Characterization and Phenanthrene Sorption of ... - ACS Publications

Subscriber access provided by Fudan University

Article

Characterization and Phenanthrene Sorption of Natural and Pyrogenic Organic Matter Fractions Jie Jin, Ke Sun, Ziying Wang, Yan Yang, Lanfang Han, and Baoshan Xing Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b04573 • Publication Date (Web): 30 Jan 2017 Downloaded from http://pubs.acs.org on January 31, 2017

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 30

Environmental Science & Technology

Characterization and Phenanthrene Sorption of Natural and

1

Pyrogenic Organic Matter Fractions

2 3 4 5 6

Jie Jin, †,‡,§ Ke Sun, ‡,* Ziying Wang, ‡ Yan Yang, ‡ Lanfang Han, ‡,§ and Baoshan Xing, §,*

7 8

†

9

Beijing 102206, China

School of Environment and Chemical Engineering, North China Electric Power University,

10

‡

11

Normal University, Beijing 100875, China

12

§

State Key Laboratory of Water Environment Simulation, School of Environment, Beijing

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

13 14 15 16 17 18 19 20 21 22

**Corresponding authors: Phone: +86 10 58807493; fax: +86 10 58807493; e-mail:

23

[email protected] (K. SUN). Phone: +1 413 545 5212; fax: +1 413 577 0242; e-mail:

24

[email protected] (B.S. XING).

25

1

ACS Paragon Plus Environment


26

ABSTRACTS: Pyrogenic humic acid (HA) is released into the environment during the

27

large-scale application of biochar. However, the biogeochemistry of pyrogenic organic matter

28

(PyOM) fractions and their sorption of hydrophobic organic compounds (HOCs) are poorly

29

understood in comparison with natural organic matter (NOM) fractions. HA and humin (HM)

30

fractions isolated from soils and the oxidized biochars were characterized. Sorption of

31

phenanthrene (PHE) by these fractions was also examined. The characterization results

32

demonstrate that pyrogenic HAs are different from natural HAs, with the former having

33

lower atomic H/C ratios, more abundant aromatic C, and higher concentrations of surface

34

carboxylic groups. Compared with the fresh biochars, the Koc of PHE on their oxidized

35

biochars, pyrogenic HA, and HM fractions were undiminished, which is encouraging for the

36

use of biochar in soil remediation. The PyOM fractions exhibited stronger nonlinear sorption

37

than the NOM fractions. In addition, the PyOM fractions had higher sorption capacity than

38

the NOM fractions due to their low polar C content and high aryl C content. The results

39

obtained from this work will shed new light for the impact of the addition of biochar on the

40

biogeochemistry of soil organic matter and on the fate of HOCs in biochar-amended soil.

41 42 43

2


Page 2 of 30

Page 3 of 30


44

INTRODUCTION

45

Soil organic matter (SOM) is composed of various organic components differing in

46

molecule size and chemical composition, 80% of which can be humic substances (HS).1

47

According to the protocol of classic chemical fractionation, HS are extracted from soils as

48

fulvic acid (FA), humic acid (HA), and humin (HM). Because of the large amounts of HS in

49

soils, small deviations in the composition of the above different fractions may have a

50

significant effect on soil properties. Vegetation fires can modify the previously existing C as

51

well as produce a considerable amount of newly formed C in the ecosystem. Globally,

52

vegetation fires produce 40 to 250 million tons of pyrogenic C per year.2 The global

53

pyrogenic C stored in sediments, soils, and waters reaches 300 to 500 giga-metric tons.3

54

Specifically, pyrogenic C can comprise up to 40% of the total SOM in grasslands and boreal

55

forests.4 Moreover, the practical applications of pyrogenic organic matter (PyOM) in the form

56

of biochar have received great attention in light of its excellent performance in soil

57

remediation and C sequestration.2 It is expected that the ubiquitous presence of PyOM, also

58

called char, charcoal, biochar or black carbon (BC), will alter the physical and chemical

59

properties of soil.

60

Specifically, humic-fractions isolated from soils, such as Amazonian Dark Earth soils and

61

volcanic ash soils in Japan, have been suggested to be enriched by PyOM-derived HA.5-9

62

These studies suggested that, with weathering, part of the biochar was subjected to oxidation

63

and hydration and transformed into FA and pyrogenic HA with graphite-like structures

64

consisting of highly condensed aromatic rings, contributing considerably to the high humus

65

accumulation in these soils. Though the chemical and structural properties of PyOM fractions 3



Page 4 of 30

66

have been detailed in these studies, it is noted that most characteristic studies for PyOM

67

fractions collected PyOM samples directly from fire-impacted soils without further

68

purification to remove the coating of natural organic matter (NOM) fractions. Even though

69

biochar shows strong sorption for natural HA,10 resulting in the contamination of PyOM by

70

natural HA,11 the interference of natural HA has been sparsely considered. Moreover, the

71

extraction of HA is an essential step in the pretreatment of charcoal for 14C measurement.12,13

72

It is reasonable to assume that the existence of natural HA will affect characteristic studies of

73

PyOM fractions. Several previous studies reported that substances consistent with HA and FA

74

have been extracted from fresh laboratory-produced biochar with the use of oxidizing agents,

75

such as HNO3.14,15 Using elemental analysis, thermogravimetry, and

76

resonance (NMR) spectra, they concluded that the HA isolated from biochars and

77

pyrogenic-derived HA extracted from fire-impacted soils had similar characteristics.14

78

Therefore, in this study, biochar-derived HA was used as the model pyrogenic HA in

79

comparison with natural HA.

