Removal of priority and emerging pollutants from aqueous media by adsorption onto synthetic organo-funtionalized high-charge swelling micas

1 REMOVAL OF PRIORITY AND EMERGING POLLUTANTS FROM AQUEOUS 1 MEDIA BY ADSORPTION ONTO SYNTHETIC ORGANO-FUNTIONALIZED 2 HIGH-CHARGE SWELLING MICAS 3 4 Julia Martín1*, María del Mar Orta2, Santiago Medina-Carrasco3, Juan Luis Santos1, Irene 5 Aparicio1, Esteban Alonso1 6 1Department of Analytical Chemistry, Escuela Politécnica Superior, University of Seville. E–7 41011 Seville, Spain. 8 2Department of Analytical Chemistry, Faculty of Pharmacy, University of Seville, E-41012 9 Seville, Spain. 10 3X-Ray Laboratory (CITIUS), University of Seville, E-41012 Seville, Spain. 11 12 13 14 15 Corresponding author: Julia Martín 16 Address: 17 Department of Analytical Chemistry, Escuela Politécnica Superior, University of Seville. C/ 18 Virgen de África, 7, E–41011 Seville, Spain 19 E-mail: [email protected] 20 Phone-number: +34-9-5455-6250 21 22 23 24 25 2 Abstract 26 In this work, the removal of different types of emerging pollutants (four perfluoroalkyl 27 compounds, two preservatives, three surfactants and nine pharmaceutical compounds) from 28 aqueous solution by adsorption onto two novel synthetic clays, a high-charge swelling mica 29 (Na-Mica-4) and an organo-functionalized mica (C18-Mica-4), was evaluated. Na-Mica-4 and 30 C18-Mica-4 were prepared and characterized by X-Ray diffraction, Zeta potential, specific 31 surface area, thermogravimetric analysis and transmission electron microscopy, before and 32 after adsorption experiments. 33 The influence of the aqueous sample pH, salt addition and extraction time in the removal 34 were evaluated. The results showed the high adsorption affinity of C18-Mica-4 for most of the 35 emerging pollutants analysed after a removal time of 24 hours (14 out of 18 pollutants were 36 effectively removed [70-100%]). A high correlation was observed between the log Kow of the 37 selected emerging pollutants and the adsorption onto C18-Mica-4. The results also indicate 38 that adsorption occurs in the interlayer space. While the removal rates with Na-Mica-4 were 39 in the range 8% to 97% after seven days, some of the compounds, perfluorobutanoic acid and 40 most of pharmaceutically active compounds, were not adsorbed onto the high-charge mica. 41 C18-Mica-4 was effectively used for the removal of contaminants from four types of water 42 samples. 43 Keywords: Emerging pollutants; High-charge swelling micas; Organic functionalization; 44 Water samples; Removal 45 46 47 48 49 50 3 Introduction 51 Preservation and improvement of water quality is paramount to keep the health and 52 sustainability of the different ecosystems. The occurrence of natural or anthropogenic 53 contaminants of emerging concern at levels between ng L-1 and μg L-1 has been reported in 54 many publications including pesticides, industrial compounds, pharmaceuticals and personal 55 care products, among others (Ruhí et al., 2016; Rodil et al., 2012; Bolong et al., 2009; 56 Caliman et al., 2009). Conventional urban wastewater treatment plants (WWTPs) are not 57 specifically designed to remove residual concentrations of organic compounds. Ultraviolet 58 lamps have been used mainly for disinfection, while alternative technologies including 59 advanced oxidation processes (such as ozonation with H2O2 and the use of Uv/H2O2), 60 nanofiltration, reverse osmosis, and adsorption (Carmalin and Eder, 2018; Capodaglio, 2017; 61 Grassi et al., 2012; Katsoyiannis et al., 2011; Liu et al., 2009), have been investigated but 62 most of them hardly implemented as tertiary treatment in WWTPs. 