Aragonite precipitated calcium carbonate from magnesium rich carbonate rock for polyethersulfone hollow fibre membrane application

Accepted Manuscript Aragonite precipitated calcium carbonate from magnesium rich carbonate rock for polyethersulfone hollow fibre membrane application

Onimisi A. Jimoh, Patrick U. Okoye, Tunmise A. Otitoju, Kamar Shah Ariffin PII:

S0959-6526(18)31538-5

DOI:

10.1016/j.jclepro.2018.05.192

Reference:

JCLP 13049

To appear in:

Journal of Cleaner Production

Received Date:

21 February 2018

Accepted Date:

23 May 2018

Please cite this article as: Onimisi A. Jimoh, Patrick U. Okoye, Tunmise A. Otitoju, Kamar Shah Ariffin, Aragonite precipitated calcium carbonate from magnesium rich carbonate rock for polyethersulfone hollow fibre membrane application, Journal of Cleaner Production (2018), doi: 10.1016/j.jclepro.2018.05.192

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ACCEPTED MANUSCRIPT 1

Aragonite precipitated calcium carbonate from magnesium rich carbonate rock for

2

polyethersulfone hollow fibre membrane application

3 4

1*Onimisi

A. Jimoh, 2Patrick U. Okoye, 3Tunmise A. Otitoju, and 1Kamar Shah Ariffin

5 1School

6 7 8

Universiti Sains Malaysia Engineering Campus, 14300 Nibong Tebal, Pulau Pinang 2School

11

of Material Science and Engineering, Shenyang University of Technology, 110870 Shenyang, China

9 10

of Materials and Mineral Resources Engineering,

3School

of Chemical Engineering, Universiti Sains Malaysia Engineering Campus, 14300 Nibong Tebal, Pulau Pinang

12 13 14

*Corresponding Authors: [email protected] , [email protected]

15 16

Tel.: +60164529526, +60175858060

17 18 19 20 21 22

1

ACCEPTED MANUSCRIPT 23

Abstract

24

A reaction-assisted synthesis using a naturally occurring dolomite and aloe vera (Aloe

25

barbadensis Miller) extract as a morphological modifier was employed for aragonite-

26

precipitated calcium carbonate (A-PCC) synthesis. The as-synthesized precipitated calcium

27

carbonate was utilized to produce a polyethersulfone (PES) hollow fiber membrane for

28

application of oil-in-water separation. The D-glucose extraction of Ca before precipitation

29

reaction with CO2 dominated the influence of tainted Mg on the as-synthesized PCC purity.

30

The reaction was carried out via the carbonation route and 1 L/min CO2 flowrate at ambient

31

conditions. The aloe vera extract (5 v/v%) and unleached in situ Mg influenced the phase

32

transformation from calcite and vaterite polymorphs to flower-like structure with radiating

33

ends. The A-PCC synthesized using aloe vera did not require external heating, thereby

34

representing an attractive energy-conserving process for this type of precipitated calcium

35

carbonate. The prepared membranes were characterized using porosity, field-emission

36

scanning electron microscope, hydrophilicity, mechanical properties, and pore size. Their

37

performances for oil-in-water filtration were evaluated. At an optimal amount of 3 wt.%

38

aragonite PCC in the hollow fiber membrane, the permeate flux and oil rejection reached 102

39

kg/m2h and >99%, respectively. Furthermore, the introduction of A-PCCs in the PES matrix

40

improved the antifouling properties of the composite membranes. Therefore, PES/A-PCC

41

composite membranes are desirable in treating wastewater and wastewater containing oil

42 43

Keywords: aloe vera; aragonite polymorph; dolomitic marble; membrane; precipitated calcium

44

carbonate.

45 46 2

ACCEPTED MANUSCRIPT LIST OF ABBREVIATIONS A-PCC

Aragonite-precipitated CaCO3

CTAB

Cetyltrimethylammonium bromide

EDX

Energy dispersive X-ray

FESEM

Field emission scanning electron microscope

GTE

Green tea extract

HF

Hollow fiber

KBr

Potassium bromide

LOI

Loss on ignition

MOL

Milk of lime

MPS

Mean pore size

PAA

Polyacrylic acid

PCC

Precipitated CaCO3

PES

Polyethersulfone

PP

Polypropylene

PSA

Particle size analysis

P-SA

Poly-2-acrylamido-2-methyl-propane sulfonic acid

PSD

Particle size distribution

PVA

Polyvinyl alcohol

PVDF

Polyvinylidene fluoride

SLS

Sodium lignosulfonate

WCA

Water contact angle

XRD

X-ray diffraction

XRF

X-ray fluorescence

47 3

ACCEPTED MANUSCRIPT LIST OF SYMBOLS

%

Percentage

°C

Degree Celsius

CO2

Carbon dioxide

CaCO3

Calcium carbonate

MgCO3

Magnesium carbonate

Ca(OH)2

Calcium hydroxide

Mg(OH)2

Magnesium hydroxide

H2O

Water

D10

10% volume of particles with size value lower than or equal to D10

D50

50% volume of particles with size value lower than or equal to D50

D90

90% volume of particles with size value lower than or equal to D90

L

Liter

Wt%

Weight percentage

mL

Milliliters

M

Mole

Aq

Aqua solution

S

Solid

G

Gas

48 49

4

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1. Introduction

51

Carbonate rocks rich in calcite are a favorable choice for industrial-scale precipitated

52

CaCO3 (PCC) synthesis. PCC has multipurpose industrial applications, and its low production

53

cost has rendered it as an attractive material in paper, paint, cosmetics, and pharmaceutical

54

industries (Jimoh et al., 2017b). The synthesis of PCC via the carbonation route presents an

55

even more viable and environmentally benign pathway because CO2 is employed in the

56

precipitation reaction. Three PCC crystal morphologies are identified, namely, calcite (most

57

stable), aragonite (metastable), and vaterite (less stable) (Jimoh et al., 2017d). As the demand

58

for PCC increases, the use of calcitic marbles will increase tremendously. Combined with other

59

uses of calcitic marbles, a drastic depletion of this mineral is realized. Hence, continued

60

research on PCC synthesis are focused on evolving crystal morphology or composite

61

morphology and the use of sustainable PCC raw materials.

62

Similar to calcitic marbles (CaCO3), dolomitic marbles contain considerable amount of

63

Ca required for industrial-scale production of PCC. However, dolomitic marbles are tainted

64

with Mg (primarily CaMg(CO3)2 and minor SiO2 content), which reduces the opacity and

65

purity of PCC (Jimoh et al., 2017a). Moreover, Mg can influence the strength or morphology

66

of the resultant PCC. Hence, green methods to separate Mg from Ca is required to boost the

67

viability of PCC to ensure that dolomite can be used to produce both controlled shaped PCC

68

and Mg-based products simultaneously (Somarathna et al., 2016). The contribution and

69

interaction of Ca and sugar in the body to provide energy and regulate blood sugar level is an

70

established phenomenon in the field of medicine. Moreover, a previous study reported the

71

extraction or leaching of Ca in dolomitic rocks by using sucrose (Mantilaka et al., 2014, 2012).

