Subscriber access provided by Fudan University
Article
Imaging Organophosphate and Pyrophosphate Sequestration on Brucite by in Situ Atomic Force Microscopy Lijun Wang, Christine V Putnis, Helen E. King, Jörn Hövelmann, Encarnacion Ruiz-Agudo, and Andrew Putnis Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b05456 • Publication Date (Web): 08 Dec 2016 Downloaded from http://pubs.acs.org on December 9, 2016
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 31
1
Environmental Science & Technology
Imaging Organophosphate and Pyrophosphate Sequestration on Brucite
2
by in Situ Atomic Force Microscopy
3 Lijun Wang,*,† Christine V. Putnis,*,‡,# Helen E. King,§ Jörn Hövelmann,∆ Encarnación
4
Ruiz-Agudo,ǁ and Andrew Putnis‡,┴
5 6 †
7
College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China ‡
8
#
9 §
10 11 12
Institut für Mineralogie, University of Münster, 48149 Münster, Germany
∆
Department of Chemistry, Curtin University, Perth, WA 6845, Australia
Department of Earth Sciences, Utrecht University, 3584 CD Utrecht, The Netherlands
Interface-Geochemistry, Geoforschungszentrum Potsdam,Telegrafenberg, 14473 Potsdam, Germany ǁ
Department of Mineralogy and Petrology, University of Granada, Fuentenueva s/n 18071, Spain ┴
13
The Institute for Geoscience Research (TIGeR), Curtin University, Perth, WA 6102, Australia
14 15
Corresponding authors
16
*College of Resources and Environment, Huazhong Agricultural University, 1 Shizishan St.,
17
Wuhan 430070, China. Phone/Fax: +86-27-87288382. E-mail:
[email protected] (Lijun
18
Wang).
19
Institut für Mineralogie, University of Münster, 48149 Münster, Germany. Phone
20
+49-251-8333454, Fax: +49-251-8338397. E-mail:
[email protected] (Christine V.
21
Putnis)
22 23
Figures: 7 figures = 7 ×300 = 2100 word eq
24
Words: max 7000-2100 = 4900
25
Total words: 4577 (the word number of references not included) 1
ACS Paragon Plus Environment
Environmental Science & Technology
26
Page 2 of 31
ABSTRACT
27 28
In order to evaluate the organic phosphorus (OP) and pyrophosphate (PyroP) cycle and their
29
fate in the environment, it is critical to understand the effects of mineral interfaces on the
30
reactivity of adsorption and precipitation of OP and PyroP. Here, in situ atomic force
31
microscopy (AFM) is used to directly observe the kinetics of coupled dissolution-precipitation
32
on cleaved (001) surfaces of brucite [Mg(OH)2] in the presence of phytate,
33
glucose-6-phosphate (G6P) and pyrophosphate, respectively. AFM results show that the
34
relative order of contribution to mineral surface adsorption and precipitation is phytate >
35
pyrophosphate > G6P under the same solution conditions and can be quantified by the
36
induction time of OP/PyroP-Mg nucleation in a boundary layer at the brucite-water interface.
37
Calculations of solution speciation during brucite dissolution in the presence of phytate or
38
pyrophosphate at acidic pH conditions show that the solutions may reach supersaturation with
39
respect to Mg5H2Phytate.6H2O as a Mg-phytate phase or Mg2P2O7 as a Mg-pyrophosphate
40
phase that becomes thermodynamically stable before equilibrium with brucite is reached. This
41
is consistent with AFM dynamic observations for the new phase formations on brucite. Direct
42
nanoscale observations of the transformation of adsorption/complexation-surface precipitation,
43
combined with spectroscopic characterizations and species simulations may improve the
44
mechanistic understanding of organophosphate and pyrophosphate sequestration by mineral
45
replacement reactions through a mechanism of coupled dissolution-precipitation occurring at
46
mineral-solution interfaces in the environment.
47 48
INTRODUCTION
49 50
Phosphorus (P) is a major growth limiting nutrient of plants and other organisms, and 2
ACS Paragon Plus Environment
Page 3 of 31
Environmental Science & Technology
51
elevated P inputs into soil solutions and aquatic environments leads to eutrophication,
52
therefore increasing the risk of environmental pollution.1 In waters and sediments, dissolved
53
or particulate organic phosphorus (OP) is found in similar amounts to inorganic P.2 Moreover,
54
OP was recently proposed as a potential pool for bioavailable P, promoting much research
55
regarding OP decomposition,3 fractionation,4,5 and characterization.6
56
OP forms include phosphonates, myo-inositol hexakisphosphate, and orthophosphate
57
mono(di)esters.7 Phosphomonoesters in supra-/macro-molecular structures were found to
58
account for the majority of soil OP across diverse soils.8 A considerable proportion of OP in
59
soils or wetlands occurs as stereoisomers of inositol hexakisphosphate (IP6).9 The most
60
abundant myo-IP6 occurs as a phosphorus storage compound in seeds.10,11 When IP6 chelates
61
metals such as Ca, Mg, or Fe it forms an insoluble phytate, for example the common cereal
62
component phytin (Ca−Mg−K phytate).12,13 Phytate has also been detected in plant root
63
exudates.14,15 Glucose-6-phosphate (G6P), a representative sugar monoester, has also been
64
detected in soils.16
65
In addition to OPs, increased amounts of pyrophosphate form after pyrolysis of raw
66
sewage sludge,17 and pyrophosphate is present in aquatic ecosystems including marine
67
particulates18
68
of pyrophosphate in terrestrial and aquatic P cycles is unclear, though it has been shown to be
69
bioavailable even in the presence of high ambient soluble reactive P.19
and estuary sediments,19 and also is common in soil samples.20 The function
70
Most inorganic phosphorus (IP) and OP in soils, eutrophic water bodies or sewage
71
sludges are present as surface adsorbed species on minerals.21,22 The concentrations of both
72
dissolved (DP) and particulate phosphorus (PP) are correlated with the organic component
73
concentration23 in sediment containing different mineral components.24 Various OP and IP
74
compounds including PyroP in these natural environments exhibit significant differences in
75
their chemical behavior with mineral surfaces, reactivity and bioavailability.25 3
ACS Paragon Plus Environment
Environmental Science & Technology
Page 4 of 31
76
OP and PyroP constitute a major component of soil phosphorus and play a key role in the
77
P cycle.26 Therefore, the dynamics of OP and PyroP in the environment,27 particularly the
78
kinetics associated with OP/PyroP-mineral surface reactions, including adsorption,
79
complexation and precipitation, will play a significant role in the biogeochemistry of these
80
molecules and their fate in different ecosystems.27 Although the roles of different mineral
81
surfaces in OP and PyroP adsorption and immobilization have been widely studied, little is
82
known regarding the kinetics of dissolution and precipitation at the brucite mineral-solution
83
interface. As a model mineral, brucite was chosen because 1) it exhibits a simple composition
84
and structure and could be an analogue for brucite-like minerals such as hydrotalcite-like
85
layered double hydroxides (LDHs that include clay minerals) with a high chemical affinity for
86
both OP and PyroP; 2) dissolution and precipitation reactions at the brucite-solution interface
87
occur easily within the AFM experimental time frame. Therefore, the objective of this study
88
was to observe the kinetic processes of brucite dissolution in the presence of phytate, G6P,
89
and pyrophosphate and coupled precipitation. In addition, we aimed to determine how the
90
number of phosphate groups in molecules regulates complexation of OP/PyroP-Mg and
91
subsequent precipitation, providing insights into the fundamental mineral interfacial
92
phenomenon in controlling OP and PyroP sequestration in the environment.
