Nanocrystalline Iron Oxide synthesised within Hierarchical

Nanocrystalline Iron Oxide synthesised within Hierarchical Porous Silica Prepared by Nanoemulsion TemplatingManal Hessien, Philippe Léone, Michel Suchaud, Bénédicte LeBeau, Habiba Nouali, Yannick Guari, and Eric Prouzet*

Supplementary InformationMaterials:The following materials were used without further purification: paraffin oil (d= 0.86) (Fluka), deionized water, Sorbitan monooleate (Span 80™, d= 1.08, Mw = 428.6g) (Across) and polyoxyethylene (20) sorbitan monooleate (Tween 80™,d=0.994, Mw =1,310g) (Sigma) . Sodium silicate solution (reagent grade, ~10.6 Na2O and ~26.5 SiO2, d = 1.39) (Sigma-Aldrich), HCl (37%, Sigma-Aldrich), Ammonium Hydroxide (28-30% , d=0.9), Oleic acid ( Technical grade, 90%, C18H34O2, FW= 282.47 g, Aldrich), Sodium oleate (C18H33 NaO2,), and Ferric chloride hexahydrate (FeCl3.6H2O, FW=270.30 g, EMD).Preparation of Nanoemulsions:Nanoemulsions were prepared according to previous reports.1, 2 Nanoemulsions were prepared by dissolving first the surfactants (Tween 80 and Span 80) into paraffin oil, using gentle magnetic stirring for 15 minutes. The required amount of water was added drop-by-drop to the mixture of oil and surfactant under slow magnetic stirring. For samples prepared at different temperatures, both the oil-surfactant mixture and water were first heated up separately to the required temperature in a heating bath before being mixed according to the previous process. The appearance of nano-emulsion depends on the oil droplet size, which is transparent for oil droplet sizes of 65-200 nm and milky for larger droplet sizes.The variation in the Span 80:Tween 80 ratio allowed us to reach different Hydrophilic Lipophilic Balance (HLB), depending on the amount of each surfactant, according to the following relationship:HLBmix = HLBT * T% + HLBS * S% = 15 * T% + 4.3 * S% where HLBT is the HLB for Tween 80 (15), T% is the mass percentage of Tween 80, HLBS is the HLB for Span 80 (4.3), and S% is the weight percent of Span 80. It was demonstrated that the HLB adjustment influences the final nanoemulsion size as a function of the total surface area of surfactants heads resulting from surfactants mixture, instead of a direct effect of the hydrophilic/lipophilic balance.2Preparation of the Hydrolysed Sodium Silicate Solution:For example of a preparation, 70 g of 0.7 M HCl solution was weighted to which 11.12 g of sodium silicate solution was added drop by drop while under stirring. The final pH of the hydrolysed sodium silicate solution was about 2.Synthesis of porous silica:If the nanoemulsion is used as prepared (pH 5-6), its addition to the solution of sodium silicate leads rapidly to the initial transparent solution turning milky, as a result of immediate silica condensation. The same result was observed even when the sequence of addition was changed, with the solution of sodium silicate being added to the nanoemulsion. Therefore, the silica condensation was slowed down by adjusting the pH of nanoemulsion at pH 2, beforehand, by adding the correct amount of a 0.7 M HCl solution to the nanoemulsion. Previous studies showed that the structure of nanoemulsion remains unchanged upon dilution.2

The nanoemulsion/silica gel, was prepared by adding different volumes of the acidified nanoemulsion to a constant volume of sodium silicate solution, with the nanoemulsion over silicate volume ratio being equal to 0, 2.5, 25, 50, 100, and 200 vol.%. The resulting solution was mixed for 2 minutes, and a molar solution of ammonia was added drop by drop until gelling occurred. Details of composition are listed in Table S1. The nano-emulsion/silica gel samples were left for ageing for one week, then freeze dried, calcined at 500 °C under air for 2 hours. They were washed by using a centrifuge to remove sodium chloride then dried again at 75 °C. At this stage, the samples were named hierarchical porous silica. The calcination burns off the paraffin oil and leaves behind only the pores.

