Influence of annealing and rinsing on magnetic and photocatalytic properties of TiO2

Samples of TiO2, calcined at 100 °C (type 1) and 200 °C (type 2), have been prepared without and with water rinsing. The crystallite sizes determined by XRD method were smaller than 15 nm for both types of samples. Magnetic resonance spectra of the obtained samples have been studied in 230–300 K temperature range. Before rinsing no magnetic spectra were observed but after rinsing the magnetic response appeared in form of a resonance line centered at geff ∼ 2.54 with linewidth ΔHpp ∼ 460 G in type 1 samples and geff ∼ 2.26 with linewidth ΔHpp ∼ 220 G in type 2 samples. The integrated intensity of the observed spectrum was two times greater in the type 1 sample. The resonance line could be attributed to the localized magnetic moments in the correlated spin system formed during rinsing. The rinsing resulted also in higher photocatalytic properties under UV–VIS irradiation. It is suggested that the number of oxygen vacancies increases after rinsing and as they are involved in the formation of low oxidation states of titanium ions, they could be responsible for the appearance of the observed magnetic properties.

► Photocatalytic activity of TiO2 nanopowders has increased after rinsing with water.
► Magnetic resonance spectrum of TiO2 nanopowders has appeared after rinsing with water.
► An increase of number of oxygen vacancies could account for both phenomena.