Advances in the development of novel cobalt Fischer-Tropsch catalysts for synthesis of long-chain hydrocarbons and clean fuels.

Spinels can serve as alternative low-cost bifunctional electrocatalysts for oxygen reduction/evolution reactions (ORR/OER), which are the key barriers in various electrochemical devices such as metal-air batteries, fuel cells and electrolysers. However, conventional ceramic synthesis of crystalline spinels requires an elevated temperature, complicated procedures and prolonged heating time, and the resulting product exhibits limited electrocatalytic performance. It has been challenging to develop energy-saving, facile and rapid synthetic methodologies for highly active spinels. In this Article, we report the synthesis of nanocrystalline M(x)Mn(3-x)O(4) (M = divalent metals) spinels under ambient conditions and their electrocatalytic application. We show rapid and selective formation of tetragonal or cubic M(x)Mn(3-x)O(4) from the reduction of amorphous MnO(2) in aqueous M(2+) solution. The prepared Co(x)Mn(3-x)O(4) nanoparticles manifest considerable catalytic activity towards the ORR/OER as a result of their high surface areas and abundant defects. The newly discovered phase-dependent electrocatalytic ORR/OER characteristics of Co-Mn-O spinels are also interpreted by experiment and first-principle theoretical studies.

Rapid room-temperature synthesis of nanocrystalline spinels as oxygen reduction and evolution electrocatalysts

Spinels with the formula of AB2O4 (where A and B are metal ions) and the properties of magnetism, optics, electricity, and catalysis have taken significant roles in applications of data storage, biotechnology, electronics, laser, sensor, conversion reaction, and energy storage/conversion, which largely depend on their precise structures and compositions. In this review, various spinels with controlled preparations and their applications in oxygen reduction/evolution reaction (ORR/OER) and beyond are summarized. First, the composition and structure of spinels are introduced. Then, recent advances in the preparation of spinels with solid-, solution-, and vapor-phase methods are summarized, and new methods are particularly highlighted. The physicochemical characteristics of spinels such as their compositions, structures, morphologies, defects, and substrates have been rationally regulated through various approaches. This regulation can yield spinels with improved ORR/OER catalytic activities, which can furth...

Spinels: Controlled Preparation, Oxygen Reduction/Evolution Reaction Application, and Beyond

Developing bifunctional efficient and durable non-noble electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is highly desirable and challenging for overall water splitting. Herein, Co–Mn carbonate hydroxide (CoMnCH) nanosheet arrays with controllable morphology and composition were developed on nickel foam (NF) as such a bifunctional electrocatalyst. It is discovered that Mn doping in CoCH can simultaneously modulate the nanosheet morphology to significantly increase the electrochemical active surface area for exposing more accessible active sites and tune the electronic structure of Co center to effectively boost its intrinsic activity. As a result, the optimized Co1Mn1CH/NF electrode exhibits unprecedented OER activity with an ultralow overpotential of 294 mV at 30 mA cm–2, compared with all reported metal carbonate hydroxides. Benefited from 3D open nanosheet array topographic structure with tight contact between nanosheets and NF, it is able to deliver a high and...

Electronic and Morphological Dual Modulation of Cobalt Carbonate Hydroxides by Mn Doping toward Highly Efficient and Stable Bifunctional Electrocatalysts for Overall Water Splitting

UV−visible diffuse reflectance spectroscopy was used to probe the electronic structure and domain size of tungsten oxide species in crystalline isopolytungstates, monoclinic WO3, and dispersed WOx species on ZrO2 surfaces. UV−visible absorption edge analysis, CO2 chemisorption, and Raman spectroscopic results show that three distinct regions of WOx coverage on ZrO2 supports appear with increasing WOx surface density:  submonolayer region (0−4 W nm-2), polytungstate growth region (4−8 W nm-2), and polytungstate/crystalline WO3 coexistence region (>8 W nm-2). The structure and catalytic activity of WOx species on ZrO2 is controlled only by WOx surface density (W nm-2), irrespective of the WOx concentration, oxidation temperature, and ZrO2 surface area used to obtain a particular density. The submonolayer region is characterized by distorted octahedral WOx species that are well dispersed on the ZrO2 surface. These species show a constant absorption edge energy, they are difficult to reduce, and contain few a...

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Structure and Electronic Properties of Solid Acids Based on Tungsten Oxide Nanostructures

Diagnostic health risk assessment of electronic waste on the general population in developing countries' scenarios

