Persona: María Hormigos, Roberto
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María Hormigos
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Publicación Disposable screen-printed electrode modified with bismuth–PSS composites as high sensitive sensor for cadmium and lead determination(Elsevier, 2016-04-15) Gismera García, María Jesús; Procopio, Jesús R.; Sevilla, M. Teresa; María Hormigos, RobertoBismuth was incorporated in screen-printed carbon electrodes (SPCEs) modified with polystyrene sulfonate (PSS) and carbon nanopowder (CnP) composites. Different strategies, based on bulk approaches using bismuth oxide particles and bismuth (III) solutions, were assayed. The features of the modified electrodes were evaluated by differential pulse anodic stripping voltammetry (DPASV) of Pb(II) and Cd(II) solutions. The best results were obtained when bismuth was incorporated as bismuth oxide particles during the preparation of the PSS–CnP aqueous suspension used to modify the electrodes. Using this optimal modified sensor, the DPASV measurement conditions for Pb(II) and Cd(II) determination were optimized and their figures of merit were evaluated. Mea- surements were performed using two experimental approaches: the “drop method”, by putting the test solution on the surface of the modified SPCE, and the “immersion method” performed by immersing the device in a stirred test solution. The limits of detection (S/N = 3) were 0.27 μg L−1 (1.3 × 10−9 M) for Pb(II) and 0.10 μg L−1 (9.0 × 10−10 M) for Cd(II), using the “drop method”, and 0.029 μg L−1 (1.4 × 10−10 M) for Pb(II) and 0.012 μg L−1 (1.1 × 10−10 M) for Cd(II) employing the immersion procedure. The optimal bismuth modified SPCE was used for Pb(II) and Cd(II) determination in natural water samples with successful results.Publicación Carbon Allotrope Nanomaterials Based Catalytic Micromotors(American Chemical Society, 2016-12-27) Jurado Sánchez, Beatriz; Vázquez, Luis; Escarpa, Alberto; María Hormigos, RobertoCarbon allotropes nanomaterials are explored here for the preparation of highly efficient tubular micromotors: 0D (C60 fullerene), 1D (carbon nanotubes), 2D (graphene), and 3D (carbon black, CB). The micromotors are prepared by direct electrochemical reduction or deposition of the nanomaterial into the pores of a membrane template. Subsequent electrodeposition of diverse inner catalytic layers (Pt, Pd, Ag, Au, or MnO2) allows for efficient bubble-propulsion in different media (seawater, human serum, and juice samples). Atomic-force microscopy (AFM) and scanning electron microscopy characterization reveals that the micromotors exhibit a highly rough outer surface and highly microporous inner catalytic structures. A key aspect derived from the AFM characterization is the demonstration that the rough outer surface of the micromotors can greatly affect their overall speed. To date, the literature has only focused on studying the effect of the inner catalytic layer upon their speed and performance and has underestimated the effect of the outer surface layer. The speed of carbon-based micromotors is a compromise between two opposite forces: the increased catalytic activity because of improved fuel decomposition in the inner catalytic layer, which propels their advance, and the friction of the rough outer surface with the fluid, which is opposed to it. The largest outer surface area associated with the highest surface roughness of C60 fullerene and carbon black-Pt micromotors leads to a large friction force, which results in a reduced speed of ∼180 μm/s (1% H2O2). In contrast, for carbon-nanotube-Pt based micromotors, the dominant force is the high catalytic activity of the micromotor, which allows them to reach ultrafast speeds up to 440 μm/s (1% H2O2). The new protocol opens new avenues for the universal preparation of carbon based multifunctional micromotors for a myriad of practical applications exploiting the features of carbon allotropes.Publicación Surfactant-Free β-Galactosidase Micromotors for “On-The-Move” Lactose Hydrolysis(Wiley Online Library, 2018) Jurado Sánchez, Beatriz; Escarpa, Alberto; María Hormigos, RobertoSurfactant-free β-galactosidase micromotors are