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The Nitrobenzene Removal Reduction in Wastewater by Nanoscale Zero Valent Iron Losing Organobentonite as the Support

Author: RenCaiXia
Tutor: ZhengXuMing
School: Zhejiang University of Technology
Course: Applied Chemistry
Keywords: nitrobenzene removal organobentonite nanoscale zero valent iron supported
CLC: X703
Type: Master's thesis
Year: 2013
Downloads: 59
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Abstract


As an important environmental contaminant, nitrobenzene is widely used in the fields of explosives, insecticides, herbicides, pharmaceuticals and dyes. But it is difficult to achieve the degradation of nitrobenzene in practical applications. In view of zero valent iron (ZVI) has the advantages of inexpensive, low running costs and easy operation. It has been extensively used to remediate inorganic and organic contaminants.It also has been reported that ZVI can be successfully employed to reduce nitrobenzene from synthetic wastewater to biodegradable aniline. Reduction of nitrobenzene by ZVI is a progress of surface-mediated electron transfer, so nanoscale zero valent iron (NZVI) owning larger surface area has a better performance to reduce nitrobenzene relative to ZVI. But freshly prepared NZVI has some drawbacks, for example, high surface energy, intrinsic magnetic interaction, which leads to NZVI is easy to agglomerate into chain and the reduction efficiency of nitrobenzene is low.Furthermore, the poor hydrophobicity of iron surface is not good to reduce nitrobenzene.Supporting of NZVI in or on solid matix is a ideal solution to solve the involved questions and improve the reactivity of NZVI. In this paper, we use the modified organobentonite (CTMA-Bent) as the support materials to support NZVI. And the iron samples were characterized by transmission electron microscope (TEM). The results showed that NZVI particles could disperse well on the bentonite. In addition, the high adsorption capacity of CTMA-Bent to organic contaminants improve the hydrophobicity of iron surface and obviously increase the vicinity the concentration of nitrobenzene which made the reduction efficiency of nitrobenzene better by NZVI/CTMA-Bent than by NZVI.In the thesis, the effects of initial solution pH and initial concentrations of NB were investigated.The product of reduction was analyzed and repetitive experiments were carried out. XPS analysis was employed to determine which chemical compositions are present on iron surface. The conclusions are as following:(1) The different initial pH had a bigger effect to NZVI. However, NZVI/CTMA-Bent had a small impact on NB removal in the different initial pH. This may be related to the buffering effect of silanol groups in the bentonite. In those disequilibrium systems, silanol groups can dissociate and provide protons to maintain the reactions. (2) The efficiency to reduce NB by NZVI/CTMA-Bent is always higher than by NZVI in different initial concentration of NB. According to the GC-MS analysis of reaction products, the intermediate products were nitrosobenzene, azobenzene, azoxybenzene and aniline. However, the reduction product of NB by NZVI/CTMA-Bent was biodegradable aniline.(3) The results indicated that NZVI/CTMA-Bent kept satisfactory long-term stability even in the fourth round. But the removal efficiency by NZVI decreased obviously from65.8%to47.4%. The XPS analysis revealed NZVI/CTMA-Bent exhibited good anti-oxidation performance during NB removal. But the NZVI was oxidated leading to the lower efficiency on the removal of NB. The CTMA-Bent as the carrier of NZVI can help decrease the formation of oxide and hydroxide on iron surface which will reduce the block of reactive site. So it was responsible for the ideal reusability.At last, we investigated the microorganism degradated aniline and hope the concentration of aniline to below detection limits.We carried out some experiments to degrade azo dyes whose nature is similar with the intermediates of nitrobenzene.

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CLC: > Environmental science, safety science > Processing and comprehensive utilization of waste > General issues > Wastewater treatment and utilization
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