72

The sucrose solution efficiently leaches Ca from dolomite, resulting in 79% PCC yield. They

73

observed that sucrose inhibits the formation of aragonite and vaterite morphologies of PCC.

5

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The evolution of these crystal phases for task-specific PCC often requires additives to

75

control morphology and particle size. Monodispersed cubic and rectangular PCC were

76

produced using small amounts of polyvinyl alcohol, polyacrylic acid (PAA), and

77

cetyltrimethylammonium bromide (CTAB) at 80 °C to influence the morphology and particle

78

size (Yu et al., 2005). El-Sheikh et al. (2013) produced calcite PCC and morphologies that

79

varied from rhombohedral (15–35 nm) to scalenohedral (length of 2 mm and diameter of 400

80

nm) by using CTAB as an additive. Moreover, Cheng et al. (2014) utilized PAA at 60 °C to 80

81

°C and CaCl2 as lime precursor to synthesize monodispersed cubic PCC particles. Hu et al.

82

(2009) synthesized needle-like aragonite whiskers with length of ca. 20 mm and aspect ratio of

83

8–12 via a reversible reaction with MgCl2 and uncalcined limestone. Most of these chemical

84

additives contain active functional groups engrossed on the surface of the PCC with possible

85

toxic effects on the end user. For instance, polyethylene glycol (PEG) has been reported to

86

contain potential toxic impurities, such as ethylene oxide and 1,4-dioxane (Andersen, 1999).

87

The use of extracts from plants and protein-containing biopolymers to control crystal

88

morphology is remarkable because they act as additives in morphology modification (Kitamura

89

et al., 2002; Onimisi et al., 2016). Precipitation tests revealed that the macromolecules of

90

proteins supports the formation of CaCO3 biominerals by providing the exoskeleton backbone

91

and regulating the dynamics of nucleation, growth, and crystal assembly (Polowczyk et al.,

92

2016). For instance, chitosan, which is a cationic biopolymer with amine groups (NH2), forms

93

a polyelectrolyte complex in carboxylic acid. Then, Ca cations attracted to the negative charge

94

of the carbonate ions during precipitation reaction result in bond cleavages in the biopolymer

95

structure (Declet et al., 2016). Polyelectrolyte provides cohesion, adhesion, and the framework

96

between the organic–inorganic layers. Mattila et al. (2012) reported that green tea extract and

97

sodium lignosulfonate influence the synthesized PCC polymorphs. In our previous work on

98

PCC synthesis with calcitic marble by using aloe vera extract as the green morphological 6

ACCEPTED MANUSCRIPT 99

modifier, an aloe vera extract concentration of 0.5 v/v% induces phase transition, thereby

100

resulting in composite (calcite and aragonite) PCC polymorph. Aloe vera extract is a

101

mucilaginous

102

immunomodulatory properties (Huang et al., 2007). Moreover, the shrinking properties of aloe

103

vera can influence the PCC particle size and restrict the size to nanometric range. In this study,

104

the synthesis of morphology-controlled PCC by using natural dolomitic rock via the

105

carbonation system and by using aloe vera extract as the green templating agent is reported.

106

New evolving shapes of PCC polymorphism are investigated. The influence of aloe vera extract

107

concentration on the resultant shape and particle size is also investigated.

gel

with

antiprotozoal,

anti-inflammatory,

UV-protective,

and

108

In the field of membrane technology, membrane is the key to pressure-driven operations

109

because it directly affects practical application and process efficiency (Otitoju et al., 2016).

110

Polyethersulfone

111

polysulfone, and polypropylene are often used to prepare polymeric membranes due to their

112

efficient performance. Among the aforementioned polymers, PES is a recognized polymeric

113

material that is widely employed in the fabrication of membranes for various applications.

114

Given its high Tg of 225 °C, as well as its amorphous and transparent properties, PES possesses

115

high mechanical, hydrolytic stability, thermal, and chemical resistances and outstanding

116

oxidative properties (Rahimpour et al., 2012), making them ideal for the preparation of

117

asymmetric membranes with different surfaces and pore sizes (Rahimpour et al., 2012; Shi et

118

al., 2007; Wang et al., 2009). However, in practical application such as H2O and wastewater

119

treatments, this performance is often compromised due to pore clogging as a result of solute

120

adsorption on membrane surface, thereby leading to poor separation efficiencies. To reduce the

121

hydrophobic nature of polymeric membranes and considerably improve application

122

performance, numerous researches have introduced minerals such as SiO2, carbon nanotubes,

123

TiO2, and Al2O3 into the polymeric matrix. For instance, Ong et al. (2015) added TiO2 into the

(PES),

polyvinylidene

fluoride

7

(PVDF),

polytetrafluoroethylene,

ACCEPTED MANUSCRIPT 124

PVDF matrix to prepare a PVDF/TiO2 HF membrane, which leads to an optimized permeate

125

flux (PF) and oil rejection of 70.48 L/m2h and 99.7%. A study of Zhang et al. (2013) showed

126

an improvement of oil rejection for the SiO2/PVDF membrane from 86.0% (neat membrane)

127

to 91.2%. Li et al. (2006) introduced Al2O3 to fabricate tubular membrane for oil-in-water

128

separation. Their results showed improved PF, whereas the oil rejection is lower than that of

129

unmodified membrane. On the basis of previous achievements, we first synthesized aragonite-

130

precipitated CaCO3 (A-PCC) from dolomite and then doped into the PES matrix to produce a

131

novel composite hollow fiber (HF) membranes. HF membranes were characterized, and their

132

performances during oil-in-water filtration were evaluated. We assumed that this study will

133

accelerate the application of dolomite and aloe vera as PCC precursors for aragonite phase

134

synthesis and application as a filler in membrane for wastewater treatment.

135

2. Material and Methods

136

2.1 Materials

137

Dolomite samples with MgO and CaO contents of 21.01% and 32.94%, respectively,

138

were sourced locally from non-active mine at the Emiworo area located at the central part of

139

Nigeria. Fresh leaves of aloe vera were collected from the University Sains Malaysia

140

engineering campus. Glucose, (D-(+)-glucose anhydrous) were purchased from Sigma-

141

Aldrich. For membrane preparation, PES (Ultrason E6020P, with molecular weight of 58,000

142

g/mol) was purchased from BASF and dried at 70 °C in the oven for 12 h prior to use. PEG

143

(MWCO, 35 kDa) was purchased from Sigma-Aldrich. 1-methyl-2-pyrrolidone (NMP) was

144

provided by Merck, Malaysia. N2 gas and liquid N2 were supplied by Wellgas, Malaysia. Crude

145

oil was obtained from Petronas, Malaysia. All chemicals were used without any purification.

146 147

2.2 Methods 8

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2.2.1

Aloe vera extract preparation

149

The collected leaves of aloe vera were washed with distilled H2O to remove sand and

150

other impurities. Then, the washed leaves were cut into small pieces, and approximately 30 g

151

of leaves were boiled in 100 mL of distilled H2O, followed by filtration by using Whatman

152

filter paper. Then, the resulting filtrate was stored at 5 °C until further experiments.

