Photo-catalyzed p-nitrophenol degradation in aqueous dispersions of ferrihydrite and H2O2

Article abstract of DOI:10.1166/jnn.2014.8979

Nitrophenols are hazardous and toxic to living organisms. For this study, ferrihydrite was prepared to test its capabilities for p-nitrophenol degradation. A ferrihydrite particle prepared in neutral environmental conditions is sphere-like with a diameter of 2-4 nm and its total surface area is approximately 229 m²g^-1. The combination of ferrihydrite and trace H₂O₂is effective for the degradation of p-nitrophenol under simulated sunlight irradiation. Hydroquinone, the initial intermediate of p-nitrophenol decomposition, autocatalyses the subsequent degradation of p-nitrophenol because it accelerates the photo-reductive dissolution of ferrihydrite. The effect of key operating parameters such as ferrihydrite dosage, initial solution pH and H₂O₂dosage were also studied on the photocatalytic degradation of p-nitrophenol. The results indicate that the combination of 0.2 g-L^-1ferrihydrite, 0.45 mmol ? L^-1H₂O₂is highly efficient for the degradation of p-nitrophenol (0.15 mmol ? L^-1) at pH 2.5～3.0. A ferrihydrite was reused several times, still keeping its original photocatalysis. Copyright

Full text of DOI:10.1166/jnn.2014.8979

Article
Journal of
Nanoscience and Nanotechnology
Vol. 14, 7325–7332, 2014
Copyright © 2014 American Scientific Publishers
All rights reserved
Printed in the United States of America
www.aspbs.com/jnn
Photo-Catalyzed p-Nitrophenol Degradation in
Aqueous Dispersions of Ferrihydrite and H O
2
2
Yongjuan Wu1
ꢀ2ꢀ3ꢀ4
, Rufen Chen , Hui Liu , Yu Wei , and Dong Wu
3
3
3ꢀ∗
1
1
Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
Key Laboratory of Inorganic Nanommaterials of Hebei Province, Hebei Normal University,
Shijiazhuang 050086, China
3
4
Huihua College of Hebei Normal University, Shijiazhuang 050091, China
Nitrophenols are hazardous and toxic to living organisms. For this study, ferrihydrite was pre-
pared to test its capabilities for p-nitrophenol degradation. A ferrihydrite particle prepared in neutral
environmental conditions is sphere-like with a diameter of 2–4 nm and its total surface area is
2
−1
approximately 229 m ·g . The combination of ferrihydrite and trace H O is effective for the degra-
2
2
dation of p-nitrophenol under simulated sunlight irradiation. Hydroquinone, the initial intermediate of
p–nitrophenol decomposition, autocatalyses the subsequent degradation of p-nitrophenol because
it accelerates the photo-reductive dissolution of ferrihydrite. The effect of key operating parameters
such as ferrihydrite dosage, initial solution pH and H O dosage were also studied on the photocat-
2
2
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−
1
alytic degradation of p-nitrophenol. The results indicate that the combination of 0.2 g·L ferrihydrite,
IP: 130.63.180.147 On: Wed, 13 Aug 2014 13:01:11
−1
−1
0
.45 mmol · L H O is highly efficient for the degradation of p-nitrophenol (0.15 mmol · L ꢀ at
Copyright: American Scientific Publishers
2
2
pH 2.5∼3.0. A ferrihydrite was reused several times, still keeping its original photocatalysis.
Keywords: Photocatalysis, p-Nitrophenol, Ferrihydrite, H O .
2
2
1
. INTRODUCTION
with many organic compounds. Among the AOPs, Fenton
2
+
p-Nitrophenol (p-NP) is a highly toxic, stable, and biore-
fractory chemical in the environment due to the presence
of a nitro-group in the aromatic ring. It widely exists
in industrial wastes derived from farm chemicals, phar-
maceuticals, and synthetic dyes. Current technologies for
the removal of p-NP include physical (e.g., screening,
mixing, flocculation, sedimentation, floatation, filtration,
microwave, radiation, extraction, adsorption, etc.), biologi-
cal (e.g., biodegradation), and chemical (e.g., electrochem-
istry, precipitation, photocatalysis, disinfection, chemical
oxidation, etc.) methods. Combination of these different
methods has been used to achieve more efficient degra-
dation of organic compounds. Advanced oxidation pro-
cesses (AOPs) such as O /H O , O /UV, UV/H O ,
Fe /H O , and photocatalytic oxidation
be effective for the decomposition of organic compounds.
