Evidence on C-C Coupling to Acetate as Key Reaction Intermediate in Photocatalytic Reduction of CO2 over Pt/TiO2.

Photocatalytic conversion of CO2 with H2O is an attractive application that has the potential to mitigate environmental and energy challenges through the conversion of CO2 to hydrocarbon products such as methane. However, the underlying reaction mechanisms remain poorly understood, limiting real progress in this field. In this work, a mechanistic investigation of the CO2 photocatalytic reduction on Pt/TiO2 is carried out using an operando FTIR approach, combined with chemometric data processing and isotope exchange of (12CO2 + H2O) toward (13CO2 + H2O). Multivariate curve resolution analysis applied to operando spectra across numerous cycles of photoactivation and the CO2 reaction facilitates the identification of principal chemical species involved in the reaction pathways. Moreover, specific probe-molecule-assisted reactions, including CO and CH3COOH, elucidate the capacity of selected molecules to undergo methane production under irradiation conditions. Finally, isotopic exchange reveals conclusive evidence regarding the nature of the identified species during CO2 conversion and points to the significant role of acetates resulting from the C-C coupling reaction as key intermediates in methane production from the CO2 photocatalytic reduction reaction.

3D multiscale analysis of the hierarchical porosity in Coscinodiscus sp. diatoms using a combination of tomographic techniques.

A full 3D analysis of the hierarchical porosity in Coscinodiscus sp. diatom structures was carried out by using a multiscale approach that combines three advanced volumetric imaging techniques with resolutions and fields of view covering all the porous characteristics of such complex architectures: electron tomography, "slice and view" approach that uses a dual-beam microscope (FIB-SEM), and array tomography consisting of serial imaging of ultrathin specimen sections. This multiscale approach allowed the whole porosity network to be quantified and provided an unprecedented structural insight into these natural nanostructured materials with internal organization ranging from micrometer to nanometer. The analysed species is made of several nested layers with different pore sizes, shapes and connectivities and characterized by the presence of interconnected pores structured in various ways. The first evidence of the presence of a nanometric porosity made of ellipsoidal pores in the siliceous diatom frustules is also provided.

Geoinspired syntheses of materials and nanomaterials.

The search for new materials is intimately linked to the development of synthesis methods. In the current urge for the sustainable synthesis of materials, taking inspiration from Nature's ways to process matter appears as a virtuous approach. In this review, we address the concept of geoinspiration for the design of new materials and the exploration of new synthesis pathways. In geoinspiration, materials scientists take inspiration from the key features of various geological systems and processes occurring in nature, to trigger the formation of artificial materials and nanomaterials. We discuss several case studies of materials and nanomaterials to highlight the basic geoinspiration concepts underlying some synthesis methods: syntheses in water and supercritical water, thermal shock syntheses, molten salt synthesis and high pressure synthesis. We show that the materials emerging from geoinspiration exhibit properties differing from materials obtained by other pathways, thus demonstrating that the field opens up avenues to new families of materials and nanomaterials. This review focuses on synthesis methodologies, by drawing connections between geosciences and materials chemistry, nanosciences, green chemistry, and environmental sciences.

Quantification and morphological characterization of microfibers emitted from textile washing.

Microplastics are a subject of growing interest as they are a potential threat for living organisms. Textile microfibers (MFs) are an important microplastics sub-group that have been reported as a major source of microplastics release into the environment. This pollution occurs mainly during the washing of synthetic garments. However, standardized methods to quantify and characterize these MFs are scarce. This study proposes a new analytical protocol to characterize these MFs in number and size by means of filtration techniques, optical and electronic microscopy and automatic image post-processing. This approach was developed and validated on effluents from washing machines produced in different conditions (5 different garments, sequential cycles, and presence or not of detergent). Among the analyzed effluents, it was found that 40 to 75% of microfibers have a length comprised between 50 and 200 µm, with average microfiber diameters ranging from 8 to 17 µm depending on the type of textile. The emission range of microfibers was estimated to be between 220,000 to 2,820,000 microfibers per kg of textile depending on the type of garment and the washing conditions. The counting method developed is adapted to a certain range of textiles, such as 100% polyester fleece jackets (PET-1), 100% smooth polyester T-shirt (PET-2) and 100% acrylic sweater (PAN), and is not affected by the presence of detergent. The proposed method of characterization of these MFs lengths can also be extrapolated to the counting of other objects that have a similar morphology to the analyzed fibers. Hence, it can be helpful to develop new testing capture technologies and, thus, contribute to the enhancement of filtering techniques of several pollutants.

In situ STEM study on the morphological evolution of copper-based nanoparticles during high-temperature redox reactions.

Despite the broad relevance of copper nanoparticles in industrial applications, the fundamental understanding of oxidation and reduction of copper at the nanoscale is still a matter of debate and remains within the realm of bulk or thin film-based systems. Moreover, the reported studies on nanoparticles vary widely in terms of experimental parameters and are predominantly carried out using either ex situ observation or environmental transmission electron microscopy in a gaseous atmosphere at low pressure. Hence, dedicated studies in regards to the morphological transformations and structural transitions of copper-based nanoparticles at a wider range of temperatures and under industrially relevant pressure would provide valuable insights to improve the application-specific material design. In this paper, copper nanoparticles are studied using in situ Scanning Transmission Electron Microscopy to discern the transformation of the nanoparticles induced by oxidative and reductive environments at high temperatures. The nanoparticles were subjected to a temperature of 150 °C to 900 °C at 0.5 atm partial pressure of the reactive gas, which resulted in different modes of copper mobility both within the individual nanoparticles and on the surface of the support. Oxidation at an incremental temperature revealed the dependency of the nanoparticles' morphological evolution on their initial size as well as reaction temperature. After the formation of an initial thin layer of oxide, the nanoparticles evolved to form hollow oxide shells. The kinetics of formation of hollow particles were simulated using a reaction-diffusion model to determine the activation energy of diffusion and temperature-dependent diffusion coefficient of copper in copper oxide. Upon further temperature increase, the hollow shell collapsed to form compact and facetted nanoparticles. Reduction of copper oxide was carried out at different temperatures starting from various oxide phase morphologies. A reduction mechanism is proposed based on the dynamic of the reduction-induced fragmentation of the oxide phase. In a broader perspective, this study offers insights into the mobility of the copper phase during its oxidation-reduction process in terms of microstructural evolution as a function of nanoparticle size, reaction gas, and temperature.