63 Adsorption is one of the alternatives for the removal of emerging pollutants due to its high 64 efficiency, selectivity, low cost, simplicity and the possibility of reusing and recycling the 65 adsorbent (Carmalin and Eder, 2018; Martins et al., 2017; Méndez et al., 2017; Tapia-Orozco 66 et al., 2016; Rashed, 2013; Park et al., 2011). The suitability of an adsorbent is determined by 67 properties such as surface area, mechanical stability or pore size. Activated carbon (AC) is 68 the most widespread adsorbent for the removal of organic pollutants because of its 69 microporosity, which ensures good sorption capacities (Rigobello et al., 2013; Djilani et al., 70 2012; Ruiz et al., 2010; Yu et al., 2008; Nevskaia and Guerrero-Ruiz, 2001). However, the 71 use of ACs is costly because only a percentage of carbons can be reused after the adsorption 72 process (Sharma and Wankat, 2010), usually no more than 40% (Wang and Balasubramanian, 73 2009). Moreover, thermal regeneration of activated carbons has been explored for emerging 74 pollutants removal from effluent wastewater (Marques et al., 2017) but it was observed that 75 4 the regenerated activated carbon was not as efficient as new activated carbon. Therefore, 76 alternative sorbents are desirable to overcome these drawbacks (Orta et al., 2018; Suna et al., 77 2017; Pazos et al., 2017). In this context, clay minerals have attracted much attention owing 78 to their high cation exchange, swelling properties, and high surface areas (Lingya et al. 2016; 79 Alba et al., 2009; Sánchez-Martín et al., 2008; Zadaca et al., 2007; Lagally, 2001). 80 Compared to other clay minerals like smectites or vermiculites, micas exhibit higher layer 81 charge density. Naturally occurring micas do not swell in water and ion-exchange reactions 82 with the interlayer cations would be extremely slow process (Kodama et al., 2000). In 83 contrast, the synthetic highly charged mica Na-mica-4 has an unusual swelling behaviour and 84 selective cation exchange properties, which may become potentially useful for hazardous 85 cation separations from solutions (Alba et al., 2006; Park et al, 2002). 86 In addition, clay minerals can be modified in order to enhance their removal efficiency in 87 aqueous media. The organo-functionalization of their surface allows for the effective sorption 88 of non-ionic pollutants in the interface. The sorption of organic micropollutants by 89 organoclays depends on the structure and size of alkylammonium ions, type of clay, cation 90 exchange capacity, density and orientation of the alkyl chains on the surface, and features 91 such as solute size, shape and relative solubility/hydrophobicity (Pazos et al., 2017; Alba et al, 92 2011a). C18-mica prepared by a cation-exchange reaction between Na-mica-4 and primary 93 alkylamine shows better expandability and structural properties than native Na-mica-4, 94 improving its adsorption capacity (Pazos et al., 2012; Alba et al., 2011a). Up to now, few 95 studies have examined the use of C18-Mica-4 as adsorbents for the retention of organic 96 pollutants. Among them, Pazos et al. (2017) and Alba et al. (2011a) studied the adsorption of 97 some pollutants from petroleum refineries such as benzene, toluene and phenol on these 98 materials. More recently Orta et al. (2018) evaluated Na-Mica-4 and C18-Mica-4 for the 99 removal of linear alkylbenzene sulfonates (LAS) from aqueous samples. More studies are 100 5 required to extend the use of this promising mica for the removal of other families of organic 101 compounds. 