Degradation Of Organic Pollutants By Activated Persulfate Over Cobalt-based Catalyst

Water is the source of life,only 0.25%of the total freshwater reserves available to humans directly.At the same time,more and more organic compounds are synthesized and used,and eventually released directly or indirectly into the natural water,which further restricts the sustainable development of the society and endangers the safety and health of human beings.Therefore,it is of great practical significance to find a green and efficient method to remove organic pollutants in water environment.Physical,chemical,or biological methods are commonly used to degrade organic compounds.Among them,the chemical method is the effective transformation of peroxidation reduction reaction to remove all kinds of biodegradable pollutants.Advance Oxidation Process（AOPs）involving hydroxyl radicals（·OH）and other high reactive oxygen species is the commonly used Oxidation technology in the past.Hydroxy radicals play a major role,but the Oxidation capacity is relatively weak.In recent years,the advanced oxidation technology of sulfate radical is mainly through the activation of persulfate to produce sulfate radical,which has a high oxidation potential and can trigger a series of free radical chain reactions,so as to efficiently degrade organic pollutants.Previous methods of activating persulfate by ultrasound,UV and heat to produce sulfate radicals are less efficient and require additional energy and complex systems.It is necessary to find an efficient and environmentally friendly activation method to activate persulfate in the oxidation process.Compared with the above activation methods,the activation of persulfate through transition metal heterogeneous catalyst may be a more simple and effective method.Transition metals such as manganese,nickel,copper,manganese and iron have been used to activate persulfate to degrade organic pollutants.In this paper,cobalt in transition metal was selected as the active species to prepare cobalt-based heterogeneous catalysts for the degradation of Rh B and other organic pollutants by activating persulfate.The degradation pathway and reaction mechanism were explored based on the structural characterization results of the catalysts.The details are as follows:（1）Preparation and characterization of Co（OH）₂/g-C₃N₄ catalyst and study on degradation of Rhodamine B and other organic compounds.Co（OH）₂/g-C₃N₄ catalyst was prepared by simple chemical impregnation method.The structure,morphology and elemental composition of Co（OH）₂/g-C₃N₄ composite were verified by various characterization methods.The catalyst was applied to the removal of various organic pollutants by single persulfate activation.The key parameters such as catalytic dose,amount of single persulfate,initial p H value,concentration of initial organic pollutants and reaction temperature were studied.At room temperature,50 mg PMS was activated with 15 mg Co（OH）₂/g-C₃N₄ catalyst,and 100 m L of20 mg/L Rh B was completely degraded in no more than 15 minutes with the apparent rate constant k_app=0.460 min^-1,which was much higher than that of Co（OH）₂ and g-C₃N₄ catalysts alone.This is because the synergistic interaction between lamellar Co（OH）₂ with rich active sites and electron-rich g-C₃N₄ with good electron transfer ability accelerates the activation of persulfate.（2）Preparation and characterization of intermetallic compound Co₃Sn₂ catalyst and study on degradation of Rh B and other organic compounds.Co₃Sn₂ catalyst was prepared for the enrichment of Co（II）in the amorphous layer under hydrothermal conditions.The intermetallic compound Co₃Sn₂ showed excellent performance in the removal of Rh B by activated mono-persulfate.Key reaction parameters,such as catalytic dose,amount of single persulfate,initial p H value,initial concentration of organic pollutants and reaction temperature,were also studied.At room temperature,100 m L of 20 mg/L Rh B was completely removed in 10 min using 10 mg of catalyst and 10 mg of PMS.The apparent rate constant was k_app=0.515 min^-1,which was higher than that of other cobalt-based catalysts under the same conditions.The excellent catalytic performance of Co₃Sn₂ is attributed to the synergistic effect between the Co（II）-layer with abundant active sites and the metal core with excellent electron conductivity.（3）The results of free radical capture experiments and electron paramagnetic resonance（EPR）analysis showed that sulfate radical and hydroxyl radical were the main active radicals in the degradation process.According to the results of positive ion analysis,literature reports and the results of LC-MS,the degradation pathway and reaction mechanism of Rh B removal by activated PMS with cobalt-based catalyst were proposed.Rh B can be further decompose into water,carbon dioxide,ammonium nitrate and so on by ring opening.