153 154

2.2.2

Preparation of calcium glucosate suspension

155

The dolomitic marble samples were crushed and pulverized using a ball mill into

156

powder with a particle size of 200 µm. Then, the samples were calcined in a muffle furnace at

157

a peak temperature of 1000 °C for 180 min. Approximately 40 g calcined dolomite was

158

dissolved in 400 mL of 0.5 M glucose solution and stirred with a magnetic stirrer for 2 h.

159

Magnetic bar also helped in removing iron impurities. The solution was filtered using a

160

Whatman filter paper under suction. The filtrate was obtained as soluble calcium glucosate.

161 162

2.2.3

Synthesis of PCC particles by using aloe vera extract

163

A total of 0.5 M of 400 mL of soluble calcium glucosate was transferred into a reactor

164

and aloe vera extract (typically 0.5–5 v/v%; i.e., volume of aloe vera extract solution relative

165

to the volume of the produced Ca glucose stock solution) was added dropwise into the solution.

166

The mixture was stirred at 500 rpm for 10 min. Afterward, CO2 gas was bubbled into the stirred

167

mixture at a rate of 1 L/min. The reaction was stopped when the pH was approximately 6.5.

168

Afterward, the product was filtered and then oven dried at 50 °C for 12 h.

169 170

2.2.4

Characterization of PCC 9

ACCEPTED MANUSCRIPT 171

Field-emission scanning electron microscopy (FESEM, Carl Zeiss SupraTM 35 VP) was

172

used to observe the morphology of the PCC products at 5 kV accelerating voltage. The Mg

173

contents of the synthesized PCC before and after D-glucose separation of Ca were also

174

determined with FESEM (Zeiss SupraTM 35 VP). In each case, readings were taken in triplicate

175

to confirm the precision of the readings. Given that the readings were much closer to each other,

176

the mean of three readings was obtained.

177

The powder X-ray diffraction (XRD) studies were carried out to reveal the crystalline

178

phases of the as-synthesized PCC samples. The spectrum was recorded with a Bruker D8

179

advance diffractometer by using Cu–Kα radiation and wavelength (λ) of 0.154 nm. The spectra

180

of the samples were analyzed using X’pert Highscore Plus software (PANanalytical version

181

2.2e). Particle size distributions (PSDs) (Malvern MasterSizer, model 3000, Worcestershire,

182

UK) after the PCC powder was redispersed in H2O were determined by laser light diffraction.

183

The average particle size was expressed as the volume/weight mean. The PSD was expressed

184

in terms of the SPAN factor, which was calculated using Eq. (1) as follows:

185

SPAN =

186

where Dv 90, Dv 50, and Dv 10 represent the particle diameters at percentiles of 90, 50, and

187

10 of the distribution curve.

Dv 90 ‒ Dv 10 Dv 50

(1)

188 189

2.3 Membrane preparation by using various amounts of A-PCC

190

The HF membranes were prepared via dry/wet spinning process (Otitoju et al., 2017;

191

Otitoju et al., 2017). All membranes were prepared by blending 17.25 wt% of PES, 1.75 wt%

192

of PEG as pore former, and varying concentrations of A-PCC (0, 1, 2, 3, 4, and 5 wt%) in NMP

193

at 80 °C under continuous stirring speed of 550 rpm for 14 h (Table 1). The homogenous 10

ACCEPTED MANUSCRIPT 194

solution was left in the dark overnight to achieve a bubble-free solution. This solution was later

195

poured in a dope tank for the spinning process. Table 2 shows the spinning conditions.

196

The produced PES HF membranes were placed in deionized H2O for 1.5 days, and H2O

197

was concurrently replaced every 5 h to enable the residual solvent to be completely removed.

198

Then, the membranes were transferred to a 50%–50% glycerol aqueous solution and then dried

199

in air for 5 days.

200 201

(Insert Table 1)

202

(Insert Table 2)

203 204

2.4 Characterization of membrane doped A-PCC

205

2.4.1

The viscosity levels of dope solutions were analyzed using the Brookfield Digital

206 207

Rheological property of dope solution

Rheometer (Model DV-III, USA) at a shear rate of 10 s−1 at 25 °C.

208 209

2.4.2

FESEM

210

The morphology of the prepared HF membranes were scanned with FESEM (TM 35

211

VP Zeiss and HITACHI Tabletop Microscope instrument [TM-3000, Japan]). For cross-

212

sectional analysis, membrane fracturing was conducted by immersing the membrane piece in

213

liquid N2 to acquire a detailed cross-sectioning without distortion. To scan the membrane’s

214

surface, we aligned the piece parallel on a stainless-steel stand as a membrane holder. Before

215

observation, membrane was sputter coated via a precision coating system (Quorum-SC7620)

11

ACCEPTED MANUSCRIPT 216

and was applied on all membrane samples to prevent any form of charge accumulation. Lastly,

217

the sample morphologies were observed and operated with an accelerating voltage of 15 kV.

218 219

2.4.3

Porosity and pore size distribution The membrane porosity was calculated using Eq. (2), as follows:

220

𝑤‒𝑑 𝜌𝑤

x 100

(2)

221

þ=

222

where þ is the porosity of the membrane (%), 𝑑 is weight of the dry membrane (g), 𝜌𝑝 is density

223

of the PES polymer at 1360 kg/m3, 𝑤 is weight of wet membrane (g), and 𝜌𝑤 is density of H2O

224

at 998 kg/m3. To prepare wet membranes, seven HFs with a length of 15 cm were kept in

225

isopropanol for 72 h and then in deionized H2O for 72 h. Prior to weighing of membranes, the

226

left-over H2O on each membrane surface was removed via airflow. To determine the weight of

227

the dried membrane, the wet membranes were dried in the oven for 10 h at 50 °C. To avoid

228

experimental error, the average membrane porosity was obtained from the seven fibers.

𝑤‒𝑑 𝑑 + 𝜌𝑝 𝜌𝑤

229

The mean pore sizes (MPSs) and the PSDs of the HF membranes were determined using

230

PEG transport approach. PEG ratio was observed with TOC analyzer (TOC-VCPH analyzer,

231

Shimadzu). The Stokes radii (Sr) of PEG can be determined using Eq. (3), as follows:

232

𝑆𝑟 = 16.73 × 10

233

where MW is the molecular weight of PEG (g/mol), and Sr is the stokes radius of PEG. Then,

234

the rejection of PEG can be expressed as log-normal probability function according to the size

235

of PEG (Michaels, 1980), as illustrated in Eq. (4) as follows:

‒ 12

0.557

(3)

× 𝑀𝑊

12

ACCEPTED MANUSCRIPT

236

𝑅 = erf (𝑦) =

1

∫𝑦 𝑒 2𝜋 ‒ ∞

2 ‒𝑢 2

𝑑𝑢,

where 𝑦 =

𝐼𝑛𝑆𝑑 ‒ In𝜇𝑑 In𝜎𝑑

(4)

237 238

where R, 𝜇𝑑, 𝑆𝑑, and 𝜎𝑑 are rejection of the PEG (%), geometric mean diameter of PEG (at R

239

= 50%), diameter of PEG, geometric SD of approximately 𝜇𝑑 (the ratios of 𝑆𝑑 at rejection were

240

84.13% and 50%), respectively.