93 94
EXPERIMENTAL SECTION
95 96
Brucite Dissolution. In situ dissolution experiments were performed using a Digital
97
Instruments (Bruker) Nanoscope IIIa AFM (Multimode) operating in contact mode. A natural
98
optically clear brucite crystal (Norberg, Sweden) was cleaved in order to expose a fresh
99
cleavage (001) surface. The brucite was characterized as single phase by X-ray diffraction.
100
The solutions of phytate, G6P, and pyrophosphate (0.01 to 5.0 mM) at different pH values 4
ACS Paragon Plus Environment
Page 5 of 31
Environmental Science & Technology
101
(2.7-9.6), adjusted by the addition of 0.01 M NaOH or HCl, were passed over the cleaved
102
brucite crystals in the AFM fluid cell. NaCl (1.0-100.0 mM at pH 7.0) was added to the
103
phytate or pyrophosphate solutions (1.0 mM) to observe the effects of ionic strength on
104
brucite dissolution. In situ experiments were conducted at a constant flow rate of 1 mL/min to
105
ensure surface-controlled reaction rather than diffusion (transport) control. Different locations
106
of three different crystals per solution condition were imaged to ensure reproducibility of the
107
results. In the present study, the formation of precipitates followed brucite dissolution; thus
108
we used the time before the first particles (about 2.0-6.0 nm in height) were observed on the
109
brucite surface to characterize the kinetics of nucleation.
110
Ex situ dissolution experiments (0.1-1.0 mM phytate at pH 2.7-3.7, 1.0 mM
111
pyrophosphate at pH 4.3, and 5.0 mM G6P at pH 3.5) were performed following in situ AFM
112
experiments. The reacted brucite samples were removed from the AFM fluid cell and placed
113
in a beaker filled with about 10 mL of the different solutions at room temperature for 16-24 h
114
in order to observe further precipitation reactions. After 16 h or 24 h, the samples were
115
removed from the solution and quickly dried using absorbent paper and then immediately
116
imaged in the AFM.
117
Raman Spectroscopy. Raman spectra were collected using a WITec Alpha 300R confocal
118
Raman spectrometer operating with the 785 nm line of a diode laser. A 50x long working
119
distance lens (NA 0.5) was used to obtain spatially constrained information from surface
120
precipitates produced during the AFM and batch experiments. As the precipitates were
121
sensitive to the laser beam, the laser intensity was lowered until no change was observed
122
optically or in the spectrum. Depth scans of the surfaces were taken using with an integration
123
time of 3 s. The brucite spectrum was generated from an average of 4 spectra taken from 5
124
µm below the surface. After positions were identified with additional peaks not related to
125
brucite at the surface, longer collection times were used to help identify the precipitates. 5
ACS Paragon Plus Environment
Environmental Science & Technology
Page 6 of 31
126
Single spectra were taken for 3 s and integrated 30 times to obtain the best signal to noise
127
ratio. All spectra were obtained using a grating of 300 grooves/mm and a pinhole of 20 µm.
128
Spectral background removal and peak fitting was conducted using the WITec Project Plus
129
software (version 4.0).
130
Scanning electron microscopy (SEM). Imaging of the phases precipitated at the brucite
131
surfaces was conducted using a FEI Helios Nanolab G3 SEM. Images of the surface
132
precipitates were taken at 10 kV acceleration voltage and 0.8 nA probe current.
133
PHREEQC Simulations. The PHREEQC program28 was used to simulate the reactions
134
between brucite and OP/PyroP solutions using the database wateq.dat. First, we calculated the
135
solution speciation using thermodynamic constants (Table S1-S7) during brucite dissolution
136
in the presence of 1.0 mM phytate at pH 2.5 and 7.0 by PHREEQC. This provided
137
simulations of brucite dissolving until equilibrium with the solution was reached. For the
138
pyrophosphate system (1.0 mM) at more acidic pH (4.3) conditions the solution reaches
139
saturation with respect to Mg2P2O7 as a Mg-pyrophosphate phase. Moreover, we made further
140
simulations for the same solutions of 1.0 mM phytate and pyrophosphate at a fixed pH of 4.3
141
or 7.0, while allowing the pH to vary as brucite dissolved.
142 143
RESULTS AND DISCUSSION
144 145
Coupled Dissolution-Precipitation at the Brucite-Solution Interface in the Presence of
146
Phytate. Following 329 s of injection of 1 mM phytate (pH 9.0), slow dissolution occurred on
147
the exposed (001) surfaces with the formation of shallow, equilateral triangular etch pits with
148
a depth of 0.5-1.0 nm (Figure 1A, B). Pit depth increased to about 1.5 nm and 2.5-3.0 nm after
149
7 min and 43 min, respectively (Figure 1C, D). The measured depth of shallow etch pits
150
(about 0.5 nm) closely resembles the thickness of one unit-cell layer (0. 47 nm) (Figure 1E). 6
ACS Paragon Plus Environment
Page 7 of 31
Environmental Science & Technology
151
Moreover, according to the brucite sheet structure with edge-sharing Mg(OH)6 octahedra
152
(Figure 1E), the equilateral triangular morphology of the etch pits results from the 3-fold
153
rotation axis normal to the (001) cleavage surface.29
154
When the brucite surface was exposed to 1 mM phytate solutions with 10 mM NaCl at
155
pH 7.0, the pit depth gradually increased to about 6.0 nm after 28 min of reaction (Figure 2A,
156
B). At the same time, spherical particles (2.0-16.0 nm in height) (Figure 2A, B) and 2-D
157
plates (14.0-16.0 nm in thickness) (Figure 2A, C) formed. As the pH of the 1 mM phytate
158
solutions was further decreased to 3.0, simultaneous occurrence of shallow and deep (>10 nm)
159
dissolution pits was observed following 279 s of dissolution reactions (Figure 2D). Rows of
160
etch pits associated with linear defects were evident on areas of the surface that remained free
161
of precipitate (Arrows in Figure 2D, E). The brucite surface became heavily pitted after 360 s
162
(Figure 2E), and finally, the surface was completely covered by nanoparticles (about 40-60
163
nm in height) after 497 s of dissolution (Figure 2F, F’). Dissolution and precipitation was
164
occurring simultaneously in a coupled process at the brucite-solution interface.30,31 The
165
dissolution of brucite releases Mg2+ ions to the interfacial solution in contact with the brucite
166
surface, so that this solution boundary layer becomes supersaturated with respect to a new
167
Mg-OP phase.
