Tetramethyl orthosilicate (TMOS) was purchased from Acros Organics, Bis(trimethoxysilylpropyl)amine (BTMSPA) from ABCR, 1-Butyl-3-methylimidazolium chloride, [Bmim][Cl] from Iolitec, FeCl*6H2O from Roanal, acetone from VWR, and n-propanol from Roth. All chemicals were used as received without further purification.
Preparation of iron-containing ionic liquid [Bmim][FeCl4]
1-Butyl-3-methylimidazolium tetrachloridoferrate(III) was synthesized in a one-step reaction. For this purpose, [Bmim][Cl] (18.5 mmol, 3.231 g) and FeCl3*6H2O (18.5 mmol, 5 g) were separately dissolved in 50 mL of n-propanol and then the two solutions were mixed. Subsequently, the solvent was removed via azeotropic distillation to obtain the dark brown liquid [Bmim][FeCl4]. The IL was freeze-dried overnight to remove water and was stored in a Schlenck flask under argon gas until use.
Preparation of iron-containing silica materials
Silica monoliths were synthesized via sol-gel reaction using the co-precursor BTMSPA as a basic catalyst following a published protocol. The total silicon concentration in the solution was 16.5 mmol from TMOS and BTMSPA combined. Notice that BTMSPA contributes 2 moles of silicon for every mole of silane. The amount of IL was 100 mg, 500 mg, or 1000 mg, respectively. For every reaction, the amount of water was 41.5 mmol (0.743 mL) and the amount of acetone was 100 mmol (5.4 mL).
In a typical experiment TMOS (0.244 mL), BTMSPA (1.127 mL), acetone (5.4 mL), and [Bmim][FeCl4] (1.0 g) were mixed in a 50 mL plastic tube. All reactants are liquid and completely miscible at room temperature. After shaking, the clear, brown liquid mixture was poured into a polypropylene mold, sealed with a septum and covered with parafilm. After 10 min gelation occurred and an off-white to yellow, solid silica monolith formed. The resulting mixture of brown IL and yellow sponge-like silica was allowed to sit without agitation for 24 h for further condensation of the silica. The resulting material was washed extensively by soxhlet extraction with methanol and dried under vacuum producing macroscopic aerogels with an off-white to light brown color.
The resulting aerogels (A) are denoted as xAy:z were x = 100, 500, 1000 (amount of IL in mg used in the synthesis), y:z = 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, and 7:3 (molar ratio of the silica precursors TMOS:BTMSPA).
Infrared (IR) spectroscopy was done in ATR mode on a Thermo Nicolet FT-IR Nexus 470 with ATR equipment. Spectra were taken from 400 to 4000 cm-1 with a resolution of 2 cm-1 and 32 scans.
TGA was done on a TGA 4000 thermal analyzer in air from 30 to 900°C with a heating rate of 10°C.min-1. The samples were placed in ceramic crucibles.
Nitrogen adsorption was done on a NOVA-4000e instrument within a partial pressure range of 10-6 to 1.0. Before measurements, the samples were degassed at 120°C for 2 h. The Brunauer-Emmett-Teller (BET) surface areas and pore volumes of each sample were measured by N2 adsorption experiments performed at -196°C (77 K). The pore volume was taken by a single point method at p/p0≈0.99.
Scanning electron microscopy (SEM) was done on a Phenom desktop electron microscope (FEI, Eindhoven, Netherlands) operated at 5 kV and on a JEOL JSM-6510 (JEOL GmbH, Eching, Germany) operated at 15 kV with a tungsten filament. EDXS measurements were done with an Oxford Instrument INCAx-act X-ray detector mounted on the JEOL SEM. Prior to measurements the samples were coated with a 100 nm carbon layer using a POLARON CC7650 Carbon Coater.
Micro X-ray computed tomography
All scans were obtained with a Skyscan 1172 high resolution micro CT at 59 kV and 165 μA, without filter, and set at 5 μm image pixel size, 360° rotation, 3 frames averaging, a rotation step of 0.02° and ring artefact correction set at 20, beam hardening correction set to 55%. The reconstruction software (NRecon v.18.104.22.168, SkyScan N.V.) was used to reconstruct cross-section images from tomography projection images. Quantitative parameters were measured by using the microCT analysis software (CTAn., v. 22.214.171.124+, SkyScan N.V.), normalization and histogram were done in Excel.
O2 Evolution measurements
Measurements of the oxygen content evolved over the course of the H2O2 decomposition were done with a fiber-optical method following a protocol published eleswhere.