These processes are based on the generation of reactive
(Fe /H
2 2
O ꢀ and Fenton-like processes are some of the
most attractive methods because their reagents are environ-
1
4
mentally benign and abundant in the earth’s crust. Previ-
1
5–17
ous studies
have described the degradation of organic
pollutants in Fenton or Fenton-like processes. Few reports
have been found for the degradation of p-NP in a Fenton-
like processes under solar light irradiation.
Ferrihydrite (FH), a poorly crystalline Fe(III) oxyhy-
droxid, is a common Fe(III) (hydr)oxide in soils and
1
8
sediments undergoing fluctuating redox conditions. Due
to its high surface area and intrinsic reactivity, ferrihydrite
serves as a dominant sink for numerous metals (e.g., As)
and nutrients (e.g., P). Ferrihydrite is also considered the
most (bio) available Fe(III) (hydr)oxide for dissimilatory
iron-reducing bacteria (DIRB) and thus greatly influences
1
–3
4
5
6
3
2
2
3
2
2
2
+
7
8–13
are known to
2
2
1
9
the global cycling of carbon.
As we know, the method reported by Cornell and
2
0
•
Schwertmann (2003) has been the method mainly used
for the preparation of FH in references. Briefly, alkaline
oxygen species such as hydroxyl radicals ( OH) that react
3
+
solution was added into Fe solution to adjust the pH
value to 7–8. In this process, the formation of FH went
∗
Author to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2014, Vol. 14, No. 9
1533-4880/2014/14/7325/008
doi:10.1166/jnn.2014.8979
7325

Photo-Catalyzed p-Nitrophenol Degradation in Aqueous Dispersions of Ferrihydrite and H O
Wu et al.
2
2
through a pH change from acidic to neutral. However, FH
occurs in many environments from environmental to alka-
line conditions.
In some case, superadded reaction (SR) was immedi-
ately followed by photocatalysis above. Briefly, after pho-
tocatalysis was completed, a p-NP solution with certain
volume and concentration was superadded into the operat-
ing batch reactors to sustain p-NP solution as 0.15 mM,
100 mL. Other steps were the same as first circle of
photocatalysis.
To test the regeneration and reusability of FH, another
photocatalytic oxidation of p-NP was followed after the
first circle of photocatalysis. Namely, after the first five
2
1ꢁ22
Here FH was prepared by simulating environmental
conditions. The process of p-NP oxidative decomposition
in the presence of ferrihydrite and trace H O under solar
2
2
light irradiation, factors such as FH dosage, initial solu-
tion pH and H O dosage on the photocatalytic degrada-
2
2
tion of p-NP and the reusability of FH were investigated
in detail. These results may provide useful information on
the migration of nitrophenols through an abiotic or biotic
process.
hours of photocatalytic oxidation of p-NP in FH/H O dis-
2
2
persion, the final reaction mixture was separated using cen-
trifuge. The supernate was decanted after a final analysis
of p-NP concentration. The sludge was then mixed with
2
2
. MATERIALS AND METHODS
.1. Materials
Ferric nitrate ninehydrate [Fe(NO ꢀ · 9H O], sodium
−1
3
0 mL of 0.01 mol·L NaOH and shaken at 150 rpm in
a constant temperature shaker at 298 K for 1 h to make
FH regeneration.
2
3ꢁ24
3
3
2
The regenerated FH was washed with
hydroxide (NaOH), p-nitrophenol and H O were of ana-
distilled water several times for the next circle of pho-
tocatalysis. Here explained that only a final analysis for
p-NP concentration was carried out to avoid the loss of
FH during each circle of photocatalytic oxidation.
2
2
lytical purity. Distilled water was used. The ferric salt
solution was filtered through a 0.22 ꢂm millipore filter to
eliminate any particulate contaminants.
