Preparation and Thermal Decomposition Kinetics of Polyoxometalate of Ciprofloxacin with 12‐Tungstosilicic Acid

A new polyoxometalate (CPFX·HCl)3H4SiW12O40·10H2O was prepared from ciprofloxacin hydrochloride and H4SiW12O40·n H2O in aqueous solution, and characterized by elemental analysis, IR spectra and DTA-TG-DTG techniques. The IR spectrum confirmed the presence of Keggin structure and the characteristic functional group for ciprofloxacin in the compound. The TG-DTA-DTG curves showed that its thermal decomposition was a four-step process consisting of simultaneous collapse of Keggin type structure. The residue of decomposition was the mixture of WO3 and SiO2, confirmed by X-ray diffraction and IR spectroscopy. The decomposition mechanism and non-isothermal kinetic parameters of the polyoxometalate were obtained from an analysis to the TG-DTG curves by the single scanning methods (the Achar method and Coats-Redfern method) and the multiple scanning methods (the Kissinger method, Flynn-Wall-Ozawa method and Starink method). The results indicate that the kinetic equations with parameters describing the thermal decomposition reaction are dα/dt=6.65×106[3(1−α)(2/3)]e(−10495.5/T) with E=87.26 kJ/mol and A=6.65×106 s−1 for the second step, dα/dt=7.01×109(1−α)e(−18770.7/T) with E=156.06 kJ/mol and A=7.01×109 s−1 for the third step, dα/dt=9.77×1043[(1−α)2]e(−88980.0/T) with E=739.78 kJ/mol and A=9.77×1043 s−1 for the fourth step.