Porous interfaces are being transformed within the framework of nanotechnology to develop highly efficient sensors, nanostructure modified microreactors, and active battery electrodes. We demonstrate the rapid and reversible sensing of HCl, NH3, CO, SO2, H2S, and NOx at or below the ppm level. Gold and tin-based nanostructured coatings are introduced to improve the detection of NH3, CO, and NOx as these coatings form the initial basis for introducing significant selectivity. These sensor suites are being extended to develop microreactors, with a goal to introduce quantum dot (QD) based photocatalysts within the porous interface structure. Highly efficient, visible light absorbing, anatase TiO2-xNx nanophotocatalysts have been formed in seconds at room temperature via the direct nitridation of anatase TiO2 nanocolloids. A tunability throughout the visible is found to depend upon the degree of nanoparticle agglomeration and upon the ready ability to seed these nanoparticles with metal (metal ions) including Pt, Co, and Ni. This metal ion seeding also leads to unique efficient phase transformations, including that of anatase to rutile TiO2, at room temperature. The visible light absorbing photocatalysts readily photodegrade methylene blue and gaseous ethylene. They can be transformed from liquids to gels and, in addition, can be placed on the surfaces of sensor and microreactor based configurations 1) to produce an improved photocatalytically induced solar based sensor response, and 2) with a goal to facilitate catalytically induced disinfection of airborne pathogens. In contrast to the nitridation process which is facile at the nanoscale, we find little or no direct nitridation of micrometer sized anatase or rutile TiO2 powders at room temperature. Thus, we illustrate an example of how a traversal to the nanoscale can vastly improve the efficiency for producing important submicron particles.
The ability to control and transform the morphology and optical properties of porous silicon (PS) interface arrays can have important implications for displays and sensors. The optoelectronic properties and interaction sensing capabilities of PS can be varied as a function of pore size and pore morphology as dictated by the manipulation of a surface structure which can be controlled with current density, the solution composition of the electrochemical etches used to prepare the pores, and careful post etch surface treatments. These treatments influence the time dependent photoluminescence (PL) emission from PS. The variation of surface structure as it effects the PL from these PS pore arrays is outlined and discussed within the framework of detailed molecular electronic structure calculations which model the excited state structure giving rise to the UV-visible PL emission from PS. Applications varying from displays to sensors to micro-reactors will be considered. Porous silicon interfaces have also been transformed within the framework of nanotechnology to create highly efficient sensors displaying a rapid, reversible, sensitive, and selective response to HCl, NH3, CO, and NO down to the ppb level. Photoluminescence induced metallization is used to obtain a highly efficient, <20Ω, electrical contact to the sensor, allowing operation at a bias voltage of 1-10mV. The introduction of gold and tin-based nanostructures to a micro/nanoporous PS array selectively modifies its impedance response to considerably improve the detection of the NH3, CO, and NO. Through FFT analysis, a gas response can be acquired and filtered on a drifting baseline, further improving sensitivity. New nanoscale exclusive techniques have been developed for the rapid formation of highly efficient TiO2-xNx nanophotocatalysts, operative and tunable throughout the visible wavelength region, to be used in conjunction with porous silicon hybrid nanopore coated micropores to form novel and efficient solar pumped sensor arrays.