Several advantages of using a microfluidic photocatalytic reactor format over conventional bulk reactors can be realized, such as large surface-area-to-volume ratio, high control of fluid flow, and reduced photon scattering. 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 fully explored.
The photocatalytic performance of a microfluidic reactor with TNA catalyst was compared with the performance of microfluidic format with TiO2 nanoparticulate (commercial P25) catalyst using a model compound, methlyene blue. Moreover, we also have examined using a titanium mesh as a substrate for TNA as opposed to a foil, and compared the degradation of methlyene blue as well as the inactivation of E. coli. The microfluidic devices were 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 (25 to 200 μL/min). The TNA on foil microfluidic system demonstrated enhanced photocatalytic performance over microfluidic TiO2 nanoparticulate layers, especially at higher flow rates (50-200 μL/min). When comparing the mesh substrate with a foil substrate, improved dye degradation and bacteria inactivation were observed using the mesh when normalized with respect to exposed substrate normal to incident light.
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 can be attributed to higher generation of and improved diffusion of oxidizing species. The model and microfluidic platform developed can easily be modified to suit other channel geometries and pollutants. A comparison of similar microfluidic photocatalytic platforms was made on the basis of dimensionless Peclet number for TNA vs. titania nanoparticles. The system described in this study demonstrates high advective flow compared to otherwise similar microfluidic photocatalytic systems.