Value-Added Humic Acid Derived from Lignite Using Novel Solid

Oct 2, 2017 - Agricultural and Biological Engineering, Institute of Food and Agricultural Sciences (IFAS), University of Florida, Gainesville, Florida...
2 downloads 12 Views 10MB Size
Subscriber access provided by UNIVERSITY OF THE SUNSHINE COAST

Article

Value-Added Humic Acid Derived from Lignite Using Novel Solid-Phase Activation Process with Pd/CeO2 Nanocatalyst: A Physiochemical Study Yafu Tang, Yuechao Yang, Dongdong Cheng, Bin Gao, Yongshan Wan, and Yuncong C. Li ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b02094 • Publication Date (Web): 02 Oct 2017 Downloaded from http://pubs.acs.org on October 2, 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.

ACS Sustainable Chemistry & Engineering 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 54

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

1

Title Page

2

Value-Added Humic Acid Derived from Lignite Using Novel Solid-Phase

3

Activation Process with Pd/CeO2 Nanocatalyst: A Physiochemical Study

4

Authors: Yafu Tang1, Yuechao Yang1,3*, Dongdong Cheng1*, Bin Gao2, Yongshan

5

Wan3, Yuncong C. Li3

6 7

Affiliations:

8

1

9

Resources; National Engineering & Technology Research Center for Slow and

National Engineering Laboratory for Efficient Utilization of Soil and Fertilizer

10

Controlled Release Fertilizers, College of Resources and Environment, Shandong

11

Agricultural University, Daizong Street No. 61, Taishan District, Taian, Shandong

12

271018, China;

13

2

14

Sciences (IFAS), University of Florida, Gainesville, FL 32611, USA.

15

3

16

IFAS, University of Florida, Homestead, FL 33031, USA.

Agricultural and Biological Engineering, Institute of Food and Agricultural

Department of Soil and Water Science, Tropical Research and Education Center,

17 18

*Corresponding author: Yuechao Yang, Dongdong Cheng

19

Phone: 86-538-824 2900

20

E-mail: [email protected]

21

[email protected] 1 ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

22 23

Page 2 of 54

ABSTRACT: Soil, air and water pollution caused by lignite is considered a serious

24

environmental problem. Activation methods thus have been developed to extract

25

humic acid from lignite to support the agricultural production as the soil amendment

26

or fertilizer synergist. The traditional activation methods of humic acid from lignite,

27

however, are not environmentally friendly. As the first study, this work developed a

28

novel solid-phase activation method with a Pd/CeO2 nanocatalyst for lignite-derived

29

humic acid. This study analyzed the morphology and structures of as-synthesized

30

Pd/CeO2 nanocatalyst with various characterization tools. The mechanisms of

31

Pd/CeO2 nanocatalyst for lignite activation were determined. The Pd/CeO2 catalyst

32

effectively promoted the production of water soluble humic acids from lignite via

33

KOH solid-phase activation at room temperature. It increased the amount of small

34

molecular active groups and the corresponding small molecules of humic acid. The

35

existence of a strong synergistic effect at the interface sites between Pd/CeO2

36

nanoparticles and lignite was one of the key factors for the outstanding catalytic

37

performance. In conclusion, this study has great application perspectives in reducing

38

lignite pollution and increasing humic acid utilization by crops, which can improve

39

the sustainability of environment and agricultural systems.

40

KEYWORDS: Lignite, Catalyst, Activation, Humic acid

41 42

2 ACS Paragon Plus Environment

Page 3 of 54

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

43 44

INTRODUCTION As the lowest rank of coal, lignite is an abundant natural resource and is often

45

piled up as wastes in coal mining area because of its low calorific value and high ash

46

content.1, 2 It not only occupied and destroyed the arable lands, but also cause

47

environmental pollution such as air pollution and surface and underground water

48

contamination.2 Mineralization process of lignite often releases acidic leachates

49

containing heavy metals and trace elements which result in serious contamination of

50

soil and water aquifers.3, 4 Therefore, the environmental problems caused by lignite

51

are of great attention. However, recent studies have suggested to use lignite for the

52

development of value-added products including humic and fulvic acids.5 Humic acid

