New Insights into Black Carbon Nanoparticle-induced Dispersibility of

Subscriber access provided by UniSA Library

Environmental Processes

New Insights into Black Carbon Nanoparticle-induced Dispersibility of Goethite Colloids and Configuration-dependent Sorption for Phenanthrene Fei Lian, Wenchao Yu, Zhenyu Wang, and Baoshan Xing Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b05066 • Publication Date (Web): 12 Dec 2018 Downloaded from http://pubs.acs.org on December 12, 2018

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 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 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.

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 39

Environmental Science & Technology

1

New Insights into Black Carbon Nanoparticle-induced Dispersibility of Goethite

2

Colloids and Configuration-dependent Sorption for Phenanthrene

3 4

Fei Lian 1, 2, Wenchao Yu 3, Zhenyu Wang 1, Baoshan Xing 2, *

5 6 7 8

1

9

Environmental and Civil Engineering, Jiangnan University, Wuxi 214122, China

Institute of Environmental Processes and Pollution Control, and School of

10

2

11

the United States

12

3

13

300071, China

Stockbridge School of Agriculture, University of Massachusetts, Amherst, MA 01003,

College of Environmental Science and Engineering, Nankai University, Tianjin

14 15 16 17 18

*corresponding author: [email protected]; 413-545-5212

19 20 21 22 1

ACS Paragon Plus Environment


23

Table of Contents (TOC) Art

24

25 26 27 28 29 30 31 32 33 34

2


Page 2 of 39

Page 3 of 39


35 36

ABSTRACT: Black carbon nanoparticles (nano-BC) are one of the most active

37

components in pyrogenic carbonaceous matter and involve in many biogeochemical

38

processes. This study investigated heteroaggregation of nano-BC with goethite (a

39

model of natural mineral colloids) and the configuration effect of heteroaggregates on

40

phenanthrene (PHE) sorption. Nano-BC could significantly enhance the dispersion of

41

goethite via heteroaggregation when its concentration was higher than the critical

42

concentration (Cc). The Cc was dependent on the surface potential of nano-BC, which

43

was directly measured for the first time in this study. Configuration and stability of the

44

heteroaggregates were regulated by BC-goethite mass ratio and solution pH. At pH 5.3,

45

oppositely charged goethite and nano-BC interacted with each other through

46

electrostatic attraction and the configuration of heteroaggregates was dependent on BC-

47

goethite mass ratio. At pH 7.4, where both goethite and nano-BC were negatively

48

charged, they heteroaggregated with each other mainly through H bonding and Lewis

49

acid-base mechanisms and the configuration of heteroaggregates was independent on

50

BC-goethite mass ratio. For PHE sorption, small-sized heteroaggregates were more

51

favorable than large ones due to higher content of active sorption sites. Interestingly, at

52

higher concentration of PHE, we found that the solute molecules could probably

53

penetrate into and/or alter the configuration of heteroaggregates and enhance its

54

sorption capacity for PHE. These findings are useful for understanding the effect of

55

nano-BC on colloidal stability and organic compound sorption of minerals.

56 3



Page 4 of 39

57 58

INTRODUCTION

59

Black carbon (BC), the carbonaceous solid of biomass residue from incomplete

60

combustion, is ubiquitous in the environment. Especially, biochar, the man-made BC,

61

is produced much more than ever before for various environmental and agricultural

62

purposes including adsorption of contaminants 1, carbon sequestration 2, and soil

63

modifiers 3. Statistically, the global production of BC is estimated to be 50-270 Tg per

64

year, and the majority of the products would be remained in the soil environments 4.

65

Although BC is recalcitrant to mineralization, a fraction of this charred material can be

66

discharged and mobilized in aquatic environments as dissolved BC (DBC)

67

amounts to ca. 10% of the dissolved organic carbon in rivers and > 2% in oceans 8, 9.

68

Furthermore, bulk BC can even be physically disintegrated into BC nanoparticles

69

(nano-BC) with size smaller than 100 nm driven by aging and weathering in the

70

environment 10. Considering the high mobility and reactivity of both DBC and nano-

71

BC 11, it is expected that they would greatly affect many biogeochemical processes in

72

environments such as contaminant transport

73

natural colloids 14.

12,

element cycling

13,

5-7,

which

and stability of

74

It has been suggested that these ultra-fine BC fractions have relatively high stability

75

in aquatic environments 15, 16. For example, critical coagulation concentration (CCC) of

76

nano-BC derived from pecan shells was 250 mmol/L and 8.5 mmol/L for Na+ and Ca2+,

77

respectively 17, higher than engineered carbon nanomaterials including carbon nanotube

78

18,

fullerene (C60) 19, and graphene oxide (GO) 20. Xu et al. 15 reported that no significant 4


Page 5 of 39


79

aggregation of DBC was observed when the concentration of NaCl was up to 800

80

mmol/L. On the other hand, naturally occurring colloids are present in almost all surface

81

waters, the transport and fate of which is vital for understanding the key environmental

82

processes in water/soil systems

83

outnumbered by natural colloids (e.g., minerals) in real environmental media and it is

84

foreseeable that heteroaggregation with oppositely charged colloids (e.g., iron oxides)

85

would be more likely to occur and have more profound environmental implications

86

relative to homoaggregation of nano-BC. Heteroaggregation of other carbon

87

nanoparticles (such as GO, carbon dots, and carbon nanotubes) with mineral colloids

88

in aqueous solutions have been investigated 21-24. It is found that carbon nanoparticles

89

are likely to aggregate with minerals via different interactions including electrostatic

90

attraction 21, hydrogen bonding, and Lewis acid-base forces 22. Heteroaggregation with

91

minerals generally decreases the colloidal stability of these carbon materials and leads

92

to their sedimentation because of the reduced electrostatic repulsion. Conversely, an

93

interesting question confronting us is if the attached carbon nanoparticles could in turn

94

contribute to the suspension of minerals in aqueous solutions. Feng et al.

95

that negatively charged GO could attach to the surface of positively charged hematite

96

to form “electrostatic patches”, which could partially neutralize its surface positive

97

charges. Theoretically, if sufficient negatively charged nano-BC attaches to the mineral,

98

its surface charge can be reversed 17, which can increase the dispersibility of minerals.

99

In that case, it is crucial to determine the critical concentration of nano-BC above which

100

the minerals can be effectively dispersed by attached nano-BC. This information has

14.

Nano-BC is negatively charged and likely

5


23

reported


Page 6 of 39

101

profound significance for exploring the role of nano-BC in the transport and fate of

102

natural colloids in the real environment. Although numerous studies have assessed the

103

influence of dissolved organic matter (DOM) on the transport and stability of various

104

colloids (listed in Table S1) in soils, it would be inaccurate to extrapolate these results

105

to the interactions between nano-BC and minerals. Nano-BC is derived from pyrogenic

106

carbon, whose property is distinct from that of natural DOM

107

different from DBC (size < 0.45 μm) 26, which contains both “undissolved” particulates

108

(i.e., nano-BC) and water-soluble fractions. We mainly focus on the aggregation

109

between solid particles in the present study, hence, a combined procedure of

110

sedimentation and centrifugation is selected to separate nano-BC from the residue of

111

DBC. We hypothesize that nano-BC could serve as a “natural dispersing agent” to

112

greatly enhance the dispersibility of natural colloids through co-assembling in aqueous

113

environments.

25.

Strictly, it is also

114

Additionally, it is still unclear that how and to what extent the attached nano-BC

115

would affect the sorption behavior of mineral colloids. It is well known that BC has

116

higher sorption affinity for hydrophobic organic compounds (HOCs) than minerals 27-

117

29.

