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Remediation and Control Technologies
Removal of Organoarsenic with Ferrate and Ferrate Resultant Nanoparticles: Oxidation and Adsorption Tao Yang, Lu Wang, Yu-Lei Liu, Jin Jiang, Zhuangsong Huang, Su-yan Pang, Haijun Cheng, Dawen Gao, and Jun Ma Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 22 Oct 2018 Downloaded from http://pubs.acs.org on October 22, 2018
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Removal of Organoarsenic with Ferrate and Ferrate
2
Resultant Nanoparticles: Oxidation and Adsorption
3 4
Tao Yang1, Lu Wang1 , *, Yulei Liu2, Jin Jiang1, Zhuangsong Huang1, Su-Yan Pang3,
5
Haijun Cheng1, Dawen Gao1, Jun Ma1,**
6
7
1
State Key Laboratory of Urban Water Resource and Environment, School of
8
Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin
9
150090, China
10
2
11
Technology, Dongguan 523808, China
12 13
Technology R & D Center for Environmental Engineering, Dongguan University of
3
School of Municipal and Environmental Engineering, Jilin Jianzhu University,
Changchun 130118, China
14
15
*Corresponding
16
*
17
**
authors:
Lu Wang, Phone/ Fax: 86 451 86283010; e-mail:
[email protected]; Jun Ma, Phone/ Fax: 86 451 86283010; e-mail:
[email protected];
18 1
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Abstract
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Many investigations focused on the capacity of ferrate for the oxidation of organic
21
pollutant or adsorption of hazardous species, while little attention has been paid on the
22
effect of ferrate resultant nanoparticles for the removal of organics. Removing organics
23
could improve microbiological stability of treated water and control the formation of
24
disinfection by-products in following treatment procedures. Herein, we studied ferrate
25
oxidation of p-arsanilic acid (p-ASA), an extensively used organoarsenic feed additive.
26
p-ASA was oxidized into As(V), p-aminophenol (p-AP), and nitarsone in the reaction
27
process. The released As(V) could be eliminated by in situ formed ferric (oxyhydr)
28
oxides through surface adsorption, while p-AP can be further oxidized into
29
4,4'-(diazene-1,2-diyl) diphenol, p-nitrophenol, and NO3-. Nitarsone is resistant to ferrate
30
oxidation, but mostly adsorbed (> 85%) by ferrate resultant ferric (oxyhydr) oxides.
31
Ferrate oxidation (ferrate/p-ASA = 20:1) eliminated 18% of total organic carbon (TOC),
32
while ferrate resultant particles removed 40% of TOC in the system. TOC removal
33
efficiency is 1.6 to 38 times higher in ferrate treatment group than those in O3, HClO, and
34
permanganate treatment groups. Besides ferrate oxidation, adsorption of organic
35
pollutants with ferrate resultant nanoparticles could also be an effective method for water
36
treatment and environmental remediation.
37 38
Keywords: Ferrate; Oxidation; Adsorption; p-Arsanilic acid; Arsenate 2
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1. Introduction
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Aromatic
organoarsenic
compounds,
such
as
p-ASA
and
41
3-nitro-4-hydroxypheyl-arsonic acid, were used as feed additive and veterinary drug to
42
promote growth of livestock and control parasitic diseases 1. Accompanied with surging
43
demand for meat products, consumption of aromatic organoarsenic compounds is
44
increasing. Studies estimated that over thousands of tons of aromatic organoarsenic
45
compounds were released into environment through solid waste and wastewater from
46
swine and poultry farms
47
and 0.5 to 5000 μg L–1 in soil and water in some regions of China 5. Although aromatic
48
organoarsenic compounds are not highly toxic, they would be transformed into
49
carcinogenic and highly mobile inorganic As species [As(III) and As(V)]
50
the pollution of aquatic systems and threating the safety of ecosystems.
2-4,
and their concentrations ranged from 0.2 to 1000 μg kg–1,
6, 7,
leading to
51
p-ASA is one of the largely used aromatic organoarsenic compounds, and many
52
studies explored the removal of p-ASA. Under ultraviolet-C light (254 nm) irradiation
53
without dissolved oxygen, p-ASA removal rate ranged from 0.077 μM min-1 at pH 1.0 to
54
3.78 μM min-1 at pH 11.0 8. When dissolved oxygen exists, hydroxyl radical and singlet
55
oxygen would form and enhance the removal of p-ASA
56
photo degradation system, pseudo first order reaction rate constants increased to 36.4 ×
57
10−3 min−1 at pH 2.0
58
efficient for the degradation of p-ASA. Under optimized condition, over 99% of p-ASA
11.
9, 10.
After H2O2 was added into
Compared with photo-degradation, chemical oxidation is more
3
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(10 mg-As L−1) would be oxidized to As(V) within 30 min at pH 4.0 in Fenton reaction,
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and the newly formed As(V) can be subsequently removed by iron oxides
61
adsorbents such as metal-organic framework 13-15 and iron-based metal oxide particle 16-20
62
could remove p-ASA in polluted source water and inhibit the release of inorganic As
63
species. However, physical adsorption mainly relies on electrostatic attraction and pore
64
filling processes, and the adsorption equilibrium time is normally longer than 5 h.
65
Adsorption process would be negatively impacted by background constituents in natural
66
waters. Previous studies also revealed that compared with those with As(V), adsorption
67
constants of p-ASA and 3-nitro-4-hydroxypheyl-arsonic acid with Fe oxides or Al oxides
68
were lower 17, 21, 22. Organic moiety of p-ASA may negatively influence the complexation
69
of organoarenicals with metal oxides. Hence, transform p-ASA to As(V) may improve
70
the overall As-removal efficiency in polluted water.
12.
Besides,
71
Ferrate [Fe(VI)] draws extensive interest as an environmentally friendly oxidant 23, 24.
72
It is highly reactive with organics containing nitrogen, sulphur, and electron rich moieties
73
(such as unsaturated bonds and aromatic ring) 25-28. Oxygen atoms were transferred from
74
ferrate to target pollutants with the formation of hydroxylation products, while ferrate
75
was simultaneously reduced into ferric (oxyhydr) oxides (Fe2O3, FeOOH, and
76
armouphous ferric). These in situ formed ferric (oxyhydr) oxides are highly dispersed,
77
small in size (nanoparticle), and have abundant hydroxylation group. They may interact
78
with oxidation products through the function of chemical bonds and hydrogen bond and 4
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adsorb them. However, previous investigations seldom examine this process and study
80
the effectiveness of ferrate resultant particles on removal of organics. Relevant
81
exploration would provide a new perspective for understanding the potential of ferrate
82
treatment on pollutants control.
