## 2 Materials and Methods
### Characterization  
Nitrogen porosimetry measurements were carried out at 77 K on a Sortomatic 1990, Thermo Finnigan porosimeter. The AC@SCF sample was outgassed under vacuum (i.e., \(10^{-6}\) mbar) at 150 \({}^{\circ}\)C for 10 h, before such measurements. Using the Corrugated Pore Structure Model (CPSM) which is reported in the literature, pore structure parameters, such as specific surface area (SSA), pore size distribution (PSD), total pore volume (TPV) [33; 34; 35], micropore volume (V\({}_{\text{micro}}\)) [36], and tortuosity factor (\(\tau_{\text{CPSM}}\)) [37], were estimated. These estimations were achieved by the simulation and interpretation of the raw nitrogen porosimetry data using the free available CPSM software [38]. For comparison reasons, the SSA was also calculated by the Brunauer-Emmett-Teller [39] and Langmuir (monolayer) methods [40], while the PSD in the micropore region was also calculated by the Density Functional Theory (DFT) model [41]. Finally, the microporosity fraction was also calculated by the Dubinnin-Raduskevitch method [42]. The overall pore volume was calculated via the total adsorbed nitrogen amount at P/P\({}_{0}\) = 0.998.  
Fourier-transformed infrared (FT-IR) attenuated total reflectance (ATR) measurements were carried out in a JASCO FT/IR-6200 instrument using the EasiDiff apparatus from PIKE Technologies. The samples were grounded and mixed with pure KBr reagent and placed in a holder (1 cm in diameter). The resultant spectra were the average of 64 scans at 2 cm\({}^{-1}\) resolution and the frequency range was from 400 to 4000 cm\({}^{-1}\). The final spectra were obtained after Kubelka-Munk calculations (F(R) = (1-R)\({}^{2}\)/2R, R is the attenuated reflectance).  
Raman spectra for the AC@SCF material were recorded using a micro-Raman RM 1000 Renishaw system. Laser excitation line was at 532 nm (Nd-YAG) and the frequency range was from 250 to 3500 cm\({}^{-1}\). The power of the laser was \(\sim\)10 mW and a 2 \(\upmu\)m focus spot was used.  
X-ray powder diffraction data were reported using a D8 Advance Bruker diffractometer. Measurements were carried out with CuK\(\alpha\) radiation (40 kV, 40 mA, \(\lambda\) = 1.54178 A) and using a secondary beam graphite monochromator. The 2\(\theta\) range of the diffraction patterns was from 0.5\({}^{\circ}\) to 80\({}^{\circ}\) and the increasing step was 0.02\({}^{\circ}\) for 2 s counting time.  
Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were performed using a Perkin Elmer Pyris Dimond instrument. Approximately 5 mg of the sample was heated from 25 \({}^{\circ}\)C to 900 \({}^{\circ}\)C following a temperature increasing rate of 5 \({}^{\circ}\)C/min.  
Scanning electron microscope (SEM) images were taken using a JEOL JSM-5600 apparatus, which is equipped with X-act EDS by Oxford Instruments company. The sample was covered by a thin gold film before the measurements.  
Observations of transmission electron microscopy (TEM) were reported using a JEOL JEM-2010 instrument equipped with an LaB6 cathode (accelerating voltage of 200 kV; point-to-point resolution of 0.194 nm).  
Finally, the concentration of the chromium solutions was calculated using the spectra of a UV-visible (UV-Vis) instrument. These measurements were performed using a quartz vesicle and aUV-2401(PC)-Shimadzu apparatus with a halogen lamp. The scanning range was 400-700 nm and the increasing step was 0.5 nm.