118

the sorption capacity of minerals because the configuration of newly formed BC-

119

mineral heteroaggregates would also affect the sorption of HOCs. It is suggested that

120

ordered assembly can be formed between carbonaceous nanomaterials and mineral

121

colloids in environmental media 17, 30, 31. For example, binary wires and closed-packed

122

structures were produced due to the association of C60 to pure and humid acid coated

However, it is worth noting that incorporation of nano-BC may not simply increase

6


Page 7 of 39


123

iron oxide colloids 30. Peng et al. 17 observed that nano-BC could heteroaggregate with

124

CeO2 nanoparticles through a charge neutralization-charge reversal mechanism at pH

125

5.3; while a charge-accumulation, core-shell structure was formed at pH 7.1. Thus, the

126

configuration effect of BC-mineral mixtures on organic compound sorption merits

127

further investigation.

128

Therefore, the overarching goals of the current work were to (1) examine the

129

colloidal stability of nano-BC produced at different heat treatment temperatures (HTTs);

130

(2) quantitatively investigate the heteroaggregation of nano-BC with a common mineral

131

colloid (goethite); and (3) reveal the sorption mechanism(s) of BC-goethite

132

heteroaggregates for HOCs. The nano-BC in this study was fractionated from rice straw

133

biochar prepared under two different HTTs, which were systematically characterized

134

by various techniques. Kinetics of nano-BC homoaggregation and its heteroaggregation

135

with goethite were determined with and without the presence of mono- and divalent

136

cations. Sorption of phenanthrene (PHE) on the BC-goethite mixtures was measured

137

for better understanding the formation of the heteroaggregates and the related

138

configuration effect on organic compound sorption.

139

EXPERIMENTAL SECTION

140

Nano-BC Preparation. Rice straw, a typical agricultural biomass waste, was selected

141

as the raw material for biochar production. Prior to use, the rice straw was washed with

142

deionized (DI) water several times to remove surface impurities. After oven-dried at 80

143

oC,

144

straw was fed into a lab-scale tubular reactor within a muffle furnace, and slowly

the material was crushed and passed through a 2.0 mm mesh. Then the powdered

7



145

pyrolyzed (10 oC/min) in a N2 atmosphere at a desired temperature (400 or 700 oC) for

146

120 min. The obtained biochar was ground, sieved through a 150 μm mesh, and referred

147

to as bulk400 and bulk700, respectively.

148

The fractionation of nano-BC was conducted by a combined procedure of

149

sedimentation and centrifugation. First, 50 g of the obtained biochar were added to 1 L

150

of DI water and stirred (150 rpm) at room temperature for 24 h. After sonication (1 h at

151

120 W), the suspension was slowly poured through a 50 μm sieve and the remained

152

particles were carefully washed with DI water to ensure that most of the desired

153

fractions (< 50 μm) can pass through the sieve. After oven-dried, the remained particles

154

were collected and used for other purposes. The filtered suspension was transferred into

155

a glass beaker, added with DI water to 3 L, and then sonicated for another 1 h. The

156

obtained suspension was left to sedimentation for 2 h to settle most of the bulk biochar

157

particles based on the Stoke’s Law. The upper layer of suspension (0-10 cm from the

158

surface) was siphoned off and then refilled with DI water to 3 L. This siphoning

159

procedure was repeated 5-10 times until the upper layer of suspension became clear and

160

had negligible Tyndall effect

161

centrifuged at 10,000 rpm for 30 min. The supernatant was carefully collected and

162

freeze-dried to obtain nano-BC. The centrifuge speed and duration were optimized

163

according to the Stoke’s Law, and particle sizes of obtained nanoparticles were verified

164

by a high-resolution transmission electron microscope (HRTEM) (JEOL, Japan) and

165

dynamic light scattering (DLS) analyzer (90Plus, Brookhaven, USA). The obtained

166

samples were referred to as nano400 and nano700, respectively. The stock suspension

32.

All the siphoned suspensions were combined and

8


Page 8 of 39

Page 9 of 39


167

of nano-BC was prepared by stirring 50 mg of nano400 or nano700 in 500 mL DI water

168

overnight, and then sonicating for 1 h. The total organic carbon (TOC) content of the

169

suspensions was 14.8 ± 0.38 and 28.3 ± 0.14 mg TOC/L for nano400 and nano700,

170

respectively, measured by a TOC analyzer (Shimadzu, Japan). The pH of both nano400

171

and nano700 suspensions was around 5.3.

172

Mineral Colloid Preparation. Goethite, purchased from Sigma-Aldrich, was used as

173

a model clay mineral. To remove organic matter from clay surface, 50 g of goethite

174

were mixed with a solution containing 100 mL DI water and 100 mL H2O2 (30% wt)

175

for 2 h in a 2 L beaker. Then the sample was rinsed thoroughly with DI water, vacuum-

176

filtrated, freeze-dried, and passed through a 150 μm sieve.

177

Homo- and Heteroaggregation Measurements. A time-resolved DLS technique was

178

employed to examine the homoaggregation kinetics of nano-BC and its

179

heteroaggregation rate with goethite using the DLS analyzer. The suspension of nano-

180

BC and goethite was sonicated, respectively, in a bath sonicator with ice cooling before

181

conducting the DLS measurements. The homoaggregation kinetics of nano-BC was

182

measured by introducing 1 mL of the suspension with a concentration of 20 mg/L into

183

disposable plastic cuvettes (Fisher, USA), and then 1 mL of NaCl or CaCl2 solution

184

with different concentrations was combined with the BC suspension in the cuvettes.

185

After briefly shaken, the cuvette was immediately inserted into the DLS cell to start the

186

measurement. To investigate the influence of goethite on nano-BC stability, the above

187

BC suspension was replaced by a BC-goethite mixture to conduct the DLS examination.

188

The DLS measurements were sustained from 10 to 120 min at different time intervals 9



189

and performed six times for each measurement. Attachment efficiencies (α) were used

190

to quantify the homoaggregation kinetics of nano-BC. The detailed determination of α

191

and CCC of nano-BC is presented in the Supporting Information (SI).

192

Heteroaggregation of nano-BC and goethite was carried out by introducing nano-BC

193

into goethite suspension and then immediately examined by the DLS analyzer. The

194

final concentration of goethite was 50 mg/L; while that of nano400 and nano700

195

increased from 0.1 to 2.0 mg TOC/L, and 0.16 to 3.2 mg TOC/L, respectively, which

196

resulted in the mass ratios of BC to goethite in the range of 0.002-0.04 for nano400 and

197

0.0032-0.064 for nano700, respectively. Note that the TOC content of nano-BC was

198

employed to calculate the mass ratio. During the heteroaggregation, the scattered light

199

intensity of goethite suspension is significantly higher than that of nano-BC, probably

200

due to the intrinsically lower ability of BC to scatter light relative to metallic particles

201

17

202

zeta potential in the process of heteroaggregation mainly represent those of the goethite

203

colloid, which can be demonstrated by the Dh measurement of goethite with and without

204

nano400 or nano700 (Figure S1).

205

Attachment of Nano-BC on Goethite. The attachment of nano-BC on goethite was

206

quantified to further elucidate the mechanism of their heteroaggregation. The

207

attachment experiment was carried out in 20-mL screw cap vials at 25 oC and

208

unadjusted pH condition according to previous studies 21, 33. Briefly, 20 mg of goethite

209

were added into the vials which already contained 15 mL of nano-BC suspensions with

210

different concentrations (0-10 mg TOC/L). The solid/liquid ratio was carefully selected

and the larger size of goethite. Thus, the recorded hydrodynamic diameters (Dh) and

10


Page 10 of 39

Page 11 of 39


211

in the preliminary experiment to achieve the removal of nano-BC between 20-80%. The

212

vials were shaken at a speed of 200 rpm for 24 h to reach equilibrium (Figure S2), and

213

then centrifuged at 3000 rpm for 20 min to separate the goethite and BC-goethite

214

aggregates from the supernatants, while the free nano-BC remained stable in the

215

supernatants. The BC concentrations in the supernatants were determined by a TOC

216

analyzer. The mass of attached nano-BC was calculated by mass balance. All the

217

experiments were performed in duplicate.