13

C nuclear magnetic

80

The fate of hydrophobic organic compounds (HOCs) in soils/sediments is mainly

81

regulated by their sorption to solid phases.16 The sorption of HOCs in soils/sediments is often

82

dominated by BC (i.e., PyOM),17-19 which exhibits as high as 1000 times higher capacity for

83

HOCs than other organic matter fractions.19,20 Therefore, biochar amendment is of interest to

84

immobilize HOCs in soils.21,22 A requirement for the successful use of biochar to restore

85

contaminated sites is that the excellent sorption capacity of HOCs by biochar can be

86

maintained over a long period of time. However, current literature still debates the effects of

87

aging on the HOC sorption of biochar. For instance, some works found that the sorption of 4


Page 5 of 30


88

HOCs by biochar can be weakened by aging,23,24 whereas several other studies reported that

89

biochar had a good sorption capacity for HOCs that was sustained during harsh aging.21,25

90

The conflicting conclusions necessitate further study of the effect of biochar oxidation on

91

HOC sorption. In most previous studies, the sorption capacity of pyrogenic HA was sparsely

92

considered. As mentioned above, with weathering, biochar will release poly-aromatic HA

93

molecules, which may affect the strength of contaminant sorption. Thus, to probe the

94

influence of oxidation on biochar sorption and accurately predict the fate of HOCs in

95

biochar-amended soils, the sorption properties of different PyOM fractions, including

96

pyrogenic HA, should be explored. Pyrogenic HA features an aromatic structure,5-9 distinct

97

from natural HA.1 In addition, it was reported that aromatic C plays an important role in HOC

98

sorption.26 We therefore hypothesize that pyrogenic fractions extracted from biochars will

99

demonstrate different sorption properties from NOM fractions. The objectives of this study

100

were to (1) provide quantitative chemical and structural information concerning PyOM

101

fractions extracted from biochar, (2) distinguish differences in composition between the

102

NOM and PyOM fractions, and (3) compare the sorption difference of phenanthrene (PHE)

103

between the PyOM and NOM fractions.

104

MATERIALS AND METHODS

105

Sorbents and Sorbates. A soil sample (AG) under slash-and-burn agricultural practices

106

(BC% = 14.5%, quantified by chemo-thermal oxidation method at 375 °C for 24 h) was

107

collected from the Sanjiang Plain, Northeast China. A soil sample (GR) with a low BC

108

content (2.2%) was collected from a grassland in Xinjiang province, Northwest China. The

109

HA and HM isolation methods have been described elsewhere.27,28 Briefly, the soil samples 5



110

were extracted with 0.1 M NaOH for 7 times. Next, the mixture of the 7 extractions was

111

acidified to pH = 2 to separate the HA precipitate from the soluble FA fraction. The HA

112

fraction was then de-ashed by mixing and shaking with 0.1 M HCl and 0.3 M HF. The

113

precipitated residue after HA extractions was de-ashed by 1 M HCl and 10% (v/v) HF to get

114

the HM fraction. After centrifugation, the isolated HA and HM were washed with deionized

115

water, freeze dried, and ground to fine powders (< 0.25-µm) for further characterization and

116

sorption experiment.

117

Wheat straw and swine manure were carbonized at various heat treatment temperatures

118

(HTT = 300, 450, and 600 °C) to produce different biochars. After being ground and sieved

119

(< 0.25 µm), the biochars were oxidized at approximately 90 °C for 4 h using 25% HNO3

120

(~5.5 M) at 1:30 solid/liquid ratio.29 After the removal of excess acid, the HA and HM of

121

biochar were extracted similarly as described for the soil. The extracted yields of HA after the

122

acid treatment of the biochars varied depending upon the different HTT (Table S1 and S2).

123

Biochars produced at 450 °C gave the highest HA yields, consistent with a previous study.14

124

At 300 °C, the biochars were not sufficiently pyrolyzed and the HNO3 treatment resulted in a

125

larger degree of oxidative degradation, producing small quantities of HA. At 600 °C, the

126

biochars were increasingly graphitized, decreasing the yield of HA.14,29 The amount of

127

pyrogenic HA obtained from biochars produced at 300 °C and 600 °C was not sufficient for

128

subsequent use. Thus, the pyrogenic HAs and HMs, extracted from the two biochars

129

produced at HTT = 450 °C, were used in this study. The temperature used was also that

130

recommended for manufacturing biochar for soil amendment purposes.30,31 Here, these

131

biochar samples were referenced according to feedstock source materials (maize straw and 6


Page 6 of 30

Page 7 of 30


132

swine manure) (i.e., MA and SW). The PyOM samples were named as MA-AO, MA-HA,

133

MA-HM, SW-AO, SW-HA, and SW-HM. AO represents acid oxidation.

134 135

The

14

C-labeled and unlabeled PHE were used as sorbates. The tested chemicals used in

this study were purchased from Sigma-Aldrich at the highest purity available.

136

Sorbent Characterization. The bulk elemental (C, H, O, and N) analysis of all sorbents

137

were determined using dry combustion with an Elementar Vario ELIII elemental analyzer

138

(Germany). The ash content was measured by heating the sorbents at 750 °C for 4 h. The

139

surface elemental composition and functionalities were examined with an X-ray

140

photoelectron spectrometer (XPS) (Thermo Scientific ESCALAB 250 XPS, USA). The XPS

141

running parameters are detailed in a previous study.32 The C1s fine spectrum was

142

deconvoluted into the following regions: C-C at 284.9 eV, C-O at 286.5 eV, C=O at 287.9 eV,

143

and COO at 289.4 eV.32 Solid-state cross-polarization magic angle spinning 13C NMR spectra

144

were obtained on a Bruker Avance 300 NMR spectrometer (Germany) at 75 MHz. The pore

145

and specific surface properties of all samples were determined by gas (CO2 and N2)

146

adsorption performed on a Quantachrome Autosorb-iQ gas analyzer (USA).

147

Sorption Experiment. Batch PHE sorption experiments were conducted as described in

148

Han et al.26 Briefly, test solutions (2-1100 µg/L) of PHE were prepared by diluting the

149

labeled and nonlabeled stock solutions using the background solution containing 0.01 M

150

CaCl2 (ionic strength adjuster) and 200 mg/L of NaN3 (biocide), and adjusted to pH 6.5 with

151

0.1 M HCl or 0.1 M NaOH. The solute solutions were slowly added into the 40-mL glass

152

vials with an amount of sorbents, ensuring that the headspace was kept to minimum. The

153

amount of sorbents was adjusted to result in 20-80% uptake of PHE. The methanol 7


14

C


154

concentration in the test solutions was always less than 0.1% (v/v) to avoid cosolvent effects.

155

The glass vials were capped with Teflon-lined screw and shaken in the dark at 23 ± 1 °C for

156

10 d. The preliminary tests showed that sorption equilibrium was reached before this time.

157

Next, after centrifugation, 1.5 mL of supernatant was withdrawn from each vial and added to

158

separate corresponding vials containing 4.0 mL of scintiverse cocktail (Fisher Scientific,

159

USA) and analyzed by liquid scintillation counting. The final pH values were in the range of

160

6.4-6.8. For each concentration point, two blanks without sorbents were run at the same time.

