Aero-Gel Based Cerium Doped Iron Oxide Solid Solution for Ultrafast Removal of Arsenic

Abstract

A solid solution of aero-gel based cerium doped iron oxide nanoparticles has been utilized for the first time for ultrasonic wave assisted adsorptive removal of arsenic from aqueous medium. The FE-SEM and HR-TEM images revealed a novel morphology of hollow architectures with irregular distribution in sizes in which the particles are interconnected with each other in a long-range network. The HR-XRD analysis indicated the cubic fluorite type structure with Fm3̅ m space group which is retained even after adsorption of As(III). The Raman study and Lebail refinement confirmed the formation of solid solution of Fe and Ce oxide nanoparticles. The room temperature ferromagnetism was observed for CeO 2 NPs (Ms 0.0209 emu g −1 ) which is attributed to higher concentration of oxygen vacancies and increased (Ms 0.0287 emu g −1 ) after doping of iron. The adsorption pattern of As(III) is well-defined by Redlich−Peterson isotherm while the adsorption is governed by pseudo-second-order kinetics. The HR-XPS and diffuse reflectance spectroscopy revealed the formation of variable oxidation state of metal ions which facilitate the oxidation of As(III) (more toxic) to As(V) (less toxic) during adsorption process. The effective removal of arsenic (more than 80%) was observed within 2.5 min of initial adsorption process and approximately 99% removal was achieved within 10 min of adsorption. The adsorption capacity of our best adsorbent was found to be 263 mg g −1 . The effect of pH and interfering ions on adsorption capacities of synthesized adsorbents revealed its efficacy over the wide range of pH.

Hollow Polyaniline Microsphere/Fe3O4 Nanocomposite as an Effective Adsorbent for Removal of Arsenic from Water

“…Here, the steeper slope indicates the rapid extraction of solute, which is directed by surface or film diffusion. The gradual slope, where the equilibrium has been reached, indicates slow adsorption attributed to intra-particle or pore diffusion 50,51 . Corresponding intra-particle diffusion model parameters for As(III) and As(V) are presented in Table S2.…”

“…6a corresponds to O 1 s (~530 eV), N 1 s (~399 eV), C 1 s (~258 eV), and Fe 2p (~723 eV and ~710 eV) indicating the presences of PANI as well as Fe 3 O 4 in the composites material 25,28 . In addition, another peak also appeared around ~42-46 eV in spent adsorbent, in all possibility due to the presence of As(III) on the surface of PNHM/Fe 3 O 4 -40 25,51 . According to available literature, spectra of Fe 2p consist of Fe 2+ as well as Fe 3+ 51,65 .…”

“…6c. The calculation based on XPS shows the presence of relatively more Fe 2+ (~58.55%) compared to Fe 3+ content (~41.44%) in spent adsorbent due to redox reaction after adsorption of As(III) 51 . Further, Fig.…”

“…6d shows the appearance of two peaks in XPS spectra of As 3d due to the presence of both As(III) (~43.70 eV) and As(V) (~44.40 eV) and their content corresponding to ~42.02 and 57.98%, respectively 13,51 . These findings further strengthen the fact that Fe 3+ present in PNHM/Fe 3 O 4 -40 plays an imperative role in oxidizing As(III) (more toxic) to As(V) (less toxic), followed by adsorption 51,66 .…”

“…Accordingly, arsenic oxyanion (AsO 3 3− ) is adsorbed on the surface of adsorbent by forming a complex with protonated surface hydroxyl (−FeOH 2 + ) groups originating from PNHM/Fe 3 O 4 -40 at pH < 7.7 (PZC), illustrated schematically in Fig. 7 42,51 . In all probability, the higher extent of inner-sphere complex formation via hydrogen bonding, as well as electrostatic attraction between arsenic species and surface hydroxyl group in PNHM/Fe 3 O 4 -40, could account for such superior adsorption capacity compared to other composite adsorbents 16,51,53 .…”