83
The objective of this study is to evaluate the effects of ferrate on p-ASA oxidation
84
and total-As control, and explore the effectiveness of ferrate resultant particles for the
85
removal of organics. Firstly, the reaction kinetics were determined in buffered waters
86
from pH 6.0 to 10.0. The variation of As species in the reaction process was investigated,
87
and removal of total-As and TOC with different dosages of oxidants (HClO,
88
permanganate, ferrate, and O3) was examined. Performance of ferrate oxidation and ferric
89
(oxyhydr) oxides adsorption on the removal of TOC was compared. Effects of natural
90
organic matters, electrolyte ions and solution pH on the oxidation of p-ASA and removal
91
of As species were analyzed subsequently. After that, the reaction mechanism was
92
proposed, and the toxicity of p-ASA oxidation products towards E.coli and P.
93
phosphoreum was evaluated.
94 95
2. Materials and methods
96
2.1 Chemicals and reagents.
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p-ASA (98% purity) was purchased from Tokyo Chemical Industry (TCI, Japan) and
98
dissolved in pure water as stock solution (1 mM). Suwannee River Humic Acids (SRHA) 5
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(2S101H) was purchased from International Humic Substances Society. Other chemicals
100
were of analytical grade and directly used as received. Potassium ferrate (K2FeO4) was
101
prepared according to previously described method 29, 30. Detailed preparation procedures
102
are listed in supporting information (SI, Text S1). In experiment, K2FeO4 powder
103
(purity > 90 %) was dissolved in 1mM NaHCO3 (pH = 9.2) as stock solution. Ferrate
104
stock solution was filtered through a hydrophilic acetate fiber membrane of 0.22 μm pore
105
size (Shanghai ANPEL, China) and concentration of ferrate was determined with a UV–
106
Visible spectrophotometry at 510 nm (Ɛ510nm = 1150 cm-1M-1)
107
defined amount of K2FeO4 stock solution was swiftly added into the reactors. Preparation
108
of SRHA stock solutions is described in Text S2.
109
2.2 Oxidation experiment
31.
After calculation,
110
Oxidation experiment was carried out in glass beakers equipped with a magnetic
111
stirrer (500 r/min) at 25.0 ± 0.2 °C. In most cases, solution pH was buffered with 20 mM
112
borate buffer. Reactions were started by adding an aliquot of ferrate stock solution
113
(filtered and standardized) to p-ASA solution under rapid mixing condition. At different
114
time intervals, 1.0 mL of the solution was sampled and added into a 2.0 mL vial
115
containing 10 μL of 700 mM hydroxylamine hydrochloride (quenching the reaction).
116
Oxidation kinetics were fitted with second-order reaction rate law [Eq (1)]. Experiments
117
were conducted under pseudo-first-order conditions (concentration of ferrate is in excess
118
to p-ASA, [ferrate]0 = 50 μM, [p-ASA]0 = 5 μM), and concentration changes of ferrate 6
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and p-ASA were recorded as a function of reaction time (Eq (1)).
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-d[p-ASA]/dt = kapp[p-ASA][ferrate]total
(1)
Eq (2) shows the integral form of Eq (1), t
122
ln([p-ASA]t/[p-ASA]0) = - kapp∫0[ferrate]dt
(2)
123
Besides ferrate, KMnO4, HClO and O3 were also used for the oxidation of p-ASA. In
124
the experiment, definite amount of KMnO4, HClO or O3 was added into pH-buffered
125
solutions (20 mM borate buffer) containing p-ASA. Solution was sampled at different
126
time intervals. Thiosulfate was used for quenching the residual HClO, and
127
hydroxylamine hydrochloride was used for quenching the residual KMnO4 in the
128
collected samples. Detailed information about the oxidation experiment is presented in
129
Text S3. Reaction kinetics study is described in Text S4. Experiment about the removal
130
profile of As is presented in Text S5.
131
2.3 Toxicity assay
132
Toxicity of p-ASA and its oxidation products towards E. coli was investigated
133
according to the procedures described in previous study 32. We initially investigated the
134
toxicity of 10 μM of p-ASA on E. coli, but no obvious antimicrobial effect was observed.
135
When the p-ASA concentration increased to 2.5 mM, the growth of E. coli was obviously
136
inhibited. In experiment, 2.5 mM of p-ASA reacted with 25 mM of ferrate for an hour.
137
Then the solution was filtered through a sterile hydrophilic acetate fiber membrane of
138
0.45 μm pore size to remove particles and floc. Five test groups were set: control group 7
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(containing 20 mL LB medium and 100 mL of 20 mM PBS, pH 7.0); ferrate treated
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p-ASA group (containing 20 mL LB medium and 100 mL sterile reaction solution);
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p-ASA group (containing 20 mL LB medium, 100 mL sterile deionized water, and 2.5
142
mM of p-ASA); As(III) group (containing 20 mL LB medium, 100 mL sterile deionized
143
water, and 2.5 mM of As(III)); As(V) group (containing 20 mL LB medium, 100 mL
144
sterile deionized water, and 2.5 mM of As(V)). E. coli K12 strain in exponential phase
145
was inoculated into the bottles and maintained at 150 rpm on a shaker (35 ºC). The
146
optical density value of bacterial culture at 600 nm was measured by UV–Visible
147
spectrophotometry.
148
The acute toxicity of p-ASA oxidation products was evaluated by marine luminescent
149
marine bacterium P. phosphoreum (purchased from ShenZhen HuaJu Scientific
150
Instrument Co.,LTD) according to national standard of China GB/T15441-1995 (Water
151
Quality: Determination of the acute toxicity-Luminescent bacteria test). After 15 min of
152
culture (25 ºC), the luminescent intensity of P. phosphoreum was recorded by a
153
microplate reader (SpectraMax M5, Molecular Devices, USA). The inhibition ratio of
154
luminescent intensity was calculated based on a toxicant-free control to reflect the acute
155
toxicity of the solution samples.
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2.4 Analytical methods
157
p-ASA and nitarsone concentrations were determined with Waters 2695 series
158
high-performance liquid chromatography (HPLC), with UV detection at 254 nm. The 8
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concentration of inorganic As species was determined by an inductively coupled plasma
160
mass spectrometer (ICP-MS, NexION 300Q, Perkin-Elmer) with a HPLC for separation.