102 In the present work, the adsorption of Na-Mica-4 and C18-Mica-4 is evaluated for the removal 103 of eighteen micropollutants including priority substances (Directive 2013/39/EU), substances 104 of the last watch list (Decision 2015/495/EU) and contaminants of emerging concern: two 105 groups of industrial compounds (surfactants and perfluoroalkyl compounds), personal care 106 products (preservatives), and multi-class pharmaceuticals (anti-inflammatory drugs, 107 antibiotics, antiepileptic drugs, β-blockers, nervous system stimulants and lipid regulators). 108 109 2. Materials and methods 110 2.1. Materials and reagents 111 SiO2 (Sigma Aldrich; CAS no. 112945-52-5, 99.8% purity), Al(OH)3 (Sigma Aldrich; CAS 112 no. 21645-51-2), MgF2 (Sigma Aldrich; CAS no. 7783-40-6), and NaCl (Sigma Aldrich; 113 CAS no. 7647-14-5, ≥99.5% purity) were purchased from Sigma-Aldrich for the synthesis of 114 Na-Mica-4. Primary alkylamine octadecylamine salt (CAS no. 124-30-1, ≥99,0% purity) was 115 purchased from Sigma Aldrich for the organo-functionalization of Na-Mica-4. 116 HPLC-grade acetonitrile (ACN), methanol (MeOH) and water were supplied by Romil Ltd. 117 (Barcelona, Spain). 118 Hydrochloric acid, sodium hydroxide, sodium chloride (NaCl), and formic acid were 119 obtained from Panreac (Barcelona, Spain). Ammonium formate and ammonium acetate were 120 purchased from Sigma-Aldrich (Steinheim, Germany). All of them were analytical grade. 121 High purity standards of perfluorobutanoic acid (PFBuA), perfluroroheptanoic acid (PFHpA), 122 perflurorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), 4-nonylphenol (NP), 123 methylparaben (MeP), and propylparaben (PrP) were supplied from Sigma-Aldrich 124 (Steinheim, Germany). Sodium dodecylsulfate (AS-C12) and sodium octadecylsulfate (AS-125 6 C18) were supplied by Alfa Aesar (Barcelona, Spain). Diclofenac (DIC), ibuprofen (IBU), 126 salicylic acid (SAL), trimethoprim (TRI), carbamazepine (CAR), propranolol (PRO), caffeine 127 (CAF), clofibric acid (CLOF), and gemfibrozil (GEM) were purchased from Dr. Ehrenstorfer 128 (Augsburg, Germany). 129 Individual stock standard solutions of each compound were prepared in methanol and stored 130 at 4 °C. Mixtures of the studied compounds at different concentration levels were prepared 131 freshly before each experiment by dilution of the stock standard solutions in a mixture 132 methanol:water (50:50, v/v). The acronym, pKa and log Kow of each analyte are shown in 133 Table 1. 134 135 2.2. Synthesis of swelling high charged micas 136 Na-Mica-4 was synthesized by the NaCl melt method following a procedure described by 137 Alba et al. (2006). Its cation exchange capacity (CEC) is 468 mequiv 100 g-1 and its structural 138 formula is Na4[Si4Al4]Mg6O20F4 · nH2O. The starting products employed were SiO2, Al(OH)3, 139 MgF2 and NaCl. The reactants were weighed and mixed in an agate mortar until the mixture 140 was homogeneous. 141 Heat treatments were carried out in a Pt crucible at 900 °C during 15 h using a heating rate of 142 10 °C·min−1. The product was washed with distilled water, and the solid was separated by 143 filtration, dried at room temperature, and then ground in agate mortar. 144 145 2.3. Organo-functionalization of Na-mica-4 146 The organomica C18-Mica-Na was prepared by a cation-exchange reaction between the mica 147 and an excess of primary octadecylamine (2 CEC of Na-Mica-4) (Alba et al., 2011a). The 148 primary amines were dissolved in an equivalent amount of HCl (0.1 M) and the resulting 149 mixture was stirred for 3 h at 80 °C. The alkylammonium solution was then mixed with 0.6 g 150 7 of Na-Mica-4 and stirred for 3 h at 80 ºC. Deionized water (50 mL at 50 ºC) was added and 151 the mixture was stirred for 30 min at 50 ºC, and the dispersion was then centrifuged at 8,000 152 rpm for 30 min at 5 ºC. The product was dissolved in a hot ethanol:water mixture (1:1) and 153 stirred for 1 h, centrifuged at 8,000 rpm for 30 min at 5 ºC. Finally, the precipitate was left to 154 dry at room temperature. 