218

Characterization. Surface chemical composition of nano400 and nano700 was

219

determined using X-ray photoelectron spectrometer (XPS) (PHI 5000 VersaProbe,

220

Japan). Binding energies were calibrated by C 1s hydrocarbon peak at 284.8 eV.

221

Deconvolution of C 1s spectra was conducted by XPSPEAK software. BET surface

222

area (SBET) and total pore volume (Vtot) were measured by nitrogen adsorption-

223

desorption at 77 K using an Autosorb-1 gas analyzer (Quantachrome, USA). The

224

functional groups were characterized using Fourier transform infrared spectroscopy

225

(FTIR) (Nexus 870, Nicolet, USA) with 4 cm-1 resolution in the range of 400 and 4000

226

cm-1. Raman spectra were obtained using a Renishaw Ramnascope (RM 2000, Wotton-

227

under-Edge, UK). Surface morphology of the nano-BC, goethite, and their

228

heteroaggregates was observed by HRTEM with optimal resolution of 2 nm at 300 kV.

229

Dh, electrophoretic mobility (EPM), and zeta potential of the particles were determined

230

in DI water by the DLS analyzer.

231

Sedimentation Kinetics. The dispersion and sedimentation of goethite in the

232

suspension of nano-BC were measured by monitoring changes in optical absorbance as 11



233

a function of time using UV-vis spectroscopy. The concentration of goethite remained

234

constant (1000 mg/L); while that of nano400 and nano700 increased from 0 to 11.68

235

mg TOC/L and 15.69 mg TOC/L, respectively, at pH 5.3 and 7.4. The suspensions of

236

BC and goethite were mixed using a shaking incubator at 150 rpm for 30 min. Then, 3

237

mL of the suspension were pipetted into a quartz cuvette and measured by a UV-vis

238

spectrometer (Agilent 8453, USA) at 800 nm, where the nano-BC had little absorbance.

239

The absorbance was recorded over 48 h at different time intervals to determine the

240

effect of nano-BC on the sedimentation rates of goethite.

241

Sorption of PHE. A batch equilibrium technique was used to compare the sorption

242

capacity of nano-BC with goethite for PHE. Details of the sorption procedure are

243

presented in the SI. Single-point sorption was carried out to explore the configuration

244

effect of BC-goethite heteroaggregates on PHE sorption. Briefly, an aliquot of goethite

245

(2 mg) and 40 mL of nano-BC suspension with different concentrations, i.e., 0 to 2 mg

246

TOC/L for nano400 and 0 to 3.2 mg TOC/L for nano700, respectively, were added into

247

the 40-mL vials. After shaken at 200 rpm for 1 h, the vials received a certain volume

248

(less than 0.1%) of PHE stock solution (1.0 mg/L) in methanol. Different initial

249

concentrations of PHE (0.263, 0.526, and 0.79 mg/L) were used to ensure the data

250

compatibility and analytical accuracy. The vials were shaken in the dark at 25 oC for 7

251

days to achieve apparent sorption equilibrium. After centrifugation (15, 000 rpm, 30

252

min) and filtration, the concentrations of PHE in the supernatant was determined by a

253

Shimadzu Prominence liquid chromatography system with a diode array detector

254

(reversed phase C18, 3.0 × 150 mm, 2.7 μm, Brownlee, SPP, USA). The mobile phase 12


Page 12 of 39

Page 13 of 39


255

consisted of 90% methanol and 10% DI water at a flow rate of 1.0 mL/min. The sorbed

256

concentrations of PHE by sorbents were calculated by mass difference.

257

RESULTS AND DISCUSSION

258

Characterization of Nano-BC and Goethite. Surface elemental composition and

259

porosity of both nano- and bulk-BC are listed in Table S2. Nano400 and nano700 have

260

much higher polarity index [(O + N)/C] and contents of Si and Ca than bulk400 and

261

bulk700, suggesting that nano-BC contains more polar functional groups and

262

crystalline inorganics, and thus higher surface activity. The polarity index is 0.633 and

263

0.606 for nano400 and nano700 in this study, similar to that of DBC derived from rice

264

straw (0.59) and bamboo BC (0.55), respectively 26. For porous structure, the SBET and

265

Vtot of nano700 are significantly higher than nano400. Notably, the difference in SBET

266

between nano700 and nano400 is much higher than that between bulk700 and bulk400,

267

indicating that the release of volatile matter (e.g., CO, CO2, and CxHyOz) from carbon

268

skeleton is probably easier for nano-sized BC than bulky BC due to the less steric

269

hindrance effect. These results reveal that nano-BC has distinct physicochemical

270

properties and would participate in more diverse biogeochemical processes in the

271

environment relative to bulk BC.

272

The structural properties of nano400 and nano700 were examined using

273

complementary spectroscopic techniques including Raman, XRD, XPS, and FTIR

274

(Figure 1). The Raman spectra exhibit two characteristic peaks at ~1350 cm-1 (D band)

275

and ~1580 cm-1 (G band) which can be assigned to sp3 and sp2 carbon configuration,

276

respectively. The intensity ratios of G to D bands (IG/ID) are very close to 1.0 for both 13



Page 14 of 39

277

nano400 (1.068) and nano700 (1.05), suggesting that they have comparable contents of

278

amorphous and graphitic carbon. This is different from many previous observations for

279

bulk biochar where the graphitization degree generally increases with increasing HTT

280

34, 35.

281

ratio of IG/ID (2.2) than that of produced at 400 oC (2.0). Similarly, the IG/ID ratios of

282

sewage sludge biochar were found to increase with increasing HTT, indicating a

283

conversion of amorphous carbon to graphene domain

284

indicate that nano-BC has higher content of amorphous C structure and relatively

285

smaller crystallite size

286

and nano700 centered at 22o (Figure 1b) also demonstrate the presence of highly

287

disordered carbon atoms. The functional groups present on the surface of nano-BC were

288

examined by XPS. The C 1s spectra can be deconvoluted into three major peaks at

289

284.6 eV (C-C/C=C), 285.2 eV (C-OH), and 286.7 eV (C=O), respectively

290

shown in Figure 1c, the peak area percent of C-C/C=C in nano700 (35.4%) is higher

291

than that in nano400 (27.1%), suggesting that nano700 has more content of sp2- and

292

sp3-hybridized carbon configurations due to higher HTT. By contrast, nano400 has

293

higher content of O-containing groups including hydroxyl (39.1%) and carboxyl

294

(33.8%) than nano700 (32.9% for -OH and 31.7% for -COOH), indicative of the higher

295

polarity and surface charge density of nano400. Surface functional groups of nano-BC

296

were also probed by FTIR (Figure 1d), including -OH at 3440 cm-1, -CH2 at 2921 cm-1

297

and 1384 cm-1, aromatic C=C and/or C=O stretching between 1626 and 1542 cm-1, C-

298

O at 1097 cm-1, and aromatic C-H at 877 cm-1. The higher intensity of nano700 from

For example, Xie et al. 34 showed that the biochar prepared at 500 oC had higher

36

35.

Our Raman spectra results

compared with bulk BC. The broad XRD peaks of nano400

14


37, 38.

As

Page 15 of 39


299

vibration of aromatic C=C/C=O and C-H bands denotes its higher degree of

300

condensation and aromaticity than nano400, consistent with the XPS data.

301 (a) D

nano400 nano700

G

(b)

C (002)

nano400 nano700

IG/ID = 1.05

Intensity (a.u.)

