Modeling the Transport of the “New-Horizon” Reduced Graphene

Mar 27, 2018 - Key Laboratory of Integrated Regulation and Resource Development on Shallow Lake of Ministry of Education, College of Environment, Hoha...
0 downloads 8 Views 1MB Size
Subscriber access provided by UNIV OF SCIENCES PHILADELPHIA

Environmental Processes

Investigating and Modeling the Transport of the ‘New-Horizon’ Reduced Graphene Oxide—Metal Oxide Nanohybrids in Water-Saturated Porous Media Dengjun Wang, Yan Jin, Chang Min Park, Jiyong Heo, Xue Bai, Nirupam Aich, and Chunming Su Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b06488 • Publication Date (Web): 27 Mar 2018 Downloaded from http://pubs.acs.org on March 27, 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 47

Environmental Science & Technology

Investigating and Modeling the Transport of the ‘New-Horizon’ Reduced Graphene Oxide—Metal Oxide Nanohybrids in WaterSaturated Porous Media Dengjun Wang,†,* Yan Jin,§ Chang Min Park,∆ Jiyong Heo,¶ Xue Bai,# Nirupam Aich,¥ and Chunming Su‡,* †

National Research Council and ‡Groundwater, Watershed, and Ecosystem Restoration Division, National Risk Management Research Laboratory, Office of Research and Development, United States Environmental Protection Agency, Ada, Oklahoma 74820, United States §



Department of Plant and Soil Sciences, University of Delaware, Newark, Delaware 19716, United States

Department of Environmental Engineering, Kyungpook National University, Buk-gu, Daegu 41566, South Korea



Department of Civil and Environmental Engineering, Korea Army Academy, Young-Cheon, Gyeongbuk 38900, South Korea #

Key Laboratory of Integrated Regulation and Resource Development on Shallow Lake of Ministry of Education, College of Environment, Hohai University, Nanjing 210098, Jiangsu Province, China ¥

Department of Civil, Structural, and Environmental Engineering, University at Buffalo, The State University of New York, Buffalo, New York 14260, United States

*

Corresponding authors: Dengjun Wang E-mail: [email protected] Phone: (580) 436-8828 Fax: (580) 436-8703 and Chunming Su E-mail: [email protected] Phone: (580) 436-8638 Fax: (580) 436-8703

1

ACS Paragon Plus Environment

Environmental Science & Technology

1 2

TOC ART

3

2

ACS Paragon Plus Environment

Page 2 of 47

Page 3 of 47

4

Environmental Science & Technology

ABSTRACT

5

Little is known about the fate and transport of the ‘new-horizon’ multifunctional

6

nanohybrids in the environment. Saturated sand-packed column experiments (n=66) were

7

therefore performed to investigate the transport and retention of reduced graphene oxide

8

(RGO)—metal oxide (Fe3O4, TiO2, and ZnO) nanohybrids under environmentally-relevant

9

conditions (mono- and di-valent electrolytes and natural organic matter). Classical colloid

10

science principles (Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and colloid filtration

11

theory (CFT)) and mathematical models based on the one-dimensional convection-dispersion

12

equation were employed to describe and predict the mobility of RGO-Fe3O4, RGO-TiO2, and

13

RGO-ZnO nanohybrids in porous media. Results indicate that the mobility of the three

14

nanohybrids under varying experimental conditions is overall explainable by DLVO theory and

15

CFT. Numerical simulations suggest that the one-site kinetic retention model (OSKRM)

16

considering both time- and depth-dependent retention accurately approximated breakthrough

17

curves (BTCs) and retention profiles (RPs) of the nanohybrids concurrently; whereas, others

18

(e.g., two-site retention model) failed to capture the BTCs and/or RPs. This is primarily because

19

blocking BTCs and exponential/hyperexponential/uniform RPs occurred, which is within the

20

framework of OSKRM featuring time- (for kinetic Langmuirian blocking) and depth-dependent

21

(for exponential/hyperexponential/uniform) retention kinetics. Employing fitted-parameters

