Furfural and 5-hydroxymethylfurfural stand out as bridges connecting biomass raw materials to the biorefinery industry. Their reductive transformations by hydroconversion are key routes toward a wide ...variety of chemicals and biofuels, and heterogeneous catalysis plays a central role in these reactions. The catalyst efficiency highly depends on the nature of metals, supports, and additives, on the catalyst preparation procedure, and obviously on reaction conditions to which catalyst and reactants are exposed: solvent, pressure, and temperature. The present review focuses on the roles played by the catalyst at the molecular level in the hydroconversion of furfural and 5-hydroxymethylfurfural in the gas or liquid phases, including catalytic hydrogen transfer routes and electro/photoreduction, into oxygenates or hydrocarbons (e.g., furfuryl alcohol, 2,5-bis(hydroxymethyl)furan, cyclopentanone, 1,5-pentanediol, 2-methylfuran, 2,5-dimethylfuran, furan, furfuryl ethers, etc.). The mechanism of adsorption of the reactant and the mechanism of the reaction of hydroconversion are correlated to the specificities of each active metal, both noble (Pt, Pd, Ru, Au, Rh, and Ir) and non-noble (Ni, Cu, Co, Mo, and Fe), with an emphasis on the role of the support and of additives on catalytic performances (conversion, yield, and stability). The reusability of catalytic systems (deactivation mechanism, protection, and regeneration methods) is also discussed.
A look at the use of perovskites as subsitutes of noble metals in heterogeneous catalysis is presented. Topics discussed include the synthesis of nanoscaled perovskite and the use of perovskites to ...replace platinum-group metals.
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•Magnetite is effective to remove tetracycline in the US/Fe3O4/H2O2 system.•The heterogeneous activation of H2O2 was enhanced by ultrasound.•The presence of different types of OH was ...verified.•A OH-based reaction mechanism for US/Fe3O4/H2O2 system was investigated.•The effect of reaction parameters on tetracycline removal was evaluated.
The degradation of tetracycline over Fe3O4 catalyst was studied by using a coupled ultrasound/heterogeneous Fenton process. The effects of some key reaction parameters, the evolution of toxicity, and the reaction mechanism were investigated. Experimental results showed that the stability of catalyst was significantly improved when ultrasound was employed. Under optimal conditions, 93.6% of tetracycline was removed after 60min of treatment. The removal efficiency of the total organic carbon (TOC) at 60min was 31.8%. The surface hydroxyl radicals were identified as the major reactive species during the oxidation process. Toxicity tests with Daphnia magna indicated that the toxicity of the solution increased during the first 60min and then decreased as the oxidation proceeded.
Within the framework of green chemistry, solvents occupy a strategic place. To be qualified as a green medium, these solvents have to meet different criteria such as availability, non-toxicity, ...biodegradability, recyclability, flammability, and low price among others. Up to now, the number of available green solvents are rather limited. Here we wish to discuss a new family of ionic fluids, so-called Deep Eutectic Solvents (DES), that are now rapidly emerging in the current literature. A DES is a fluid generally composed of two or three cheap and safe components that are capable of self-association, often through hydrogen bond interactions, to form a eutectic mixture with a melting point lower than that of each individual component. DESs are generally liquid at temperatures lower than 100 °C. These DESs exhibit similar physico-chemical properties to the traditionally used ionic liquids, while being much cheaper and environmentally friendlier. Owing to these remarkable advantages, DESs are now of growing interest in many fields of research. In this review, we report the major contributions of DESs in catalysis, organic synthesis, dissolution and extraction processes, electrochemistry and material chemistry. All works discussed in this review aim at demonstrating that DESs not only allow the design of eco-efficient processes but also open a straightforward access to new chemicals and materials.
Deep Eutectic Solvents (DES) are an emerging new class of solvents that are highly attractive for the design of eco-efficient processes.
Wavefunction engineering using intraband transition is the most versatile strategy for the design of infrared devices. To date, this strategy is nevertheless limited to epitaxially grown ...semiconductors, which lead to prohibitive costs for many applications. Meanwhile, colloidal nanocrystals have gained a high level of maturity from a material perspective and now achieve a broad spectral tunability. Here, we demonstrate that the energy landscape of quantum well and quantum dot infrared photodetectors can be mimicked from a mixture of mercury selenide and mercury telluride nanocrystals. This metamaterial combines intraband absorption with enhanced transport properties (i.e. low dark current, fast time response and large thermal activation energy). We also integrate this material into a photodiode with the highest infrared detection performances reported for an intraband-based nanocrystal device. This work demonstrates that the concept of wavefunction engineering at the device scale can now be applied for the design of complex colloidal nanocrystal-based devices.
Abstract
Place cells exhibit spatially selective firing fields that collectively map the continuum of positions in environments; how such activity pattern develops with experience is largely unknown. ...Here, we record putative granule cells (GCs) and mossy cells (MCs) from the dentate gyrus (DG) over 27 days as mice repetitively run through a sequence of objects fixed onto a treadmill belt. We observe a progressive transformation of GC spatial representations, from a sparse encoding of object locations and spatial patterns to increasingly more single, evenly dispersed place fields, while MCs show little transformation and preferentially encode object locations. A competitive learning model of the DG reproduces GC transformations via the progressive integration of landmark-vector cells and spatial inputs and requires MC-mediated feedforward inhibition to evenly distribute GC representations, suggesting that GCs slowly encode conjunctions of objects and spatial information via competitive learning, while MCs help homogenize GC spatial representations.