IG/ID = 1.068

1000

1500

2000

(c) C-OH (39.1%)

C=C/C-C (27.1%)

C=C/C-C (35.4%)

280

302

2500

3000

20

-1

Raman shift (cm )

282

C-OH (32.9%)

284

286

288

40

60

80

2 theta (degree) nano400

(d)

C-O -CH21097 1384

-CH2-

C=O (33.8%)

nano400 nano700

2921

-OH 3440

nano700 C=O (31.7%)

290

292

877 1542 1626 aromatic C=C/C=O CH

294

1000

2000

3000

4000

-1

Binding energy (eV)

Wavenumber (cm )

303

Figure 1. Characterization of nano-BC (nano400 and nano700). (a) Raman spectra; (b)

304

XRD spectra; (c) high-resolution XPS C 1s spectra; and (d) FTIR spectra.

305 306 307

Colloidal Stability of Nano-BC and Goethite. The size distribution of nano-BC and

308

goethite after 20 min sonication is presented in Figure S3, where the Dh of nano400

309

(~280 nm) and nano700 (~220 nm) remained constant during the test time at an

310

unadjusted pH (5.3), however, that of goethite gradually increased from 700 to 1200 15



311

nm at the same condition. After sonicated for another 60 min, the Dh of goethite greatly

312

decreased and remained at 400-600 nm (Figure S4). Thus, the nano-BC is more stable

313

to homoaggregation than the goethite colloids. Therefore, all the goethite samples

314

employed in the following heteroaggregation were sonicated for 80 min before use to

315

keep them relatively stable. As shown in Figure S5a, the zeta potential of nano-BC

316

decreased from ~ -5 mV to ~ -40 mV when the solution pH increased from 2 to 10;

317

while that of goethite decreased from ~ +30 mV to ~ -20 mV and its isoelectric point

318

was around 6. The negative zeta potential of nano-BC over the entire pH range is

319

indicative of a stable suspension. Given the limitation of zeta potential to directly reflect

320

the surface charge density of colloidal particles 39, surface potentials (Ψo) of nano400

321

and nano700 were directly determined from measured EPM values via Henry equation

322

40,

323

detailed calculation is presented in the SI.

and the value for nano400 and nano700 is -6.11 mV and -5.30 mV, respectively. The

324

Homoaggregation kinetics of nano-BC was examined in a range of NaCl or CaCl2

325

concentrations. The attachment efficiencies () of nano-BC as a function of electrolyte

326

concentration at different pHs are given in Figure 2a. The corresponding aggregation

327

profiles are shown in Figure S6 and S7. Both reaction- and diffusion-limited

328

aggregation regimes can be observed in the measurements, consistent with the classic

329

DLVO theory. The attachment efficiencies () of nanoparticles increased with

330

increasing electrolyte concentrations until approaching to 1 when the CCC was

331

achieved. The CCC values of nano400 were up to 700 mmol/L for Na+ and 4.3 mmol/L

332

for Ca2+, and those of nano700 were 140 mmol/L for Na+ and 2.7 mmol/L for Ca2+, 16


Page 16 of 39

Page 17 of 39


333

respectively, at an unadjusted pH (5.3). The ratio of CCC for nano400 and nano700 in

334

CaCl2 to NaCl is 2-7.35 and 2-5.80, respectively, which is basically consistent with the

335

prediction of the Schulze-Hardy model (z-6 where z represents the cation valence) 41, 42.

336

The higher CCC of nano400, especially in NaCl, is attributed to its higher surface

337

charge density due to plenty of O-containing groups although the Dh of nano400 is

338

larger than that of nano700 (Figure S3). The result suggests that aggregation behavior

339

of nano-BC is not only determined by particle size but also by surface charge, and the

340

latter is highly dependent on HTT. Table S3 lists the CCC values of several

341

carbonaceous nanomaterials with NaCl and CaCl2, where the CCC of nano400 in NaCl

342

is much higher than the others indicating its greater stability in aqueous solutions. We

343

also examined the CCCs of nano400 and nano700 at a weak alkaline condition (pH 7.4)

344

and found that the values did not change greatly (Figure S8), showing that the nano-BC

345

could remain stable in a variety of natural freshwater and soil environments.

346

17



nano400/CaCl2 nano400/NaCl

(a) 1

Page 18 of 39

nano700/CaCl2 nano700/NaCl

0.1

0.01

2.7

140

4.3

1

10

700

100

1000

80

500

Attachment Efficiency, 

1

(b) pH = 5.3 NaCl 0.1

0.01 nano400+Goe nano700+Goe 10 1

100

1000

(c) pH = 7.4 NaCl

0.1

0.01 10

nano400+Goe nano700+Goe

110

100

580 1000

Electrolyte concentration (mmol/L)

347 348

Figure 2. Attachment efficiencies of BC nanoparticles (nano400 and nano700) as a

349

function of NaCl or CaCl2 concentration at an unadjusted pH (5.3) (a) and the influence

350

of goethite (Goe) on attachment efficiencies of BC nanoparticles at pH 5.3 (b) and 7.4

351

(c), respectively. The concentration of nano-BC and goethite was 20 mg/L and 50 mg/L,

352

respectively.

353 354 355

Heteroaggregation of Nano-BC with Goethite. The CCCs of nano400 and nano700 18


Page 19 of 39


356

in NaCl were greatly decreased by the presence of goethite at pH 5.3 and 7.4 (Figure

357

2b and c), respectively, hence, goethite could interact with nano-BC and affect its

358

stability. The heteroaggregation at pH 5.3 can be mainly explained by the electrostatic

359

attraction between negatively charged nano-BC and positively charged goethite. At pH

360

7.4, however, both nano-BC and goethite were negatively charged according to their

361

zeta potentials (Figure S5a). Thus, additional interaction(s) may contribute to the

362

attachment of nano-BC to goethite at pH 7.4.

363

The heteroaggregation rates of nano-BC with goethite were only determined at pH

364

5.3 since the electrostatic repulsion greatly prevented the Dh growth of BC-goethite

365

heteroaggregates at pH 7.4 (Figure S9). At pH 5.3, the Dh of BC-goethite mixture

366

significantly increased with increasing BC-goethite mass ratio due to the favorable

367

heteroaggregation between the two oppositely charged particles (Figure 3a and b). For

368

comparison, the homoaggregation rates of nano400 and nano700 under diffusion

369

limited conditions are plotted in Figure 3c. It is shown that the maximum

370

heteroaggregation rates of goethite with nano400 (6.18 nm/min) and nano700 (8.12

371

nm/min) are significantly higher than the respective homoaggregation rates of nano400

372

(3.99 nm/min) and nano700 (6.62 nm/min). The maximum heteroaggregation rates

373

were obtained as the concentration of nano400 and nano700 reached to 0.4 and 0.64

374

mg TOC/L, respectively, which corresponded to the mass ratio of 0.008 for nano400-

375

goethite and 0.0128 for nano700-goethite. The lower ratio of nano400 suggests that it

376

may be more effective in dispersing goethite than nano700 due to its higher surface

377

charge density. The zeta potential changes of BC-goethite heteroaggregates with 19



378

increasing BC concentrations are shown in Figure S5b. The zeta potential decreased

379

greatly with BC concentrations and approached to zero when the concentration of

380

nano400 and nano700 was up to 0.4 and 0.6 mg TOC/L, respectively, which is

381

consistent with the concentration at which the maximum heteroaggregation rate

382

occurred (Figure 3c). The lower zeta potential of nano400-goethite heteroaggregate

383

indicates its higher stability than that of nano700-goethite cluster. Figure S5a also

384

depicts the zeta potential variations of BC-goethite heteroaggregates as a function of

385

pH. The zeta potential of formed heteroaggregates is much lower (up to -20 mV) than

386

the bare goethite, indicating the enhanced dispersibility of goethite by attached nano-

387

BC.

