Experimental procedure 160 mL of a solution of nitrobenzene (cNB = 0.1 mmol L -1 ) and triflate (ctriflat = 1.0 mmol L -1 ) in absolute ethanol were transferred to the reactor and pumped for 5 min at 100 mL min -1 . Subsequently, 100 mg of TiO2 (cTiO2 = 0.625 g L -1 ) were added for experiments with suspensions and the suspension was pumped for additional 15 min. After taking a reference sample, the experiment was started by switching on the LED. The LED was operated at 0.2 A, except when stated otherwise. Samples were taken out of the reservoir. To enable UV/vis analysis, the catalyst was separate using centrifugation in a CM-70M.07 centrifuge (neoLab MiggeGmbH) for 30 min at a rotational speed of 7000 min -1 .