168
It is apparent that phytate-mediated brucite dissolution occurs via a different process
169
depending on the pH range. Dissolution at point defects dominated at higher pH (>7.0), and at
170
linear defects (including screw defects, line dislocations, and dislocation loops) at lower pH
171
( indicates a surface
180
site).33,35 Increasing H+ activity results in enhanced protonation of >MgOH0 surface sites and
181
the formation of >MgOH2+, thus promoting brucite dissolution.33 In addition, etch pit
182
spreading is also promoted by the presence of background electrolytes such as NaHCO3 at a
183
constant pH.33
184
Step velocity in the presence of phytate perceptibly increased as pits deepened (depth >
185
10 nm in Figure 2D), although the relationship between step retreat velocity and pit depth and
186
dependence on pH could not be determined in the present AFM experiments. The increase of
187
step velocity in phytate solutions would have contributions from the shallower, slow-retreat
188
pits at point defects promoted by water and the deeper, fast-retreat pits along linear defects
189
promoted by organic ligands such as phytate. These observations are similar to those reported
190
for the case of calcite dissolution in the presence of ethylenediamine tetraacetate (EDTA).32
191
Linear defects (such as dislocations) penetrate deeply into the mineral structure, resulting in
192
deeper pits.32,36,37
193
Coupled Dissolution-Precipitation at the Brucite-Solution Interface in the Presence of
194
Pyrophosphate. In the presence of 1 mM pyrophosphate at pH 9.6 for 23 h, scarce isolated
195
nanoparticles (about 2.0-6.0 nm) were formed along step edges on dissolving brucite surfaces,
196
where dissolution occurred through the formation of typical equilateral triangular etch pits
197
(Figures 3A, S1A’). When the pH was lowered to 7.0 and the pyrophosphate concentration
198
was raised to 5 mM, some particles of size 10-20 nm were present after 43 min of brucite
199
dissolution (Figures 3B, S1B’). When the pH was further decreased to 4.3 in 1 mM
200
pyrophosphate, the immediate formation of pits associated with linear defects (depths in 8
ACS Paragon Plus Environment
Page 9 of 31
Environmental Science & Technology
201
2.0-4.0 nm) was observed after 103 s of dissolution (Figures 3C, D, and S1D’). Spherical
202
particles (about 2.0-10.0 nm in height) (Figures 3E, S1E’) and conical precipitates (about
203
40.0-120.0 nm in height) (Figures 3F, S1F’) were formed after 192 s and 37 min, respectively.
204
Coupled Dissolution-Precipitation at the Brucite-Solution Interface in the Presence of
205
G6P. In the presence of 1 mM G6P at pH 5.9, dissolution occurred with the formation of
206
equilateral triangular etch pits on the brucite (001) surfaces, and their depth gradually
207
increased from about 4.0 nm at 13 min, to about 8.0 nm at 41 min, and 8.0-10.0 nm at 81 min
208
(Figure 4). At the same time, their sizes (width) also increased (Figure 4A’-C’). However, no
209
precipitates were observed even after 17 h of ex situ reactions (Figure S2). As the G6P
210
concentration was increased to 5 mM at pH 5.8, precipitates were formed after 18 h in ex situ
211
reactions (Figure S3). When the pH of 5 mM G6P solutions was decreased to 3.5, etch pits
212
rapidly formed (Figure 5); the brucite surfaces were completely covered by particles (Figure 5)
213
with a height of 40-50 nm (Figure S4A, B) after 16 h of dissolution reactions.
214
Dynamics of Nucleation and Growth of Mg-OP/PyroP on Brucite. The dissolving brucite
215
surfaces in the presence of OPs and pyrophosphate provided a source of Mg2+ ions, resulting
216
in supersaturation of the solution in the brucite-solution boundary layers with respect to an
217
OP/PyroP-Mg phase.38 This will drive surface-induced nucleation and growth on the brucite
218
surface. According to classical nucleation theory (CNT), the steady-state nucleation rate
219
(number of nucleation events per square meter per second), J, can be calculated as:39,40
220
exp
∆
(1)
221
where A is a kinetic constant, depending on physical parameters such as diffusional
222
barriers,39,40 ΔG* is the total free-energy cost to form a spherical crystallite, kB is Boltzmann’s
223
constant, and T is temperature.39,40 The technical difficulties involved in directly evaluating
224
crystal nucleation rates41 have led to an approach to measure the induction period (t) prior to
225
nucleation based on the equation J =1/(tV),41 where V is the volume of the entire system (i.e. 9
ACS Paragon Plus Environment
Environmental Science & Technology
Page 10 of 31
226
fluid + crystal, about 50 μL). In the present study, we used the time required to observe the
227
occurrence of the first smallest particles (about 2.0-6.0 nm in height) on brucite to
228
characterize the kinetics of nucleation. Moreover, we only compared the induction times for
229
phytate and pyrophosphate solutions on brucite surfaces because a relatively longer time was
230
required to form nucleated particles for solutions containing G6P (Figure S2). The most likely
231
explanation for delayed nucleation in GP6 solutions is that G6P contains the lowest number of
232
phosphate groups 1) compared to the other two molecules tested, 2) and hence indicates a
233
lower chelation ability. The induction time significantly increased with the increase in pH for
234
both phytate and pyrophosphate solutions at 1 mM, and at the same alkaline pH, the induction
235
time for pyrophosphate (1 mM) is much longer than that of phytate (1 mM)
236
Shorter induction times were observed with increasing phytate or pyrophosphate solution
237
concentration (Figure 6B) or NaCl concentration (in 1 mM phytate or pyrophosphate) (Figure
238
6C) when the solution pH was kept constant (7.0).
(Figure 6A).
