Eric P. Lee

Functionalization of Electrospun TiO2 Nanofibers with Pt Nanoparticles and Nanowires for Catalytic Applications

This paper reports a simple procedure for derivatizing the surface of anatase TiO2 nanofibers with Pt nanoparticles and then Pt nanowires. The nanofibers were prepared in the form of a nonwoven mat by electrospinning with a solution containing both poly(vinyl pyrrolidone) and titanium tetraisopropoxide, followed by calcination in air at 510 degrees C. The fiber mat was then immersed in a polyol reduction bath to coat the surface of anatase fibers with Pt nanoparticles of 2-5 nm in size with controllable density of coverage. Furthermore, the coated fibers could serve as a three-dimensional scaffold upon which Pt nanowires of roughly 7 nm in diameter could be grown at a high density and with a length up to 125 nm. The fiber membranes functionalized with Pt nanoparticles and nanowires are interesting for a number of catalytic applications. It was found to show excellent catalytic activity for the hydrogenation of azo bonds in methyl red, which could be operated in a continuous mode by passing the dye solution through the membrane at a flow rate of 0.5 mL/s.

Facile Synthesis of Highly Faceted Multioctahedral Pt Nanocrystals through Controlled Overgrowth

Highly faceted Pt nanocrystals with a large number of interconnected arms in a quasi-octahedral shape were synthesized simply by reducing H2PtCl6 precursor with poly(vinyl pyrrolidone) in aqueous solutions containing a trace amount of FeCl3. The iron species (Fe(3+) or Fe(2+)) play a key role in inducing the formation of the multioctahedral structure by decreasing the concentration of Pt atoms and keeping a low concentration for the Pt seeds during the reaction. This condition favors the overgrowth of Pt seeds along their corners and thus the formation of multiarmed nanocrystals. Electron microscopy studies revealed that the multioctahedral Pt nanocrystals exhibit a large number of edge, corner, and surface step atoms. The size of the multioctahedral Pt nanocrystals can be controlled by varying the concentration of FeCl3 added to the reaction and/or the reaction temperature. These multioctahedral Pt nanocrystals were tested as electrocatalysts for the oxygen reduction reaction in a proton exchange membrane fuel cell and exhibited improved specific activity and durability compared to commercial Pt/C catalyst.

Electrocatalytic Properties of Pt Nanowires Supported on Pt and W Gauzes

This paper describes the preparation of Pt- or W-supported Pt nanowires by directly growing them on the surface of Pt or W gauze. The growth direction of the nanowires was determined to be along the <111> axis. Electrochemical measurements were performed to investigate their catalytic performance toward methanol oxidation. It was found from cyclic voltammetry that the Pt nanowires supported on Pt gauze had the largest electrochemically active surface area with the greatest activity toward methanol oxidation reaction. They also exhibited a slightly slower current decay over time, indicating a higher tolerance to CO-like intermediates. Furthermore, electrochemical impedance spectroscopy measurements showed that the catalytic performance of the supported Pt nanowires prepared with a H(2)PtCl(6) precursor concentration of 40 mM is significantly better for methanol oxidation than the samples prepared at a concentration of 80 mM. This was due partially to the incomplete removal of poly(vinyl pyrrolidone) (PVP) from the more concentrated sample. In contrast, the Pt nanowires supported on W gauze performed the worst.

Functionalization of electrospun ceramic nanofibre membranes with noble-metal nanostructures for catalytic applications

This article reports a simple method for functionalizing the surface of TiO2 (both anatase and rutile) and ZrO2nanofibre membranes with Pt, Pd, and Rh nanoparticles. The TiO2membranes were prepared in the form of nonwoven mats by electrospinning with a solution containing both poly(vinyl pyrrolidone) and titanium tetraisopropoxide, followed by calcination in air to generate anatase (at 510 °C) or rutile (at 800 °C). The ZrO2membranes were fabricated with a solution of poly(vinyl pyrrolidone) and zirconium acetylacetonate, followed by calcination in air at 550 °C to yield the tetragonal phase. The fibre mats were then immersed in a polyol reduction bath to coat the surface of the nanofibres with Pt, Pd, or Rh nanoparticles of 2–5 nm in size. In addition, the ceramic fibres decorated with Pt nanoparticles could serve as a substrate to grow Pt nanowires ∼7 nm in diameter with lengths up to 125 nm. We subsequently demonstrated the use of Pd-coated anatase fibre membranes as a catalytic system for cross-coupling reactions in a continuous flow reactor. Contrary to the conventional setup for an organic synthesis, a continuous flow system has advantages such as short reaction time and no need for separation. The membrane-based catalytic system can also be fully regenerated for reuse.

Hierarchical nanostructures of K-birnessite nanoplates on anatase nanofibers and their application for decoloration of dye solution

This paper reports a simple method for fabricating hierarchical nanostructures consisting of K-birnessite (KxMnO2) nanoplates on anatase (TiO2) nanofibers. The nanofibers were prepared in the form of a composite by electrospinning, followed by calcination at 500 °C in air for 2 h. The nanofibers were then immersed in a sulfuric acid solution containing KMnO4 at 90 °C for 20 min to deposit the KxMnO2 nanoplates. The nanoplates had a thickness of ∼5 nm and an edge length of ∼150 nm, and were oriented perpendicular to the nanofibers. They were confirmed as K-birnessite by XRD and EDX measurements. The density of the KxMnO2 nanoplates could be controlled by simply adjusting the concentration of KMnO4 and/or the deposition time. We also investigated the growth mechanism in light of surface roughness for the nanofibers and spatial confinement for the plates. We further demonstrated the potential use of these hierarchical nanostructures for waste water treatment by removing congo red from an aqueous solution. They exhibited good performance in both batch and continuous flow studies.