Effect of Citric Acid Surface Modification on Solubility of

Subscriber access provided by Caltech Library

Agricultural and Environmental Chemistry

Effect of Citric Acid Surface Modification on Solubility of Hydroxyapatite Nanoparticles Ranuri Samavini, Chanaka Sandaruwan, Madhavi de Silva, Gayan Priyadarshana, Nilwala Kottegoda, and Veranja Karunaratne J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.7b05544 • Publication Date (Web): 22 Mar 2018 Downloaded from http://pubs.acs.org on March 22, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 39

Journal of Agricultural and Food Chemistry

1

Effect of Citric Acid Surface Modification on Solubility of Hydroxyapatite Nanoparticles

2

Ranuri Samavini,1 Chanaka Sandaruwan,2 Madhavi De Silva,1, 2, 3 Gayan Priyadarshana,2 Nilwala

3

Kottegoda,*1,2, 3 Veranja Karunaratne2

4

1 Department of Chemistry, University of Sri Jayewardenepura, Nugegoda, Sri Lanka.

5

2 Sri Lanka Institute of Nanotechnology (SLINTEC), Nanotechnology and Science Park,

6 7

Center for Excellence in Nanotechnology, Mahenwatte, Pitipana, Homagama, Sri Lanka. 3 Center for Advanced Materials Research (CAMR), Faculty of Applied Sciences,

8

University of Sri Jayewardenepura, Nugegoda, Sri Lanka.

9

*[email protected], [email protected], Tel: + 94 11 4650509, Fax: + 94 11 4741995

10

Abstract

11

Worldwide, there is an amplified interest in nanotechnology based approaches to develop

12

efficient nitrogen, phosphorous and potassium fertilizers to address major challenges pertaining

13

to food security. However, there are significant challenges associated with fertilizer manufacture

14

and supply as well as cost in both economic and environmental terms. The main issues relating

15

to nitrogen fertilizer surround the use of fossil fuels in its production and the emission of

16

greenhouse gases resulting from its use in agriculture; phosphorus being a mineral source, make

17

it non-renewable and casts a shadow on its sustainable use in agriculture. This study focuses on

18

development of an efficient P nutrient system that could overcome the inherent problems arising

19

from current P fertilizers. Here, attempts are made to synthesize citric acid surface modified

20

hydroxyapatite nanoparticles using wet chemical precipitation. The resulting nanohybrids were

21

characterized using powder X-Ray diffraction to extract the crystallographic data while

22

functional group analysis was done by Fourier transform infrared spectroscopy. Morphology and

23

particle size were studied using scanning electron microscopy along with elemental analysis

ACS Paragon Plus Environment


24

using energy dispersive X-Ray diffraction spectroscopy. Its effectiveness as a source of P were

25

investigated using water release studies and bio availability studies using Zea mays as the model

26

crop. Both tests demonstrated the increased availability of P from nanohybrids in the presence of

27

an organic acid compared to pure hydroxyapatite nanoparticles and rock phosphate.

28

Keywords: P fertilizers, hydroxyapatite nanoparticles, organic acids, citric acid modified

29

hydroxyapatite nanoparticle, Nanohybrids, bioavailability

30

Introduction

31

Due to advances in agriculture during the ‘green revolution’, food production has increased

32

globally, in order to meet the requirements of a growing population.1 Agricultural food

33

production basically relies on the external supply of major nutrients such as N, P, and K to the

34

plants for their proper growth as soil itself does not have enough nutrient quantities.2 However,

35

due to low nitrogen utilizing efficiency (NUE) by plants, high cost of N fertilizers together with

36

environmental issues have spurred a research towards developing slow release N fertilizers that

37

focused mainly on various polymer based strategies3-16 and considering the sustainability

38

challenges of P due to its non-renewable nature, effective use of P resources have also drawn a

39

greater attention worldwide.1, 17-19

40

There are different sources of P used in agriculture such as ground rock phosphate and

41

commercial fertilizers for instance mono-ammonium phosphates (MAP), di-ammonium

42

phosphates (DAP), triple superphosphates (TSP).20-21 Importantly, the plant availability and

43

water solubility of these sources are different from each other. Rock phosphates are not water-

44

soluble whereas commercial P fertilizers are highly water-soluble. As a result the availability of

45

P from rock phosphates is less for plants whereas major portion of water soluble commercial


Page 2 of 39

Page 3 of 39


46

fertilizers are wasted without being available for plants making major environmental issues, such

47

as eutrophication.2, 20-21

48

The major P source, rock phosphate, being a mineral source makes it a non- renewable resource

49

and the absence of a gaseous phase in its biogeochemical cycle makes its depletion harder to

50

replenish.22 Since P plays a critical role in living organisms including respiration, photosynthesis,

51

protein and nucleic acid synthesis6, its gradual scarcity does not bode well for advances in the

52

agriculture and food production in the future. Especially, plants will not gain their maximum

53

yield without adequate levels of P. As a result, external fertilizer application is needed for crop

54

plants where soil has no adequate amounts of P.2 As agriculture uses ~ 80-90% of mined P, its

55

sustainable use at a global level is an urgent priority.1 Therefore, effective use of P through

56

smart fertilizers with minimum leaching and optimized solubility6,

57

research proposition.

58

In this connection, reports on the use of synthetic hydroxyapatite nanoparticles (HANP) for

59

controlled P release in soybean6, use of HANP as a P fertilizer in wheat24, the work carried out

60

by Giroto et al. (2015) where HANP was incorporated into biodegradable, soluble host

61

matrixes25 and our work where urea coated HANP was used for slow release of N in rice, there is

62

a paucity of research on controlled release of P in agriculture. In this paper, we report citric acid

63

(CA) modified hydroxyapatite nanoparticles (CMHANPs) to achieve optimum release of P in

64

corn.

