Catalytic and photocatalytic behavior of TiO₂ based nanoparticles—their use in the synthesis of a novel TICT probe

Biologically inspired synthesis of titanium dioxide (TiO₂) nanoparticles (NPs) and Au/TiO₂ nanocomposites (NCs) using L-tryptophan is reported. Highly crystalline composite NPs are obtained by this totally 'clean' synthesis. The TiO₂ NPs and Au/TiO₂ NCs cause efficient photocatalytic degradation of the well-known dye pollutant malachite green. The surface area, pore volume and probability of dye reduction by photogenerated electrons and holes are important considerations for the photodegradation efficiency. Contrary to popular belief, the Au/TiO₂ NCs show decreased photocatalytic efficiency. The TiO₂ NPs and Au/TiO₂ NCs also function as very efficient catalysts in a novel multi component reaction (MCR). In contrast to photocatalysis, Au/TiO₂ NCs shows better catalytic efficiency. A comparison is made of the difference in photocatalytic and catalytic behaviors of the NPs. This is the first report of the catalysis of an MCR by TiO₂-based NPs. The product of the MCR is a novel fluorescent probe which shows evidence for the existence of a twisted intramolecular charge transfer state. Thus this work shows promise for the development of new catalysts for synthesis of novel fluorescent probes. (paper)