239
Mineral dissolution kinetics is complicated in the presence of inorganic/organic ligands42
240
and background electrolytes.34,43 Background electrolytes can enhance the mineral dissolution
241
rate due to the ability of salt ions to modify water structure as well as solute and mineral
242
surface hydration.43,44 The amount of released Mg2+ ions by dissolution is increased in the
243
presence of NaCl, thereby resulting in rapid nucleation of a Mg-OP/PyroP phase with shorter
244
induction times because a higher degree of supersaturation is reached within the boundary
245
layers. This phenomenon has also been observed in the calcite-G6P system.44
246
Identification of Precipitates on Brucite (001) Cleavage Surfaces. Using Raman
247
spectroscopy, the cleaved brucite surface shows two sharp, intense peaks at 281 and 446 cm-1
248
and two broad peaks with centres at 725 and 809 cm-1 (Figure 7A). This is consistent with
249
previous analysis of brucite using spectroscopic methods.45 In contrast, precipitates on the
250
brucite surface show additional peaks depending on the organophosphate present in the 10
ACS Paragon Plus Environment
Page 11 of 31
Environmental Science & Technology
251
experiment solution. In experiments with G6P, the precipitates were highly reactive to the
252
laser beam and even at the lowest laser intensity were burnt during analysis. However, the
253
burnt material produced broad peaks at 1332 and 1575 cm-1 (Figure 7B) that are characteristic
254
for amorphous carbon material46 implying the original material was carbon-bearing,
255
consistent with the precipitation of an organic-C phase during the experiments. Precipitates on
256
the surface of brucite produced during the phytate experiments were stable in the Raman laser
257
and produced clear peaks in the Raman spectra (Figure 7C). Additional peaks were observed
258
as a broad peak at 544 cm-1, three sharp and one broad peak at 954, 993, 1034 and 1100 cm-1
259
and two broad bands at 1282 and 1372 cm-1. These peaks are consistent with known Raman
260
peaks for solid samples of phytate47,48 and particularly those between 950 and 1100 cm-1 are
261
related to the symmetrical stretch of the phosphate moiety within the phytate molecule.
262
However, the peaks are consistently shifted to higher wavenumbers in comparison to previous
263
studies by as much as 10 cm-1 compared to the initial sodium salt.49 Such a shift could imply a
264
difference in chemistry of the precipitates through the incorporation of Mg released from the
265
dissolving brucite, as Mg-acetate has been found to show a shift to higher wavenumbers in
266
comparison to the Na-acetate salt.50 No additional bands to those belonging to brucite were
267
observed on the pyrophosphate sample surface. This can be explained from the SEM
268
observations because the precipitate forms very thin, spread out crystals on the surface
269
(Figure S5). In this case the laser beam would not sample enough of the precipitate during
270
Raman analysis to produce bands in the spectra, precluding any possible identification of
271
other vibrational peaks from any nanometer thin precipitate layer.
272
PHREEQC Simulations. Finally, we calculated the solution speciation using thermodynamic
273
constants (Table S1-S7) during brucite dissolution in the presence of 1.0 mM phytate at pH
274
2.5 and 7.0 by PHREEQC.28 This allowed simulations of brucite dissolving until equilibrium.
275
The simulations show that for both initial pH values, the solution (volume of solution is 11
ACS Paragon Plus Environment
Environmental Science & Technology
Page 12 of 31
276
equivalent to that of the AFM fluid cell, about 35-50 μL) would reach supersaturation with
277
respect to Mg5H2Phytate.6H2O as a Mg-phytate phase (Supporting Data 1 and 2). This is
278
consistent with the AFM results (Figure 2). For the pyrophosphate system (1.0 mM) at more
279
acidic pH (4.3) the solution reaches saturation with respect to Mg2P2O7 as a
280
Mg-pyrophosphate phase, that may become stable before equilibrium with brucite is attained
281
(Supporting Data 3). At pH ≥7.0, the solution is saturated with respect to brucite before
282
saturation with respect to Mg2P2O7 is attained (Supporting Data 4 and 5). This means for the
283
formation of Mg2P2O7 at higher pH more brucite would need to dissolve (to release enough
284
Mg2+) through the addition of higher pyrophosphate concentrations and/or longer reaction
285
times. These simulation results are also consistent with the AFM observations (Figure 3).
286
Moreover, we made further simulations for the same solutions of 1.0 mM phytate and
287
pyrophosphate at a fixed pH of 4.3 or 7.0, while allowing the pH to vary as brucite dissolved.
288
Results showed that both Mg5H2Phytate.6H2O and Mg2P2O7 become thermodynamically
289
stable due to the solutions reaching supersaturation with respect to these two phases
290
(Supporting Data 6-8). Because it is impossible to include all possible species in the database
291
and appropriate equilibrium constants are mostly lacking, the simulations are incomplete,
292
especially for the formation of other solid phases, for example hydrated Mg2P2O7.
293
Due to the limitation of appropriate thermodynamic data, all PHREEQC simulations were
294
an approximation to the real scenario. However the simulations predicted the fast formation of
295
a Mg-phytate phase at the pH values tested. The Mg-PyroP phase did not form at pH ≥ 7 and
296
only became significant at lower pH values when dissolution of brucite was enhanced. This is
297
in accordance with the AFM observations and Raman analyses, especially, as Raman analyses
298
for ex situ formation of precipitates on the surface of brucite verify the utility of speciation
299
modeling. The lack of equilibrium constant data did not allow for simulations with G6P.
300
In summary, from our observations a higher number of phosphate groups in a phosphate 12
ACS Paragon Plus Environment
Page 13 of 31
Environmental Science & Technology
301
molecule seems to enhance the chelating ability of the molecule to sequester Mg2+. The
302
reaction rates of dissolution and subsequent precipitation followed the order: phytate (with 6
303
phosphate groups per molecule) > pyrophosphate (2 phosphate groups) > G6P (1 phosphate
304
group) at all pH values tested.
