Optofluidic planar reactors for photocatalytic water treatment using solar energy

Abstract

Optofluidics may hold the key to greater success of photocatalytic water treatment. This is evidenced by our findings in this paper that the planar microfluidic reactor can overcome the limitations of mass transfer and photon transfer in the previous photocatalytic reactors and improve the photoreaction efficiency by more than 100 times. The microreactor has a planar chamber $\left(5\text{cm}\times 1.8\text{cm}\times 100\mu \text{m}\right)$ enclosed by two ${\text{TiO}}_2$ -coated glass slides as the top cover and bottom substrate and a microstructured UV-cured NOA81 layer as the sealant and flow input/output. In experiment, the microreactor achieves 30% degradation of 3 ml $3\times {10}^{-5}M$ methylene blue within 5 min and shows a reaction rate constant two orders higher than the bulk reactor. Under optimized conditions, a reaction rate of $8\mathrm{\%}{\text{s}}^{-1}$ is achieved under solar irradiation. The average apparent quantum efficiency is found to be only 0.25%, but the effective apparent quantum efficiency reaches as high as 25%. Optofluidic reactors inherit the merits of microfluidics, such as large surface/volume ratio, easy flow control, and rapid fabrication and offer a promising prospect for large-volume photocatalytic water treatment.