161
The chemical state of As in p-ASA and the settled solids in the reaction of p-ASA with
162
ferrate is examined by Thermo Fisher (ESCALAB 250Xi) X-ray photoelectron
163
spectrometer (XPS). Fourier transform infrared spectroscopy (FTIR) analysis of the
164
settled solids was conducted on a PerkinElmer Spectrum One FTIR. Solid samples were
165
diluted to a concentration of 2% with IR-grade KBr. FTIR spectra were collected at 4
166
cm-1 resolution in the IR region of 4000 - 400 cm-1 for pure KBr and the samples.
167
High-resolution transmission electron microscope (HR-TEM) samples were prepared by
168
depositing a drop of solution sample onto a 200-mesh carbon film supported by copper
169
grids. TEM samples were analyzed by JEM-2100 transmission electron microscope
170
(JEOL, Japan) at accelerating voltage of 200 kV. TOC content of solution samples was
171
determined by TOC-VCHS (Shimadzu, Kyoto, Japan). Content of NO3- was determined
172
with a DIONEX ICS ion chromatography system. Concentration of p-AP was determined
173
by HPLC at a flow rate 1.0mL/min. The mobile phase was water and methanol (70:30,
174
v/v), and determined at wavelength of 317 nm. Zeta potential of ferric (oxyhydr) oxide
175
was determined by Malvern Zetasizer (Malvern Instruments Ltd., Worcestershire, UK).
176
Mass spectrum analysis was carried out with a high-resolution hybrid quadrupole
177
time-of-flight mass spectrometer (QTOF 5600, AB Sciex, USA) equipped with an
178
electrospray ion (ESI) source. Detailed information is listed in Text S6. 9
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3. Results and discussion
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3.1 Ferrate oxidation of p-ASA and reaction stoichiometry
182
Reaction kinetics of p-ASA with ferrate under different pH conditions were initially
183
investigated. When 5 μM of p-ASA reacted with 50 μM of ferrate at pH 6.0, the
184
concentration of residual p-ASA decreased below HPLC detection limit (< 0.05 μM)
185
within 10 s. Over 90% of p-ASA was removed within 1 min in pH 7.0 and 7.5 groups,
186
and the concentration of residual p-ASA decreased below detection limit within 1.5 and
187
10 min, respectively (Figure 1A). When solution pH increased to 8.0, 8.5, and 9.0, time
188
for the removal of over 90% of p-ASA prolonged to 10 min, 30 min, and 40 min,
189
respectively. Ferrate oxidation of p-ASA was pH-dependent, and acidic condition is in
190
favor for the reaction process.
191
Second-order reaction rate law [Eq (1)] was used to study the reaction kinetics. By
192
plotting natural logarithm of p-ASA concentrations with ferrate exposure (∫0[ferrate]dt),
193
reaction kinetics under various pH conditions were obtained (Table S1 and Figure S1). At
194
pH 6.0, the determined kapp value was 8.4 × 103 M-1s-1. As solution pH increased to 7.0,
195
7.5, 8.0, 8.5, 9.0, and 10.0, the kapp values were 2.0 × 103 M-1s-1, 7.1 × 102 M-1s-1, 1.2 ×
196
102 M-1s-1, 2.9 × 10 M-1s-1, 2.1 × 10 M-1s-1, and 2.9 M-1s-1, respectively. Previous studies
197
reported that for ferrate oxidation of As(III), the kapp value is 3.54 × 105 M-1s-1 at pH 8.4;
198
for ferrate oxidation of p-AP, the kapp values are 6.6 × 103 M-1s-1 at pH 7.0 and 7.2 × 103
t
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M-1s-1 at pH 8.0, respectively
200
of ferrate with As(III) or p-AP is much faster. Chemically, arsenic group, amino group,
201
and benzene ring of p-ASA are electron rich moieties. Electron cloud of these moieties
202
would interact with each other, leading to the formation of π-conjugated system and
203
homogeneity of electron distribution. This would improve the chemical stability of
204
p-ASA and decrease its reactivity with ferrate.
33, 34.
Compared with ferrate oxidation of p-ASA, reaction
205 206
Figure 1. Concentration change of p-ASA (5 μM) in the reaction with ferrate (50 μM) as a function of
207
reaction time under different pH conditions (A); comparison of kapp values of p-ASA with ferrate,
208
HClO, and permanganate [Mn(VII)] (B); stoichiometry of the reaction between ferrate and p-ASA
209
(pH 9.0) ([Fe(VI)]R represents the amount of ferrate reacted with p-ASA, as other part of ferrate
210
would self-decay in water) (C); variation of p-ASA, As(III), As(V), p-AP, nitarsone, and NO3-
211
concentration in the reaction of ferrate with p-ASA (25 μM) (D); variation of total-As (solution
212
samples were filtered with 0.22 μm membrane before detection) and nitarsone (solution samples were
213
acidified with HCl, without filtration) content in the reaction of ferrate (50 μM) with nitarsone (5 μM) 11
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(E).
Ferrate is a diprotic acid [H2FeO4 = HFeO4- + H+, pKa, H2FeO4 = 3.5; HFeO4- = FeO42-
216
+ H+, pKa, HFeO4- = 7.23]
217
9.2) 20. pH dependency of kapp for ferrate with p-ASA could be modeled by eq 3.
218
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and p-ASA is a triprotic acid (pKa1 = 1.9; pKa2 = 4.1; pKa3 =
𝑖 = 1,2
𝑘[𝐹𝑒(𝑉𝐼) ― 𝑝 ― 𝐴𝑆𝐴] = ∑𝑗 = 1,2𝑘𝑖,𝑗𝛼𝑖𝛽𝑗
(3)
219
Where αi and βj represent the fractions of different ferrate and p-ASA species
220
respectively, i and j represent the respective different species of ferrate and p-ASA
221
species, and ki,j represents the species-specific second-order rate constants of the
222
reactions for each i and the corresponding j. From pH 6.0 to 10.0, model fitting result is
223
in accordance with the determined rate constants (R2 = 0.998) (Text S4, Figure S2).
224
Based on the results, the calculated k11 [(5.3 ± 0.2) × 105 M-1s-1] is over 200 times higher
225
than k12 [(2.3 ± 0.2) × 103 M-1s-1], which indicates that the reaction of HFeO4- species with
226
deprotonated p-ASA dominants the overall reaction from pH 6.0 to 10.0.
