2 Photo-Fenton Catalyst
2.1 Fe-PILC Synthesis
The catalyst used to conduct the study described here was an iron-pillared clay
(Fe-PILC), and it was prepared by the method reported by Martin del Campo and
Valverde [11, 13] as follows: 300 mL FeCl 3 Á6H 2 O (aqueous solution 0.2 M) was
slowly added to 600 mL of NaOH aqueous solution 0.2 M at room temperature
under continuous stirring. The so obtained mixture was stirred for 4 h at room
temperature and pH between 1.78 and 1.8 using hydrochloric acid 5 M. These pH
values are important in order to generate the corresponding iron hydroxides in
solution. The pillaring solution was slowly added to the 0.1 wt% aqueous bentonite
suspension under stirring. The next step was to recover the clay by centrifugation
and washed with distilled and deionized water in order to remove the chlorides. The
product was dried overnight at 75
C and calcined for 2 h at 400
C. For this
synthesis, the following reagents were employed sodium hydroxide (NaOH), ferric
chloride hexahydrate (FeCl 3 Á6H 2 O with purity of 99%), and hydrochloric acid
(37%). Moreover, deionized and distilled water were provided by HYCEL and
bentonite (pure grade) supplied by Thermo Fisher Scientific. This clay has a particle
size >2 μm and a cation exchange capacity of 94 meq/100 g.
2.2 Fe-PILC Characterization
Figure 1 is the diffractogram of iron-pillared clay (Fe-PILC). This XRD pattern was
obtained by a Bruker Advance 8 instrument using Cu-Kα radiation at 35 kV and
30 mA and was collected from 0 to 40
(2θ) with a step of 0.04
/min. At 4
(2θ), a
small reflection that is commonly associated with pillaring processes can be
observed [11, 14]. Three reflections of interest are observed, the first at 20
corresponding to (FeO(OH), the other two at 26 and 35 related to hematite
(Fe 2 O 3 ) [15].
Figure 2 shows the room temperature Mössbauer spectrum of pure bentonite, and
it was fitted with two doublets. One doublet with isomer shift δ ¼ 0.32 mm/s and a
quadrupole splitting ΔQ ¼ 0.44 mm/s corresponding to Fe
3+ in octahedral site and
the other one with δ ¼ 1.02 mm/s and ΔQ ¼ 2.95 mm/s corresponding to Fe
2+ [16–
19]. The ratio Fe
2+ /Fe
3+ in this bentonite is unusually high.
Figure 3 shows the Mössbauer spectrum of Fe-PILC at room temperature. We can
see that there is no contribution of Fe
2+ to the signal probably because Fe
2+ ions
migrated to Fe
3+ into the pillared clay layers [20, 21] or because Fe
2+ stabilizes the
formation of Fe 3 O 4 . The Fe-PILC Mössbauer data was fitted with three doublets, one
of them corresponding to Fe
3+ in octahedral site of bentonite with δ ¼ 0.36 mm/s and
ΔQ ¼ 0.43 mm/s, another with δ ¼ 0.36 mm/s and ΔQ ¼ 0.69 mm/s corresponding
to Fe
3+ in γ-FeOOH [22–24], and the doublet with the major contribution, with
244
R. Natividad et al.
2.1 Fe-PILC Synthesis
The catalyst used to conduct the study described here was an iron-pillared clay
(Fe-PILC), and it was prepared by the method reported by Martin del Campo and
Valverde [11, 13] as follows: 300 mL FeCl 3 Á6H 2 O (aqueous solution 0.2 M) was
slowly added to 600 mL of NaOH aqueous solution 0.2 M at room temperature
under continuous stirring. The so obtained mixture was stirred for 4 h at room
temperature and pH between 1.78 and 1.8 using hydrochloric acid 5 M. These pH
values are important in order to generate the corresponding iron hydroxides in
solution. The pillaring solution was slowly added to the 0.1 wt% aqueous bentonite
suspension under stirring. The next step was to recover the clay by centrifugation
and washed with distilled and deionized water in order to remove the chlorides. The
product was dried overnight at 75
C and calcined for 2 h at 400
C. For this
synthesis, the following reagents were employed sodium hydroxide (NaOH), ferric
chloride hexahydrate (FeCl 3 Á6H 2 O with purity of 99%), and hydrochloric acid
(37%). Moreover, deionized and distilled water were provided by HYCEL and
bentonite (pure grade) supplied by Thermo Fisher Scientific. This clay has a particle
size >2 μm and a cation exchange capacity of 94 meq/100 g.
2.2 Fe-PILC Characterization
Figure 1 is the diffractogram of iron-pillared clay (Fe-PILC). This XRD pattern was
obtained by a Bruker Advance 8 instrument using Cu-Kα radiation at 35 kV and
30 mA and was collected from 0 to 40
(2θ) with a step of 0.04
/min. At 4
(2θ), a
small reflection that is commonly associated with pillaring processes can be
observed [11, 14]. Three reflections of interest are observed, the first at 20
corresponding to (FeO(OH), the other two at 26 and 35 related to hematite
(Fe 2 O 3 ) [15].
Figure 2 shows the room temperature Mössbauer spectrum of pure bentonite, and
it was fitted with two doublets. One doublet with isomer shift δ ¼ 0.32 mm/s and a
quadrupole splitting ΔQ ¼ 0.44 mm/s corresponding to Fe
3+ in octahedral site and
the other one with δ ¼ 1.02 mm/s and ΔQ ¼ 2.95 mm/s corresponding to Fe
2+ [16–
19]. The ratio Fe
2+ /Fe
3+ in this bentonite is unusually high.
Figure 3 shows the Mössbauer spectrum of Fe-PILC at room temperature. We can
see that there is no contribution of Fe
2+ to the signal probably because Fe
2+ ions
migrated to Fe
3+ into the pillared clay layers [20, 21] or because Fe
2+ stabilizes the
formation of Fe 3 O 4 . The Fe-PILC Mössbauer data was fitted with three doublets, one
of them corresponding to Fe
3+ in octahedral site of bentonite with δ ¼ 0.36 mm/s and
ΔQ ¼ 0.43 mm/s, another with δ ¼ 0.36 mm/s and ΔQ ¼ 0.69 mm/s corresponding
to Fe
3+ in γ-FeOOH [22–24], and the doublet with the major contribution, with
244
R. Natividad et al.