65

Materials and Methods

66

All reagents and chemicals used in this study were purchased from the Sigma Aldrich Company,

67

USA and were of analytical grade and used without further purification. Eppawala Rock

68

phosphate (ERP), triple superphosphates (TSP) were used as the commercial phosphate sources


23

becomes an attractive


69

during experiments, purchased from Lanka Phosphate Ltd. All solutions were prepared using

70

distilled water.

71

Experimental methods

72

Synthesis of pure hydroxyapatite nanoparticles (HANPs)

73

Pure HANPs were synthesized according to the wet chemical precipitation method discussed by

74

Kottegoda et al.11, 15 Calcium hydroxide (8.12 g) was dissolved in distilled water (100 cm3) by

75

stirring.

76

Into that slurry, 0.6 mol dm-3 orthophosphoric acid (100.0 cm3) was added drop wise under 1000

77

rpm of continuous agitation. The stoichiometry of the reaction was maintained such that Ca:P is

78

1.67 which is in agreement with that in hydroxyapatite. The pH of the reaction mixture was

79

checked during the reaction in order to assure basic pH medium at 10.

80

Synthesis of citric acid surface modified hydroxyapatite nanoparticles (CMHANPs)

81

In-situ modification method

82

Here, CA modification was performed while synthesizing HANP. CA solution of 50 mM was

83

prepared in 100.00 cm3 volumetric flask using CA monohydrate. Calcium hydroxide (8.12 g)

84

was dispersed in distilled water (200.00 cm3) by mechanical agitation at 1000 rpm. Phosphoric

85

acid (0.6 mol dm-3, 100.00 cm3) was prepared to meet the molar ratio of Ca:P, 1.67 in

86

hydroxyapatite. Into the slurry of Ca(OH)2, two acid solutions were added in a controlled

87

manner. Each drop of phosphoric acid added was followed by the addition of a drop of CA under

88

continuous agitation (~0.4 mL/min flow rate of each solution was maintained resulting ~ 4 ½ h

89

of reaction time). Reaction mixture pH was monitored and maintained at 10 by adding

90

ammonium hydroxide (25% w/w). Same procedure was followed as above for the CA solutions


Page 4 of 39

Page 5 of 39


91

of 150 mM and 250 mM to prepare different compositions of CMHANPs (In50mM CMHANPs,

92

In150mM CMHANPs and In250mM CMHANPs).

93 94

Ex-situ modification method

95

Here, CA modification was performed after the synthesis of HANP. Firstly, phosphoric acid (0.6

96

mol dm-3,100.00 cm3) was added to a slurry of calcium hydroxide (8.12 g, 200.00 cm3) under

97

continuous stirring to prepare HANP suspension. Then, the CA solution (50 mM, 100.00 cm3)

98

was added drop wise to HANP suspension maintaining pH at 10 by adding ammonium

99

hydroxide (25% w/w). Same procedure was repeated with 150 mM and 250 mM CA

100

concentrations to prepare Ex50mM CMHANPs, Ex150mM CMHANPs, Ex250mM CMHANPs

101

nanohybrids.

102

Characterization of nanohybrids

103

Scanning Electron Microscopy (SEM) characterization

104

The SEM images of the synthesized nanohybrids were obtained using the Hitachi SU6600

105

scanning electron microscope. The secondary electron mode was used for imaging. Samples

106

were coated with a thin layer of gold in order to make it conductive.

107

Energy Dispersive X-ray Spectroscopy (EDXS) analysis

108

EDXS analysis was conducted using Hitachi SU6600 SEM operating in secondary electron mode

109

with an accelerating voltage of 20 kV and working distance of 10 mm, equipped with EDXS

110

detector to determine elemental composition.

111

Fourier Transform Infra-Red (FTIR) spectroscopy

112

Nicolet IS 10 in diffuse reflection mode with the frequency range 4000 cm-1 to 500 cm-1 was

113

used to determine the chemical structure and the bonding nature of resulted nanohybrids.



114

Powder X-Ray Diffraction (PXRD) studies

115

PXRD patterns of powdered samples of HANPs and CMHANP composites were obtained using

116

Rigaku X-ray, Ultima IV diffractometer using Cu Kα radiation of wavelength 1.540 Å in 2θ scan

117

axis over scan range of 5 to 80 degree with a scanning speed of 2.0 degrees/min.

118

UV-Visible spectroscopy

119

Genesys 10s UV-Vis spectrometer using Vision Lite software was used to determine total P

120

content of resulted hybrids.

121

Total P content determination

122

The standard procedure given by SLS 645 for total P determination in organic fertilizers was

123

followed.26

124

Then, the absorbance was measured at 420 nm in 1 cm cell using 5.00 mg solution as the blank.

125

HANP (2.50 g) was mixed with calcium oxide (0.50 g) and calcined at 500°C to ash the sample

126

and allowed to cool. Then, 50.00 cm3 of distilled water was added and stirred thoroughly. This

127

was then heated to the boiling point. Conc. HCl (5 cm3) followed by conc. HNO3 (5 cm3) were

128

added to the boiling solution. Solution was boiled for 10 min until the solution became clear. The

129

prepared sample was allowed to cool, filtered and transferred into a 250.00 cm3 (Vo) volumetric

130

flask, and diluted to the mark. V1 volume from this solution was used for the test using 12.50

131

cm3 of vanadomolybdate reagent and top up to mark with distilled water. Relevant P2O5 content

132

was calculated as follows.

133

𝑃2 𝑂5 % 𝑏𝑦 𝑚𝑎𝑠𝑠 =

𝑦 × 𝐷𝐹 × 𝑉𝑜 × 100 1000 × 𝑉1 × 𝑀

134 135


Page 6 of 39

Page 7 of 39


136

y - Concentration relevant to absorbance from standard curve

137

DF- Dilution Factor

138

M - Mass of the sample

139

Above procedure was followed for CMHANP composites. Same procedure was followed for

140

pure HANP, ERP, and TSP samples without calcination due to the absence of organic

141

components.