227
Besides ferrate, other oxidants such as chlorine (HClO) and permanganate could also
228
react with p-ASA. The reaction kinetics of p-ASA with HClO and permanganate were
229
determined respectively (Figure 1B). Similar with that of ferrate, permanganate oxidation
230
of p-ASA is pH-dependent and fast under acidic condition. Reaction rates of
231
permanganate with p-ASA decreased from 14.9 M-1s-1 at pH 4.0 to 0.03 M-1s-1 at pH 7.0,
232
4 ~ 5 orders of magnitude lower than that of ferrate with p-ASA under similar pH
233
conditions. At pH 7.0, less than 20% of p-ASA was oxidized by permanganate in 24 h. 12
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For the chlorination of p-ASA, profile of rate constants as a function of solution pH is
235
bell-shaped. Rate constants increased from 27.4 M-1s-1 at pH 6.0 to 211.2 M-1s-1 at pH 7.5,
236
and decreased to 74 M-1s-1 at pH 9.0. The pKa value of HOCl is 7.54, and reactivity of
237
HOCl is higher than that of OCl-. This property makes the oxidation ability of HOCl to
238
be the highest at pH 7.54, and dissociation of HOCl results in low rate constants with
239
p-ASA under alkaline condition. Compared with permanganate oxidation and
240
chlorination, ferrate oxidation of p-ASA is the rapidest under circumneutral pH
241
condition.
242
Reaction stoichiometry of p-ASA with ferrate was determined at pH 9.0 (adsorption
243
of As would be minimized under alkaline condition) (Figure 1C). Plot of [p-ASA] vs
244
[ferrate]reacted showed a linear relationship, and the calculated slope is - 0.44 ± 0.04. This
245
reveals that the stoichiometric ratio of ferrate with p-ASA is around 2:1, and reaction
246
follows the stoichiometry:
247
9 Fe(VI) + 4 p-ASA → 9 Fe(III) + products
248
Previous studies showed that inorganic As species would be released in the oxidation
249
of p-ASA. By analyzing the samples with mass spectrometry (ICP-MS and
250
HPLC/ESI-QTOF-MS) and comparing mass spectrum information with chemical
251
standards, it was found that As(V) is the dominant component of inorganic As species,
252
while p-AP and nitarsone are the main organic oxidation products. Besides, NO3- was
253
also formed in the ferrate oxidation of p-ASA (Figure S3) (detailed information about the 13
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254
identification of oxidation products is shown in Text S7; proposed reaction pathway is
255
shown in “reaction mechanism” section). Formation profile of As(V), NO3-, p-AP, and
256
nitarsone in the ferrate oxidation of p-ASA at different molar ratios was examined
257
(Figure 1D). When low level of ferrate (ferrate/p-ASA < 1) was applied, less than 30% of
258
p-ASA was oxidized into As(V) and p-AP. As(V) is stable and can be removed by ferrate
259
resultant ferric (oxyhydr) oxides 33. p-AP could be further oxidized when higher level of
260
ferrate was applied
261
p-ASA could be oxidized with the formation of As(V) species and trace amount of
262
nitarsone and NO3-. When ferrate/p-ASA molar ratio surpassed 3.3, 80% of p-ASA was
263
oxidized into As(V) and 20% of p-ASA was oxidized into nitarsone based on As mass
264
balance. No abatement of nitarsone was observed when high level of ferrate was applied.
265
When 5 μM of nitarsone reacted with 50 μM of ferrate, no oxidation of nitarsone was
266
observed either (Figure 1E). These results suggested that nitarsone was resistant to ferrate
267
oxidation, while over 85% of nitarsone was adsorbed by ferrate resultant particles and
268
removed in filtration process (Figure 1E). Besides, the content of NO3- also increased
269
when high level of ferrate was used. This indicates that some N-containing compounds
270
were further oxidized by ferrate with the cleavage of C-N bond and formation of NO3- in
271
the system.
272
3.2 Removal of total-As and TOC
34, 36.
When ferrate/p-ASA molar ratio increased to 2.3 ~ 2.5, all of
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Carcinogenic As species could be released in the transformation of organoarsenicals
274
2, 37,
275
organoarsenicals pollution. Variation of p-ASA, As(III), As(V), and the total As content
276
as a function of reaction time was examined (ferrate/p-ASA = 10:1, pH = 7.0) (Figure
277
2A). Concentration of p-ASA decreased rapidly with the increase of As(V) content. One
278
minute later, p-ASA concentration was 0.13 μM, and As(V) concentration was 4.07 μM.
279
Concentration of As(III) was below 0.02 μM during the reaction process. This data is in
280
accordance with above result (Figure 1D and S15), that over 80% of p-ASA was
281
transformed into As(V) and around 20% of p-ASA was transformed into nitarsone.
and controlling the released inorganic As is a critical issue for the remediation of
282
Removal of total-As in the ferrate oxidation of p-ASA was studied (Figure 2B).
283
When 5 μM of p-ASA reacted with 50 μM, 75 μM and 100 μM of ferrate, total-As
284
content decreased to 0.56 μM, 0.23 μM and 0.09 μM respectively in filtered solution
285
samples after 10 min of reaction. This suggests that ferrate could effective control
286
total-As content in the reaction with p-ASA.
287
Chemical state of As in p-ASA and ferrate resultant particles was analyzed by XPS
288
(Figure S4). As 3d fitting peak binding energy (BE) of p-ASA was 44.4 eV and can be
289
assigned to As(III) (44.3 ~ 44.5 eV). As 3d fitting peak BE of ferric particles was 45.3 eV
290
and can be assigned to As(V) (45.2 ~ 45.6 eV)
291
oxidation of p-ASA, the -AsO(OH)2 moiety was oxidized to As(V). Prucek et al
292
investigated the ferrate oxidation of As(III) and found that the oxidation products [As(V)]
38.
This indicates that in the ferrate
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could be removed by ferric (oxyhydr) oxides through crystal structure incorporation
294
Besides the peak centered at 45.2 eV of As-bearing samples, they observed another small
295
peak closing to 48 eV. Together with Mössbauer data, they concluded that this
296
phenomenon represents that As species incorporated into the crystal structure of ferric
297
(oxyhydr) oxides. We also studied the reaction of ferrate with inorganic As(III), and
298
observed two XPS peaks (one main peak is at 45.2 eV, and a small peak is at 47.8 eV)
299
exist in the ferric solids (Figure S4D). In comparison, only one XPS peak at 45.2 eV
300
exists in the ferric solids formed in the ferrate oxidation of p-ASA (Figure S4B). This
301
indicates that the As(V) species formed in the ferrate oxidation of p-ASA was mainly
302
removed by ferric (oxyhydr) oxides through surface adsorption.
