Recent progress on photoreactions in microreactors

Abstract

A microreaction system for organic photoreactions was developed, and the processes of diastereo-differentiating photosensitized reaction, photocatalytic oxidation and reduction of organic compounds, and amine N-alkylation were examined in microspace. These model reactions proceeded very rapidly with considerably large photonic efficiencies because of some distinct properties of microreactors for photoreactions, such as higher spatial illumination homogeneity and better light penetration through the entire reactor depth, and large surface-to-volume ratio in comparison with large-scale batch reactors. These results suggest feasibility of microreaction systems on organic photoreactions.

Flow photochemistry: Old light through new windows

“…Use of a microsystem conferred a number of advantages over the same reaction under batch conditions: dialkylation could be suppressed as monoalkylated product was removed from the reactor as it formed, avoiding over-reaction; UV-LED light sources could be employed, requiring less power than the lamps typically used for the same reaction under batch conditions; and the reaction could be performed by using Pt-free titanium dioxide, something which had been shown to be unsuccessful under batch conditions. Nevertheless, the low flow rates and low concentrations involved limited output to 2.4 µmol/h, leaving significant questions over its synthetic utility [48–50]. …”

Design Consideration of Continuous-Flow Photoreactors

“…On contrast, microflow reactors generally consist of fabricated microchannels usually less than 0.5 mm in thickness that are milled or etched into a planar surface, ranging from bespoken "lab-on-a-chip" designs to highly engineered glass and metal systems (for reviews on microflow photochemistry, see Refs. 11,[17][18][19][20][21][22][23][24][25][26][27][28].…”

Modified Graphitic Carbon Nitrides for Photocatalytic Hydrogen Evolution from Water

“…Though, in these experiments TiO 2 was used as the photoanode, while platinum was used as the metal cathode, it was postulated, that colloid systems would also split water. [16,17] Nevertheless, a first commercial attempt of using titania for solar energy conversion was done by Grätzel: a combination of nanocrystalline TiO 2 and certain dyes supported on a transparent conducting oxide as anode. [18] As described in section 2.1.1, water can be split by electrical current.…”

“…[19] Although early results of Grätzel neglected a satisfactory water splitting reaction, re- Although cobalt modifications of these materials were performed to enhance the photocurrent, they lack in catalytic activity towards water splitting experiment. [16,40] The performance is better with materials containing niobates, which would be expensive in a large scale. Furthermore, nickel and tantalum catalyst showed recently a reasonable activity.…”