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An easily recoverable and recyclable heterogeneous catalyst renders possible the synthesis of secondary amines from azobenzenes (I) and alcohols (II) or (IV) under mild reaction conditions.

Photoirradiation (λ > 300 nm) of TiO2 loaded with Pd nanoparticles (2 wt%, ca. 5 nm diameter) in water containing benzyl alcohol and nitrobenzene at room temperature successfully produces the corresponding secondary amine (N-benzylaniline) with 96% yield. This is achieved via three consecutive catalytic reactions: (i) photocatalytic oxidation of alcohol (aldehyde formation) and reduction of nitrobenzene (aniline formation); (ii) catalytic condensation of the formed aldehyde with aniline on the TiO2 surface (imine formation); and, (iii) photocatalytic hydrogenation of the formed imine (secondary amine formation). This catalytic system successfully produces several kinds of secondary amines, even those containing reducible substituents such as –CN, –COOH, or –CHO with >76% yields.

Pyromellitic diimide is incorporated into graphitic carbon nitride, g-C3N4 by calcination of a mixture of melem and pyromellitic dianhydride at 598 K for 4 h.