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.