Sample 1: porous silica is prepared at room temperature by mixing 2.5 mL of a nanoemulsion and 100 ml sodium silicate solution and 1.4 mL ammonia. This nanoemulsion was prepared at 50°C, with an HLB= 11.7, and a droplet size Dh= 200 nm (determined by DLS). The following table contains the amounts of components of nanoemulsion and sodium silicate solution.

Nanoemulsion= 2.5 mLNanoemulsion= 2.5 mLNanoemulsion= 2.5 mLNanoemulsion= 2.5 mLNanoemulsion= 2.5 mL Sodium silicate solution =100 mL

Sodium silicate solution =100 mL

Ammonia (mL)

Span 80 (g) Tween 80 (g)

Paraffin Oil (g)

Water (g) 0.7 M diluted HCl

(g)

Sodium silicate (g)

0.7 M diluted HCl

(g)

Ammonia (mL)

0.10 0.22 0.21 1.60 0.36 13.85 86.15 1.40

CREATED USING THE RSC COMMUNICATION TEMPLATE (VER. 3.0 OOo) - SEE WWW.RSC.ORG/ELECTRONICFILES FOR DETAILS

ARTICLE TYPE www.rsc.org/xxxxxx | XXXXXXXX

This journal is © The Royal Society of Chemistry [year] Journal Name, [year], [vol], 00–00 | 1

Electronic Supplementary Material (ESI) for Chemical CommunicationsThis journal is © The Royal Society of Chemistry 2012

http://www.rsc.org/xxxxxx


Sample 2: porous silica is prepared at room temperature by mixing 50 ml of a nanoemulsion sample, and 100 mL sodium silicate solution and 2.8 mL ammonia. This nanoemulsion is prepared at 70°C, with an HLB= 11.7 and a droplet size Dh= 65 nm. (Determined by DLS) The following table contains the amounts of components of nanoemulsion and sodium silicate solution.

Nanoemulsion= 50 mLNanoemulsion= 50 mLNanoemulsion= 50 mLNanoemulsion= 50 mLNanoemulsion= 50 mL Sodium silicate solution =100 mL

Sodium silicate solution =100 mL

Ammonia (mL)

Span 80 (g) Tween 80 (g)

Paraffin Oil (g)

Water (g) 0.7 M diluted HCl

(g)

Sodium silicate (g)

0.7 M diluted HCl

(g)

Ammonia (mL)

2 4.4 4.2 32 7.2 13.85 86.15 2.8

Synthesis of the iron oxide/silica materials:The iron–oleate was prepared by reacting iron chlorides and sodium oleate. In a typical synthesis of iron–oleate complex, 40 mmol of iron chloride (FeCl3•6H2O,) and 120 mmol of sodium oleate was dissolved in a mixture solvent composed of 80 ml ethanol, 60 mL distilled water and 140 ml hexane. The resulting solution was heated to 70°C and kept at that temperature for four hours. When the reaction was completed, the upper organic layer containing the iron–oleate complex was washed three times with 30 mL distilled water in a separatory funnel.3 40 mmol of the iron-oleate were finally mixed with 20 mmol of oleic acid as a capping agent and the resulting compound was named iron oleate complex.In a typical preparation of iron oleate nanoemulsion, 80 g paraffin oil, 41.4 g Span 80, 18.6 g Tween 80 and 80 g of iron oleate complex were mixed together and heated at 70°C for 30 minutes, then 180 g water was added drop by drop to oily phase mixture while under stirring. This iron oleate nanoemulsion was acidified at pH 2, before being mixed with a solution of sodium silicate, the resulting iron oleate silica gel being obtained by basic catalysis upon addition of ammonia. When this gel was calcined, the initial iron oleate turns iron oxide. The final amount of iron oxide was adjusted between 8 and 50 wt% by changing the initial amount of iron oleate (20 g or 80 g) added to the nanoemulsion, and also by changing the amount of iron oleate nanoemulsion (2.5 , 25, 50, 100 and 200 mL) added to 100 mL sodium silicate solution.