161

In view of the negligible mass loss of PHE in controls, sorbed concentrations of PHE by

162

sorbents were calculated by mass difference. Data Analysis. Three nonlinear models were used for fitting sorption data of PHE in this

163 164

study. They are the Freundlich (FM), Polanyi-Dubinin (PD), and Dubinin-Radushkevich (DR)

165

models. More details can be found in the Supporting Information.

166

RESULTS AND DISCUSSION

167

Characteristics of Natural and Pyrogenic Organic Matters. HNO3 oxidation of MA

168

and SW resulted in an obvious increase in the bulk O and N concentrations (Table 1 and

169

Figure 1). The high O content of the oxidized biochar is probably due to a rise in

170

O-containing functional groups, such as carboxylic, phenolic, and nitro groups, introduced by

171

HNO3 treatment, whereas the elevated N concentrations might be caused by the formation of

172

the nitro groups from HNO3.14 By contrast, from the OC recovery (%) of the oxidized

173

biochars (Table S2), both MA and SW suffered OC loss after HNO3 oxidation, consistent

174

with previous studies.11,33

175

After fractionation of the oxidized biochars, the pyrogenic HA was found to be the major 8


Page 8 of 30

Page 9 of 30


176

component, comprising 63.1 wt% and 45.0 wt% of MA and SW, respectively; meanwhile,

177

OC recovery (%) was 45.5% and 69.3% for MA-HA and SW-HA, respectively (Table S2).

178

The proportions of HA released from the biochars were comparable to those reported in the

179

literature.14 The elemental compositions of HA fractions from different sources were also

180

analyzed. Whereas the HA extracted from AG soil subject to frequent burning gave an OC

181

content of 49.0%, the biochar HAs showed slightly higher OC contents (51.9% and 53.6%),

182

both of which were much higher than GR-HA (16.5%) with little BC input (Table 1 and

183

Figure 1). A high OC content was also found in the HAs obtained from other pyrogenic

184

C-rich soils, which was in the range of 57-63%.34 AG-HA, MA-HA, and SW-HA possessed

185

comparable bulk polarity, lower than GR-HA (Figure 1). To better compare the elemental

186

composition of pyrogenic HA and natural HA, the atomic H/C and O/C ratios of biomass,

187

pristine biochar produced at 450 °C, and HA isolated from biochars, pyrogenic C-rich (black)

188

soils, pyrogenic C-deficient (non-black) soils, and litters from the literature were also

189

tabulated in Table S3 and presented in the van Krevelen diagram (Figure 2). The oxidative

190

degradation of biochar with dilute HNO3 and subsequently NaOH extraction resulted in

191

overall oxidation and dehydrogenation of the samples, as shown in the change in atomic H/C

192

and O/C ratios (Figure 2). In general, the biochar HAs were plotted near the black soil HAs in

193

the Van Krevelen diagram (Figure 2). By contrast, the position of non-black soil HAs is

194

concentrated near the melanoidin/lignin zone (Figure 2). Additionally, both biochar HAs and

195

black soil HAs had lower H/C atomic ratios than the non-black soil HA samples, indicating

196

that the formers had higher aromaticity and higher degree of condensation.

197

The surface elemental compositions as indicated by the XPS analysis had a similar but 9



198

more obvious trend compared to the bulk elemental analysis (Table 1 and Figure 1). For

199

instance, the bulk O contents slightly increased from 10.2-11.8% in the fresh biochars to

200

16.3-18.3% in the oxidized biochars, whereas the surface O contents increased dramatically

201

from 16.0-25.7% to 51.1-51.9% (Table 1). The XPS C1s spectra clearly showed that the

202

increments of O were attributed to the incorporation of O-containing functional groups,

203

mainly carboxylic groups (Table S4). Unlike bulk OC, the surface C consistently decreased

204

after acid oxidation (Figure 1). These results suggested that the external surface of biochar

205

particles suffered a higher degree of oxidation than the interior. In addition, pyrogenic and

206

natural HAs had similar surface polarities (Figure 1f). However, pyrogenic HAs were

207

characterized by more surface COO(H) groups than natural HAs, which could account for the

208

higher CEC of black soils in comparison to the non-black soils.7

209

The 13C NMR spectra also illustrated that remarkable chemical modifications of biochars

210

were detected after HNO3 treatment, such as increments in polar groups and the formation of

211

carboxylic groups (Table S5 and Figure S1), consistent with the elemental analysis and XPS

212

results. The polar C content of the PyOM fractions ranged from 21.0% to 26.1%, lower than

213

those of the tested NOM fractions (35.9-43.5%) (Table S5). The aromaticity of MA-AO and

214

SW-AO were slightly higher than their corresponding pristine biochar samples (Table S5).

215

This might be because aliphatic groups can be selectively lost during oxidation.35 In addition,

216

the

217

Amazonian Dark Earth soil36 were replotted in Figure 3 so that comparisons among HAs

218

from different sources can be better visualized. As expected, the 13C NMR spectra of the HAs

219

extracted from MA and SW are similar to that of HA from the Amazonian Dark Earth soil,

13

C NMR spectra of the natural and pyrogenic HA as well as the HA extracted from an

10


Page 10 of 30

Page 11 of 30


220

confirming that PyOM may be a possible source of the HA fraction in soils. In addition,

221

pyrogenic HAs primarily consisted of aromatic and carboxyl C, whereas natural HAs clearly

222

showed the aliphatic signals (0-93 ppm) (Figure 3). Moreover, the aromaticity of pyrogenic

223

HAs was approximately twice that of natural HAs (Table S5).

