Particle Size Controls on Water Adsorption and Condensation Regimes at Mineral Surfaces

Transcription

1 SUPPLEMENTARY MATERIAL Particle Size Controls on Water Adsorption and Condensation Regimes at Mineral Surfaces Merve Yeşilbaş, Jean-François Boily* Department of Chemistry, Umeå University, SE Umeå, Sweden *tel ; 1

2 1. Modeling of Dynamic Vapor Sorption Data The following sections detail the salient equations used to predict water vapor binding as a function of p w /p sat where p w is the partial pressure of water vapour and p sat is the pressure at saturation (23.76 Torr at 25 C) 1.1 Bruauner-Emmet-Teller (BET) The well-known BET 1 equation typically applied for determination of specific surface area using N 2 (g) is written as: C µ =S o p w /p sat c (1-p w /p sat )(1-p w /p sat +c p w /p sat ) (1) where S! is the water-binding site density, and!=e ( desh 0 - vap H 0 )/RT, namely where!"# and!"# are the standard enthalpy of water desorption and evaporation, respectively. 1.2 Freundlich The single-site Freundlich 2 equation C µ =S o K p w /p sat (2) where K is the adsorption constant, and where S o is a site density. It can an be readily adapted to the multisite case through: C µ,tot = i C µ,i (3) and effectively mimic the Do-Do 3 equation (Section 1.4) by providing a means to predict an adsorption regime at low p w /p sat and a condensation regime at high p w /p sat. 1.3 Frenkel-Halsey-Hill This formulation is expressed as 4-8 : C! = S!!!!!!!" ( /"# ) (4) 2

3 where K 1 pertains to interactions between the mineral surface and the first water layer, while K 2 with longer range water molecules on thicker water layers. 1.4 Do and Do This model was originally developed to predict water vapor adsorption and condensation in carbon-based materials through the following equation 3 :!!!!!! C! = S!!!!!!!!!!!!!! + C!!!!!!!!!!!!!!!! (5) The left-hand term pertains to the adsorption and the right-hand term to the condensation regime which, we argue, could be translated to the case of water vapor adsorption and condensation at mineral surfaces. Parameters for each regime include water-binding sites densities (S o, C µs ) association constant (K f, K µ ) but also hydration numbers (β,α). The latter numbers are fixed to β=2 for the adsorption regime, to denote that a singly (hydr)oxo group can be involved in 2 (donating and/or accepting) hydrogen bonds, and α=6 for the condensation regime to denote that the nominal population of a water nanocluster needed for condensation at the mineral surface. These numbers may optionally be co-optimized to predict adsorption data, yet must be confined to physically realistic values. 3

4 Supplementary Table 1. Salient chemical and physical properties of minerals under study. Mineral name Atomic Ratio by XPS a Particle Size b Average Particle B.E.T Surface B.J.H Maximal Maximal ζ-potential (mv) f Size b Area (m 2 /g) c Micropore volume (cm 3 /g) d pore water (mg H 2 O/m 2 mineral) e pore water (H 2 O sites/nm 2 mineral) e Goethite Fe:O:OH = 1.35:1.0: nm 75 ± 9.4 nm Lath- Fe:O:OH = 1.4:1.0: nm 70 ± 9 nm Lepidocrocite Rod- Fe:O:OH = 1.3:1.0: nm 60 ± 7.1 nm * * 379 * 7 Lepidocrocite Akaganéite Fe:O:OH:Cl = 100 nm 102 ± 11 nm :0.82:1.22:0.17 Ferrihydrite Fe:O:OH = 1.5:1.3: nm 34 ± 5.4 nm * Hematite (10 nm) Fe:O:OH = 4.1:4.5: nm 10 ± 0.01 nm * Hematite (50 nm) Fe:O:OH = 2.8:3.88: nm 50 ± 6 nm Hematite (4µm) Fe:O:OH = 1.5:1.9: µm 3.66 ± 0.82 µm Hematite (5µm) Fe:O:OH = 1.7:2.0: µm 4.5 ± 0.6 µm Gibbsite Al:OH = 1.0: nm 255 ± 35 nm Kaolinite (CMS) K:Al:Si:O = 0.0:2.0:2.0: nm 600 ± 110 nm Kaolinite (Fluka) K:Al:Si:O = 0.2:2.0:2.6: µm 745 ± 15 nm Illite K:Al:Si:O = 0.3:1.0:2.5: nm 50 ± 15 nm Na- Na:Fe:Mg:Al:Si:O = nm 520 ± 110 nm Montmorillonite 0.1:0.1:0.1:1.0:2.3:7.8 Ca- Ca:Fe:Mg:Al:Si:O = nm 230 ± 40 nm Montmorillonite 0.1:0.1:0.1:1.0:2.3:8.2 Quartz Si:O = 1.0: µm 14 ± 0.7 µm * 3.33 * 45 * Microcline Na:K:Al:Si:O µm 11 ± 0.5 µm =0.2:0.8:1.0:2.8:7.2 Olivine Fe:Mg:Si:O = 0.1:0.95:1.0: µm 13.7 ± 0.7 µm

