Self-doped TiO2 hierarchical hollow spheres with enhanced visible-light photocatalytic activity

• Self-doped TiO2 hierarchical hollow spheres were prepared by facile sol–gel methods.
• The photocatalyst has stable Ti3+ even after annealing at high temperature in air.
• Enhanced visible and solar light photocatalytic activity was obtained on the catalyst.
• The stable Ti3+ play an important role in improving the visible light absorption.

The self-doped TiO2 hierarchical hollow spheres were successfully prepared by a facile sol–gel method using the carbon spheres as templates. Characteristics and properties of the products were investigated using differential scanning calorimetry/thermogravimetry (DSC/TG), X-ray diffraction (XRD), UV–vis diffuse reflectance spectra (UV–vis DRS), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), electrochemical impedance spectroscopy (EIS), photocurrent measurements, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the self-doped TiO2 hierarchical hollow spheres, with diameters about 800–950 nm and shell thickness of 20–30 nm, were constituted with thousands of self-doped TiO2 nanoparticles with diameters of 20–30 nm. The Ti3+ was investigated in the calcinated samples which suggested that there existed stable Ti3+ in the bulk of self-doped TiO2 hollow spheres. The as prepared samples showed improved solar light and visible light induced photocatalytic activities by decomposing Rhodamine B. The improved visible light photocatalytic activities may be due to the oxygen vacancies and Ti3+ localized states of the self-doped TiO2 hierarchical hollow spheres.