224

The gas adsorption isotherms and DFT pore size distribution of the tested samples are

225

shown in Figure S2 and S3. The micropore volume of organic matters was found to be

226

positively correlated with their OC content,26,37 consistent with our data (Figure S4). Thus, in

227

comparison with fresh biochar, the micropore volume of MA-AO declined due to the loss of

228

OC after acid oxidation, whereas that of SW-AO increased with an elevated OC content

229

(Table 1 and S6). The N2 surface area (N2-SA) values of biochars were consistently decreased

230

after HNO3 treatment (Table S6). N2 can probe the outer surface of minerals;38 therefore the

231

obvious lower N2-SA of SW-AO than that of SW could be explained by the removal of some

232

mineral within SW by HNO3 treatment. The micropore volumes were 0.020 cm3/g and 0.025

233

cm3/g for MA-HA and SW-HA, respectively, much lower than those of the pristine biochars

234

(0.111 cm3/g for MA and 0.046 cm3/g for SW). Additionally, the micropore volumes of the

235

pyrogenic HAs were slightly lower than those of natural HAs (Table S6), despite the fact that

236

biochar is very porous.26,39 Moreover, natural HAs had 1-2 magnitude higher N2-SA than

237

pyrogenic HAs (Table S6), likely caused by the high ash content of natural HAs. To test this,

238

the ash component of GR-HA was obtained after combustion at 750 °C for 4 h and its N2-SA

239

was measured, which was 132.6 m2/g. The high N2-SA of the ash component of GR-HA

240

implies that the ash component greatly contributed to the N2-SA of GR-HA. A previous study

241

also found that N2-SA of organic sorbents increased with increasing ash content.38 11



242

Impact of Acid Oxidation on PHE Sorption. The sorption isotherms of PHE by the

243

original biochars were highly nonlinear (Figure S5 and Table S7). The acid treatment caused

244

the increase of n values (Table S7), implying that a more expanded sorbent was produced by

245

HNO3 oxidation. The acid treatment exerted dissimilar influences on the logKd and logKoc

246

values of the tested biochars (Figure 4). A statistical comparison of the logKd and logKoc

247

values before and after HNO3 oxidation was conducted by taking three selected isotherm

248

points at Ce = 0.01Sw, 0.1Sw, and 1Sw as individual measurements, giving three values for the

249

statistical analysis (Table S7). The results show that influence of HNO3 oxidation on PHE

250

sorption by SW was statistically nonsignificant (paired t-test p = 0.08 for logKd and p = 0.79

251

for logKoc). A previous study also found that the fresh biochar produced from hardwood and

252

the correspond aged biochar had comparable sorption capacity for simazine.21 By contrast,

253

the sorption of PHE by MA-AO was unexpectedly elevated compared with the untreated

254

sample (paired t-test p < 0.05 for logKd and p < 0.01 for logKoc).

255

From the XPS and

13

C NMR analysis, it was observed that acid treatment caused the

256

development of surface O-containing functional groups, mainly carboxyl groups (Table S4

257

and S3). The hydrophilic moieties of biochars can facilitate the coating of water films at the

258

surface of the sorbents through H-bonding. The water films can weaken the sorption of HOC

259

molecules by decreasing the accessibility of target solutes to sorption domains as well as

260

occupying the sorption sites. Apparently, the surface hydrophobic mechanism cannot

261

dominate the sorption of PHE to the oxidized biochars. The undiminished PHE sorption on

262

the oxidized biochars may be attributed to the rise in aromaticity (Table S5), which benefits

263

the π-π electron donor-acceptor (EDA) interactions between PHE molecules and the aromatic 12


Page 12 of 30

Page 13 of 30


264

domains within the oxidized biochars. The role of biochar aromaticity in PHE sorption has

265

been documented in previous studies.26,37 Moreover, compared with the fresh biochars, the

266

oxidized biochars may have greater π-acceptor strength as a result of the attachment of

267

carboxylic groups, introduced by HNO3 oxidation, to the aromatic rings. This will aid strong

268

EDA interactions between the oxidized biochars and PHE molecules (π-donor).

269

Additionally, it has been shown that the pore-filling mechanism dominate the PHE

270

sorption by biochars.26,39 PD and DR models were therefore employed to determine the role

271

of micropore filling in PHE sorption. Sorption isotherms fitted using PD and DR models are

272

shown in Figure S6. The fitted data (Table S8 and Table S9) indicate that better fitting was

273

obtained for the PD model, as indicated by the higher R2 values. Therefore, the adsorption

274

parameters of PHE from the PD model were used in the following discussion. The adsorbed

275

volume capacities (Q0) were approximately 0.74 and 0.91 cm3/kg for MA and SW,

276

respectively (Table S8), both of which were reduced after oxidation. In addition, there is a

277

positive correlation between the Q0 of PHE on the tested PyOMs (except for MA, MA-HA,

278

and SW-HA) and their micropore volume (Figure S7), indicating that the pore-filling

279

mechanism also contributed to PHE sorption by the samples.

280

Sorption of PHE to Pyrogenic Humic Acid and Humin Fractions. The nonlinear

281

coefficients (n) of the pyrogenic HA and HM fractions were in the range of 0.45-0.64 (Table

282

S7). The Koc values of MA-HA and MA-HM were obviously higher than those of the fresh

283

biochars (Figure 4). This might arise from the increased aromaticity (Table S5) after a series

284

of chemical treatments as mentioned above. By contrast, the Koc values of SW-HA and

285

SW-HM were comparable to that of SW. These results demonstrate that the feedstock of 13



286

biochars will affect the sorption properties of their PyOM fractions. Additionally, as shown in

287

Figure S7, the pore-filling mechanism may also contribute to PHE sorption by pyrogenic HM

288

fractions. The sorption affinity (Kd and Koc) for PHE by MA-HM is higher than that by

289

SW-HM (Table S7), which might be partly explained by the larger micropore volume of

290

MA-HM (Table S6). For the pyrogenic HA fractions, their Q0 for PHE deviated from the

291

relationship between the Q0 and the micropore volume (Figure S7). In addition, although

292

their micropore volumes were much lower than those of the fresh biochars (Table S6), they

293

still demonstrated higher (MA-HA) or comparable (SW-HA) Koc values compared with the

294

fresh biochars (Table S7). Therefore, the pore-filling mechanism may not regulate the

295

sorption of PHE by the pyrogenic HA fractions.