39.
303 304
Figure 2. Variation of total As, p-ASA, As(III), and As(V) content in the reaction of p-ASA (5 μM) 16
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305
with ferrate (50 μM) [1 mM of hydroxylamine hydrochloride and 0.5% (v.t.) of HCl were added to
306
dissolve the ferric particles] (A). Variation of total As content when different dosages of ferrate
307
reacted with p-ASA (5 μM) (solution samples were filtered with 0.22 μm glass fiber membrane) (B).
308
FTIR result about the ferric particles formed in the self-decomposition of ferrate and in the ferrate
309
oxidation of p-ASA. Green areas indicate peaks with similar vibration, while gray areas indicate peaks
310
with different vibration (C). Removal ratio of TOC of p-ASA treated by different molar ratios of
311
ferrate, HClO, permanganate [Mn(VII)], and ozone within 2 hours. Fe(VI) (acidified) indicates that
312
the solution samples (ferric solids) were dissolved with HCl, which represents the eliminated TOC in
313
ferrate oxidation process. Fe(VI) (filtered) indicates that the solution samples were filtered through
314
0.22 μm glass fiber filter to remove ferric particles (D). Experimental conditions: T = 25 °C, pH = 7.0.
315
As(V) species could be removed by ferrate resultant particles, and FTIR analysis is
316
used to study the chemical properties of ferric particles formed in the self-decomposition
317
of ferrate and in the reaction of p-ASA with ferrate (Figure 2C). Both samples have
318
intense peaks at 3400 and 1640 cm-1, which can be assigned to the stretch of OH groups
319
of H2O 40. The peaks at 1120 cm-1 could be assigned to OH stretch of α-FeOOH 41, while
320
the peaks near at 680, 610, and 480 cm-1 corresponded to the vibration of Fe–O bonds
321
42-44.
322
836 cm-1, that can be ascribed to the symmetric stretching vibration of As-(OFe) 21, 45.
323 324
In comparison, the sample formed in ferrate/p-ASA group has a vibrational peak at
The peaks at 1527, 1420, 1358 cm-1 can be attributed to vibrations correlating with -COO- symmetric stretching, CH2 wagging, and C-O stretching, respectively 17
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45-47.
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325
Besides FTIR, XPS analysis also showed that four peaks corresponding to C-C/C=C/C-H
326
(284.8 eV), C-C(OH)=O (285.7 eV), C-O (286.8 eV) and O=C-O (289.2 eV)
327
enveloped in the C1s peak of the ferric solids resulted in the ferrate oxidation of p-ASA
328
(Figure S4C). These organics may be the oxidation products formed in the ferrate
329
oxidation of p-ASA, and were adsorbed or complexed onto the surface of ferrate resultant
330
ferric (oxyhydr) oxides.
48
were
331
TOC removal efficiency is a critical standard for evaluating the quality of treated
332
water and effectiveness of water treatment procedure. Compared with ferrate oxidation
333
and ozonation, HClO oxidation and Mn(VII) oxidation are less effective for the removal
334
of TOC in the system. For chlorination of organics, chlorine atoms would be added onto
335
the structure of target compound through substitution reaction, and HClO was always
336
used as disinfectant agent. Mn(VII) could react with p-ASA but the reactivity is not high
337
(Figure 1B). These factors made the TOC removal efficiencies in HClO and Mn(VII)
338
groups lower than 5%. Ozone is a strong oxidant and could react with p-ASA. Ozonation
339
removed around 18.4%, 29.2%, and 37.6% of TOC in the three groups, respectively.
340
Compared with chlorination, Mn(VII) oxidation, and ferrate oxidation, ozonation is the
341
most effective method for the oxidation of p-ASA.
342
Interestingly, for the p-ASA treated by different level of ferrate, the TOC removal
343
ratio was largely improved in filtered samples than those in acidified samples (Figure
344
2D). When the initial molar ratio of ferrate/p-ASA is 20:1, TOC removal efficiency is 18
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345
18.1% in ferrate (acidified) group and 58.3% in ferrate (filtered) group. Compared with
346
ferrate oxidation, ferrate resultant particles removed around 40% of TOC in the system.
347
In above section we showed that nitarsone is a resistant oxidation product and could be
348
adsorbed by ferrate resultant ferric (oxyhydr) oxides (Figure 1E). Considering that 20%
349
of p-ASA was oxidized into nitarsone (Figure 1D) and around 85% of nitarsone was
350
adsorbed (Figure 1E), the amount of nitarsone removed in ferrate (filtered) group equals
351
to 17% of TOC. This indicates that ferrate resultant particles removed around 23% of
352
organics (oxidation products of p-ASA, besides nitarsone) in the system. This TOC
353
removal efficiency is much higher than the organics eliminated in ferrate oxidation
354
process.
355
Literally, chemical oxidation of organic pollutants refers to the transformation of
356
structure of target pollutants through oxygen transfer process, and elimination of function
357
groups of target pollutants with non-oxidative mechanism such as β-elimination 49. These
358
processes may degrade organic pollutant into lower molecular weight products. In
359
comparison, mineralizing dissolved organics through chemical oxidation is difficult and
360
energy consuming. Ozone is a strong oxidant and ozonation of p-ASA removed 37.6% of
361
TOC in 20:1 group, 2 to 25 times higher than the TOC removal in chlorination,
362
permanganate oxidation and ferrate oxidation processes. However, ferrate resultant
363
particles removed 40% of TOC in 20:1 group (Figure 1D), much higher than those
364
eliminated by ferrate oxidation and even higher than those eliminated by ozonation. 19
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365
Besides ferrate oxidation, ferrate resultant particles have great potential for the removal
366
of organics.
367
Considering that the ferrate resultant ferric (oxyhydr) oxides are composed by Fe2O3,
368
FeOOH and amorphous ferric, effects of Fe2O3, FeCl3 and ferrate resultant particles on
369
nitarsone adsorption were compared (Figure S5). Ferrate resultant particles showed
370
highest nitarsone adsorption ratio (> 85%) and shortest reaction time (< 1 min) than that
371
of Fe2O3 and FeCl3. These ferric (oxyhydr) oxides are small in size (nano size), highly
372
dispersed in water (in situ formed in the reduction of ferrate), and have large specific
373
surface area. These factors could enhance the interaction opportunity of ferric (oxyhydr)
374
oxides with target pollutants and facilitate their removal.
