Reduction Of Nitroaromatic Compounds Using Nanoscale Zero-valent Iron Confined In Channels Of Ordered Mesoporous Silica

Nanoscale zero-valent iron(NZVI) is prone to agglomerate and be easily oxidized by oxygen in air.Immobilizing of NZVI in or on ordered mesoporous silica can enhance the dispersion and stability of NZVI. While almost of the synthesized NZVI particles could not be encapsulated inside the mesoporous channels in recent research, and hence large metal aggregates would form on the external surface of supports during thermal treatments or reactions.In this work,a novel platelet SBA-15(Zr-Ce-SBA-15) with short and parallel channels and a conventional fiber SBA-15with long and curved pores were synthesized as supports of NZVI.NZVI supported on the two materials was synthesized via "two solvents" impregnation,calcinations followed by H2reduction process.The synthesized materials were charactered by X-ray diffraction,scanning electron microsopy,transmission electron microscopy and N2adsorption/desorption.Nitroaromatic compounds were selected as model compounds to examine the reduction ability of these composites.The results showed that:(1)The composites still matintained the well-ordered patterns after iron nanoparticles were into the supports.α-Fe0nanoparticles were well dispersed in the supports and most of them were confined in mesoporous channels.At the reaction time of12h,the removal efficiency of NB achieved to94.0%in the liquid conducted with NZVI/Zr-Ce-SBA-15and83.9%for NZVI/SBA-15,higher than that non-supported NZVI(56.0%). Besides, NZVI/Zr-Ce-SBA-15possess much higher reduction reactivity for NB than NZVI/SBA-15.It could be proposed that shorter channels mesoporous materials are favorable for the reactants and products diffusion during reactions,and hence reduce the possibility of pore blockage.Nitrosobenzene and phenylhdroxylamine were detected as intermediate products and aniline was the final reductive product.(2)The platelet Zr-Ce-SBA-15with short channels was synthesized as support of NZVI. With increasing the percentage of iron species in composite,the BET surface area,pore size and the total pore volume decreased,but still maintained the well-ordered structure.NZVI/Zr-Ce-SBA-15with was used to remove2,4,6-Trinitrotoluene(TNT) from aqueous solution.The removal rate of TNT increased as the percentage of iron species in composites and dosage increased.The acidic condition was conducive to enhancement of reaction rate.but the alkaline condition prevented the reaction rate.The removal rate of TNT decreased as the initial concentration of TNT increased. With the analysis of the FTIR,there was amido-group in the reductive products of TNT by NZVI.