Generally, the N-balance could not be closed as the azo-products could not be quantified with the employed analytical techniques and increased with reaction time up, reaching an N-loss of up to 50 %. The formation of azo-products is also in line with the observed coloration of the reaction solution from almost colorless to orange/yellow. The most likely products azoxybenzene and azobenzene possess an absorption band at 365 nm, which interferes with the photocatalytic step. The light of the 365 nm LED is competitively absorbed by these products, eventually contributing to a slowdown of the photoreaction.