Photocatalytic transformation in aerogel-based optofluidic microreactors

Abstract

Here, we demonstrate a new type of microphotoreactor formed by a liquid-core optofluidic waveguide fabricated inside aerogel monoliths. It consists of microchannels in a monolithic aerogel block with embedded anatase titania photocatalysts. In this reactor system, aerogel confines core liquid within internal channels and, simultaneously, behave as waveguide cladding due to its extremely low refractive index of similar to 1. Light is confined in the channels and is guided by total internal reflection (TIR) from the channel walls. We first fabricated L-shaped channels within silica aerogel monoliths (rho= 0.22 g/cm(3), n=1.06) without photocatalyst for photolysis reactions. Using the light delivered by waveguiding, photolysis reactions of methylene blue (MB) were carried out in these channels. We demonstrated that MB can be efficiently degraded in our optofluidic photoreactor, with the rate of dye photoconversion increasing linearly with increasing power of incident light. For photocatalytic transformation in this reactor system, titania particles were successfully embedded into the mesoporous network of silica aerogels with varying amount of the titania in the structure from 1.7 wt % to 50 % wt. The presence of titania and its desired crystalline structure in aerogel matrix was confirmed by XRF, XRD patterns and SEM images. Band gap of silica-titania composites was estimated from Tauc plot calculated by Kubelka-Munk function from diffuse reflectance spectra of samples as near expected value of approximate to 3.2 eV. Photocatalytic activity and kinetic properties for photocatalytic degradation of phenol in the channels were investigated by a constant flow rate, and longer-term stability of titania was evaluated.