Preparation of TiO2 Nanoparticle Aggregates and Capsules by the ‘Two-Emulsion Method’
Abstract
:1. Introduction
2. Materials and Methods
2.1. Materials
2.2. Methods and Procedures
2.2.1. Two-Emulsion Method
- (1)
- A water–oil premix of each initial emulsion was prepared by addition of the necessary amount of water phase in the oily phase under continuous stirring to form coarse emulsion. To form the premix we first prepared the oily phase which consisted of Span 80 (in the concentration range between 0.1 and 3 wt % with respect to the oily phase of the emulsion) dissolved in 24 g of the oil (hexadecane or heavy oil) at room temperature on a magnetic stirrer.The volume of the aqueous phase of the NH4OH-emulsion was 6.3 mL. The aqueous phase of the TiCl4-emulsion, containing 8.94 M TiCl4, was prepared by dissolving 1.67 mL TiCl4 into 4.03 mL concentrated 10.2 M HCl. The addition was performed dropwise on a magnetic stirrer in an ice bath. Due to the decrease of the solution volume during mixing (by a factor of 1.23 ± 0.01), the obtained final volume of the TiCl4 + HCl solution was 4.63 mL.
- (2)
- The water volume fraction of the NH4OH-emulsion was 17 vol % when working with hexadecane and 18 vol % when working with heavy oil. With account of the decrease of the volume upon mixing of TiCl4 and HCl in the aqueous phase, we calculated the water volume fraction of the respective initial TiCl4-emulsions to be 13 vol % when working with hexadecane and 14 vol % when working with heavy oil.
- (3)
- Rotor-stator emulsification device Ultra Turrax (Janke & Kunkel GmbH & Co, IKA-Labortechnik, Germany) was used for homogenization of the two W/O premixes in order to obtain the two initial emulsions. The homogenization time was set to 5 min. The rotation speed of the homogenizing element was fixed at 8000; 13,500; or 20,500 rpm in the various experiments, all performed at room temperature.
- (4)
- The NH4OH-emulsion was then added to the TiCl4-emulsion under mild stirring. Next, we homogenized the mixed emulsion with Ultra Turrax to realize drop-drop coalescence under well-defined conditions and, thus, to trigger the reaction leading to Ti(OH)4 precipitation. In these series of experiments, we varied systematically the homogenization time (10, 15, 20, 30, or 40 min) and the rotation speed (8000; 13,500; 20,500 rpm). The average concentrations of the reactants with respect to the water phase in the mixed emulsions were calculated to be 1.37 M for TiCl4, 3.75 M for HCl, and 7.7 M for NH4OH. Note that, along with the formed Ti(OH)4 precipitate, about 7.7 M NH4Cl is formed in the aqueous phase as a reaction byproduct, see Equation (1).
- (5)
- Finally, the mixed emulsion was heated at 100 °C for 30 min under stirring on a magnetic stirrer for Ti(OH)4 transformation into TiO2. In this way, we obtained W/O emulsion with water volume fraction of ≈15% using hexadecane as the oily phase and ≈16% using heavy oil, with about 11 wt % of TiO2 particles and agglomerates residing in the aqueous drops.
2.2.2. Determination of Drop Size Distribution
2.2.3. Particle Separation
2.2.4. Analysis of the Particles
Dynamic Light Scattering (DLS) Analysis
Scanning Electron Microscopy (SEM) and Elemental Analysis (EDX)
X-ray Analysis
Transmission Electron Microscopy (TEM)
3. Results and Discussion
3.1. Selection of Appropriate Emulsifier for Stabilization of Water-in-Oil Emulsions with Controllable Stability
3.2. Synthesis of TiO2 Particles and Analysis of the Obtained Structures
3.2.1. Effect of Emulsifier Concentration
3.2.2. Effect of the Oily Phase
3.2.3. Effect of the Precursor Concentration
3.2.4. Effect of Emulsification Conditions—Homogenization Time and RPM
4. Conclusions
Supplementary Materials
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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TiCl4, M | Hexadecane | Heavy Oil | ||||||
---|---|---|---|---|---|---|---|---|
Before Drying | After Drying | Before Drying | After Drying | |||||
dN, nm | dV, nm | dN, nm | dV, nm | dN, nm | dV, nm | dN, nm | dV, nm | |
0.66 | 430 | 520 | 430 | 900 | 420 | 500 | 420 | 900 |
1.37 | 240 | 390 | 430 | 5000 | 420 | 500 | 420 | 660 |
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Politova-Brinkova, N.I.; Tsibranska-Gyoreva, S.R.; Tcholakova, S.S.; Denkov, N.D.; Danner, T. Preparation of TiO2 Nanoparticle Aggregates and Capsules by the ‘Two-Emulsion Method’. Colloids Interfaces 2020, 4, 57. https://0-doi-org.brum.beds.ac.uk/10.3390/colloids4040057
Politova-Brinkova NI, Tsibranska-Gyoreva SR, Tcholakova SS, Denkov ND, Danner T. Preparation of TiO2 Nanoparticle Aggregates and Capsules by the ‘Two-Emulsion Method’. Colloids and Interfaces. 2020; 4(4):57. https://0-doi-org.brum.beds.ac.uk/10.3390/colloids4040057
Chicago/Turabian StylePolitova-Brinkova, Nadya I., Sonya R. Tsibranska-Gyoreva, Slavka S. Tcholakova, Nikolai D. Denkov, and Thomas Danner. 2020. "Preparation of TiO2 Nanoparticle Aggregates and Capsules by the ‘Two-Emulsion Method’" Colloids and Interfaces 4, no. 4: 57. https://0-doi-org.brum.beds.ac.uk/10.3390/colloids4040057