Zinc oxide nano-enabled microfluidic reactor for water purification and its applicability to volatile organic compounds

This paper reports fast and efficient chemical decontamination of water within a tree-branched centimeter-scale microfluidic reactor.The microreactor integrates Zinc oxide nanowires(ZnO NWs)in situ grown acting as an efficient photocatalytic nanomaterial layer.Direct growth of ZnO NWs within the microfluidic chamber brings this photocatalytic medium at the very close vicinity of the water flow path,hence minimizing the required interaction time to produce efficient purification performance.We demonstrate a degradation efficiency of 95%in o5 s of residence time in one-pass only.According to our estimates,it becomes attainable using microfluidic reactors to produce decontamination of merely 1 l of water per day,typical of the human daily drinking water needs.To conduct our experiments,we have chosen a laboratory-scale case study as a seed for addressing the health concern of water contamination by volatile organic compounds(VOCs),which remain difficult to remove using alternative decontamination techniques,especially those involving water evaporation.The contaminated water sample contains mixture of five pollutants:Benzene;Toluene;Ethylbenzene;m–p Xylenes;and o-Xylene(BTEX)diluted in water at 10 p.p.m.concentration of each.Degradation was analytically monitored in a selective manner until it falls below 1 p.p.m.for each of the five pollutants,corresponding to the maximum contaminant level(MCL)established by the US Environmental Protection Agency(EPA).We also report on a preliminary study,investigating the nature of the chemical by-products after the photocatalytic VOCs degradation process.

Silicon micromirrors with three-dimensional curvature enabling lensless efficient coupling of free-space light

Miniaturized optical benches process free-space light propagating in-plane with respect to the substrate and have a large variety of applications,including the coupling of light through an optical fiber.High coupling efficiency is usually obtained using assembled micro-optical parts,which considerably increase the system cost and integration effort.In this work,we report a high coupling efficiency,monolithically integrated silicon micromirror with controlled three-dimensional(3D)curvature that is capable of manipulating optical beams propagating in the plane of the silicon substrate.Based on our theoretical modeling,a spherical micromirror with a microscale radius of curvature as small as twice the Gaussian beam Rayleigh range provides a 100%coupling efficiency over a relatively long optical path range.Introducing dimensionless parameters facilitates the elucidation of the role of key design parameters,including the mirror’s radii of curvature,independent of the wavelength.A micromachining method is presented for fabricating the 3D micromirror using fluorinated gas plasmas.The measured coupling efficiency was greater than 50%over a 200-mm optical path,compared to less than 10%afforded by a conventional flat micromirror,which was in good agreement with the model.Using the 3D micromirror,an optical cavity was formed with a round-trip diffraction loss of less than 0.4%,resulting in one order of magnitude enhancement in the measured quality factor.A nearly 100%coupling was also estimated when matching the sagittal and tangential radii of curvature of the presented micromirror’s surface.The reported class of 3D micromirrors may be an advantageous replacement for the optical lenses usually assembled in silicon photonics and optical benches by transforming them into real 3D monolithic systems while achieving wideband high coupling efficiency over submillimeter distances.

On-chip parallel Fourier transform spectrometer for broadband selective infrared spectral sensing

Optical spectrometers enable contactless chemical analysis.However,decreasing both their size and cost appears to be a prerequisite to their widespread deployment.Chip-scale implementation of optical spectrometers still requires tackling two main challenges.First,operation over a broad spectral range extending to the infrared is required to enable covering the molecular absorption spectrum of a broad variety of materials.This is addressed in our work with an Micro-Electro Mechanical Systems(MEMS)-based Fourier transform infrared spectrometer with an embedded movable micro-mirror on a silicon chip.Second,fine spectral resolutionΔλis also required to facilitate screening over several chemicals.A fundamental limit states thatΔλis inversely proportional to the mirror motion range,which cannot exceed the chip size.To boost the spectral resolution beyond this limit,we propose the concept of parallel(or multi-core)FTIR,where multiple interferometers provide complementary optical paths using the same actuator and within the same chip.The concept scalability is validated with 4 interferometers,leading to approximately 3 times better spectral resolution.After the atmospheric contents of a greenhouse gas are monitored,the methane absorption bands are successfully measured and discriminated using the presented device.

Spatiotemporal dynamics of nanowire growth in a microfluidic reactor

Co-integration of nanomaterials into microdevices poses several technological challenges and presents numerous scientific opportunities that have been addressed in this paper by integrating zinc oxide nanowires(ZnO-NWs)into a microfluidic chamber.In addition to the applications of these combined materials,this work focuses on the study of the growth dynamics and uniformity of nanomaterials in a tiny microfluidic reactor environment.A unique experimental platform was built through the integration of a noninvasive optical charaaerization technique with the microfluidic reactor.This platform allowed the unprecedented demonstration of time-resolved and spatially resolved monitoring of the in situ growth of NWs,in which the chemicals were continuously fed into the microfluidic reactor.The platform was also used to assess the uniformity of NWs grown quickly in a 10-mm-wide microchamber,which was intentionally chosen to be 20 times wider than those used in previous attempts because it can accommodate applications requiring a large surface of interaction while still taking advantage of submillimeter height.Further observations included the effects of varying the flow rate on the NW diameter and length in addition to a synergetic effect of continuous renewal of the growth solution and the confined environment of the chemical reaction.