142

P release study

143

P release studies were carried out according to the standard dialysis membrane method described

144

in the literature.27 Each prepared sample in solid form (1.00 g) was weighed and put into a semi-

145

permeable membrane bag. Then, 50.00 cm3 of distilled water was added into 100 cm3 beakers

146

and initial pH was measured. Then, the membrane bags having each sample was dipped in the

147

beaker and kept closed. From each setup 1.00 cm3 was sampled out periodically after proper

148

stirring to make sure that the sample resembles the whole solution. This sample was then

149

treated with the standard vanadomolybdate method developed for the examination of water and

150

waste water.28 Then, P content was quantified using UV- Vis spectrometer. Final pH of the

151

solution is measured and the solution was topped up with distilled water after each withdrawal of

152

the sample. This was repeated for CMHANP composites, HANP and ERP.

153

Release kinetics

154

P release kinetics for HANP and CMHANP nanohybrids were studied using existing release

155

models. Here, release data from each experiment were fitted with the zero order model, first

156

order model, Higuchi and Korsmeyer-Pappas model and the R2 values of the linear graphs were

157

compared to derive the mechanism of the release of phosphate.29

158



Page 8 of 39

159

Bio-availability studies

160

Corn (Zea mays) plants were used for bio-availability studies.30 Fertilizer application was

161

conducted as recommended by the Department of Agriculture (DOA), Sri Lanka as given in the

162

Table 1. To minimize the complexity arisen from the natural soil, coco peat which can be used as

163

an inert growing medium was used in the experiment.31

164

Table 1: DOA fertilizer recommendation for Zea mays. DOA recommendation for Time of application Before

Amounts per pot

irrigated cultivation for corn Urea

TSP

(kg/ha) (kg/ha) 75

100

MOP

Urea

TSP

MOP

(kg/ha)

(g/pot)

(g/pot)

(g/pot)

50

2

3

1.4

3

1.4

planting 4 weeks after

250

7

planting Total

325

100

50

9

165 166

To minimize the interferences from the complex soil structure, coco peat was used as the inert

167

growing medium. Three sets of ten fertilizing schemes were conducted as (T1) Pure HANP

168

(T2) In50mM CMHANP (T3) In150mM CMHANP (T4) In250mM CMHANP (T5) Ex50mM

169

CMHANP (T6) Ex150mM CMHANP (T7) Ex250mM CMHANP (T8) ERP (T9) TSP, (T10)

170

Fertilizer without P, each pot having two plants. All the pots were treated in a similar manner

171

including N, P, K fertilizer application and watering, except for different sources of P. Urea

172

and muriate of potash (MOP) were used as N and K sources, respectively. External


Page 9 of 39


173

micronutrient solution (50 cm3) was supplied for all experimental pots in order to minimize

174

other nutrient deficiencies (See supplementary-Table S1).32 Total P of each sample was

175

determined as described in methods and an equal amount of P was supplied (See

176

supplementary-Table S2) to each pot at the same time period based on TSP amount, before

177

planting. The growth of the plants was monitored by measuring the height of plants and

178

number of unrolled leaves weekly. Once the lifecycle of the plants were completed, the

179

yield of cobs was monitored. Dry mass yield of the plants were also measured compared to

180

the regular P treatments.

181

Results and Discussion

182

The SEM image of pure HA (Figure 1(a)) exhibits the nanorod like morphology with a diameter

183

less than 50 nm confirming the synthesis of HA in nanoscale. As shown in Figure 1 (b) the

184

morphology of CMHANP in ex-situ modification is retained more or less even after the

185

modification while the diameter of the particle has increased (100 nm) due to surface coating of

186

the CA.



187 188

Figure 1: SEM images of (a) pure HANP (b) ex-situ modified CMHANP nanohybrids (c) in-situ

189

modified CMHANP nanohybrids.

190

Interestingly, in in-situ modified nanoparticles, the nanorod like morphology has changed into

191

blunt ended spherical particles with a diameter of ~500 nm (Figure 1 (C)). This observation

192

reveals that the two synthetic approaches have an effect on the morphology of the CA surface

193

modified HANP. According to the EDXS analysis, an increment of the C% in the samples were

194

observed (Table 2). The maximum CA loading is observed for In250mM CMHANP.

195 196 197


Page 10 of 39

Page 11 of 39

198


Table 2: Elemental composition of resulting nanohybrids Sample

Elemental Composition (Average %) C

O

P

Ca

Pure HANP In50mM CMHANP

0.00 23.18

58.45 36.02

14.17 11.03

27.38 35.33

In150mM CMHANP

31.19

19.98

13.51

35.33

In250mM CMHANP

49.23

41.19

2.28

7.30

Ex50mM CMHANP

42.48

37.24

7.41

12.87

Ex50mM CMHANP

45.81

42.62

3.56

8.05

Ex50mM CMHANP

47.20

37.75

2.58

12.26

199

In order to understand the nature of interactions between the nanoparticles and CA, FTIR spectra

200

were compared with that of pure HANP. Peak shifts, peak broadenings, new peaks appearing or

201

disappearing due to phosphate, hydroxyl, and carbonyl regions were compared to obtain

202

conclusive evidence. A significant shift in the peak due to stretching vibrations of the phosphate

203

group, from 1041 cm-1 to ~1020 cm-1 was observed for all in-situ modified samples (Figure 2

204

(i)).



205 206

Figure 2: FTIR spectra for the (i) PO43- stretching, (ii) C=O stretching and OH bending, and (iii)

207

OH stretching regions of (a) Pure HANP, (b) In50mM CMHANP, (c) In150mM CMHANP, (d)

208

In250mM CMHANP, and (e) Pure CA.