305
Implications. A fundamental challenge in the study of soil organic and inorganic phosphate
306
dynamics is to assess the relative importance of adsorption and precipitation processes on
307
mineral surfaces in the environment as this plays an important role in the global P cycle.44 In
308
this study, direct AFM observations and kinetic analyses have been applied to observe and
309
predict the behavior of OPs and PyroP on brucite mineral surfaces. Our results may provide
310
dynamic insights into how OP and PyroP can be sequestered through mineral interfacial
311
dissolution-precipitation reactions.51 The approach used in this study may readily extend to
312
further investigate the adsorption and precipitation dynamics of guest anions/cations on the
313
surfaces and in the interlayer spaces in brucite-like minerals such as hydrotalcite-like layered
314
double hydroxides (LDHs).52 These minerals are of considerable environmental relevance
315
because of their anion-exchange capacity that can affect the mobility of chemical species and
316
removal of toxic anions.52 Moreover, these materials can accommodate a wide range of
317
different cations in the interlayer spaces for use in environmental remediation of heavy
318
metals.52,53
319 320
ASSOCIATED CONTENT
321 322
Supporting Information. AFM images and depth profiles of brucite dissolution and
323
precipitation in the presence of pyrophosphate (Figure S1); ex situ reaction of 1 mM G6P with
324
brucite (Figure S2); ex situ reaction of 5 mM G6P with brucite (Figure S3); depth profile of
325
brucite substrates covered by larger nanoparticles in 5 mM G6P at pH 3.5 (Figure S4); SEM 13
ACS Paragon Plus Environment
Environmental Science & Technology
Page 14 of 31
326
images of brucite with OPs under different reaction conditions (Figure S5); Protonation
327
constants for phytate (Table S1); Association constants for Mg-phytate complexes (Table S2).
328
Solubility constants of possible solid phases (Mg-phytate) (Table S3). Protonation constants
329
for pyrophosphate (PyroP) (Table S4). Association constants for Na-pyrophosphate
330
complexes (Table S5). Association constants for Mg-pyrophosphate complexes (Table S6).
331
Solubility constants of possible solid phases (Mg-PyroP) (Table S7), and PHREEQC
332
calculations (Supporting Data 1-8). This material is available free of charge via the Internet at
333
http://pubs.acs.org.
334 335
AUTHOR INFORMATION
336 337
Corresponding authors
338
*E-mail:
[email protected] (Lijun Wang);
[email protected] (Christine V. Putnis)
339 340
ACKNOWLEDGMENT
341
This work was supported by the National Natural Science Foundation of China (41471245
342
and 41071208), a Specialized Research Fund for the Doctoral Program of Higher Education
343
(20130146110030), and the Fundamental Research Funds for the Central Universities
344
(2662015PY206, 2662015PY116). C.V. Putnis and A. Putnis acknowledge support through
345
EU Marie Curie initial training networks (FlowTrans and CO2 React). E.R.-A. acknowledges
346
a Ramón y Cajal grant and support from the Research Group RNM-179 of the Junta de
347
Andalucía.
348 349
REFERENCES 14
ACS Paragon Plus Environment
Page 15 of 31
350
Environmental Science & Technology
(1)
351 352
10, 439–454. (2)
353 354
Baldwin, D. S. Organic phosphorus in the aquatic environment. Environ. Chem. 2013,
Turner, B. L.; Frossard, E.; Baldwin, D. S. Organic Phosphorus in the Environment; CABI Publishing: Cambridge, 2005.
(3)
Dyhrman, S.; Chappell, P.; Haley, S.; Moffett, J.; Orchard, E.; Waterbury, J.; Webb,
355
E.
356
Trichodesmium. Nature 2006, 439, 68−71.
357
(4)
Phosphonate
utilization
by
the
globally
important
marine
diazotroph
Zhu, Y. R.; Wu, F. C.; He, Z. Q.; Guo, J. Y.; Qu, X. X.; Xie, F. Z.; Giesy, J. P.; Liao,
358
H. Q.; Guo, F. Characterization of organic phosphorus in lake sediments by sequential
359
fractionation and enzymatic hydrolysis. Environ. Sci. Technol. 2013, 47, 7679−7687.
360
(5)
Lu, C.; Wang, B.; He, J.; Vogt, R. D.; Zhou, B.; Guan, R.; Zuo, L., Wang, W.; Xie, Z.;
361
Wang, J.; Yan, D. Responses of organic phosphorus fractionation to environmental
362
conditions and lake evolution. Environ. Sci. Technol. 2016, 50, 5007−5016.
363
(6)
Ahlgren, J.; Tranvik, L.; Gogoll, A.; Waldebäck, M.; Markides, K.; Rydin, E.
364
Sediment depth attenuation of biogenic phosphorus compounds measured by 31P
365
NMR. Environ. Sci. Technol. 2005, 39, 867−872.
366
(7)
Cade-Menun, B. J.; Navaratnam, J. A.; Walbridge, M. R. Characterizing dissolved
367
and particulate phosphorus in water with 31P nuclear magnetic resonance
368
spectroscopy. Environ. Sci. Technol. 2006, 40, 7874−7880.
369
(8)
McLaren, T. I.; Smernik, R. J.; McLaughlin, M. J.; McBeath, T. M.; Kirby, J. K.;
370
Simpson, R. J.; Guppy, C. N.; Dooletter, A. L.; Richardson, A. E. Complex forms of
371
soil organic phosphorus-A major component of soil phosphorus. Environ. Sci.
372
Technol. 2015, 49, 13238−13245.
15
ACS Paragon Plus Environment
Environmental Science & Technology
373
(9)
Page 16 of 31
Sims, J. T.; Pierzynski, G. M. Chemistry of Phosphorus in Soils. In Chemical
374
Processes in Soils; Tabatabai, M. A., Sparks, D. L., Eds.; Soil Science Society of
375
America: Madison, WI, 2005; pp 151−192.
376
(10) Turner, B. L.; Cheesman, A. W.; Godage, H. Y.; Riley, A. M.; Potter, B. V. L.
377
Determination of neo- and D-chiro-inositol hexakisphosphate in soils by solution 31P
378
NMR spectroscopy. Environ. Sci. Technol. 2012, 46, 4994−5002.
379
(11) Azeem, M.; Riaz, A.; Chaudhary, A. N.; Hayat, R.; Hussain, Q.; Tahir, M. I.; Imran,
380
M. Microbial phytase activity and their role in organic P mineralization. Arch. Agron.
381
Soil Sci. 2015, 61, 751−766.
382 383
(12) Turner, B. L.; Paphazy, M. J.; Haygarth, P. M.; McKelvie, I. D. Inositol phosphates in the environment. Philos. Trans. R. Soc., B 2002, 357, 449−469.
384
(13) Thavarajah, P.; Thavarajah, D.; Vandenberg, A. Low phytic acid lentils (Lens
385
culinaris L.): a potential solution for increased micronutrient bioavailability. J. Agric.
386
Food Chem. 2009, 57, 9044−9049.
387
(14) Tu, S. X.; Ma, L.; Luongo, T. Root exudates and arsenic accumulation in arsenic
388
hyperaccumulating Pteris vittata and nonhyperaccumulating Nephrolepis exaltata.
389
Plant Soil 2004, 258, 9−19.