22

(maximum solid-phase retention capacity: Smax=0.0406–3.06 cm3/g; and first-order attachment

23

rate coefficient: ka=0.133–20.6 min–1) extracted from the OSKRM and environmentally-

24

representative physical variables (flow velocity (0.00441–4.41 cm/min), porosity (0.24–0.54),

25

and grain size (210–810 µm)) as initial input conditions, the long-distance transport scenarios (in

26

500-cm long sand columns) of nanohybrids were predicted via forward simulation. Our findings

3

ACS Paragon Plus Environment

Environmental Science & Technology

Page 4 of 47

27

address the existing knowledge gap regarding the impact of physicochemical factors on the

28

transport of the next-generation, multifunctional RGO—metal oxide nanohybrids in the

29

subsurface.

30 31

INTRODUCTION

32

Compared with single-component nanomaterials (NMs), the ‘new-horizon’ nanohybrids

33

that are nano-/hierarchical assemblies of multiple NMs hold great promise for addressing issues

34

and meeting challenges within water-energy-agriculture-environment nexus,1 due to their

35

enhanced properties, optimized multi-functionalities, and maximized performances.2, 3 Among

36

others, the reduced graphene oxide (RGO)—metal oxide nanohybrids are the most commonly

37

pursued combinations owing to their exceptional and highly-tunable physicochemical (electronic,

38

thermal, mechanical, optical, photocatalytic, and magnetic) and biological (bioactive,

39

biocompatible, and antimicrobial) properties4 arising from the synergistic interplay of parent NM

40

components within the nanoheterostructures.5,

41

RGO-titanium dioxide (RGO-TiO2), and RGO-zinc oxide (RGO-ZnO) nanohybrids have

42

attracted immense interest for various applications including drug delivery,7 sensors,8

43

supercapacitors,9 solar cells,10 biomolecule immobilizer,11 and environmental remediation

44

(removing heavy metals, organic contaminants, and pathogens).12 Of considerable interest within

45

the framework of environmental remediation is the employment of magnetically-recyclable

46

RGO-Fe3O4

47

photoredox/photocurrent/photocatalytic degradation of diverse recalcitrant compounds.12, 13 This

48

is because nanoheteroconjugating Fe3O4, TiO2, and ZnO NMs with two-dimensional RGO

49

nanosheets that can strongly pre-concentrate contaminants via sorption, effectively inhibits the

and

easily-regenerative

6

For example, RGO-magnetite (RGO-Fe3O4),

RGO-TiO2

4

and

ACS Paragon Plus Environment

RGO-ZnO

nanohybrids

for

Page 5 of 47

Environmental Science & Technology

50

aggregation and surface passivation of metal oxide NMs14 and decreases the recombination rate

51

of photo-generated electron-hole pairs,12,

52

efficiency of contaminants. Increasing production and use of multifunctional RGO—metal oxide

53

nanohybrids necessitate fundamental understandings of environmental remediation and potential

54

environmental/human health impacts and risks (e.g., unknown toxicity of nanohybrids, or

55

detached RGO, TiO2, and ZnO NMs, or dissolved Zn(II) ions)2, 16 due to unintentional release

56

during nanohybrids production, usage, and other relevant end-of-life stages17 (e.g., wastewater

57

treatment plant18, 19 and land application of sewage sludge20).

15

thereby significantly improving degradation

58

Aggregation and transport propensities of single-component NMs and multi-component

59

nanohybrids dictate their performances in environmental remediation (e.g., in-situ contaminated

60

site nanoremediation),21-23 fate,24 transformations,25 and potential environmental/human health

61

impacts and risks.26 Over the past decade, substantial efforts have been devoted to unravelling

62

the transport of singular NMs in the subsurface, documenting that NMs’ mobility is governed by

63

the interplay of physicochemical properties of NMs (e.g., size/shape/coating/surface charge) and

64

porous media (e.g., grain size/porosity/surface chemistry), hydrodynamics (e.g., flow velocity),

65

and surrounding solution chemistries (e.g., pH/ionic strength (IS)/natural organic matter

66

(NOM))27,

67

Verwey-Overbeek (DLVO) theory29,

68

semi-quantitatively. However, little is known about the transport of nanohybrids in the

69

subsurface; and the critical knowledge gaps such as “Will nanohybrids behave/transport

70

similarly (or distinctly) as NMs do?” and “Can DLVO theory and CFT qualitatively or semi-

71

quantitatively describe the transport behaviors of nanohybrids as well?” need to be addressed

72

before mass production and widespread application of multifunctional nanohybrids occur.

