Supporting Information

Manganese incorporated iron(III) oxide-graphene magnetic nanocomposite: Synthesis, characterization and application for the arsenic(III)-sorption from aqueous solution

Debabrata Nandia, Kaushik Guptaa, Arup Kumar Ghosha, Amitabha Deb,

Sangam Banerjeeb and Uday Chand Ghosha*

aDepartment of Chemistry & Biochemistry, PresidencyUniversity, 86/1 College Street, Kolkata-700073, India

bChemical Science Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata-700073, India

*Corresponding author, e-mail: Tel: 913322413893 Fax: 913322413893

Chemicals:Graphite Flake (Alfa Aesar, England) used for the graphene synthesis and Arsenic(III) oxide (As2O3, purity: 99.99 %), used for the preparation of stock solution, was of analytical reagent (BDH, England). The other chemicals such as hydrazine hydrate (N2H4.H2O), ammonium ferric sulphate hexa hydrate ((NH4)2Fe(SO4)2 · 6H2O), potassium permanganate (KMnO4) ,ferric chloride hexa hydrate (FeCl3· 6H2O), sodium hypochloride(NaOCl), hydrochloric acid (HCl), sulfuric acid (H2SO4) and sodium nitrate (NaNO3) used were guaranteed reagent and purchased from E. Merck (India) Ltd., Mumbai excepting sodium hydroxide(NaOH) (SD Fine Chemicals, India) and manganous chloride hexa hydrate (MnCl2 · 6H2O) (Loba Chemie, India) were of laboratory reagent grade samples.

Analytical tools for characterization:

The powderX-ray diffraction (XRD) patterns of samples were taken using an X-ray diffractometer (Philips Analytical PW-1710) equipped with Cu Kα radiation at a scanning speed 0.4° minute-1 between the angle 10° and 70° operated at voltage 40 kv and applied potential current 30mA.Raman scattering measurements were performed in the back scattering configuration using micro-Raman Jobin Yvon T64000 system to establish the bond formation among different species.Scanning electron microscopic (SEM) (Tescan Vega, U.K.; model LSU+) images were recorded for the sample by mountingon copper grids.Transmission electron micrograph (TEM) images were recorded on a H800 transmission electron micrograph operated at 200 kV. The sample for the TEM was dispersed in isopropanol by sonication, and the drop cast onto 200 meshes copper grids coated with a holey carbon film.Atomic force microscopic (AFM) images were recorded on a commercial Nanoscope-III (Digital Instruments, Santa Barbara, CA) using optical beam deflection to monitor the displacement of a micro fabricated silicon cantilever having a spring constant of 80 N.m-1.The Föurier Transform Infrared (FTIR) spectra of samples were recorded by the Jasco 680 plus (Japan) spectrophotometer with a resolution of 2 cm-1 taking the thin film of samples that made by mixing with spec pure KBr in a ratio 3:100.The specific surface area and pore width distributions were analysed by Quatachrome Autosorb-1C surface analyzer.

Stock As(III) solution.A stock of standard As(III) solution (1000 mg. L-1) was prepared by dissolving 348.5 mgAs2O3in arsenic free 4% NaOH solution in 1.0 L volumetric flask, and placed in a refrigerator. The measured volume of the stock was diluted to a desired level for a required As(III) concentration with 0.2 % (v/v) HCl.The stock was prepared afresh after an interval of fifteen days.

Arsenic analysis. Arsenic samples were analyzed by hydride generator atomic absorption spectrophotometer (Perkin Elmer, Aanalyst 200) and UV-VIS spectrophotometer (Hitachi, model U3210) using the methods as described in ‘Standard Methods for the Examination of Water and Wastewater’ by AWWA, APHA and WEF (1998).

Sorption experiments

Batch experiments were conducted to determine the amount of As(III) sorption by graphene-based super paramagnetic iron-manganese oxide nano composite (GC)from the aqueous phases. Experiments were set inside the well caped PET bottles of capacity 0.25 L. Here, 25 mg GC was mixed with 50mlof aqueous As(III) solution (ionic strength, I = 0.01M adjusted by NaNO3 solution) at some designated initial pH (pHi), adjusted by 0.1 M solution of HNO3 and/or NaOH. The reaction mixtures were agitated by a fixed speed (ST) = 280 (± 5) rpm at temperature (T) = 300 (± 1.0) K for a duration of 2.5 hours.

Effects of pHi on the sorption of As(III) by the materials from aqueous solutions (initial As(III) concentration, CI = 5.0 mg.L-1) were investigated using the set up and conditions described above at separate pHi 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0 and 10.0. The solid materials were separated fro the agitated (2.5 hours) reaction mixtures by applying 0.3 tesla magnetic field externally.The equilibrium pH (pHf) (ELICO model LI-127) and the As(total) concentrations (CR, mg.L-1) remained were analysed from the supernatant.

Experiments for the kinetics of As(III) sorption reaction with GC were carried out maintaining other conditions as described in first paragraph. Here, 0.25 g GC was mixed with 500 mlof As(III) solution (C0 = 1.84 and 4.3 mg. L-1 at pHi = 7.0 ± 0.1) into a glass beaker of capacity 1.0 L, and agitated at ST = 280 (± 5) rpm at room temperature (300 K). The change of pH, if any, was monitored at an interval of 15 minutes, and adjusted with 0.1M solution of HNO3 and/or NaOH, as required. Samplings from the reaction mixture of size 5.0 and 10 ml were done at first three and next stages, respectively, at an interval of time 5 and 10 minutes, which were centrifuged and analyzed for the CR of arsenic.

Isotherm experiments for the equilibrium of As(III) sorption reaction with GC were carried out using C0of As(III) ranged in 1.0to8.0mg.L-1 (pHi = 7.0 ± 0.1) by the batch procedure. Other conditions fixed up for the experiments were as described at first paragraph of this sub-section. The pH of each reaction mixture was checked at time (t) = 0.5 and 1.5 hours of agitation from t = 0. The major change of pH, if noted any, was adjusted using specified acid/alkali solution. The CR of arsenic was analyzed from the centrifuged solutions.

Calculation of As(III) sorption amount.Amount of As(III) sorption by theGC at equilibrium (or any time, t), qe (or qt) was calculated using this equation, qe (or qt) = [(C0 – CR)×(V/W)], where V is the volume (L) of test solution, W the mass (g) of GC and the significances of C0 and CR are given earlier.

FIGURES

Fig. S1A -XRD pattern of IMBO calcined at (a) 373K, (b) 473K, (c) 573K, (d) 673K and (e) 773K.

Fig.S1B- XRD pattern of (a) GO, (b) GR, (c) GC.

Fig. S2- FTIR spectra of (a) IMBO, (b) GC, (c) Graphite powder, (d) GO, and (e) GR.

Fig.S3 - FT-IR spectra of pure composite (GC) and As(III) sorped GC.