ExperimentalThe porosity of silica powder samples have been analyzed by mercury intrusion porosimetry (Micromeritics, Autopore IV). This apparatus allows getting pressures between 2.6.10-6 and 400 MPa. Prior to measurements silica powders were degassed at 150°C under vacuum (100 Pa) for about 12 hours. About 40 mg of dried silica powder were introduced in the penetrometer, which was introduced in the low pressure chamber (2.6.10-6 - 0.2). During this first stage, the cell was vacuum and filled by mercury. The penetrometer containing silica powder and mercury was then placed in the high pressure chamber (0.2 - 333 MPa). During this second stage, pressure was applied to force mercury diffusion into porous sample. As intrusion occurs, the mercury level in the stem varies. The Washburn equation [Washburn EW, Phys. Rev. 1921, 17, 273] was used to treat data: Pr = -2σcosθ, where P is the applied pressure, r is the radius of the pore, σ is the interfacial tension and the θ contact angle (for mercury σ = 485mN/m and θ = 130°).The size of the nano-emulsion droplets was studied by dynamic light scattering, using a VASCO DLS granulometer (Cordouan Technologies). This system allowed us to determine the diffusion coefficient of emulsion droplets, even in very concentrated systems, from which the hydrodynamic diameter was deduced by the Stokes-Einstein Equation: D = (kB*T)/(3*π*η*Dh),where D is the diffusion coefficient, η is the viscosity of the emulsion, T is the temperature, kB is the Boltzmann constant, and Dh is the hydrodynamic diameter. A 60 mW monomode red laser (λ = 658 nm) with variable intensity was used, and measurements were carried out at 25°C with a detector set at 135°. The correlator parameters were adapted for each sample (sampling time x number of channels) to collect the whole autocorrelation curve. Accuracy and reproducibility of the results were checked with several measurements ran with various recording times. Most of of the autocorrelation curves were fitted with a single size cumulant model, the lack of polydispersity being checked in parallel with Padé-Laplace fits.4, 5 When the cumulant fit did not converge, we used the Padé-Laplace fit, which still led to single size results. In that case, the value of the Diffusion coefficient cannot be provided.SEM images on gold-coated samples were collected with a LEO FSEM 1530 working at 5 kV. Iron-silica samples for TEM were prepared using extractive replicas of ultramicrotomy techniques deposited onto copper grids. TEM measurements were carried out at 100kV with a JEOL 1200 EXII microscope.The 57Fe Mössbauer spectra were obtained in the constant-acceleration mode and in transmission geometry using a spectrometer composed of devices from Wissel (velocity transducers) and Canberra (interface acquisition). A room-temperature 57Co(Rh) source has been used. Calibration of the velocity scale was done using absorption lines of iron foil, and isomer shifts are given relative to α−Fe. After folding, the spectra (256 channels) were computed with a least-squares routine using Lorentzian lines. Spectra were acquired with a velocity scale of ±7,74 mm/s. The statistical rate for the base line spectra points was 7.4 106.

References1. W. Liu, D. Sun, C. Li, Q. Liu and J. Xu, J. Coll. Interface Sci., 2006, 303, 557-563.2. M. Hessien, N. Singh, C. Kim and E. Prouzet, Langmuir, 2011, 27, 2299-2307.







3. I.-W. Park, M. Yoon, Y. M. Kim, Y. Kim, I. R. Kim, S. Kim and V. Volkov, J. Magnetism Magnetic Mater., 2004.4. J. Aubard, P. Levoir, A. Denis and P. Claverie, Comput. Chem., 1987, 11, 163-178.5. Z. Bajzer, A. C. Myers, S. S. Sedarous and F. G. Prendergast, Biophysics Journal, 1989, 56, 79-93.

Figure S1: SEM micrography of (a,b) silica prepared with an excess of silicate, (c,d) silica prepared with a deficit of silicate.







Figure S2: Preparation of the nanoemulsion/iron oxide/silica gel







Figure S3: EDAX Analysis of the 8% Fe2O3-SiO2 sample: (a) global mapping, (b) local mapping.

Figure S4: XRD of γ-Fe2O3 particles recovered by HF etching of the 50% Fe2O3-SiO2 sample







Nanocrystalline Iron Oxide synthesised within Hierarchical

Documents

Transcript of Nanocrystalline Iron Oxide synthesised within Hierarchical