Fluorosurfactants‐Directed Preparation of Homogeneous and Hierarchical‐Porosity CMP Aerogels for Gas Sorption and Oil Cleanup

Homogeneous, hierarchical‐porosity and highly hydrophobic conjugated microporous polymer (CMP) aerogels are facilely prepared assisted by fluorosurfactants. The fluorosurfactants show several roles in controlling the gelation process, modulating pore structures, and raising the hydrophobicity of materials, thus giving rise to aerogels with exceptional gas sorption and oil cleanup performance.


Preparation of poly(1,3,5-triethynylbenzene) (PTEB) Organogel
PTEB organogel was prepared by homocoupling of TEB with CuCl as catalyst in the pyridine solution as reported elsewhere. [1] Difference lies in the extra addition of specific amount of fluorosurfactant. In a typical formula, fluorosurfactant (20 mg, 0.037 mmol) and CuCl (5 mg, 0.05 mmol) were dispersed in pyridine (1 mL) in a glass bottle, followed by the addition of pyridine (1 mL) solution containing TEB (30mg, 0.2mmol). Then the mixture was subjected to sonication for ca. 10s, followed by grounding in the water bath at 40 º C for 72 h to allow the formation of PTEB organogel. The resultant gel was washed sequentially with pyridine, chloroform, methanol and ethanol, which ensure the complete removal of impurities.

Preparation of PTEB Aerogel
Two drying methods were employed to prepare aerogel. The former is freeze-drying, where the solvent inside PTEB wet gel was exchanged with water by the method similar to the purification step described above. Then the gel was flash-frozen by liquid nitrogen, followed by freeze-drying for 24 h. The latter method was supercritical fluid drying using CO 2 as medium. The solution inside PTEB wet gel was exchanged with alcohol, followed by subjecting in drying chamber of the Thar Supercritical Fluid Extraction. The ethanol solvent was replaced by liquid CO 2 by flushing the chamber for several minutes. The chamber was then sealed and heated above the critical point of CO 2 (31.1 º C, 72.8 atm). After stabilizing for several minutes, the pressure in the chamber was slowly released over ca. 90 min at a constant temperature.

Part II Characterization IR and Raman Spectroscopy
FT-IR spectra were recorded by micro FT-IR spectroscopy (Thermo Scientific NICOLET iN10 MX). The Raman spectra were obtained by Raman Imaging Microscope System (LabRAM HR800), with excitation laser wavelength at 632.8 nm.

Dissolved oxygen test
To test the dissolved oxygen (DO) evolution during the gelation process, a pen dissolved oxygen meter (AMT08) was used to record the real-time DO value.
To facilitate measurement and get a more clear picture, the reaction system was scaled up to 9 mL pyridine solution (contain 135mg TEB, 27mg CuCl, 0 or 135mg fluorosurfactant). The reaction took place in a glass bottom, where the total height of the solution was ~30 mm. For measurement, the pen was directly put into the reaction system and kept for 2~3 seconds before obtaining a DO value. The measurement position was ca. 1mm (top), 15mm (middle) and 29 mm (bottom) beneath the solution surface.
Firstly, the CuCl and fluorosurfactant were dissolved in 9 mL pyridine solution, and the first set of DO values (top, middle and bottom section) before reaction was obtained (the time was 0 min). Secondly, the TEB was added followed by mixing with assistance of sonication for ~15s, achieving a homogeneous solution. After then, a series set of DO values at different height position were recorded by a fixed time interval. The measurement was continued for ca. 5 hours until the gel appeared.

Electron Microscopy
Scanning electron microscopy (SEM) was performed on a Hitachi S-4800 fieldemission-gun scanning electron microscope. The samples were prepared by directly putting aerogels on the conductive tape followed by gold sputtering.
Transmission electron microscopy (HRTEM) analysis was carried out by Tecnai F20 at 200 kV. The samples were prepared by dispersing aerogels in chloroform with assistance of ultrasonication, followed by dropping the dispersion onto carbon coated copper grids and drying at ambient temperature.