390
(15) Liu, X.; Fu, J. W.; Guan, D. X.; Cao, Y.; Luo, J.; Rathinasabapathi, B.; Chen, Y. S.;
391
Ma, L. Q. Arsenic induced phytate exudation, and promoted FeAsO4 dissolution and
392
plant growth in As-hyperaccumulator Pteris vittata. Environ. Sci. Technol. 2016, 50,
393
9070−9077.
394
(16) Espinosa, M.; Turner, B. L.; Haygarth, P. M. Preconcentration and separation of trace
395
phosphorus compounds in soil leachate. J. Environ. Qual. 1999, 28, 1497−1504.
16
ACS Paragon Plus Environment
Page 17 of 31
396 397
Environmental Science & Technology
(17) Huang, R. X.; Tang, Y. Z. Speciation dynamics of phosphorus during (hydro)thermal treatments of sewage sludge. Environ. Sci. Technol. 2015, 49, 14466−14474.
398
(18) Paytan, A.; Cade-Menun, B. J.; McLaughlin, K.; Faul, K. L. Selective phosphorus
399
regeneration of sinking marine particles: evidence from 31P NMR. Mar. Chem. 2003,
400
82, 55−70.
401
(19) Sundareshwar, P. V.; Morris, J. T.; Pellechia, P. J.; Cohen, H. J.; Porter, D. E.; Jones,
402
B. C. Occurrence and implications of pyrophosphate in estuaries. Limnol. Oceanogr.
403
2001, 46, 1570−1577.
404 405 406 407
(20) Cade-Menun, B. J. Organic Phosphorus in the Environment; CABI Publishing: Oxon, U.K., 2005. (21) Selig, U.; Hübener, T.; Michalik, M. Dissolved and particulate phosphorus forms in a eutrophic shallow lake. Aquat. Sci. 2002, 64, 97–105.
408
(22) Nõges, P.; Tuvikene, L.; Nõges, T.; Kisand, A. Primary production, sedimentation
409
and resuspension in large shallow Lake Võrtsjärv. Aquat. Sci. 1999, 61, 168–182.
410
(23) Shinohara, R.; Imai, A.; Kawasaki, N.; Komatsu, K.; Kohzu, A.; Miura, S.; Sano, T.;
411
Satou, T.; Tomioka, N. Biogenic phosphorus compounds in sediment and suspended
412
particles in a shallow eutrophic lake: A
413
Environ. Sci. Technol. 2012, 46, 10572−10578.
31
P-nuclear magnetic resonance study.
414
(24) Shinohara, R.; Imai, A.; Kohzu, A.; Tomioka, N.; Furusato, E.; Satou, T.; Sano, T.;
415
Komatsu, K.; Miura, S.; Shimotori, K. Dynamics of particulate phosphorus in a
416
shallow eutrophic lake. Sci. Total Environ. 2016, 563-564, 413–423.
417
(25) Condron, L. M.; Turner, B. L.; Cade-Menun, B. J. Chemistry and dynamics of soil
418
organic phosphorus. In Phosphorus: Agriculture and the Environment; Sims, T., 17
ACS Paragon Plus Environment
Environmental Science & Technology
Page 18 of 31
419
Sharpley, A. N., Eds.; American Society of Agronomy: Madison, Wisconsin, 2005;
420
pp 87–121.
421
(26) Turner, B. L.; Newman, S.; Ramesh Reddy K. Overestimation of organic phosphorus
422
in wetland soils by alkaline extraction and molybdate colorimetry. Environ. Sci.
423
Technol. 2006, 40, 33493–3354.
424 425
(27) Turner, B. L., Frossard, E., Baldwin, D. S. Organic Phosphorus in the Environment; CAB International: Wallingford, 2005.
426
(28) Parkhurst, D. L.; Appelo, C. A. J. Users guide to PHREEQC (Version 3). A Computer
427
Program for Speciation, Batch-Reaction, One-Dimensional Transport, and Inverse
428
Geochemical Calculations: U.S. Geological Survey Techniques and Methods; U.S.
429
Geological Survey: Washington, DC, 2013.
430
(29) Kudoh, Y.; Kameda, J.; Kogure, T. Dissolution of brucite on the (001) surface at
431
neutral pH: in situ atomic force microscopy observations. Clays Clay Miner. 2006, 54,
432
598−604.
433
(30) Putnis, A. Mineral replacement reactions. In: Oelkers, E.H., Schott, J. (Eds.), Thermo-
434
dynamics and Kinetics of Water–Rock Interaction. Reviews in Mineralogy & Geoche
435
mistry 2009, 30, 87–124.
436 437
(31) Ruiz-Agudo, E.; Putnis, C.V.; Putnis, A. Coupled dissolution and precipitation at min eral–fluid interfaces. Chem. Geol. 2014, 383, 132–146.
438
(32) Perry, T. D.; Duckworth, O. W.; Kendall, T. A.; Martin, T. A.; Mitchell, R. Chelating
439
ligand alters the microscopic mechanism of mineral dissolution. J. Am. Chem. Soc.
440
2005, 127, 5744−5745.
441
(33) Hövelmann, J.; Putnis, C. V.; Ruiz-Agudo, E.; Austrheim, H. Direct nanoscale
442
observations of CO2 sequestration during brucite [Mg(OH)2] dissolution. Environ. Sci. 18
ACS Paragon Plus Environment
Page 19 of 31
443
Environmental Science & Technology
Technol. 2012, 46, 5253−5260.
444
(34) Wang, L. J.; Ruiz-Agudo, E.; Putnis, C. V.; Menneken, M.; Putnis, A. Kinetics of
445
calcium phosphate nucleation and growth on calcite: Implications for predicting the
446
fate of dissolved phosphate species in alkaline soils. Environ. Sci. Technol. 2012, 46,
447
834−842.
448
(35) Pokrovsky, O. S.; Schott, J. Experimental study of brucite dissolution and
449
precipitation in aqueous solutions: surface speciation and chemical affinity control.
450
Geochim. Cosmochim. Acta 2004, 68, 31−45.
451 452 453
(36) MacInnis, I. N.; Brantley, S. L. The role of dislocations and surface morphology in calcite dissolution. Geochim. Cosmochim. Acta 1992, 56, 1113−1126. (37) Duckworth, O. W.; Martin, S. T. Dissolution rates and pit morphologies of
454
rhombohedral carbonate minerals. Am. Mineral. 2004, 89, 554−563.
455
(38) Putnis, A. Why mineral interfaces matter. Science 2014, 343, 1441−1442.
456
(39) Liu, X. Y.; Lim, S. W. Templating and supersaturation driven anti-templating:
457
Principles of biominerals architecture. J. Am. Chem. Soc. 2003, 125, 888−895.