5 Calcium carbonate Mg:Ca:C:O = 0.3 : 0.7 : 1.1 : 3.6 Volcanic ash Na:K:Ca:Mg:Fe:Al:Si:O = 0.4:0.1:0.3:0.3:1.0:1.0:3.4:12.5 Arizona Test Na:K:Mg:Fe:Al:Si:O = Dust (ATD) 0.2:0.3:0.1:0.1:1.0:7.1: µm 1.2 ± 0.12 µm µm 11 ± 1.6 µm µm 6.4 ± 1.5 µm a. In vacuo XPS measurements: b. Size range obtained by SEM or TEM imaging; c. From B.E.T. analysis of 90-point N 2 (g) adsorption/desorption isotherms at LN 2 ; d. From B.J.H. analysis of 90-point N 2 (g) adsorption/desorption isotherms at LN 2 ; ( * Single point adsorption total pore volume of pores) e. Derived from B.J.H pore volume. f. Obtained from electrophoretic mobility of 2g/L suspensions of particles in distilled deionized water at 298 K. 5

6 Supplementary Figure 1. Relationship between N 2 -BET specific surface area (s s in m 2 /g) and particle size (D d in nm) estimated by scanning and transmission electron imaging. Both parameters can be related with the empirical function (dashed line) log(d d ) = log(s s ) 3.62 where s s is in m 2 /g and D d is in m. Theoretical predictions assuming cubic-shaped particles of quartz (density of 2.6 g/cm 3 ) and hematite (density of 5.3 g/cm 3 ) underestimate the experimentally measured N 2 -BET values. Discrepancies between theoretical and experimental values are caused by a bias in the sampling of the larger-sized particles, as well as micropore surface area. Supplementary Figure 2. Example of FTIR spectra of illite in the O-H stretching region during water vapor adsorption at 25 C. 6

7 References 1 Brunauer, S., Emmet, P. H. & Teller, A. Adsorption of gases in multimolecular layers. J. Am. Chem. Soc. 60, (1938). 2 HMF, F. Ûber die Adsorption in Lösnungen. Z. Phys. Chem. 57, (1906). 3 Do, D. D. & Do, H. D. A model for water adsorption in activated carbon. Carbon 38, , doi: /s (99) (2000). 4 J., F. Kinetic Theory of Liquids. (Oxford University Press, 1946). 5 Halsey, G. Physical Adsorption on Non Uniform Surfaces. J Chem Phys 16, , doi:doi: (1948). 6 Hill, T. L. Statistical Mechanics of Multimolecular Adsorption II. Localized and Mobile Adsorption and Absorption. J Chem Phys 14, , doi:doi: (1946). 7 Hill, T. L. Statistical Mechanics of Multimolecular Adsorption. III. Introductory Treatment of Horizontal Interactions. Capillary Condensation and Hysteresis1 a. J Chem Phys 15, , doi:doi: (1947). 8 Hill, T. L. Extension of Fowler's Treatment of Surface Tension to Physical Adsorption. J Chem Phys 17, , doi:doi: (1949). 9 Petters, M. D. & Kreidenweis, S. M. A single parameter representation of hygroscopic growth and cloud condensation nucleus activity. Atmos. Chem. Phys. 7, , doi: /acp (2007). 10 Sorjamaa, R. & Laaksonen, A. The effect of H2O adsorption on cloud drop activation of insoluble particles: a theoretical framework. Atmos Chem Phys 7, (2007). 11 Boily, J. F. Water structure and hydrogen bonding at goethite/water interfaces: implications for proton affinities. J. Phys. Chem. C 116, , doi:doi /Jp (2012). 7