Photosensitive Spatiotemporal Dynamics In The Hydrogen Peroxide-Sulfite-Ferrocyanide System

The reaction between sulfur-oxygen compound and different oxidizing agent is one of the most important research branch in nonlinear chemistry,which is accompanied by complex self-organized phenomena in both homogeneous and reaction-diffusion medium.Maintained out of equilibrium,the nonlinear chemical reaction containing proton feedbacks could generate various ordered spatial-temporal self-organization phenomena,such as pH oscillation and Turing pattern.Due to the presence of photosensitive intermediate,the dynamics of hydrogen peroxide-sulfiteferrocyanide system can be tuned under light illumination.Complex dynamical behavior is derived from the OH·autocatalysis,a new feedback to the system.Thiswork investigates the photo-responsiveness of thehydrogen peroxide-sulfite-ferrocyanide system from low pH state in both homogeneous and reaction-diffusion system.In the reaction-diffusion system,when the degree of chemical reaction in the gel is relatively high,the system is at low pH,it is called the M state,and vice versa its state is F state.In homogeneous study,the experiments are implemented in continuously flow stirred tank reactor under the conditions of [Fe?CN?₆^4-]0 = 6.0 mM,[H₂O₂]0 = 25.0 mM,[SO₃^2-]0 = 14.0 mM,with constant temperature of 25 °C and constant flow rate of 3.33 × 10-3 s-1.An ultraviolet light with a wavelength of 385 nm is used as pertubation in the whole experiment.When [H₂SO₄]0 = 0.90 mM,the system is at low pH steady state.By using illumination light of fixed duration of 10 s,multiple excitation oscillations can be observed when the light intensity is higher than 13.25 mW cm-2.Consequently,when the initial concentration of H₂SO₄ is increased,the greater the intensity of light is required for the same number of excitation oscillations.Keeping the light intensity of 0.28 mW cm-2,multiple oscillatory pulses can be observed by changing the light duration only when the duration is above 120 s.The higher the initial concentration of H₂SO₄ is imported to the system,the longer the light duration is required for the same number of excitation oscillations.Furthermore,sustained pH oscillation can be obtained by introducing continued light to the system where the light intensity is 0.091 mW cm-2 and the initial concentration of sulfuric acid is 1.0 mM.In addition,the oscillatory periodis increased against the decreased intensity.The oscillation can be suppressed to high pH state when the light intensity moves to a higher level as 0.596 mW cm-2.As a result,greater intensity of light illumination is required to generate or suppress the oscillation if higher concentration of sulfuric acid is included in the influx.In reaction-diffusion medium of the hydrogen peroxide-sulfite-ferrocyanide system,the experiments are implemented in one side fed reactor under the conditions of [SO₃^2-]0 = 14.0 mM,[H₂O₂]0 = 25.0 mM,with constant temperature of 25 °C and constant flow rate of 3.33 × 10-3 s-1.Using the initial concentration of H₂SO₄ and Fe?CN?₆^4-as the control variable,there are F state,M state,spatial bistability,and stable patterns.Here conditions of [Fe?CN?₆^4-]0 = 6.0 mM and [H₂SO₄]0 = 0.48 mM are used as initial reactant concentration in the experiments,where the reaction solution in the gel shows the M state.With the duration of light illumination fixed at 10 s,the light illumination can produce responsiveness in the form of multiple pulse waves when the intensity of light perturbation is increased to 0.99 mW cm-2 or above.The pulse damps to low pH state after a long enough period of relaxation.The number of pulse is increased along with the increase of light intensity.Then the light intensity of 3.02 mW cm-2 is applied on the system,which leads to a single pulse.Greater light intensity is required for the system to stimulate and suppress the process with higher concentration of sulfric acid.Reaction-diffusion dynamics study is also included in this work with low concentration of sodium polyacrylate.The introduction of sodium polyacrylate can make it more conducive to the formation of pulse waves by reducing the rate of diffusion of hydrogen ions in the gel.F state,M state,and pulse waves can be obtained under different reactant concentrations.When the reactant is fixed at [SO₃^2-]0 = 14.0 mM,[H₂O₂]0 = 25.0 mM,[Fe?CN?₆^4-]0= 7.0 mM,[PA]0 = 0.50 mM and [H₂SO₄]0 = 0.27 mM,the system exhibits steady pulse waves.The light illumination is introduced to the system with duration of 10 s and intensity of at 10 s duration and intensity of 0.99 mW cm-2.The introduction of sodium polyacrylate can broaden the wave width as well as prolong the period of the pulse.