458
(40) Nielsen, A. E. Kinetics of Precipitation; Pergamon: Oxford, U.K., 1964
459
(41) Wang, L. J.; Guan, X.; Tang, R.; Hoyer, J. R.; Wierzbicki, A.; De Yoreo, J. J.;
460
Nancollas, G. H. Phosphorylation of osteopontin is required for inhibition of calcium
461
oxalate crystallization. J. Phys. Chem. B 2008, 112, 9151−9157.
462
(42) Qin, L. H.; Zhang, W. J.; Lu, J. W.; Stack, A. G.; Wang, L. J. Direct imaging of
463
nanoscale dissolution of dicalcium phosphate dihydrate by an organic ligand:
464
Concentration matters. Environ. Sci. Technol. 2013, 47, 13365−13374.
465
(43) Ruiz-Agudo, E.; Kowacz, M.; Putnis, C. V.; Putnis, A. The role of background 19
ACS Paragon Plus Environment
Environmental Science & Technology
Page 20 of 31
466
electrolytes on the kinetics and mechanism of calcite dissolution. Geochim.
467
Cosmochim. Acta 2010, 74, 1256−1267.
468
(44) Wang, L. J.; Qin, L. H.; Putnis, C. V.; Ruiz-Agudo, E.; King, H. E.; Putnis, A.
469
Visualizing organophosphate precipitation at the calcite-water interface by in situ
470
atomic-force microscopy. Environ. Sci. Technol. 2016, 50, 259−268.
471
(45) Dawson, P.; Hadfield, C. D.; Wilkinson, G. R. The polarized infra-red and Raman
472
spectra of Mg(OH)2 and Ca(OH)2. J. Phys. Chem. Solids 1973, 34, 1217–1225.
473
(46) Ferrari, A. C.; Robertson, J. Interpretation of Raman spectra of disordered and
474
amorphous carbon. Phys. Rev. B 2000, 61, 14095–14107.
475
(47) Kolozsvari, B.; Firth, S.; Saiardi, A. Raman spectroscopy detection of phytic acid in
476
plant seeds reveals the absence of inorganic polyphosphate. Molecular Plant 2015, 8,
477
826–828.
478
(48) Yang, H. F.; Feng, J.; Liu, Y. L.; Yang, Y.; Zhang, Z. R.; Shen, G. L.; Yu, R. Q.
479
Electrochemical and surface enhanced Raman scattering spectroelectrochemical study
480
of phytic acid on the silver electrode. J. Phys. Chem. B 2004, 108, 17412–17417.
481
(49) Yang, H.; Yang, Y.; Yang, Y.; Liu, H.; Zhang, Z.; Shen, G.; Yu, R. Formation of
482
inositol hexaphosphate monolayers at the copper surface from a Na-salt of phytic acid
483
solution studied by in situ surface enhanced Raman scattering spectroscopy, Raman
484
mapping and polarization measurements. Anal. Chim. Acta 2005, 458, 150–165.
485
(50) Frost, R. L.; Kloprogge, J. T. Raman spectroscopy of the acetates of sodium,
486
potassium and magnesium at liquid nitrogen temperature. J. Mol. Struct. 2000, 526,
487
131–141.
488
(51) Putnis, C.V.; Ruiz-Agudo, E. The mineral-water interface: where minerals react with 20
ACS Paragon Plus Environment
Page 21 of 31
489
Environmental Science & Technology
the environment. Elements 2013, 9, 177–182.
490
(52) Sideris, P. J.; Nielsen, U.; Gan, Z.; Grey, C. P. Mg/Al ordering in layered double
491
hydroxides revealed by multinuclear NMR spectroscopy. Science 2008, 321,
492
113–117.
493
(53) Liang, X.; Zang, Y.; Xu, Y.; Tan, X.; Hou, W.; Wang, L.; Sun, Y. Sorption of metal
494
cations on layered double hydroxides. Colloids and Surfaces A: Physicochem. Eng.
495
Aspects 2013, 433, 122– 131.
496 497
Figure Legends
498 499
Figure 1. Time sequence AFM (deflection mode) images of natual brucite dissolution. (A-D)
500
Time-lapse images show equilateral triangular etch pit formation and evolution on the (001)
501
cleavage plane (the white circles in B-D) after injection of 1 mM phytate (pH 9.0) into a
502
flow-through cell. Images A-C, 3×3 μm; D, 5×5 μm. (A’-D’) Depth profile of the etch pit at
503
t =245 s, 329 s, 7 min, or 43 min, respectively, measured along the white dashed lines in
504
(A-D). (E) The brucite atomic structure projected along the b-axis (in right panel of E; 0.47
505
nm of the thickness of one Mg(OH)2 layer), and the c-axis (in left panel of E; the morphology
506
and crystallographic orientation of the edges of the triangular etch pits is indicated).
507 508
Figure 2. Time sequence AFM (deflection mode) images of brucite dissolution and
509
precipitation in the presence of phytate. (A) In situ AFM images show both etch pit formation
510
and precipitation on a brucite (001) surface in 1 mM phytate + 10 mM NaCl (pH 7.0) at t =28
511
min. (B and C) Height profiles of nucleated nanoparticles (about 2-16 nm) and 2-D nanoplates
512
(about 16 nm in thickness) along the dashed lines 1→1’ and 2→2’, respectively. (D and E) 21
ACS Paragon Plus Environment
Environmental Science & Technology
Page 22 of 31
513
Time-resolved AFM images show the coexistence of point and line defects formed in 1 mM
514
phytate (pH 3.0). Pits associated with observable line defects are apparent (Arrows). (D’ and
515
E’) Depth profiles of etch pits and line defects along the dashed lines 3→3’ and 4→4’,
516
respectively. (F) After 497 s, brucite substrates were covered by larger nanoparticles (about
517
50 nm in F’). Image A, 3×3 μm; D-F, 5×5 μm.
518 519
Figure 3. Time sequence AFM (deflection mode) images of brucite dissolution and
520
precipitation in the presence of pyrophosphate. In situ AFM images show coupled dissolution
521
(by etch pit formation) and precipitation on a brucite (001) surface in (A) 1 mM
522
pyrophosphate (pH 9.6) at t =23 h and (B) 5 mM pyrophosphate (pH 7.0) at t =43 min.
523
Time-resolved AFM images show (C and D) the formation of pits associated with line defects,
524
and (E and F) spherical particles and conical precipitates in 1 mM pyrophosphate (pH 4.3).
525
Images A and C-F, 3×3 μm; B, 5×5 μm.