155 156 2.4. Sample collection 157 Influent and effluent wastewater collected in September 2016 from a wastewater treatment 158 plant located in Seville (Spain). Six daily-composite samples were obtained by mixing 159 sample volumes collected every hour by an automatic device (Sigma 900 MAX Portable 160 Sampler) over a 24-hour period. Surface water samples from the Guadalquivir River (Seville, 161 Spain) and tap water samples were collected during the same period in Seville city. Water 162 samples were taken in amber glass bottles pre-cleaned with acetone and methanol. Samples 163 were stabilized with acetonitrile (final concentration 0.5% v/v) and were stored at 4 °C until 164 analysis, which was carried out within 48 h after sample collection. Prior to the experiments, 165 samples were filtered through a 1.2 μm glass-microfiber membrane filter GF/CTM (Whatman, 166 Mainstone, UK) to remove suspended matter. 167 168 2.5. Adsorption experiments 169 A volume of 8 mL of filtered sample was placed in a 25 mL flask containing 50 mg of Na-170 Mica-4 or C18-Mica-Na. A mixture of the selected pollutants was added to achieve 171 concentration levels of 10 μg mL-1. The solution was stirred at 800 rpm for 24 h. The 172 supernatants were then filtered through a 0.22 µm nylon filter and a 20 µL aliquot was 173 injected into the chromatography instrument. 174 8 The parameters affecting pollutant adsorption, such as type of synthetic mica, sample pH and 175 extraction time were optimised. The experiments were run in triplicate. Removal rates of the 176 selected pollutants from water solution were calculated from the equation: Cspiked-177 Cblank)/Cstandard, where Cspiked is the concentration measured from spiked samples; Cblank is the 178 concentration obtained from a blank of reagents; and Cstandard is the concentration obtained by 179 direct injection of standard solutions at the same concentration level. The linearity of the 180 method was studied by analysing standard solutions in triplicate at concentrations ranging 181 from 0.1 μg mL-1 to 10000 μg mL-1. 182 183 2.6. Techniques 184 X-ray diffraction results were obtained in a Bruker D8 Advance A25 diffractometer (Bruker, 185 Germany) in Bragg-Brentano configuration. The detector was a Lynxeye PSD detector 186 (Bruker, Germany) equipped with a copper Kα radiation source (0.15405 nm wavelength). 187 Measurements were taken with a 2θ range between 1° and 70°, a step of 0.03°, time per step 188 of 0.1 s, and tube conditions of 40 kV and 30 mA. The diffractometer was calibrated 189 mechanically according to the manufacturer specifications and corundum standard was used 190 to check the resolution in a wide range of angles. 191 The Zeta potential was obtained from the mobility of the particles using the Smoluchowski 192 equation (Smoluchowski, 1941). Before and after of adsorption experiments, C18-Mica-Na 193 was suspended in water (1 g L−1) and the zeta potentials was measured on a Zetasizer 194 Nanosystem system (Malvern Instruments, Southborough, MA). The pH of the solution was 195 measured with Crison GLP 21 pH meter. 196 The specific surface area was determined by the Brunauer-Emmett-Teller (BET) method 197 using an ASAP 2420 analyser (Micromeritics, USA) with N2 sorption (Brunauer S., Emmett 198 P.H. and Teller, E., 1938). 199 9 Simultaneous differential scanning calorimetry and thermal gravimetric analyses (DSC-TGA) 200 were performed on a Q600 STD (TA instruments, USA). The samples were heated from 201 20 °C to 700 °C at a heating rate of 10 °C min–1 in a nitrogen atmosphere. 