Nano-galvanic Cell Based On Fe₃O₄ Nanoparticles With Dual Electromagnetic Functions As Highly Efficient Catalytic Advanced Oxidation Processes For Water Remediation

Electrochemical advanced oxidation processes represent one of the most promising strategies to produce powerful reactive oxidizing species to deal with the ever-growing water pollution.However,devising new catalytic systems with high activity and stability for effective removal of organic pollutants is a long-term goal for practical application.Although nanoparticle-promoted electrochemical systems have been extensively studied for the oxidative degradation of organic pollutants,their degradation mechanisms based on general principles are not clear yet.In this work,we describe a general approach of electrochemical advanced oxidation processes?AOPs?for effective removal of organic pollutants.We propose the concept of nano-galvanic cell,with the goal providing a promising alternative strategy,new insight and a guide for highly efficient degradation of water pollutants from contaminated sites.Magnetic Fe3O4 was chosen and prepared as model nanoparticles?NPs?because of its excellent recyclability,good conductivity and toxicologically uncritical constituents,which is a common mineral and can be used as an environment benign material.The synergistic electrochemical oxidation system of Fe₃O₄ nanoparticles shows excellent ability to remove organic pollutants,and its mineralization of 4-cp can reach100%.Fe₃O₄ nanoparticles exhibits dual functions as a galvanic cell and a magnet at the same time in the electrochemical system.On one hand,the spherical Fe3O4 NPs are polarized to create numerous nano-galvanic cells under the electric field through the electrostatic induction effect,with high accumulation of positive charges?e.g.,Fe-based species?on one side and negative charges(i.e.,electrons,or O^2-)on the other,which simultaneously facilitates electron transfer for triggering reduction?e.g.,O2 reduction to produce H2O2 and O2^-·?and oxidation?e.g.,4-CP and its intermediates activation?reactions in the system.On another hand,the charged NPs caused by the electrostatic induction effect and the nature of Fe3O4 can give rise to magnetic field,which further exerts forces on the charges at the NPs surface and results in impacts on the distribution as well as the fate and the releasing behavior of iron species,and in turn,contributes to creating nano-galvanic cell system.It is of interest to note that a complete mineralization of 4-CP was achieved in this work,which is by far the most impressive performance of electrochemical AOPs by comparing with previous other AOPs works,suggesting a much stronger oxidation ability.The radical scavenger experiments confirmed and the resultant·OH and O₂^-·,which was produced from O2reduction reaction at the anode side of nano-galvanic cell,as critical reactive species for the efficient degradation of 4-CP.In the electrochemical system constructed by Fe3O4 and Pd/Fe3O4,Pd can catalyze H₂ and O₂ produce a large amount of H₂O₂,which makes O2^-·and·OH show significant different contribution rate in the degradation of 4-CP in these two systems.Different hydrogen evolution electrodes have little effect on the degradation of 4-CP in the electrochemical oxidation system promoted by Pd/Fe3O4.It is further proved that the heterogeneous catalytic reaction on the electrode surface has little contribution to the system,Its main function is to provide constant current to maintain a stable external electric field,promoting particles to nano-galvanic cells,which opens up the possibility of other inexpensive,cost-effective metal materials as cathode electrodes.At the same time,Fe3O4nanoparticles have excellent stability and reusability in the constructed electrochemical system,demonstrating their potential to remove organic pollution.In addition,experiments have compared the different degradation rates of the three isomers of monochlorophenol in the constructed NPs-promoted electrochemical systems.The structure indicates that the degradation rate of monochlorophenol in the system shows the following order due to the synergistic effect of the ortho and para-targeting orientation of the hydroxyl group and the chlorine atom substituent and steric hindrance:3-CP>4-CP>2-CP.It is the synergetic effect between electrochemistry and nanotechnology in the nano-galvanic cell demonstrated,which is simply consisting of NPs in the electrochemical system,that contributes to the highly efficient catalytic oxidation performance.The strength of this approach lies in a methodology that overcomes the common problems of heterogeneous electrochemical process,such as limited electrode area,mass transfer limitation and poor current efficiency,and realizes a synergistic electromagnetic interaction for effective degradation of organic pollutants.The principle and the nano-galvanic cell demonstrated details the first insight into the magnetic NPs with dual electromagnetic functions for efficient and sustainable remediation of water pollutants,and importantly,it could be the basis for NPs-promoted electrochemical AOPs that sheds light on the development of other novel nanomaterials for practical application.