2
.2. Preparation of Ferrihydrite
2.4. Characterization and Analysis
−1
NaOH solution (6.0 mol · L ꢀ and Fe(NO ꢀ solution
Transmission electron microscopy (TEM) observation
of samples was carried out on a JEM 2010 elec-
tron microscope (Tokyo, Japan). X-ray diffraction (XRD)
measurement was performed on a D8-Advance XRD
3
3
−1
(
25 mL, 2.0 mol·L ꢀ were added simultaneously into cer-
tain water at RT under stirring. The rate of adding two
solutions was controlled by maintaining pH 7 with accu-
racy of better than 0.5 pH units .I PT :h 1e 3a 0g .i 6t a 3t i. o1 n8 0w . 1a s4 7c o On t ni n: -Wed d, i 1f f3r a Ac tuo gm 2e t0e 1r 4( B1 3r u: 0k 1e r: ,1 1G erman) at a scan rate of 4
ued for an additional 30 min until theC po Hp ywr iag sh at :d Aj u ms t ee dr i ct oa n S c2 i ꢄe nmt i if ni c P fur bo ml is h1 e0 rsto 80 with Cu Kꢅ target. Surface area
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ꢀ
−
1
ꢀ
ꢀ
a stable one by adding NaOH (1.0 M). At the same time
the total volume of the system was adjusted to 100 mL.
In this system, a gel-like deposit was formed. The product
was filtered and washed thoroughly with distilled water
measurements were taken with a Brunauer, Emmett, Teller
(BET) (Coulter SA-3100, USA) analyzer at liquid nitrogen
temperature using conventional gas adsorption apparatus.
Total organic carbon (TOC) analysis was carried out by
means of a Shimadzu TOC-V CPH total organic carbon
analyzer. Following the method described in Ref. [25] the
infrared (IR) spectroscopy (FTIR–8900) was used to mon-
itor the course of the photo-induced conversion of p-NP in
ferrihydrite/H O dispersion. Namely, dispersions of pre-
ꢀ
and then dried at about 40 C for 12 h.
2
.3. Photocatalytic Oxidation Process
All experiments were carried out in a pyrex glass vessel
with a water jacket at (298± 0ꢃ5) K. Aqueous suspensions
were prepared by adding FH powder to p-NP [0.15 mmol·
2
2
and post-reaction were extracted, filtered and added into
vessels with KBr powder to form homogeneous solutions.
−
1
L
(mM), 100 mL] solution. The suspension pH was
ꢀ
Then they were dried at 40 C under vacuum for final anal-
adjusted with NaOH or HCl to keep deviation within
.02 pH units. Prior to irradiation, the suspensions were
ysis of IR spectroscopy. The concentration of H O was
2
2
0
determined using a photo metric method, in which N,N-
diethyl-p-phenylenediamine (DPD) is oxidized through a
magnetically stirred in the dark for 1 h to establish the
adsorption/desorption equilibrium between p-NP and FH
particles. It is noteworthy that the amount of p-NP physi-
cally adsorbed on FH was lower than 2% of the initial one.
So the adsorbed p-NP was neglected. Subsequently, the
Fenton-like reaction was started with the introduction of
hydrogen peroxide (H O ꢀ and irradiation simultaneously.
2
6
peroxidase catalyzed reaction. Ferrous iron was deter-
mined spectrophotometrically using a modified phenan-
2
7
throline method; the detection limit was 8 mM.
3. RESULTS AND DISCUSSION
2
2
A General electric ELH projection lamp, 200 W/120 V,
3.1. Characterization of Ferrihydrite
−
2
was used as the light source at an intensity of 700 W·m .
These lamps provide an illumination spectrum similar to
sunlight (380–780 nm). Samples were periodically taken
and filtered through a 0.22 ꢂm millipore filter. The con-
centration of p-NP was measured by HPLC at 317 nm.
The position and intensity of the XRD peaks of FH
confirms that the analysis sample is 2-line ferrihydrite
(Fig. 1(a)), and is consistent with the results calculated
2
8
by Drits et al. The mesoporous structure of FH has
been confirmed by N2 adsorption/desorption isotherms
7
326
J. Nanosci. Nanotechnol. 14, 7325–7332, 2014

Wu et al.
Photo-Catalyzed p-Nitrophenol Degradation in Aqueous Dispersions of Ferrihydrite and H O
2 2
Figure 1. XRD pattern (a) and nitrogen adsorption/desorption
isotherms (b) of FH.
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Fig. 1(b)). The sample presents type III isotherm (defi-
(
Copyright: American Scientific Publishers
2
9
nition by IUPAC), and this is a characteristic of meso-
porous material. The appearance of type H-4 hysteresis
loop in the isotherm indicates the presence of slot pores
3
0
in the mesoporous FH. N sorption analysis shows that
2
Figure 2. HRTEM image (a) and electron diffraction pattern of FH.
the total and external surface surface areas of FH are
2
−1
2
−1
2
28.83 m · g and 158.97 m · g , respectively. The
diffraction rings are 110 and 300, respectively. These
results are consistent with the crystalline planes of XRD
peaks.
mean pore size and total pore volume are 16.38 nm and
3
−1
6
9.85 cm ·g , respectively (Table I).