241

The rejection of the PEG at different MWs, such as 35000, 20000, 10000, 4000, and

242

1500 Da, were plotted against the PEG Stokes– Einstein diameters on a scale of lognormal

243

probability. Afterward, the results were fitted linearly by using the Eq. (5) below:

244

𝐹(𝑅) = 𝑦 + 𝑚 (In 𝑆𝑑)

245

where y is the intercept, and m is the slope. Ignoring the effects of hydrodynamic and steric

246

interactions between the pore and PEG, the effective MPS (𝜇𝑝) and the geometric SD (𝜎𝑝) can

247

be assumed the same value as (𝜇𝑑) and (𝜎𝑑), respectively (Michaels, 1980; Yang et al., 2007).

248

With respect to 𝜇𝑝 and 𝜎𝑝, the PSD (𝑑𝑝) can be expressed by the probability density function

249

given in Eq. (6) as follows:

250

𝑑𝑅 (𝑑𝑝) 𝑑𝑑𝑝

[

𝑒𝑥𝑝 ‒

𝑑𝑝In𝜎𝑝 2𝜋

(In𝑑𝑝 ‒ In μp) 2(In𝜎𝑝)

2

]

2

(6)

Using the values of MPS and geometric standard deviations for prepared membranes,

251 252

=

1

(5)

the probability density function and the cumulative PSD curves can be obtained.

253 254

2.4.4

Mechanical properties

13

ACCEPTED MANUSCRIPT 255

To investigate the effects of adding different A-PCC ratios on the mechanical property

256

of the PES HF membranes, the elongation at break (%) and tensile strength (MPa) of HF

257

membranes were determined with the Instron 3366 (USA) with a load cell of 10 kN at room

258

temperature. Prior to measurement, individual membrane sample were cut into 10 cm in length

259

(at a temperature of 25 °C and relative humidity of 67%) and attached vertically to 2 clamps

260

and stretched in tension with a strain rate of 5 mm/min. Their responses were documented until

261

failure.

262

2.4.5

Water contact angle (WCA) measurement

263

The WCA was measured using Rame-Hart 250-F1 goniometer (USA) at ambient

264

temperature to evaluate the hydrophilicity of the prepared membrane. Membrane samples were

265

affixed parallel on a microscope slide with a double-sided adhesive tape. Afterward, 0.25 µL

266

of deionized H2O was dropped on samples with a microsyringe, and the micrograph was

267

captured with a microscopic camera attached to the instrument. The average WCA values of

268

the 5 readings taking at different positions on each membrane sample at ambient temperature

269

were calculated to reduce error.

270 271

2.4.6

Membrane performance for wastewater treatment

272

All membranes were soaked in ethyl alcohol for 3 h and then in deionized H2O for at

273

least 42 h before ultrafiltration experimental run. Membrane modules containing eight fibers

274

with effective filtration length and active filtration area of 46.8 cm and of 0.0083 m2,

275

respectively, were constructed. Prior to testing, membranes were compressed at 2 bar by using

276

deionized (DI) H2O. All other experiments were performed under ambient temperature,

277

transmembrane pressure, flow rate, and filtration time of 22 °C, 1.5 bar, 400 mL/min, and 3 h,

278

respectively. Water flux (WF) was calculated using Eq. (7) as follows: 14

ACCEPTED MANUSCRIPT 279

𝑊𝑝 =

V A ∆t

(7)

280 281

where 𝑊𝑝, V, ∆t, and A are the pure WF in (kg/m2h), permeate volume (kg), filtration time (h),

282

and filtration area (m2), respectively.

283

Removal of oil from waste-water is regarded as a main challenge in treatment practices

284

(An et al., 2017). Oil-in-water emulsion was prepared by mixing 500 mg crude oil in 1 L of

285

deionized (DI) H2O. The detailed synthesis of oil-in-water emulsion, preparation of filtration

286

module, and experimental procedure can be found in previous work by (Elanchezhiyan and

287

Meenakshi, 2016; Otitoju et al., 2017). The size distribution of oil droplets ranges from 0.2 to

288

3.5 µm with an average particle size of 1.54 µm (Fig. 1). All membranes were tested under

289

cross-flow mode at the same transmembrane pressure and feed flow rate of 1.5 bar and 400

290

mL/min, respectively. The PF (𝑃𝐹) was calculated using the same equation used for the WF

291

(Eq. 7), while oil rejection can be determined using Eq. (8) as follows:

292

293

(

𝑅𝑒𝑗𝑒𝑐𝑡𝑖𝑜𝑛 (%) = 1 ‒

𝑂𝑝𝑒𝑟𝑚 𝑂𝑓𝑑

)

X 100

(8)

where Ofd (mg/L) and Operm (mg/L) are the oil contents in feed and permeate, respectively.

294

To recover membrane, membranes were cleaned with DI H2O for 30 min at 0.8 L/min.

295

Flux recovery ratio (FRR) was determined using Eq. (9). The higher the FRR, the better the

296

recovery will be.

297

𝐹𝑅𝑅 =

( ) 𝑊𝑝2 𝑊𝑝

X 100

(9)

298 299

where 𝑊𝑝2 is pure WF after cleaning (kg/m2h), and 𝑊𝑝 is the initial pure WF (kg/m2h).

300

Meanwhile, fouling resistance of all membranes can be estimated using Eqns. (10) – (13), as

301

follows:

15

ACCEPTED MANUSCRIPT

302

𝑅𝑡 =

303

𝑅𝑟 =

304 305

( ( (

𝑅𝑖𝑟 =

𝑊𝑝 ‒ 𝑃𝐹 𝑊𝑝

)

𝑊𝑝2 ‒ 𝑃𝐹 𝑊𝑝

X 100

(10)

)

(11)

X 100

𝑊𝑝 ‒ 𝑊𝑝2 𝑊𝑝

)

X 100

(12) (13)

𝑅𝑡 = 𝑅𝑟 + 𝑅𝑖𝑟

306 307

where Rt, Rir, and Rr are the total resistance, irreversible resistance, and reversible resistance,

308

respectively.

309 310

(Insert Figure 1)

311 312

3. Results and Discussion

313

3.1 Process for Ca extraction and industrial features of the developed technique

314

Fig. 2 present the overall PCC synthesis process designed to meet the industrial

315

requirement. At 1000 °C, the dolomite (mixture of CaO and MgO) in the marble converts

316

completely into calcined dolomite with minor impurities, such as silicate and iron that cannot

317

decompose at this temperature. During the mixing of calcined dolomite with the glucose

318

solution, CaO reacts with glucose to form calcium glucosate. MgO together with silicates and

319

other impurities remained as precipitates in the solution, which can be removed using

320

centrifuge and filtration. Moreover, the concentration of D-glucose or calcium glucosate did

321

not influence the morphologies and phase of final PCC products.

322

Recycling the glucose and/or unreacted CO2 back to the same process increases

323

efficiency and reduces the production cost. Similarly, MgO separated from the calcined

324

dolomite during glucose extraction of Ca can be utilized to produce Mg-based nanomaterials, 16

ACCEPTED MANUSCRIPT 325

desiccant, catalyst, toxic waste absorbent, bactericide, refractory materials, and electrical

326

insulators (Das et al., 2007). Moreover, aloe vera is highly soluble in glucose, which facilitates

327

mass transport and sufficient miscibility to effectively tailor the shape or morphology of as-

328

synthesized PCC.

