Photocatalytic performances of ZnO nanoparticle film and vertically aligned nanorods in chamber-based microfluidic reactors: Reaction kinetics and flow effects

Abstract

The nanoparticle seed layer (a film) and vertically aligned nanorods of zinc oxide (ZnO) with different lengths were fabricated within a novel chamber-based microfluidic (microchamber) reactor with a varying height of 0.127-5mm and characterized with their microstructures, photocatalytic performances as well as qualitative reaction kinetics. The ZnO seed layer was produced by a sol-gel procedure and the nanorods were hydrothermally grown on seed layer coated glass substrates. These ZnO samples were integrated into the microchamber reactor through a seven-layer sandwiched configuration. The aqueous methyl orange (MO) solution was chosen as a model polluted water. By comparing the ultraviolet-visible (UV-Visible) absorbance of the original MO solution and the post-treatment sample, the reaction constants were calculated, representing the efficiencies of the reactors. The ZnO samples, usually possessing a large amount of defects, with a higher crystal quality showed an enhanced activity. The reaction constant was featured of a plateau with accelerating flow rates, exhibited an exponentially decreasing function of the chamber height, and declined with increasing the initial concentration of the MO solution. The efficiency of the microchamber reactor was found to be one to two orders of magnitude higher than that of a batch reactor. The rate determining step was suggested to be the mass transport related adsorption of MO on ZnO. The measured reaction properties and the reactor design should be of considerable significance to the scaling-up and optimization of microchamber catalytic reactors dedicated to water purification and other applications.

Fabrication, functionalization and performance of doped photocatalysts for dye degradation and mineralization: a review

“…There are also microreactors (microfluidic reactors) which have been gaining research attention in the design of pollutant remediation systems in contrast to the conventional macroscale reactors (CoMRs) (Hamaloğlu et al 2017;Zhao et al 2017c;de Sá et al 2018;Yusuf et al 2018;Rashmi Pradhan et al 2019). Unlike the case of CoMRs which are impeded in their performance because of mass transfer limitations and poor photon management (Jayamohan et al 2016;Zhao et al 2017c), microfluidic reactors are characterized by the presence of a thin liquid layer on the surface of the catalyst which limits the loss of photons (Jayamohan et al 2016).…”

“…There are also microreactors (microfluidic reactors) which have been gaining research attention in the design of pollutant remediation systems in contrast to the conventional macroscale reactors (CoMRs) (Hamaloğlu et al 2017;Zhao et al 2017c;de Sá et al 2018;Yusuf et al 2018;Rashmi Pradhan et al 2019). Unlike the case of CoMRs which are impeded in their performance because of mass transfer limitations and poor photon management (Jayamohan et al 2016;Zhao et al 2017c), microfluidic reactors are characterized by the presence of a thin liquid layer on the surface of the catalyst which limits the loss of photons (Jayamohan et al 2016). There are key advantages which are associated with microfluidic reactors, namely that they offer more interaction of species involved with the catalysts because of greater surface-to-volume ratio, they have shorter diffusion distance, better mass transport, higher photocatalytic efficiency (Meng et al 2013;Jayamohan et al 2015), low consumption of reagents, decreased generation of waste materials and reduced energy consumption.…”

Microfluidics for ZnO micro-/nanomaterials development: rational design, controllable synthesis, and on-chip bioapplications

“…2A). 48,76 Specifically, along the flow direction, the length of nanowires decreased and the morphology changed from pyramidal tops to flat tops. 48,49 By modulating the synthesis parameters such as the seed preparation, residence time, and heating locations, ZnO nanowire arrays could be synthesized either on the entire substrate/patterned area, 53,57,78 or along the microheaters inside the microchannel (Fig.…”

“…Microfluidic chips have attracted great attention for catalytic applications due to their inherently large surface-to-volume ratios, short diffusion distance, rapid mass transfer, and high integration capabilities. By easy interfacing with UV light, microchips find great application in photocatalysis for the photodegradation of methylene blue (MB), 50,60,73 phenol, 85 methyl orange, 76 and volatile organic compounds (benzene, toluene, ethylbenzene, m-p xylenes, and o-xylene). 79 ZnO nanowires have a high electron transfer rate and could be grown on a patterned area over a glass substrate 60,76 (Fig.…”

Bridging the gap between laboratory and application in photocatalytic water purification

“…9 are used. Zhao et al 54 recently studied the effectiveness of a ZnO nanorod based system formed using a combination of sol gel and hydrothermal syntheses in a microfluidic chamber type reactor. The authors of this work observed a large improvement over the batch type process, ascribing this to improved mass transport when run in flow.…”