Preparation Of Iron-based Nanocomposites And Their Applications On Refractory Organics Removal

With an explosion of improving urbanization, and rapid development of industry and agriculture, the environmental pollution is getting more serious and displaying diversity on pollution components and patterns. Meanwhile, the self-purification capacity of the natural environment, and the development of techniques for environmental control and remediation can not keep pace with the increasing pollution rate, leading to the growing crisis in environmental contamination issues. Thus, it is imperative to explore and improve economical, effective and environmental-friendly materials and techniques. Based on previous studies, iron-based materals including FeS2 and nanoscale zero-valent iron (nZVI) were modified with graphene oxide (GO) or chitosan (CS). New advance oxidation techniques were also developed based on the resulting composites for the removal of 4-chlorophenol (4-CP), antibiotics in water and atrazine, acetochlor in soil. The main contents of this work include:(1) High-dispersive FeS2/graphene oxide composite (FeS2@GO) was prepared via a one-pot hydrothermal process, which was used for aqueous 4-CP removal. FeS2@GO was more dispersive and Fenton reactive compared to naked FeS2 crystals. Under acidic and slight alkaline conditions, FeS2@GO demonstrated an excellent capacity to remove 4-CP. More than 97% of 4-CP (Co=128.6 mg/L) was eliminated within 60 min in pH 7.0 reaction solutions initially containing 0.2 g/L FeS2@GO and 50 mM H2O2 at 25℃. The removal of 4-CP was further enhanced with increasing FeS2@GO loading. In the meantime, the FeS2@GO also achieved a lower iron leaching and a more complete TOC removal compared with FeS2. Furthermore, acetic acid, oxalic acid and chloroacetic acid were identified as the carboxylic acid by-products. The remarkable capacity of the FeS2@GO-based Fenton system in removing 4-CP displays its potential application in the treatment of organic compound-contaminated water. Though modification by GO enhanced the catalytical activity, the difficulty of catalyst separation in heterogeneous system limits its applications. The huge surface area and controlable hydrophilicity of GO makes it an excellent sorbent for aqueous organics. Applicablity of materials is going to be enhanced if the separation issue was overcome.(2) A novel composite GO/nZVI with macroscopic structure was prepared via the self-assembly of GO and nZVI. Besides, a pH-responsive and magnetically separable dynamic system based on GO/nZVI was established for rapid adsorption and oxidative degradation of micro-antibiotics. At pH< 9, GO/nZVI can fast adsorbe both quinolones and tetracyclines antibiotics. Take enrofloxin (ENR, Co=40μg/L) as the example, in solutions with different chemical conditions, over 97% of ENR were removed within 5 min, and low pH facilitated adsorption process. After adsorption, GO/nZVI was conveniently separated by magnetic system and put into NaOH solution (0.1 M) for regeneration. It is observed that at pH> 9, GO/nZVI disassembles partly upon increasing pH value, and antibiotics were eluted into solution. As a result, it can be oxidative removal by ozonation. The pH-responsive GO/nZVI system exhibited high removal efficiency, high reusability and easily separability, making it a promising method for treatment of water with low concentration contaminants.(3) Single material or technique can not effectively solve actual issues in view of the fact that actual pollution medium and treatment conditions are complicated. Practical issues required integration of approriate materials and feasible techniques. As a result, an applicable chitosan/nanoscale zero-valent iron (CS/nZVI) was prepared as sorbent. Also, an in situ soil remediation technique combined with activated solubilization, adsorptive enrichment and oxidative degradation was proposed. In this process, organic contaminants were first transferred into leaching well by the solubilization effect of cyclodextrin. Then the dissolved contaminants were sorbed by CS/nZVI, achieving the purpose of soil remediation. It was found that hydroxypropyl-β-cyclodextrin (HP-β-CD) exhibited the most obvious solubilization effect on atrazine and acetochlor. When soil solution contained 15% HP-β-CD,58% of atrazine and 42% of acetochlor can release to solution after 96 h. The field study exhibited that CS/nZVI was effective on atrazine and acetochlor adsorption in soil solution,90% of atrazine and 88% of acetochlor were sorbed after 120 min. Finally, CS/nZVI was separated using magnet and was regenerated in NaOH solution by ozone. CS/nZVI is applicable and reusable. The subsequent field experiments confirmed that more than 80% of atrazine and acetochlor were eliminated in 14 d.