A Modular Low‐Cost 3D Uniformly Illuminated Mini‐Photoreactor with Versatile In‐Situ Analysis

Abstract Photons are widely used for producing and degrading matter, yet current approaches for their delivery to unstirred light‐absorbing media give poor uniformity and energetic efficiency. Here, a cheap modular Do‐It‐Yourself (DIY)‐realizable mini‐photoreactor is introduced that addresses these issues, and additionally allows for in situ absorption, fluorescence, and Nuclear Magnetic Resonance (NMR) spectroscopy. Its first configuration features an internal light‐scattering cylindrical liquid‐filled waveguide to scatter light outward into the medium, while its second configuration, meant for more strongly absorbing media, adds an external coaxial light‐scattering liquid‐filled envelope, allowing balanced light injection from both sides of the medium. Extensive NMR‐ and fluorescence‐based characterizations with new actinometers, together with optical simulations, are performed; the latter allowing the key factors that govern photon flux density and its distribution to be unraveled. The insights go beyond the reactor design, and have relevance in analytical photochemistry and photocatalysis, where poor characterization of light is widespread.