Effect of a Chelating Agent on the Physicochemical Properties of TiO2: Characterization and Photocatalytic Activity

Abstract

In the current study, it was found that the physiochemical properties of TiO2 are effected with formic acid as a chelating agent in a sol–gel process. From XRD studies it was revealed that due to the chelation of formate group with titanium precursor, anatase/brookite mixture of 86:14 is obtained while the control sample which has been prepared without formic acid showed pure anatase at 400 °C. FTIR studies indicated that, the formate group favored a monodentate mode of coordination with titanium precursor under the effect of addition of increasing amount of formic acid, while under the effect of increasing titanium precursor content the formate group is chelated with titanium atoms in a bidentate bridging mode. In addition, from the FTIR study it was demonstrated that increasing the amount of water in the hydrolysis step, a reduction in the intensity of the carboxylate (COO−) stretches was observed indicating that the titania formate bridging complex becomes weaker, resulting in a weakened titanium gel network structure which could readily collapse during calcination favoring early rutile formation. Raman spectroscopy showed that as a result of sample composite nature and presence of oxygen vacancies as demonstrated by PL analysis causes the broadening and frequency shifting of the Raman bands. Photocatalytic studies demonstrated that the formic acid modified sample composed of anatase/rutile mixture of 94:6 calcined at 600 °C show significantly higher catalytic activity compared to the control sample prepared under similar conditions. Kinetic analysis show first order kinetics for the decomposition of methylene blue, a rate constant (kapp) of 0.074 min−1 was obtained with anatase/rutile (94:6) mixture which is even higher than the Degussa P25 (0.067 min−1).