Fabrication and Characterization of Novel Iron Oxide/ Alumina Nanomaterials for Environmental Applications

Abstract

One-dimensional (1D) nanomaterials such as nanowires, nanotubes, nanorods, nanofibers and nanobelts have drawn a lot of attention because of their novel and unique properties and a wide range of applications. In particular, ceramics and polymers with 1D nano-architectures have received increasing interest since it provide a good material system to investigate the shape, size and dimensionality dependent electrical, optical, thermal and mechanical properties. 1D ceramic nanomaterials with their large surface-to-volume ratio shows the tremendous application potential in various fields. Recent research focused on the applications of nanomaterials for environmental clean-up and preventing environmental pollution. Using nanomaterials to solve environmental issues will become an inexorable trend in the future. Developing simpler and versatile approach to synthesize one dimensional nanostructure still remains a technical challenge. In the past few decades a large number of synthesis techniques have been adopted world wide by many researchers.
In the present study we have chosen three convenient bottom-up methods such as sol-gel, hydrothermal and electrospinning method for synthesis of boehmite (AlOOH), alumina (Al2O3) and Fe2O3-Al2O3 mixed oxide composite nanomaterials. The synthesized boehmite, alumina and their mixed oxides nanocomposite were characterized by UV-Vis, FT-IR spectroscopy, SEM, TEM, XRD, BET surface area, TGA-DTA, and AAS analytical techniques.
The SEM and TEM images of the synthesized nanomaterials confirm the formation of 1D nanostructures. The XRD studies indicate the formation of different crystalline phases of aluminum and iron oxides nanomaterials. The obtained nanomaterials and nanocomposites were used as adsorbents for environmental applications, especially decontamination of toxic metal ions like Cr (VI), Pb (II), Hg (II), Ni (II), fluoride ions and organic dye from aqueous solution. Batch experiments were carried out for adsorption studies by varying pH, contact time, adsorbent dose and initial concentration. Furthermore, the kinetics and isotherm studies have also been investigated. The needle shaped boehmite nanomaterials synthesized by sol-
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gel method have been used for removal of Congo red. It shows 99% removal of Congo red within a short contact time of 10 min and removal capacity of 198 mg/g. Similarly, alumina nanofibers of diameters in the range of 100-500 nm were synthesized by electrospinning method and have been used for adsorption of Cr (VI) and fluoride ion from aqueous solution.
We have also synthesized iron oxide-alumina mixed oxide nanocomposite in two different methods such as hydrothermal and electrospinning. These as prepared materials have been sintered in air at different temperatures to obtain alpha and gamma crystalline phases. The gamma phase mixed oxide nanocomposite synthesized by hydrothermal method has been found to be very efficient adsorbent for removal of Congo red and adsorption capacity was found to be 498 mg/g. However, electrospun mixed oxide nanocomposite shows better result for removal of toxic metal ions such as Cu2+, Pb2+, Ni2+ and Hg2+. The removal percentage was found to be in the order of Cu2+ < Pb2+ < Ni2+ < Hg2+.
Furthermore, we have also synthesized PAN-Ag composite nanofibers by electrospinning method. Here, the surface of PAN nanofiber was functionalized with 5-15 nm sized spherical silver nanoparticles. From the TEM studies it was observed that, nano-sized silver particle were uniformly distributed on the surface of PAN nanofibers. These composite nanofibers membrane has been used for antibacterial studies which show promising anti-bacterial properties against E.coli, S.aures and S.bacillus microorganisms.