388

20


Page 20 of 39

Page 21 of 39


Hydrodynamic diameter (nm)

1000

(a) nano400

0 mg TOC/L 0.1 mg TOC/L 0.2 mg TOC/L 0.4 mg TOC/L 0.6 mg TOC/L 0.8 mg TOC/L 1.0 mg TOC/L 1.5 mg TOC/L 2.0 mg TOC/L

800 600 400 0

20

40

60

80 0 mg TOC/L 0.16 mg TOC/L 0.32 mg TOC/L 0.64 mg TOC/L 0.96 mg TOC/L 1.28 mg TOC/L 1.6 mg TOC/L 2.4 mg TOC/L 3.2 mg TOC/L

1000 (b) nano700 800 600

Initial growth rate of hydro-dynamic diameter (nm/min)

400

389

0 10

20

40

60

80

Time (min)

6

nano400 nano700 6.62 nm/min

4

3.99 nm/min

8

(c)

0.64 mg TOC/L 0.40 mg TOC/L

2 0 -2 -0.5 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Concentration of BC nanoparticles (mg TOC/L)

390

Figure 3. Heteroaggregation profiles of BC nanoparticles (nano400 and nano700) and

391

goethite (Goe) with increasing concentration of nano-BC at pH 5.3. Error bars represent

392

standard deviations of six samples (a, b). Initial growth rates of hydrodynamic diameter

393

of the heteroaggregates as a function of nano-BC concentration at pH 5.3 (c). The

394

concentration of goethite is 50 mg/L.

395 396 397

Enhanced Dispersion of Goethite by Nano-BC. The dispersion of goethite in the

398

suspension of nano-BC was also measured by sedimentation kinetics experiments. At

399

pH 5.3, the bare goethite settled down completely within 4-8 h; meanwhile very low 21



Page 22 of 39

400

concentrations of nano-BC had little effect on improving its dispersion (Figure 4).

401

However, when the concentration of nano400 and nano700 increased higher than 1.307

402

and 2.277 mg TOC/L, respectively, the sedimentation rate of goethite was greatly

403

reduced during the period of 48 h. The enhanced dispersion of goethite by nano-BC can

404

be seen more clearly from the photographs of corresponding goethite-BC mixtures after

405

undisturbed standing for 48 h (Figure S10). The critical concentration (Cc) of nano-BC

406

to enhance goethite dispersion was around 1 mg TOC/L for nano400 and 2 mg TOC/L

407

for nano700, respectively. When the concentration of nano-BC was higher than its Cc,

408

the color of the mixtures changed into light brown and then to dark brown with

409

increasing BC concentration demonstrating the enhanced dispersion of goethite. On the

410

other hand, goethite can be also well dispersed at pH 7.4, but the Cc of nano400 and

411

nano700 increased to ~1.9 and 3.0 mg TOC/L (Figure S11), respectively, suggesting

412

that nano-BC had lower adhesion affinity to goethite at this pH condition. To further

413

support the observation, pH effect on dispersion of nano-BC, goethite, and their

414

aggregates was examined, respectively (Figure S12 and S13). Both nano400 and

415

nano700 were deposited at pH 2 by forming aggregates due to decreased negative

416

charge but they can be well dispersed in the pH range of 4-10, which is similar to other

417

carbonaceous nanomaterials such as GO

418

however, most of the particles quickly settled in the pH of 2 to 6 until the pH increased

419

to 8-10 where the goethite was well dispersed because of the abundance of negative

420

charges at the highly basic condition. Note that the goethite can be well dispersed with

421

the presence of nano-BC at a wide pH range (4-8), illustrating that other interactions

43

and carbon nanotubes

22


18.

For goethite,

Page 23 of 39


422

also contributes to the adhesion of nano-BC to goethite besides electrostatic attraction.

423

Previous studies showed that carbonaceous nanomaterials can interact with goethite

424

through H-bonding and/or Lewis acid-base interactions 22. The pKa values of carboxyl

425

and phenolic hydroxyl groups are around 4.3 and 9.8, respectively 21. Thus, at the tested

426

pH conditions (5.3 and 7.4), H-bonding can be formed between the hydroxyl groups on

427

surface of goethite and oxyl groups on the nano-BC (especially nano400). Lewis

428

acid−base interactions could also contribute to their association, wherein the hydroxyl

429

groups serve as Lewis base due to the lone electron pairs of oxygen atoms, and Lewis

430

acid centers can be formed on BC surface because of electron withdrawal capacity by

431

its O-containing groups. Both hydrogen-bonding and Lewis acid−base interactions may

432

overcome the electrostatic repulsion and lead to the relatively weak attachment of nano-

433

BC on goethite at pH 7.4.

23



(a) nano400

A/A0 at 800 nm

1.0

0 mg TOC/L 0.917 mg TOC/L 1.051 mg TOC/L 1.307 mg TOC/L 1.949 mg TOC/L 2.810 mg TOC/L 5.081 mg TOC/L 7.324 mg TOC/L 9.567 mg TOC/L 11.68 mg TOC/L

0.8

0.6

0.4

0.6

0.4

0.0

0.0 20

30

40

0 mg TOC/L 0.921 mg TOC/L 1.127 mg TOC/L 1.507 mg TOC/L 2.277 mg TOC/L 3.765 mg TOC/L 6.782 mg TOC/L 9.825 mg TOC/L 12.79 mg TOC/L 15.69 mg TOC/L

0.8

0.2

10

(b) nano700

1.0

0.2

0

Page 24 of 39

50

0

10

20

30

40

Time (h) 434 435

Figure 4. Sedimentation kinetics of BC nanoparticle (nano400 and nano700)-goethite

436

heteroaggregates with increasing BC concentration. The concentration of goethite was

437

1000 mg/L.

438 439

Consistently, the results show that the attachment capacity of goethite for nano400

440

and nano700 is around 2 and 1 mg TOC/g, respectively, in the tested BC concentrations

441

(Figure S14). The attachment capacity of goethite for nano700 is almost the same to

442

that of other iron oxide minerals (e.g., hematite) for GO 23, indicating similar surface

443

properties of nano-700 and GO. The higher attachment of nano400 can be attributed to

444

the stronger electrostatic attraction and/or its higher content of O-containing groups. 24


50

Page 25 of 39


445

Surface-potential-normalized attachments of nano-BC on goethite were compared to

446

directly illustrate the effect of functional groups on the interaction (Figure S15), where

447

the large difference in the normalized attachment demonstrated the crucial role of oxyl

448

groups in the enhanced attachment of nano400.

449

Given the larger particle size of nano400 (Figure S1), it is likely that the attached

450

nano400 has a higher surface coverage per particle on goethite than nano700. We

451

calculated the BC-goethite mass ratio at Cc of nano400 and nano700, respectively,

452

where the mass ratio (0.001) of nano400 is lower than that (0.002) when the attachment

453

equilibrium of nano400 on goethite is achieved, but the mass ratio (0.002) of nano700

454

is higher than that (0.001) when the attachment equilibrium of nano700 is obtained. The

455

results suggest that goethite could be well dispersed by nano400 before its complete

456

attachment is reached, while additional nano700 particles are needed to effectively

457

disperse goethite after the attachment, indicating that the dispersion of mineral colloids

458

is mainly dependent on surface charge of nano-BC and attachment capacity on minerals.

459

Sorption of PHE by BC-goethite Heteroaggregates. As expected, nano-BC has much

460

higher sorption affinity for PHE than goethite verified by the higher distribution

461

coefficients (Kd) (Figure S16). Thus, it is inclined to believe that the sorption of HOCs

462

on minerals would have been enhanced via heteroaggregation with nano-BC in aqueous

463

solutions 44. However, we found for the first time that both BC-goethite mass ratio and

464

solute concentration play a critical role in manipulating the PHE sorption on BC-

465

goethite heteroaggregates. As depicted in the grey area of Figure 5, for lower

466

concentration of PHE (i.e., 0.236 and 0.526 mg/L), the sorption of PHE showed little 25



467

increase at low BC concentrations and then significantly increased when it was higher

468

than ~0.4 and 0.6 mg TOC/L for nano400 and nano700, respectively. Interestingly,

469

these concentrations were consistent with those at which the maximum

470

heteroaggregation rates of goethite and nano-BC occurred as mentioned above (i.e., 0.4

471

mg TOC/L for nano400 and 0.64 mg TOC/L for nano700) (Figure 3), which directly

472

demonstrates that BC-goethite mass ratio could control the configuration of

473

heteroaggregates and consequently affecting the sorption patterns for organic chemicals.