28

, which can be explained by colloid science principles of Derjaguin-Landau30

and colloid filtration theory (CFT)31 qualitatively or

5

ACS Paragon Plus Environment

Environmental Science & Technology

Page 6 of 47

73

Numerical simulations have long-been used to mechanistically describe the transport and

74

retention of colloids/NMs in porous media, and model-fitted parameters, in turn, furnish valuable

75

insights into understanding the intrinsic mechanisms dominating colloids/NMs’ mobility. For

76

instance, upon incorporating a depth-dependent straining term into the one-dimensional (1D)

77

convection-dispersion

78

hyperexponential deposition of colloids, introducing a new mechanism (physical straining) for

79

colloid retention. In addition to the data-fitting functionality (inverse-algorithm), numerical

80

simulation (e.g., forward-algorithm) also has enormous potential to forecast possible outcomes of

81

colloids/NMs with adjustable input parameters including initial boundary conditions.33 This is of

82

practical significance given that laboratory experiments are costly, time-consuming, or even

83

impossible to implement due to certain limitations. Specifically, forward simulation can predict

84

the long-distance transport of colloids/NMs with varying input conditions (e.g., flow velocity,

85

porosity, and grain size)33 commonly encountered in the subsurface, some of which cannot be

86

achieved or maintained in laboratory experiments (e.g., one cannot experimentally investigate

87

the mobility of colloids/NMs at low subsurface flow velocity scenarios since low-flow-rate

88

injection of NMs results in particle clogging in packed-column tubing system due to

89

aggregation/agglomeration).

equation

(CDE),

Bradford

et

al.32

accurately

simulated

the

90

This research is set forth to bridge the knowledge gap regarding the influence of

91

physicochemical factors on the transport of RGO—metal oxide nanohybrids in the subsurface.

92

The most influential environmental factors (mono- and di-valent electrolytes and NOM)34

93

controlling NMs’ mobility were chosen. Saturated sand-packed column experiments were

94

conducted to investigate the transport and retention of RGO-Fe3O4, RGO-TiO2, and RGO-ZnO

95

nanohybrids under environmentally-relevant concentrations of NaCl, CaCl2, and NOM. DLVO

6

ACS Paragon Plus Environment

Page 7 of 47

Environmental Science & Technology

96

theory, CFT, and numerical simulation were employed to delineate the transport behaviors of

97

nanohybrids. Fitted-parameters from the best modelling approach were used in combination with

98

the physical variables commonly encountered in the subsurface to predict long-distance transport

99

(in 500-cm long sand columns) of nanohybrids via forward-simulation. Coupling laboratory

100

experiments with numerical simulations provides a robust venue for accurately describing and

101

assessing the mobility of the ‘new-horizon’ nanohybrids in the subsurface.

102 103

MATERIALS AND METHODS

104

Preparation of RGO-Fe3O4, RGO-TiO2, and RGO-ZnO Nanohybrid Influent

105

Suspensions and Solution Chemistries

106

The RGO-Fe3O4 nanohybrid stock suspension (10,000 mg/L) well-dispersed in acetone

107

(~80%, v/v) was purchased from Sigma-Aldrich (product #803804). The RGO-TiO2 and RGO-

108

ZnO nanohybrid powders were synthesized in-house. Physicochemical properties of the RGO-

109

Fe3O4, RGO-TiO2, and RGO-ZnO nanohybrids were characterized using multiple techniques