53

contains various types of acidic functional groups that play an important role in

54

regulating many crucial ecological and environmental processes. Previous studies

55

have demonstrated that humic acid can be used as a remediation agent in many

56

environmental applications as well as soil amendment to improve soil properties.6

57

Several studies have indicated that humic substances may have stronger effects on

58

plant growth and crop yield than some of the traditional inorganic fertilizers.7 In

59

particular, humic substances can not only enhance nutrient uptake and utilization in

60

plants through chelating minerals, but also be the main source of organic carbon to

61

plants through their own degradation.8 However, the humic substances in lignite

62

cannot be directly utilized by crops. Activation processes thus are often needed to

63

convert these humic substances into water-soluble forms that further stimulated the 3 ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 54

64

growth of the plants.9 Physical and chemical activation methods have been

65

developed recently to better utilize the humic substances in lignite.6, 10 The

66

traditional activation of humic acid from lignite often uses oxidants such as HNO3,

67

H2O2 and KMnO4 to pretreat the samples to increase yield. However, most of these

68

methods use liquid phase reactions and require external heating with high demand of

69

energy, relatively long reaction time, and high standard of equipment.6 Furthermore,

70

the activation process may not be environmentally friendly and release undesired

71

byproducts into the natural environment. These drawbacks have limited the

72

development of activation technologies for utilizing humic substances of lignite. It is

73

thus necessary to develop novel activation methods that are low-cost, highly

74

effective, and environmentally friendly to utilize lignite.

75

With the development of nanotechnology, nanosized catalysts have attracted much

76

attention recently.11 Metal and metal oxide-based composites are recognized as

77

promising catalysts.12 In particular, Pd/CeO2 composites have been used as low-cost

78

and high-efficiency catalysts in various applications.13-15 Pd/CeO2 composites as a

79

three-way catalytic convertor are currently used in vehicles to oxidizing

80

methane.16-18 In this case, ceria is an ideal support for methane oxidation catalysis

81

because of it high oxygen storage capacity and high oxygen mobility.19 Vayssilov

82

studied model Pt/CeO2 catalysts on electron and oxygen transfer and showed

83

favorable interactions on nanostructured ceria that enhances activity.20 It has been

84

demonstrated that, among the combination of noble metals (e.g., Pt, Ru, Pd and Au) 4 ACS Paragon Plus Environment

Page 5 of 54

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

85

and rare earth oxides (e.g., ZrO2, TiO2, and CeO2) for a single nanostructure for

86

catalytic reactions, the Pd/CeO2 catalyst is considered the most effective one for the

87

water-gas-shift (WGS) reaction.21-23 Tan et al. used CeO2 of different morphologies

88

to support Pd nanocatalyst and found that Pd/ CeO2 can fully convert indoor

89

formaldehyde into CO2 at ambient temperature.24 This is partially due to the fact that

90

Ce is a multivalent ion (III and IV) and thus CeO2 has excellent redox potential with

91

superior oxygen storage and release capacities.12 It has also been demonstrated that

92

the CeO2 (100) surface is highly defective and contains more oxygen vacancies than

93

the (111) and (110) surfaces.25 Additionally, it has been reported that the energy

94

required for the formation of reactive oxygen vacancies on (100) surface is lower

95

compared with (111) surface.26 Therefore, the CeO2 (100) surface is favorable for

96

catalytic applications.

97

Findings from previous studies have all pointed out that the Pd/CeO2

98

nanocomposite is an excellent catalyst that can be used to oxidize and convert

99

methane, formaldehyde, water gas, and other hydrocarbons with complicated carbon

100

structures.17, 22, 24 Because lignite has high volatile hydrocarbons and is rich in

101

carboxyl, hydroxyl, and phenol functional groups,27 it is anticipated that Pd/CeO2

102

nanocomposites can also oxidize and activate the humic substances from lignite to

103

promote its applications. However, little research has been conducted on the use of

104

Pd/CeO2 catalyst to active lignite via solid-phase reaction at room temperature.