209

Other than that, the peak intensity of phosphate stretching mode decreased with increasing the

210

loading of CA. According to the literature, inorganic phosphate group stretching appears around

211

~1050

212

compounds like aliphatic groups which explains the observed peak shift. This can be further

213

explained by observing the lowering of intensity of the phosphate peak with increasing CA

214

concentrations.

cm-1 and shifts to ~1020 cm-1

(1050-990 cm-1)33 upon interaction with organic


Page 12 of 39

Page 13 of 39


215

The peak at 1395 cm-1 (1310-1410 cm-1) is assigned to the bending mode of tertiary OH group in

216

CA while the peak at 1475 cm-1 is corresponding to the bending modes of CH in methylene

217

group of CA (Figure 2 (ii)). Peak around 1725 cm-1 represents the carbonyl group of carboxylic

218

acid group in pure CA and C-O stretching mode of carboxylic acid appears as a shoulder peak at

219

~1425 cm-1 while the bending mode of OH in the carboxylic acid group is given around ~1600

220

cm-1 which are in agreement with those reported by Coates et al.33 The weak carbonyl stretching

221

peak has disappeared after modification with CA suggesting the appearance of strong

222

interactions between HA and CA molecules. In CMHANP composites, hydroxyl group of HANP

223

is bonded with the carbonyl groups and hydroxyl groups arising from the CA molecule. Bending

224

mode of OH in CA has appeared with a reduced intensity with considerable peak shifts from

225

1600 cm-1 to around ~1570 cm-1 (Figure 2 (ii)) in CMHANP composites further confirming the

226

presence of strong H bonding between HANP and CMHANP.

227

According to literature, the carbonyl group of carboxylate anion can be assigned to the peak

228

around 1610–1550 cm-1.33 Therefore, the peak centered on ~1570 cm-1 in in- situ modified

229

samples was assigned to the carbonyl group in carboxylate anion form which suggests the

230

presence of carboxylate anions in the nanocomposite. The appearance of this peak in the

231

nanocomposite with the disappearance of the peak relevant to carbonyl group in pure CA (~1725

232

cm-1) suggests that favorable interactions exist between the two species (Figure 2 (ii)). Further

233

elaboration of this behavior interpret that some CA molecules can substitute as an anion with

234

phosphates in the HANP crystal structure. The peak centered around ~3450 cm-1 in pure HANP

235

spectrum was broaden in CMHANP composites with the center of the peak being shifted towards

236

lower frequencies around 3300 cm-1 (Figure 2 (iii)) which concluded that H-bonding has taken

237

place during the binding of CA onto HA.33



Page 14 of 39

238

Importantly, similar behavior of shifts was also observed for ex-situ modified nanocomposites.

239

Table 3 summarizes the major FTIR peak position values for both in-situ modified and ex-situ

240

modified nanocomposites. Here, in all nanocomposites, the region of tertiary OH bending of

241

citric acid is overlapped with C-O stretching of carboxylic group to give a single peak which has

242

been denoted using * mark. Notably, higher extent of interactions can be seen for in-situ

243

modified samples.

244

Table 3: Major FTIR peak value comparison of in-situ and ex-situ modified nanocomposites Sample

FTIR peaks positions (cm-1) P-O OH stretching stretching

OH bending of CA

Pure HANP

1041

3450

-

In50mM CMHANP

1020

3350

1573

OH bending of tertiary - alcohol group of CA 1416*

C-O stretching of CA

In150mM CMHANP

1019

3346

1569

1413*

-

In250mM CMHANP

1019

3349

1570

1412*

-

Ex50mM CMHANP

1019

3344

1577

1416*

-

Ex150mM CMHANP

1022

3265

1566

1428*

-

Ex250mM CMHANP

1025

3225

1560

1408*

-

Pure CA

-

32003500

1600

1395

-

C=O stretching of CA -

1425

1725

245 246

PXRD characterization was done in order to extract crystallographic data of synthesized HANP

247

and CMHANP samples. Except for the In250mM CMHANP sample, all other samples were


Page 15 of 39


248

verified as hydroxyapatite (HA) crystalline structure according to the reported powder diffraction

249

data (PDF No: 01-089-4405). However, most of the peaks corresponding to the HA were

250

identified together with the peaks arising from CA. Peaks denoted by an * represents the

251

corresponding peaks for the CA. It is clear that the major mineral phase of the modified samples

252

were HA and with the increment of citric acid loading, the extra peaks relevant for citric acid

253

also appeared. Interestingly, both in-situ and ex-situ modified samples have broader diffraction

254

peaks than those of the pure HANP and the three major peaks (e), (f), and (g) have been merged.

255

These observations suggest that some extent of modification has occurred in HA crystalline

256

structure without changing its major mineral phase. Merging of nearby peaks due to broadening

257

is characteristic for monocrystalline materials.34 This confirms the successful synthesis of

258

monocrystalline CMHANP. As shown in Figures 3 (i) and (ii), the peaks denoted by a-l

259

represents the major peaks relevant to pure HA in comparison with the modified samples.

260 261

Figure 3: Comparison of PXRD pattern of (a) Pure HANP, and (i) in-situ modified

262

nanocomposites of (b) In50mM

263

CMHANP and (ii) ex-situ modified nanocomposites of (b) Ex50mM CMHANP, (c) Ex150mM

264

CMHANP, and (d) Ex250mM CMHANP.

CMHANP, (c) In150mM


CMHANP, and (d) In250mM


Page 16 of 39

265

Table S3 and table S4 summarizes the major crystallography planes for both in-situ modified and

266

ex-situ modified nanocomposites (see supplementary).

267

Total P content of all nanocomposites, pure HANP, TSP and ERP was calculated and given in

268

Table 4.