329 330

(Insert Figure 2)

331 332

3.2 EDAX analysis and PCC yield

333

The PCC purity obtained under the best conditions of 5 v/v% of initial concentration of

334

aloe vera and yields of samples 1 to 4 at different aloe vera concentrations are presented in Fig.

335

3 and Table 3, respectively. As shown in Table 3, PCC yield increases marginally as the aloe

336

vera concentration increases. This result can be attributed to the higher CO2 solubility in the

337

aloe vera solution (consisting of mainly amino acids and proteins) than that in ordinary H2O

338

(Díaz-Reinoso et al., 2006). The higher CO2 content is favorable to obtain more PCC yields at

339

higher aloe vera concentrations. Hence, the high reactivity of the aloe vera extract with the

340

calcium glucosate solution and CO2 at room temperature achieves 82% of PCC yield under

341

reaction conditions of 5 v/v% of initial concentration of aloe vera, pH level of 6.5, and glucose

342

solution concentration of 0.5 M. Comparatively, Somarathna et al. (2016) reported a PCC yield

343

of 79% by using sucrose as the Ca extractor.

344 345

(Insert Figure 3)

346

(Insert Table 3)

347 348

3.3 Analysis of the crystalline structures of the synthesized PCC samples

17

ACCEPTED MANUSCRIPT 349

The XRD spectrum of raw powdered dolomite carbonate rock sample obtained from

350

the Emiworo area is shown in Fig. 4a. The high intensity peak at 30.97° indicates the presence

351

of dolomite as a prominent constituent mineral. The peak at 24.1° represents the presence of

352

low amount of calcite in the sample. The XRD pattern of each sample prepared using different

353

aloe vera extract concentration at room temperature and final pH level of 6.5 was analyzed to

354

determine the presence of calcite, aragonite, and vaterite crystalline phases (Fig. 4b–d). Fig. 4b

355

shows that the three PCC phases, namely calcite (104), aragonite (021, 221), and vaterite (100),

356

are present without the addition of aloe vera. Meanwhile, Fig. 4c reveals only calcite and

357

aragonite phases at an aloe vera concentration of 0.5 v/v%. As the concentration of aloe vera

358

extract was increased to 5 v/v%, only the aragonite phase with sharp peak reflections of (021),

359

(221), and (102) was observed, as shown in Fig. 4d.

360

Acicular calcite and aragonite CaCO3 with vast application potentials have been

361

synthesized by Kajiyama et al. (2014). Aragonite phase PCC has been widely studied and

362

synthesized above room temperature in the range of 35 °C–70 °C (Ramakrishna et al., 2016;

363

Santos et al., 2012; Shafiu Kamba et al., 2013). Temperature is crucial to ensure the formation

364

of aragonite phase in the composite polymorph, which increases the net energy required for

365

this phase PCC. Hence, this phenomenon is unattractive from an industrial standpoint. In

366

addition, by using 5 v/v% of aloe vera extract, the aragonite phase PCC was synthesized.

367

(Insert Figure 4)

368 369 370

3.4 Formation mechanism of flower-like structure with radiating ends aragonite PCC over aloe vera extract

371

Aloe vera extract contains acid proteins and polysaccharides within the protoplast of

372

the parenchyma cell wall matrixes. Parenchymal cell walls have active hydroxyl functional

373

groups. Microscopy study of the aloe vera leaves cell revealed that the pulp consists of 18

ACCEPTED MANUSCRIPT 374

transparent large (1000 μm) mesophyll with a hexagonal or elongated hexagonal shape (Ni et

375

al., 2004). Previous reported studies have shown that acid proteins can significantly influence

376

the crystallization of CaCO3 (Friedman et al., 1962; Han et al., 2005). Bio-based additives can

377

poison the calcite crystallization in situ and induce the transformation transit to aragonite phase

378

(Greer et al., 2015). Declet et al. (2016) conducted studies on PCC synthesis by using chitin,

379

containing repeating chains of 𝛽-(1,4)N-acetyl glucosamine and substantial amount of H ions.

380

The chitin as an additive revealed that amino groups could induce phase transformation from

381

calcite polymorph to aragonite. Moreover, aloe vera extract containing polysaccharides and

382

acid proteins can influence the morphology of synthesized PCC, thereby resulting in composite

383

(calcite and aragonite) polymorph (Jimoh et al., 2017c). In addition, the detailed plausible

384

formation mechanism for this type of PCC with a polycrystalline dumbbell-like structure has

385

been adequately reported in our previous work. The crystal growth of the obtained flower-like

386

structure with radiating ends was propagated by unleached in-situ Mg, higher concentration of

387

aloe vera, and glucose that allows calcite and aragonite phase formation. Hu et al. (2009)

388

reported that needle-like aragonite can be achieved using Mg as a structure directing agent.

389

3.5 Particle size of the synthesized PCC samples

390

Particle size analysis presented in Fig. 5a shows that approximately 90% (Dv 90) of the

391

synthesized A-PCC particles were within the size of 3.34 μm. Meanwhile, 10% of the particles

392

(Dv 10) was 1.26 μm, and the average size (Dv 50) of the particles is 1.02 μm with a recorded

393

span value of 2.04. The PCC without aloe vera extract (Fig. 5b) had a higher particle size, as

394

shown in Table 4a and 4b. The results showed that 90% (Dv 90) of the particle had a size of

395

33.5 μm, 50% (Dv 50) of particles had a size of 16.30 μm, and 10% (Dv 10) of the particles

396

had a size of 6.53 μm with a span value of 1.65. Aloe vera has been employed as a reducing

397

agent to tailor the synthesis of Au and Ag nanoparticle sizes in previous studies (Chandran et

398

al., 2006; Muralikrishna et al., 2014). Therefore, the decrease in particle size is ascribed to the 19

ACCEPTED MANUSCRIPT 399

volume contraction/shrinking of the PCC particles by the resulting surface compounds of the

400

aloe vera extract.

401

In addition, the result of the SEM micrographs showed smaller particles size, which is

402

anticipated as by laser light diffraction. This result indicates that the measurement contained

403

agglomerates. Accordingly, various polymorphs and particle sizes of synthesized PCC have

404

been employed for specific applications (Jimoh et al., 2017c). Conducted studies indicated that

405

the PCC particles of approximately 15 μm in diameter are more effective in rheology

406

modification and strengthening of sealants and adhesives (Brockman et al., 2009). Meanwhile,

407

the PCC particle size in the range of 5–14 μm is used to control the flow properties to provide

408

body, thereby maintaining dispersion in flat and semigloss paints and to adjust the consistency

409

and minimize paint sag (Ciullo, 1996).

