Research On The Synthesis Of Nano-valent Iron And Its Properties And Mechanism Of Cr(?)

With the rapid development of industrialization and urbanization,a large amount of heavy metals from the factory workshop discharge to the water environment,such as chromium,the heavy metal pollution of water bodies has become the most concerned problem in modern society.It is a very active research field to reduce heavy metals by zero-valent iron.However,its application is limited because of the limitation of Z?.Due to its large specific surface area and strong reaction activity,Nano zero-valent iron?nZ??is widely used in the treatment of pollutants such as heavy metals,nitrates and organic pollutants.But the process of nZ? reaction with heavy metals in the presence of oxygen,nZ? is easy to react with oxygen to generate the passivation layer and prone to reunite,leading to the reactivity of n Z? reduced greatly.Moreover,the specific mechanism of the reaction between nZ? and heavy metal is still unclear.Regarding the above issues,this article used the improved reduction method in liquid phase synthesis of nano zero-valent iron to improve the reactivity of removing Cr???with nano zero-valent iron?nZ??,delving into nanometer zero-valent iron?nZ??removal efficiency of Cr???in water and main influence factors,further study of Cr???removal kinetics and thermodynamic process,and its removal mechanism is studied in-situ XPS technique.The specific contents are as follows:?1?explain why nZ?'s removal of Cr???will have different removal efficiency in different atmosphere environments;?2?Clarify the different effects of different interfering ions in the process of removing Cr???with n Z?;?3?Clarify the detailed mechanism of nZ? removal of Cr???.This experiment Synthesized high specific surface area of nZ??182.97 m²/g?by improved liquid phase reduction method and characterized crystal structure,morphology structure of materials through the X-ray diffraction spectrum?XRD?,scanning electron microscope?SEM?,transmission electron microscopy?TEM?and Zeta potential of characterization methods etc.The novel synthesized nZ? had a good crystallinity and a loose chain structure.Comparison of the performance of Cr???removal under different atmosphere conditions shows that the Cr???can be completely removed in the anaerobic acid condition in 20 mins while the removal efficiency was only 43%in the presence of oxygen after 60minutes of reaction.The removal of Cr???by nZ? under different atmosphere conditions are consistent with pseudo-second-order kinetics.The ability of n Z? to remove Cr???under anaerobic conditions can reach 123.85mg/g and its reaction rate(0.017g·mg^-1·min^-1)is 4 times higher than that in aerobic conditions(0.004 g·mg^-1·min^-1).The formula calculation and the results of various experiments indicate that the reason why the Synthesized nZ? for Cr???removal under anaerobic conditions is much better than under aerobic conditions is that the oxygen molecules consume the electrons from nZ? corrosion.The formation of passivation layers of iron or chromium-containing oxides and hydroxides?or oxyhydroxides?hinders the transfer of electrons,while Cr???removal under anaerobic acidic conditions does not form the passivation layer described above and only a Fe-Cr oxygen-containing oxide FeCr₂O₄ is formed,which is a new reaction process and can obtain better reaction rate and reactivity than reported in the literature.In the process of nZ? removal of Cr???,the Langmuir model?R²=0.99?is more suitable to describe the adsorption isotherm model of Cr???than the Freundlich model?R²=0.96?which indicated that Cr???on the surface of nZ? is single-layer molecular adsorption.Compared with the adsorption property of iron in the literature,the q_e of n Z? is 150.60mg/g.The experimental results of Cr???removal from simulated Cr???-contaminated tap water,drinking water,and actual lake water nZ? show that the synthesized nZ? is an effective Material which can rapidly remove Cr???from Cr-containing drinking water or actual chromium-contaminated lake water.The results of cyclic experiments show that the removal efficiency of nZ? can be maintained at 72.3%after five cycles.The synthetic nZ? is useful for Cr???because of its excellent removal performance and reusability.The mechanism of excellent Cr???removal performance under anaerobic acidic conditions was elucidated by means of the X-ray photoelectron spectroscopy?XPS?technique and the experimental characterization of the adjacent phenol.In situ XPS indicates that the peak intensity of Fe⁰ on the surface of nZ? decreases gradually with time,while the peak intensity of FeCr₂O₄ is gradually increasing.The presence of phenanthroline hinders the reduction of Cr???.The removal efficiency of Cr???in the presence or absence of adjacent phenanthroline in solution was 80%and 100%respectively,which means Fe²⁺was responsible for only 20%Cr???removal.This result confirms that the electron transfer process from Fe⁰ to Cr???which adsorbed on nZ? surface is the main removal process.Therefore,n Z? under anaerobic conditions on the mechanism of Cr???can be summarized as follows:first,Oxygen-containing Cr???anions are rapidly adsorbed on the nZ? surface due to the large specific surface area and positive surface charge of nZ?.then,Fe⁰redox reaction with Cr???is the main reaction process,under the condition of oxygen and acid,fast Fe⁰ and iron oxide corrosion lead to the formation of nZ? surface Fe²⁺,at the same time,provides for Cr???to Cr?III?provides a large number of electrons.In finally,the co-precipitation products of the oxygen-containing Cr?III?anions(Cr₂O₄^2-)and Fe²⁺rapidly formed FeCr₂O₄.