296

Here, the oxidized biochars and biochar-derived pyrogenic HA and HM fractions

297

maintained excellent sorption for PHE, implying that the high sorption capacity of PHE by

298

biochars may be long-lasting in the environment. This confirms the promising future of

299

biochar application in the context of contaminated site remediation. It should be noted that

300

the coating of the biochar surface by microbially produced organic matter11 or native HS,22

301

which was a general phenomenon in the natural environment and might weaken the sorption

302

capacity of biochar, cannot be simulated by simple HNO3 oxidation. It was found that the

303

sorption capacity of hydroquione was substantially reduced from 9.61 mg/g by the fresh

304

biochar to 4.28 mg/g by the field aged biochar.40

305

Comparison of PHE Sorption between the NOM and PyOM Fractions. The nonlinear

306

coefficients (n) of the NOM fractions are in the range of 0.58-0.89. The natural HA and HM

307

fractions exhibit higher n values than the corresponding PyOM fractions (Table S7), which 14


Page 14 of 30

Page 15 of 30


308

might be attributed to their different aromatic C contents. PHE could be adsorbed to aromatic

309

domains via π-π interactions.26,41 This process is expected to generate nonlinear sorption.26,41

310

Consistently, the n values of PHE for all the natural and pyrogenic HA and HM fractions are

311

correlated negatively with the aromatic C content (Figure S8a). Therefore, it was concluded

312

that the nonlinear PHE sorption by the NOM and PyOM fractions was regulated by their

313

aromatic C content.

314

It is noted that the sorption affinity (Kd and Koc) of pyrogenic HAs was an order of

315

magnitude higher than that of natural HAs (Table S7). The pyrogenic HM fractions also

316

displayed larger Kd and Koc values for PHE than the natural HM fractions (Table S7). As

317

shown in Figure S8, the logKoc of PHE of all the HAs is inversely correlated with the bulk

318

polar C content and positively correlated with the aromatic C content, implying that

319

hydrophobic partitioning and π-π EDA interactions between PHE and the aromatic moieties

320

contributed to the overall PHE sorption by the HA fractions, supported by other studies.26,27,32

321

In addition, the logKoc of PHE by the HA fractions is generally negatively correlated with the

322

surface C-O and C=O content of the HA fractions, but positively correlated with the surface

323

COO C content (Figure S8). As mentioned above, the formation of carboxylic groups on the

324

edge of aromatic components may lead to the elevated sorption of PHE via enhanced π-π

325

EDA interactions. Besides COO, C=O can also attract electrons from the benzene rings.

326

However, the functional groups of COO and C=O exerted opposite effects on PHE sorption.

327

The reason for this observation remains unclear and further study is needed. For the HM

328

samples, the logKoc of PHE is negatively correlated with the alkyl C content, carbohydrate C

329

content, bulk and surface polar C content, and estimated surface polarity, and positively 15



330

correlated with the aryl C content (Figure S9). Thus, PHE sorption by the natural and

331

pyrogenic HM may also be regulated by the hydrophobic mechanism and π-π EDA

332

interactions. Taken together, in comparison with NOMs, PyOMs showed superior sorption

333

capacities due to their low polar C content and high aryl C content.

334

Environmental Implications. The use of large amounts of biochar and subsequent aging

335

may release pyrogenic HA into the environment, which in turn will change the composition

336

of the organic matter fractions in soils, affecting HOC sorption. The results in this study

337

demonstrated that pyrogenic HAs were characterized by lower atomic H/C ratios, more

338

surface –COO(H) groups, and higher aromaticity compared to natural HAs. In addition,

339

pyrogenic HA had a much larger sorption capacity for PHE. Elucidating the distinct

340

composition and HOC sorption properties of pyrogenic HA makes it possible to better

341

understand the effect of biochar addition on the biogeochemistry of SOM and more

342

accurately assess the mobility and bioavailability of HOCs in biochar-amended soils. This

343

study also implies that using the protocol of classic chemical fraction method, not only

344

geologically formed HA, but also pyrogenic-derived HA can be isolated from soils. Therefore,

345

the “pollution” of HA by the pyrogenic HA should be taken into consideration in HA studies.

346

347

Supporting Information

348

The Supporting Information is available free of charge on the ACS Publications website. Nine ﬁgures and nine tables are provided (PDF).

349

350

ASSOCIATED CONTENT

AUTHOR INFORMATION 16


Page 16 of 30

Page 17 of 30


351

Corresponding Author

352

* Phone: +86 10 58807493; fax: +86 10 58807493; e-mail: [email protected] (K.

353

SUN). Phone: +1 413 545 5212; fax: +1 413 577 0242; e-mail: [email protected] (B.S.

354

XING).

355

Notes

356

The authors declare no competing ﬁnancial interest.

357

358

This research was supported by the National Natural Science Foundation--Outstanding

359

Youth Foundation (41522303), the National Natural Science Foundation of China

360

(41473087), and the USDA NIFA McIntire-Stennis Program (MAS 00028). J.J. also

361

thanks the China Scholarship Council for supporting her study at the University of

362

Massachusetts, Amherst.

363

364

(1) Steelink, C., Peer reviewed: investigating humic acids in soils. Anal. Chem. 2002, 74 (11), 326 A-333

365

A.

366

(2) Lehmann, J., A handful of carbon. Nature 2007, 447 (7141), 143-144.

367

(3) Hockaday, W. C.; Grannas, A. M.; Kim, S.; Hatcher, P. G., The transformation and mobility of

368

charcoal in a fire-impacted watershed. Geochim. Cosmochim. Acta. 2007, 71 (14), 3432-3445.

369

(4) Preston, C.; Schmidt, M., Black (pyrogenic) carbon: a synthesis of current knowledge and

370

uncertainties with special consideration of boreal regions. Biogeosciences 2006, 3 (4), 397-420.

371

(5) Mao, J.-D.; Johnson, R.; Lehmann, J.; Olk, D.; Neves, E.; Thompson, M.; Schmidt-Rohr, K.,

ACKNOWLEDGMENTS

REFERENCES

17



372

Abundant and stable char residues in soils: implications for soil fertility and carbon sequestration. Environ.

373

Sci. Technol. 2012, 46 (17), 9571-9576.

374

(6) Haumaier, L.; Zech, W., Black carbon-possible source of highly aromatic components of soil humic

375

acids. Org. Geochem. 1995, 23 (3), 191-196.

376

(7) Novotny, E. H.; deAzevedo, E. R.; Bonagamba, T. J.; Cunha, T. J.; Madari, B. E.; Benites, V. d. M.;

377

Hayes, M. H., Studies of the compositions of humic acids from Amazonian dark earth soils. Environ. Sci.

378

Technol. 2007, 41 (2), 400-405.

379

(8) Shindo, H.; Honna, T.; Yamamoto, S.; Honma, H., Contribution of charred plant fragments to soil

380

organic carbon in Japanese volcanic ash soils containing black humic acids. Org. Geochem. 2004, 35 (3),

381

235-241.

