Flame Spray Synthesis and Ammonia Sensing Properties of Pure α-MoO3 Nanosheets

This paper highlights the flame spray synthesis of α-MoO3 using ammonium molybdate as precursor. The as-synthesized particles obtained were found to be ammonium molybdenum oxide and belonged to the triclinic crystal system. The particles crystallized to α-MoO3 upon thermal treatment at 500°C. Sensors were prepared by drop coating the powders onto alumina substrates coated with platinum electrodes and sensing tests were conducted evaluating the detection of ammonia concentrations down to ppb level concentration in air. The flame synthesized α-MoO3 based sensors show high sensitivity towards ammonia and may potentially be used in breath ammonia gas diagnostics

Optimized nanostructured TiO2 photocatalysts

Titania is the most widely studied photocatalyst. In it’s mixed-phase configuration (anatase-rutile form) -as manifested in the commercially available P25 Degussa material- titania was previously found to exhibit the best photocatalytic properties reported for the pure system. A great deal of published research by various workers in the field have not fully explained the underlying mechanism for the observed behavior of mixed-phase titania photocatalysts. One of the prevalent hypothesis in the literature that is tested in this work involves the presence of small, active clusters of interwoven anatase and rutile crystallites or catalytic hot-spots. Therefore, non-woven nanofibrous mats of titania were produced and upon calcination the mats consisted of nanostructured fibers with different anatase-rutile ratios. By assessing the photocatalytic and photoelectrochemical properties of these samples the optimized photocatalyst was determined. This consisted of TiO2 nanostructures annealed at 500˚C with an anatase /rutile content of 90/10. Since the performance of this material exceeded that of P25 complete structural characterization was employed to understand the catalytic mechanism involved. It was determined that the dominant factors controlling the photocatalytic behavior of the titania system are the relative particle size of the different phases of titania and the growth of rutile laths on anatase grains which allow for rapid electron transfer between the two phases. This explains how to optimize the response of the pure system

Flame-Sprayed Pure and Ce-Doped TiO2 Photocatalysts

Pure and Ce-doped TiO2 nanoparticles were successfully synthesized in one step by means of the scalable flame spray pyrolysis (FSP) process. Complete structural and chemical characterization of these materials revealed that the majority of the nanoparticles are crystalline and spherical, ranging from 5 to 45 nm in diameter. The band gap of TiO2 was reduced by doping with Ce from 2.43 to 3.06 eV and the Ce-TiO2 nanoparticles exhibit a strong photoelectrical response to visible light illumination. Ce-TiO2 nanoparticles obtained with this scalable method are trivially scalable to industrial level manufacturing, granting and enabling additional approaches for the actual application of ceramic oxide nanomaterials to combat challenges such as environmental cleanup and energy production from the visible part of solar inputs

Single Exhale Biomarker Breathalyzer

A single exhale breathalyzer comprises a gas sensor that satisfies the following stringent conditions: high sensitivity to the target gas, high selectivity, stable response over extended period of time and fast response. Breathalyzer implementation includes a front-end circuit matching the sensitivity of the sensor that provides the readout of the sensor signal. We present here the characterization study of the response stability and response time of a selective Nitric Oxide (NO) sensor using designed data acquisition system that also serves as a foundation for the design of wireless handheld prototype. The experimental results with the described sensor and data acquisition system demonstrate stable response to NO concentration of 200 ppb over the period of two weeks. The experiments with different injection and retraction times of the sensor exposure to constant NO concentration show a fast response time of the sensor (on the order of 15 s) and the adequate recovery time (on the order of 3 min) demonstrating suitability for the single exhale breathalyzer