Sourav Biswas

National Institute of Technology, Durgapur, Chemistry, Graduate Student

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Template-free synthesis of flower-shaped zero-valent iron nanoparticle: Role of hydroxyl group in controlling morphology and nitrate reduction

by Sourav Biswas, Suvanka Dutta, and Rajnarayan Saha

Well-dispersed single phasic flower-like zero valent iron nanoparticles have been synthesized und... more Well-dispersed single phasic flower-like zero valent iron nanoparticles have been synthesized under aer-obic conditions using a facile approach without the addition of any additives or templates. The role of hydroxyl groups of polyhydroxy alcohols in controlling surface morphology of nanoparticles has been thoroughly investigated. The obtained nanoparticles have been characterized by TEM, FE-SEM, XRD and BET surface area analyzer. Electron microscopy analyses reveal that the solvent plays a pivotal role in determining the morphology of the particles. With increase in viscosity of the solvent, formations of 'petal-like' structures, which are joined at the center are formed. The nitrate removal efficiency of the iron nanoparticles synthesized in different solvents has been studied and it is seen that the ''flower-like " iron nanoparticles were most active in the removal of nitrate. Experiments have been done by varying (i) nitrate concentrations, (ii) nanoparticle dose, and (iii) type of nanoparticles. The results conclude that highest removal efficiency ($100%) was achieved when the nanoparticle dose was 2.88 g/L, even for high nitrate concentrations up to 400 mg/L. The major highlight of this work is the fact that even though the nanoparticles synthesized in glycerol-water mixture have larger size in comparison to the other nanopar-ticles, still they remove the nitrates with highest efficiency. "

$glycol-water (Eth-gly-NP) and glycerol-water (Gly-NP). The as- prepared nanoparticles were characterized with different physico-chemical techniques and finally used as a reducing agent to reduce nitrate. A structure-activity correlation is aimed to see the effect of morphology of nZVI particles on nitrate reduction. Fig. 1 represents the X-ray diffraction patterns of the as-prepared samples. All three samples have characteristic diffraction lines near$

$Fig. 3. (a)-(c) FESEM and (d)-(e) TEM of as-prepared iron nanoparticles synthesized in water-ethanol, water-ethylene glycol, and water-glycerol medium respectively. 44.5° which is characteristic of (011) set of planes of zero valent iron (ICSD Card No. 98-002-1567). Two other diffraction lines (marked with asterisk) were also observed for the sample that was grown using ethanol-water mixture as solvent. These peaks match well with (311) and (511) set of plane of Fe30,4 (ICSD Card No. 029129). Such presence of Fe30, along with Fe is found to be completely absent in case of the samples, which were grown either using ethylene glycol-water mixture or glycerol-water mixture. The as-synthesized powder samples were further characterized by electron microscopy to ascertain the morphology as well as compositional analysis. The BET surface area analysis of the parti- cles (Fig. 2(a) and (b)) reveal that those Eth-NPs have larger surface area (65.74 m? g~') in comparison to Gly-NPs which have surface area value of (49.46 m? g~'). Fig. 3(a) displays the FE-SEM image of the as-grown nanoparticles in ethanol, which shows that the nanoparticles are agglomerated to form chain like structures. The detailed TEM analysis (Fig. 3(d)) shows that the particles are hav- ing diameter of approx. 20 nm. A shell layer of thickness ~3 nm is also observed around every individual nanoparticle. This may occur due to the rapid formation of oxide layer. The chain-like clus- tering is more much more prominent in FE-SEM image (Fig. 3(a)) which is likely due to the highly magnetic nature [39,49] of the as-grown nanoparticles. The characteristic EDX spectra (spectra not shown) shows that there is no presence of any other impurity than iron and oxygen in the as- grown samples. In the next process, the reaction medium of the synthesis was changed to water- ethylene glycol mixture. In this case, the FESEM image (Fig. 3(b)) shows the presence of spherical particles of dimension ~70 nm. Agglomeration of particles is found to be reduced noticeably as compared to the particles that were grown in ethanol-water med- ium. The TEM images (Fig. 3(e)) show that the particles are sheathed with some flaky material. The EDX spectra here also con- firm the presence of only iron with no other impurities. Further, the reaction medium was modified with a mixture of more viscous solvent i.e. glycerol along with water. In this case also, formations of spherical particles were observed (Fig. 3(c)). The TEM image (Fig. 3(f)) shows very interesting observation. Instead of agglomer- ated nanostructures, individual nanoparticles are found to be formed here. Unlike the Eth-gly-NP sample, no flaky material is present here. A closer look reveals that many petals like structures$

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