Thiourea has exhibited extremely rich dynamical behavior when being oxidized either through a chemical approach or via an electrochemical method.In this study,thermodynamic properties of thiourea and its oxides are investigated by measuring their thermogravimetry (TG),differential thermogravimetry (DTG),and differential scanning calorimetry (DSC) simultaneously.Online FT-IR measurements show that products of the thermal decomposition vary significantly with the reaction temperature.In addition to the determination of their apparent activation energy (E),preexponential factor (A),and entropy (△S≠),enthalpy (△H≠),and Gibbs energy (△G≠) of thermal decomposition,our investigation further illustrates that the decomposition kinetics of thiourea and thiourea oxides follows the Johnson-Mehl-Avrami Equation,f(α)=n(1-α)-[-ln(1-α)]1-1/n and G(α)=[-ln(1-α)]1/n with n equal to 2,3.43,and 3,respectively.

The ferroin-catalyzed Belousov-Zhabotinsky (BZ) reaction was studied in a batch reactor under anaerobic conditions and was found to evolve through two separated regimes of complex oscillations.Significantly,the two bifurcation regimes exhibited qualitatively different dependence on compositions of the reaction mixture,i.e.,initial concentrations of bromate, sulfuric acid,malonic acid,and ferroin.The reaction temperature also showed opposite effects on the two bifurcation regimes,in which complexities of the first bifurcation regime were enhanced while oscillations in the second bifurcation regime became simpler as a result of decreasing temperature.Numerical simulations with a 12-variable model developed specifically for the ferroin-BZ system were able to reproduce transient complex oscillations observed in experiments.These calculations further illustrated that reactions such as ferroin and HOBr,ferroin and HBrO2,and ferriin and Br- were not essential in describing complex dynamics of the ferroin-BZ reaction.

The electrochemical oxidation of thiosulfate is revealed to have two distinct oscillatory regimes in both linear potential and galvanic voltammograms,where various nonlinear behaviors such as period-2,mixed-mode and quasi-periodic oscillations,and chaos are observed under potentiostatic or galvanostatic conditions.Electrochemical impedance spectroscopy and iR compensation characterization indicate that,depending on the operating conditions,the system could be either a strictly potentiostatic oscillator or an S-shaped negative differential resistance oscillator.Chronoamperometry measurements reveal that the first oscillatory process involves a single-electron transfer,whereas within the second oscillatory regime the average number of electrons transferred is around 3.8.Measurements with capillary electrophoresis and chemical methods illustrate that the oxidation products include S2O62-,S4O62-,S5O62-,S3O62-,and SO42-.

The electro-oxidation of sulfide on a Pt electrode is found to exhibit both N-NDR (negative differential resistance) and HN-NDR (hidden negative differential resistance) types of oscillations,making it the first system known to be capable of supporting both types of nonlinear instabilities without changing electrolyte compositions.Six distinct oscillation windows are observed when the external current is adjusted as the control parameter.In addition,temperature also exhibits subtle influences on the observed reaction behavior,where varying the temperature from 30.0℃ results in more complicated oscillatory phenomena.

The electrochemical oxidation of thiourea on a Pt electrode was found to exhibit both simple and period-doubled oscillations.Measurements of the potentiostatic I/