Sensor elements

We have designed a kind of sensor elements by microfabrication technologies, which are intended to detect and identify the gas or liquid species with high sensitivity.

Hierarchically Structured Cobalt Oxide (Co₃O₄): The Morphology Control and Its Potential in Sensors

A polyol process was developed to synthesize Co₃O₄ with controllable superstructures. By tuning the reaction conditions, the prepared Co₃O₄ were readily regulated in its morphologies, which could vary from nanosphere to two-dimensional (2D) nanoplates and 3D hierarchical structures, and finally to microspheres. The growth kinetics of such a process was also studied. The synthesized Co₃O₄ exhibited good sensitivity, remarkable selectivity, and high stability as an alcohol sensor material. (J. Phys. Chem. B, 2006, 110, 15858-15863)

A novel kinetic approach was developed to identify volatile organic compounds (VOCs) and to determine their concentrations with a single SnO₂ gas sensor. Traditional array-based electronic noses usually rely on the saturation level of the response between target molecules and sensing materials, and our approach is kinetic based. It is more straightforward and simpler than traditional pattern recognition systems. An effective algorithm is developed for this system. The algorithm can identify chemicals with high accuracy regardless of their concentrations, and it is able to estimate the concentrations of the analytes. It reduces the complexity of hardware as well as software in traditional array-based electronic nose systems. (Sens. Actuators B: Chem. (2006), doi:10.1016/j.snb.2006.09.051)

The needs in public security and environmental protection accelerate the research and development efforts to detect ultra-trace nitroaromatic compounds (NACs). In this lab, simple electrochemical sensors based on sensitive materials-modified electrodes had been developed to achieve the detection of ultra-trace NACs. The effective sensitive materials include mesoporous SiO₂ of MCM-41 (Left, Anal. Chem., 2006, 78, 1967), carbon nanotubes functionalized by triphenylene (Right, Phys. Chem. Chem. Phys., 2006, 8, 3567), and other nanomaterials (not shown). Further, SPM technology has been adopted to study in-situ the status of modified electrodes and sensing mechanism.

Self-Assembled Vanadium Pentoxide (V₂O₅) Hollow Microspheres from Nanorods and Their Application in Lithium-Ion Batteries

"Hedgehog" or "nest" microspheres of V₂O₅ are formed when nanorods of V₂O₅ are synthesized in a mediated polyol process. When the concentration of the starting material is low, a nest shape is preferred, whereas a high concentration of [V(acac)₃] affords hedgehog-shaped microspheres (see picture). The V₂O₅ microspheres exhibit remarkable electrochemical properties when used as the cathode material in a lithium-ion battery.(Angew. Chem. Int. Ed., 2005, 44, 4391-4395)

Tin/platinum bimetallic nanotube array and its electrocatalytic activity for methanol oxidation

A well-aligned Sn/Pt bimetallic nanotube array is fabricated by directly evaporating tin onto a porous anodic aluminum oxide film followed by electrodeposition of platinum. The composite nanostructures contain a large number of Pt nanoparticles inlaying the inner-wall surfaces of the Sn nanotubes. The novel Sn/Pt nanotube array shows remarkable activity toward methanol oxidation and hence could be used as an effective anode for direct methanol fuel cells (see Figure). (Adv. Mater., 2005, 17, 746.)

Controllable Pt Nanoparticle Deposition on Carbon Nanotubes as an Anode Catalyst for Direct Methanol Fuel Cells

We report a novel process to prepare well-dispersed Pt nanoparticles on CNTs. Pt nanoparticles, which were modified by the organic molecule triphenylphosphine, were deposited on multiwalled carbon nanotubes by the organic molecule, which acts as a cross linker. By manipulating the relative ratio of Pt nanoparticles and multiwalled carbon nanotubes in solution, Pt/CNT composites with different Pt content were achieved. The so-prepared Pt/CNT composite materials show higher electrocatalytic activity and better tolerance to poisoning species in methanol oxidation than the commercial E-TEK catalyst, which can be ascribed to the high dispersion of Pt nanoparticles on the multiwalled carbon nanotube surface. (J. Phys. Chem. B, 2005, 109, 22212-22216)

Pt hollow nanospheres: Facile synthesis and enhanced electrocatalysts

A facile large-scale preparation of Pt hollow nanospheres (see TEM image) makes use of Co nanoparticle as sacrificial templates. The nanospheres exhibit enhanced electrocatalytic activity. This method has been extended to the fabrication of industrially potentially useful Au, Pd, and other mono- and multimetallic hollow nanospheres. (Angew. Chem. Int. Ed., 2004, 43, 1540-1543)

Self-Assembled 3D Flowerlike Iron Oxide Nanostructures and Their Application in Water Treatment

An ethylene-glycol-mediated self-assembly process is adopted to synthesize 3D flowerlike nanostructures of iron oxide (see figure) using inexpensive and nontoxic ferric chloride. A two-stage growth process is identified during the morphological evolution of the iron oxide precursor. α-Fe₂O₃, γ-Fe₂O₃, and Fe₃O₄ with the same flowerlike structure are readily obtained from the same precursor but by different calcination procedures. The as-obtained iron oxides show excellent ability to remove various pollutants from water. (Adv. Mater., 2006, 18(18), 2426-2431)

Mass Production and High Photocatalytic Activity of ZnS Nanoporous Nanoparticles
　

Self-assembly of hexagonal 3-5-nm ZnS nanocrystals can be used for the large-scale production of zinc sulfide nanoporous nanoparticles (NPNPs). The uniform, spherical NPNPs are monodisperse and have surface areas on the order of 156 m² g-1. The ZnS NPNPs are more effective photocatalysts than Degussa P25 titania or ZnS nanocrystals in the photodegradation of eosin B at ambient temperature (see picture).(Angew. Chem. Int. Ed., 2005, 44, 1296-1273)

BEDT-TTF Charge-Transfer Salt Nanotube Arrays

b"-(BEDT-TTF)₄[H₂O·Fe(C₂O₄)₃]·C₆H₅NO₂ nanotube arrays with uniform size and highly ordered arrangement were fabricated via an electrocrystallization process on porous anodic aluminum oxide (AAO) template. The I-V characteristics of both nanotube arrays and single nanotube as well as temperature dependence of resistance of nanotube arrays were also studied. This method represents an important step toward the development of nanoscale electronic devices and chemical sensors based on these organic materials.(Adv. Mater., 2006, 18, 2753)

A self-assembly technique assisted with surfactant is developed to fabricate one-dimensional (1D) nanostructure of zinc meso-tetra (4-pyridyl) porphyrin. The so-prepared nanostructure appears in a shape of hollow hexagonal nanoprism with uniform size. The length and aspect ratio of the nanoprisms is easily tunable by controlling the stoichiometric ratio of porphyrin over surfactant. Furthermore, as a result of dispersivity and regular geometric shape, these nanoprisms can readily self-organize into an ordered, smectic three-dimensional (3D) architecture through simple evaporation of the solvent. The results should be significant in porphyrin crystallization and porphyrin application in optoelectronic device, catalysis, drug delivery, and molecular filtration. (J. Am. Chem. Soc., 2005, 127(48), 17090)