Use of liquid-core waveguides as photochemical reactors and/or for chemical analysis – An overview

The study of photochemical reactions is of great importance in many fields including the pharmaceutical, food, and paint industry. Most of these photochemical processes are being studied to better understand how to apply them for a specific purpose or how unwanted effects can be prevented. Advances are still being made in photoreactor design, where in-situ detection of the involved reagents and products is an important development. Liquid-core waveguides (LCWs) allow simultaneous illumination and optical assessment of liquid samples and, therefore, constitute one way of combining photoreactor design with on-line or in-situ analytical detection methods. LCWs possess several interesting characteristics, such as low light loss, increased optical path length, and possibilities for coupling with spectroscopic techniques. The current review discusses the state-of-the-art of LCWs applied as photoreactors, for analytical detection, and their combinations. We discuss the differences between several total internal reflection (TIR)-based LCWs, including polymer and polymer-coated capillaries, and silica aerogels, and interference-based waveguides, including Bragg fibers, holey fibers, Kagomé fibers and anti-resonance reflecting optical waveguides (ARROWs). Assessed characteristics include the (freedom of) design, the degree of light attenuation, the range of transmittable wavelengths, gas permeability, compatibility with analytical techniques, current challenges, and applications.