526 527
Figure 4. Time sequence AFM (deflection mode) images of brucite dissolution in the
528
presence of G6P. (A-C) In situ AFM images of a brucite (001) surface dissolving in 1 mM
529
G6P (pH 5.9). (A’-C’) Depth profiles of the etch pits evaluated along the white dashed lines
530
in A-C. Images A-C, 3×3 μm.
531 532
Figure 5. Time-resolved AFM (deflection mode) images of brucite dissolution and
533
precipitation in the presence of G6P. In situ AFM images show both (A-C) etch pit formation
534
and evolution, and (D) precipitation on a brucite (001) surface in 5 mM G6P (pH 3.5). After
535
16 h, brucite substrates were covered by larger nanoparticles. Images A-D, 3×3 μm.
536 537
Figure 6. Induction times for precipitate formation on the brucite (001) surfaces under 22
ACS Paragon Plus Environment
Page 23 of 31
Environmental Science & Technology
538
various experimental conditions in the presence of phytate or pyrophosphate. (A) A range of
539
pH values, (B) Phytate or pyrophosphate concentrations at pH 7.0, and (C) NaCl
540
concentrations with 1 mM phytate or pyrophosphate at pH 7.0. Induction times are reported as
541
mean ± SD.
542 543
Figure 7. Raman spectra taken from (A) brucite, and surface precipitates from an AFM
544
experiment run with (B) G6P or (C) phytate. Asterisks indicate peaks unrelated to the
545
underlying brucite generated by the surface precipitates in the different organic phosphate
546
experiments.
547 548 549 550 551
23
ACS Paragon Plus Environment
Environmental Science & Technology
A’
A
Page 24 of 31
3.0
Depth (nm)
2.5 2.0 1.5 1.0 0.5
~0.5 nm
0.0 0.7
B’
0.8
0.9 1.0 1.1 1.2 Distance (μm)
1.3
1.4
1.7
1.8
3.5 3.0
1 mM phytate, pH 9.0 t = 245 s
Depth (nm)
2.5
B
2.0 1.5 1.0
~1.0 nm
0.5 0.0 1.1
C’
1.2
1.3
1.4 1.5 1.6 Distance (μm)
5
Depth (nm)
4
329 s
3 2 1
~1.5 nm
0 1.0
C
1.2 1.4 Distance (μm)
1.6
D’ 7 6
Depth (nm)
5
~3 nm
4 3 2
~2.5 nm
1 0 1.4
1.6
1.8
2.0 2.2 2.4 Distance (μm)
2.6
2.8
E
7 min
0.47 nm
D
b
552 553
43 min
c
c a
b
a
Figure 1
24
ACS Paragon Plus Environment
Page 25 of 31
Environmental Science & Technology
A B
2
C
25
15
~2.0 nm
10 5
2’
1
~16.0 nm
~6.0 nm 0.5
1.0 1.5 2.0 Distance (μm)
1 mM phytate + 10 mM NaCl pH 7.0 t = 28 min
2.5
3’
4
15 10 5
555
E’
1
2 3 Distance (μm)
4
5
2.5
3.0
497 s
4’
4
30 20 10
7000 6000 5000 4000 3000 2000 1000 0
0
1.0 1.5 2.0 Distance (μm)
F’ 8000
50
0
0
0.5
4’
40
20
2 0.0
360 s
Depth (nm)
Depth (nm)
25
3’
3
2’
F
1 mM phytate, pH 3.0 t = 279 s
D’ 30
18 16 14 12 10 8 6 4 2 0
3.0
E
3
554
1’
0 0.0
D
Height (nm)
20
Number of events
1’
Height (nm)
1
0
1
2 3 4 Distance (μm)
5
0
10 20 30 40 50 60 70 80 Height (nm)
Figure 2
556 557 558 559 560 561 562 563 564 565 25
ACS Paragon Plus Environment
Environmental Science & Technology
A
1 mM pyrophosphate, pH 9.6 t = 23 h
B
C
H2O, pH 4.3
D
E
192 s
F
Page 26 of 31
5 mM pyrophosphate, pH 7.0 t = 43 min
1 mM pyrophosphate, pH 4.3 t = 103 s
37 min
566 567
Figure 3
568 569 570 571 572 573 574 575 576 26
ACS Paragon Plus Environment
Environmental Science & Technology
A
1 mM G6P, pH 5.9 t = 13 min
10 Depth (nm)
B’ 12
4 Depth (nm)
578
41 min
A’ 5 3 2 1
0.0
1.0 1.5 2.0 Distance (μm)
2.5
3.0
10
8 6 4
0.0
81 min
12 8 6 4 2
0
0.5
C
C’ 14
2
0
577
B
Depth (nm)
Page 27 of 31
0 0.5
1.0 1.5 2.0 Distance (μm)
2.5
3.0
0.0
0.5
1.0 1.5 2.0 Distance (μm)
2.5
3.0
Figure 4
579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 27
ACS Paragon Plus Environment
Environmental Science & Technology
Page 28 of 31
A
H2O, pH 6.0
B
5 mM G6P, pH 3.5 t = 109 s
C
43 min
D
16 h
594 595
Figure 5
596 597 598 599 600 601 602 603 604 605 606 607 608 28
ACS Paragon Plus Environment
Page 29 of 31
Environmental Science & Technology
A 1600 1400 1200 1000 800 600 400 200 0
Induction time (min)
Pyrophosphate 1 mM Phytate or Pyrophosphate
Phytate
3
4
5
6
7
8
9
10
pH
Induction time (min)
B 250 Phytate pH 7.0
200 150 100 50 0
0.01
0.1 1 Concentration (mM)
Induction time (min)
C 180 160 140 120 100 80 60 40 20 0
610
10
1 mM Phytate or Pyrophosphate pH 7.0
Pyrophosphate Phytate
0
609
Pyrophosphate pH 7.0
20
40 60 NaCl (mM)
80
100
Figure 6
611 612 613 614 615 616 617 618 619 29
ACS Paragon Plus Environment
Intensity (a. u.)
Environmental Science & Technology
*
* * ** * * * *
Page 30 of 31
Phytate on brucite
C G6P on brucite
*
B brucite
A
0 620
500 1000 1500 -1 Wavenumbers (cm )
2000
621 622
Figure 7
623 624 625 626 627 628 629 630 631 632 633 634 635 636 30
ACS Paragon Plus Environment
Page 31 of 31
Environmental Science & Technology
1 mM phytate, pH 3.0
5 mM pyrophosphate, pH 7.0
1 mM pyrophosphate, pH 4.3
or 5 mM G6P, pH 3.5
637 638
TOC Graphical abstract
31
ACS Paragon Plus Environment