375 376
Figure 3. TEM photos of particles formed in ferrate oxidation of p-ASA (in situ), mixture of ferrate 20
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resultant particles (self-decay for an hour) with p-ASA (ex situ), and ferrate resultant particles
378
(self-decomposition for an hour) (blank). Experimental conditions: [p-ASA]0 = 5.0 μM, [ferrate]0 =
379
50.0 μM, T = 25 °C, pH = 7.0.
380
TEM was used to analyze the physical properties of ferrate resultant particles (Figure
381
3). The average size of particles in situ formed in the ferrate oxidation of p-ASA is 4.37
382
nm. In comparison, the average size of particles formed in the reduction of ferrate
383
without p-ASA is 6.45 nm. Particles formed in the reaction of ferrate with p-ASA is
384
smaller than the particles in “blank” and “ex situ” groups. As mentioned in above section,
385
inorganic As(V) species and organics (such as nitarsone) could be adsorbed by ferric
386
(oxyhydr) oxides. These foreign components may inhibit the growth of ferric
387
nanoparticles 39.
388
Besides particle size, TEM photos showed that compared with the particles formed in
389
blank group, the “in situ” and “ex situ” formed particles are surrounded/coated with
390
semi-transparent amorphous substance (Figure 3 and Figure S16). This substance may be
391
the
392
microscopy/energy-dispersive
393
confirmed that the ferric (oxyhydr) oxides particles are mixed with C and As elements
394
(Figure S6). Combining with above analysis, As species and organics formed in the
395
ferrate oxidation of p-ASA may be adsorbed by ferrate resultant nanoparticles or be
396
complexed on their surface, which inhibit the growth of these ferric nanoparticles.
organics
adsorbed
by
ferric
X-ray
(oxyhydr)
spectrometry
oxides.
Scanning
(SEM-EDX)
21
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electron
analysis
further
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397
3.3 Reaction mechanism
398
In above sections we showed that As(V), p-AP, and nitarsone are formed in the
399
ferrate oxidation of p-ASA when the initial ferrate/p-ASA ratio is below 3:1. As(V) and
400
nitarsone are resistant to ferrate oxidation, while p-AP can be further oxidized 34, 36. In the
401
reaction process, solution color was shifted from transparent to pale pink in an hour
402
(Figure S7). We speculate that azo compounds may form in the ferrate oxidation of p-AP
403
18.
404
(4,4'-(diazene-1,2-diyl) diphenol and 4,4'-(hydrazine-1,2-diyl) diphenol) showed similar
405
ionization patterns with that of p-AP from m/z 40 to 90 Da (Figure S8). These
406
compounds contain similar chemical moieties or functional groups with p-AP, and may
407
be the oxidation product of p-AP. Besides 4,4'-(diazene-1,2-diyl) diphenol and
408
4,4'-(hydrazine-1,2-diyl) diphenol, another compound (m/z = 138.02 Da) was identified
409
under ESI- mode. After comparing with chemical standard, we confirmed that this
410
compound is p-nitrophenol (MW = 139.02 Da), and it can be oxidized by ferrate with the
411
formation of benzoquinone and NO3- (Figure S9 and S3).
By analyzing the oxidation products under ESI+ mode, 2 identified compounds
412
Combining the identified products, reaction stoichiometry, and concentration
413
variation of relevant products, reaction pathway of p-ASA with ferrate is illustrated in
414
Figure 4. Ferrate initially attacks the As-C bond of p-ASA through oxygen transfer
415
process, with the formation of p-AP and As(V). When high level of ferrate
416
(ferrate/p-ASA > 3.5) was applied, around 80% of p-ASA would be oxidized into As(V) 22
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417
and p-AP, while the residual p-ASA would be transformed into nitarsone. Compared with
418
As(V) and nitarsone, p-AP is easily oxidized. Aminophenol radicals would form in the
419
ferrate oxidation of p-AP through one-electron transfer process. These radicals can
420
further react with ferrate, with the formation of p-nitrophenol, benzoquinone, NO3-, and
421
other oxidation products. On the other hand, some aminophenol radicals would combine
422
via radical−radical self-coupling process, with the formation of 4,4'-(hydrazine-1,2-diyl)
423
diphenol and 4,4'-(diazene-1,2-diyl) diphenol in the system. 4,4'-(diazene-1,2-diyl)
424
diphenol may be further oxidized by ferrate. Based on N-mass balance, around 17% of
425
p-ASA was oxidized by ferrate with the formation of NO3- as the end product
426
(ferrate/p-ASA = 10:1, pH 7.0).
427 428 429
Figure 4. Proposed reaction pathway of p-ASA with ferrate.
Over 98% of As(V) species formed in the reaction process would be adsorbed by 23
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430
ferrate resultant ferric (oxyhydr) oxides through surface adsorption process. Firstly,
431
hydroxy groups of ferric (oxyhydr) oxides would interact with As(V) species through
432
hydrogen bond and lead to the adsorption of As(V) onto the particle surface. Secondly,
433
As(V) species is negatively charged, while the zeta potential of ferrate resultant ferric
434
(oxyhydr) oxides is around 0 mV at pH 7.0 (Figure S10). Electrostatic attraction among
435
As(V) species and ferric (oxyhydr) oxides could enhance to the adsorption of As(V).
436
Thirdly, As(V) species could complex with ferric (oxyhydr) oxides through the formation
437
of As-(OFe) bond (Figure 2C). Compared with ferrate oxidation of inorganic As(V), no
438
incorporation of As(V) species into the crystal structure of ferric (oxyhydr) oxides was
439
observed (Figure S4).
440
Nitarsone would form in the ferrate oxidation of p-ASA, and over 85% of nitarsone
441
was removed when the initial ferrate/nitarsone molar ratio is 10:1 (Figure 1E). Based on
442
As-mass balance, over 90% of total As was removed in the forms of As(V) and nitarsone
443
by the ferric nanoparticles (ferrate/p-ASA = 10:1, pH 7.0). When high level of ferrate
444
was applied (i.e. ferrate/p-ASA = 20:1), total-As removal efficiency could surpass 99%
445
(Figure 2B).