110

including high-resolution transmission electron microscopy (HR-TEM), field-emission scanning

111

electron microscopy (FE-SEM), Fourier-transform infrared (FT-IR) spectroscopy, X-ray

112

photoelectron spectroscopy (XPS), and ultraviolet-visible (UV-Vis) spectroscopy. Detailed

113

procedures of synthesizing the RGO-TiO2 and RGO-ZnO, and physicochemical characterizations

114

of the three nanohybrids are provided in the Supporting Information (SI) S1. Environmentally-

115

relevant solution chemistries (Table 1) were chosen to examine the mobility of RGO-Fe3O4,

116

RGO-TiO2, and RGO-ZnO nanohybrids in water-saturated porous media including mono- (1, 10,

117

50, and 100 mM NaCl) and di-valent (0.5, 1, 5, and 10 mM CaCl2) electrolytes, and the presence

118

of NOM (0, 1, 5, and 10 mg C/L Suwannee River humic acid (SRHA); procedures for preparing

7

ACS Paragon Plus Environment

Environmental Science & Technology

119

SRHA stock suspension are given in SI S2). The nanohybrid influent suspensions at the desired

120

solution chemistries (Table 1) were freshly prepared via ultrasonication (100 W and 42 kHz;

121

Branson 3510R-DTH sonicator, Danbury, CT) for 30–60 min at 25 °C. The concentration of all

122

nanohybrid influents for column experiments was 10 mg/L, and influent pH was unadjusted

123

(pH=7.0–7.5). Compared to the RGO-TiO2 and RGO-ZnO nanohybrids suspended in water

124

(100%), the RGO-Fe3O4 influent suspension includes ~0.08% (v/v) acetone (10,000 mg/L stock

125

suspension was diluted 1,000 times to obtain 10 mg/L influent).

126 127

Column Experiments

128

Ottawa sands (U.S. Silica, Berkeley Springs, WV) having an average diameter of 360-µm

129

were selected as representative aquifer materials. Prior to use, the sands were cleaned using a

130

sequential acid-deionized (DI) water wash procedure.35 Transport experiments were conducted in

131

duplicates using glass chromatography columns (1.7-cm i.d. × 10-cm long). The column was

132

dry-packed with cleaned sands, purged with CO2 gas for 30 min, and then slowly-saturated with

133

DI water. Column porosity was gravimetrically determined to be ~0.334. Following the

134

saturation step, a nonreactive tracer (50 mM NaNO3) experiment was performed to determine the

135

hydrodynamic properties of the packed-columns, including pore-water velocity and dispersivity,

136

which were then used in numerical modeling of the transport of nanohybrids in the column

137

experiments.

138

Following the completion of tracer experiment, the column was pre-equilibrated with

139

desired background electrolyte solution (Table 1) to standardize pore-water solution chemistries.

140

A two-step transport experiment was then initiated by injecting 3 pore volumes (PVs) of 10

141

mg/L of nanohybrid influents (Table 1) followed by elution with 7 PVs of nanohybrid-free

8

ACS Paragon Plus Environment

Page 8 of 47

Page 9 of 47

Environmental Science & Technology

142

background electrolyte solution. Darcy velocity was maintained at 0.44 cm/min35 for all

143

experiments. Column effluents were collected continuously via a fraction collector. After

144

completion of each breakthrough experiment, the spatial distribution of nanohybrids retained in

145

the column was determined (dissection experiment; SI S3). The concentrations of RGO-Fe3O4,

146

RGO-TiO2, and RGO-ZnO nanohybrids in the effluents and retentates (collected from dissection

147

experiments) were determined spectrophotometrically at their peak wavelengths (264, 252, and

148

264 nm, respectively, for RGO-Fe3O4, RGO-TiO2, and RGO-ZnO nanohybrids; SI Figure S4).

149

Calibration curves were constructed by diluting 10 mg/L nanohybrid influent suspension, which

150

was linear within the concentration range of 0–10 mg/L (R2=1.0; SI Figure S5). Mass balances

151

were calculated by comparing the quantities of nanohybrids recovered in the effluents and

152

retentates to those injected in the column.

