Acid-base Polymeric Engineered Foams for Adsorption of Micro-Oil Droplets from Industrial Effluents

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1 Supporting Information for Acid-base Polymeric Engineered Foams for Adsorption of Micro-Oil Droplets from Industrial Effluents Pavani Cherukupally,, Edgar J. Acosta, Juan P. Hinestroza, Amy M. Bilton, and Chul B. Park, * Microcellular Plastics Manufacturing Laboratory, Department of Mechanical and Industrial Engineering, University of Toronto, 5 King s College Road, Toronto, Ontario M5S 3G8 Laboratory of Colloid and Formulation Engineering, Department of Chemical Engineering and Applied Chemistry, 200 College Street, Toronto, Ontario, M5S 3E5 Fiber Science Program, Cornell University, 37 Forest Home Drive, Ithaca, New York Water and Energy Research Lab, Department of Mechanical and Industrial Engineering, University of Toronto, 5 King s College Road, Toronto, Ontario M5S 3G8 *Corresponding author: Address: 5 King s College Rd, Toronto, ON, Canada, M5S 3G8; Phone: +1 (416) , Fax: +1 (416) ; park@mie.utoronto.ca TABLE OF CONTENTS The number of pages: 10 The number of text: 5 The number of figures: 4 S1

2 S1. Inverse Gas Chromatography. All surface area, Gutmann acid-base profile measurements were carried out using an IGC Surface Energy Analyzer, IGC-SEA, (Surface Measurement Systems, Alperton, UK) and the data were analyzed using both standard and advanced SEA Analysis Software. The injection system used by the IGC-SEA allows for precise control of the injection size, therefore different amounts (mole, n) of probe vapor can be chosen to pass through the sample column to achieve different concentrations and subsequently different surface coverages, n/n m. For all experiments, approximately 10 mg of each foam sample was packed into individual silanized glass columns (300 mm long by 4 mm inner diameter) using the Column Packing Accessory. Each column was conditioned for a period of 60 minutes at 50 C and 0% RH with helium gas prior to any measurements. All the experiments were conducted at 50 C with 5 sccm total flow rate of helium gas, using methane for dead volume corrections. For the surface area measurements, methanol (Aldrich, HPLC grade) sorption isotherms were collected on the samples at the desired temperature, using the IGC pulse sorption method. IGC has been used previously as a reliable method to determine isotherms using organic probe molecules at finite concentration and ambient temperatures. 1,2 Methanol isotherms exhibited significant Type II behavior and extended well into the 0.05 to 0.35 P/P o range. Both requirements were necessary to apply the traditional Brunauer, Emmett and Teller (BET) model, which is based on the physical adsorption of a vapor or gas onto the surface of a solid. 3 The IGC technique has been previously used to accurately determine BET surface areas for a wide range of materials. 4-6 Further details on IGC theory and applicability to determining BET surface area values can be found elsewhere. 4-6 The surface energy and Gibbs specific free energy values can be determined if a series of probe vapors are injected at the same surface coverage. Consequently, the injections of these same probe vapors at different surface coverages will result in a distribution of surface energy as a function of S2

3 surface coverage, which is referred to as a surface energy profile. The detailed methodology for this characterization has been described elsewhere. 7,8 Samples were run at a series of surface coverages with n-alkanes (decane, nonane, octane, and heptane; Aldrich, HPLC grade) and polar probe molecules (acetone, methanol, acetonitrile, ethyl acetate, and dichloromethane; Aldrich, HPLC grade) to determine the dispersive surface energy as well as the specific free energies of adsorption. The method of Dorris and Gray was employed for the dispersive surface energy component. 8 For the specific free energies of desorption, the Polarization approach was employed. Acid-base surface energy components are determined using the Good-van Oss-Chaudhry (GvOC) AB model (equation 1) where the acid-base (γ s ) component is taken as the geometric mean of the Lewis acid parameter and Lewis base parameter. The total surface energy is given by: Total surface energy, γ 2 = γ 45 + γ 78 (1) where γ :; is Lifshitz-van der Waals surface energy component (mj/m 2 ) and γ <= is acid-base surface energy component (mj/m 2 ). For acid-base surface energies and profiles, samples were run at the same surface coverage with polar probe molecules and Gibbs specific free energy values were determined. Consequently, the injections of these same probe vapors at different surface coverages will result in a distribution of surface acidity and basicity as a function of surface coverage, which is referred to as Gutmann acid and base numbers. The detailed methodology has been described elsewhere. 7,8 S3

4 S2. Characterization of oil/water emulsion. Model oil/water emulsions were used to evaluate the adsorption properties of the foam. The crude oil density was measured gravimetrically and the viscosity was measured by a shear rheometer (TA Instruments AR2000). The oil total acidity number (TAN) was estimated using titration method. For dilute oil/water emulsions, approximately 8, 000 mg L-1 of crude oil was mixed with 100 ml deionized water in a high-speed blender at 22, 000 rpm for 30 min. The crude oil droplet size was measured according to dynamic light scattering method using Malvern Zetasizer Nano system (Nano-ZS) in a universal dip cell. The stability of the emulsions was verified by observing the change in droplet size at 0 minutes and after 5 hours of preparation to verify its kinetic stability (Figure S1). No significant change in droplet size was observed and the emulsions were assumed as kinetically stable for the length of the experiments. Crude oils also constitute acid-base compounds, surfactants, and impurities that contribute to oil droplets surface charge. Droplet size, polydispersity index (PDI), and zeta potential of emulsions were measured using Zetasizer Nano system. The PDI was calculated according to, PDI = (Width of the droplets distribution/mean) 2 (2) where a PDI between indicates the droplets are moderately distributed, while above 0.4 represents that the distribution is broad. The zeta potential was measured according to electrophoretic mobility. The emulsions were diluted with 0.1 M KCl and ph adjusted with 0.05 M NaOH and 0.05 M HCl. The data was processed using Malvern Zetasizer software adjusting for emulsion conditions and using the Smoluchowski approximation. S4

5 Intensity distribution (%) min after preparation 5 hr after preparation Droplet size (nm) Figure S1. Stability of emulsions: Droplet size distribution at 0 min and 5 h after preparation of emulsions. Plots show no significant change in droplet size therefore, model emulsions are assumed as kinetically stable. S5

6 S3. Foam regeneration by simple compression Figure S2. Absorbent foam regeneration by simple compression. The high compressive strength of the foam in conjunction with low bonding strength between oil droplets and the foam aids easy oil recovery by mechanical compression. S6

7 S4. PESPU foam selectivity: oil and water uptake curves Mass uptake (g g -1 of foam) Time (s) Crude oil Water Figure S3. The mass uptake of the absorbent foam with pure crude oil and water. High porosity and large pores allowed instantaneous oil uptake by displacement mechanism (pore filling) while, due to low density, the water uptake is very low. S7

8 S5. Nanoroughness profile of the PESPU films a 50 nm b 50 nm Ra=17.2 nm -50 nm Ra=10 nm -50 nm c 250 nm d 250 nm Ra=67.7 nm -250 nm Ra=54.1 nm -250 nm Figure S4. Sample AFM scans of the PESPU films: a) and b) roughness profiles at 1x1 µm2, c) and d) roughness profiles at 5x5 µm2. These films were used for underwater oil wetting studies in Section S8

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