410 411

(Insert Figure 5)

412 413

3.6 SEM analysis of the PCC samples

414

Fig. 6 presents SEM images of PCC particles synthesized at different aloe vera extract

415

volume concentrations. Traditionally, PCC formed in H2O without additives are characterized

416

by rhombohedral-ordered structures composed of six facets, most of which are microscopic

417

epitome of the unit cells (Jimoh et al., 2016). PCC formed without aloe vera extract revealed

418

an agglomerated cluster with visible calcite phase (Fig. 6a). At extract volume concentration

419

of 0.5 v/v%, the morphology of the PCC was rhombohedral calcite and needle-like aragonite

420

with a diameter in the range of 1.2–1 µm. This result is contrasting to the results of the PCC

421

synthesized in the absence of aloe vera extract (Fig. 6b). Previous studies showed that

422

morphological modifiers can increase or decrease the particle size (Alvarez and Paulis, 2017). 20

ACCEPTED MANUSCRIPT 423

Hence, the reduced particle diameter range confirms the addition of aloe vera and suggest

424

possible versatility of the synthesized PCC for a variety of applications. Further increase in the

425

extract concentration to 5 v/v% transforms the aragonite PCC particle from monocrystalline

426

elongated phase to hierarchical morphology of flower-like structures with radiating ends (Fig.

427

6c). The formed crystal particles at 5 v/v% extract concentration have almost similar

428

dimensions with the added aloe vera concentration of 0.5 v/v%. Therefore, the evolved particle

429

morphology suggests that the aloe vera extract and in situ Mg have significant influences on

430

the crystalline structure of PCC.

431 432

(Insert Figure 6)

433 434

3.7 Viscosity of membranes

435

The viscoelastic properties of dope solution is a major parameter, which can affect the

436

kinetics of phase inversion and spinning process. The viscosities of all prepared dope solutions

437

were measured as a function of A-PCC content (Fig. 7). As shown in the figure, the viscosities

438

of the dope solutions were significantly increased with the increase in A-PCC content. This

439

reason can be interpreted that the addition of A-PCC in the solution matrix increased the

440

concentration of casting solution and consequently intensified the interacting force among the

441

PES macromolecules, thereby resulting in the increase in the casting solution system with the

442

increase in A-PCC content.

443 444

(Insert Figure 7)

445

21

ACCEPTED MANUSCRIPT 446

3.7 Scanning electron microscopy analysis of the membranes

447

The surface and cross-sectional micrographs of composite and neat HF membranes are

448

shown in Fig. 8. The outer and inner cross-sections of all membranes had skin layers on both

449

surfaces. All membranes displayed a similar structure consisting of asymmetric structure of UF

450

membranes, a dense top layer, fully grown macrovoids at the bottom layer, and a highly porous

451

finger-like sublayer. As observed from the surface images of the composite membranes, A-

452

PCC particles formed aggregates on the membrane surfaces. These clusters were increased in

453

number with the increase in loading of A-PCC. Furthermore, this increase in A-PCC aggregates

454

was expected to cause pore plugging during phase separation process especially with high A-

455

PCC contents.

456 457

(Insert Figure 8)

458 459

3.8 Influence of A-PCC content on membrane pore size and porosity

460

The pore size and porosity of membranes are presented in Table 5. The membrane

461

porosity was decreased upon the introduction of A-PCC as the solid content was increased.

462

Meanwhile, pore size was increased as the A-PCC content was increased and reached a

463

maximum of 171 nm where the A-PCC content was 3 wt.%. The same trend was observed by

464

Li et al. (2009), who found that membrane porosity decreases linearly with TiO2 loading.

465

However, further increase in the A-PCC content (above 3 wt.%) decreased the pore

466

size. A similar observation was obtained in a study conducted by Alsalhy et al., (2013), who

467

found that the addition of low ZnO content in the polymer matrix results in the increase in

468

membrane pore size, which may be attributed to the increase in surface roughness. Thus, upon

22

ACCEPTED MANUSCRIPT 469

the addition of a small amount of A-PCC particles, dope solution with low viscosity is obtained

470

(Fig. 7). Moreover, membrane with small dense skin layer, which can suppress the defects in

471

the membrane, was formed. However, when the A-PCC content was high, the membrane with

472

a loose skin layer, which will cause the bubble point pressure to decrease, was formed.

473 474

(Insert Table 5)

475 476

3.9 Mechanical property of PES blend membranes

477

The mechanical properties of membranes are important for practical application

478

(Ghasem et al., 2012). The elongation at break and tensile strength of all membranes are

479

presented in Table 6. As shown in the table, the tensile strength was increased from 3.12 MPa

480

to 4.17 MPa and the elongation at break was decreased from 15.26% to 11.57% with increasing

481

A-PCC content from 0 to 5 wt.%. This result indicates that the introduction of A-PCC in the

482

PES causes a significant improvement in the membrane. This phenomenon may be the result

483

of strong interacting force between PES and A-PCC. The addition of A-PCC can serve as a

484

cross-linker in the composite membrane to link the polymer chain, which will enhance the

485

rigidity of the polymer chain, as well as confined PES crystallization. Thus, more energy is

486

needed to break down the bond between PES and A-PCC. As a result, the mechanical properties

487

was improved. With high A-PCC content of >2 wt.%, significant decrease in the elongation at

488

break was observed. This result is similar to that of the study conducted by Razmjou et al.

489

(2012), who observed that the TiO2 content of below 2 wt.% provides membrane with

490

improved elastic behavior.

491 492

(Insert Table 6) 23

ACCEPTED MANUSCRIPT 493 494

3.10

Influence of A-PCC on WCA of HF membrane

495

The hydrophilicity of membranes can affect PF and oil rejection. Generally, contact

496

angle (CA) is ineffective in estimating hydrophilicity because CA is also dependent on the

497

porosity, which is driven by the capillary action (Yip et al., 2010). WCA is a clear indicator of

498

interfacial energy (IE) between water droplet and membrane surface. The lower the CA is, the

499

higher the IE will be, which will lead to high hydrophilicity. The hydrophilicity of all

500

membranes was determined by WCA. Fig. 9 presents the dynamic CA with different A-PCC

501

contents, which can be influenced by surface chemistry, roughness, and porosity. The time

502

variation of membrane hydrophilicity was achieved by observing the CA for 600 s. The results

503

showed that the initial CA of the neat membrane was higher than that of all modified

504

membranes. The initial CA values were 72.3 ± 2.22º, 62.7 ± 2.01º, 63.5 ± 1.75º, 62.5 ± 0.49º,

505

60.3 ± 045º, and 60.3 ± 0.62º for membranes PC-0, PC-1, PC-2, PC-3, PC-4, and PC-5,

506

respectively. In addition, the water drop diameters of all membranes were almost constant with

507

time. Thus, the decline in time is caused by H2O penetrating through the membranes.

508

Meanwhile, the CA curve showed that the CA of the composite membrane was decreased

509

rapidly with the increase in the A-PCC contents. Thus, upon the introduction of A-PCC into

510

the PES matrix, the membrane hydrophilicity is improved. Improved hydrophilicity can be as

511

a result of the effect of the A-PCC particles. In addition, H2O molecules found within the

512

membrane matrix tends to be attracted and directed to pass through membrane pores, which

513

will improve water permeability (Otitoju et al., 2017; Yang et al., 2007).

514 515

(Insert Figure 9)

516 24

ACCEPTED MANUSCRIPT 517

3.11

Effects of A-PCC content on membrane performance

518

The addition of A-PCC particles can influence the flux at least in two aspects. Firstly,

519

the A-PCC can increase the hydrophilicity of the membrane, which could enhance the flux.