382

(9) Shindo, H.; Nishimura, S., Pyrogenic organic matter in Japanese Andosols: occurrence,

383

transformation, and function. In: Agricultural and Environmental Applications of Biochar: Advances and

384

Barriers; Guo, M., He, Z., and Uchimiya, M., Eds.; SSSA Spec. Publ. 63. SSSA: Madison, WI 2016; pp 29-62.

385

doi:10.2136/sssaspecpub63.2014.0036.5

386

(10) Kasozi, G. N.; Zimmerman, A. R.; Nkedi-Kizza, P.; Gao, B., Catechol and humic acid sorption onto a

387

range of laboratory-produced black carbons (biochars). Environ. Sci. Technol. 2010, 44 (16), 6189-6195.

388

(11) Cheng, C.-H.; Lehmann, J.; Engelhard, M. H., Natural oxidation of black carbon in soils: changes in

389

molecular form and surface charge along a climosequence. Geochim. Cosmochim. Acta. 2008, 72 (6),

390

1598-1610.

391

(12) McGeehin, J.; Burr, G.; Jull, A.; Reines, D.; Gosse, J.; Davis, P.; Muhs, D.; Southon, J.,

392

Stepped-combustion 14C dating of sediment: a comparison with established techniques. Radiocarbon 2001,

393

43, 255-262. 18


Page 18 of 30

Page 19 of 30


394

(13) Miyairi, Y.; Yoshida, K.; Miyazaki, Y.; Matsuzaki, H.; Kaneoka, I., Improved 14C dating of a tephra

395

layer (AT tephra, Japan) using AMS on selected organic fractions. Nucl. Instrum. Meth. B. 2004, 223,

396

555-559.

397

(14) Trompowsky, P. M.; de Melo Benites, V.; Madari, B. E.; Pimenta, A. S.; Hockaday, W. C.; Hatcher, P.

398

G., Characterization of humic like substances obtained by chemical oxidation of eucalyptus charcoal. Org.

399

Geochem. 2005, 36 (11), 1480-1489.

400

(15) Hiemstra, T.; Mia, S.; Duhaut, P.-B.; Molleman, B., Natural and pyrogenic humic acids at goethite

401

and natural oxide surfaces interacting with phosphate. Environ. Sci. Technol. 2013, 47 (16), 9182-9189.

402

(16) Luthy, R. G.; Aiken, G. R.; Brusseau, M. L.; Cunningham, S. D.; Gschwend, P. M.; Pignatello, J. J.;

403

Reinhard, M.; Traina, S. J.; Weber, W. J.; Westall, J. C., Sequestration of hydrophobic organic

404

contaminants by geosorbents. Environ. Sci. Technol. 1997, 31 (12), 3341-3347.

405

(17) Allen-King, R. M.; Grathwohl, P.; Ball, W. P., New modeling paradigms for the sorption of

406

hydrophobic organic chemicals to heterogeneous carbonaceous matter in soils, sediments, and rocks. Adv.

407

Water Resour. 2002, 25 (8), 985-1016.

408

(18) Sullivan, J.; Bollinger, K.; Caprio, A.; Cantwell, M.; Appleby, P.; King, J.; Ligouis, B.; Lohmann, R.,

409

Enhanced sorption of PAHs in natural-fire-impacted sediments from Oriole Lake, California. Environ. Sci.

410

Technol. 2011, 45 (7), 2626-2633.

411

(19) Ran, Y.; Sun, K.; Yang, Y.; Xing, B.; Zeng, E., Strong sorption of phenanthrene by condensed organic

412

matter in soils and sediments. Environ. Sci. Technol. 2007, 41 (11), 3952-3958.

413

(20) Cornelissen, G.; Gustafsson, Ö.; Bucheli, T. D.; Jonker, M. T.; Koelmans, A. A.; van Noort, P. C.,

414

Extensive sorption of organic compounds to black carbon, coal, and kerogen in sediments and soils:

415

mechanisms and consequences for distribution, bioaccumulation, and biodegradation. Environ. Sci. 19



416

Technol. 2005, 39 (18), 6881-6895.

417

(21) Jones, D.; Edwards-Jones, G.; Murphy, D., Biochar mediated alterations in herbicide breakdown and

418

leaching in soil. Soil Biol. Biochem. 2011, 43 (4), 804-813.

419

(22) Teixidó, M.; Hurtado, C.; Pignatello, J. J.; Beltrán, J. L.; Granados, M.; Peccia, J., Predicting

420

contaminant adsorption in black carbon (biochar)-amended soil for the veterinary antimicrobial

421

sulfamethazine. Environ. Sci. Technol. 2013, 47 (12), 6197-6205.

422

(23) Yang, Y.; Sheng, G., Pesticide adsorptivity of aged particulate matter arising from crop residue burns.

423

J. Agric. Food Chem. 2003, 51 (17), 5047-5051.

424

(24) Chen, B.; Yuan, M., Enhanced sorption of polycyclic aromatic hydrocarbons by soil amended with

425

biochar. J. Soil. Sediment. 2011, 11 (1), 62-71.

426

(25) Hale, S. E.; Hanley, K.; Lehmann, J.; Zimmerman, A.; Cornelissen, G., Effects of chemical, biological,

427

and physical aging as well as soil addition on the sorption of pyrene to activated carbon and biochar.

428

Environ. Sci. Technol. 2011, 45 (24), 10445-10453.

429

(26) Han, L.; Sun, K.; Jin, J.; Wei, X.; Xia, X.; Wu, F.; Gao, B.; Xing, B., Role of structure and

430

microporosity in phenanthrene sorption by natural and engineered organic matter. Environ. Sci. Technol.

431

2014, 48 (19), 11227-11234.

432

(27) Sun, K.; Jin, J.; Kang, M.; Zhang, Z.; Pan, Z.; Wang, Z.; Wu, F.; Xing, B., Isolation and

433

characterization of different organic matter fractions from a same soil source and their phenanthrene

434

sorption. Environ. Sci. Technol. 2013, 47 (10), 5138-5145.

435

(28) Kang, S.; Xing, B., Phenanthrene sorption to sequentially extracted soil humic acids and humins.

436

Environ. Sci. Technol. 2005, 39 (1), 134-140.