269

Table 4: Total P content as % P2O5 by mass Sample

Total P content as % P2O5 by mass

Pure HANP

35.59

In50mM CMHANP

34.62

In150mM CMHANP

32.24

In250mM CMHANP

27.43

Ex50mM CMHANP

35.02

Ex150mM CMHANP

33.78

Ex250mM CMHANP

28.10

TSP

50.31

ERP

43.26

270

The total P content of ex-situ modified samples was higher compared to the corresponding in-situ

271

modified samples. This observation suggests that in the in-situ modification there is greater

272

interactions of CA with HANP prior to agglomeration due to the presence of CA in the reaction

273

system whereas in the ex-situ method, there is more time for the agglomeration of HANP that

274

lower the surface area, which leads to lower interactions between CA and HANP.

275

Release behavior of phosphate ions from the nanohybrid was studied in distilled water (pH=6.8).

276

Final pH of the released medium was recorded as 5.9 for pure HANP sample, 6.0 for ERP and

277

5.8-6.0 for CMHANP nanohybrids. Interestingly, lowering of the pH can be observed due to the


Page 17 of 39


278

release of phosphate ions from nanohybrids accompanied by the leaching of citric acid into the

279

released medium. CMHANP nanohybrids showed an increased release of phosphorus compared

280

to that of pure HANP and ERP (Figure 4). As shown in Figure 4, the ex-situ modified samples

281

exhibited an initial burst release of phosphorus followed by a slow release whereas in-situ

282

modified samples showed a gradual increment of phosphate release. Release profiles of ex-situ

283

and in-situ modified samples can be correlated with the synthesis pathway used. For an example,

284

CA modification was done after the synthesis of HANP in ex-situ modification, while HANP

285

synthesis was carried out in the presence of CA in solution in the in-situ modification. As a

286

result, in ex-situ method there is a chance of agglomeration of HANP where the binding of CA

287

on to HANP is poorly expected. The initial rapid phosphate release of ex-situ modified samples

288

is owing to rapid pH increment due to weakly bound CA on HANP being released into the

289

medium. Once the nanohybrid is exposed to the water medium, the hydrogen bonded surface

290

interactions with citric acid is diminished resulting in an equilibrium with water to give H+ to the

291

medium which leads to greater HA dissolution.35 Compared to in-situ modified samples, ex-situ

292

modified samples reached this equilibrium faster resulting in increased dissolution of HANP in

293

the initial stages. The slow release rate of phosphate in the later stage is due higher particle size

294

compared to in-situ modified samples. This means that due to agglomeration, the surface area of

295

the solid that H+ can attack is lower in the ex-situ modified sample.



296 297

Figure 4: Overall comparison of release profiles, (a) Ex250mM CMHANP, (b) In250mM

298

CMHANP, (c) Ex150mM CMHANP, (d) In150mM CMHANP, (e) Ex50mM CMHANP (f)

299

In50mM CMHANP, (g) Pure HANP, and (h) ERP.

300

Gradual increment of phosphorus release throughout 60 days was observed (Figure 4). Since in-

301

situ modification was done simultaneously with the synthesis of HANP, citrate ions could be

302

replaced with phosphate ions in the HA crystal structure which was also evident from reduced

303

crystallinity as shown by PXRD data compared to pure HANP. The dissolution in in-situ

304

modified samples thus aided by two factors in the aspect of release of H+ from surface bonded

305

CA and citrate ions that have been replaced in HA lattice. Based on the release kinetics and the

306

chemical model used to explain the dissolution, two types of interactions (a) surface addition,

307

and (b) Intercalation, can be deduced between CA and HANP. The release data was further

308

analyzed by fitting with different kinetic models relevant to controlled release formulations.


Page 18 of 39

Page 19 of 39


309

Using this data the mechanism behind the release of P from the nanohybrid was derived. As

310

shown in the Table 5, four different models were manipulated to derive the release kinetics of

311

modified HANP.

312

Table 5: Comparison of release kinetics for CMHANP nanohybrids Sample

R2 value for each kinetic model Zero-order First-order Higuchi Korsmeyer

Best fitted model

(ZOM)

(FOM)

model

-Peppas

(HM)

(KPM)

Pure HANP

0.937

0.925

0.690

0.972

KPM

In50mM CMHANP

0.958

0.814

0.773

0.962

KPM

In150mM CMHANP

0.988

0.806

0.843

0.984

ZOM

In250mM CMHANP

0.950

0.887

0.937

0.992

KPM

Ex50mM CMHANP

0.972

0.770

0.931

0.934

ZOM

Ex150mM CMHANP

0.115

0.620

0.818

0.883

KPM

Ex250mM CMHANP

0.237

0.462

0.647

0.736

KPM

ERP

0.905

0.954

0.671

0.992

KPM

313 314

Based on the results, samples had the best fit with the zero order model and the Korsmeyer-

315

Pappas model as shown in the Table 5. Even though In150mM CMHANP and Ex50mM

316

CMHANP release profiles best fitted the zero order model with R2 values of 0.988 and 0.972,

317

respectively; the R2 values for the Korsmeyer-Pappas model were 0.984 and 0.934 respectively,

318

showing close agreement. Except these two samples, all other systems behave according to the

319

Korsmeyer-Pappas model. Korsmeyer–Peppas model is applied for controlled release systems

320

where the matrix is cylindrical which release active species by diffusion. Further investigation of



321

the release profiles that were fitted with the Korsmeyer–Peppas model reveals the release

322

mechanism in relation to its exponential factor as given in the table S5 (See supplementary).

323

According to the results, the kinetic model of the nanohybrid can be explained as the

324

Korsmeyer–Peppas model which follows a non Fickian transport mechanism.

325

Maximum average height of the plants after 9th week was identified for In250mM CMHANP

326

treatment. Average height of the plants are significantly higher compared to No P, pure HANP,

327

and ERP treatments while in-situ modified samples depicted higher growth than the

328

corresponding ex-situ modified treatments Figure 5.

