Study On Electro-assisted Cobalt-silicon Catalyst Activated Sulfite System

Sulfate radicals(SO₄^·-)based advanced oxidation process have great advantages in water treatment field.Sulfite（S（Ⅳ））has the potential to replace persulfate and permonosulfate,can be activated by transition metal ions,ultraviolet light,electricity,etc,to generate strong oxidative SO₄^·-.However,the homogeneous transition metal ion activated sulfite system has some disadvantages.Therefore,the preparation of excellent heterogeneous solid-phase catalysts,the influencing factors and related mechanisms of activated sulfite systems have become new research hotspots.Regarding the issue above,this paper studied the preparation of stable and efficient heterogeneous solid-phase catalysts and the way of activated sulfite.First,using silica particles as a support,heterogeneous cobalt-silicon catalysts（CoNSi,CoASi）were prepared.The property of the cobalt-silicon catalysts was evaluated by taking the degradation effect of target pollutants,the leached amount of metal ions,and the recycling of catalyst as evaluation indicators.Then,the effectiveness of CoNSi/S（Ⅳ）system degrading acid orange 7（AO7）was analyzed,and various influencing factors and reaction mechanism of the system were revealed.Finally,using CoASi catalyst as particle electrode,the electrochemical（EC）has introducted to CoASi/S（Ⅳ）system in order to degradation X-3B.The influencing factors and mechanism of EC/CoASi/S（Ⅳ）system were also revealed.The main content and results consist of:（1）Modified with ammonia,using cobalt amine complex as precursor,CoNSi and CoASi catalyst were prepared by adsorption roasting.The results of field transmission electron microscope,X-ray diffraction,X-ray photoelectron spectroscopy and other characterization technologies indicate that CoO,Co₃O₄ nanoparticles are highly dispersed on the silica support.The structure and morphology of cobalt-silicon catalysts,valence and content of cobalt have not changed significantly before and after use.Control experiments show that cobalt-silicon catalyst activated sulfite system can effectively degrade AO7 and X-3B.After the reaction,the leaching amount of cobalt ions in the solution is only 0.01 mg L^-1.（2）Study on degradation of AO7 in CoNSi/S（Ⅳ）system.The results indicated that the degradation efficiency of AO7 of 7 mg L^-1 in aerobic environment could reach 79.4%under the conditions of initial pH of 9.0,CoNSi of 0.25 g L^-1,sulfite of 1.0 mM and temperature of 303.13K after 20 minutes.Compared with acidic environment,the process of degrading AO7 in CoNSi/S（Ⅳ）system is better in alkaline environment.An increase in temperature can promote the degradation of AO7.The activation energy for degrading AO7 in CoNSi/S（Ⅳ）system is 11.61±0.25 k J mol^-1.Oxygen is an important factor of CoNSi/S（Ⅳ）system.The degradation rate of AO7 is reduced to about 5%in an anaerobic condition.Aeration increases the degradation rate of AO7,but the final degradation rate decreases slightly.Phosphate anions have an inhibitory effect on the degradation of AO7in the CoNSi/S（Ⅳ）system.However,Cl^-,HCO₃^-anions have no obvious effect.The degradation rate of AO7 in five water body was investigated thoroughly.The results indicate that the degradation rate of AO7 is inhibited in raw wastewater,not decreased significantly in other water body.Finally,this article systematically explores the reaction mechanism of CoNSi/S（Ⅳ）system.The results show that sulfite has a dual role as a ligand on the surface of the CoNSi catalyst and a precursor of sulfate radicals.Free radical capture experiments and electron spin resonance（ESR）experiments show that SO₄^·-radicals bound on the catalyst surface and free in solution are the main active radicals that degrade AO7.The large number of hydroxyl groups on the surface of the silica support promote the hydroxylation of Co（Ⅱ）,which helps to generate>Co（Ⅱ）-SO₃ complex and ultimately improves the activation capacity of the catalyst.In addition,under the condition of CoNSi dosage is 0.25 g L^-1,the steady state approximation of SO₄^·-radicals was studied,and the apparent reaction rate constant of SO₄^·-is 0.60±0.07 M^-1 s^-1.（3）Study on degradation of active brilliant red X-3B in EC/CoASi/S（Ⅳ）synergistically system.The results indicate that the degradation efficiency of X-3B of 40mg L^-1 in aerobic environment could reach 88.0%under the conditions of current density of 8 m A cm^-2,initial pH of 7.2,CoASi dosage of 0.1 g L^-1,sulfite concentration of 1.0mM and temperature of 303.13K after 60 minutes.Increasing the current density can promote the degradation of X-3B.In the pH range of 4-9,the degradation rate of X-3B reach more than 85%.Meanwhile,the effects of Cl^-,HCO₃^-,H₂PO₄^-and humic acid（HA）on the degradation of X-3B in the EC/CoASi/S（Ⅳ）system were also investigated.The results show that Cl^-and low concentration HA can promote the degradation of X-3B,HCO₃^-,H₂PO₄^-and high concentration HA can significantly inhibit the degradation of X-3B.Finally,the article explores the reaction mechanism of EC/CoASi/S（Ⅳ）system.The results of free radical capture experiments and ESR experiments show that SO₄^·-radicals play a leading role.CoASi has the dual function of particle electrode and catalyst in the electric field.The external electric field makes CoASi catalyst particles form microelectrodes,which promotes the adsorption of sulfites and organic molecules on the surface of the CoASi catalyst and enhances the contact between the reactants and the catalyst.In addition,the anode can degrade part of X-3B.SO₃^·-radicals directly generated through a single electron transfer reaction from the anode to sulfite make the EC/CoASi/S（Ⅳ）system have a stronger oxidation capacity.