explored here as moving biocatalyst for highly efficient lactose hydrolysis from raw milk. The coupling of the hydrolytic properties of such enzyme with the efficient movement of carbon nanotube tubular micromotors results in nearly 100% lactose hydrolysis and two fold removal efficiency as compared with static conditions and with free enzyme. The incorporation of an inner Ni layer allows its reusability to operate in batch mode. The rough micromotor surface area allows the immobilization of a high loading of β-galactosidase and results in an increase in the enzyme affinity toward lactose. The new micromotor concept opens new avenues for the use of micromotors as moving immobilized biocatalyst to improve the technological process not only in food industry but also in other fields.Publicación Self-Propelled Micromotors for Naked-Eye Detection of Phenylenediamines Isomers(ACS Publications, 2018) Jurado Sánchez, Beatriz; Escarpa, Alberto; María Hormigos, RobertoTubular micromotors composed of a hybrid single-wall carbon nanotube (SW)−Fe2O3 outer layer and powered by a MnO2 catalyst are used for phenylenediamines isomers detection and discrimination. Catalytic decomposition of H2O2 as fuel results in the production of oxygen bubbles and hydroxyl radicals for phenylenediamines dimerization to produce colorful solutions in colorimetric assays. The combination of Fe2O3 nanoparticles along with the irregular SW backbone results in a rough catalytic layer for enhanced hydroxyl radical production rate and improved analytical sensitivity. Such self-propelled micromotors act as peroxidase-like mobile platforms that offer efficient phenylenediamines detection and discrimination in just 15 min. Factors influencing the colorimetric assay protocol, such as the navigation time and number of motors, have been investigated. Low limits of detection (5 and 6 μM) and quantification (17 and 20 μM) were obtained for o-phenylenediamine and p- phenylenediamine, respectively. The magnetic properties of the outer SW−Fe2O3 hybrid layer allow the reusability of the micromotors in the colorimetric assay. Such attractive performance holds considerable promise for its application in sensing systems in a myriad of environmental, industrial, and health applications.Publicación Carbon nanotubes-ferrite-manganese dioxide micromotors for advanced oxidation processes in water treatment(Royal Society of Chemistry, 2018) Pacheco Jerez, Marta; Jurado Sánchez, Beatriz; Escarpa, Alberto; María Hormigos, RobertoMultifunctional SW-Fe2O3/MnO2 tubular micromotors are used for ‘on-the-fly’ advanced water oxidation of industrial organic pollutants. Catalytic decomposition of H2O2 as an oxidation agent results in the production of oxygen bubbles and hydroxyl radicals for complete mineralization of model pollutants into CO2 and H2O. The carbon backbone with Fe2O3 nanoparticles results in a rough catalytic layer for increased speed (16-fold acceleration as compared with smooth counterparts) and a higher radical production rate. The micromotors can propel autonomously in complex wastewater samples (400 μm s−1, 2% H2O2) using a biocompatible surfactant and obviating the need for expensive Pt catalysts. Such self-propelled micromotors act as highly efficient dynamic oxidation platforms that offer significantly shorter and more efficient water treatment processes, reducing the use of chemical reagents. The effective operation of the SW-Fe2O3/MnO2 micromotors is illustrated towards the oxidative degradation of mg L−1 levels of Remazol Brilliant blue and 4-chlorophenol. Factors influencing the micromachine-enhanced oxidation protocol, such as the pH, navigation time and number of motors, have been investigated. High degradation rates of ∼80% are obtained for both pollutants following 60 min treatment of spiked wastewater samples at pH 4.0–5.0. The unique magnetic properties of the outer Fe2O3 layer allow the reusability of the micromotors and its convenient recovery and disposal after treatment. Such attractive performance holds considerable promise for its application in large scale water treatment systems and for a myriad of environmental, industrial and security defense fields