329 330

Figure 5: Comparison of maximum heights of the plants at 9th week (a) No P, (b) Pure HANP,

331

(c) TSP, (d) ERP, (e) In50mM CMHANP, (f) In150mM CMHANP, (g) In250mM CMHANP,

332

(h) Ex50mM CMHANP, (i) Ex150mM CMHANP, and (j) Ex250mM CMHANP.


Page 20 of 39

Page 21 of 39


333

Interestingly, maximum average dry weight of the cobs resulted for In250mM CMHANP and

334

In150mM CMHANP treatments (Figure 6).

335 336

Figure 6: Average dry weight of the cobs from plants under different treatments.

337

This observation can be justified by referring to the extent of growth of the root system. As can

338

be seen by figure 7, the roots are efficiently developed for the treatments f and g which received

339

highest amount of P while all the treatments received same amount of nitrogen. Therefore, the

340

similar plant height was observed for in-situ and ex-situ while cob development was retarded by

341

the unavailability of sufficient P. This observation can also be further explained by referring to

342

the water release profiles given in figure 4 where efficient and gradual release of P was observed

343

for in-situ composites.



344 345

Figure 7: The root system of plants under different treatments

346

The results from the pot experiments, the optimum growth parameters were obtained with the in-

347

situ modified samples compared to the conventional P fertilizers. In250mM CMHANP treatment

348

displayed the best crop productivity over ERP and TSP treatment used as conventional

349

fertilizers. A significant increment of the growth and crop productivity of all nanohybrid

350

treatments were observed compared to ERP or TSP. According to the results from the release

351

study and plant uptake studies, it can be concluded that the developed nanohybrids have opened

352

up a new pathways for development of an efficient P nutrient system with increased solubility

353

and plant availability.

354 355 356 357 358 359 360 361 362 363


Page 22 of 39

Page 23 of 39


364

Supporting information

365

Table S1: General micronutrient formulation as recommended. Nutrient

Concentration (ppm)

Ca

180

Mg

48

S

336

Fe

3

Cu

0.02

Zn

0.11

Mn

0.62

B

0.44

366 367

Table S2: Amount of sample used as the source of P in pot experiments Source of P

Total P content as % P2O5

Mass

of

each

sample

applied to the experimental by mass (pot / g) Pure HANP

35.59

4.24

In50mM CMHANP

34.62

4.36

In150mM CMHANP

32.24

4.68

In250mM CMHANP

27.43

5.50

Ex50mM CMHANP

35.02

4.30

Ex150mM CMHANP

33.78

4.47

Ex250mM CMHANP

28.10

5.37

TSP

50.31

3.00

ERP

43.26

3.49



368

Page 24 of 39

Table S3: Major peaks assigned for PXRD pattern of in-situ modified samples. Peak Peak

Pure HANP

In50mM CMHANP 2θ d (nm)

Index

2θ

d (nm)

a

100

10.78

0.820

b

200

25.76

0.346

25.79

0.345

d

210

29.10

0.307

28.43

0.314

e

211

31.84

0.281

31.97

f

112

32.90

0.272

g

300

33.94

0.264

h

310

39.88

0.226

39.60

i

222

46.69

0.194

j

312

48.07

0.189

k

213

49.38

0.184

49.68

0.183

l

400

52.98

0.173

53.19

0.172

In150mM CMHANP 2θ d (nm)

In250mM CMHANP 2θ d (nm) 11.51

0.768

25.86

0.344

26.01

0.342

0.280

32.13

0.278

31.94

0.280

0.227

39.46

0.228

40.10

0.225

46.36

0.196

49.72

0.183

53.13

0.172

49.38

369 370 371 372 373 374 375 376 377


0.184

Page 25 of 39

378


Table S4: Major peaks assigned for PXRD pattern of ex-situ modified samples. Peak Peak

Pure HANP

Ex50mM CMHANP 2θ d (nm)



10.76

0.822

11.51

0.768

25.85

0.344

25.83

0.345

28.90

0.309

31.85

0.281

32.85

0.272

Index

2θ

d (nm)

a

100

10.78

0.820

b

200

25.76

0.346

25.81

0.345

d

210

29.10

0.307

28.39

0.314

e

211

31.84

0.281

31.85

0.281

f

112

32.90

0.272

g

300

33.94

0.264

33.91

0.264

33.98

0.264

33.97

0.264

h

310

39.88

0.226

39.78

0.226

39.81

0.226

39.79

0.226

i

222

46.69

0.194

46.77

0.194

46.65

0.195

j

312

48.07

0.189

k

213

49.38

0.184

49.41

0.184

49.31

0.185

l

400

52.98

0.173

53.17

0.172

53.06

0.172

49.71

0.183

31.86

379 380 381 382 383 384 385 386 387


0.281


388

Table S5: Exponential factor and relevant mechanism of the samples behaving KPM Sample

Exponential factor (n)

Transport mechanism

Pure HANP

1.461

Super case II transport

In50mM CMHANP

2.188


In250mM CMHANP

0.618

Non -Fickian transport

Ex150mM CMHANP

0.770

Non -Fickian transport

Ex250mM CMHANP

0.919


ERP

1.774


389 390

Acknowledgements

391

Authors wish to acknowledge University of Sri Jayewardenepura for offering facilities for the

392

research.

393

Author Contributions

394

NK developed the idea, designed the project, supervised, provided the leadership and finalized

395

the manuscript. VK mentored the project and finalized the manuscript. RS designed and

396

performed the experiments, analyzed the data and participated in manuscript preparation. CS

397

designed the pot experiments, analyzed the data and prepared the manuscript. MS and GP

398

analyzed the data and participated in manuscript preparation.

