Enhanced photocatalytic activity of hierarchical titanium dioxide microspheres with combining carbon nanotubes as "e-bridge".

Enhancing photocatalytic activity of titanium dioxide (TiO2) by efficient charge separation is essential but challenging. Herein, the recombination between photo-generated e--h+ pairs is effectively hindered owing to the "e-bridge" formed between hierarchical TiO2 microspheres and carbon nanotubes (CNTs). The as-prepared three-dimensional TiO2 microspheres covered by intercrossing lamellar crystals are abundant in pores and sharp edges, forming an ideal interface with large surface area and numerous active sites for photocatalysis. Combined with CNTs, the TiO2 microspheres are connected and stabilized. Moreover, the CNTs serve as pathways for electrons, benefiting the effective separation of e--h+ pairs and accounting for the superior photocatalytic activity. Transient fluorescence spectra shows that the lifetime of electrons on TiO2 prolongs from 5.23 ns to 10.14 ns assisted by CNTs. In aqueous matrix, electrons gathering on the CNTs can react with O2 to produce O2-, and simultaneously, plenty of holes left in TiO2 host generate OH by oxidizing adsorbed H2O, producing abundant active species for photocatalytic degradation of 4-nitrophenol. The highest degradation efficiency in removing organic contaminants is achieved on TiO2@CNTs hybridized with CNTs weight ratio being 5%.