Direct Oil Recovery from Saturated Carbon Nanotube Sponges

Transcription

1 Supporting Information Direct Oil Recovery from Saturated Carbon Nanotube Sponges Xiying Li 1, Yahui Xue 1, Mingchu Zou 2, Dongxiao Zhang 3, Anyuan Cao 2,* 1, 4,*, and Huiling Duan 1 State Key Laboratory for Turbulence and Complex Systems, Department of Mechanics and Engineering Science, College of Engineering, Peking University, Beijing , P. R. China hlduan@pku.edu.cn 2 Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing , P. R. China anyuan@pku.edu.cn 3 ERE & SKLTCS, College of Engineering, Peking University, Beijing , P. R. China 4 CAPT, HEDPS and IFSA Collaborative Innovation Center of MoE, BIC-ESAT, Peking University, Beijing , P. R. China

2 Content: Figure S1: Electrocapillary imbibition into an oil-saturated CNT sponge using other electrolyte systems during a cyclic potential eep. Figure S2: Pictures of electrolyte droplets containing surfactant placed on the surface of a CNT sponge. Figure S3. Spontaneous imbibition of surfactant-added electrolyte into an empty CNT sponge. Figure S4.Electrocapillary imbibition of SDS-added electrolyte into an oil pre-filled CNT sponge. Movie S1. An oil-saturated CNT sponge completely immersed in the electrolyte to show the oil displacement process. Theory derivation S-1

3 Figure S1. Electrocapillary imbibition into an oil-saturated CNT sponge using other electrolyte systems during a cyclic potential eep. Mass change with time during a cyclic potential eep at a scanning rate of 5 mv/s using (A) saturated Na 2 SO 4 solution (at 20, 1 wt% DTAB) in the potential range of [-0.8 V, 0.2 V] and (B) 1 M KCl solution (1 wt% DTAB) in the potential range of [-0.7 V, 0.2 V]. Both graphs show on-off behavior. In (A), the on state corresponds to a potential range of -0.8 to ~-0.26 V, and the off state corresponds to a potential range of ~-0.26 V to 0.2 V. In (B), the on state corresponds to a potential range of -0.7 V to ~-0.23 V, and the off state corresponds to a potential range of ~-0.23 V to 0.2 V. S-2

4 Figure S2. Pictures of electrolyte droplets containing surfactant placed on the surface of a CNT sponge. It showed the evolution of the droplets over time and the surfactant concentration is (A) 0 wt%, (B) 0.02 wt%, (C) 0.3 wt% and (D) 1 wt%, respectively. S-3

5 Figure S3. Spontaneous imbibition of surfactant-added electrolyte into an empty CNT sponge. (A) Measured mass change of the sponge per cross-section ( m/ A ) (versus square root of time t 1/2 ) during spontaneous imbibition, at different surfactant concentrations (0 to 2 wt%). (B) Capillary pressure (P c ) derived for data in Figure S2A (experimental) and theoretical fitting results depending on the surfactant concentration (C), here n= S-4

6 Figure S4. Electrocapillary imbibition of SDS-added electrolyte into an oil pre-filled CNT sponge. (A) Measured mass change of displaced oil ( mo L/ A ) under -1.2 V using different SDS concentrations (0 to 2 wt %, 1 M KOH). (B) Capillary pressure Pc derived from data in Figure S4A (experimental) and theoretical fitting (n=1.53). The oil recovery rate is much lower than DTAB. Movie S1. An oil-saturated CNT sponge completely immersed in the electrolyte, from which gas bubbles and oil droplets were extruded out when a potenital of -1.2 V was applied (snapshots were shown in Figure 1C in the main text). S-5

7 Theory derivation The influence of potential on capillary pressure P c at a constant surfactant density. The wetting property of liquid-solid surface depends on electrode potential according to the electrocapillary effect, which is described by the Lippmann equation, S1 dσ = qde (S1) where σ is the electrode-electrolyte surface tension, and q is the charge density, which can be obtained by integrating cyclic voltammogram with potential of zero change set as 0 V, as reported in Ref. S2. The critical potential for wetting transition of oil-saturated CNT sponges was measured to be V here (see Figure 2A in the main text), indicating contact angle, θ = 90 at E = V. Then, combining the Young equation (σ wo cosθ = σ so -σ, where σ is interface tension, and subscripts wo, so and denote water-oil, solid-oil and solid-water interfaces, respectively) leads to E σ cos θ ( E) σ ( 0.24) σ ( E) qde = = (S2) wo 0.24 Since the capillary pressure, P c = 2σ wo cosθ/r c (see Equation 1 in the main text), we derive the relationship between potential (E) and capillary pressure (P c ) (the theoretical calculation in Figure 3B in the main text) as, 2 2 E P ( E) = [ σ ( 0.24) σ ( E) ] = qde r (S3) 0.24 c rc c The influence of surfactant density on capillary pressure P c at constant potential. A general isotherm equation, capable of explaining various types of isotherms for adsorption of surfactant molecules at the solid-liquid interface, has been given by Zhu and Gu, S3 that is, S-6

8 1 Γ k C + Γ= n + + n 1 1 ( k 2C ) n 1 1 k1c (1 k2c ) (S4) where Γ is the amount of surfactant adsorbed at surfactant concentration C, Γ is the limiting adsorption at high concentration, k 1 and k 2 are the equilibrium constants, describing a two-step adsorption mechanism (first step: the surface-active species are adsorbed through the interactions between the surface-active species and the solid surface; second step: through the hydrophobic interaction between the adsorbed surface-active species), and n is the aggregation number (surface hydrophobic aggregates or hemimices). The relationship between surface tension and limiting adsorption surfactant is described by the Gibbs adsorption equation, S4 1 dσ Γ= RT d ln C where R is the gas constant and T is the temperature. Combing Equations S4 and S5 yields, (S5) 1 n 1 Γ k1( + k2c ) dσ = RT n dc 1 (1 ) n 1 + k1c + k2c (S6) By the integral of Equation S6, the surfactant adsorption-induced change of the solid-electrolyte interface tension ( σ ) is obtained, 0 RT n 1 σ = σ σ = Γ ln[1 + k1c (1 + k2c )] (S7) n 0 where σ is the solid-electrolyte surface tension without surfactant. Then, with P c = 2σ wo cosθ/r c and σ wo cosθ = σ so -σ, we have Equation 3 in the main text, that is, S-7

9 2 RT P ( C) = P + Γ ln[1 + k C(1 + k C )] (3) 0 n 1 c c 1 2 rc n where P = 2( σ σ ) / r, is the capillary pressure in the pure system without surfactant. 0 0 c so c References: [S1] Lippmann G. Relations Entre Les Phénomènes Electriques et Capillaires. Ann. Chim. Phys., 1875, 5, [S2] Xue, Y.; Yang, Y.; Sun, H.; Li, X.; Wu, S.; Cao, A.; Duan, H. A Switchable and Compressible Carbon Nanotube Sponge Electrocapillary Imbiber. Adv. Mater. 2015, 27, [S3] Zhu, B.; Gu, T. General Isotherm Equation for Adsorption of Surfactants at Solid/ Liquid Interfaces. J. Chem. Soc., Faraday Trans , 85, [S4] Gibbs, J. W. The Collected Works Longmans: Green and Co., New York, 1928, Vol. I, pp 300. S-8