CO₂ hydrogenation toward methane, a reaction of high environmental and sustainable energy importance, was investigated at 200–600 °C and H₂/CO₂ = 4/1, over Rh nanoparticles dispersed on supports with different oxygen storage capacity characteristics (γ-Al₂O₃, alumina-ceria-zirconia, and ceria-zirconia). The effects of the support OSC and Rh particle size on reaction behavior under both integral and differential conditions were investigated, to elucidate the combined role of these crucial catalyst design parameters on methanation efficiency. A volcano-type variation of methanation turnover frequency was found in respect to support OSC; Rh/ACZ, with intermediate OSC, was the optimal catalyst. The structure sensitivity of the reaction was found to be a combined function of support OSC and Rh particle size: For Rh/γ-Al₂O₃ (lack of OSC) methanation was strongly favored on small particles—the opposite for Rh/CZ (high OSC). The findings are promising for rational design and optimization of CO₂ methanation catalysts by tailoring the aforementioned characteristics.

The special electronic, optical, thermal, and mechanical properties of graphene resulting from its 2D nature, as well as the ease of functionalizing it through a simple acid treatment, make graphene an ideal building block for the development of new hybrid nanostructures with well-defined dimensions and behavior. Such hybrids have great potential as active materials in applications such as gas storage, gas/liquid separation, photocatalysis, bioimaging, optoelectronics, and nanosensing. In this study, luminescent carbon dots (C-dots) were sandwiched between oxidized graphene sheets to form novel hybrid multilayer films. Our thin-film preparation approach combines self-assembly with the Langmuir–Schaefer deposition and uses graphene oxide nanosheets as template for grafting C-dots in a bidimensional array. Repeating the cycle results in a facile and low-cost layer-by-layer procedure for the formation of highly ordered hybrid multilayers, which were characterized by photoluminescence, UV–visible, X-ray photoelectron, and Raman spectroscopies, as well as X-ray diffraction and atomic force microscopy.

In this work, hybrid zinc oxide–iron oxide (ZnOFe) magnetic nanoparticles were synthesized employing Olea europaea leaf aqueous extract as a reducing/chelating and capping medium. The resulting magnetic nanoparticles were characterized by basic spectroscopic and microscopic techniques, namely, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), fourier-transform infrared (FTIR) and atomic force microscopy (AFM), exhibiting a spherical shape, average size of 15–17 nm, and a functionalized surface. Lipase from Thermomyces lanuginosus (TLL) was efficiently immobilized on the surface of ZnOFe nanoparticles through physical absorption. The activity of immobilized lipase was found to directly depend on the enzyme to support the mass ratio, and also demonstrated improved pH and temperature activity range compared to free lipase. Furthermore, the novel magnetic nanobiocatalyst (ZnOFe-TLL) was applied to the preparation of hydroxytyrosyl fatty acid esters, including derivatives with omega-3 fatty acids, in non-aqueous media. Conversion yields up to 90% were observed in non-polar solvents, including hydrophobic ionic liquids. Different factors affecting the biocatalyst performance were studied. ZnOFe-TLL was reutilized for eight subsequent cycles, exhibiting 90% remaining esterification activity (720 h of total operation at 50 °C). The green synthesized magnetic nanoparticles, reported here for the first time, are excellent candidates as nanosupports for the immobilization of enzymes with industrial interest, giving rise to nanobiocatalysts with elevated features.

We report the preparation, characterization and application of a novel magnetic four-enzyme nanobiocatalyst prepared by the simultaneous covalent co-immobilization of cellulase (CelDZ1), β-glucosidase (bgl), glucose oxidase (GOx) and horseradish peroxidase (HRP) onto the surface of amino-functionalized magnetic nanoparticles (MNPs). This nanobiocatalyst was characterized by various spectroscopic techniques. The co-immobilization process yielded maximum recovered enzymatic activity (CelDZ1: 42%, bgl: 66%, GOx: 94% and HRP: 78%) at a 10% v/v cross-linker concentration, after 2 h incubation time and at 1:1 mass ratio of MNPs to total enzyme content. The immobilization process leads to an increase of K_m and a decrease of V_max values of co-immobilized enzymes. The thermal stability studies of the co-immobilized enzymes indicated up to 2-fold increase in half-life time constants and up to 1.5-fold increase in their deactivation energies compared to the native enzymes. The enhanced thermodynamic parameters of the four-enzyme co-immobilized MNPs also suggested increment in their thermal stability. Furthermore, the co-immobilized enzymes retained a significant part of their activity (up to 50%) after 5 reaction cycles at 50 °C and remained active even after 24 d of incubation at 5 °C. The nanobiocatalyst was successfully applied in a four-step cascade reaction involving the hydrolysis of cellulose.