FH particle is small and easy to aggregation together.
However, the single FH particle and the stripe of its crys-
tal lattice can be made out from the edge of the aggre-
gation unit in the high resolution transmission electron
microscopy (HRTEM) image (Fig. 2(a)). FH particles are
sphere-like nanosheets with a diameter of 2–4 nm. The
3
3
.2. Photocatalytic Oxidation Study
.2.1. Photocatalytic p-NP Degradation in
FH/H O Dispersion
2
2
Control experiments are carried out using only H O or
FH under irradiation (Figs. 3(a) and (b), respectively) or
the combination of FH and H O in the dark (Fig. 3(c)).
The results of Figures 3(a)–(c) show negligible degra-
dation of the substrate within the given timescale. The
decomposition rate of p-NP notably increases under the
same conditions as Figure 3(c) except for under irradia-
tion (Fig. 3(d)). After 5 h of irradiation, 95.5% of p-NP
are decomposed when the molar ratio of H O to the sub-
2
2
electron diffraction pattern of FH (ED ꢀ is diffraction ring
FH
instead of diffraction spot (Fig. 2(b)), indicating that FH
sample has polycrystalline structure. Calibration results
2
2
of ED , the miller indices of the brighter and darker
FH
Table I. Main characteristics of FH.
Parameters
Value
2
2
2
−1
−1
strate ꢆMH/Sꢀ is 3:1, far below the H O dosage reported
BET surface area (m ·g
ꢀ
228ꢃ83
69ꢃ85
0ꢃ036
158ꢃ97
16ꢃ38
2 2
3
Total pore volume (cm ·g
)
in Ref. [31] (MH/S = 1300:1 in the dark) and Ref. [32]
(MH/S = 15:1 under ultraviolet irradiation). Therefore, the
photocatalytic decomposition of p-NP was investigated in
detail in FH/H O dispersion.
3
−1
Microporel volume (cm ·g
)
2
−1
)
Exterior surface area (m ·g
Average pore width (nm)
2
2
J. Nanosci. Nanotechnol. 14, 7325–7332, 2014
7327

Photo-Catalyzed p-Nitrophenol Degradation in Aqueous Dispersions of Ferrihydrite and H O
Wu et al.
2
2
due to the ring opening to generate low-molecular-weight
acids, e.g., maleic acid. These species have characteristic
3
3ꢁ34
absorption in these regions.
The pH obviously decreased from 3.00 to 2.10 during
the first 6 h of irradiation, and then slowly increased from
2.10 to 2.14 during the subsequent irradiation (Fig. 4(d)).
The decrement of pH is ascribed to the hydrolysis of newly
generated Fe(III) species from reaction (1) and the gen-
eration of low-molecular-weight organic acids from p-NP
degradation. The slight increment of pH is due to the min-
eralization of organic acids.
•
−
FeꢆIIꢀ+H O → FeꢆIIIꢀ+ OH+OH
(1)
2
2
Changes in the Fe(II) and H O concentrations were
2
2
also observed during the photoreaction (Fig. 4(e)). The
concentration of Fe(II) slowly increases within 1 h while
it sharply increases to 76.6 and 170 ꢂM at 4 and 5 h,
about two times of that at 2 and 4 h respectively. Accord-
ingly, the concentration of H O straightly decreases from
Figure 3. Changes of p-NP concentration versus reaction time at pH 3.
−1
Adding 0.45 mM H O under irradiation (a); adding 0.2 g·L FH under
2
2
−1
irradiation (b); coexistence of 0.2 g · L FH and 0.45 mM H O in
2
2
−1
the dark (c); coexistence of 0.2 g · L FH and 0.45 mM H O under
2
2
irradiation (d).
2
2
4
50 ꢂM to 20 ꢂM coupled with p-NP degradation.
The initial intermediate of p-NP decomposition is
The normalised concentration profiles displays a lag
phase followed by a fast phase where the decomposition
rate of p-NP substantially increased from 8% at 1 h to
hydroquinone (HQ) and its corresponding retention time
(T ) is about 2.510 min (Figs. 5(a)–(b)). No catechol
R
9
0% at 3.5 h (Fig. 4(a)). The decomposition rate (95.5%)
appears (T = 3ꢃ991 min, Fig. 5(c)) during p-NP decom-
R
of p-NP was significantly higher than the removal rate of
TOC (17.5%) after 5 h of irradiation, indicating that most
p-NP is decomposed into organic intermediates rather than
position. The peaks at T = 1ꢃ574–2.008 min ascribed to
R
1
lower molecular organic acids (Fig. 5(a)). The peak at
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T = 2ꢃ320 min ascribes to an impurity (Figs. 5(a)∼(c)).