105

The objective of this work was to take advantage of the excellent oxidation 5 ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

106

catalytic ability of Pd/CeO2 to develop and optimize the solid-phase activation

107

process to produce value-added water-soluble humic substances from lignite. The

108

activation of lignite often involves the convention of the insoluble calcium and

109

magnesium humic matters into soluble potassium (sodium) salts through KOH

110

treatment. In this work, a novel ball milling process was applied in the solid-phase

111

activation process of lignite to promote the KOH conversion in the presence of

112

Pd/CeO2 catalysts of different morphologies. Various laboratory experiments were

113

conducted to determine the solid-phase activation mechanisms. In particular, the

114

catalytic mechanisms of the Pd/CeO2 nanocomposites in surface oxidation of humic

115

substances in lignite were explored. Findings from this work can be used to inform

116

the development of low cost, highly effective, and environmentally friendly

117

technologies to reduce the environmental pollution of lignite and produce

118

value-added humic acid from lignite.

119

EXPRIMENTAL SECTION

120

Materials. Lignite (Shanxi, China), Ce(NO)3·6H2O (analytical grade, Aladdin

121

Chemistry Co, Ltd, Shanghai, China), NaBH4 (analytical grade, Aladdin Chemistry

122

Co, Ltd, Tianjin, China), PdCl2 (Aladdin Chemistry Co, Ltd, Shanghai, China), and

123

KOH (analytical grade; Tianjin Kaitong Chemical Industry Co, Ltd, Tianjin, China)

124

were used in this study. The solutions were made with deionized water.

125

Synthesis of the CeO2 Catalysts. The CeO2 catalyst was prepared according to

126

the previous methods.12, 24 The ceria materials were prepared via the template-free

Page 6 of 54

6 ACS Paragon Plus Environment

Page 7 of 54

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

127

alkaline hydrothermal method.24 In brief, 1 g of Ce(NO)3·6H2O was dissolved in 30

128

mL deionized water under stirring conditions. 10 mL NaOH (800 g/L) solution was

129

then added. The mixture was stirred for 30 min at room temperature and then rapidly

130

sealed into a 50 mL autoclave. The hydrothermal treatment was conducted at 473 K

131

for 24 h. The final product was collected by filtration, centrifuged and rinsed several

132

times with deionized water to remove any possible ionic remnants, and then dried

133

and calcined at 337 K for 4 h.

134

Preparation of the Pd/CeO2 Nanoparticles. The Pd/CeO2 nanoparticles were

135

synthesized using a wet impregnation method.24 0.3 g of CeO2 samples were mixed

136

with 100 mL deionized water and sonicated for 10 min at room temperature, then

137

0.005 g of PdCl2 was added to the above solution and then the reaction mixture

138

stirred for an hour. Afterward, the pH of the mixture was buffered to neutral using

139

5% NaOH solution. Then, 2 mL of 0.005 g/ml NaBH4 solution was added into the

140

suspension under stirring conditions. The final precipitates were thoroughly washed

141

4 times with deionized water and ethanol. The resulting Pd/CeO2 nanoparticles were

142

dried at 337 K overnight.

143

Catalyst Characterization. The size and morphology of the synthesized sample

144

were obtained by followed methods. Filed-emission scanning electron microscopy

145

(FESEM, S-4800, Japan) was conducted at an accelerating voltage of 15 K.

146

Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM)

147

images were obtained with field emission transmission electron microscope (Tecnai 7 ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

148

Page 8 of 54

G2 F20, USA) at an a working voltage of 200 kV.

149

A JSM-6360LV scanning electron microscope (SEM) (JEOL) equipped with an

150

X-act energy-dispersive X-ray spectrometer (EDX) (Oxford) was used to analyze the

151

morphology and surface elemental composition of the synthesized sample.

152

The powder X-ray diffraction (XRD) analysis of the synthesized sample was

153

performed using an X-ray diffractometer (D8 ADVANCE, Germany) with

154

Ni-filtered Cu Kα radiation (λ = 0.1541 nm), The 2θ angular region between 5 and

155

90o was operated at a scan rate of 4 min−1.

156

Raman spectra of the synthesized sample was conducted by spectrometer

157

equipped with a liquid N2 cooled charge-coupled device detector and a confocal

158

microscope (Renishaw inVia, Britain). A 350 mW near-infrared 785 nm laser was

159

used for analysis under ambient conditions. The wavenumber values reported from

160

the spectra are accurate to within 2 cm−1.

