Applied Catalysis B: Environmental 174–175 (2015) 167–175 Contents lists available at ScienceDirect Applied Catalysis B: Environmental j ourna l h om epage: www.elsevier.com/locate/apcatb Anodized titania nanotube array microfluidic device for photocatalytic application: Experiment and simulation Harikrishnan Jayamohan a , York R. Smith b,∗ , Lauryn C. Hansen b , Swomitra K. Mohanty c , Bruce K. Gale a , Mano Misra b,c,∗∗ a Department of Mechanical Engineering, University of Utah, Salt Lake City, UT 84112, USA b Department of Metallurgical Engineering, University of Utah, Salt Lake City, UT 84112, USA c Department of Chemical Engineering, University of Utah, Salt Lake City, UT 84112, USA a r t i c l e i n f o Article history: Received 22 October 2014 Received in revised form 25 February 2015 Accepted 27 February 2015 Available online 2 March 2015 Keywords: Anodization Titania nanotubes Photocatalysis Microfluidic reactors Simulation a b s t r a c t Microfluidic photocatalytic reactors have advantages over conventional bulk reactors such as large surface-area-to-volume ratio and high control of fluid flow. Although titania nanotubular arrays (TNA) have shown enhanced photocatalytic degradation compared to nanoparticle films in a batch reactor configuration, their application in a microfluidic format has yet to be explored. The photocatalytic per- formance of a microfluidic reactor with TNA catalyst was compared with the performance of microfluidic format with TiO 2 nanoparticulate (commercial P25) catalyst. The microfluidic device was fabricated using non-cleanroom based soft lithography, making it suitable for economical large scale manufacturing. The photocatalytic performance was evaluated at different flow rates ranging from 25 to 200 L/min. The TNA microfluidic system demonstrated enhanced photocatalytic performance over microfluidic TiO 2 nanoparticulate layers, especially at higher flow rates (50–200 L/min). For instance, 12 m long TNA was able to achieve 82% fractional conversion of 18 mM methylene blue in comparison to 55% conversion in case of the TiO 2 nanoparticulate layer at a flow rate of 200 L/min. A computational model of the microfluidic format was developed to evaluate the effect of diffusion coefficient and rate constant on the photocatalytic performance. The improved performance of the TNA photocatalyst over the nanoparticle film can be attributed to higher generation of oxidizing species. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Water based pollutants are a big concern and serious chal- lenge in both developed and developing nations. Photocatalytic environmental remediation has been widely investigated for the degradation of water based pollutants [1]. Recently, nanomaterials such as nanoparticles, nanowires and nanoporous films have been applied to photocatalytic reactions due to their interesting proper- ties over bulk materials. Many studies have used photocatalysts in the form of a powder. However, the use of powdered photocatalysts necessitates their downstream recovery, which can be costly. The immobilization or growth of photocatalysts as a film eliminates this drawback. Many studies involve conventional macroscale reactors ∗ Corresponding author. Tel.: +1 801 581 6386; fax: +1 801 581 4937. ∗∗ Corresponding author at: Department of Metallurgical Engineering, University of Utah, Salt Lake City, UT 84112, USA. Tel.: +1 801 581 6386; fax: +1 801 581 4937. E-mail addresses: york.smith@utah.edu (Y.R. Smith), mano.misra@utah.edu (M. Misra). with limited mass transport and poor photon transport. This can potentially limit the degradation performance of the system [2–4]. The use of microfluidic system has the potential to reduce such aforementioned reactor limitations. Microfluidic systems have inherent advantages such as large surface to volume ratio, smaller diffusion distance, uniform irra- diation over the whole catalytic surface, self-refreshing property [5] and large mass transfer efficiency [6,4]. Microfluidic photocat- alytic reactors have demonstrated higher photocatalytic efficiency compared to conventional reactors. For example, Lei et al. reported reaction rate constants in microreactors to be 100 times more than in bulk reactors [3]. In bulk reactors, there is a loss of photons reach- ing the photocatalyst surface due to scattering effects in the liquid [7]. In contrast, in microfluidic reactors, the thin layer of liquid over the catalyst ensures that less photons are lost due to scat- tering. Microfluidic reactors can also be used for rapid screening of photocatalysts [4,8]. Of the semiconductor materials studied for photocatalytic environmental remediation, titanium dioxide (e.g., nanoparti- cles, nanowires, nanotubes) is widely used due to its desirable http://dx.doi.org/10.1016/j.apcatb.2015.02.041 0926-3373/© 2015 Elsevier B.V. All rights reserved.