The preparation and characterization of TiO2/r-GO/Ag nanocomposites and its photocatalytic activity in formaldehyde degradation

A series of TiO2-rGO-Ag nanocomposites were prepared in this work via a facile one-pot hydrothermal method utilized for formaldehyde (HCHO) photodegradation; using TiO2, graphene oxide(GO) as well as AgNO3 as the raw materials, and sodium citrate as a reducing agent. Characterization by X-ray diffraction (XRD), Raman spectra, Transmission electron microscopy (TEM) and Field emission scanning electron microscopy (FESEM) demonstrated that GO and Ag+ were reduced during the formation of TiO2-rGO-Ag nanocomposites. X-ray photoelectron spectroscopy(XPS), UV–vis diffuse reflectance spectroscopy (DRS), photoluminescence spectra(PL) and Photocurrent spectrum measurement were applied to quantitatively characterize the bonding between TiO2 and rGO, the band gap energy of catalysts as well as electron–hole pairs recombination rate. The results revealed that the introduction of rGO sheets and Ag nanoparticles reduced the band gap energy of catalysts; it also suppressed the recombination of electron–hole pairs. However, C–O–Ti bond, which played a key role in photocatalysis, was reduced to some extent by the existence of Ag. Photodegradation results showed that, when the Ag loading was 9 mol% of TiO2, the reaction rate constant of formaldehyde (HCHO) removal improved distinctly, by about 22.3 times that of TiO2. The radical scavenger tests and electron paramagnetic resonance(EPR) analysis revealed that superoxide radical (·O2−), hole (h+), and hydroxylradical (·OH) were reactive species of formaldehyde photodegradation.