Synthesis Of Modified Nanoscale Zero-iron And Its Performance And Reaction Mechanism In Remediation Of P-nitrophenol

Recently,aqueous organic contaminant ation has increasingly aggravated.Due to the high reduction reactivity of nanoscale zero-valent iron(NZVI)on degradation of various organic pollutants,in order to enhance the practical performace of the nanomaterial,a series of modified NZVI were prepared and applied to treat the aqueous organics.In this study,two kinds of modified NZVI,including NZVI immobilized on mesoporous silica and sulfidated NZVI,were successfully synthesized,and then applied to test their ability to degrade p-nitrophenol.Several techniques were utilized to characterize their physicochemical properties and the p-nitrophenol degradation mechanisms in anoxic or aeraobic conditions were also thoroughly investigated using a variety of physical and chemical methods.Chapter 2 of the paper investigated the preparation and degradation performance of NZVI immobilized on mesoporous silica(NZVI/SBA-15).Specifically,SB A-15 was firstly prepared via the traditional hydrothermal synthesis method.Then,NZVI/SBA-15 composite was synthesized utilizing the "two solvents" technique.After that,TEM,XPS and N2 ad sorption-desorption techniques were used to study the morphology,structure and main components on the solid.Results showed that abundant ultrasmall nanoscale zero-valent iron particles were formed and well dispersed in the channels or on surface of SBA-15.Batch experiments revealed that p-nitrophenol removal declined from 96.70%to 16.14%as solution pH increased from 3.0 to 9.0.Besides,degradation equilibrium was reached within 5 min.The p-nitrophenol removal was a reductive degradation process,which was proved by the detected intermediates using gas chromatography-mass spectrometry(GC/MS).The excellent antioxidation ability had been discovered with more than 80%of p-nitrophenol being removed by NZVI/SB A-15 treated with 30 days'exposure to air.These results demonstrated the feasible and potential application of NZVI/SBA-15 composites in organic wastewater treatment.Chapter 3 of the paper focuses on sulfidated NZVI(S-NZVI)degrading p-nitrophenol under anoxic or aerobic conditions.In this chapter,a series of S-NZVI materials with different Fe/S molar ratios are prepared by simple ultrasonic treatment of NZVI in Na2S solution.Compared with NZVI,S-NZVI possesses the iron sulfides shell,which boosts the reactivity and hydrophobicity of NZVI.Batch experiments indicated anoxic S-NZVI systems preferred to weaker alkaline solution,whereas aerobic S-NZVI systems performed better in acidic solution.The highest TOC removal efficiencyof p-nitrophenol(17.59%)was achieved in the aerobic S-NZVI system at pH 6.77.revealing that oxygen improved the degradation of p-nitrophenol by excessive amounts of hydroxyl radicals in slightly acidic conditions,and the TOC removal efficiency was supposed to be further improved in moderate acidic solution.Acetic acid,a nontoxic ring opening by-product,confirms that the S-NZVI system could be a promising alternative for noble metal doped NZVI and may be used to treat industrial wastewater containing sulfide ions.