202 Transmission Electron Microscope (TEM) images were acquired in a Talos Field Emission 203 TEM (FEI, USA). 204 Liquid Chromatography-tandem mass spectrometry (LC-MS/MS) analyses were performed 205 on an Agilent 1200 series HPLC system (Agilent, USA) equipped with a vacuum degasser, a 206 binary pump, an autosampler and a thermostatic column compartment. MS analyses were 207 done with a 6410 QqQ instrument equipped with an electrospray ionization source (ESI) 208 (Agilent). Ionization of analytes was carried out using the following settings: MS capillary 209 voltage 3000 V, drying-gas flow rate 9 L min-1, drying-gas temperature 350 ºC, and nebulizer 210 pressure 40 psi. Separation of analytes was carried out using a HALO C18 (50x4.6 mm i.d.; 211 2.7 µm) analytical column (Teknokroma, Spain) protected by a HALO C18 (5x4.6 mm 1.d.; 212 2.7 µm) guard column (Teknokroma, Spain). Elution was performed at a flow rate of 0.6 mL 213 min-1 with a column temperature of 30 °C. More details about mobile phase and gradient 214 elution applied to the separation of the studied compounds can be found in Supplementary 215 material. Detection was performed in multiple reaction-monitoring mode (MRM), and 216 positive and negative ionization were simultaneously monitored. Two MRM transitions were 217 selected for each analyte, one was applied for quantification (MRM1) and another for 218 confirmation (MRM2). MRM transitions, fragmentor voltage, collision energy and ionization 219 mode are summarized in Table S1. 220 221 3. Results and discussion 222 3.1. Characterization of adsorbents 223 16 samples and also to be used as a sorbent material in sample treatments such as the removal of 374 interfering compounds. 375 376 Acknowledgement 377 This work was supported by the Spanish Ministry of Economy, Industry and Competitiveness 378 (Project No. CTM2017-82778-R). 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Thermal gravimetric (a) and differential scanning calorimetry (b) analysis for Na-507 4-Mica, C18-Mica-4 and C18-Mica-4 after adsorption. 508 Figure 2. Transmission Electron Microscopy picture of C18-Mica-4. 509 Figure 3. Effect of Na-Mica-4 and C18-Mica-4 on the removal of emerging pollutants (n=3). 510 Figure 4. (a) Influence of log Kow on the removals by using C18-Mica-4; (b) Effect of pH on 511 the removals of the emerging pollutants (C18-Mica-4, n=3). 512 Figure 5. Effect of time on the removal of emerging pollutants (C18-Mica-4, n=3). 513 Table 1. Acronym and physico-chemical properties of the selected pollutants. Compound Acronym pKa Log Kow Methylparaben MeP 8.3 1.7 Propylparaben PrP 8.2 2.6 Perfluorobutanoic acid PFBuA 0.2-0.4 2.4 Perfluoroheptanoic acid PFHpA - 5.3 Perfluorooctanoic acid PFOA 2.8 6.3 Perfluorooctane sulfonic acid PFOS -3.3 4.1 Nonylphenol NP 10.7 4.5 Dodecyl sulfate AS C12 <1 2.4 Octadecyl sulfate AS C18 <1 2.6 Diclofenac DIC 4.1 4 Ibuprofen IBU 4.4 3.8 Salycilic acid SAL 3.5 2.3 Trimethoprim TRI 6.6 1.4 Carbamazepine CAR 13.9 2.3-2.5 Propranolol PRO 9.5 0.7 Caffeine CAF 14 -0.1 Clofibric acid CLOF 2.5-3.2 2.6 Gemfibrozil GEM 4.7 4.8 Table 1 Table 2. Pollutant removal (%) in real spiked water samples (10 μg mL-1) after C18- Mica-4 adsorption (n=3). Compound Removal (%) in water samples Tap water Superficial water Effluent wastewater Influent wastewater MeP 51 58 58 31 PrP 73 75 78 55 PFBuA 78 76 78 68 PFHpA 80 79 77 59 PFOA 87 94 91 84 PFOS 98 100 100 100 NP 98 99 99 99 ASC12 100 100 100 99 ASC18 100 103 100 100 DIC 91 85 78 76 IBU 87 88 78 75 SAL 96 100 90 70 TRI 54 53 55 40 CAR 61 42 58 59 PRO 41 39 15 17 CAF 56 30 52 49 CLOF 90 82 81 40 GEM 92 85 86 81 Table 2 Figure 1 Click here to download high resolution image Figure 2 Click here to download high resolution image