Albert Serrà

Green Electrochemical Template Synthesis of CoPt Nanoparticles with Tunable Size, Composition, and Magnetism from Microemulsions Using an Ionic Liquid (bmimPF6)

Electrodeposition from microemulsions using ionic liquids is revealed as a green method for synthesizing magnetic alloyed nanoparticles, avoiding the use of aggressive reducing agents. Microemulsions containing droplets of aqueous solution (electrolytic solution containing Pt(IV) and Co(II) ions) in an ionic liquid (bmimPF6) define nanoreactors in which the electrochemical reduction takes place. Highly crystalline hcp alloyed CoPt nanoparticles, in the 10-120 nm range with a rather narrow size distribution, have been deposited on a conductive substrate. The relative amount of aqueous solution to ionic liquid determines the size of the nanoreactors, which serve as nanotemplates for the growth of the nanoparticles and hence determine their size and distribution. Further, the stoichiometry (Pt(x)Co(1-x)) of the particles can be tuned by the composition of the electrolytic solution inside the droplets. The control of the size and composition of the particles allows tailoring the room-temperature magnetic behavior of the nanoparticles from superparaparamagnetic to hard magnetic (with a coercivity of HC = 4100 Oe) in the as-obtained state.

Highly efficient electrochemical and chemical hydrogenation of 4-nitrophenol using recyclable narrow mesoporous magnetic CoPt nanowires

Toxic nitro-compounds, such as 4-nitrophenol, are one of the most common wastewater industrial pollutants. Thus, efficient ways to neutralize them are actively pursued. Here novel procedures to degrade these types of compounds based on the use of mesoporous magnetic nanowires are demonstrated. Fully-mesoporous magnetic narrow (25 nm) CoPt nanowires with an extraordinary effective area are grown using ionic liquid-in-water microemulsions in alumina templates. These mesoporous nanowires are shown to be efficient catalysts for the hydrogenation of 4-nitrophenol by electrocatalysis. Additionally, these nanowires also present exceptional conventional catalytic activity when used in conjunction with NaBH4, particularly when magnetic stirring is utilized. In fact, magnetically actuated mesoporous CoPt nanowires drastically outperform all state-of-the-art 4-nitrophenol catalysts. Additionally, given their magnetic character, these nanowires can be easily recycled and reused. Thus, the outstanding catalytic performance of mesoporous CoPt nanowires makes them excellent candidates for wastewater treatment agents.

Effective ionic-liquid microemulsion based electrodeposition of mesoporous Co–Pt films for methanol oxidation catalysis in alkaline media

Pt-based direct methanol fuel cells are attracting increasing interest as environmentally friendly alternative energy sources. However, the high price of Pt and the difficulty to prepare favourable morphologies for catalysis (e.g., mesoporous materials) are hampering their development into feasible products. Here, we demonstrate a novel approach to efficiently grow mesoporous films of Pt-poor alloys (Co3Pt and CoPt3), based on electrodeposition in ionic liquid-in-water (IL/W) microemulsions. The high proportion of the electrolytic aqueous solution in the IL/W microemulsion favors a significant deposition rate, while the presence of IL drops induces the formation of highly mesoporous films. The mesoporous alloys, with pores in the 8–11 nm range, exhibit excellent durability in acidic and alkaline aggressive media, maintaining their peculiar morphology. The structures are very efficient for the catalysis of methanol electro-oxidation in alkaline media, with minimal poisoning of the catalysts. These results pave the way to develop simple, versatile environmentally friendly fuel cell catalysts to commercialize new viable ecological alternative energy sources.

Electrochemical Synthesis of Mesoporous CoPt Nanowires for Methanol Oxidation

A new electrochemical method to synthesize mesoporous nanowires of alloys has been developed. Electrochemical deposition in ionic liquid-in-water (IL/W) microemulsion has been successful to grow mesoporous CoPt nanowires in the interior of polycarbonate membranes. The viscosity of the medium was high, but it did not avoid the entrance of the microemulsion in the interior of the membranes channels. The structure of the IL/W microemulsions, with droplets of ionic liquid (4 nm average diameter) dispersed in CoPt aqueous solution, defined the structure of the nanowires, with pores of a few nanometers, because CoPt alloy deposited only from the aqueous component of the microemulsion. The electrodeposition in IL/W microemulsion allows obtaining mesoporous structures in which the small pores must correspond to the size of the droplets of the electrolytic aqueous component of the microemulsion. The IL main phase is like a template for the confined electrodeposition. The comparison of the electrocatalytic behaviours towards methanol oxidation of mesoporous and compact CoPt nanowires of the same composition, demonstrated the porosity of the material. For the same material mass, the CoPt mesoporous nanowires present a surface area 16 times greater than compact ones, and comparable to that observed for commercial carbon-supported platinum nanoparticles.

Magnetic Propulsion of Recyclable Catalytic Nanocleaners for Pollutant Degradation

Electrochemically fabricated magnetic mesoporous CoNi@Pt nanorods are excellent nanomotors with controlled magnetic propulsion and excellent catalytic properties. The core-shell structure allows a double functionality: (i) controlled motion of the nanorods by applying rotating magnetic fields at different frequencies and field strengths and (ii) effective catalytic activity of the platinum shell for reactions involving sodium borohydride. The structure and magnetic properties of the CoNi core are not modified by the presence of the Pt shell. Nanorods were propelled via a tumbling-like dynamic by a rotating magnetic field. While in absence of NaBH4, nanorods move at constant speed showing a linear path; in the presence of NaBH4, they showed an intermittent trajectory. These catalytic nanorods can be used as nanocleaners with controlled directionality for pollutants degradation in the presence of borohydride. Their magnetic character allows control of the velocity and the direction throughout the contaminated solution by degrading the different pollutants in their path. The magnetic character of nanorods also allows their easy recycling.

