CO(2) adsorption behavior of several different classes of solid carbon dioxide adsorbents, including zeolites, activated carbons, calcium oxides, hydrotalcites, organic-inorganic hybrids, and metal-organic frameworks. These adsorbents are evaluated in terms of their equilibrium CO(2) capacities as well as other important parameters such as adsorption-desorption kinetics, operating windows, stability, and regenerability. The scope of currently available CO(2) adsorbents and their critical properties that will ultimately affect their incorporation into large-scale separation processes is presented.

Adsorbent Materials for Carbon Dioxide Capture from Large Anthropogenic Point Sources

Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40th anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochemical water splitting, and organic reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful theoretical methods are dee...

Fundamentals and Catalytic Applications of CeO2-Based Materials

Post-combustion CO2 capture from the flue gas is one of the key technology options to reduce greenhouse gases, because this can be potentially retrofitted to the existing fleet of coal-fired power stations. Adsorption processes using solid sorbents capable of capturing CO2 from flue gas streams have shown many potential advantages, compared to other conventional CO2 capture using aqueous amine solvents. In view of this, in the past few years, several research groups have been involved in the development of new solid sorbents for CO2 capture from flue gas with superior performance and desired economics. A variety of promising sorbents such as activated carbonaceous materials, microporous/mesoporous silica or zeolites, carbonates, and polymeric resins loaded with or without nitrogen functionality for the removal of CO2 from the flue gas streams have been reviewed. Different methods of impregnating functional groups, including grafting techniques and modifying the support materials, have been discussed to en...

Post-Combustion CO2 Capture Using Solid Sorbents: A Review

Catalytic aqueous-phase aldol-condensation of acetone and furfural has been studied in this work. Three different mixed-oxides catalysts (Mg–Zr, Mg–Al and Ca–Zr, with different basic sites distribution) were studied, their activity and selectivity being correlated with their physico-chemical properties. Catalysts with the highest concentration of basic sites (especially medium-strength basic sites) are the most active and selective for the C13 fraction, whereas molar ratios of 1:1 yield the highest selectivities for C13 fraction (more than 60% atomic yield for the Mg–Zr mixed oxide). Concerning to reaction mechanism, cis isomers are the first ones formed, whereas trans isomers are the most abundant at higher reaction times. The main causes of catalysts deactivation are the modification of the physico-chemical properties of catalysts – because of the interaction with water – and in minor extent, the leaching effect; although homogeneous catalytic effects are discarded at studied conditions. The products formed, and the kinetic dependence on reactant concentration, are consistent with a catalytic mechanism in which the rate-determining step is the formation of the enolate species. The model considers consecutive reversible reactions yielding C8, in the first step, and C13, in the second step; with a first-order dependence on the species with α-hydrogen (acetone and C8), and zero-th order on those species without it (furfural and C13).

Aqueous-phase furfural-acetone aldol condensation over basic mixed oxides

Magnesium−aluminum double oxides derived from the thermal treatment of layered hydroxides (hydrotalcites) have been tested for CO2 adsorption. The effects of various preparation parameters, such as the incorporated cation (K or Na), the mode of addition of magnesium and aluminum precursors, the presence of sonication, and the calcination temperature, on the adsorption capacity under mild conditions were studied using thermogravimetry and calorimetry. Calorimetric and FTIR data were used to explain the adsorption mechanisms leading to the undesirable irreversible adsorption. This adsorption was related to the formation of unidentate CO2-adsorbent species with the strongest adsorption sites, whereas bidentate and surface bicarbonates lead to highly reversible adsorption. In conclusion, preparation procedures that lead to an increase in the strength of basic sites do not lead to significant increases in the adsorption capacity, but rather lead to more difficult regeneration of the saturated support.

Adsorption of CO2 on Hydrotalcite-Derived Mixed Oxides: Sorption Mechanisms and Consequences for Adsorption Irreversibility

Ethanol catalytic condensation over Mg–Al mixed oxides derived from hydrotalcites

The adsorption of different alkanes (linear and cyclic), aromatics, and chlorohydrocarbons onto different nonmicroporous carbons—multiwalled carbon nanotubes (CNTs), carbon nanofibers (CNFs), and high-surface-area graphites (HSAGs)—is studied in this work by inverse gas chromatography (IGC). Capacity of adsorption was derived from the isotherms of adsorption, whereas thermodynamic properties (enthalpy of adsorption, surface free energy characteristics) have been determined from chromatographic retention data. HSAGs present the highest adsorption capacity, followed by CNTs and CNFs (although CNTs present an intermediate surface area between the two HSAG studied). Among the different adsorbates tested, benzene exhibits the highest adsorption capacity, and the same trend is observed in the enthalpy of adsorption. From surface free energy data, enthalpies of adsorption of polar compounds were divided into dispersive and specific contributions. The interactions of cyclic (benzene and cyclohexane) and chlorinated compounds (trichloroethylene, tetrachloroethylene, and chloroform) with the surfaces are mainly dispersive over all the carbons tested, CNTs being the material with the highest dispersive contribution, as was deduced also from the entropy parameter. Adsorption parameters were correlated with morphological and chemical properties of the materials.

Adsorption of volatile organic compounds onto carbon nanotubes, carbon nanofibers, and high-surface-area graphites.

Graphitic carbon nitride assisted partial photocatalytic oxidation of 5-hydroxymethyl-2-furfural (HMF) in aqueous medium was investigated. Different carbon nitride precursors were considered, being melamine the one yielding the most efficient photocatalyst. The obtained 30% selectivity of HMF oxidation to 2,5-furandicarboxaldehyde (FDC) is higher than those reported up to now. A further thermal exfoliation of the g-C3N4 samples showed under artificial light irradiation both an enhanced photocatalytic activity in conversion of HMF, and selectivity (ca. 42–45%) to FDC. The performance of the catalysts increased when the experiments were carried out under real outdoor illumination, reaching 50% of selectivity versus FDC formation at 40% of HMF conversion. The utilization of radical scavengers revealed that O2 − was the main reactive species responsible for HMF oxidation to FDC. The photocatalytic test carried out under natural solar irradiation resulted in higher yields of FDC compared to that observed in the laboratory UV irradiated set-up, thus demonstrating the applicability of the exfoliated carbon nitride material in real-life conditions.

Eva Díaz

Papers

Aqueous-phase furfural-acetone aldol condensation over basic mixed oxides

Adsorption of CO2 on Hydrotalcite-Derived Mixed Oxides: Sorption Mechanisms and Consequences for Adsorption Irreversibility

Ethanol catalytic condensation over Mg–Al mixed oxides derived from hydrotalcites

Adsorption of volatile organic compounds onto carbon nanotubes, carbon nanofibers, and high-surface-area graphites.

Selective photocatalytic oxidation of 5-hydroxymethyl-2-furfural to 2,5-furandicarboxyaldehyde in aqueous suspension of g-C3N4