Sample preparation
In the single-reverse microemulsion technique, just one reverse microemulsion is used. The
reverse microemulsion used for this study consisted of CTAB as surfactant (s), 1-butanol as cosurfactant (cs), and cyclohexane as oil phase (o). In all of the reverse microemulsions, the mass ratio
of (cs) to (s) was 1.5. An aqueous solution (w) of FeCl3.6H2O (0.75 M; Sigma-Aldrich, assay > 99%) and
M2+ salt (0.75 M; iron (II) chloride tetrahydrate - Merck, 99%, nickel (II) nitrate hexahydrate - SigmaAldrich, 99%, copper nitrate hydrate - Sigma-Aldrich, 98%, or manganese nitrate tetrahydrate - Merck,
99%) containing a total metal concentration of 1.5 M was added dropwise to four different ratios of
the mixture (s+cs):(o) for mass ratios of 0.2 (A1), 0.4 (A2), 0.6 (A3), and 0.8 (A4). All solutions of
different salts behaved similar trends in the formation of the microemulsions. The experimental
details of the Fe3+/Fe2+ microemulsions will be taken as example for other microemulsions in this
study.
In Fig. S1, the compositions of the Fe3+/Fe2+ microemulsions used for this study are shown with
the aid of a triangle diagram. In this diagram, the initial (s+cs):(o) ratios (0.2, 0.4, 0.6 and 0.8) are
shown on the base of the triangle. The addition of FeCl 3.6H2O (0.75 M) + FeCl2.4H2O (0.75 M) took
place upwards along the dashed lines A1- A4.
During the addition of the aqueous mixture of salts, FeCl 3.6H2O + FeCl2.4H2O, into the (o) + (s) +
(cs) mixtures, the conductivity (σ) of the solution was affected. The variation in conductivity was
studied using a bench-top Hanna conductivity meter kept at 25 °C with circulating water from a
controlled temperature stabilizer. The obtained results are shown in Fig. S2 in the form σ = f (φ), as
well as in the form dσ/dφ= f (φ). The fraction φ is equal to V w/(Vw+Vo+Vs+Vcs), where Vw is the volume
of aqueous phase, Vo is the volume of oily phase, Vs is the volume of surfactant, and Vcs is the volume
of co-surfactant. The volume of surfactant (Vs) was not taken into account since the volume of CTAB
as a solid was negligibly small.
Fig. S2 shows that a gradual increase in φ (aqueous ratio) results in an increase in conductivity
(σ), because both the number and the size of the micelles increase. The variation of dσ/dφ= f (φ) is
also shown in Fig. S2. The conductivity maximum can be attributed to the saturation of the micelles
and the percolation phenomenon [Košak et al., 2004]. When more water was added to the system, it
led to a phase separation, and conductivity was lowered. The point (P) in Fig. S2 is the saturation
point. The larger the region between the initial and maximum conductivity, the greater the W/O
micelle region, and the better the system is for producing a microemulsion [1].
In the triangular diagram shown in Fig. S1, we have chosen one point (A) corresponding to
microemulsion A4 for preparing the different solids, designated FFO, FNO, FCO, and FMO referring to
Fe3O4, NiFe2O4, CuFe2O4, and MnFe2O4 respectively. The composition of the chosen point (A), as
shown in Fig. S1, was (s) = 15 g, (o) = 31.25 g, (cs) = 7.5 g and (w) = 13 g. The corresponding solids
were developed by adding an aqueous NH4OH solution (4 M) to the vigorously stirred microemulsion
A4 as a precipitating agent.
After adding ammonia in excess, a precipitate was formed due to the formation of hydroxide
species. The oxy-hydroxy species was precipitated in the pH range of 8-10 in the presence of
ammonium hydroxide as reagent [2].
The hydroxide mixture was then filtered, washed alternatively three times with deionized water
and an alcohol mixture, and then dried at 100 °C overnight. The dried powder was ground in an agate
mortar and calcined for 4 hours under atmospheric conditions. The final calcination temperature was
selected after thermogravimetric experiments.
Fig. 2 shows that a gradual increase in φ (aqueous ratio) results in an increase in conductivity (σ),
because both the number and the size of the micelles increase. The variation of dσ/dφ= f (φ) is also
shown in Fig. 2. The conductivity maximum can be attributed to the saturation of the micelles and
the percolation phenomenon [3]. When more water was added to the system, it led to a phase
separation, and conductivity was lowered. The point (P) in Fig. 2 is the saturation point. The larger
the region between the initial and maximum conductivity, the greater the W/O micelle region, and
the better the system is for producing a microemulsion [1].
References
[1] Li F, Vipulanandan C, Mohanty KK (2003) Microemulsion and solution approaches to
nanoparticle iron production for degradation of trichloroethylene. Colloids Surf, A 223:103112.
[2] Aman D, Zaki T, Mikhail S, Selim SA (2011) Synthesis of a perovskite LaNiO3 nanocatalyst
at a low temperature using single reverse microemulsion. Catalysis Today, 164:209–213.
[3] Košak A, Makovec D, Drofenik M (2004) The preparation of MnZn-ferrite nanoparticles in
a water/CTAB, 1-butanol/1-hexanol reverse microemulsion. Phys Stat Sol, C 1:3521-3524.
Fig. S1. Phase diagram of the reverse microemulsion system. The conductivity experiments in Fig. S2
were performed along the dotted lines (– – –). The upper bold line (–) corresponds to the upper limits
of the experiment. The dashed dotted line (-..-..-) corresponds to the maximum of dσ/dφ curves in Fig.
S2 and roughly divides the region of the reverse microemulsion from that of bicontinuous
microemulsion. The lower bold line is the approximate limit at the percolation threshold. The point (A)
corresponds to the composition chosen for the synthesis of solids.
Fig. S2. Variation of the conductivity (σ) of the system by the addition of the aqueous solution (●). The
variation of dσ/dφ= f (φ) is also shown. The dashed vertical line separates roughly the reverse region
(left) and bicontinuous region (right) of microemulsion (■).
Fig. S3. DTA and TGA curves of typical (a) FFO, (b) FNO, (c) FCO, and (d) FMO samples.
Fig. S4. Nitrogen adsorption-desorption isotherms of (a) FFO, (b) FNO200, (c) FNO300, (d) FNO450,
(e) FNO700, (f) FCO900, and (g) FMO400 samples.
Fig. S5. BJH desorption pore size distributions of (a) FFO, (b) FNO200, (c) FNO300, (d) FNO450, (e)
FNO700, (f) FCO900, and (g) FMO400 samples.
Fig. S6. EDX spectra of (a) FFO, (b) FCO900 and (c) FMO400 samples.
Fig. S7. Effect of (a) contact time, (b) adsorbent dose and (c) adsorption bed temperature on DBT
adsorption on FMO200 sample.