R
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completely oxidized into CO and H O. The TOC removal
Previous studies have provided strong evidence that
2
2
Copyright: American Scientific Publishers
3
+
rate increases from 17.5% to 24% with increased irradia-
tion from 5 h to 8 h, indicating the further mineralization
of organic intermediates.
some phenolic intermediates can reduce aqueous Fe to
2
+
Fe without special irradiation to accelerate the degra-
1
7ꢁ35
dation of nitroaromatic compound.
Here HQ was the
Infrared spectroscopy was also used to monitor the evo-
lution of the photo-induced conversion of p-NP. As shown
in Figure 4(b), the principal bands at 1500–1670 cm
initial intermediate of p-NP decay and the concentration
of Fe(II) increased as the reaction went on (shown in
Fig. 2(e)). To understand the role of HQ and FH, several
groups of control experiments were designed.
−
1
correspond to the aromatic ring vibration of p-NP. They
are not obviously changed before and after irradiation,
indicating that there exist a large number of aromatic
rings. During the photo-oxidation, the characteristic band
As shown in Figure 6, HQ is ineffective for the degra-
dation of p-NP without H O (SR-a, Fig. 6). About 10%
2
2
p-NP was decomposed from FH/H O dispersion in the
2
2
−
1
of the nitro group (1335 cm ꢀ disappears coupled with
dark after 5 h (SR-b, Fig. 6). Under the same experimen-
tal conditions as SR-b, Figure 6 except under irradiation,
the lag phase disappeared within 1 h and the degradation
rate of p-NP increased linearly from the initial irradiation
to reaction termination in the superadded reaction (SR-c,
Fig. 6).
−
1
a notable increase of nitrate absorption peak (1380 cm ꢀ
after 5 h of irradiation. The C–O vibration of phenol
−1
at 1250–1000 cm weakens, indicating that the phenol
structure is partly destroyed. The IR results clearly illus-
trated that the nitro group and part of the phenol structure
were destroyed with the formation of nitrate.
To confirm the role of the initial intermediate, extra HQ
(0.03 mM) was added into the present photo-catalyzed
FH/H O . As shown in Figure 7, Extra addition of HQ
The changes of Uv-Vis absorption spectra are shown in
Figure 2(c). The characteristic absorption band of p-NP is
at 317 nm. The absorption band at 225–265 nm is assigned
to nitro group. The peak at 204 nm is ascribed to char-
acteristic absorption of phenyl ring. The absorption peaks
at 317 nm and 227–238 nm obviously weaken as irradia-
tion go on, indicating the decomposition of p-NP and the
removal of nitro group. The absorptions at 200–220 nm
and 238–260 nm exhibit an increment followed by a decre-
ment along with the reaction time. The increment may be
2
2
noticeably accelerates the degradation of p-NP. p-NP con-
centration sharply decreases within 2 h in comparison with
that without extra addition of HQ (Fig. 3(d)), and the Fe(II)
concentration also linearly increases up.
The results of Figures 6–7 provided strong evidence that
the HQ generated in the initial phase accelerated the sub-
sequent degradation of p-NP due to its accelerating the
photoreductive dissolution of Fe(III).
7
328
J. Nanosci. Nanotechnol. 14, 7325–7332, 2014

Wu et al.
Photo-Catalyzed p-Nitrophenol Degradation in Aqueous Dispersions of Ferrihydrite and H O
2
2
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Figure 4. Changes of TOC and p-NP concentration (a); IR spectra of the samples at different irradiation time (b); Uv-vis absorption spectra for
p-NP (c); pH variation (d); changes of Fe(II) concentration (filled columns) and H O (open circles) (e).
2
2
3
.2.2. Effect of Catalyst FH
penetrate inner side of the solid particles with an increase
3
7
The photocatalytic degradation of many pollutants is a
function of the catalyst dosage. To investigate the effect
of the FH dosage on p-NP removal, several experiments
of FH dosage. Moreover, FH was also more prone to
aggregation with large dosage of FH, leading to a decrease
of effective catalyst. Considering the ideal p-NP degrada-
3
2
−
1
−1
were performed with varied loads from 0.1 g · L to
.5 g·L in the presence of H O (0.45 mM) under irra-
tion, 0.2 g·L FH was chosen as the optimal dosage for
−
1
0
further experiments.