The aim of this work was to obtain an in-depth understanding of the U(VI) adsorption mechanism over amino-functionalized mesoporous silica SBA-15 and highlights its high efficiency in aqueous media ...for U(VI) removal and preconcentration. The samples were synthesized and functionalized by both grafting and co-condensation methods, using different alkyl-substituted amine groups and were characterized using X-ray diffraction, N2 physisorption, Fourier transform infrared spectroscopy, and elemental C–H–N–S analyses. The properties for U(VI) adsorption were evaluated under discontinuous conditions, with the determination of the effect of several parameters (initial pH, contact time, initial U(VI) concentration, functionalization method, and organic moiety composition). U(VI) adsorption over grafted materials reached equilibrium at around 30 min, with a maximum adsorption capacity of 573 mgU·gads –1 for the most efficient material at its optimal adsorption pH (equal to 6) at 20 °C. Functionalized materials by grafting exhibit better adsorption capacities than co-condensed samples because of higher function surface density and function availability. U(VI) adsorption mechanisms were also studied by measuring the electrophoretic mobilities of the particles, aqueous U(VI) speciation, in situ attenuated total reflection infrared and Raman spectroscopies, and transmission electron microscopy analysis. U(VI) adsorption occurred through the formation of an inner sphere complex. The localization of adsorbed U(VI) has also been determined inside of the mesopores, with the formation of several particles on the nanometer scale, in the size of U-hydroxy phases. Besides, the study of the reusability of amino-functionalized SBA-15 by applying adsorption–desorption cycles was also conducted. The adsorption capacity of the material remains stable for at least four adsorption–desorption cycles without any noticeable capacity decrease.
The hippocampus is thought to guide navigation by forming a cognitive map of space. Different environments differ in geometry and the availability of cues that can be used for navigation. Although ...several spatial coding mechanisms are known to coexist in the hippocampus, how they are influenced by various environmental features is not well understood. To address this issue, we examined the spatial coding characteristics of hippocampal neurons in mice and rats navigating in different environments. We found that CA1 place cells located in the superficial sublayer were more active in cue-poor environments and preferentially used a firing rate code driven by intra-hippocampal inputs. In contrast, place cells located in the deep sublayer were more active in cue-rich environments and used a phase code driven by entorhinal inputs. Switching between these two spatial coding modes was supported by the interaction between excitatory gamma inputs and local inhibition.
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•Deep and superficial CA1 place cells were differentially expressed across environments•Cue-poor environments were represented by CA1 superficial place cells using a rate code•Cue-rich environments were represented by CA1 deep place cells using a phase code•Switching between spatial codes was mediated by gamma inputs and local inhibition
Sharif et al., demonstrated the existence of segregated hippocampal circuits for spatial coding across heterogeneous environments. Deep and superficial CA1 place cells used different codes for space depending on the availability of cues. A rapid switch between these two spatial coding modes was supported by the interaction between gamma inputs.
NiO and NiO–CuO polycrystalline rodlike nanoparticles were confined and stabilized within the channels of ordered mesoporous SBA-15 silica by a simple and viable approach consisting in incipient ...wetness impregnation of the calcined support with aqueous solutions of metal nitrates followed by a mild drying step at 25 °C and calcination. As revealed by low- and high-angle XRD, N2 adsorption/desorption, HRTEM/EDXS and H2 TPR analyses, the morphostructural properties of NiO–CuO nanoparticles can be controlled by adjusting their chemical composition, creating the prerequisites to obtain high performance bimetallic catalysts. Experimental evidence by in situ XRD monitoring during the thermoprogrammed reduction indicates that the confined NiO–CuO nanoparticles evolve into thermostable and well-dispersed Ni–Cu heterostructures. The strong Cu–Ni and Ni–support interactions demonstrated by TPR and XPS were put forward to explain the formation of these new bimetallic structures. The optimal Ni–Cu/SBA-15 catalyst (i.e., Cu/(Cu+Ni) atomic ratio of 0.2) proved a greatly enhanced reducibility and H2 chemisorption capacity, and an improved activity in the hydrogenation of cinnamaldehyde, as compared with the monometallic Ni/SBA-15 or Cu/SBA-15 counterparts, which can be associated with the synergism between nickel and copper and high dispersion of active components on the SBA-15 host. The unique structure and controllable properties of both oxidic and metallic forms of Ni–Cu/SBA-15 materials make them very attractive for both fundamental research and practical catalytic applications.
Environmental cues affect place cells responses, but whether this information is integrated versus segregated in distinct hippocampal cell populations is unclear. Here, we show that, in mice running ...on a treadmill enriched with visual-tactile landmarks, place cells are more strongly controlled by landmark-associated sensory inputs in deeper regions of CA1 pyramidal layer (CA1d). Many cells in CA1d display several firing fields correlated with landmarks, mapping positions slightly before or within the landmarks. Supporting direct involvement of sensory inputs, their firing fields show instantaneous responses to landmark manipulations, persist through change of context, and encode landmark identity and saliency. In contrast, cells located superficially in the pyramidal layer have single firing fields, are context specific and respond with slow dynamics to landmark manipulations. These findings suggest parallel and anatomically segregated circuits within CA1 pyramidal layer, with variable ties to landmarks, allowing flexible representation of spatial and non-spatial information.
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