161

X-ray photoelectron spectroscopy (XPS) was recorded using a Thermo escalab

162

250Xi photoelectron spectrometer (USA) with a monochromatic Al Kα (hν = 1486.6

163

eV) radiation source. The charging shift was calibrated with C 1 s value of

164

adventitious carbon at binding energy of 284.8 eV. Smart background correction was

165

used for peak fits with Avantage program.

166

H2 temperature-programmed reduction (H2-TPR) was performed using a

167

ChemiSorb 2720 (USA) apparatus equipped with a TCD detector. TPR was carried

168

out at a heating rate of 5 oC min−1 using 10 vol % H2-Ar mixture and at a flow rate of 8 ACS Paragon Plus Environment

Page 9 of 54

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

169 170

15mL·min−1 to examine the redox behaviors of the samples. The Brunauer-Emmett-Teller (BET) surface area and pore volume of the sample

171

were determined with N2 adsorption−desorption isotherms at −196 °C using

172

Micrometrics ASAP 2020 (USA).

173

Activation of Lignite. Lignite was milled and dried and then sieved to pass an 80

174

mesh. Solid KOH was used as the activation agent. The experiment included four

175

treatments: 1) raw lignite (RL) as the control; 2) 10% activation agent with lignite

176

(AL); 3) 10% activation agent and 1% CeO2 nanocatalyst with lignite (ACL), and 4)

177

10% activation agent and 1% Pd/CeO2 nanocatalyst with lignite (APL). The same

178

amount of lignite was used in the above treatments. Each treatment was placed in a

179

ball mill (QM-10-15, China) and was ground for 60 min at a speed 80 r/min. The

180

experiments were repeated 3 times.

181

Catalytic Activity Evaluations. After each of the treatments (RL, AL, ACL,

182

APL), elemental compositions of the samples were determined using an elemental

183

analysis instrument (Model 1106, Germany).Total humic acid and water soluble

184

humic acid in the four treatments were determined with previously reported

185

methods.28, 29 To observe the static grading phenomena of the four treatments, 1 g of

186

each sample was added in 1,000 mL of water and place for 1 year. To further explore

187

the catalytic effect, the humic acid was fractionated into 3 size ranges: below10,000

188

Da; 10,000-50,000 Da and over 50,000 Da by continuous flow analytical system

189

(DMJ60, China). Each molecular size fraction was determined following the 9 ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 54

190

methods of previous studies.30, 31 The light absorbance at 465 nm and 665 nm of the

191

four treated humic acid was obtained using a Spectronic 20 Genesys

192

Spectrophotometer on solution of 3.0 mg of each HA in 10 mL of 0.05 M NaHCO3

193

and then the E4/E6 ratios were calculated.32, 33

194

To further understand the activation and catalytic mechanisms, water-soluble

195

calcium and magnesium in lignite was determined with atomic absorption

196

spectrometer (AA-700, Japan). A JSM-6360LV scanning electron microscope (SEM,

197

S-4800, Japan) equipped with an X-act energy-dispersive X-ray spectrometer (EDX)

198

(Oxford) was also used for the morphological survey and elemental identification of

199

the surface of the four treatments. Solid-state NMR spectroscopy

200

(13C-CPMAS-NMR) was performed on a Bruker AV-300 (Germany) equipped with

201

a 4 mm wide-bore MAS probe and NMR spectra were obtained by applying the

202

following parameters: 13,000 Hz of rotor spin rate; 1 s of recycle time; 1 ms of

203

contact time; 20 ms of acquisition time; 5,000 scans. Samples were packed in 4 mm

204

zirconia rotors with Kel-F caps. The four treatment samples were re-dissolved in 1

205

mL of hexane and transferred in a glass vial for gas chromatography-mass

206

spectrometry (GC-MS, MSQ8100 GC/MS, China) analysis.

207

Statistical Analysis. Tukey’s multiple range testing was performed to compare the

208

average values among the parameters. The statistical significance was at a

209

probability level of p