A Graphene Acid - TiO 2 Nanohybrid as Multifunctional Heterogeneous Photocatalyst for the Synthesis of 1,3,4-Oxadiazoles.

The immobilization of TiO 2 nanoparticles on graphene acid (GA), a conductive graphene derivative densely functionalized with COOH groups, is presented. The interaction between the carboxyl groups of the surface and the titanium precursor leads to a controlled TiO 2 heterogenization on the nanosheet according to microscopic and spectroscopic characterizations. Electronic communication shared among graphene and semiconductor nanoparticles shifts the hybrid material optical features toward less energetic radiation but maintaining the conductivity. Therefore, GA-TiO 2 is employed as heterogeneous photocatalyst for the synthesis of 2,5-disubstituted 1,3,4-oxadiazoles using ketoacids and hydrazides as substrates. The material presented enhanced photoactivity compared to bare TiO 2 , being able to yield a large structural variety of oxadiazoles in reaction times as fast as 1 h with full recyclability and stability. The carbocatalytic character of GA is the responsible for the substrates condensation and the GA-TiO 2 light interaction ability is able to photocatalyze the cyclization to the final 1,3,4-oxadiazoles, demonstrating the optimal performance of this multifunctional photocatalytic material.