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

Abstract

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%.

Keywords: Carbon nanotubes; Organic pollutant; Photocatalytic degradation; Titanium dioxide; e-Bridge.