520

Secondly, its effect on the membrane morphology would affect the permeation properties. The

521

results of pure WF of fresh and fouled membranes are presented in Fig. 10. The pure WF (fresh

522

membranes) increases with increasing A-PCC content up to 3 wt.% but decreases with further

523

addition. A maximum PWF of 180 kg/m2h was achieved when the content of A-PCC was 3

524

wt.%. However, upon further introduction of A-PCC up to 5 wt.% caused the PWF to decrease

525

to 161 kg/m2h. In the case of fouled membrane, a similar trend was observed.

526

The relationship of the PF of membrane against varying A-PCC contents is presented

527

in Table 7. Evidently, the PF of the membranes increased with the increase in the amount of

528

A-PCC content (0 - 3 wt.%), which can be attributed to the improvement in hydrophilicity due

529

to increased membrane pore size. However, with further increase in the A-PCC content of up

530

to 5 wt%, the PF was decreased. This result can be ascribed to the observed decrease in pore

531

size. The decrease in the PF at above 3 wt.% A-PCC content can be ascribed to the formation

532

of thicker skin layer and pore blockage as a result of PCC particle agglomeration on the

533

membrane surface (Fig. 8). Conducted studies revealed that excessive loading of nanoparticles

534

as additives in membrane matrix can adversely affect membrane properties and performance

535

mainly due to the nonuniformity in particle dispersion on the membrane surface (Chen et al.,

536

2009; Jamshidi et al., 2015; Shen et al., 2011).

537 538

(Insert Table 7)

539

(Insert Table 8)

540

(Insert Figure 10) 25

ACCEPTED MANUSCRIPT 541

The results of the oil rejection for the modified and unmodified membranes determined

542

from Eq. (7) are presented in Table 7. The oil rejection performance of the A-PCC membrane

543

is comparable with other reported HF membrane with even enhanced permeate flux as shown

544

in Table 8. All membrane exhibited a rejection rate of >94% as compared with the controlled

545

membrane of 93.9%. However, considering the PF and rejection, the PES membrane prepared

546

by adding 3 wt.% A-PCC was the optimum membrane because it achieved the highest WF and

547

superior oil rejection of above 99%. To determine the antifouling capability of the membranes,

548

the total flux losses, FRR, and irreversible and reversible resistances were calculated and are

549

presented in Table 7. The recoverable flux of all modified membranes were higher than those

550

of the unmodified membrane, thereby demonstrating a high recyclable ability of the composite

551

membrane. In terms of the total flux loss and irreversible resistance, all modified membranes

552

displayed lower values than that of unmodified membrane. Furthermore, the reversible

553

resistance of the modified membranes was comparably higher than that of neat membrane. This

554

result can be ascribed to the hydrophilic properties of the composite membrane because

555

membranes with improved hydrophilicity will produce low tendency to fouling due to the lower

556

adsorption between the membrane surface and oil.

557 558

4. Conclusions

559

Precipitated CaCO3 nanoparticles with aragonite morphologies by using natural

560

dolomite, glucose, and aloe vera as environmentally-friendly morphological modifiers were

561

synthesized. Glucose solution was suitable in the extraction of Ca (calcium glucosate) from

562

dolomite, thereby resulting in the PCC yield of 82%. The addition of aloe vera and in situ Mg

563

modifies the PCC structure and mechanism. Hence, at a concentration of 5 v/v% aloe vera,

564

flower-like structure with radiating ends of only PCC aragontie phase is produced. The

565

synthesized aragonite PCC was utilized to produce PES HF membrane, and it contributed to 26

ACCEPTED MANUSCRIPT 566

an improved mechnical properties of the membrane. Performance test for oil-to-water

567

separation showed an optimal oil rejection of >99% at 3 wt.% A-PCC content in the membrane.

568

Further increase was observed in the A-PCC content of above 3 wt.% in the HF membrane.

569

Moreover, the permeate WF was decreased due to agglomeration and consequent pore

570

blockage. Furthermore, the result showed that the antifouling ability of the membrane can be

571

enhanced upon the introduction of A-PCC in the PES matrix. Thus, the synthesized aragonite

572

PCC polymorphs offers beneficial application in membrane technology for wastewater

573

treatment and a profitable utilization of dolomite as a PCC precusor. The process also presents

574

low energy intensive route to aragonite synthesis.

575 576

Conflict of Interest

577

We declare that there is no conflict of interest in this work.

578

Acknowledgement

579

The second author acknowledges Postdoctoral Fellowship from the Shenyang University of

580

Technology, Shenyang, Liaoning Province, China for their aid in this research.

581 582 583 584 585 586 587 588 589 590 27

ACCEPTED MANUSCRIPT 591 592 593 594 595 596 597

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Figure Captions

773

Figure 1: Size distribution of oil droplet in the oil in water emulsion for the ultra-filtration

774

separation.

775

Figure 2: Process flow diagram for dolomite PCC synthesis.

776

Figure 3: EDAX of (a) samples without D-glucose and aloe vera extract and (b) samples with D-glucose and aloe vera extract.

777 778 779 780 781

Figure 4: X-ray diffraction (XRD) pattern of PCC. (a) Dolomite, (b) without additive, (c) with 0.5 v/v% aloe-vera extract, and (d) with 5 v/v% of aloe vera extract. Figure 5: Particle size distribution of the synthesized PCC (a) with aloe vera extract (b) without aloe vera extract.

782

Figure 6: SEM of the samples obtained at different aloe vera extract concentrations: (a)

783

without additive, (b) with added 0.5 v/v% of aloe vera, and (c) with added 5 v/v% of

784

aloe vera.

785

Figure 7. Viscosity of dope solutions with different A-PCC content.

786

Figure 8. FESEM cross sectional structure of membrane (a) surface at 1200 × , (b) cross-

787 788

section at 500 × . Figure 9. Water contact angles with time of PES membranes as a function of A-PCC content.

35

ACCEPTED MANUSCRIPT 789

Figure 10. Water flux of membranes after and before membrane filtration.

790 791 792 793 794

List of Tables:

795

Table 1. Recipes to prepare PES/A-PCC HF membranes.

796

Table 2. PES Hollow fibre membrane spinning conditions.

797

Table 3. Mg2+ content and yields of the PCCs prepared at different additive concentrations.

798

Table 4a. PCC Microparticles with aloe vera extract.

799

Table 4b. PCC Microparticles without aloe vera extract.

800

Table 5. Influence of A-PCC content on membrane pore size and porosity.

801

Table 6. Influence of A-PCC content on mechanical property of PES blend membranes

802

Table 7. Effect of A-PCC contents on permeate flux, oil rejection, and anti-fouling

803

parameters of membranes.

804

Table 8. Performance comparison of A-PCC/PES HF membrane with reported HF membrane

805

for wastewater applications.

806

36

ACCEPTED MANUSCRIPT 11 10 9 Intensity (%)

8 7 6 5 4 3 2 1 0 0

1

2

3 4 Droplet size (µm)

5

6

7

Figure 1. Size distribution of oil droplet in the oil in water emulsion for the ultra-filtration separation.

