Photocatalytic degradation of dyes using rutile TiO2 synthesized by reverse micelle and low temperature methods: real-time monitoring of the degradation kinetics

Abstract

The study proposes two new TiO2 photocatalysts with excellent photocatalytic properties obtained by the reverse micelle (RM-TiO2) and low temperature (LT-TiO2) methods. The crystal structure and morphology of the obtained TiO2 samples were analyzed by X-ray diffraction, scanning electron microscopy and IR-spectroscopy. The chosen synthesis conditions lead to pure rutile modification. FTIR spectra of the obtained samples contain characteristic bands, attributed to stretching vibrations of Ti–O bonds and to deformation vibrations of Ti–OH bonds. The average crystallite sizes for RM-TiO2 and LT-TiO2 samples are 5.4 and 9 nm, respectively. SEM analysis showed that the RM-TiO2 consists of TiO2 particles, assembled into spherical aggregates, while LT-TiO2 consists of smaller aggregates and is mostly mesoporous. The BET surface areas of the RM-TiO2 and LT-TiO2 samples are 39 and 63 m2/g, respectively. The photocatalytic degradation of the Congo Red (CR), Methyl Orange (MO) and Direct Red 23 (DR23) dyes in water medium has been studied under UV LED irradiation with H2O2 as an auxiliary oxidant. Both the RM-TiO2 and LT-TiO2 samples are active photocatalysts. The optimal dosages are 1.5 and 0.5 g/L respectively. The maximum photodegradation efficiency of RM-TiO2 is observed when the concentration of H2O2 is 15 mM for CR, 5 mM for MO and 10 mM for DR23. The maximum photodegradation efficiency of LT-TiO2 is observed when the concentration of H2O2 is 10 mM for CR, 2.5 mM for MO and 1.5 mM for DR23. The boosting effect of H2O2 on the degradation efficiency can be explained by an increased generation of •OH radicals. The real-time monitoring of degradation kinetics has been performed using measurements of light reflected from TiO2 suspension. The proposed technique allows the use of small volume of solution and amount of photocatalyst. The synthesized rutile photocatalysts may be used for wastewater treatment.