In this work the results of a TPR and XPS investigation of CoxOy–CuO mixed oxides in the range of composition Co : Cu=100:0–8:92 are reported and compared. The final catalysts were obtained by thermal decomposition in air and N2 at 723 K for 24 h of single‐phase cobalt–copper hydroxycarbonates prepared by coprecipitation at constant pH. The Co : Cu=100 : 0 specimen calcined in air formed the Co2+[Co3]2O4 (Co3O4) spinel phase. The copper‐containing catalysts (Co : Cu=85 : 15–8 : 92) showed mainly two phases: (i) spinels, like Co2+[Co3+]2O4, Co 1-x 2+ Cu x 2+ [Co3+]2O4 and (ii) pure CuO, the relative amount of each phase depending on the Co : Cu atomic ratio. The results of the XPS study are consistent with the bulk findings and revealed the presence of Co2+, Co3+ and Cu2+ species at the catalyst surface. Moreover, the surface quantitative analysis evidenced a cobalt enrichment, in particular for the most diluted cobalt samples. The TPR study showed that the catalyst reduction is affected by a strong mutual influence between cobalt and copper. The reducibility of the mixed oxide catalysts was always promoted with respect to that of the pure Co3O4 and CuO phases and the reduction of cobalt was markedly enhanced by the presence of copper. Cobalt and copper were both reduced to metals regardless of the catalyst composition. On the other hand, the Co : Cu=100 : 0 specimen calcined in N2 formed, as expected, CoO. The initial addition of copper resulted in the formation of the Cu+Co3+O2 compound, besides CoO, up to a Co/Cu=1 atomic ratio at which the CuCoO2 phase was the main component. A further addition of copper led to the formation of CuCoO2 and CuO phases. The XPS results were in good agreement with these findings and the surface quantitative analysis revealed a less enrichment of cobalt with respect to the catalysts calcined in air. The TPR analysis confirmed that the reduction of the N2‐calcined catalysts was also remarkably promoted by the presence of copper. Also in this case cobalt and copper metal were the final products of reduction.

TPR and XPS study of cobalt–copper mixed oxide catalysts: evidence of a strong Co–Cu interaction

Nanomaterials are increasingly being used in new products and devices with a great impact on different fields from sensoristics to biomedicine. Biosynthesis of nanomaterials by microorganisms is recently attracting interest as a new, exciting approach towards the development of 'greener' nanomanufacturing compared to traditional chemical and physical approaches. This review provides an insight about microbial biosynthesis of nanomaterials by bacteria, yeast, molds, and microalgae for the manufacturing of sensoristic devices and therapeutic/diagnostic applications. The last ten-year literature was selected, focusing on scientific works where aspects like biosynthesis features, characterization, and applications have been described. The knowledge, challenges, and potentiality of microbial-mediated biosynthesis was also described. Bacteria and microalgae are the main microorganism used for nanobiosynthesis, principally for biomedical applications. Some bacteria and microalgae have showed the ability to synthetize unique nanostructures: bacterial nanocellulose, exopolysaccharides, bacterial nanowires, and biomineralized nanoscale materials (magnetosomes, frustules, and coccoliths). Yeasts and molds are characterized by extracellular synthesis, advantageous for possible reuse of cell cultures and reduced purification processes of nanomaterials. The intrinsic variability of the microbiological systems requires a greater protocols standardization to obtain nanomaterials with increasingly uniform and reproducible chemical-physical characteristics. A deeper knowledge about biosynthetic pathways and the opportunities from genetic engineering are stimulating the research towards a breakthrough development of microbial-based nanosynthesis for the future scaling-up and possible industrial exploitation of these promising 'nanofactories'.

Microbial Nanotechnology: Challenges and Prospects for Green Biocatalytic Synthesis of Nanoscale Materials for Sensoristic and Biomedical Applications.

The recently reported interesting behavior of the EPR spin intensity as freshly prepared CuZSM-5 is dehydrated has been confirmed, and the interpretation offered in explanation has been tested by extending the data. Magnetic susceptibility and optical diffuse reflection spectroscopy have been used to show that the anomalous EPR data correspond to changes in symmetry rather than disproportionation of [CuOH]+ into Cu+ and Cu2+O- as H2O is removed, as previously suggested. Moreover, the relatively small negative Weiss constants suggest that antiferromagnetic coupling through the supposedly EPR silent conventional bridge species, [Cu2+−O2-−Cu2+]2+, cannot be responsible for the relatively large changes in observed EPR spin intensity on dehydration. EPR measures selectively individual paramagnetic species and ignores those of low symmetry, while magnetic susceptibility integrates over all magnetic species in the sample. The changes in the EPR intensities were much larger than those observed by magnetic suscept...

Zeolite Chemistry of CuZSM-5 Revisited

Three cobalt–copper hydroxysalts with chemical formulae Co(CO3)0.5(OH)1.0· 0.11H2O, Co0.67Cu0.33(CO3)0.4(OH)1.2 and Co0.49Cu0.51(CO3)0.43(OH)1.14 have been obtained and characterised by powder X-ray diffraction (XRD), thermal analysis (TG, DTG and DTA), diffuse reflectance spectroscopy (DRS), magnetic susceptibility and X-ray photoelectron spectroscopy (XPS). The above precursors treated at 723 K for 24 h both in N2 and in air give several cobalt and copper oxides which were characterised by magnetic susceptibility, X-ray diffraction, X-ray photoelectron spectroscopy and diffuse reflectance. Depending on the Co : Cu atomic ratios and on the treatments with various gases, the products consist of oxides such as CoO, CuxCo1–xO, CuCoO2 and CuxCo3–xO4 for the samples calcined in N2, and Co3O4, CuxCo3–xO4 and CuO for those calcined in air.

Roberto Dragone

Papers

Diagnostic health risk assessment of electronic waste on the general population in developing countries' scenarios

TPR and XPS study of cobalt–copper mixed oxide catalysts: evidence of a strong Co–Cu interaction

Microbial Nanotechnology: Challenges and Prospects for Green Biocatalytic Synthesis of Nanoscale Materials for Sensoristic and Biomedical Applications.

Zeolite Chemistry of CuZSM-5 Revisited

Preparation and characterisation of cobalt–copper hydroxysalts and their oxide products of decomposition