2
2
diation at pH 3 (Fig. 8). At 4.5 h, 83%, 95%, and 83% of
−
1
p-NP disappears when the FH dosage is 0.1–0.3 g · L ,
3.2.3. Effect of pH
respectively. However, the decomposition rate (65%) of
Under the given experimental conditions, the effect of
pH on p-NP degradation is illustrated in Figure 9. The
decomposition rate of p-NP at 5 h follows the precedence
−
1
p-NP obviously decreases when 0.5 g · L FH is loaded
due to the face that too many photons were blocked to
J. Nanosci. Nanotechnol. 14, 7325–7332, 2014
7329

Photo-Catalyzed p-Nitrophenol Degradation in Aqueous Dispersions of Ferrihydrite and H O
Wu et al.
2
2
Figure 6. Changes of p-NP concentration versus reaction time. Without
H O under irradiation (a); with 0.45 mM H O in the dark (b); with
2
2
2
2
0
.45 mM H O under irradiation (c) in the superadded reaction (SR)
2 2
without extra addition of HQ.
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Figure 7. Changes of p-NP concentration (solid squares) and Fe(II)
concentration (open circles) versus reaction time with the extra addition
of HQ (0.03 mM).
Figure 5. HPLC chromatograms of (a) post-reaction sample; (b) stan-
dard hydroquinone; (c) standard catechol.
relationship: pH 2ꢃ5 ≈ pH 3.0 (95.5%) pH > 2ꢃ0 (55%) >>
pH 3.5 (30%) > pH 4.0 (15%) > pH 5.0 (0%). The highest
value of p-NP degradation occurs at pH 2.5–3.0, and is
consistent with that reported in Refs. [32, 33].
3
.2.4. Effect of H O Dosage
2 2
The H O dosage is a key factor in the photo-degradation
2
2
of p-NP in the FH/H O system (Fig. 10). The decompo-
2
2
sition rate of p-NP increases significantly as H O dosage
2
2
increases from 0.15 mM to 0.45 mM. More than 94.5%
of p-NP disappears at 5 h when H O concentrations are
2
2
0
.45–0.75 mM. At 5 h, 65% and 35% p-NP were removed
when the H O dosage was 0.30 and 0.15 mM, respec-
2
2
tively. Although the decomposition rate of p-NP increased
with an increase of H O dosage, no obviously changes
2
2
Figure 8. The effect of FH dosage on the decomposition rate of p-NP
were observed as H O dosage was beyond 0.45 mM.
with 0.45 mM H O under irradiation at pH 3.
2
2
2
2
7
330
J. Nanosci. Nanotechnol. 14, 7325–7332, 2014

Wu et al.
Photo-Catalyzed p-Nitrophenol Degradation in Aqueous Dispersions of Ferrihydrite and H O
2
2
Therefore, the optimum molar ratio of p-NP to H O
2
2
is 1:3.
3.2.5. Reusability of FH
In a wastewater treatment process, reusability of the cat-
alyst is crucially important. To test the regeneration and
reusability of FH, FH was used in five consecutive cir-
cles of photocalysis. As shown in Figure 11, the degrada-
tion rates of p-NP are 95.5%∼90% in the five consecutive
cycles of photocatalytic oxidation, indicating that FH is of
good reutilization.
4
. CONCLUSIONS
This investigation illustrates the fact the combination of
FH and trace H O is effective for the degradation of p-NP
Figure 9. The removal of p-NP under different initial pH with 0.45 mM
−1
2
2
H O and 0.2 g·L FH under irradiation.
2
2
under simulated sunlight irradiation. The combination of
−
1
0
.2 g·L FH, 0.45 mM of H O is highly photoactive for
2
2
the degradation of p-NP (0.15 mM) at pH 2.5–3.0. Hydro-
quinone, the initial intermediate of p-NP decomposition,
autocatalyses the subsequent p-NP degradation due to its
accelerating the photo-reductive dissolution of ferrihydrite.
A ferrihydrite was reused several times, still keeping its
original photocatalysis.
Acknowledgments: This work was supported by the
National Natural Science Foundation of China (21077031).
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Copyright: American S Rc i ee nf et i fr i ec nP cu eb sl is ah ne rds Notes
1
2
3
4
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