A new type of microphotoreactor with integrated optofluidic waveguide based on solid-air nanoporous aerogels

Abstract

In this study, we developed a new type of microphotoreactor based on an optofluidic waveguide with aqueous liquid core fabricated inside a nanoporous aerogel. To this end, we synthesized a hydrophobic silica aerogel monolith with a density of 0.22 g cm−3 and a low refractive index of 1.06 that—from the optical point of view—effectively behaves like solid air. Subsequently, we drilled an L-shaped channel within the monolith that confined both the aqueous core liquid and the guided light, the latter property arising due to total internal reflection of light from the liquid–aerogel interface. We characterized the efficiency of light guiding in liquid-filled channel and—using the light delivered by waveguiding—we carried out photochemical reactions in the channel filled with aqueous solutions of methylene blue dye. We demonstrated that methylene blue could be efficiently degraded in the optofluidic photoreactor, with conversion increasing with increasing power of the incident light. The presented optofluidic microphotoreactor represents a versatile platform employing light guiding concept of conventional optical fibres for performing photochemical reactions.

Review of Experimental Setups for Plasmonic Photocatalytic Reactions

“…These reactors characterized by a small size, low power consumption, and waste reduction properties, rendering them green technologies. MOFC reactors [70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][85] have been used in some photocatalytic reactions. Although they have low processing volume, MOFC reactors have features that contribute to high processing efficiency in many applications: (i) Their small fluid channel size results in a high mass transfer rate, thus enabling effective transportation of reactants and products.…”

“…Reactors with waveguide features or the potential to couple with light for an increased wavevector variation are particularly suitable for studying plasmonic photocatalytic reactions. Fixed-bed or MOFC reactors [71,81,85] with thin and flat glass substrates are also suitable for use as waveguides for delivering light energy. These reactors might help studies on plasmonic photocatalytic reactions.…”

Aerogel-Lined Capillaries for Raman Signal Gain of Aqueous Mixtures

“…Several groups report optofluidic step-index waveguides, which were based on hydrophobised silica aerogel [22][23][24][25][26][27][28]. Silica aerogel is a material which features indices of refraction close to those of air.…”

“…While Erkey et al [23] produced these optofluidic waveguides by manually drilling channels into aerogel blocks, Fraval et al [22] produced them by coating the inner surface of capillaries with silica aerogel linings. Advanced applications of these aerogel-based optofluidic waveguides have been reported, where the light induces a reaction in the aqueous mixture (photochemistry) [25], or where chemical compounds in the aqueous mixture are detected by analysing the spectrum of the transmitted light (absorption spectroscopy) [24,25].…”