Green Synthesis by Microwave Irradiation of TiO2 Using Cinnamomum verum and the Application in Photocatalysis

Abstract

The extraction process of bioactives from the aqueous extract of cinnamon (Cinnamomum verum) was optimized using the Design Expert 11 program and analysis of variance (ANOVA) by considering the following parameters: cinnamon weight (g), power (W), and time (s) of microwave irradiation. The optimal conditions are cinnamon weight of 4.5 grams, time of 600 seconds, and power of 150 watts of microwave irradiation. With Cinnamomum verum extract under optimal conditions and titanium (IV) tetrachloride as a precursor, TiO2 nanostructures were synthesized using the sol-gel method assisted by microwave irradiation in the crystallization stage with a power and irradiation time of 150 W and 600 sec, respectively. Similarly, a sample without extract was synthesized under the same conditions. The following techniques characterized the materials: X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, UV-vis diffuse reflectance, Raman spectrometry, and high-resolution transmission electron microscopy (HRTEM). It was feasible to obtain nanocrystalline solids of TiO2 anatase phase with and without cinnamon extract; the particle size and the crystallinity were influenced by the bioactive agents during the synthesis (aqueous extract of Cinnamomum verum) and the synthesis method (microwave irradiation); a smaller crystal size, a smaller particle size, a higher crystalline order, and a lower band gap were achieved for the material synthesized with cinnamon extract compared to the material synthesized without extract and other methods. The synthesized materials were evaluated in the photodegradation of methyl orange (as a model of photodegradation), employing as reference parameters the commercial TiO2 brand Sigma-Aldrich phase anatase and the photolysis of the system. The amount of dye adsorbed in the tested materials was quantified, finding an equilibrium time of 15 min, where the TiO2 synthesized with Cinnamomum verum extract was the material that most adsorbed methyl orange at 7.5%. In the case of photodegradation, the TiO2 synthesized with cinnamon extract apparently promoted the total mineralization of methyl orange in 40 minutes of reaction, making it the best material of those evaluated in the photodegradation. In all cases, the degradation models were adjusted to a first-order kinetic model, where it was confirmed that the highest reaction rate corresponded to TiO2 synthesized with Cinnamomum verum.