Element Analysis
X-Ray photoelectron spectroscopy (XPS) was performed using an Axis Ultra spectrometer (Kratos, UK) with a high-performance Al monochromatic source operated at 15 kV. The XPS spectra were taken after all binding energies were referenced to the C 1s neutral carbon peak at 284.8 eV, and the elemental compositions were determined from peak area ratios after correction for the sensitivity factor for each element. Deconvolution of the XPS C 1s peak was performed by CasaXPS.
Elemental analysis of C and H was further determined by using elemental analyzer (vario EL, from Elementar Analysensysteme GmbH).

Nitrogen Adsorption Measurement
Nitrogen adsorption experiments were performed with ASAP 2020 (Micromeritics, USA) at 77 K. The sample was outgassed at 45 º C for at least 15 hours under vacuum before measurement.

Thermal Properties Characterization
Thermogravimetric analysis (TGA) was conducted by Q600 STD with heating rate of 10 K min -1 in nitrogen or air atmosphere.

Contact Angle Measurement
Contact angle measurement was directly conducted on the aerogel at room temperature. The data was collected by OCA20 (Dataphysics).

Oil Uptake Measurement
Typically, a piece of aerogel (ca. 2 mg) was dropped into organic solvent or oil for 24 hours to achieve adsorption equilibrium. Then the weight gain (%) of the aerogel was calculated by Where m 0 and m represent the mass of aerogel before and after adsorption, respectively.
The regeneration of aerogel was achieved by heating the saturated gel at 60 º C for a period of time (which was dependent on the adsorbed solvent, e.g. 10 min for acetone).

Oil/water Separation
The PTEB-F-10 was loaded on polyurethane (Pu) sponge by dipping the Pu sponge (with pore size of hundreds of micrometers) into the chloroform dispersion of PTEB-F-10 for 3 days. Then the modified Pu sponge was taken out and the remained solvent was evaporated by vacuum drying at 45 º C. The separation device was constructed by sandwiching the modified Pu sponge between two hollow glass-made cylinders with a clamp as shown in Figure S11. The oil/water mixture was prepared by mixing deionized water and dichloromethane (dyed by Sudan III) together.
For measurement, the oil/water mixture was dropped on the separator by a straw.
When the mixed solution went through the modified sponge, the water was passed by while the dichloromethane was adsorbed, thus achieving the separation.
For a rough estimation of separation ratio for water/organic solvent system, following method was used. After dropping the mixture of water and organic solvent (toluene, dichloromethane or chloroform), the mixed solution passing through (ca. 10 mL) the modified Pu foam was collected by a graduated cylinder (25 mL). Hence the solution volume (V tot ) can be directly read from the cylinder, and the weight of solution (m tot ) was obtained by weighing incremental mass of cylinder after collecting the solution. Hence the apparent density (ρ app ) of filtered solution can be calculated by ρ app = m tot / V tot Since the water and organic solvent were immiscible, then we have m tot = ρ w *V w +ρ org *V org , V tot = V w + V org Then we can get that V org = (ρ app -ρ w )*V tot / (ρ org -ρ w ) Then the separation ratio can be calculated as, x = 1-V org / V tot = (ρ org -ρ app ) / (ρ org -ρ w )  In S2a, the gradually lighter color of the gel suggested the gradually lower polymerization degree with increasing initial fluorosurfactant concentration. The slightly increased gel height from left to right indicate that for surfactant-free gel, only a part of system (top section) can form the gel, limiting its scaling production.

S2b-d indicated that addition of enough fluorosurfactant can result into homogeneous
and "big" gel, important for scaling production.
S2e indicated that too much fluorosurfactant would suppress the gelation process.
S2f showed that the color of pyridine solution turned from olive to green upon the addition of fluorosurfactant, suggesting the coordination of Cu(I).
S2g showed that supercritical drying often resulted into integral and crack-free aerogels with better mechanical strength than freeze-dried samples. Figure S3. The in-situ dissolved oxygen (DO) measurement at different solution height in the reaction system with (the hollow data point) and without (the solid data point), respectively. The inspection time was end at 5 hours when the gel occurred.
Both reaction system (with or without addition of fluorosurfactants) underwent obvious oxygen consumption at initial stage (about 1 hour). However, it can be seen that fluorosurfactants-containing system can significantly suppress the oxygen consumption compared with surfactant-free system.