474

For higher concentration of PHE (i.e., 0.79 mg/L), however, its sorption significantly

475

increased with the introduction of nano-BC and no plateau for PHE sorption was

476

observed at low nano-BC concentrations (the grey area in Figure 5), indicating its

477

different sorption pattern. Recently, morphology transformation of a biomass-

478

converted nanomaterial induced by the sorption of naphthalene (NAPH) and PHE was

479

reported 45. The authors suggested that the formation of ordered structure was ascribed

480

to the sorbate molecule-induced self-assembly of graphene nanosheets. Additionally,

481

Yang et al. 46 found that negative charges on surface of BC colloids can be significantly

482

shielded by the sorbed NAPH, which reduced the mobility of BC colloids in porous

483

media. These results reveal that the structure of BC-goethite heteroaggregates may be

484

relatively incompact and the surface charge of nano-BC could be modified by PHE

485

sorption; therefore, the PHE molecules with a sufficiently high concentration are likely

486

to (1) enter into the interior of BC-goethite heteroaggregates, or (2) alter the

487

configuration of heteroaggregates due to strong sorption affinity to BC, which may

488

result in different sorption patterns compared with that at low concentrations of PHE. 26


Page 26 of 39

Page 27 of 39


489 (a) nano400

Sorbed concentration of PHE (mg/g)

8

6 C0 = 0.236 mg/L C0 = 0.526 mg/L C0 = 0.790 mg/L

4

2 8

0.0

0.5

1.0

1.5

2.0

2.5

(b) nano700 6

4

2 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Concentration of BC nanoparticles (mg TOC/L)

490 491

Figure 5. The effect of nano-BC concentration on PHE sorption by the BC-goethite

492

heteroaggregates (n = 3). The grey area denotes the different sorption patterns of PHE

493

on the heteroaggregates at different concentrations of PHE; i.e., the sorption of PHE

494

almost did not increase with increasing BC concentrations at low PHE concentrations,

495

while it increased significantly at higher PHE concentration. The concentration of

496

goethite was 50 mg/L.

497

Mechanism of Heteroaggregation between Nano-BC and Goethite. The

498

representative TEM images of nano-BC and goethite are presented in Figure 6 (a and

499

b) and more images of nano400 and nano700 can be found in Figure S17. Figure 6 (c

500

and d) exhibits the configurations of nano700-goethite heteroaggregates at two different 27



501

mass ratios (i.e., 0.008 and 0.04). These mass ratios were selected based on the

502

observation that the maximum heteroaggregation rate was obtained as the nano700-

503

goethite mass ratio was 0.008 at an unadjusted pH condition (5.3). It is evident that a

504

plenty of nano700 and goethite can bind together to form bigger clusters when the mass

505

ratio was 0.008, where the nano700 played an important bridging role in connecting

506

different goethite particles (Figure 6c). However, when the BC-goethite mass ratio

507

increased to 0.04, the majority of goethite surface was covered by nano700 and the

508

bridging effect was greatly inhibited. As a result, the bigger clusters split into smaller

509

BC-goethite heteroaggregates (Figure 6d). On the other hand, at a weak alkaline

510

condition (pH = 7.4) where both nano-BC and goethite were negatively charged, they

511

can only bind to form small clusters due to the hinderance of electrostatic repulsion

512

(Figure S18). Meanwhile, we noticed that the Dh of heteroaggregates was independent

513

of the BC-goethite mass ratio (0.008-0.04) at pH 7.4. These observations are consistent

514

with our DLS results shown in Figure 3 and S9.

515

Based on the above TEM results, the possible mechanisms for BC-goethite

516

heteroaggregation at different mass ratios and the corresponding impact on goethite

517

sorption for PHE are proposed and illustrated in Figure 6e. At very low BC

518

concentration, nano-BC has little effect on increasing the dispersion of goethite

519

because the enhanced dispersibility by attached nano-BC is not sufficient enough to

520

overcome its deposition potential. When the concentration of BC is higher than its Cc

521

(i.e., CBC > Cc), the goethite can be effectively dispersed via heteroaggregation with

522

nano-BC. After that, there are two different situations: (1) At pH 5.3, the positively 28


Page 28 of 39

Page 29 of 39


523

charged goethite can strongly bind with the negatively charged BC through

524

electrostatic attraction to form primary heteroaggregates, and then the attached BC,

525

serving as a bridge, can also interact with other goethite colloids to form large-sized

526

heteroaggregates when the CBC is in a range of Cc to CH (i.e., Cc < CBC ≤ CH). CH is the

527

concentration at which the maximum heteroaggregation rate occurs. As CBC further

528

increased (i.e., CBC > CH), nano-BC binds to the surface of goethite to form a

529

negatively charged shell around it

530

bridge because most of the active sites on goethite are occupied by nano-BC. In that

531

case, the BC-goethite clusters could only maintain their primary structure (i.e., small-

532

sized heteroaggregates), which is more stable than the larger aggregates. (2) At pH

533

7.4, although both goethite and nano-BC are negatively charged, they can also bind

534

with each other to some extent via H-bonding and Lewis acid-base interactions as

535

indicated by the attachment result and TEM observation (Figure S11 and S18). Due to

536

the negatively charged nature of both nano-BC and goethite at this weak alkaline

537

condition, the large-sized heteroaggregates could not be formed via the BC-bridge

538

mechanism and only small-sized heteroaggregates can be observed.

17,

which greatly inhibits the occurrence of BC-

539

Figure 6e also illustrates the sorption mechanism of PHE on BC-goethite

540

heteroaggregates with different mass ratios at an unadjusted pH condition. Nano-BC

541

has much higher sorption affinity for PHE than goethite as shown in Figure S16 (i.e.,

542

QBC > Qgoe). However, the attached BC could not greatly increase the sorption of

543

goethite at low BC-goethite ratios (i.e., Cc < CBC ≤ CH) due to the formation of large-

544

sized heteroaggregates, where a number of BC particles are probably wrapped into the 29



545

interior of the heteroaggregates and become ineffective sorption sites. However, with

546

increasing PHE concentration, the PHE molecules could penetrate into and alter the

547

configuration of heteroaggregates, making the wrapped nano-BC become effective for

548

PHE sorption (Figure 5). At high BC-goethite ratios (i.e., CBC > CH), only small-sized

549

heteroaggregates are formed and thus most of the attached BC particles are located on

550

the surface of goethite and can effectively enhance the goethite sorption for PHE.

551

552 553

Figure 6. The representative TEM images of nano700 (a), goethite (Goe) (b), and nano700-

554

goethite heteroaggregates at different mass ratios at pH 5.3 (c and d); as well as the proposed

555

mechanism of BC-Goe heteroaggregation and its effect on the sorption of phenanthrene (PHE)

556

(e). CBC and CPHE denote the concentration of nano-BC and PHE in the aqueous solution,

557

respectively; both Cc1 and Cc2 denote the critical concentration of nano-BC to enhance the 30


Page 30 of 39

Page 31 of 39


558

dispersion of goethite at pH 5.3 and 7.4, respectively; CH denotes the nano-BC concentration at

559

which the maximum heteroaggregation rates occurred at pH 5.3; QBC and Qgoe denote the

560

sorption capacity of nano-BC and goethite for PHE, respectively.

561 562 563

Environmental Implication. Nano-BC has unique physicochemical properties and can

564

be released from bulk BC materials, participating in various environmental processes.