399 400


Page 26 of 39

Page 27 of 39


401

References

402

(1)

403

Phosphorus and Food: Solutions from Closing the Human Phosphorus Cycle. Bioscience 2011,

404

61 (2), 117-124.

405

(2)

Fageria, N. K., The use of nutrients in crop plants. CRC press: 2016.

406

(3)

Majeed, Z.; Ramli Nur, K.; Mansor, N.; Man, Z., A comprehensive review on

407

biodegradable polymers and their blends used in controlled-release fertilizer processes. Rev.

408

Chem. Eng. 2015, 31 (1), 69.

409

(4)

410

Navia, R., Evaluation of biodegradable polymers as encapsulating agents for the development of

411

a urea controlled-release fertilizer using biochar as support material. Sci. Total Environ. 2015,

412

505, 446-453.

413

(5)

414

characterization of controlled-release fertilizers coated with marine polysaccharide derivatives.

415

Chin. J. Oceanol. Limn. 2017, 35 (5), 1086-1093.

416

(6)

417

(Glycine max). Sci. Rep-UK. 2014, 4, 5686.

418

(7)

419

characterization of slow-release fertilizer encapsulated by starch-based superabsorbent polymer.

420

Carbohyd. Polym. 2016, 147, 146-154.

421

(8)

422

methods to produce controlled release coated urea fertilizer. J. Control. Release 2014, 181, 11-

423

21.

Childers, D. L.; Corman, J.; Edwards, M.; Elser, J. J., Sustainability Challenges of

González, M. E.; Cea, M.; Medina, J.; González, A.; Diez, M. C.; Cartes, P.; Monreal, C.;

Wang, J.; Liu, S.; Qin, Y.; Chen, X.; Xing, R. e.; Yu, H.; Li, K.; Li, P., Preparation and

Liu, R.; Lal, R., Synthetic apatite nanoparticles as a phosphorus fertilizer for soybean

Qiao, D.; Liu, H.; Yu, L.; Bao, X.; Simon, G. P.; Petinakis, E.; Chen, L., Preparation and

Azeem, B.; KuShaari, K.; Man, Z. B.; Basit, A.; Thanh, T. H., Review on materials &



424

(9)

425

slow-release urea fertiliser: Physical and chemical analysis of its structure and study of its release

426

mechanism. Biosyst. Eng. 2013, 115 (3), 274-282.

427

(10)

428

for increasing the crop use efficiency of fertilizer-micronutrients. Biol. Fert. Soils 2016, 52 (3),

429

423-437.

430

(11)

431

fertilizer composition based on urea-modified hydroxyapatite nanoparticles encapsulated wood

432

Curr. Sci. India 2011, 101 (1), 6.

433

(12)

434

Priyadarshana, W. M. G. I.; Siriwardhana, A.; Madhushanka, B. A. D.; Rathnayake, U. A.;

435

Karunaratne, V., Two new plant nutrient nanocomposites based on urea coated hydroxyapatite:

436

Efficacy and plant uptake. Indian J. Agr. Sci. 2016, 86 (4).

437

(13)

438

Amaratunga, G. A. J.; Karunaratne, V. Composition and Method for Sustained Release of

439

Agricultural Macronutrients. US Patent 8696784, April 15, 2014.

440

(14)

441

A.; Karunaratne, V.; Amaratunga, G. A. J., Urea–hydroxyapatite-montmorillonite nanohybrid

442

composites as slow release nitrogen compositions. Appl. Clay. Sci. 2017, 150, 303-308.

443

(15)

444

Madushanka Berugoda Arachchige, D.; Kumarasinghe, A. R.; Dahanayake, D.; Karunaratne, V.;

445

Amaratunga, G. A., Urea-Hydroxyapatite Nanohybrids for Slow Release of Nitrogen. ACS Nano

446

2017, 11 (2), 1214–1221.

Xiaoyu, N.; Yuejin, W.; Zhengyan, W.; Lin, W.; Guannan, Q.; Lixiang, Y., A novel

Monreal, C.; DeRosa, M.; Mallubhotla, S.; Bindraban, P.; Dimkpa, C., Nanotechnologies

Kottegoda, N.; Munaweera, I.; Madusanka, N.; Karunaratne, V., A green slow-release

Gunaratne, G. P.; Kottegoda, N.; Madusanka, N.; Munaweera, I.; Sandaruwan, C.;

Kottegoda, N.; Priyadharshana, G.; Sandaruwan, C.; Dahanayake, D.; Gunasekara, S.;

Madusanka, N.; Sandaruwan, C.; Kottegoda, N.; Sirisena, D.; Munaweera, I.; De Alwis,

Kottegoda, N.; Sandaruwan, C.; Priyadarshana, G.; Siriwardhana, A.; Rathnayake, U. A.;


Page 28 of 39

Page 29 of 39


447

(16)

448

Madushanka, D. A. D.; Rathnayake, U. A.; Gunasekara, S.; Dahanayake, D.; DeAlwis, A.;

449

Kumarasinghe, A., Compositions and methods for sustained release of agricultural

450

macronutrients. US Patent Application US20140165683, June 19, 2014.

451

(17)

452

Sustainable Agriculture: Current State and Future Perspectives. J. Agr. Food Chem. 2017.

453

(18)

454

agronomic productions. Sci. Total Environ. 2015, 514, 131-139.

455

(19)

456

Surfactant-Modified Zeolite as a Slow Release Fertilizer for Phosphorus. J. Agr. Food Chem.

457

2006, 54 (13), 4773-4779.

458

(20)

459

phosphorus trilemma. Nat. Geosci. 2013, 6 (11), 897.

460

(21)

461

W.; Rabaey, K.; Meesschaert, B., Global phosphorus scarcity and full-scale P-recovery

462

techniques: a review. Crit. Rev. Env. Sci. Tec. 2015, 45 (4), 336-384.

