Modification of hydrogen titanate nanotubes-graphene oxide photocatalysts with Au nanoparticles and their performance in the degradation of methylene blue upon UV and genuine solar light

The present study aims to synthesize and characterize hydrogen titanate nanotubes-graphene oxide composites modified with Au ( x Au/NTGO2, x = 0.5-4 wt.% Au) for the photocatalytic degradation of methylene blue (MB) under UV and natural sunlight. The novelty of this work consists in combining titania-based semiconductor with graphene-type nanomaterial and Au nanoparticles to improve charge separation and enhance visible light absorption for degradation of organic dyes under natural solar light. Hydrogen titanate nanotubes and graphene oxide (GO) maintained their characteristic structures in the NTGO2 material. Addition of GO to titanate nanotubes significantly decreased recombination of photo-generated electron/hole pairs. The x Au/NTGO2 catalysts showed the presence of two types of Au nanoparticles: highly-dispersed (< 2 nm) and large (~20-40 nm size) ones. Addition of Au did not change the bandgap energy of NTGO2 (~3.3 eV), but increased visible light absorption. The x Au/NTGO2 catalysts showed increased adsorption of cationic MB dye due to the cation exchange ability of titanate nanotubes, electrostatic interactions with negatively-charged Au nanoparticles and π-π interactions with aromatic structure of GO. The x Au/NTGO2 catalysts achieved higher MB degradation (~97%) and mineralization (~95-97%) under both UV and natural solar light than Degussa P25. Scavenger tests showed that the two most effective agents in the photodegradation of MB are superoxide ( O 2 • − ) and hydroxyl ( OH • ) radicals. Addition of Au nanoparticles was especially beneficial for photocatalytic activity under natural solar light making the x Au/NTGO2 catalysts promising for photocatalytic elimination of cationic dyes under this irradiation. However, their cytotoxicity and ecotoxicity should be evaluated.