437

(29) Shindo, H.; Honma, H., Comparison of humus composition of charred Susuki (Eulalia, Miscanthus 20


Page 20 of 30

Page 21 of 30


438

sinensis) plants before and after HNO3 treatment. Soil Sci. Plant Nutr. 1998, 44 (4), 675-678.

439

(30) Jones, D. L.; Rousk, J.; Edwards-Jones, G.; DeLuca, T. H.; Murphy, D. V., Biochar-mediated changes

440

in soil quality and plant growth in a three year field trial. Soil Biol. Biochem. 2012, 45, 113-124.

441

(31) Chan, K. Y.; Van Zwieten, L.; Meszaros, I.; Downie, A.; Joseph, S., Agronomic values of greenwaste

442

biochar as a soil amendment. Soil Res. 2007, 45 (8), 629-634.

443

(32) Jin, J.; Sun, K.; Wang, Z.; Han, L.; Pan, Z.; Wu, F.; Liu, X.; Zhao, Y.; Xing, B., Characterization and

444

phthalate esters sorption of organic matter fractions isolated from soils and sediments. Environ. Pollut.

445

2015, 206, 24-31.

446

(33) Singh, B. P.; Cowie, A. L.; Smernik, R. J., Biochar carbon stability in a clayey soil as a function of

447

feedstock and pyrolysis temperature. Environ. Sci. Technol. 2012, 46 (21), 11770-11778.

448

(34) de Melo Benites, V.; de Sá Mendonça, E.; Schaefer, C. E. G.; Novotny, E. H.; Reis, E. L.; Ker, J. C.,

449

Properties of black soil humic acids from high altitude rocky complexes in Brazil. Geoderma 2005, 127 (1),

450

104-113.

451

(35) Cody, G. D.; Alexander, C. M. D., NMR studies of chemical structural variation of insoluble organic

452

matter from different carbonaceous chondrite groups. Geochim. Cosmochim. Acta. 2005, 69 (4),

453

1085-1097.

454

(36) Araujo, J. R.; Archanjo, B. S.; de Souza, K. R.; Kwapinski, W.; Falcão, N. P.; Novotny, E. H.; Achete,

455

C. A., Selective extraction of humic acids from an anthropogenic Amazonian dark earth and from a

456

chemically oxidized charcoal. Biol. Fert. soils 2014, 50 (8), 1223-1232.

457

(37) Jin, J.; Sun, K.; Wu, F.; Gao, B.; Wang, Z.; Kang, M.; Bai, Y.; Zhao, Y.; Liu, X.; Xing, B.,

458

Single-solute and bi-solute sorption of phenanthrene and dibutyl phthalate by plant-and manure-derived

459

biochars. Sci. Total Environ. 2014, 473, 308-316. 21



460

(38) Ran, Y.; Yang, Y.; Xing, B.; Pignatello, J. J.; Kwon, S.; Su, W.; Zhou, L., Evidence of micropore

461

filling for sorption of nonpolar organic contaminants by condensed organic matter. J. Environ. Qual. 2013,

462

42 (3), 806-814.

463

(39) Xiao, F.; Pignatello, J. J., Interactions of triazine herbicides with biochar: steric and electronic effects.

464

Water Res. 2015, 80, 179-188.

465

(40) Cheng, C.-H.; Lehmann, J., Ageing of black carbon along a temperature gradient. Chemosphere 2009,

466

75 (8), 1021-1027.

467

(41) Chefetz, B.; Xing, B., Relative role of aliphatic and aromatic moieties as sorption domains for organic

468

compounds: a review. Environ. Sci. Technol. 2009, 43 (6), 1680-1688.

469 470 471 472

22


Page 22 of 30

Page 23 of 30

473 474 475 476


Figure Captions:

477 478

Figure 1. Bulk (a, b, and c) and surface (d, e, and f) elemental composition for the two

479

biochars produced from maize straw (MA) and swine manure (SW), the oxidized biochars,

480

and humic acids (HA) as well as humins (HM) extracted from the two biochars, an

481

agriculture soil (AG), and a grassland soil (GR).

482 483

Figure 2. Atomic H/C and O/C ratios in biomass (plants before burning), biochars produced

484

at 450 °C, humic acids (HA) extracted from biochars, black and non-black soils, and litters,

485

and separate plant components (carbohydrate, lignin, protein, and lipids) (IHSS peat HA was

486

presented as reference) (the H/C and O/C data of the samples are cited from

487

literatures7,9,14,28,34). Linear regressions for biochars and corresponding pyrogenic HAs

488

extracted from biochars are shown.

489 490

Figure 3. Cross-polarization magic angle spinning 13C NMR spectra of humic acids (HAs)

491

isolated from an agriculture soil (AG), a grassland soil (GR), biochars produced from swine

492

manure (SW) and maize straw (MA), and an Amazonian Dark Earth (ADE) soil (the NMR

493

spectrum of ADE-HA is cited from the report by Araujo et al.36).

494 495

Figure 4. Concentration-dependent distribution coefficients (Kd and Koc) of fresh biochars

496

produced from maize straw (MA) and swine manure (SW), oxidized biochars (MA-AO and

497

SW-AO), and humic acids (HA) and humins (HM) isolated from biochars and soils. “GR”

498

and “AG” denote grassland soil and agriculture soil, respectively.

499 500 501 502 23



503 504 505 506

Table Caption:

507 508

Table 1．Bulk and Surface Elemental Composition of the Biochars, Soils, and Pyrogenic and

509

Natural Organic Matter Fractions

510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 24


Page 24 of 30

Page 25 of 30


526

100

Biochar Oxidized biochar

100

HM HA

a 80 Surface C, %

Bulk C, %

80 60 40 20

SW

GR

60 40

AG

HM HA


MA

SW

GR

AG

70

b

60 Surface O, %

30 Bulk O, %

d

0 MA

40

HM HA


20

0

20 10


HM HA

e

50 40 30 20 10

0

0 MA

SW

GR

AG

MA 0.8

1.0

Biochar or soil Oxidized biochar

HM HA

0.8 0.6 0.4 0.2

c

Estimated surface (O+N)/C

1.2

Bulk (O+N)/C

527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560

0.0

SW

GR

AG

Biochar

HM

Oxidized biochar

HA

f

0.6 0.4 0.2 0.0

MA

SW

GR

AG

MA

SW

GR

AG

561 562

Figure 1. Bulk (a, b, and c) and surface (d, e, and f) elemental composition for the two

563

biochars produced from maize straw (MA) and swine manure (SW), the oxidized biochars,

564

and humic acids (HA) as well as humins (HM) extracted from the two biochars, an

565

agriculture soil (AG), and a grassland soil (GR).

