Removal Of P-Chloronitrobenzene And Cr(Ⅵ)with Amorphous Zero-valent Iron

Water is an important material basis for human survival.With the continuous acceleration of the modern industrial process,the water pollution problem is becoming more and more serious,and it is urgent to find green and economical water pollution control technologies.Zero-valent iron is environmentally friendly and easy to obtain,it has broad prospects for the treatment of environmental pollutants.However,zero-valent iron faces bottlenecks such as low activity.In recent years,researchers have proposed a series of strategies to improve the performance of zero-valent iron in treating pollutants,and most of these strategies focus on surface modification of zero-valent iron.In our previous research,we found that the reactivity of zero-valent iron was closely related to its crystallinity.Therefore,we took amorphous zero-valent iron as the research object in this thesis to explore the performance and mechanism of amorphous zero-valent iron in removing typical environmental pollutants.The specific research content is as follows:Firstly,amorphous zero-valent iron(A-mZVI)and crystalline zero-valent iron(C-mZVI)were successfully synthesized by liquid phase reduction method.The structure and morphology of the samples were systematically analyzed by XRD and SEM.Subsequently,the performance of two kinds of zero-valent iron was investigated in heterogeneous Fenton degradation of p-chloronitrobenzene.The heterogeneous Fenton system based on A-mZVI could effectively degrade p-chloronitrobenzene,and its rate constant was more than 8 times that of the C-mZVI system.The decomposition experiment of H2O2 and the quantitative analysis of·OH showed that the amorphous structure enhanced the ability of zero-valent iron to react with H2O2 to produce·OH.We also tested the intermediate products of p-chloronitrobenzene and found that the oxidation products and reduction products coexist in the system.The analysis results of p-chloronitrobenzene reduction process showed that·H was the main reducing species and A-mZVI was conducive to the production of·H.On this basis,we believed that the amorphous structure was helpful for the zero-valent iron in activation of H2O2 to produce·OH,and facilitated the transfer of electrons to H2O or H+ to produce ·H.In addition,Cr(Ⅵ)was adopted as a model heavy metal pollutant,the effect of amorphous structure was investigated in reduction-adsorption removal of Cr(Ⅵ)by zero-valent iron.The experimental results showed that C-mZVI could effectively remove Cr(Ⅵ)in the initial stage of the reaction,and its rate constant was 4.5 times that of A-mZVI.A-mZVI and C-mZVI exhibited different Cr(Ⅵ)removal performance,which might be due to the two zero-valent irons had different Cr(Ⅵ)removal mechanisms.In order to explore the removal mechanism of Cr(Ⅵ),the following experiments were designed and carried out in this chapter,such as,exploring the active species of Cr(Ⅵ)removal by A-mZVI and C-mZVI,verifying the adsorption of Cr(Ⅵ)by two kinds of zero-valent iron,analyzing the ratio of adsorbed-reduced chromium species through quantification,and analyzing the adsorption coordination mode of Cr(Ⅵ)by in-situ attenuated total reflection Fourier transform infrared spectroscopy(ATR-FTIR).The above experimental results proved that the removal of Cr(Ⅵ)by A-mZVI was mainly dominated by the reduction of surface iron,while the removal of Cr(Ⅵ)by C-mZVI not only had the reduction of surface iron,but also Cr(Ⅵ)direct adsorption on the surface of C-mZVI.Although A-mZVI was helpful for the Cr(Ⅵ)reduction,C-mZVI was beneficial to adsorb Cr(Ⅵ).Therefore,the rate of A-mZVI to remove Cr(Ⅵ)would be slower than that of C-mZVI at the initial stage of the reaction,it would surpass C-mZVI when C-mZVI adsorbed Cr(Ⅵ)to saturation.Through the research in this article,we understood the ways and mechanisms of A-mZVI to remove different pollutants,and we also proved that the amorphous structure could significantly affect the activity of zero-valent iron in removing pollutants.Our research provided reference significance for the study of the intrinsic relationship between the removal of pollutants and the crystallinity of A-mZVI.