153 154

Electrokinetic Properties and Hydrodynamic Sizes of Nanohybrids and Sand

155

Grains

156

Electrokinetic properties and hydrodynamic sizes of nanohybrids indicating their

157

aggregation and transport propensities36 were determined. Specifically, electrophoretic mobility

158

of RGO-Fe3O4, RGO-TiO2, and RGO-ZnO nanohybrids in the influents (10 mg/L) and sand

159

grains (pulverized colloidal particles of sands as surrogates)35 at desired solution chemistries

160

(Table 1) was determined using the Zetasizer Nano-ZS ZEN3600 analyzer (Malvern Instruments

161

Ltd., Malvern, Worcestershire, U.K.) in triplicates at 25 °C, and then converted to zeta (ζ)-

162

potential using the Smoluchowski equation.37 The hydrodynamic diameter (DH) of nanohybrids

163

in the influents was determined using dynamic light scattering (DLS) on the same Zetasizer

164

analyzer in triplicates at 25 °C.35 Prior to measurements, ultrasonication was performed in a

9

ACS Paragon Plus Environment

Environmental Science & Technology

165

water bath (25 °C) at 100 W and 42 kHz for 30 min to obtain a homogeneous suspension. The ζ-

166

potential and DH values of nanohybrids and sand grains were used to calculate the average

167

interaction energy between nanohybrids and sand grains under different experimental conditions

168

using DLVO theory. Within the framework of the DLVO theory, the van der Waals and

169

electrostatic double layer interaction energies were calculated for the nanohybrid-sand system,

170

assuming a sphere-plate configuration (SI S4).

171 172

Numerical Simulations

173

The breakthrough curves (BTCs) and retention profiles (RPs) of RGO-Fe3O4, RGO-TiO2,

174

and RGO-ZnO nanohybrids under different experimental conditions were simulated using the 1D

175

CDE with one- (site 1) or two-site (sites 1 and 2, respectively) kinetic retention. The one-site

176

kinetic retention model (OSKRM) is described as follows:40 

177



+ 







=    −



 

[1]



178

  =   −    [2]

179

 = 1 − 







 ! "# 



[3]

180

where θ is volumetric water content [–]; C is nanohybrid concentration in aqueous-phase [NL–3,

181

where N and L denote number and length, respectively]; t is time [T, where T denotes time]; ρb is

182

bulk density of porous media [ML–3, where M denotes mass]; S is nanohybrid concentration on

183

solid-phase [NM–1]; x is the spatial coordinate [L]; D is the hydrodynamic dispersion coefficient

184

[–]; q is flow rate [LT–1]; ka and kd are first-order attachment and detachment rate coefficients [T–

185

1

186

retention; Smax is the maximum solid-phase retention capacity [NM–1]; dc is average diameter of

], respectively; ψ is a dimensionless function considering both time- and depth-dependent

10

ACS Paragon Plus Environment

Page 10 of 47

Page 11 of 47

Environmental Science & Technology

187

sand grains; and β is an empirical parameter controlling the shape of RPs [–]. The OSKRM can

188

describe time-dependent BTCs (e.g., kinetic Langmuirian blocking)41 and RPs that are uniform,

189

exponential, or hyperexponential with depth.40, 42 The first and second terms on the right-hand

190

side of equation [3] account for time-dependent Langmuirian attachment,41 and depth-dependent

191

retention, respectively. Exponential RPs occur when β=0, consistent with CFT prediction.31

192

Conversely, when β>0, hyperexponential RPs occur with greater retention near the column

193

inlet.43 Four model formulations (M1–M4) were considered within the framework of OSKRM

194

(SI Table S1): M1—CFT when ψ=1; M2—time-dependent Langmuirian attachment when β=0;

195

M3—depth-dependent retention when β=0.432;32 and M4—both time- and depth-dependent

196

retention when β=0.432 and (1-S/Smax)