Enhanced Fenton-like Oxidation Of 2,4-dichlorophenol In Aqueous Solution By Nano-zero-valent Iron Supported On Magnetic Fe₃O₄ Nanoparticles

Chlorophenols are widely used in medicine,agriculture,papermaking,dyes and other industries as an important chemical raw material,2,4-dichlorophenol is a very representative one among them,because it has a stable chemical properties and is easy to be enriched in the environment and in vivo,on the other hand,It is a difficult-to-treat organic compound due to combines biological toxicity,mutagenicity and carcinogenicity.Once it flows into the water environment or transports to soil,it will cause serious harm to human health and the ecological environment.In recent years,nano-zero-valent iron has been used to remove chlorophenols because of its large specific surface area,strong reducing ability,and high reactivity,however,nano-zero-valent iron doesn't completely degrade pollutants,and may produce more toxic intermediates and a large amount of ferrous ions in the reaction system,these will cause secondary pollution.In order to solve the above problems,nano-zero-valent iron combined with Fenton technology is a promising method.In this work,co-precipitation method was used to prepare nano-triiron tetraoxide as carrier,liquid phase reduction method was used to prepare nano-zero-valent iron,this obtain a supported nano-zero-valent iron.In this way,not only the supported nano-zero-valent iron can be used to degrade2,4-dichlorophenol,but also it can be recycled by virtue of the magnetic properties of nano-triiron tetraoxide.Fenton technology is combined to form a Fenton-like system for degrade2,4-dichlorophenol.The prepared materials were characterized and used to degrade2,4-dichlorophenol in aqueous solution.The effects of factors on removal of2,4-dichlorophenol were investigated,the reaction stage and reaction mechanism existing in the reaction process were speculated.The characterization of the prepared material showed that nanoparticles of nano-zero-valent iron supported on magnetic Fe₃O₄ are relatively uniform and spherical,and there is agglomeration between the particles.During the preparation process,the nanoparticles may be oxidized,so that the outer layer has iron oxide oxidation Layer,showing the shell-core structure.The experiment of the removal of 2,4-dichlorophenol showed that,compared with a single nano-particle,the nano-zero-valent iron supported by nano-Fe₃O₄ has multiple characteristics such as adsorption,reduction and recyclability.The removal rate is 68.8%under the conditions of dosage 1 g/L,p H 3,pollutant concentration 40 mg/L,and temperature25?.Factors such as the pH of the solution,the addition of nanoparticles of nano-zero-valent iron supported on Fe₃O₄,and the concentration of pollutants all have an effect on2,4-dichlorophenol.Lowering the pH value of the solution can quickly dissolve the iron oxide on the surface of the supported nano-zero-valent iron,and increase the removal rate;As the concentration of pollutants increases,2,4-dichlorophenol competes with the active sites in the reaction system,resulting in a decrease in removal rate.With the increase of the dosage,the active sites in the reaction gradually increase and the removal rate increases However,when the dosage is 0.8 g/L,the increase in removal rate slows down.Increasing the reaction temperature can promote the homogenization of hydrogen peroxide,speeding up the reaction process and enhancing the removal effect.The results of batch experiments showed that the pH value of the solution,the addition of nanoparticles of nano-zero-valent iron supported on Fe₃O₄,the concentration of pollutants,the concentration of hydrogen peroxide,and the coexisting cations(Ca²⁺)in aqueous solution all had significant effects on the removal of 2,4-dichlorophenol.Decreasing the pH of the solution can increase the corrosion rate of the supporting material,thereby improving the removal of 2,4-dichlorophenol,but when the pH is 2,it will not be conducive to the oxidative degradation of pollutants by the Fenton system.Increasing hydrogen peroxide Concentration can improve the removal of 2,4-dichlorophenol,but excess hydrogen peroxide will become a scavenger for hydroxyl radicals,leading to a reduction in the removal effect.Reducing the concentration of pollutants or increasing the addition of loading materials are to increase the degradation of 2,4-dichlorophenol by increasing the active sites in the reaction system.The coexistence of Ca²⁺in the reaction system will react with the OH^-in the solution to form a precipitate and deposit on the surface of the supporting material,hindering the reaction from continuing,and reducing the removal rate.After the nano-zero-valent iron has been reused ten times,the removal rate of2,4-dichlorophenol is still more than 65%.It has good recyclability and can be used as an environmental functional load material.