565

The aggregation results indicate that nano-BC with higher surface potential and oxyl

566

groups is expected to be more stable to homoaggregation, wherein HTT is one of the

567

dominating factors in regulating its colloidal behavior in aqueous environments. Nano-

568

BC could enhance dispersibility of mineral colloids through heteroaggregation when

569

the concentration of nano-BC exceeds its Cc, which mainly depends on the surface

570

potential of nano-BC and its attachment affinity to minerals. Given the relatively low

571

Cc of nano-BC to disperse minerals (e.g., goethite), it is foreseeable that the mineral

572

colloids are likely to be dispersed when encountering nano-BC in natural aqueous

573

systems despite the generally low mass ratio of nano-BC to minerals. Conversely, at

574

higher concentrations of nano-BC, mineral colloids could lead to the deposition of

575

nano-BC by attaching and forming large particulates, which have a weak colloidal

576

stability. Thus, the effect of BC-mineral interactions on carbon storage and flux in the

577

terrestrial ecosystem needs further study. Moreover, we found that the sorption of PHE

578

was regulated by the configuration of BC-goethite heteroaggregates. A number of

579

active sorption sites (mainly nano-BC) might be wrapped into the interior of the large31



580

sized BC-mineral clusters and contribute little to the sorption of PHE. By contrast, the

581

small-sized clusters exhibit higher sorption capacity for PHE. Thus, it should be noted

582

that nano-BC can not only contribute to the dispersion of minerals but also make them

583

efficient sorbents and potential carriers for organic compounds by forming stable

584

clusters in the environments. Therefore, besides nano-BC itself, the BC-mineral

585

heteroaggregates should also be considered when evaluating the transport and related

586

environment risk of nano-BC. In addition, how and to what extent the sorbate molecule

587

could induce the structural transformation of BC-mineral heteroaggregates deserve

588

more detailed investigations in the future.

589 590

Supporting Information

591

Determination of α, CCCs, and surface potentials of nano-BC; Dh of goethite and nano-

592

BC; attachment kinetics; Zeta potentials; aggregation of nano-BC; heteroaggregation

593

of nano-BC and goethite at pH 7.4; photographs of BC-goethite mixtures; UV-vis of

594

goethite; sorption of PHE; TEM images; selected physicochemical properties of nano-

595

and bulk-BC (18 figures and 3 tables).

596 597

AKNOWLEDGEMENTS

598

We gratefully acknowledge ﬁnancial support from the National Natural Science

599

Foundation of China (41573127), China Scholarship Council (201503250054) for F.L.

600

to study at UMass Amherst, USDA McIntire-Stennis Program (MAS 00028), and NSF

601

(CBET 1739884). 32


Page 32 of 39

Page 33 of 39


602 603

REFERENCES:

604

1.

605

chlorobenzenes in soil using wheat straw biochar. J. Agr. Food Chem. 2013, 61, (18),

606

4210-4217.

607

2.

608

as a function of feedstock and pyrolysis temperature. Environ. Sci. Technol. 2012, 46,

609

(21), 11770-11778.

610

3.

611

properties of cornstraw biochar: agronomic implications. Environ. Sci. Technol. 2010,

612

44, (24), 9318-9323.

613

4.

614

and related implications. Curr. Sci. India 2010, 99, (9), 1218-1225.

615

5.

616

Discharge of dissolved black carbon from a fire-affected intertidal system. Limnol.

617

Oceanogr. 2012, 57, (4), 1171-1181.

618

6.

619

spatial variability of dissolved black carbon in a subtropical watershed. Environ. Sci.

620

Technol. 2018, 52, (15), 8104-8114.

621

7.

622

black carbon in the changjiang and huanghe rivers, China. Estuar. Coast 2016, 39, (6),

623

1617-1625.

Song, Y.; Wang, F.; Kengara, F. O.; Yang, X.; Gu, C.; Jiang, X. Immobilization of

Singh, B. P.; Cowie, A. L.; Smernik, R. J. Biochar carbon stability in a clayey soil

Silber, A.; Levkovitch, I.; Graber, E. R. pH-dependent mineral release and surface

Jha, P.; Biswas, A. K.; Lakaria, B. L.; Rao, A. S. Biochar in agriculture - prospects

Dittmar, T.; Paeng, J.; Gihring, T. M.; Suryaputra, I. G. N. A.; Huettel, M.

Roebuck, J. A., Jr.; Seidel, M.; Dittmar, T.; Jaffe, R. Land use controls on the

Xu, C.; Xue, Y.; Qi, Y.; Wang, X. Quantities and fluxes of dissolved and particulate

33



624

8.

625

organic matter. Nature Geoscience 2009, 2, (3), 175-179.

626

9.

627

M.; Campbell, J.; Dittmar, T. Global charcoal mobilization from soils via dissolution

628

and riverine transport to the oceans. Science 2013, 340, (6130), 345-347.

629

10. Spokas, K. A.; Novak, J. M.; Masiello, C. A.; Johnson, M. G.; Colosky, E. C.;

630

Ippolito, J. A.; Trigo, C. Physical disintegration of biochar: An overlooked process.

631

Environ. Sci. Technol. Let. 2014, 1, (8), 326-332.

632

11. Qian, L. B.; Zhang, W. Y.; Yan, J. C.; Han, L.; Gao, W. G.; Liu, R. Q.; Chen, M.

633

F. Effective removal of heavy metal by biochar colloids under different pyrolysis

634

temperatures. Bioresource Technol. 2016, 206, 217-224.

635

12. Grolimund, D.; Borkovec, M.; Barmettler, K.; Sticher, H. Colloid-facilitated

636

transport of strongly sorbing contaminants in natural porous media: A laboratory

637

column study. Environ. Sci. Technol. 1996, 30, (10), 3118-3123.

638

13. Wigginton, N. S.; Haus, K. L.; Hochella, M. F. Aquatic environmental

639

nanoparticles. J. environ. Monitor. : JEM 2007, 9, (12), 1306-1316.

640

14. Philippe, A.; Schaumann, G. E. Interactions of dissolved organic matter with

641

natural and engineered inorganic colloids: A review. Environ. Sci. Technol. 2014, 48,

642

(16), 8946-8962.

643

15. Xu, F.; Wei, C.; Zeng, Q.; Li, X.; Alvarez, P. J. J.; Li, Q.; Qu, X.; Zhu, D.

644

Aggregation behavior of dissolved black carbon: Implications for vertical mass flux

645

and fractionation in aquatic systems. Environ. Sci. Technol. 2017, 51, (23), 13723-

Dittmar, T.; Paeng, J. A heat-induced molecular signature in marine dissolved

Jaffe, R.; Ding, Y.; Niggemann, J.; Vahatalo, A. V.; Stubbins, A.; Spencer, R. G.

34


Page 34 of 39

Page 35 of 39


646

13732.

647

16. Chen, C.; Huang, W. Aggregation kinetics of diesel soot nanoparticles in wet

648

environments. Environ. Sci. Technol. 2017, 51, (4), 2077-2086.

649

17. Yi, P.; Pignatello, J. J.; Uchimiya, M.; White, J. C. Heteroaggregation of cerium

650

oxide nanoparticles and nanoparticles of pyrolyzed biomass. Environ. Sci. Technol.

651

2015, 49, (22), 13294-13303.

652

18. Saleh, N. B.; Pfefferle, L. D.; Elimelech, M. Aggregation kinetics of multiwalled

653

carbon nanotubes in aquatic systems: Measurements and environmental implications.

654

Environ. Sci. Technol. 2008, 42, (21), 7963-7969.

655

19. Mashayekhi, H.; Ghosh, S.; Du, P.; Xing, B. Effect of natural organic matter on

656

aggregation behavior of C60 fullerene in water. J. Colloid Interface Sci. 2012, 374, (1),

657

111-117.