446
In above sections we showed that adsorption is also a main pathway for the removal
447
of organics in the system. The results of TOC (Figure 2), TEM (Figure 3), and
448
SEM-EDX (Figure S6) analysis suggested that ferric particles adsorbed organics. The
449
result of FTIR and XPS (Figure S4) analysis revealed that -COO- bond may form in the 24
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450
complexation of organics with ferric particles. Besides complexation, hydrogen bond
451
between negatively charged ferric (oxyhydr) oxides and hydroxy groups of organics may
452
also facilitate the adsorption of organics.
453
3.4 Influence of background constituents on the oxidation of p-ASA and removal of
454
As
455
Background constituents such as dissolved organic matter (DOM) and electrolytes
456
ubiquitously exist in natural waters and would influence the chemical oxidation of
457
pollutants 50. The effects of SRHA, Ca2+, Cl-, and PO43- on the ferrate oxidation of p-ASA
458
were investigated. When the content of SRHA increased from 0 mg/L to 1 mg/L, 3 mg/L,
459
and 5 mg/L, the residual ratio of p-ASA increased from 0% to 6%, 16%, and 30% in 10
460
min of reaction, respectively (Figure 5A). SRHA negatively influenced the ferrate
461
oxidation of p-ASA, and the depression effect increased with the elevation of SRHA
462
content.
463
Previous investigations explored the effects of HA on the control of environmental
464
pollutants with ferrate, and many of them found that HA would decrease the removal
465
ratio of target pollutants by ferrate. Wenk et al. investigated the influence of DOM on the
466
oxidation of organic compounds, and speculated that the oxidation intermediate may be
467
reduced back to the parent form by the co-existing DOM 51. This process would result in
468
the decrease of removal of target pollutants. On the other hand, SRHA may competitively
469
react with ferrate and affect ferrate exposure concentration in the system, which in turn 25
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470
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negatively influence the ferrate oxidation of p-ASA.
471 472
Figure 5. Influence of SRHA (A) and electrolytes (B) on the ferrate oxidation of p-ASA; effects of
473
cationic species (Ca2+, Mg2+), anionic species (SiO32-, PO43-), SRHA, and solution pH on the removal
474
of total-As (C), and zeta potential of ferrate resultant particles (D). Experimental conditions: [p-ASA]0
475
= 5 μM, [ferrate]0 = 50 μM, T = 25 ℃, reaction time: 60 min.
476
For the co-existing electrolytes, Ca2+ and Cl- (10 mM) showed no obvious effects,
477
while PO43- (10 mM) negatively influenced the oxidation process (Figure 5B). After 3
478
min of reaction, the content of p-ASA was below HPLC detection limit in control, Cl-
479
and Ca2+ groups, while 93% of p-ASA was oxidized in PO43- group. Previous studies
480
showed that phosphate would inhibit the ferrate oxidation of Br- and HOI
481
speculate that PO43- species may complex with ferrate and affect ferrate exposure
482
concentration, but the difference of ferrate content in relevant groups was below 4 μM 26
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52, 53.
We
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483
(Figure S11). The effect of PO43- on ferrate exposure concentration was not obvious.
484
Considering that intermediate iron species [Fe(IV) and Fe(V)] may form in ferrate
485
oxidation process, PO43- may influence the oxidation ability of intermediate iron species
486
and thus impact the oxidation of p-ASA. The underlying mechanism warrants further
487
investigation.
488
Background constituents would affect the removal of hazardous ion with ferrate
489
resultant particles, and lead to the desorption of captured ion 54. When 10 mM of Ca2+,
490
Mg2+, and HCO3- exist in the solution (pH = 7.0), the removal of total-As was not greatly
491
influenced (Figure 5C). Acidic condition (pH 6.0) is in favor for the removal of As (>
492
99%), while the As removal ratio decreased under alkaline condition (pH 8.0, ~ 34%).
493
The point of zero charge (pHpzc) of ferrate resultant nanoparticles was 6.8 (Figure S10).
494
These ferric particles were positively charged under acidic conditions and negatively
495
charged under alkaline conditions. Electrostatic force makes the As(V) (AsO43-) easily
496
captured by ferric particles under acidic condition and hard to be captured under alkaline
497
condition.
498
Total-As removal ratios decreased with the existing of SRHA, PO43- and SiO32-.
499
When the content of SRHA, PO43- and SiO32- increased from 0 to 0.5 mgC/L, 0.1 mM and
500
1 mM, respectively, removal ratios of As decreased from 90% to 15%, 10%, and 12%,
501
respectively. In above section we speculated that there are 3 kinds of functions
502
participating in the removal of As species with ferric (oxyhydr) oxides: hydrogen bond, 27
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503
electrostatic attraction, and surface complexation. When SiO32-, PO43-, SRHA and OH-
504
exist in the solution, they would coat on the surface of ferric (oxyhydr) oxides 55 or form
505
inner-sphere complexes 56, decreasing the zeta potential of ferric (oxyhydr) oxides. As(V)
506
species is negatively charged under neutral pH condition. The electrostatic repulsion
507
among negatively charged ferric (oxyhydr) oxides and As(V) species would decrease the
508
removal ratio of As(V), and hinder the aggregation of ferric nanoparticles into floc. In
509
comparison, ferric (oxyhydr) oxides is positively charged under acidic condition (pH
510
6.0), and As(V) mainly exists as HAsO42- specie at pH 6.0. The removal efficiency of
511
As(V) is higher in pH 6.0 group than those in other groups, which also suggests that
512
electrostatic attraction plays an important role for the removal of As(V) with ferric
513
(oxyhydr) oxides.
514
3.5 Toxicity assay
515
p-ASA would be oxidized by ferrate and the total-As can be simultaneously
516
removed, while the toxicity of soluble oxidation products is unknown. The effects of
517
p-ASA, As(V), As(III), and ferrate treated p-ASA solution on the growth of E. coli K12
518
and on the luminescent intensity of P. phosphoreum were investigated (Figure 6). For the
519
E. coli K12 cultured in control group, the OD600 value increased to 2.3 within 24 h, and
520
maintained around 2.5 in the following 24 h (Figure 6A). In comparison, when 2.5 mM
521
of inorganic As(V) and As(III) exist in the medium, the solution OD600 values were
522
around 0.6 in both groups. The inorganic As(V) and As(III) species severely inhibited the 28
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523
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growth of E. coli K12.
