Kinetic spectrophotometric method for real-time monitoring of ultraviolet photoreactions: A mini-photoreactor.

It is proposed a new approach to evaluate the performance of ultraviolet photoreactions by integrating UV-LED and a UV-Vis cuvette as a mini-reactor for kinetic monitoring in a spectrophotometer not influenced by external light. This system uses only 3.0 mL of solutions in a rectangular quartz cuvette with a mini-bar magnetic stirrer in a cell holder and a UV-LED of 5 W with λ at 370 nm was positioned on the top of the cuvette and maintained at 25.0 C. The effectiveness of this photoreactor was demonstrated by measuring the real-time degradation of two model compounds, salicylic acid and methylene blue, in homogeneous and heterogenous systems. Photolysis of MB with HO results in increasing of rate constants as [HO] increased. Heterogeneous photocatalysis of MB and SA was fastest achieved in ZnO dosage of 0,20 g.L. This mini-photoreactor allows monitoring the real-time kinetic performance collecting almost a thousand points in each experiment, leading to accurate rate constants. Moreover, this system presented positive environmental aspects such as: lower reactants and catalyst amounts, lower cost and waste amounts, use of the UV-LED radiation and labor time saving. This is a novel approach to determine the photoreaction effectiveness and it can be applied to systematic studies especially for the kinetic parameter determinations.