463

(22)

464

478 (7367), 29-31.

465

(23)

466

Release Characteristics of Coated Fertilizers by Superfine Phosphate Rock Powder and its

467

Effects on Physiological Traits of Chinese Cabbage. J. Plant. Nutr. 2015, 38 (8), 1254-1274.

468

(24)

469

as phosphorus fertilizer in andisols and oxisols. Soil Sci. Soc. Am. J. 2015, 79 (2), 551-558.

Kottegoda, N.; Siriwardhana, D. A. S.; Priyadarshana, W. M. G. I.; Sandaruwan, C.;

Raliya, R.; Saharan, V.; Dimkpa, C.; Biswas, P., Nanofertilizer for Precision and

Liu, R.; Lal, R., Potentials of engineered nanoparticles as fertilizers for increasing

Bansiwal, A. K.; Rayalu, S. S.; Labhasetwar, N. K.; Juwarkar, A. A.; Devotta, S.,

Obersteiner, M.; Peñuelas, J.; Ciais, P.; Van Der Velde, M.; Janssens, I. A., The

Desmidt, E.; Ghyselbrecht, K.; Zhang, Y.; Pinoy, L.; Van der Bruggen, B.; Verstraete,

Elser, J.; Bennett, E., Phosphorus cycle: a broken biogeochemical cycle. Nature 2011,

Hou, J.; Dong, Y.-J.; Liu, C.-S.; Gai, G.-S.; Hu, G.-Y.; Fan, Z.-Y.; Xu, L.-L., Nutrient

Montalvo, D.; McLaughlin, M. J.; Degryse, F., Efficacy of hydroxyapatite nanoparticles



470

(25)

471

nanoparticles incorporated into biodegradable, soluble host matrixes. RSC Advances 2015, 5

472

(126), 104179-104186.

473

(26)

474

content. Sri Lanka Standards Institution: Sri Lanka, 1985; p 9.

475

(27)

476

Advances in Pharmaceutics 2014, 2014.

477

(28)

478

Water and Wastewater. American Water Works Association: 1999; pp 817-820.

479

(29)

480

controlled drug delivery systems. Acta Pol. Pharm. 2010, 67 (3), 217-23.

481

(30)

Alley, M. M., Nitrogen and phosphorus fertilization of corn. 1997.

482

(31)

Jones Jr, J. B., Hydroponics: a practical guide for the soilless grower. CRC press: 2016.

483

(32)

Trejo-Téllez, L. I.; Gómez-Merino, F. C., Nutrient solutions for hydroponic systems. In

484

Hydroponics–a standard methodology for plant biological researches, 2012; p 23.

485

(33)

486

analytical chemistry, 2000.

487

(34)

488

suspension. Journal of Nanoparticle Research 2009, 11 (5), 1235-1240.

489

(35)

490

literature. World Journal of Methodology 2012, 2 (1), 1-17.

Giroto, A. S.; Fidelis, S. C.; Ribeiro, C., Controlled release from hydroxyapatite

Institution, S. L. S., Methods of test for fertilizers Part 5 - Determination of phosphorous

D’Souza, S., A review of in vitro drug release test methods for nano-sized dosage forms.

Water Environment Federation, A. P. H. A., Standard Methods for the Examination of

Dash, S.; Murthy, P. N.; Nath, L.; Chowdhury, P., Kinetic modeling on drug release from

Coates, J., Interpretation of infrared spectra, a practical approach. In Encyclopedia of

Han, Y.; Wang, X.; Li, S., A simple route to prepare stable hydroxyapatite nanoparticles

Dorozhkin, S. V., Dissolution mechanism of calcium apatites in acids: A review of

491 492


Page 30 of 39

Page 31 of 39

493


TOC Graphic

494



SEM images of (a) pure HANP (b) ex-situ modified CMHANP nanohybrids (c) in-situ modified CMHANP nanohybrids 752x564mm (96 x 96 DPI)


Page 32 of 39

Page 33 of 39


FTIR spectra for the (i) PO43- stretching, (ii) C=O stretching and OH bending, and (iii) OH stretching regions of (a) Pure HANP, (b) In50mM CMHANP, (c) In150mM CMHANP, (d) In250mM CMHANP, and (e) Pure CA 1695x1442mm (96 x 96 DPI)



Comparison of PXRD pattern of (a) Pure HANP, and (i) in-situ modified nanocomposites of (b) In50mM CMHANP, (c) In150mM CMHANP, and (d) In250mM CMHANP and (ii) ex-situ modified nanocomposites of (b) Ex50mM CMHANP, (c) Ex150mM CMHANP, and (d) Ex250mM CMHANP 1699x717mm (96 x 96 DPI)


Page 34 of 39

Page 35 of 39


Overall comparison of release profiles, (a) Ex250mM CMHANP, (b) In250mM CMHANP, (c) Ex150mM CMHANP, (d) In150mM CMHANP, (e) Ex50mM CMHANP (f) In50mM CMHANP, (g) Pure HANP, and (h) ERP 271x229mm (300 x 300 DPI)



Comparison of maximum heights of the plants at 9th week (a) No P, (b) Pure HANP, (c) TSP, (d) ERP, (e) In50mM CMHANP, (f) In150mM CMHANP, (g) In250mM CMHANP, (h) Ex50mM CMHANP, (i) Ex150mM CMHANP, and (j) Ex250mM CMHANP 265x228mm (300 x 300 DPI)


Page 36 of 39

Page 37 of 39


Average dry weight of the cobs from plants under different treatments 260x229mm (300 x 300 DPI)



The root system of plants under different treatments 1449x345mm (96 x 96 DPI)


Page 38 of 39

Page 39 of 39


2376x1040mm (96 x 96 DPI)


Effect of Citric Acid Surface Modification on Solubility of

Recommend Documents