566 25



2.5

Decarboxylation Oxidation Carbonization

2.0

Hydration

Lipid Protein

Biomass

Cellulose

1.5 Melanoidin/lignin

H/C

567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591

Page 26 of 30

1.0

Biochar Biochar HA Black soil HA Non black soil HA Biomass IHSS peat HA Litter HA

Coal

0.5

0.0 0.0

0.2

0.4

0.6

0.8

1.0

O/C

592

Figure 2. Atomic H/C and O/C ratios in biomass (plants before burning), biochars produced

593

at 450 °C, humic acids (HA) extracted from biochars, black and non-black soils, and litters,

594

and separate plant components (carbohydrate, lignin, protein, and lipids) (IHSS peat HA was

595

presented as reference) (the H/C and O/C data of the samples are cited from

596

literatures7,9,14,28,34). Linear regressions for biochars and corresponding pyrogenic HAs

597

extracted from biochars are shown.

598 599

26


Page 27 of 30

600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619


ADE-HA MA-HA

SW-HA

GR-HA

AG-HA

250

200

150

100

50

0

-50

13

C chemical shift, ppm

620 621

Figure 3. Cross-polarization magic angle spinning 13C NMR spectra of humic acids (HAs)

622

isolated from an agriculture soil (AG), a grassland soil (GR), biochars produced from swine

623

manure (SW) and maize straw (MA), and an Amazonian Dark Earth (ADE) soil (the NMR

624

spectrum of ADE-HA is cited from the report by Araujo et al.36).

625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 27



642 643 644 645

Page 28 of 30

106

106

Koc

Kd

646 105

647 105

648

104

649 103 10-1

650

MA MA-AO MA-HM MA-HA

MA MA-AO MA-HM MA-HA

100

101

102

103

104

104 10-1

651

656

Kd or Koc, mL/g

655

102

103

104

Koc

Kd

652

654

101

107

106

653

100

105

106

104 3

10

657

102 10-1

658

104

105

SW SW-AO SW-HM SW-HA 0

10

1

10

2

10

3

4

10

10

104 10-1

SW SW-AO SW-HA SW-HM

100

101

102

103

104

106 Kd

659

Koc 105

660 103

104

661 GR-HM GR-HA AG-HM AG-HA

662 663

102 10-1

100

103

101

102

103

104

664 665

102 10-1

GR-HM GR-HA AG-HM AG-HA

100

101

102

103

104

Ce, µg/L

666 667

Figure 4. Concentration-dependent sorption coefficients (Kd and Koc) of fresh biochars

668

produced from maize straw (MA) and swine manure (SW), oxidized biochars (MA-AO and

669

SW-AO), and humic acids (HA) and humins (HM) isolated from biochars and soils. “GR”

670

and “AG” denote grassland soil and agriculture soil, respectively.

671 672

28


Page 29 of 30


Table 1．．Bulk and Surface Elemental Composition of the Biochars, Soils, and Pyrogenic and Natural Organic Matter Fractions

Bulk elemental composition Samples

MA

C

O

N

H

C/N

(%)

(%)

(%)

(%)

74.4

11.8

1.0

3.8

85.9

Surface elemental composition (XPS) O/C

0.12

H/C

0.61

(O+N)/C

0.13

(O+N) /Cc

Ash

C

O

N

Si

(%)

(%)

(%)

(%)

(%)

9.1

73.7

16.0

2.1

8.3

0.31

SW

33.7

10.2

2.6

2.6

15.3

0.23

0.91

0.29

50.9

48.5

25.7

4.6

12.3

0.33

MA-AO

54.6

18.3

3.4

2.9

18.5

0.25

0.64

0.31

20.8

41.3

51.9

4.6

2.2

0.40

SW-AO

48.7

16.3

6.3

2.8

9.0

0.25

0.68

0.36

25.9

42.8

51.1

0.0

2.0

0.43

MA-HA

53.6

31.5

3.5

3.1

17.8

0.44

0.69

0.50

8.2

64.7

28.5

4.0

1.2

0.41

SW-HA

51.9

30.0

6.6

3.3

9.1

0.43

0.76

0.54

8.2

73.2

25.7

0.0

1.1

0.39

MA-HM

52.1

29.0

3.0

3.2

20.2

0.42

0.74

0.47

12.7

65.6

26.0

3.5

0.8

0.16

SW-HM

4.7

1.4

0.4

0.3

13.0

0.22

0.90

0.30

93.2

10.1

45.8

0.0

30.0

0.23

GR

3.6

nd a

0.4

0.8

11.1

nd

2.53

nd

nd

nd

nd

nd

nd

nd

b

b

b

b

b

GR-HM

5.5

16.1

0.5

0.8

13.2

2.19

1.70

2.27

77.1

69.9

28.2

1.9

0.0

0.45

GR-HA

16.5

17.6

1.7

3.0

11.5

0.80

2.17

0.88

61.2

75.7

22.5

1.8

0.0

0.40

AG

1.4

nd

0.1

0.5

12.1

nd

4.40

nd

nd

nd

nd

nd

nd

nd

b

b

96.1

18.4

17.6

0.0

0.0

0.24

11.4

19.5

42.0

2.0

24.3

0.58

b

b

b

AG-HM

1.1

2.7

0.0

0.2

85.5

1.86

2.02

1.87

AG-HA

49.0

29.7

4.2

5.7

13.5

0.46

1.39

0.53

a

Not detected. b It is noted that GR-HM and AG-HM showed abnormally high O/C and (O+N)/C ratios, indicating that the measurements of O and H of GR-HM and AG-HM may be not correct.

The C contents of these two samples were too low; therefore, the measurements of O and H may be affected by mineral-bound water. cThe surface (O+N)/C ratios were estimated using the XPS data of surface functional groups listed in Table S4. Maize straw-derived biochcar (MA), swine manure-derived biochar (SW), oxidized biochar (AO), humic acids (HA), humins (HM), grassland soil (GR), and agriculture soil (AG).

29



For Table of Contents Only

30


Page 30 of 30

Characterization and Phenanthrene Sorption of ... - ACS Publications

Recommend Documents