524 525
Figure 6. Growth curve of E. coli K12 in control group (LB medium), p-ASA (2.5 mM), As(V) (2.5
526
mM), As(III) (2.5 mM), and ferrate treated p-ASA solution (2.5 mM of p-ASA reacted with 25 mM of
527
ferrate for an hour, filtered) (A), and evaluation of acute toxicity of ferrate (1 mM, self-decay for 24
528
h), p-ASA (0.1 mM), p-AP (0.1 mM), nitarsone (0.1 mM), As(III) (0.1 mM), As(V) (0.1 mM), and
529
oxidation products of p-ASA and p-AP ([p-ASA]0 = 0.1 mM, [p-AP]0 = 0.1 mM, reacted with 1 mM
530
of ferrate for 2 h, filtered) with P. phosphoreum (B).
531
For the microbes in p-ASA group, the OD600 peak value approached 1.7 after 34 h
532
of culture, 0.67 lower than those in control group. This suggests that p-ASA (2.5 mM)
533
would inhibit the growth of E. coli K12, while the antibiotic effect is less severe than that 29
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534
of As(V) and As(III). For the E. coli K12 cultured in ferrate treated p-ASA solution, the
535
OD600 peak value increased to 2.7 after 48 h of culture, 0.2 higher than that in control
536
group, and much higher than those in p-ASA, As(III) and As(V) groups. In above
537
sections we showed that 1), ferrate oxidation could degrade p-ASA into As(V),
538
p-aminophenol (p-AP), nitarsone, NO3-, and other products; 2), over 90% of total As
539
could be removed by ferrate resultant particles (ferrate/p-ASA = 10:1, Figure 2B); 3),
540
around 37% of organics could be removed by ferrate resultant particles (ferrate/p-ASA =
541
10:1, Figure 2D). These processes largely eliminated the antibiotic effect of p-ASA and
542
residual products on the growth of E. coli K12.
543
The inhibition effect of relevant samples on the luminescent intensity of P.
544
phosphoreum is used to reflect the acute toxicity (Figure 6B). Decomposition products of
545
ferrate (ferric particles) showed no influence on the luminescent intensity of P.
546
phosphoreum, while over 40% of luminescent intensity was inhibited by As(III), As(V),
547
and nitarsone. In comparison, luminescent intensity inhibition ratios in p-ASA and p-AP
548
groups were around 10% and 18%, respectively. These results are in accordance with
549
previous data, in which the inorganic As species [As(V) and As(III)] are highly toxic, and
550
toxicity of p-ASA is not severe. Toxicity of nitarsone is more severe than that of p-ASA,
551
suggesting that toxic compounds may form in the transformation of organic pollutants.
552
Compared with p-ASA, the ferrate oxidation products formed in ferrate/p-ASA = 5:1
553
group were more toxic. This may because some oxidation products (such as nitarsone, 30
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554
As(V) and p-nitrophenol) formed in the reaction process were not fully oxidized or
555
removed by ferrate resultant particles. When higher levels of ferrate were applied
556
(ferrate/p-ASA = 10:1 and 20:1), luminescent intensity inhibition ratios were negative.
557
This suggests that the activity and metabolization of P. phosphoreum was not depressed.
558
In above sections we showed that p-ASA would be oxidized by ferrate with the formation
559
of As(V), p-AP, nitarsone, and NO3-. The As(V), nitarsone and some part of organics can
560
be removed through adsorption process by the ferrate resultant particles, and p-AP can be
561
further oxidized into p-nitrophenol, 4,4'-(diazene-1,2-diyl) diphenol, NO3- and other
562
products. When 0.1 mM of p-AP was oxidized by 1 mM of ferrate for an hour, the
563
resultant solution also showed no toxicity to P. phosphoreum. This indicates that ferrate
564
treatment (including oxidation and adsorption) is effective for eliminating the toxicity of
565
p-ASA.
566
4. Environmental implications
567
Physical adsorption has many advantages for eliminating pollutants from water. It
568
does not introduce additional chemicals (under ideal condition), and no hazardous
569
transformation products would be formed. However, emerging organic pollutants always
570
exist at low concentration level. Large amount of adsorbent is required to achieve
571
satisfactory removal efficiency. Nanomaterials have been designed for the removal of
572
pollutants, yet they are case-specific, expensive, and would be influenced by background
573
water matrix. 31
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574
Chemical oxidants could effectively degrade organic pollutants, but toxic
575
transformation by-products may be formed in the reaction process. The easily assimilable
576
organic carbon formed in the transformation of organics would negatively influence the
577
microbiological stability of treated water
578
release organics into water. Some transformation products and microbe metabolites may
579
even become disinfection by-products precursors in following water treatment procedures
580
57.
581
microbiological stability of treated water, yet mineralization of organic pollutants with
582
chemical oxidation was energy consuming. Even advanced oxidation processes could
583
mineralize small part of dissolved organics in polluted water.
25,
and reproduced microbes would in turn
Ultimately removing organic components could improve the chemical and
584
Ferrate draws extensive attention as a promising multi-purpose water treatment agent
585
for oxidation, adsorption, coagulation, and disinfection 58. Studies showed that ferrate is
586
effective for the oxidation of organics and controlling inorganic species, while the effect
587
of ferrate resultant nanoparticles on the adsorption of organics received little attention.
588
Oxygen transfer is a main reaction pathway happening in ferrate oxidation process, and
589
the hydroxylation products formed in reaction process have high affinity with ferric
590
(oxyhydr) oxides. Meanwhile, ferric (oxyhydr) oxides newly formed in the reduction of
591
ferrate is well dispersed and small in size. These properties make ferrate resultant
592
nanoparticles a promising agent for the subsequent removal of organic compounds after
593
ferrate oxidation. Investigating the effectiveness and mechanism of ferrate resultant 32
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594
nanoparticles on removal of organic pollutants, and developing relevant methods to
595
enhance this process could provide a new perspective for pollutants control.
596 597
Acknowledgments
598
The authors sincerely appreciate the thoughtful comments and constructive
599
suggestions from the anonymous reviewers and editor. This work was financially
600
supported by the National Key R&D Program of China (2017YFA0207203), and the
601
National Natural Science Foundation of China (Grant No. 51808163).
602 603
Supporting Information
604 605
Seven text, one table, sixteen figures about the experimental operation procedures and additional experimental data are presented in supporting information.
606 607
References
608
1.
Jones, F., A broad view of arsenic. Poultry science 2007, 86, (1), 2-14.
609
2.
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