Nanostructured materials for photodynamic therapy: synthesis, characterization and in vitro activity

Three nanostructured vehicles are proposed as potential carriers for photosensitizers to be used in photodynamic therapy: spherical nanoparticles, hexahedral microparticles and cylindrical magnetic nanorods. A comparative study of their photodynamic properties was performed, and the influence of their size and the amount of loaded porphyrin was considered to discuss their effects in the observed photodynamic activity. All the vehicles have a gold surface, allowing functionalization with a disulfide-containing porphyrin as the photosensitizer, as well as with a PEG-containing thiol to improve their biocompatibility and water solubility. The activity of the porphyrin loaded in each vehicle was assessed through in vitro photocytotoxicity studies using HeLa cells. A synergic effect for the porphyrin toxicity was observed in all of the vehicles. The zinc-containing porphyrin showed better production of singlet oxygen, and proved more photocytotoxic both in solution and loaded in any of the vehicles. The magnetism of the nanorods allows targeting with a magnetic field, but causes their aggregation, hampering the porphyrins activity. Microparticles showed lower cell internalization but their bigger size allowed a high porphyrin loading, which translated into high photocytotoxicity. The highest cell internalization and photocytotoxicity was observed for the porphyrin-loaded nanoparticles, suggesting that a smaller size is favored in cell uptake.

Effective new method for synthesizing Pt and CoPt3 mesoporous nanorods. New catalysts for ethanol electro-oxidation in alkaline medium

In this work, an electrochemical methodology consisting of electrodeposition in ionic liquid-in water (IL/W) microemulsions has been revealed as an excellent pathway to prepare highly mesoporous nanorods with pore sizes of a few nanometers, with a significant growth rate. The nanochannels of a polycarbonate membrane (hard template) define the diameter of the nanorods, the deposited charge controls its length and the mesoporous structure replicates the structure of the microemulsion (soft template). This procedure has been used to prepare mesoporous nanorods of pure metal (Pt) or of alloy (CoPt3) with very high electrochemically active surface area (228 and 235 m2 g−1, respectively), as a consequence of the accessible three-dimensional interconnected network formed by the mesopores. When the synthesised mesoporous nanorods were tested as catalysts for ethanol electrooxidation in alkaline medium, excellent catalytic performance was found, with significant improvements over the performance of compact nanorods or commercial PtRu nanoparticles. The oxidation current/mass ratio of the mesoporous nanorod catalyst is significantly higher and, moreover, the onset potential of the ethanol oxidation is clearly advanced. Mesoporous CoPt3 nanorods show similar performance with pure platinum mesoporous nanorods and good stability in the alkaline medium, which makes them very good candidates as catalysts of the anodic reaction in direct ethanol fuel cells, with greater economy with respect to pure Pt catalysts.

Electrosynthesis method of CoPt nanoparticles in percolated microemulsions

An electrochemical synthesis of CoPt nanoparticles on Si/Ti/Au substrates has been performed in percolated water-in-oil (w/o) microemulsions to define the nanoparticle size and composition. The results allowed us to propose this method for direct growth of nanoparticles over substrates, avoiding overlapping of the particles during the deposition. We use proportions of an aqueous CoPt solution, surfactant and oil components to form w/o microemulsions in which droplets of the aqueous solution could be dispersed in the oil, but in a percolated state, to enhance the global conductivity of the system, allowing the electrodeposition process, although at a moderate rate. Under these conditions isolated nanoparticles have been obtained, whose composition is dependent on the composition of the solution of the aqueous droplets. Nanoparticles obtained at very low deposition rate aggregate by superficial diffusion leading to some well-defined hexagonal particles, reflecting their crystalline structure. When the proportions of the microemulsion components lead to a bicontinuous structure, growing particles overlap and branched structures have been obtained by electrodeposition.

Magnetic Actuation of Multifunctional Nanorobotic Platforms to Induce Cancer Cell Death

Single‐bath potentiostatic‐pulsed electrodeposition enables the synthesis of bicomponent (i.e., gold and nickel–nickel oxide) multi‐segmented magnetic nanowires that, with extraordinarily low cytotoxicity, are ideal three‐functional medical nanoplatforms because they can transport two types of functional molecules and be magnetically actuated for both controlled targeting and inducing cancer cell death. Alternated segments of Au and Ni–Ni oxide are selected to confer a magnetic character to the nanowires, prevent their dissolution in the cellular medium, and permit selective bio‐functionalization with thiol and porphyrin test molecules. The bi‐functionalized nanowires internalized in HeLa cancer cells, similar to other organelles, move inside the living cells. Applying the rotating magnetic fields cause them vibrate and increase their motion, although high viscosity and the presence of the cytoskeleton and other protein matrices preclude their rotation inside cells. Since no magneto‐mechanical destruction of the HeLa cells occurs on their membranes, organelles, or cytoskeletons programmed cancer cell death is likely induced by the vibration and translation of the nanowires, not by mechanical destruction.