658

20. Wu, L.; Liu, L.; Gao, B.; Muñoz-Carpena, R.; Zhang, M.; Chen, H.; Zhou, Z.;

659

Wang, H. Aggregation kinetics of graphene oxides in aqueous solutions: Experiments,

660

mechanisms, and modeling. Langmuir 2013, 29, (49), 15174-15181.

661

21. Zhao, J.; Liu, F.; Wang, Z.; Cao, X.; Xing, B. Heteroaggregation of graphene oxide

662

with minerals in aqueous phase. Environ. Sci. Technol. 2015, 49, (5), 2849-2857.

663

22. Liu, X.; Li, J.; Huang, Y.; Wang, X.; Zhang, X.; Wang, X. Adsorption, aggregation,

664

and deposition behaviors of carbon dots on minerals. Environ. Sci. Technol. 2017, 51,

665

(11), 6156-6164.

666

23. Feng, Y.; Liu, X.; Huynh, K. A.; McCaffery, J. M.; Mao, L.; Gao, S.; Chen, K. L.

667

Heteroaggregation of graphene oxide with nanometer- and micrometer-sized hematite 35



668

colloids: Influence on nanohybrid aggregation and microparticle sedimentation.

669


670

24. Huynh, K. A.; McCaffery, J. M.; Chen, K. L. Heteroaggregation of multiwalled

671

carbon nanotubes and hematite nanoparticles: Rates and mechanisms. Environ. Sci.

672

Technol. 2012, 46, (11), 5912-5920.

673

25. Jin, J.; Sun, K.; Wang, Z.; Yang, Y.; Han, L.; Xing, B. Characterization and

674

phenanthrene sorption of natural and pyrogenic organic matter fractions. Environ. Sci.

675

Technol. 2017, 51, (5), 2635-2642.

676

26. Qu, X.; Fu, H.; Mao, J.; Ran, Y.; Zhang, D.; Zhu, D. Chemical and structural

677

properties of dissolved black carbon released from biochars. Carbon 2016, 96, 759-

678

767.

679

27. Yu, X. Y.; Ying, G. G.; Kookana, R. S. Sorption and desorption behaviors of diuron

680

in soils amended with charcoal. J. Agr. Food Chem. 2006, 54, (22), 8545-8550.

681

28. Jeong, S.; Wander, M. M.; Kleineidam, S.; Grathwohl, P.; Ligouis, B.; Werth, C.

682

J. The role of condensed carbonaceous materials on the sorption of hydrophobic organic

683

contaminants in subsurface sediments. Environ. Sci. Technol. 2008, 42, (5), 1458-1464.

684

29. Tang, J. X.; Weber, W. J. Development of engineered natural organic sorbents for

685

environmental applications. 2. Sorption characteristics and capacities with respect to

686

phenanthrene. Environ. Sci. Technol. 2006, 40, (5), 1657-1663.

687

30. Ghosh, S.; Pradhan, N. R.; Mashayekhi, H.; Dickert, S.; Thantirige, R.; Tuominen,

688

M. T.; Tao, S.; Xing, B. Binary short-range colloidal assembly of magnetic iron oxides

689

nanoparticles and fullerene (nC60) in environmental media. Environ. Sci. Technol. 36


Page 36 of 39

Page 37 of 39


690

2014, 48, (20), 12285-12291.

691

31. Smith, B. M.; Pike, D. J.; Kelly, M. O.; Nason, J. A. Quantification of

692

heteroaggregation between citrate-stabilized gold nanoparticles and hematite colloids.

693


694

32. Tang, Z.; Wu, L.; Luo, Y.; Christie, P. Size fractionation and characterization of

695

nanocolloidal particles in soils. Environ. Geochem. Health 2009, 31, (1), 1-10.

696

33. Huang, G.; Guo, H.; Zhao, J.; Liu, Y.; Xing, B. Effect of co-existing kaolinite and

697

goethite on the aggregation of graphene oxide in the aquatic environment. Water Res.

698

2016, 102, 313-320.

699

34. Xie, M.; Chen, W.; Xu, Z.; Zheng, S.; Zhu, D. Adsorption of sulfonamides to

700

demineralized pine wood biochars prepared under different thermochemical conditions.

701

Environ. Pollut. 2014, 186, 187-194.

702

35. Zhang, J.; Lu, F.; Zhang, H.; Shao, L.; Chen, D.; He, P. Multiscale visualization of

703

the structural and characteristic changes of sewage sludge biochar oriented towards

704

potential agronomic and environmental implication. Scientific Reports 2015, 5, 9406.

705

36. Cancado, L. G.; Takai, K.; Enoki, T.; Endo, M.; Kim, Y. A.; Mizusaki, H.; Jorio,

706

A.; Coelho, L. N.; Magalhaes-Paniago, R.; Pimenta, M. A. General equation for the

707

determination of the crystallite size L-a of nanographite by Raman spectroscopy. Appl.

708

Phys. Lett. 2006, 88, (16), 163106.

709

37. Yang, Y.; Shu, L.; Wang, X.; Xing, B.; Tao, S. Impact of de-ashing humic acid and

710

humin on organic matter structural properties and sorption mechanisms of

711

phenanthrene. Environ. Sci. Technol. 2011, 45, (9), 3996-4002. 37



712

38. Dong, X.; Ma, L. Q.; Zhu, Y.; Li, Y.; Gu, B. Mechanistic investigation of mercury

713

sorption by brazilian pepper biochars of different pyrolytic temperatures based on X-

714

ray photoelectron spectroscopy and flow calorimetry. Environ. Sci. Technol. 2013, 47,

715

(21), 12156-12164.

716

39. Smith, B.; Wepasnick, K.; Schrote, K. E.; Bertele, A. R.; Ball, W. P.; O’Melia, C.;

717

Fairbrother, D. H. Colloidal properties of aqueous suspensions of acid-treated, multi-

718

walled carbon nanotubes. Environ. Sci. Technol. 2009, 43, (3), 819-825.

719

40. Li, K.; Zhao, X.; K. Hammer, B.; Du, S.; Chen, Y. Nanoparticles inhibit DNA

720

replication by binding to dna: Modeling and experimental validation. ACS Nano 2013,

721

7, (11), 9664-9674.

722

41. Overbeek, J. T. G. The rule of schulze and hardy. Pure Appl. Chem. 1980, 52, (5),

723

1151-1161.

724

42. Elimelech, M.; Gregory, J.; Jia, X.; Williams, R. A., Particle deposition and

725

aggregation: measurement, modelling and stimulation. Butterworth-Heinemann:

726

Oxford, U.K., 1995.

727

43. Chowdhury, I.; Duch, M. C.; Mansukhani, N. D.; Hersam, M. C.; Bouchard, D.

728

Colloidal properties and stability of graphene oxide nanomaterials in the aquatic

729

environment. Environ. Sci. Technol. 2013, 47, (12), 6288-6296.

730

44. Lian, F.; Xing, B. Black carbon (biochar) in water/soil environments: Molecular

731

structure, sorption, stability, and potential risk. Environ. Sci. Technol. 2017, 51, (23),

732

13517-13532.

733

45. Xiao, X.; Chen, B.; Zhu, L.; Schnoor, J. L. Sugar cane-converted graphene-like 38


Page 38 of 39

Page 39 of 39


734

material for the superhigh adsorption of organic pollutants from water via coassembly

735

mechanisms. Environ. Sci. Technol. 2017, 51, (21), 12644-12652.

736

46. Yang, W.; Wang, Y.; Sharma, P.; Li, B.; Liu, K.; Liu, J.; Flury, M.; Shang, J. Effect

737

of naphthalene on transport and retention of biochar colloids through saturated porous

738

media. Colloids and Surfaces A 2017, 530, (Supplement C), 146-154.

39


New Insights into Black Carbon Nanoparticle-induced Dispersibility of

Recommend Documents