1

ACCEPTED MANUSCRIPT Emiworo Dolomite Sample Processing  Grinding by ball mill  Screening to 10 mm-20 mm Calcine at temperature of  1000 oC for 180 min

Calcined dolomite (s)

CO2 (g)

Calcium glucosate (aq)

Mg (s)

Unreacted CO2 (g) Filtration

CO2 (g) Source

Calcium glucosate (aq)

Aloe vera extract

Reactor

PCC

Figure 2: Process flow diagram for dolomite PCC synthesis 2

Glucose recycle

ACCEPTED MANUSCRIPT

(a)

keV

(b)

keV

Figure 3: EDAX of (a) without D-glucose and aloe vera extract and (b) with D-glucose and aloe vera extract.

3

ACCEPTED MANUSCRIPT

a)

102000 68000 34000 0

b)

900

021

Intensity (a.u.)

600

104

100

221

300 0 4000

c)

3000

104

2000 1000

012

0 3400

021

d)

2550 1700

221

102 850 0 10

20

30

40

2 Theta (degrees)

50

60

Figure 4: X-ray diffraction (XRD) pattern of PCC (a) Dolomite (b) without additive (c) with 0.5 v/v% aloe-vera extract (d) with 5 v/v% aloe Vera extract.

4

ACCEPTED MANUSCRIPT

Volume (%)

12

(a)

10 8 6 4 2 0 0.01

0.1

1

10 100 Particle (µm)

1000

10000

1000

10000

12 Volume (%)

(b) 10 8 6 4 2 0 0.01

0.1

1

10

100

Particle (µm) Figure 5: Particle size distribution of the synthesized PCC (a) with aloe vera extract (b) without aloe vera extract.

5

ACCEPTED MANUSCRIPT

(a)

(b)

(c)

Figure 6: SEM of the samples obtained different concentration of aloe-vera extract. (a) Without additive (b) with 0.5 v/v% of aloe-vera additive (c) with 5v/v% of aloe-vera additive.

6

ACCEPTED MANUSCRIPT

Viscosity (cP)

1400 1200 1000 800 600 400 0

1

2 3 A-PCC content (wt.%)

4

Figure 7. Viscosity of dope solutions with different A-PCC content.

7

5

ACCEPTED MANUSCRIPT

Figure 8. FESEM cross sectional structure of membrane (a) surface at 1200 x, (b) crosssection at 500 x.

8

ACCEPTED MANUSCRIPT

Figure 9. Water contact angles with time of PES membranes as a function of A-PCC content.

Pure water flux (kg/m2h)

Fresh Membrane

Fouled Membrane

180 150 120 90 60 30 0 0

1

2 3 A-PCC content (wt.%)

4

5

Figure 10. Water flux of membranes after and before membrane filtration.

9

ACCEPTED MANUSCRIPT Table 1. Recipes to prepare PES/A-PCC HF membranes. Membrane PES

PEG

A-PCC

NMP

PC-0

17.25

3.75

0

79

PC-1

17.25

3.75

1

78

PC-2

17.25

3.75

2

77

PC-3

17.25

3.75

3

76

PC-4

17.25

3.75

4

75

PC-5

17.25

3.75

5

74

Table 2. PES Hollow fibre membrane spinning conditions. Spinning parameters

Values

Coagulation bath (°C)

25

Bore fluid flow rate (ml/min)

1.8

External coagulant

Tap water

Air gap (cm)

25.5

Spinneret internal diameter (mm)

0.35

Bore fluid

Distilled water

Spinneret external diameter (mm)

1

Room temperature (°C)

21-23

Collection drum (rev/min)

8

Gear pump (rev/min)

18

Relative humidity (%)

61-68

1

ACCEPTED MANUSCRIPT Table 3. Mg2+ content and PCC yields prepared from different additive concentration. D-glucose

Aloe-vera

Mg+ content

concentration

concentration

(%)

(mol dm-3)

(v/v%)

1

0

0

28.60

51

2

0.5

0.5

0.26

68

3

0.5

2

0.19

79.5

4

0.5

5

0.30

81.2

Sample name

Table 4a. PCC Microparticles with aloe vera extract. Particle characterization Dv (10)

1.26 μm

Dv (50)

1.02 μm

Dv (90)

3.34 μm

Span

2.041 2

Yield (%)

ACCEPTED MANUSCRIPT

Specific Surface Area

411.6 m²/kg

Table 4b. PCC Microparticles without aloe vera extract Particle characterization Dv (10)

6.53 μm

Dv (50)

16.30 μm

Dv (90)

33.5 μm

Span

1.653

Specific Surface Area

201.1 m²/kg

Table 5. Influence of A-PCC content on membrane pore size and porosity. A-PCC content

Pore size (nm)

Porosity (%)

0

34.4 ± 1.04

77.2 ± 2.59

1

35.8 ± 1.75

76.3 ± 2.48

2

37.32 ± 1.70

75.5 ± 3.07

(wt.%)

3

ACCEPTED MANUSCRIPT 3

42.06 ± 1.30

73.3 ± 1.56

4

39.8 ± 1.10

72.2 ± 2.29

5

38.58 ± 1.18

71.5 ± 2.38

Table 6. Influence of A-PCC content on mechanical property of PES blend membranes A-PCC content

Elongation at break

Tensile strength

(wt.%)

(%)

(MPa)

0

15.26

3.12

1

15.15

3.41

2

15.23

3.67

3

13.76

3.98

4

12.06

4.18

5

11.57

4.17

Table 7. Effect of A-PCC contents on permeate flux, oil rejection and anti-fouling parameters of membranes. A-PCC content

Permeate flux Rejection FRR

Rr

Rir

Rt

(wt.%)

(kg/m2h)

(%)

(%)

(%)

(%)

(%)

0

49.87

93.9

61.8

13.2

38.3

51.5

4

ACCEPTED MANUSCRIPT 1

55.08

94

82.8

33.8

17.2

51.0

2

96.58

98.6

87.4

31.2

12.6

43.8

3

102.15

99.8

86.4

31.4

11.9

43.3

4

96.20

94.3

82.8

19.5

23.8

43.3

5

91.06

96.5

70.2

5.2

38.5

43.7

Table 8. Performance comparison of A-PCC/PES HF membrane with reported HF membrane for wastewater applications. Material

Application

Oil droplet (µm)

TMP (bar)

Permeate flux Rejection (kg/m2h) (%)

Ref.

Cellulose

Machine oil

-

1

7.7

[1]

5

-

ACCEPTED MANUSCRIPT PVDF/P(VDFco-CTFE)-gPMAAgfPEG(PVDF/AP

Hexadecane oil

1-50

3.4

~70

98

[2]

Polyphenylene sulfone (sPPSU)

Soybean oil

0.1 - 6

-

23.3

99.62

[3]

TiO2-Mullite

Soybean oil

1.08

0.025

150

97

[4]

PVDF-PVPTiO2

Cutting oil

1.08

0.5

70.48

99.7

[5]

PVDF-PVPTiO2

Cutting oil

1.08

0.5

72.2

94

[6]

Sulfonated Petroleum oil polyphenylenesu lfone (PPSU

-

1

~220

95.4

[7]

PES/A-PCC

1.54

1.5

102.15

99.8

This work

Crude oil

6