The Study On The Removal Mechanism Of Typical Pollutants In Aqueous Solution Based On Iron-based Nanomaterials

With the rapid development of global economy,the pollution of water body is more and more serious.Heavy metals and antibiotics are typical pollutants in water environment which can pose a great threat to human health and ecological security.Thus,it is an urgent task to find simple,efficient and low cost water purification methods and materials.Iron based nanomaterial has aroused great attention in the field of water restoration because they are abundant?inexpensive and environmentally friendly in nature.In this paper,arsenic and tetracycline hydrochloride are selected as two typical target pollutants.The removal mechanism of arsenic based on the shape engineering regulation and functional modification of nanoscale zero valent iron(n ZVI)and the removal mechanism of tetracycline hydrochloride based on the preparation and electronic structure modification of new base metal iron based anode materials are studied.In this paper,the effect of the micro structure,physicochemical and electronic structure properties of materials on the pollutant removal process is investigated.The catalytic reaction mechanism is further explored by the density functional theory(DFT)from the perspective of materials science and environmental science.The specific research contents and results are as follows:The first section is based on n ZVI,which is modified by the shape engineering.A layer Fe₂O₃ shell with controllable thickness is self-grown on the surface of n ZVI by controlling the aging time.The existence of Fe₂O₃ shell can not only improve the stability of n ZVI,but also change the electron transfer path of molecular oxygen activate by n ZVI.Thus,it can improve the ability of catalytic oxidation of As(?)to As(V).Furthermore,the adsorption capacity of the modified n ZVI to arsenic is 60 times higher than that of the unmodified n ZVI.This unique core-shell structure n ZVI can also effectively reduce the bioavailability and mobility of arsenic in the process of sediment restoration,and thus it can accelerate arsenic transformation into residual arsenic with poor bioavailability.Moreover,a new Fenton-like system is proposed in this study which can effectively purify arsenic polluted groundwater under anoxic condition.Meanwhile,the impact of environmental factors is also considered and the performance of the modified n ZVI in the actual arsenic containing river water and smelting wastewater is also evaluated.This will provide a promising method and technical scheme for the remediation of environmental hazards caused by arsenic pollution.The second section is based on the research in the first section.The core-shell structure n ZVI is further functional optimized through doping copper.This distinctive copper doped core-shell structure greatly improves the adsorption capacity,removal rate and catalytic oxidation ability of n ZVI to arsenic.Under the same experimental conditions,the removal capacity of arsenic by copper doped core-shell structure n ZVI is 4 times higher than that of pure core-shell structure n ZVI.Furthermore,the number of paths to activate molecular oxygen by n ZVI is also increased fourfold after copper doped compared to pristine n ZVI.The yield of radials and corrosion products of n ZVI are greatly improved,and thus accelerated the removal of arsenic from water body.In general,environmental researchers attributed the low yield of radicals produced by n ZVI to the precipitate of iron,the high reaction activity between n ZVI and H₂O₂,and low rate of Fenton reaction,but they ignore the importance of molecular oxygen activation and free radical formation pathway.This is not conducive to the wide application of n ZVI.Therefore,this paper proposed a new strategy which can increase the production of radical by increasing the molecular oxygen pathway activated by n ZVI,and thus accelerate the process of arsenic pollution purification in water body.This study provides a promising strategy to reduce the impact of arsenic pollution on the surrounding environment.The third section is based on the base metal iron-cobalt layered double hydroxide(Fe_1-xCo_xLDH)anode material.It can be further transformed into Fe_1-xCo_xP anode material by high temperature phosphorylation.The obtained Fe_1-xCo_xP anode material has high stability in the process of electro-oxidation degradation of organic pollutants and it effectively reduces the release of iron ions and the formation of iron sludge.The results of XPS and DFT are consistently showed that the electronic structure of Fe_1-xCo_xP anode material can be modified by controlling the molar ration of Fe/Co.Furthermore,it can change the electron density at the active site which will make the metal cobalt with more positive charge and phosphorus with more negative charge,and thus accelerate the adsorption and activation of water molecules.Moreover,the modification of electronic structure can effectively reduce the energy barrier produced by hydroxyl radicals,resulting in the production of more hydroxyl radicals.This will significantly improve the ability of electro-catalytic oxidation to degrade organic pollutants.The experimental results show that the degradation efficiency of the anode material designed in this study is better than that of boron doped diamond anode and platinum plate anode.The self-grown Fe_1-xCo_xP nanosheet arrays anode material has a wide range of p H applications compared to the traditional electro-Fenton process.Therefore,this study can provide a new approach for the design of more advanced anode materials for electrocatalytic oxidation water purification and other fields.The fourth section is based on the base Fe_1-xCo_xLDH anode material.It can be further optimized and modified to obtain phosphorous hybrid Fe_1-xCo_xLDH deposited with Cu nanodots(Cu NDs/P-Fe_1-xCo_xLDH)through chemical vapor deposition and one-step chemical reduction.The deposition of Cu NDs can effectively improve the adsorption and dissociation ability of water molecules and the phosphorus doping can accelerate desorption of adsorbed hydrogen,and thus can make the anode material to produce more hydroxyl radical.The results of XPS and DFT are consistently showed that this strategy optimizes the electronic structure of the anode material which makes the Cu NDs with more positive charge and P-Fe_1-xCo_xLDH with more negative charge.The modification of electronic structure can produce an unbalanced?pulling force?on OH_ads and H_ads in water molecules,resulting in the polar water molecules adsorbed on the anode material to become unstable.Therefore,this unbalanced force will cause the H-O bond in water molecules to break more easily,thus accelerate the production of hydroxyl radical.This strategy increases the energy barrier of the oxygen evolution reaction and the overpotential of the byproduct oxygen.It can provide a reasonable method and technical scheme for the application of base metal iron-based materials in the electro-oxidation water purification technology.